MANUFACTURING AND ANALYSIS OF BIOACTIVE GLASS FIBER, …

MANUFACTURING AND ANALYSIS OF BIOACTIVE GLASS FIBER,

AND ITS APPLICATION IN BIOMEDICAL ENGINEERING

SERGI ROCA PUERTAS

Master of Science thesis

Supervisor in home university: Manuel Laso Carbajo Supervisor in receiving university: Jonathan Massera

AGRADECIMIENTOS

Gracias a todos y cada uno de las personas y situaciones que me han traído hasta aquí, hasta

este único y preciso momento en el que la entrega de la Master Thesis supone el fin de un ciclo

personal. Todo empezó en Septiembre de 2009 que tan lejano queda ya, ahora, 7 años después,

tras muchas historias, se da por concluido un proyecto en el que me embarque a ciegas, y que

paso a paso ha ido resultando ser sorprendente e inquietante.

Más concretamente, muchas gracias a todos los que me apoyaron y me permitieron ir un paso

más lejos y poder realizar este proyecto en la Universidad de Tampere TUT, y contar con un

equipo de especialistas que me han guiado a lo largo del mismo, enseñándome tanto de esta

temática, que era totalmente nueva para mí, como a trabajar en un laboratorio y poder contar

con un equipo multicultural con mucho que ofrecer.

MANUFACTURING AND ANALYSIS OF BIOACTIVE GLASS FIBER, AND ITS APPLICATION IN BIOMEDICAL ENGINEERING

SERGI ROCA PUERTAS

RESUMEN EJECUTIVO

En el presente trabajo de investigación, se pretende hacer un estudio de como varían las pro-

piedades térmicas, mecánicas y químicas de las fibras de vidrio bioactivo de fosfato en función

de su composición.

A rasgos generales se puede decir que en lo que consiste el trabajo es en la fabricación de vidrio

bioactivo, extrusión de fibras e inmersión de las mismas en un tampón químico llamado SBF

(Simulated Body Fluid). Luego se procede al análisis de los resultados, para ello se realizaron

diversos estudios en los que se incluyen la Espectroscopia de Absorción Atómica (AAS), Es-

pectroscopia en Transformada de Fourier (FTIR), ensayos mecánicos de tensión, Análisis Tér-

mico Diferencial (DTA).

Se podrá concluir con una comparación entre los diferentes tipos de vidrios para obtener fibras,

ventajas y desventajas entre unos y otros, y sobretodo profundizar y encaminar unos futuros

estudios para su desarrollo e inclusión en el mercado.

Introducción

El presente TFM se encarga de profundizar y colaborar en el avance y la evolución de los ma-

teriales biocerámicos (en concreto el vidrio bioactivo). Se entiende por biomaterial aquel que

puede interactuar con los tejidos del ser humano sin ser dañino. Podríamos encontrar dos tipos,

los bioactivos y los materiales biocompatibles. El estudio se centrará en los primeros. Son ma-

teriales que además de no tener ningún efecto perjudicial para el cuerpo humano, son favorables

para la regeneración del tejido óseo. Son reabsorbibles y favorecen la creación de Hidróxiapa-

tita.

Podemos encontrar tres tipos de vidrios bioactivos, de silicio, de fosfato, o de boro. Este pro-

yecto se ha centrado en los vidrios de fosfato, los cuales están en pleno desarrollo y aun se

ofrece un amplio campo de investigación. En concreto, el TFM se puede dividir en dos partes

claramente diferenciadas, el estudio y caracterización de diferentes vidrios de fosfato en función

de sus propiedades química para la elaboración de fibras. Y segundo, el estudio de cómo se

comportan dichas fibras dentro del fluido corporal mediante análisis in-vitro.

Procedimientos y análisis utilizados

A continuación, se enumeran los procesos que se han ido siguiendo, de la forma más ordenada

posible en relación con cómo se han hecho en la realidad, aunque realmente la mayor parte

estaban entrelazados y se solapaban:

Preparación y fundición de las muestras de vidrio.

Preparación de los compuestos iniciales.

Fundición del vidrio.

Extrusión de fibra de vidrio.

RESUMEN EJECUTIVO

ii ESCUELA SUPERIOR DE INGENIERIEROS INDUSTRIALES (UPM)

DTA.

Test SBF.

Inmersión temporal en SBF.

Análisis de PH de la muestra.

AAS.

Tensile test

FTIR.

Explicación teórico práctica y análisis de resultados de cada una de los pun-

tos previos.

Preparación de los vidrios, en forma de disco

El vidrio que más ha sido utilizado durante el proyecto ha sido llamado Sr50, además, se ha

experimentado con otro tipo de vidrios que comparten la misma composición base (Si5, Mg5,

Ti5 y Cu5). Su preparación partía de la mezcla de su composición, debiendo previamente for-

mar la materia prima. Un horno especializado para ello, y un programa de temperatura adecuado

a ellos creaban el vidrio fundido que posteriormente había que verter en el molde y mantenerlos

durante 5 horas a temperatura de recocido.

A continuación se comprueba la calidad del vidrio y si no hay problemas de cristalización, se

almacena para el siguiente paso.

Extrusión de la fibra de vidrio

Una vez se obtenían muestras de unos 25 g aproximadamente, se comprobaba que eran de ca-

lidad y no estaban parcialmente cristalizadas, se rompía en trozos grandes, una cantidad de unos

80 g de vidrio, y se depositaba en un nuevo crisol de platino, en este caso un crisol especial,

perforado por la parte inferior, para que el vidrio pueda caer cuando se está fundiendo. El Sr50

se posicionaba en el interior del horno, el cual tenía un conducto que permitía al vidrio caer del

crisol directamente al exterior.

La temperatura deseada se encuentra entre los 880 y los 900 C, como se pudo comprobar. Si

permanece a temperaturas inferiores, se cristaliza. Si, sin embargo, se expone a temperaturas

superiores, se funde demasiado y cae de golpe en forma líquida. El punto deseado es intermedio

entre sólido y líquido, lo suficiente líquido para que, por su propio peso, una primera gota caiga,

pero manteniendo la viscosidad que lo haga permanecer en el crisol.

Una vez obtenida la primera gota, esta arrastraba una fina fibra que la unía con el resto del

vidrio dentro del crisol. A continuación, se tracciona dicha fibra a un ritmo lo más constante

posible, para obtener una fibra uniforme, sin llegar a romperla.


SERGI ROCA PUERTAS iii

DTA: Differential Thermal Analysis.

El Análisis térmico diferencial es utilizado para comprobar las propiedades térmicas de cada

uno de los diferentes vidrios. Su funcionamiento queda explicado en la memoria, al igual que

para el resto de análisis. Una vez obtenido el análisis DTA, quedan fijos datos de relevancia de

cada uno de los vidrios como su temperatura de cristalización o temperatura de fusión. La má-

xima estabilidad en el perfil térmico, nos ofrece a su vez una mayor facilidad para extraer las

fibras.

SBF: Simulated body fluid

Queda mencionada la primera parte del trabajo, de extrusión de fibra de vidrio y comienza la

siguiente. Es la inmersión de las fibras en SBF, una solución tampón que simula las propiedades

de los fluidos corporales. Es una solución acelular con el mismo PH y que contiene los mismos

iones inorgánicos que el plasma sanguíneo, pero con falta de proteínas u otros constituyentes

orgánicos.

Inmersion de SC2, CC2, Sr50 y Sr5

Previamente, se contaba con dos tipos de fibra de vidrio distintos, ambos hechos con base de

Sr50, añadiéndoles un 2,50% molar de B2O3. Su composición se muestra en la tabla siguiente.

La diferencia entre ambos, como puede verse, es que el Cc2 cuenta además con el núcleo do-

pado de Cerio.

También se sumergieron las fibras obtenidas por extrusión de Sr50, y otras fibras con las que

se contaba, llamadas Sr5, de vidrio de silicio, con la siguiente composición, para comparar su

comportamiento con las fibras de fosfato.

El objetivo de sumergir las diferentes fibras en SBF por diferentes períodos de tiempo, es ver

como ese hecho afecta a las propiedades físicas de la fibra, estudiar su biodegradabilidad en

función del tiempo y ser capaces de caracterizar los diferentes vidrios para poder ajustar su

buen uso. Las fibras se sumergen por periodos de 6, 24, 48 y 72 h, y 1 y 2 semanas.

Medida del PH

Al finalizar el tiempo de inmersión de cada una de las muestras, se extraían del líquido con

mucho cuidado, se rociaban de etanol para limpiar bien las partículas de SBF y se secaban en

una incubadora durante 24 horas. El Líquido SBF resultante, se utiliza para medir su PH, y ver

cómo éste ha variado con el tiempo. El PH varía en función del tiempo de inmersión debido a

que a medida que el vidrio va reaccionando, se disuelve y aportan iones y moléculas de fosfato

cálcico al medio reactivo.

RESUMEN EJECUTIVO

iv ESCUELA SUPERIOR DE INGENIERIEROS INDUSTRIALES (UPM)

AAS: Atomic Absorption Spectroscopy. Medida de la concentración de iones Ca2+

Se prepara una disolución con el SBF resultante y agua (destilada), el objetivo es una disolución

ten-fold (decúpula), para reducir su concentración. Una vez obtenidas todas las muestras, se les

realizaba el análisis AAS con un espectrómetro Perkin Elmer AAnalyst 300, utilizando una

llama de aire-acetileno. De esta forma se cuantificaba la cantidad de iones Ca2+ libres en la

composición, y se analizan los resultados en busca de conocer la capacidad de degradación del

vidrio.

Ensayos mecánicos

Una vez que cada muestra (10 fibras de vidrio) era retirada por completo del SBF, como se ha

explicado antes, se procedía a realizar el ensayo mecánico de tracción. Para ello se utilizó una

Instron 4411. A través de los ensayos mecánicos se obtenía la gráfica de tensión y deformación

característica de cada fibra. Una a una, las 390 fibras fueron ensayadas, la curvas obtenidas,

procesadas y corregidas, mediante Origin, seleccionando solo la parte lineal de la curva, para

que el resto no influyera de forma negativa manipulando los resultados de la pendiente (Modulo

de Young).

FTIR: Fourier Transform Infrared Spectroscopy

Este método mide las transiciones vibracionales entre su estado fundamental y estados de exci-

tación. Estas transiciones son medidas mediante absorción o emisión de luz. El material a tratar

se expone a radiación IR. Parte de esa radiación simplemente pasa a través del material, y otra,

en cambio, es absorbida. Esta energía transmitida, supone el espectro buscado. Ya que no puede

haber dos moléculas diferentes que emitan el mismo espectro infrarrojo, a través de su lectura,

se puede observar perfectamente de qué tipo de sustancias estamos analizando. Es decir, FTIR

puede mostrarnos materiales desconocidos, es decir, mostrarnos la composición de dichos ma-

teriales.

Cada molécula, teniendo n átomos, tiene 3n grados de libertad. 6 de ellos son para la propia

molécula, y 3n-6 para los distintos modos de vibración que son: Estiramiento simétrico, tijere-

teo, aleteo, estiramiento asimétrico, balanceo y torsión.

La vibración IR puede ser activa o inactiva, dependiendo si hay absorción del espectro IR o no.

En este ensayo, el FTIR se realizó por medio de una máquina Perkin Elmer FTIR spectrum.

Todo el espectro fue grabado en una banda desde 600 a 2000 cm-1. FTIR se aplicó a todas las

muestras de Sc2 y Cc2 para 0 y 72 horas, y 1, 2 y 3 semanas, ya que para tiempos de inmersión

menores a 72 horas, no se observó cambio.

El objetivo, y los resultados obtenidos nos acercan a conocer la evolución de la composición

de las fibras en función del tiempo de inmersión, lo cual nos acerca al conocimiento de la for-

mación de fosfato cálcico, necesario para la regeneración del hueso y formación de apatita.


SERGI ROCA PUERTAS v

Conclusiones y futuras líneas de investigación

Es este trabajo de investigación se ha contribuido al estudio de la fibra de vidrio de una forma

muy exhaustiva.

Se ha profundizado en el estudio de creación, por medio de la extrusión, de fibras de vidrio con

nuevas composiciones, distintas a las que hoy en día se utilizan. Métodos que aún no están muy

desarrollados, y que necesitan de nuevas y numerosas pruebas. El análisis térmico (DTA), nos

deja claro cuáles son las composiciones más apropiadas para ellos, por una mayor estabilidad

energética del vidrio. Para ello se ha estudiado el vidrio protagonista de este estudio, Sr50. Pese

al pequeño cambio en la composición (5% molar), se observaron grandiosos cambios en sus

propiedades térmicas. Como conclusión se deduce que debería seguir profundizándose en la

creación de fibras de vidrio del tipo Si5 y Ti5, las cuales pueden suponer una muy buena apuesta

futura, a un precio razonable, ya que serían las más fáciles de extrudir.

De forma independiente, se han analizado las propiedades de las fibras de fosfato fabricadas en

este mismo estudio, de Sr50, y de otras, también de base de Sr50, con una composición ligera-

mente modificada, Sc2 y Cc2.

Sc2 y Cc2 tienen un muy buen comportamiento reactivo al cuerpo humano. Se degradan de

forma gradual, reducen sus propiedades físicas también de forma gradual. De este estudio se

puede analizar, en función del tipo de aplicación biomédica, el tipo de fibra más conveniente.

Como refuerzo para materiales compuestos, queda claro, que la fibra de vidrio puede jugar un

papel fundamental en la fuerza de dichos materiales. En este estudio se observó la dureza y

Modulo de Young en función del tiempo de inmersión, el cual permanece prácticamente cons-

tante hasta el paso de cierto tiempo.

Como complemento, se está produciendo, y se prevé un cambio aun mayor, un incremento del

uso de materiales no metálicos en implantes. Para ello es necesaria la creación de nuevos bio-

materiales compuestos. En este caso, las fibras de fosfáto cálcico, no solo proveen al implante

de una mayor fuerza, sino que apoyan con sus propiedades osteoconductivas (capacidad de un

material para actuar como un substrato en el cual las células puedan adherirse y desarrollar sus

funciones).

Para finalizar se concluye afirmando que este tipo de vidrios bioactivos, ofrece una gran opor-

tunidad para el desarrollo de nuevos materiales compuestos y técnicas, como materiales cons-

tructivos en ingeniería de tejidos.

RESUMEN EJECUTIVO

vi ESCUELA SUPERIOR DE INGENIERIEROS INDUSTRIALES (UPM)


SERGI ROCA PUERTAS

RESUMEN

Alcance

En el presente trabajo de investigación, se pretende hacer un estudio de como varían las pro-

piedades térmicas, mecánicas y químicas de las fibras de vidrio bioactivo de fosfato en función

de su composición.

A rasgos generales se puede decir que en lo que consiste el trabajo es en la fabricación de vidrio

bioactivo, extrusión de fibras e inmersión de las mismas en un tampón químico llamado SBF

(Simulated Body Fluid). Luego se procede al análisis de los resultados, para ello se realizaron

diversos estudios en los que se incluyen la Espectroscopia de Absorción Atómica (AAS), Es-

pectroscopia en Transformada de Fourier (FTIR), ensayos mecánicos de tensión, Análisis Tér-

mico Diferencial (DTA).

Se podrá concluir con una comparación entre los diferentes tipos de vidrios para obtener fibras,

ventajas y desventajas entre unos y otros, y sobretodo profundizar y encaminar unos futuros

estudios para su desarrollo e inclusión en el mercado.

Introducción

Los materiales utilizados en biomedicina para realizar implantes, y que, en definitiva, tienen

contacto directo con el interior del cuerpo humano, se hacen llamar biomateriales. Aunque el

uso de materiales en implantes ha sido aplicado durante siglos, es en el siglo XX cuando real-

mente se produjeron los primeros grandes avances. El objetivo de ellos es mejorar la salud de

la gente que ha sufrido accidentes, problemas óseos de nacimiento, o desordenes de la edad, a

través de la ayuda a la reconstrucción de los huesos.

Los avances más importantes en el campo de los biomateriales, se ha producido gracias al desa-

rrollo de Biocerámicos y vidrios bioactivos. Pueden considerarse dos tipos de biomateriales:

Biocompatibles y Bioactivos. Los primeros son materiales que liberan compuestos No-tóxicos

en el cuerpo humano, si modificar, en ningún aspecto su composición. Los bioactivos, en cam-

bio, tienen un efecto positivo en el tejido óseo y favorecen su regeneración. Estos últimos,

siendo reabsorbibles (Se descomponen y se asimilan por el cuerpo) desaparecen del cuerpo por

ser degradables hidrolítica y enzimáticamente. Es muy importante su caracterización, y debido

a que, en fases iniciales de investigación, no se permite ensayar con animales, es necesario

realizar análisis in-vitro.

Podemos encontrar tres tipos de vidrios bioactivos, de silicio, de fosfato, o de boro. Este trabajo

se centrará en el estudio de vidrios del fosfato, y se hará una ligera comparación con estudios

previos de otros vidrios de silicio.

RESUMEN


Literatura y Teoría

Biomateriales, huesos y tejido óseo

El objetivo de los biomateriales es adaptarse al cuerpo humano para desempeñar una función

reparadora cumpliendo con los requerimientos mecánicos, térmicos y biocompatibles del

cuerpo (tensiones de cizalladura, Modulo de Young, coeficiente térmico…).

El esqueleto es el principal sostenedor del cuerpo humano. Está diseñado para soportar todo

tipo de esfuerzos de la vida cotidiana del ser humano, incluida la constante fuerza de la grave-

dad. Su composición puede ser dividida en dos, cortical y trabecular. La primera constituye el

80%wt de la composición del esqueleto. El 70% del hueso es de origen mineral (Ca2+, PO43-

son sus principales constituyentes y CO32- se muestra en menor proporción). La parte orgánica

contiene agua, proteínas (colágeno de tipo I) y otras proteínas. Todo este tipo de compuestos

que lo conforman, hacen que el hueso se considere un material compuesto.

El fosfato cálcico que constituye el hueso es Hidróxiapatita, Ca10(PO4)6(OH)2(HA). Su for-

mación, gracias a la reacción con el vidrio de fosfato que ha sido analizado en este estudio,

supone la regeneración del hueso.

El hueso tiene un módulo de Young que abarca un rango de 17 a 24 GPa, dependiendo del

hueso, sexo, edad en tracción axial.

Vidrios de fosfato y propiedades

El vidrio está definido como un sólido rígido, amorfo con una viscosidad más alta de 1013 poise.

Puede haber vidrios compuestos por los siguientes óxidos B2O3, SiO2, GeO2, P2O3, As2O3, Sb2O3,

In2O3, Tl2O3, SnO2, PbO2 and SeO2. Dentro de todos estos, los óxidos capaces de formar vidrio

son tres, y los vidrios se catalogarán dentro de esos tres, SiO2, P2O5 and B2O3. Siendo los vidrios

de silicio los más utilizados.

Los vidrios de fosfato están constituidos de cadenas de estructura polimérica de tetraedros de

fosfato unidos entre ellos a través de átomos de Oxígeno. Los tetraedros son de PO4, y usual-

mente se dividen en grupos Qn desde n=0 hasta n=3. Q0 se corresponde con el orto-fosfato

aislado. Q1 son los tetraedros de comienzo y fin de la cadena de fosfato. Q3 son la unidad rama.

En dichos casos, n sería el número de oxígenos “puente” por cada tetraedro. Por ello, Q2 es una

unidad que se encuentra en medio de la cadena polimérica, con un tetraedro a cada lado.


SERGI ROCA PUERTAS iii

Procedimientos y análisis utilizados

A continuación, se enumeran los procesos que se han ido siguiendo, de la forma más ordenada

posible en relación con cómo se han hecho en la realidad, aunque realmente la mayor parte

estaban entrelazados y se solapaban:

Preparación y fundición de las muestras de vidrio.

Preparación de los compuestos iniciales.

Fundición del vidrio.

Extrusión de fibra de vidrio.

DTA.

Test SBF.

Inmersión temporal en SBF.

Análisis de PH de la muestra.

AAS.

Tensile test

FTIR.

Explicación teórico práctica y análisis de resultados de cada una de los pun-

tos previos.

Preparación de los vidrios, en forma de disco

El vidrio que más ha sido utilizado durante el proyecto ha sido llamado Sr50, además, se ha

experimentado con otro tipo de vidrios. La composición de cada uno de los vidrios de fosfato

con los que se ha trabajado se muestra a continuación:

•Sr50: 50 P2O5 – 10 Na2O – 20 SrO – 20 CaO

•Si5: 45 P2O5 – 10 Na2O – 20 SrO – 20 CaO – 5 SiO2

•Cu5: 45 P2O5 – 10 Na2O – 20 SrO – 20 CaO – 5 CuO

•Mg5: 45 P2O5 – 10 Na2O – 20 SrO – 20 CaO – 5 MgO

•Ti5: 45 P2O5 – 10 Na2O – 20 SrO – 20 CaO – 5 TiO2

Como se puede comprobar, todos guardan la composición del Sr50, salvo que se les añade un

5% molar de Si, Cu, Mg o Ti. Para su preparación se precisaba de Sr(PO3)2, Ca(PO3)2 y NaPO3.

Los dos primeros había que prepararlos haciendo uso de CaCO3 y SrCO3, como se muestra en

la siguiente tabla y siguiendo un programa térmico de temperatura máxima de 1100 C, con una

duración de 50 h.

RESUMEN

iv ESCUELA SUPERIOR DE INGENIERIEROS INDUSTRIALES (UPM)

Ca(PO3)2 Sr(PO3)2 50 g 50 g

CaCO3 (NH4)2HPO4 SrCO3 (NH4)2HPO4

15.023 g 26.894 g 12.636 g 33.3502 g

15.023 g 26.894 g 12.636 g 33.3502 g

Finalmente, los compuestos químicos necesarios para elaborar 30 g de cada uno de dichos vi-

drios se muestran en la tabla siguiente.

Kind of Glass

Sr50 Si5 Ti5 Mg5 Cu5

Raw material Composition (grams) for 30 g of glass

Ca(PO3)2 10.88935 9.965877 9.872275 10.06126 9.873777

Sr(PO3)2 13.50371 12.35853 12.24245 12.47682 12.24432

NaPO3 5.606939 5.864506 5.809424 5.920637 5.810308

CaCO3 0.719584 0.712825 0.726471 0.712934

SrCO3 1.061392 1.051423 1.071551 1.051583

SiO2 0.863963

TiO2 1.137619

MgO 0.585091

CuO 1.133227

Con dichas composiciones, y utilizando un crisol de patino, se sigue

un programa de calor especifico (se puede encontrar en la sección 4.2

Glass melting), y una vez terminado, se vierte el vidrio fundido en un

molde de carbono, y se le somete a un nuevo programa térmico de

recocido de 5 horas a 350 C. En la imagen se muestra un disco de 30 g

de Ti5

Se fundió también un vidrio de silicio nombrado B50 para comparar las facilidades de extru-

sión. Su composición y procedimientos están explicados en la memoria.

Extrusión de la fibra de vidrio

Una vez se obtenían muestras de unos 25 g aproximadamente, se comprobaba que eran de ca-

lidad y no estaban parcialmente cristalizadas, se rompía en trozos grandes, una cantidad de unos

80 g de vidrio, y se depositaba en un nuevo crisol de platino, en este caso un crisol especial,

perforado por la parte inferior, para que el vidrio pueda caer cuando se está fundiendo. El Sr50

se posicionaba en el interior del horno, el cual tenía un conducto que permitía al vidrio caer del

crisol directamente al exterior.

La temperatura deseada se encuentra entre los 880 y los 900 C, como se pudo comprobar. Si

permanece a temperaturas inferiores, se cristaliza. Si, sin embargo, se expone a temperaturas


SERGI ROCA PUERTAS v

superiores, se funde demasiado y cae de golpe en forma líquida. El punto deseado es intermedio

entre sólido y líquido, lo suficiente líquido para que, por su propio peso, una primera gota caiga,

pero manteniendo la viscosidad que lo haga permanecer en el crisol.

Una vez obtenida la primera gota, esta arrastraba una fina fibra que la unía con el resto del

vidrio dentro del crisol. A continuación, se tracciona dicha fibra a un ritmo lo más constante

posible, para obtener una fibra uniforme, sin llegar a romperla.

DTA: Differential Thermal Analysis.

El análisis térmico tiene como objetivo estudiar una propiedad física en una sustancia, en fun-

ción de la temperatura. En este caso, se estudia la cantidad de energía necesaria para mantener

la muestra a cierta temperatura comparado con otra muestra de la que previamente se saben sus

propiedades. Se miden cambios en la absorción o emisión de energía y se comparan con la

muestra. Este análisis muestra los cambios de fase del material. Es interesante en este estudio,

para controlar los puntos de cristalización y fusión del vidrio, y así saber qué materiales tendrán

mejor comportamiento y menos tendencia a la cristalización a la hora de producir las fibras.

Para realizar el análisis térmico diferencial y poder interpretar bien las propiedades térmicas de

cada uno de los vidrios, era necesario, por medio de un mortero, convertir el vidrio en pequeñas

partículas de entre 125 y 250 micrómetros. Para ello se hizo uso de un filtro con el que diferen-

ciar las partículas.

30 mg de vidrio, en un crisol diminuto, se ensayaban térmicamente en el horno

DTA, Netszch F1 JUPITER con el procedimiento explicado previamente.

El resultado obtenido fueron las gráficas mostradas en la siguiente figura. Una por una, se su-

perpusieron utilizando Origin (software utilizado para el procesamiento de datos a lo largo de

todo el proyecto):

Para explicar la gráfica, se prestará atención a la curva rosa, Mg5. El pico más alto, que se

encuentra a aproximadamente 620 C, corresponde con la temperatura de cristalización Tb. El

pico mínimo absoluto, situado en 700 es la “liquidous temperature” y es el punto endotérmico

donde el vidrio comienza a fundirse. Para una mayor estabilidad a la hora de fundir de nuevo

el vidrio para poder extraer las fibras, se busca que la curva DTA sea lo más lisa posible, con

poco cambio energético.

Es por ello, que los mejores vidrios para extraer fibras son el Si5 y el Ti5 (entre los estudiados).

Aun así, solo se extrajo fibra del Si5 ya que no se disponía de un crisol perforado de silicio, y

en el de platino resulta imposible porque se forma aleación entre los dos metales.

RESUMEN

vi ESCUELA SUPERIOR DE INGENIERIEROS INDUSTRIALES (UPM)

100 200 300 400 500 600 700 800 900 1000 1100

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

35

40

45

DS

C (

mW

)

Temperatures (°C)

Sr50

Ti5

Si5

Mg5

Cu5

SBF: Simulated Body Fluid

Es una solución tampón utilizada en ensayos in-vitro, para simular la degradación de los mate-

riales dentro del cuerpo humano. Es una solución acelular con el mismo PH y que contiene los

mismos iones inorgánicos que el plasma sanguíneo, pero con falta de proteínas u otros consti-

tuyentes orgánicos.

Su preparación siempre tuvo que ser muy precisa y está detalladamente explicada a lo largo de

la memoria. Tiene una duración aproximada de 5 horas en total. Y el objetivo final es ajustar

su PH al del cuerpo humano en 7,4.

Inmersión de SC2, CC2, Sr50 y Sr5

Previamente, se contaba con dos tipos de fibra de vidrio distintos, ambos hechos con base de

Sr50, añadiéndoles un 2,50% molar de B2O3. Su composición se muestra en la tabla siguiente.

La diferencia entre ambos, como puede verse, es que el Cc2 cuenta además con el núcleo do-

pado de Cerio.

Sample

Diameter

(μm) P2O5 CaO SrO Na2O B2O3 CeO2

Sc2 125 125 47.50% 20% 20% 10% 2.50% -

Sc2 250 250 47.50% 20% 20% 10% 2.50% -

Cc2 125 125 47.50% 20% 20% 10% 2.50% 0.25%

Cc2 250 250 47.50% 20% 20% 10% 2.50% 0.25%

*Core doped with Cerium (mol%)


SERGI ROCA PUERTAS vii

También se sumergieron las fibras obtenidas por extrusión de Sr50, y otras fibras con las que

se contaba, llamadas Sr5, de vidrio de silicio, con la siguiente composición, para comparar su

comportamiento con las fibras de fosfato.

•Sr5: 53.85SiO2 1.72P2O5 16.77CaO 22.66Na2O 5SrO

El objetivo de sumergir las diferentes fibras en SBF por diferentes períodos de tiempo, es ver

como ese hecho afecta a las propiedades físicas de la fibra, estudiar su biodegradabilidad en

función del tiempo y ser capaces de caracterizar los diferentes vidrios para poder ajustar su

buen uso.

Antes de su inmersión en SBF, se procede a medir su diámetro, para después comprobar, tam-

bién, cómo estos varían. Las fibras se sumergen por periodos de 6, 24, 48 y 72 h, y 1 y 2 sema-

nas. En total, para cada uno de los períodos, se sumergen 10 fibras de 15 centímetros cada una.

Cada grupo de 10 fibras, considerémoslo como una muestra, estaba clasificado por tipo de vi-

drio y diámetro. Sc2 y Cc2 fueron ensayados con diámetros de 125 y 250 micrómetros.

Medida del PH

Al finalizar el tiempo de inmersión de cada una de las muestras, se extraían del líquido con

mucho cuidado, se rociaban de etanol para limpiar bien las partículas de SBF y se secaban en

una incubadora durante 24 horas. El Líquido SBF resultante, se utiliza para medir su PH, y ver

cómo éste ha variado con el tiempo. Para ello se usa una máquina Mettler To-ledo Seven-

Multi™ pH/conductivity meter.

Los resultados se plasmaron en las gráficas siguientes, y fueron analizados.

Como se puede comprobar, en las tres muestras de fibras de vidrio de fosfato, el PH tiende a

disminuir de acorde con el tiempo que las fibras permanecen inmersas. Esto es debido a que las

fibras, a medida que van reaccionando, se disuelven y aportan iones y moléculas de fosfato

cálcico al medio reactivo.

7,24

7,26

7,28

7,3

7,32

7,34

7,36

7,38

7,4

7,42

0h 6h 24h 48h 72h 1 w 2 w 3 w

PH

PH SBF SC2/CC2

PH Sc2 125 microns

PH Sc2 250 microns

PH Cc2 125 microns

PH Cc2 250 microns

PH Sr50

RESUMEN

viii ESCUELA SUPERIOR DE INGENIERIEROS INDUSTRIALES (UPM)

Aunque no se ha incluido su gráfica en este resumen, para el Sr5, el PH, sin embargo, se veía

incrementado con el paso del tiempo. Debido a que simplemente se desintegran las fibras, pero

existe formación de dicho fosfato cálcico.

AAS: Atomic Absorption Spectroscopy. Medida de la concentración de iones Ca2+

Se prepara una disolución con el SBF resultante y agua (destilada), el objetivo es una disolución

ten-fold (decúpula), para reducir su concentración. Una vez obtenidas todas las muestras, se les

realizaba el análisis AAS con un espectrómetro Perkin Elmer AAnalyst 300, utilizando una

llama de aire-acetileno. De esta forma se cuantificaba la cantidad de iones Ca2+. De la misma

forma que en el análisis de PH, como comprobamos en la siguiente figura, el contenido de Ca2+

disminuye en función del tiempo en los vidrios de fosfato. Al contrario ocurre de nuevo con el

Sr5 (vidrio de silicio), de nuevo.

Una vez más, este descenso de concentración de Ca2+ es debido a la formación de fosfato cál-

cico, que era lo que buscábamos, la prueba de su desintegración bajo la formación del mismo,

para facilitar la formación de Hidróxiapatita. Se puede comprobar en esta figura.

La degradación de las fibras, y su correspondiente formación de fosfato cálcico, es mayor para

las fibras sin dopaje de Cerio (Sc2).

Ensayos mecánicos

Una vez que cada muestra (10 fibras de vidrio) era retirada por completo del SBF, como se ha

explicado antes, se procedía a realizar el ensayo mecánico de tracción. Para ello se utilizó una

Instron 4411. A través de los ensayos mecánicos se obtenía la gráfica de tensión y deformación

característica de cada fibra. Una a una, las 390 fibras fueron ensayadas, la curvas obtenidas,

procesadas y corregidas, mediante Origin, seleccionando solo la parte lineal de la curva, para

que el resto no influyera de forma negativa manipulando los resultados de la pendiente (Modulo

de Young).

0

1

2

3

4

5

6

6h 24h 48h 72h 1 w 2 w 3 w

Ca2

+co

nce

ntr

atio

n (

mg/

l)

Ca (mg/l) Sc2/Cc2

Sc2 125microns Ca(mg/l)

Sc2 250microns Ca(mg/l)

Cc2 125microns Ca(mg/l)

Cc2 250microns Ca(mg/l)


SERGI ROCA PUERTAS ix

Finalmente se obtienen gráficas comparativas para Modulo de Young (E) y Tensión admisible

a máxima carga. A continuación se muestra el Modulo de Young E, para Sc2 y Cc2 de 250

micrómetros.

Como se puede comprobar, el Modulo de Young no varía prácticamente en función del tiempo

de inmersión, sino que se mantiene constante. Era exactamente el resultado que buscábamos,

que indica que el material sigue siendo el mismo pese a su degradación.

Aparece en cambio factor muy curioso a partir de las 72 h o 1 semana. La gráfica comienza a

dividirse en dos. Hay ciertas fibras que tienen un comportamiento totalmente distinto al resto,

y su E disminuye. Como se observa en la gráfica, a dichas fibras se les ha llamado Sc2 y Cc2

system.

Este resultado, lo que nos indica, es que las fibras más degradadas, con mayor cantidad de

fosfato cálcico en la superficie, como parte de un sistema fibra+fosfato, tienden a comportarse

con otras propiedades físicas. Sin embargo, sigue habiendo otras que han sido menos atacadas

por la solución tampón, que siguen comportándose como el material que eran. Es decir, la for-

mación de fosfato cálcico no es uniforme para todas las fibras).

En este caso, son las fibras de Sc2, en comparación con las de Cc2 las que ofrecen unas mejores

propiedades mecánicas en función del tiempo de inmersión. Sr5 y Sr50 mostraron muy malas

propiedades físicas, que no sobrepasó su posible estudio por más de 24 horas.

FTIR: Fourier Transform Infrared Spectroscopy

Este método mide las transiciones vibracionales entre su estado fundamental y estados de exci-

tación. Estas transiciones son medidas mediante absorción o emisión de luz. El material a tratar

se expone a radiación IR. Parte de esa radiación simplemente pasa a través del material, y otra,

en cambio, es absorbida. Esta energía transmitida, supone el espectro buscado. Ya que no puede

haber dos moléculas diferentes que emitan el mismo espectro infrarrojo, a través de su lectura,

0

10000

20000

30000

40000

50000

60000

0 6 24 48 72 1w 2w 3w

E M

Pa

YOUNG MODULUS ESC2/CC2 250 micrometers

E SC2 system

E SC2

E CC2 system

E CC2

RESUMEN

x ESCUELA SUPERIOR DE INGENIERIEROS INDUSTRIALES (UPM)

se puede observar perfectamente de qué tipo de sustancias estamos analizando. Es decir, FTIR

puede mostrarnos materiales desconocidos, es decir, mostrarnos la composición de dichos ma-

teriales.

Cada molécula, teniendo n átomos, tiene 3n grados de libertad. 6 de ellos son para la propia

molécula, y 3n-6 para los distintos modos de vibración que son: Estiramiento simétrico, tijere-

teo, aleteo, estiramiento asimétrico, balanceo y torsión.

La vibración IR puede ser activa o inactiva, dependiendo si hay absorción del espectro IR o no.

En este ensayo, el FTIR se realizó por medio de una máquina Perkin Elmer FTIR spectrum.

Todo el espectro fue grabado en una banda desde 600 a 2000 cm-1. FTIR se aplicó a todas las

muestras de Sc2 y Cc2 para 0 y 72 horas, y 1, 2 y 3 semanas, ya que para tiempos de inmersión

menores a 72 horas, no se observó cambio.

A continuación se mostrará el ejemplo del Sr50, que fue la que mejor comportamiento tuvo al

realizar el análisis, y es más fácil observar los cambios producidos en el material debidos a la

inmersión.

Una vez realizado el FTIR, y para analizar los resultados, el espectro IR fue normalizado apro-

ximadamente en 880 cm-1, donde se presenta el mayor pico.

Se pueden apreciar 3 zonas perfectamente diferenciadas en el rango de 600 a 1400 cm-1:

Vibración de grupos de fosfato PO2 “no-puente” o Q2 en 1400-1150 cm-1.

Región terminal de grupos P-O y PO3, Q0 y Q1, en 1150-900 cm-1.

Vibración de los grupos P-O-P, 900-700 cm-1

Se pueden comprobar, con este previo y breve resumen de cómo se distribuye el fosfato en el

espectro IR, los resultados siguientes. Se produce un incremento de los grupos Q1 y descenso

de los grupos Q2. Este hecho significa que la estructura del vidrio está sufriendo una despoli-

merización de las cadenas de fosfato desde Q2 a Q1, es decir, se están rompiendo dichas cadenas,

y, por tanto, formando cadenas más cortas (mayor número de Q1 indica mayor número de ex-

tremos de cadenas).


SERGI ROCA PUERTAS xi

700 800 900 1000 1100 1200 1300 1400

0,0

0,2

0,4

0,6

0,8

1,0

A.U

.

Wavenumber (cm-1)

Sr50-0

Sr50-24

Sr50-48

Sr50-72

Sr50-1w

Son grandes noticias, ya que el objetivo de los vidrios bioactivos, es el de disolverse en el

cuerpo humano.

Los resultados son variados para el resto de vidrios, mostrando algunos de ellos ciertas anoma-

lías, las cuales sería preciso seguir investigando, para ver si se repiten.

El vidrio de silicio Sr5, muestra un espectro totalmente distinto al de los de fosfato, que puede

ser apreciado en la “Figure 5.20. FTIR spectra of Sr5 glass fibers, as function of the immersion

time.” Unos resultados bastante buenos en los que se aprecia muy bien. La curva se normaliza

en este caso para 960 cm-1. Es este cado las variaciones se muestran en el incremento de con-

centración de unidades de SiO4 y descenso de unidades de Si-O-.

Conclusiones y futuras líneas de investigación

Es este trabajo de investigación se ha contribuido al estudio de la fibra de vidrio de una forma

muy exhaustiva.

Se ha profundizado en el estudio de creación, por medio de la extrusión, de fibras de vidrio con

nuevas composiciones, distintas a las que hoy en día se utilizan. Métodos que aún no están muy

desarrollados, y que necesitan de nuevas y numerosas pruebas. El análisis térmico (DTA), nos

deja claro cuáles son las composiciones más apropiadas para ellos, por una mayor estabilidad

energética del vidrio. Para ello se ha estudiado el vidrio protagonista de este estudio, Sr50. Pese

RESUMEN

xii ESCUELA SUPERIOR DE INGENIERIEROS INDUSTRIALES (UPM)

al pequeño cambio en la composición (5% molar), se observaron grandiosos cambios en sus

propiedades térmicas. Como conclusión se deduce que debería seguir profundizándose en la

creación de fibras de vidrio del tipo Si5 y Ti5, las cuales pueden suponer una muy buena apuesta

futura, a un precio razonable, ya que serían las más fáciles de extrudir.

De forma independiente, se han analizado las propiedades de las fibras de fosfato fabricadas en

este mismo estudio, de Sr50, y de otras, también de base de Sr50, con una composición ligera-

mente modificada, Sc2 y Cc2.

Sc2 y Cc2 tienen un muy buen comportamiento reactivo al cuerpo humano. Se degradan de

forma gradual, reducen sus propiedades físicas también de forma gradual. De este estudio se

puede analizar, en función del tipo de aplicación biomédica, el tipo de fibra más conveniente.

Como refuerzo para materiales compuestos, queda claro, que la fibra de vidrio puede jugar un

papel fundamental en la fuerza de dichos materiales. En este estudio se observó la dureza y

Modulo de Young en función del tiempo de inmersión, el cual permanece prácticamente cons-

tante hasta el paso de cierto tiempo.

Como complemento, se está produciendo, y se prevé un cambio aun mayor, un incremento del

uso de materiales no metálicos en implantes. Para ello es necesaria la creación de nuevos bio-

materiales compuestos. En este caso, las fibras de fosfáto cálcico, no solo proveen al implante

de una mayor fuerza, sino que apoyan con sus propiedades osteoconductivas (capacidad de un

material para actuar como un substrato en el cual las células puedan adherirse y desarrollar sus

funciones).

En este estudio también se ha comprobado que, en principio, las fibras de vidrio de fosfato

cálcico, no suponen ningún peligro, ni riesgo potencial para el cuerpo humano ya que no se

libera ningún tipo de ion dañino al diluirlos en SBF.

Para finalizar se concluye afirmando que este tipo de vidrios bioactivos, ofrece una gran opor-

tunidad para el desarrollo de nuevos materiales compuestos y técnicas, como materiales cons-

tructivos en ingeniería de tejidos.

SERGI ROCA PUERTAS

CONTENTS

1. INTRODUCTION ..................................................................................................... 1

2. OBJECTIVES ........................................................................................................... 3

3. THEORY AND LITERATURE REVIEW ............................................................... 5

3.1 Biomaterials .................................................................................................... 5

3.2 Bone and hard tissue ....................................................................................... 5

3.2.1 Bone mechanical properties ............................................................. 6

3.3 Glasses and their properties ............................................................................ 7

3.4 Phosphate glasses ........................................................................................... 8

3.5 Differential Thermal Analysis (DTA) ............................................................ 9

3.6 SBF ............................................................................................................... 10

3.7 FTIR ............................................................................................................. 10

3.7.1 FTIR Spectrum absorption of hydroxyapatite (HAp) .................... 13

3.8 AAS .............................................................................................................. 13

3.9 Mechanical properties of glass fibers ........................................................... 14

4. EXPERIMENTAL PROCEDURE ......................................................................... 17

4.1 Preparing calcium and strontium phosphate ................................................ 17

4.2 Glass melting ................................................................................................ 18

4.3 Glass crushing .............................................................................................. 19

4.4 Making fibers ............................................................................................... 20

4.4.1 Sr50 ................................................................................................ 21

4.4.2 Si5 .................................................................................................. 21

4.4.3 B50 ................................................................................................. 21

4.5 Making SBF ................................................................................................. 21

4.6 SBF Test ....................................................................................................... 22

4.6.1 Mechanical test ............................................................................... 23

4.6.2 Tensile Test .................................................................................... 25

4.7 PH Measurement .......................................................................................... 26

4.8 Atomic Absorption Spectroscopy ................................................................ 26

4.9 Fourier transform infrared spectroscopy ...................................................... 27

4.10 Differential thermal analysis ........................................................................ 27

5. RESULTS................................................................................................................ 29

5.1 DTA .............................................................................................................. 29

5.2 SBF Test ....................................................................................................... 30

5.2.1 AAS and PH measurement ............................................................. 30

5.2.2 Mechanical test ............................................................................... 32

5.2.3 FTIR ............................................................................................... 37

6. CONCLUSIONS AND FUTURE LINES OF RESEARCH .................................. 43

7. CORPORATE SOCIAL RESPONSIBILITY ......................................................... 45

8. TIMING AND BUDGET........................................................................................ 47


LIST OF SYMBOLS AND ABBREVIATIONS

AAS Atomic absorption spectroscopy

DTA Differential thermal analysis

FTIR Fourier transform infrared spectroscopy

HAp Hydroxyapatite

SBF Simulated Body Fluid

Glasses:

Sr50 50 P2O5 – 10 Na2O – 20 SrO – 20 CaO

Si5 45 P2O5 – 10 Na2O – 20 SrO – 20 CaO – 5 SiO2

Cu5 45 P2O5 – 10 Na2O – 20 SrO – 20 CaO – 5 CuO

Mg5 45 P2O5 – 10 Na2O – 20 SrO – 20 CaO – 5 MgO

Ti5 45 P2O5 – 10 Na2O – 20 SrO – 20 CaO – 5 TiO2

B50 26,93 SiO2 – 26,93 B3O3 – 22,66 NaO2 – 21,76 CaO – 1,72 P2O5

Sr5 53.85SiO2 1.72P2O5 16.77CaO 22.66Na2O 5SrO


SERGI ROCA PUERTAS 1

1. INTRODUCTION

Materials used to be in contact with human tissue are known as biomaterials. This material

application in the human body is not new. It is something that has been made for centuries

although the real successful advantages take part in the 20th century [1] [2]. Objective of them

is to improve health in people with accidental, birth or age disorders by reconstructing the miss-

ing or broken part of the human body.

These biomaterials can be divided in two different groups, biocompatible and bioactive mate-

rials. While biocompatible materials release non-toxic substances to the body that do not alter

the constitution of it, bioactive materials have a positive impact on the tissue e.g. the forming

of the bone on the proximities of the scaffold. Then, resorbable materials completely disappear

from your body after a period of time by being hydrolytically or enzymatically degradable.

Characterization of biomaterials is fundamental, and as they cannot be proven in animals at

least in their earlier stage of development, the best option until now are in-vitro cell tests.

The ideal biomaterial for applying in bone replacement or fixation would be one that adapts

itself to the repairing process. That its absorption does not exceed the rate of bone formation

and also this ratio goes weakening the scaffold at the same time that bone tissue gets stronger.

The use of these kinds of material that promote the bone regeneration in exchange of the tradi-

tional screws and plates that remain constant would mean an improvement not just economi-

cally but in people’s health.

Problems with metal and alloy materials in scaffolds comes because, even though the help in

the healing process, their stiffness is much higher than the bone itself, which made needs of

mandatory removal of the material after the bone is fixed.

Recently (from 1906), the use of ceramics and glasses in scaffolds is raising and has opened a

new science of study in biomedical field. Most common bioactive glass used is Bioglass®.

Silicate glass which has been proved that is stable to hydrolysis due to its silica content, but still

creates osteoblast cell attachment and proliferation

In the other hand, phosphate glasses constitute an alternative to previous silica glasses. Their

properties make them soluble in water and adjustable by altering glass composition. Hence,

they have a big potential in being applied as a bioresorbable implant materials. As good char-

acteristics we can mention their processibility (Low melting glass transition and melting tem-

peratures), and their adjustable solubility. [3]

INTRODUCTION

2 ESCUELA SUPERIOR DE INGENIERIEROS INDUSTRIALES (UPM)



2. OBJECTIVES

The goal of this study is the development of new phosphate glasses by studying their chemical,

thermal and mechanical properties comparing them between each other’s and with other previ-

ous studies in order to improve the current implementation of biomaterials in bioresorbable

bone replacement and degradable scaffolds in tissue engineering. The use of degradable mate-

rials for bone repairing and regeneration is a great advance in surgery. The point is approach

the phosphate properties of the glass to a bone holding by its strength and being enough de-

gradable in accordance to bone healing process.

Phosphate glasses with suitable additives in their composition can be adjusted in terms of crys-

tallization tendency or solubility. The release of particles from these glasses has to be always

constituted by those which are already present in the human body. Optimization of the degra-

dation rate improves biocompatibility and bioactivity in the material.

Taking in account silica glasses and comparing them with phosphate ones, the phosphate

glasses have higher crystallization tendency. This tendency has to be reduced as much as pos-

sible in order to improve producibility.

In this thesis, the process made was as follow. First of all, manufacturing of the glasses. This

has been a task included during all the process of the research, every week, every day. Once

that some samples of glass were made, DTA studies the thermal properties of them in order to

determine which are easier to draw (for making fiber) according with a more stable energy

during the melting process. Once the glasess are chosen due to be the ones that fit the best

profile, was time to draw the first fibers.

When all the fibers were ready, they were immersed in SBF (simulated body fluid) to prove

their biocompatibility and bioactivity. Afterwards, the glass fiber was tested in a tensile ma-

chine, the chemical properties to determine biodegradability were tested using AAS and FTIR.

The goal of the thesis is being able to specify which glasses have the best properties and try to

understand why. Make a comparison between them. And describe which could be a good way

to keep researching them in the most efficient way, rejecting the ones that, here, we will prove,

are not the best option.

OBJECTIVES




3. THEORY AND LITERATURE REVIEW

3.1 Biomaterials

Nowadays, a very large variety of sophisticated materials have been used in biomedicine. From

some years ago, new polymers and metals started to be used in medicine as scaffolds. From that

moment, the use of these kind of materials is more and more commonly used, hence, new tech-

nologic advances need to be reached.

A biomaterial is a nondrug element ready to get into a physiological system for improving or

substituting the functions of the body tissues or organs. The bio material must fit perfectly in

the system, hence it has to have the mechanical, thermal and chemical requirements from the

body as shear, strain, Young’s modulus, temperature coefficient, being compatible with the

biological body system, inert… Biomaterials can be polymers and plastics, metals, ceramics or

treated natural materials. They most important property of the biomaterials is the biocompati-

bility; in some applications the contact of them with the implant is necessary, for example using

the fibrous capsule to hold the implant from moving [3], [4].

The use of materials in surgery is coming from long time ago. Already, in the pre Christian era,

replacements for broken bones were used. During this ancient times bronze and copper implants

were mainly utilized for repairing bones. The risk of poisoning was low as the Cu2+ ions circu-

lating in the body were overwhelmed once the copper element had completely dissolved in the

body fluid when the fractures were repaired.

Until mid-nineteenth century bronze or copper were not considered as an option for implants.

A wide range of new sophisticated materials are currently studied and used in biomedical fields

as implants, it just occurs some years ago. [5].

3.2 Bone and hard tissue

Human skeleton is constituted by bones. Bones are a the main important mechanical holder of

the human body, therefore, it is defined to resist stress providing internal support again the

external human body forces including the constant gravity. Its composition depends on the kind

of bone, age, sex and physiological conditions.

Bone composition can be divided in cortical bone and trabecular. Cortical bone is 80% in mass

of the whole body skeleton.

Bones are composed by around 70%wt of mineral which is almost the 40% of the bone volume.

These mineral constitutors are mainly calcium Ca2+ and phosphate PO43- and also a small part

of carbonates CO32-. The organic matrix constitutes around 40%wt. It is constituted by around

THEORY AND LITERATURE REVIEW


90%wt, 30% of the volume, protein collagen type I. Non collagenous proteins complete the rest

of the small percentage composition, they are small part, but also important for the bone char-

acteristics and functions. Water is the 25% of the bone volume. [6]

The calcium phosphates that constitute the bone are hydroxyapatite, Ca10(PO4)6(OH)2 (HA).

Figure 3.1 Hydroxyapatite structure [6]

Apatite in bones is characterized by containing fluorine, sodium and magnesium in small

amounts. The different amount of constituents, apatite, collagen and water, all of them with

completely different properties, makes bones a composite material. [6] [7]

3.2.1 Bone mechanical properties

For this engineering study, the main mechanical properties of the bone are deformation (strain),

Young’s modulus and strength. Strain is the deformation of a solid as a function of the stress

applied. It can be expressed by:

ɛ =𝜎

𝐸

While ɛ is the strain and 𝜎 the stress and E the Young’s modulus. An example can be seen in

the next figure of the relation between strain and stress in the human femoral bone. The slope

of the linear part of the curve is exactly the Young’s modulus of the material.



Figure 3.2. Stress-strain curves of human femoral bone. Adapted from Evans (1969). [8]

The term strength represents the stress at the breaking point.

For the cortical bone the Young’s modulus values are in the range from 17 to 24 GPa depending

on the age, sex, location of the bone, and many other factors. The tensile and compressive

strengths for bones in axial direction are around 130 and 200 MPa respectively. While in per-

pendicular direction to the axe are 50 and 130 MPa respectively. [7] [9]

3.3 Glasses and their properties

Glass is defined as an amorphous, rigid solid with a viscosity higher than 1013 poise. Next

oxides can be made into glass: B2O3, SiO2, GeO2, P2O3, As2O3, Sb2O3, In2O3, Tl2O3, SnO2,

PbO2 and SeO2 [10].

Oxides that are able to form glasses are going to be divided in three groups namely glass-for-

mers, intermediates and modifiers, in accord with their single strength bond value [11]. The

mainly primary glass formers are SiO2, P2O5 and B2O3 with the ability of forming single com-

ponent glass. The most used currently are the silica glasses. They have the highest melting

point, hence, in the main composition are added other components in order to reduce this tem-

perature. Phosphate glasses have the problem of being very reactive and hygroscopic, so the

aim of adding other components is increase its durability. The structure of phosphate and silica

glasses network forming tetrahedral can be notices in the figure below.



Figure 3.3. Phosphate and silica tetrahedron.

Figure 3.4.Glass characterization examples [10]

3.4 Phosphate glasses

Phosphate glasses are a network of phosphate tetrahedron bonded each other using the bonding

corner sharing atoms of oxygen. Oxygen atoms linking two phosphate tetrahedrons are called

bridging atoms, and all who does not link it are non-bridging atoms.

Phosphate glasses are made by PO4 tetrahedrons which are usually divided in Qn groups. The

phosphate can be bonded in 4 different ways which compound each of the 4 different groups,

Q0 would be the isolated orthophosphate group, Q1 is the end unit, Q2 is the middle unit, and

finally the branch unit Q3. For Qn, n means the number of bridging oxygen atoms per tetrahe-

dron. For example, Q2 is linking two phosphate tetrahedrons in a polymeric phosphate chain,

being Q1 as the end of the chain. Next Figure 3.5 represents very well how are these phosphates

bonded with oxygen atoms [12] [13].

Figure 3.5. Phosphate tetrahedral units. Oxygen atoms (pink) connected to phosphorus at-

oms (blue). Q3 crosslinking units; Q2 middle units; Q1 end units; Q0 isolated units. [13]



3.5 Differential Thermal Analysis (DTA)

Thermal analyses are made in order to study a physical property of a substance as a function of

temperature. In this case, Differential Thermal analysis study the amount of energy needed to

keep the sample to a chosen temperature comparing with another reference sample which we

know previously its properties. It is applied the same heat treatment for both of them, and it is

measured the energy needed to keep them at exactly the same temperature.

DTA involves heating or cooling down the desired sample and another reference sample in the

same conditions. The differences between the temperatures of the inert reference and the sample

are measured and plotted as a function of time or temperature. The changes on the sample,

absorption or emission of energy are measured comparing them with the reference sample.

DTA can measure phase changes, hence, its curve present changes and can be appreciate on it

the transition points for the sample material as is wanted in this thesis for the having knowledge

of the crystallization or melting temperatures of the glass.

The Differential Thermal Analysis instrument is composed by the next components shown in

the picture below:

Thermocouples and ceramic or metallic crucible for putting the study material inside.

PLC, controlling the heating program.

Furnace.

Recording system.

Figure 3.6. Structure of a DTA instrument.

The two containers are filled with the sample and with the inert reference. It works due to the

deflection of the voltmeter depending on the temperature variation [14].



3.6 SBF

It is mentioned before that one of the most recent and important advantage made by the ortho-

pedic industry is producing biomaterials able to replace bone in human body. It is known that

this is possible because these biomaterials (bioactive glasses, glass ceramics…) and the bone

tissue are biocompatible. When these materials are incorporated in the bone in the human body,

they form a fibrous tissue interface layer. The apatite forming ability of the biomaterials can be

measured using Simulated Body Fluid (SBF) in-vitro and the results can predict the ability of

these biomaterials in-vivo [15].

SBF has been used in hundreds of researches when need to evaluate the performance of new

biomaterials for replacing a bone. The test in-vitro is always an excellent pre-test.

Methods for testing SBF in-vitro have been standardized [16]. Their ion concentrations similar

to the blood are represented in the next Table 3.1.

Table 3.1. Ion concentration of SBF comparing with human blood plasma according to the

ISO standard [16]

Concentration (10-3 mol)

Ion SBF (PH=7.4) Blood plasma (PH=7.2-7.4)

Na+ 142 142

K+ 5 5

Mg2+ 1.5 1.5

Ca2+ 2.5 2.5

Cl- 147.8 103

HCO3- 4.2 27

HPO42- 1 1

SO42- 0.5 0.5

3.7 FTIR

Infrared spectroscopy measures the vibrational transitions between the ground and the first ex-

ited states. It could be measure by absorption or emission of light [17].

Fourier Transform Infrared is the most common method of infrared spectroscopy. The sample

material is exposed to a IR radiation. Some of the radiation is passed through the sample and

some is absorbed. The transmitted radiation and the absorbed one is the spectrum result and it

gives a fingerprint of the structure of the sample. Depending on the infrared spectrum, the struc-

tural composition of the sample can be known because cannot be two different molecular struc-

tures emitting the same infrared spectrum [18]. Therefore, FTIR can define unknown materials;

determine the composition of a sample and its consistency. Figure 3.7 shows how it works.



FTIR has many benefits used for chemical analysis of calcium phosphate components. Basi-

cally the resultant spectrum obtained gives information about the location, intensity and other

properties for the desired wavelength [19].

Figure 3.7. FTIR, main principle of who it works [18].

The wavelength resultant is the wavelength transmitted without taking in consideration the

wavelength absorbed by the material, so its structure is known from now.

In order to explain better how it works and how it is going to be used first of all, has to be

explained the electromagnetic spectrum. IR waves travel at light speed and they have a specific

range of wavelength and frequency which is from 8x10-5 cm to 1x10-2 cm. Wavelength is the

measured distance between two peaks in a wave, λ. It is inversely proportional to the frequency

ν. While c is the speed of light.

λ = c/ν

Being photons packs of energy, when they strike a molecule, depending on its energy, they can

be absorbed by it which will produce a reaction. The energy absorbed by the molecules under

the IR is enough to make atoms vibrate but not to make electronic transitions.

The result vibration transitions give information about how atoms are bonded between each

other.

Every molecule having n atoms has 3n degrees of freedom. 6 of them are for the molecule itself.

Hence, there are 3n-6 of them for vibrational modes which can be divided in stretching, twist-

ing, rocking, bending and scissoring. Next Figure 3.8 shows the main vibrational modes.



Figure 3.8. Vibrational modes of a molecule. [20]

Vibration IR can be active or inactive depending if there is absorption of the IR spectrum of

not. Symmetrical bonds have zero dipole moment and when they are stretched the dipole is still

zero, hence, there is no absorption of energy. It is inactive IR vibration.

In the next Figure 3.9 will be shown an example on how IR spectrometry works in order to

determine the different kind of bond between the molecules using molecular vibrations pro-

duced by IR absorption. Next example shows the infrared spectrum of methanol. Being finger-

print the region from 600-1400 cm-1, the most complex and informative part of the spectrum

that contains wagging, twisting, scissoring and rocking vibrations [20].

Figure 3.9. Infrared spectrum of methanol, which shows O-H, C-H and C-O stretching ab-

sorptions from several bending modes. [20]



3.7.1 FTIR Spectrum absorption of hydroxyapatite (HAp)

Hydroxyapatite (HAp) Ca10(PO4)6(OH)2 is the most significant mineral phase belonging to the

bones and bone tissues. The most common component groups in the IR spectrum of HAp are

OH-, HPO42- and PO4

3-.

PO43- are the most interesting for this project and form and intensive IR absorption at 560, 600

and 1000-1100 cm-1. More specifically HAc present bands of PO43- that have the following

vibration modes: 460 cm-1 has v2 vibration mode. 560-600 have v4 bending vibrational mode.

960 has v1 vibrational mode. 1020, 1120, 1040 have v3 Bending vibrational mode (Destain-

ville, et al., 2003), (Han J-K., et al., 2006). Next Figure 3.10 shows the IR spectrum of HAc.

Figure 3.10. Typical FTIR spectrum of hydroxyapatite (Ratner, 2004). [19]

3.8 AAS

It is a technique used for determining the concentration of an element in the sample. This

method can be used to determine 70 kind of different elements in a solution or even in the solid

samples.

AAS main principle is based on that metal atoms absorb characteristic wavelengths and this

absorption is the same as the emission spectra of this particular metal [21].

The technique works taking in account that free atoms (gas) generated in an atomizer can absorb

radiation at specific frequency. These atoms absorb radiation and make transitions to higher

electronic energy levels. Depending on the amount of absorption the concentration is deter-

mined. The instrumentation is composed by the following parts; Hollow Cathode Lamp, De-

tector, Nebulizer, Atomizer and Monochromator.

Hollow cathode lamp is the radiation source most common in AAS.



The Nebulizer sucks up liquid at a controlled rate and convert the sample in an aerosol spray

for introduce it into the flame.

The Atomizer converts the elements in atomic state by separating the particles into individual

molecules and breaking them in atoms. In the case of this thesis, the atomizer was flame atom-

izer. The flame is formed by mixing oxidant gas and fuel.

The Monochromator is used to separate all of thousands of lines and select the specific wave-

length absorbed by the sample by excluding all the other wavelengths. It makes possible the

determination of the selected element in presence of the others.

Finally the light goes to the Detector which converts the light into an electrical signal as a

function of the intensity. [22]

Figure 3.11. Structure of AAS instrument. [23]

3.9 Mechanical properties of glass fibers

Fibers are the principal load carrying component of a composite. The characteristics of the fiber

significantly influence the effective mechanical and damage properties of the composite fabri-

cated from it. The mechanical and damage properties of individual constituents, that is fiber

and matrix, are essential in a micromechanical analysis of composites for effective properties

and damage evaluation. These experiments are conducted on single filaments. In most of the

micromechanical analysis the mean or average properties are used. However, the variation of

properties can have significant effect on the final results. Hence, one needs statistical infor-

mation about the individual constituent properties for detailed micromechanical analysis. In the

present study another emphasis is given to create the statistical data for the behavior of these

fibers. The experimental procedures to determine the axial Young’s modulus and ultimate axial

tensile strength of single fiber have been explained in detail in this work. This has been possible

following Standard Test Method for Tensile Strength and Young’s Modulus of Fibers, ASTM

C1557. [24]

Even being more recommended making these studies using specific statistic models to study

the mechanical properties. In this case, due to the lack of time sources and specimens, the me-

chanical test will follow the standard process.



Tensile test will give us information about Young’s modulus which is a mechanical property of

linear elastic solid materials. It relates stress and strain in a material.

E=𝜎

ℇ=

𝐹𝐿𝑜

𝐴𝑜∆𝐿

This modulus is a measure of the stiffness of the material. As It is shown in the picture below,

the slope of the first linear ramp indicates the Young’s modulus. In the test, we are going to use

the average of these slopes (for each group of samples) in order to determine the modulus. We

will also obtain values related with stress at maximum load force. The purpose of that is know-

ing how the mechanical properties decrease in function of the time they spend immersed on the

SBF, which will indicate the degradation that they experiment.

Figure 3.12. Young’s Modulus



4. EXPERIMENTAL PROCEDURE

4.1 Preparing calcium and strontium phosphate

The preparation of Sr50, the phosphate glass most used during this thesis, needed to obtain

Sr(PO3)2 and Ca(PO3)2 previously. For the preparation of these two chemical were used

Ca(CO3)2, Sr(CO3)2 and (NH4)2HPO4 following the next heating program and quantities. Each

week were made 50 grams of Sr(PO3)2 and 50 grams of Ca(PO3)2 in 4 different crucibles by

mixing the components in as follows in the next table.

Table 4.1. Amount in grams of the raw materials needed for making Ca(PO3)2 and Sr(PO3)2

Ca(PO3)2 Sr(PO3)2 50 g 50 g

CaCO3 (NH4)2HPO4 SrCO3 (NH4)2HPO4

15.023 g 26.894 g 12.636 g 33.3502 g

15.023 g 26.894 g 12.636 g 33.3502 g

The heating program is shown in the figure below. It means an amount of 49.2 hours. Hence,

the easiest solution was to leave the components in the oven all the weekend in order to avoid

having problems with people working in the laboratory while the ammonium could be in the

air. Therefore, this procedure was followed every Friday.

Figure 4.1. Heating program for preparing Ca(PO3)2 and Sr(PO3)2.

0

100

200

300

400

500

600

700

800

0 3:40 15:40 22:20 34:20 38 50

Temperature (C)

EXPERIMENTAL PROCEDURE


4.2 Glass melting

Glasses were made by melting mixtures of chemicals as oxides and phosphates. First of all, the

calculation of the chemical quantities for each glass had to be made. Afterwards, measuring is

the next step with a scale keeping the tolerance of ±5 mg. Once the mixture is ready and homo-

geneous by mixing in the mortar, the batch is placed into a platinum crucible or in a glass silica

crucible (in case of glasses with titanium or cupper in order to avoid the formation of alloys

between the crucible and the glass).

According with the DTA results and the difficulty to get fibers from Sr50, the glasses made

were:

• Sr50: 50 P2O5 – 10 Na2O – 20 SrO – 20 CaO

• Si5: 45 P2O5 – 10 Na2O – 20 SrO – 20 CaO – 5 SiO2

• Cu5: 45 P2O5 – 10 Na2O – 20 SrO – 20 CaO – 5 CuO

• Mg5: 45 P2O5 – 10 Na2O – 20 SrO – 20 CaO – 5 MgO

• Ti5: 45 P2O5 – 10 Na2O – 20 SrO – 20 CaO – 5 TiO2

Next Table 4.2 shows the needed amount of raw materials for each glass. As it has been said

before, the phosphates were made apart. The main structure of the glass is Sr50. Afterwards,

due to the difficulties to draw the fibers; the other glass compositions consist in a small variation

of Sr50 in order to make it more stable improving the thermal properties.

Table 4.2. Raw material quantities for each glass composition

Kind of Glass

Sr50 Si5 Ti5 Mg5 Cu5


Ca(PO3)2 10.88935 9.965877 9.872275 10.06126 9.873777

Sr(PO3)2 13.50371 12.35853 12.24245 12.47682 12.24432

NaPO3 5.606939 5.864506 5.809424 5.920637 5.810308

CaCO3 0.719584 0.712825 0.726471 0.712934

SrCO3 1.061392 1.051423 1.071551 1.051583

SiO2 0.863963

TiO2 1.137619

MgO 0.585091

CuO 1.133227



The crucible will be placed in an electric furnace following the corresponding heating program.

It is taking the crucible in at 600 C and waiting for 30 minutes, after increase to 1100 C with a

ramp approximately of 20 C/min and leaving the crucible inside for another 30 minutes, after-

wards mix the glass and leaving it for another 5 minutes. Later, casting in the carbon mold and

leave the solidified glass annealing for 5 hours at 350 C.

Figure 4.2. Ti5 glass disc after melting process.

Despite from all of these phosphate glasses, a silica glass B50 was also made in order to also

try to make fibers and see how the easy or difficult it is. The glass formula is written next.

B50: 26,93 SiO2 – 26,93 B3O3 – 22,66 NaO2 – 21,76 CaO – 1,72 P2O5

Below in the next table is shown the chemicals needed for preparing B50 glass.

Table 4.3. Raw material quantities for B50

Kind of Glass

B50


SiO2 10.174

CaCO3 11.528

Na2CO3 15.102

H3BO3 20.935

CaHPO4 2H2O 3.721

4.3 Glass crushing

Afterwards, DTA will be explained. For that it is need to have the glass crushed in small parti-

cles between 125 and 250 micrometers.



The glass was crushed with a mortar and filtered in sieves with a vibration machine. Grains

were classified in 250-500, 125-250 and 50-125 micrometers, even though for this study are

only going to be useful the ones said before, the rest could be used in future researches.

Figure 4.3. Ti5 glass during the crushing process

4.4 Making fibers

One of the main points of this thesis was being success in getting bioactive glass fibers drawn

from melting. For this purpose, was needed a special furnace with a tube in the bottom part, in

order to draw the fibers from there when the glass is in the right melted point. The structure of

the furnace can be appreciated in the Figure 4.4.

Figure 4.4. Structure of the furnace used for drawing fibers from melting

The process was at it follows. After collecting between 60 or 80 grams of the desired glass, it

was placed in a platinum crucible with small holes in the bottom. The platinum crucible was

placed in the furnace and looking with a mirror trying to appreciate the state of the glass, the

temperature was being modified until the first drop comes.



4.4.1 Sr50

It was the main glass composition tried to be drawn. It was also the most difficult because was

not easy finding the right point in which it was not solidified but either not completely liquid.

Many times all the glass was wasted without success due to the high temperature after waiting

for hours the first drop to form. Still, fibers were obtained the last time and they could be ana-

lyzed. These difficulties to draw fibers made us have to try new glass compositions varying

slightly the composition of Sr50 in order to have more energy stability improving the thermal

properties of the glass.

4.4.2 Si5

Si5, looking at the Thermal properties obtained from DTA, together with Ti5, they seem to be

the ones that have the most stable thermal properties form the crystallization point to the melting

one. The impossibility of drawing fibers using Platinum crucible with Titanium (they would

form an alloy and ruin the crucible) made us choose Ti5 as the next glass to try.

Surprisingly, fibers were obtained from the first try. They were really easy to get in a tempera-

ture of 875 C. The problem was that they were crystallized. A second try was done in order to

verify that it was not a problem of the impurity of the glass. This time, the glass was introduced

at a higher temperature (920 C) in order to not let it dangerously remain at a crystallization

temperature. Afterwards, the temperature was adjusted again to 875. And for the second time,

the fibers were really easy to obtain but still all the glass was crystallized.

4.4.3 B50

Finally, non-phosphate but silica glass was tried for drawing fibers from melting and compare

the pros and contras. It was the best of the glasses to be drawn. Fibers were obtained at first

chance at a temperature of 870 C. They were obtained in no longer than 15 minutes and they

were not crystallized.

4.5 Making SBF

SBF was first used, introduced and create by Kokubo. It is really important, as was said before,

the creation of apatite in the surface of the scaffolds in order to help the material to cohere and

be able to be part of the bone. SBF is used to test biocompatibility in vitro of biomaterials and

it helps to study the formation of apatite in the surface of scaffold.

The steps followed for the preparation of 1 liter of SBF are described below:

Put 700 ml of distilled water in a container and place it in the mixer covering it with

parafilm.

Add following chemicals:



o 7,996 g of NaCl

o 0,350 g of NaHCO3

o 0,224 g of KCl

o 0,228 g of K2HPO43H2O

o 0,305 g of MgCI26H2O

o Add 35 ml of HCl

o CaCl2

o Na2SO4

Add 6,057 g of NH2C(CH2OH)3 bit a bit. Careful, putting too much at the same time,

will make solution precipitate.

When it is completely dissolved, place the container in the waterbath for 3 hours at 38 C.

Measure the PH and add more acid bit a bit until it is 7,4.

Add distilled water until 1 liter.

Being careful adding the chemicals in really accurate measures is really important for Ca2+ to

not precipitate, if not, SBF solution will not be as good as it could and results after immersion

of fibers could not be real.

4.6 SBF Test

As it has been said before, were immersed in 30 ml of SBF for 6, 24, 48 and 72 hours, and 1

and 2 weeks (3 weeks as well the SC2 fibers). Glass fibers studied in this part of the research

have been SC2, CC2, Sr5 and Sr50. Sc2 and Cc2 fiber compositions are shown in the next Table

4.4. Sc2 is a single core fiber and Cc2 is a fiber composer by core and cladding. They have two

different thicknesses, 125 and 250 micrometers. Each fiber had been spun and stored as one

continuous fiber. For the experiment they will be cut in segments of 15 cm length each, 10

specimens of each kind of fiber.

Another kind of fibers, apart from Sc2, Cc2 and Sr50, has been tested. It is a silicate glass fiber

called Sr5, which composition is shown below. The aim of this was, being able, as well, to

compare both, phosphate and silicate glass reactions to SBF.

Table 4.4. Composition of Sc2 and Cc2.Phosphate glass fibers under investigation

Sample

Diameter

(μm) P2O5 CaO SrO Na2O B2O3 CeO2

Sc2 125 125 47.50% 20% 20% 10% 2.50% -

Sc2 250 250 47.50% 20% 20% 10% 2.50% -

Cc2 125 125 47.50% 20% 20% 10% 2.50% 0.25%

Cc2 250 250 47.50% 20% 20% 10% 2.50% 0.25%

*Core doped with Cerium (mol%)

•Sr5: 53.85SiO2 1.72P2O5 16.77CaO 22.66Na2O 5SrO



The reason of doping the fiber with CeO2 is that in previous experiments was proved that this

fact increases the cross linking induced by a change of the Q2 units to Q1 units aiming the

depolymerization of the phosphate chains. As well, the variations in the glass transition tem-

perature and the non-variations in the activation energy for crystallization (Ec) indicated that

the doping would be better for improving the glass fiber making [25].

After the immersion time, fibers were taken off the SBF dissolution correspondingly, rinsed

with ethanol and properly dried and stored in a Dry-Keeper desiccator cabinet being ready for

the next steps which would be:

• Analyzing the mechanical properties.

• Measure the Calcium concentration in the dissolution.

• Measure the PH of the dissolution.

4.6.1 Mechanical test

Mechanical properties were measured by using tensile test in an Instron 4411 universal testing

machine. The machine was calibrated with the following parameters:

500 N load cell for testing bioactive glasses.

50 mm of grip distance.

10 mm/min of a crosshead speed.

Table 4.5. Fiber diameters corresponding for each immersion time period for Sc2 and Cc2.

Immer-

sion time Fiber diameter (mm)

Number

of sam-

ples

Grip

(mm)

Sc2 Cc2 125 250 125 250

0h 90 216.67 92.5 216.67 10 50

6h 90 210 91.25 220 10 50

24h 90 220 90 220 10 50

48h 90 218.89 90 220 10 50

72h 90 213.34 90 220 10 50

1w 82 210 90 220 10 50

2w 81 211.67 220 10 50

3w 81.1 210 10 50

Before starting testing, the diameter of each fiber was measured using a digital caliper (toler-

ance of 0.01 mm). Hence, in each set, there were 10 fibers, and all of them were measured



correspondingly. Later, for the results, the average of them would be used as well. In Table 4.5

are shown the average of the diameters for Sc2 and Cc2 fibers for each period of time.

Correspondingly, in Table 4.6, can be found the average of the diameters for Sr5 and Sr50

fibers. It is possible to notice that there are some cells empty in both tables. It means that these

fibers could not afford the immersion time and broke in the mechanical test before even the

system could measure the stress. Also must be said that only Sc2 fibers were immersed for 3

weeks, all the others were immersed from 6 hours to 2 weeks.

Table 4.6. Fiber diameters corresponding for each immersion time period for Sr5 and Sr50.

Immer-

sion time Fiber diameter (mm)

Number

of sam-

ples

Grip

(mm)

Sr5 Sr50 125

0h 81.11 68 10 50

6h 81.25 10 50

24h 76.667 10 50

Below are represented the graphs with the curves of how the diameters vary depending on the

immersion time.

Figure 4.5. Average values of different diameters depending on immersion time for Sc2 and

Cc2 250 micron fibers.

200

205

210

215

220

225

0 6 24 48 72 1w 2w 3w

Diameter 125 micron fibers

DIAMETER SC2 250

DIAMETER CC2 250



Figure 4.6. Average values of different diameters depending on immersion time for Sc2, Cc2

and Sr5 125 micron fibers.

4.6.2 Tensile Test

In this part the mechanical properties were studied in order to get the Young’s modulus results

for characterizing the stiffness of the fibers. The different kinds of glasses are separated in the

next section by Sc2 and Cc2, Sr50, and Sr5 groups. This has been done for comparing mechan-

ical properties of glasses almost similar, just different because the cerium clad core in case of

Sc2 and Cc2. In the case of Sr50 phosphate glass and Sr5 silicate glass, their mechanical prop-

erties were tested in order to know how they are.

As it was said before, the tensile test was made using the Instron 4411 universal testing machine.

Using the software provided by Instron gave back the values to make the curves needed. After-

wards, using Origin software, the graphs were plotted. An example of one of these graphs is

shown below in Figure 4.7.

The software used gave values of load at break point, stress and Young’s modulus. But the

values had to be recalculated because they were not accurate. Young’s modulus was calculated

by using the slope, but when we tried to do it manually by using Origin, the values were not

exactly the slope in the linear part. Hence, one by one, all the curves were analyzed. We took

just the linear part of the curve and calculate the slope from there.

Afterwards, having the slope, the initial distance between cells (L0) and the area of the fiber,

applying the next formula, the entire Young’s modulus was obtained.

𝐸 =𝐿0 ∙ 𝐹

𝐴 ∙ ∆𝐿

Being 𝐹

∆𝐿 the slope calculated previously.

70

75

80

85

90

95

100

0 6 24 48 72 1w 2w 3w

Diameter 125 micron fibers

DIAMETER SC2 125

DIAMETER CC2 125

DIAMETER SR5



0,0 0,2 0,4 0,6 0,8 1,0 1,2

-0,0005

0,0000

0,0005

0,0010

0,0015

0,0020

0,0025

0,0030

0,0035

0,0040

LO

AD

(kN

)

DISPLACEMENT (mm)

Figure 4.7. Stress-strain curve of Sc2 125 fiber, 6h immersion time, specimen 1.

4.7 PH Measurement

PH was measured with a Mettler To-ledo SevenMulti™ pH/conductivity meter for every sam-

ple and plotted in a curve in which can be observed each value and the variation in function of

the immersion time. Hence, PH was measured before and after the immersion process.

SBF is temperature dependent, thus, PH was always measured at 37 C as a simulation of the

human body. SBF is a composition without cells with the same PH and the same inorganic ions

as the human blood plasma but it does not content any protein or organic constituents [26].

Depending on if it was phosphate or silica glass, the PH values were decreasing or increasing.

4.8 Atomic Absorption Spectroscopy

Atomic Absorption Spectroscopy (AAS) was used to measure the concentration of calcium ions

(Ca2+) of the SBF solutions. The results were plotted in function of the immersion time. For the

AAS analysis was used an acetylene-air flame due to quantify the concentration of Ca2+. The

machine used was Perkin Elmer AAnalyst 300. Previously, before starting with the measure-

ment, the machine was properly calibrated.



4.9 Fourier transform infrared spectroscopy

The IR absorption spectra of the fibers were measured using the Fourier transform infrared

spectroscopy (FTIR). The instrument used was the machine Perkin Elmer FTIR spectrum.

All IR spectra were recorded in a range between 600-2000 cm-1 and 8 accumulations in order

to make it as much accurate as possible avoiding noisy signals. FTIR was applied to all the

samples for the periods of time 0, 72 hours, and 1, 2 and 3 weeks in the case of Sc2 and Cc2,

due that there was no variation for the periods of immersion time below 72 hours.

4.10 Differential thermal analysis

Differential thermal analysis (DTA) was used to analyze the thermal properties of the different

glasses in order to determine which ones are more valuable for drawing fibers. It is important

to not have very big differences of energy between crystallization temperature, Tg, and melting

temperature, Tm, hence they should be as smooth as possible.

For this analysis was used DTA, Netszch F1 JUPITER. And the process was as it follows.

From the beginning, the blank sample must be calculated to use it afterwards as a reference.

First of all, measure the mass of the crucible and add around 30 mg of the glass in particles

between 125 and 250 micrometers. Then set the computer up for a platinum rhodium crucible

and the variation of temperature from 40 to 1000 C. Nitrogen was used as a protective gas.



5. RESULTS

5.1 DTA

Glass transition temperatures and crystallization temperatures were determined using differen-

tial thermal analysis. Crystallization behavior of the phosphate glasses was investigated by heat-

ing glass samples of approximately 30 ºC at temperatures between 100 and 1000 °C in a linear

ramp of time.

As we can see in the Figure 5.1 below, can be found a comparison between the DTA curves of

the different glasses that were studied.

100 200 300 400 500 600 700 800 900 1000 1100

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

35

40

45

DS

C (

mW

)

Temperatures (°C)

Sr50

Ti5

Si5

Mg5

Cu5

Figure 5.1. DTA comparison between 5 different glasses; Sr50, Ti5, Si5, Mg5 and Cu5.

The point of this analysis was finding the range of temperatures for drawing fibers without

risking because of crystallization of the glass. The most desirable then, was a smooth curve

with no big changes of energy. The one best looking is Ti5 followed by the Si5.

The very best option for trying drawing fibers would have been Ti5. Our problem was that we

did not have enough sources to proceed due the material of our drawing crucible. It was a plat-

inum crucible. Titanium glass melting would have made an alloy. Then, the chosen glass is

finally Si5.

RESULTS


It can be notice as well as Mg5 has the bigger differences of energy in the heating process,

followed by Cu5 and Sr50. That is the reason why was very difficult drawing fibers from Sr50.

As it was described on 4.4.1Sr50, was very difficult finding a temperature between crystalliza-

tion and melting. Many times, glass was crystallized and many others, liquid wasted.

5.2 SBF Test

5.2.1 AAS and PH measurement

The PH of the SBF was measured when it was prepared, before the fibers were placed on it,

and right after the immersion of the fibers in the SBF. PH was stablished on 7,4 when the

preparation of the SBF. As it is going to be explained right now, in phosphate glasses, PH

decreases as a function of the immersion time, and increases in silicate glasses, as well as a

function of the immersion time.

Figure 5.2. PH measured in SBF solution as a function of immersion time for Sc2 and Cc2.

By studying the Figure 5.2 above, can be noticed, as it was expected, that the pH is seen to

slightly decrease as the fibers slowly dissolves and leeches out ions and molecules into the reaction

medium.

In case of Sr5, silicate glass, PH increases in function of the immersion time due to there is no

calcium phosphate formation. As shown in Figure 5.3, there is a pick in 1-week that as it is going

to be explained below, means that there was some irregularity.

7,24

7,26

7,28

7,3

7,32

7,34

7,36

7,38

7,4

7,42

0h 6h 24h 48h 72h 1 w 2 w 3 w

PH

PH SBF SC2/CC2

PH Sc2 125 microns

PH Sc2 250 microns

PH Cc2 125 microns

PH Cc2 250 microns

PH Sr50



Figure 5.3. PH measured in SBF solution as a function of immersion time for Sr5.

Afterwards, when the fibers finalized their immersion time, a sample of the resultant SBF was

analyzed by AAS. AAS quantify the Calcium ion Ca2+ concentration of the SBF solution.

Again, as in the PH test. It can be noticed that in phosphate glasses, Ca2+ ions decrease and in

the meanwhile, they increase in silicate glasses.

Figure 5.4. Measured calcium ion concentration of SBF plotted as a function of immersion

time for Sc2 and Cc2.

As it will show up again studying FTIR, the fact that Ca2+ ions decrease is due to the forming

of the calcium phosphate. In this case, Figure 5.4, calcium phosphate, forms earlier in Sc2 fibers

than in Cc2 fibers. It can be an interesting point that indicates that degradation of the fiber in

the human body would occur earlier in Sc2 fibers. Hence, they would last shorter time. It de-

pends on the use of the scaffold, which will be more convenient to use.

7,3

7,4

7,5

7,6

7,7

7,8

7,9

6h 24h 48h 72h 1 w 2 w

PH

PH SBF Sr5

PH Sr5

0

1

2

3

4

5

6

6h 24h 48h 72h 1 w 2 w 3 w

Ca2

+co

nce

ntr

atio

n (

mg/

l)

Ca (mg/l) Sc2/Cc2

Sc2 125micronsCa(mg/l)

Sc2 250micronsCa(mg/l)

Cc2 125micronsCa(mg/l)

Cc2 250micronsCa(mg/l)

RESULTS


In the SBF of the Sr5 immersion time, the effect is the opposite. It is because in this case, there

is no formation of calcium phosphate as it was predicted (silicate glass). Studying the graph in

Figure 5.5, there is a strange pick in 1-week immersion time. This pick, fits perfectly with the

pick in Figure 5.3, in which PH was higher than expected. This case should be studied again to

see how it reacts, but results are expected both in PH and Ca2+ concentration.

Figure 5.5. Measured calcium ion concentration of SBF plotted as a function of immersion

time for Sr5.

5.2.2 Mechanical test

5.2.2.1 Mechanical properties of Sc2 and Cc2

The average of Young’s modulus for each immersion time has been calculated. The results of

250 micrometers diameters are shown in the Figure 5.6.

For both glasses, Sc2 and Cc2 can be appreciated that from 72 hours in the case of Cc2 and 2

weeks in the case of Sc2, the curves are divided in two. They were called “glass name + system”

and just “glass name”. System refers to the actual average of all fibers which can be noticed

decreasing. It is due to the calcium phosphate formation. The question, why the curve separates

in two lines? Can be answered as: because the formation of calcium phosphate is not uniform

in the surface of all the fibers.

There are some fibers which the Young’s modulus remains constant even after the degradation

because of the immersion time. One of the reasons why it could happen is that into the SBF

tube, if the fibers keep the position together, the ones in the center have less contact with the

SBF. As well, would be nice to mention that cannot be guaranteed that all the fibers are exactly

the same considering that the fibers were melted from preform with a glass made by us. It was

4

4,5

5

5,5

6

6,5

7

7,5

8

8,5

6h 24h 48h 72h 1 w 2 w

Ca2

+co

nce

ntr

atio

n(m

g/l)

Ca (mg/l) Sr5

Sr5 125micronsCa(mg/l)



not a standard glass fiber produced in mass. And this fact aims to the possibility of irregular

diameters and variations in the structure of the fibers.

Figure 5.6.Average of Young’s modulus in function of the immersion time for Sc2 and Cc2

250 micrometers.

Figure 5.7. Average of Young’s modulus in function of the immersion time for Sc2 and Cc2

125 micrometers.

Above are shown in Figure 5.7 the results for 125 micrometers. In this new Figure 5.7 can be

appreciated the division of Sc2 in two for the same reason as the previous one.

0

10000

20000

30000

40000

50000

60000

0 6 24 48 72 1w 2w 3w

E M

Pa

YOUNG MODULUS ESC2/CC2 250 micrometers

E SC2 system

E SC2

E CC2 system

E CC2

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

100000

0 6 24 48 72 1w 2w 3w

E M

Pa

YOUNG MODULUS ESC2/CC2 125 micronmeters

E SC2 system

E SC2

E CC2

RESULTS


Figure 5.8. Average of Young’s modulus in function of the immersion time for Sr50.

Figure 5.9. Average of Young’s modulus in function of the immersion time for Sr5.

From the mechanical test and studies, was passible as well to obtain data and results about the

stress reached by the fiber when the maximum load is applied before it breaks.

Again, as in the study of the Young’s Modulus, can be appreciated how the maximum stress

remains constant until degradation of the fiber. Usually, big changes start appearing from 1

week period time.

Figure 5.10 and Figure 5.11 show, again, how it is a bit bigger the resistance to SBF degradation

(related with mechanical properties) for Sc2 than for Cc2. Maximum stress start decreasing

before for Cc2 than for Sc2.

70000

80000

90000

100000

110000

120000

130000

140000

150000

0 6

E M

Pa

E Sr50

E Sr50

95000

100000

105000

110000

115000

120000

0 6

E M

Pa

E SR5

E SR5



Figure 5.10. Average stresses at maximum load before the break of the fiber in function of

the immersion time for Sc2 and Cc2 250 micrometers.


the immersion time for Sc2 and Cc2 125 micrometers.

Both studies, for Sr5 and Sr50, mechanical test did not show what was searched. Fibers start

being really weak from the first immersion times and tensile test is not able to operate from 6

hours in advance. Still we had some results for Young’s Modulus and stress at maximum load

for 0 and 6 hours immersion time. It gives us knowledge about the initial mechanical properties

and creates the need of improving the fibers in order to make them more resistant to degrada-

tion.

0

50

100

150

200

250

300

350

0 6 24 48 72 1w 2w 3w

Stre

ss a

t m

axim

um

load

MP

aSTRESS SC2/CC2 250

STRESS SC2 250

STRESS CC2 250

0

100

200

300

400

500

600

700

0 6 24 48 72 1w 2w 3w

Stre

ss a

t m

axim

um

load

MP

a

STRESS SC2/CC2 125

STRESS CC2 125

STRESS SC2 125

RESULTS



the immersion time for Sr50.


the immersion time for Sr5.

0

100

200

300

400

500

600

700

800

900

0 6

Stre

ss a

t m

axim

um

load

MP

aSTRESS SR50

STRESS SR50

0

100

200

300

400

500

600

0 6

Stre

ss a

t m

axim

um

load

MP

a

STRESS SR5

STRESS SR5



5.2.3 FTIR

In this section will be shown the IR spectra obtained using FTIR method for all the kind of

fibers.

5.2.3.1 Phosphate glasses, Sc2, Cc2 and Sr50.

All the phosphate glass fibers showed the same behavior after the immersion time. Hence, for

explaining the degradation of the phosphate fibers will be taken as reference the fibers called

Sr50, considering that they had the best reaction at the exposure to SBF and it is easier to see

the changes as a function as the immersion time in their curves.

700 800 900 1000 1100 1200 1300 1400

0,0

0,2

0,4

0,6

0,8

1,0

A.U

.

Wavenumber (cm-1)

Sr50-0

Sr50-24

Sr50-48

Sr50-72

Sr50-1w

Figure 5.14. FTIR spectra of Sr50 glass fibers as function of the immersion time.

All the IR spectra were normalized at approximately 880 cm-1 wavenumber band which is the

higher peak for all of them. In the spectra are exhibited 5 absorption bands situated at 718, 775,

880, 1085 and 1260 cm-1 and two shoulders at 1154 and 980 cm-1. For detecting which wave-

lengths correspond to each phosphate vibration, will be nice to look at [27] and analyzing the

next Figure 5.15 will be useful to detect them.

Can be noticed three main regions in the range from 600 to 1400 cm-1:

Vibration of non-bridging PO2 groups, Q2, 1400-1150 cm-1.

RESULTS


The region of terminal P-O and PO3 groups, Q0 and Q1, 1150-900 cm-1.

Vibration of bridging P-O-P groups, 900-700 cm-1.

Figure 5.15. Infra red spectra: (a) P40B10Na50, (b) P40B15Na45, (c) P40B20Na40, (d)

P40B25Na35, (e) P40B30Na30. [27]

The band around 1250 cm-1 can be assigned to asymmetric stretching modes, νas(PO2), of the

non-bridging oxygens bonded to a phosphorous atom in Q2 phosphate tetrahedron. The bands

observed at about 900 cm-1, νas(P–O–P) is the vibration of asymmetric stretching between the

bridging oxygen atoms bonded to a phosphorous atom in Q2. It is the same but symmetrically

in the bands 700-750 cm-1, νs(P–O–P) [27].

The band situated at about 1158 cm-1 is assigned to (PO3)2- symmetric stretching vibrations of

Q1 species. As well, 1122 cm-1 band is attributed to (PO3)2- asymmetric stretching vibration of

Q1 species. 1045 cm-1 band is due to the symmetric stretching vibrations of (PO3)2- of Q1 species

[12].

The band at about 1085 can be attributed to asymmetric stretching vibration of (PO3)2- in Q1

units, or as well as an overlap between PO3 Q1 and terminal group and PO3 Q2 groups in meta-

phosphate [28].

Looking again at Figure 5.14 having the analysis done above of the phosphate vibrating groups,

can be noticed the increase of Q1 groups and the decrease of Q2 groups. It means that the fiber

glass structure is undergoing a depolymerization of the phosphate chain from Q2 to Q1 due to

the dissolution in SBF. It is great news considering that the objective of the bioactive glass is

to dissolve in the human body.

In the next pages the FTIR curves of the other fibers will be shown, being able to compare them.

For appreciating better the differences as function of the immersion time, will be scale increas-

ing the zoom from the Figure 5.14.



700 800 900 1000 1100 1200 1300 1400

0,4

0,6

0,8

A

.U.

Wavenumber (cm-1)

Sc2-125-0

Sc2-125-72

Sc2-125-1w

Sc2-125-2w

Sc2-125-3w

Figure 5.16. FTIR spectra of Sc2 glass fibers, 125 micrometer diameter, as function of the

immersion time.

700 800 900 1000 1100 1200 1300 1400

0,4

0,6

0,8

A.U

.

Wavenumber (cm-1)

Sc2-250-0

Sc2-250-72

Sc2-250-1w

Sc2-250-2w

Sc2-250-3w

Figure 5.17. FTIR spectra of Sc2 glass fibers, 250 micrometer diameter, as function of the

immersion time.

RESULTS


700 800 900 1000 1100 1200 1300 1400

0,4

0,6

0,8

Cc2 125 0

Cc2-125-72

Cc2 125 1w

Cc2 125 2w

A.U

.

Wavenumber (cm-1)

Figure 5.18. FTIR spectra of Cc2 glass fibers, 125 micrometer diameter, as function of the

immersion time.

700 800 900 1000 1100 1200 1300 1400

0,4

0,6

0,8

A.U

.

Wavenumber (cm-1)

Cc2 250 0

Cc2-250-72

Cc2-250-1w

Cc2-250-2w

Figure 5.19. FTIR spectra of Cc2 glass fibers, 250 micrometer diameter, as function of the

immersion time.



5.2.3.2 FTIR spectrum in Sc2 Fibers

They show a good evolution of dissolution in SBF, big changes can be noticed in the decrease

of Q2 phosphate groups by the time of 2 weeks, small changes already appear for 1 week period

of immersion time. Bigger degradation can be appreciated in 250 micrometer fibers, in spite

there is an irregularity due to the Q2 groups are lower for 2 weeks than for 1 week, still, Q1

groups behave as was expected, increasing the amount which means the depolymarization of

the phosphate chains.

5.2.3.3 FTIR spectrum in Cc2 Fibers

Fibers with diameter of 125 micrometers show a very good degradation comparing with what

was expected and can be noticed the progressive breaking of the phosphate Q2 chains forming

Q1 chains and depolymerizing the phosphate chain. Whereas, the results obtained in 250 mi-

crometers fibers were not expected considering that the variation of the phosphate chains does

not seem to follow the previous criteria, which means that the degradation of the fiber could

not be happening.

5.2.3.4 FTIR spectrum in Sr50 Fibers

Sr50 fibers were the ones who showed the best expected behavior. In the curve can be perfectly

appreciated the depolymerization of the phosphate chains. Changes can be already noticed from

the first 24 hours.

5.2.3.5 Silicate glass Sr5

The spectrum of all the different immersion time samples was normalized to the 930 cm-1 band

which was the one with highest intensity. It can be noticed that the spectra show absorption

bands at 930, 748 and 1023 cm-1 approximately. The band at 748 cm-1 refers to the Si-O bend-

ing. The band situated at 930 cm-1 corresponds with the Si-O- in SiO4 and the other band,

1023 cm-1 is the absorption of the asymmetric stretching in SiO4 units [29] [30] [31] [32].

The differences in the intensities for the band of 930 and 1030 cm-1 for the sample with no

immersion time (0 h) means that the glass has not similar ratio between non-bridging and bridg-

ing oxygens in his network.

As a function of the immersion time, can be noticed a decrease in the band at 930 cm-1, hence

decrease in the concentration of Si-O- and increase in SiO4 units. The shoulder that appears at

about 960 cm-1 can be attributed to the C-O vibration modes in CO32- modes and P-O-P bond-

ing. The shoulder formed at about 875 cm-1 is the vibration of P-O. [32]

RESULTS


700 800 900 1000 1100 1200 1300 1400

0,0

0,2

0,4

0,6

0,8

1,0

Sr5

0

A

Sr5-0

Sr5-6

Sr5-48

Sr5-72

Sr5-1w

Sr5-2w

Figure 5.20. FTIR spectra of Sr5 glass fibers, as function of the immersion time.



6. CONCLUSIONS AND FUTURE LINES OF RE-

SEARCH

In this research, have been made many different kind of studies related with the availability of

the appliance of new kind of bioactive phosphate glass fibers. Some conclusions, within the

different studies, will help future researches to keep moving forward in the development and

implementation of bioceramics and composite materials for tissue engineering. Mainly, the aim

of this research was the development and characterization of new kind of bioactive phosphate

glasses.

In the development of creating a process for drawing phosphate glasses from melting, there

were two factors pushing great importance. Thermal analysis of new phosphate glasses, and the

way and difficulties while applying theory to the task of drawing. At this point, it has been

valued the importance of thermal properties. Differences of energy in DTA from crystallization

temperature point to melting and liquidus temperature points has to be as low as possible in

order to do the process easy, in order to be able to draw without crystallization or melting prob-

lems.

As a conclusion, we found that Sr50 phosphate glasses operate better and have more stable

thermal properties when in their composition appear Si or Ti (Si5 and Ti5). Future investiga-

tions will study more deeply these new glasses. About the procedure of drawing fibers from

melting, it has been realized that it is a complicated task. As it is currently with Bioglass, the

necessity of standardize these new glasses will help to make it easier. For future research, my

advice, is keep trying, keep working and analyzing data results about temperature, quality of

fiber obtained, timing, speed of fiber drawing and its relation with size and quality of the fiber…

While studying different properties of bioactive phosphate glasses we already had from a pro-

fessional lab, and our own fibers, results gave us knowledge about the characterization of these

new kinds of phosphate glasses. We could characterize their behavior within the human body,

their biodegradation and biocompatibility, and about their mechanical behavior.

Sc2 and Cc2 had really similar behaviors. The main differences were related to mechanical

properties. Sc2 is able to resist longer the degradation in SBF in terms of mechanical strength.

It is an indicator to use Cerium as a core when the aim of the scaffold is being useful for less

time. It provides also to surgery and medicine the possibility to investigate and develop new

possibilities for bone fixing, considering that, composites can be designed with different prop-

erties. It is an advance in bioceramics, comparing with metal scaffolds, due to the rigidity of

these last ones.

Using FTIR, Cc2 showed better calcium phosphate generations than Cc2, though pretty similar,

which means it can regenerate better the bone tissue and help to it.

CONCLUSIONS AND FUTURE LINES OF RESEARCH


Still, looking at the AAS results, Ca2+ decreasing in the SBF solution shows us that Cc2 is more

stable in decreasing it and it happens stronger.

My conclusions are that the results were really approximated to what was expected. Many other

researches with same samples should be done to reach clearer and more precise conclusions.

As future lines of studies, I recommend keep investigating the new phosphate glasses that were

develop in this thesis, Ti5 and Si5, study and try to again develop new methods to operate with

Mg5 and Cu5. Mg5, personally, is one of my favorites, even being difficult to draw, due to its

thermal properties. It is because it was really easy and comfortable to melt from raw materials.

As well, keep developing and characterizing Sc2, Cc2 and Sr50, which in my opinion will play

a decisive role in the future of tissue engineering. I encourage researchers to deep into bioc-

eramics world and help developing techniques that will create many chances to biomedicine to

improve our health and life.



7. CORPORATE SOCIAL RESPONSIBILITY

As engineers, our main professional goal is to create, to innovate, to help and develop the evo-

lution of technology and processes. Side effect of every new discovery causes impacts either in

society or in the environment.

Within this thesis, many new techniques have been applied. As social impact, through a way of

researching and developing new ways to increase human health, it has just positive impacts. In

order to value that fact, think how many things it is possible to change and help positively and

how many negatively. When talking about medicine, it is hard to say negative effects if, in fact,

they do not exist.

These studies will help medicine keep going forward, moving on the way to improve human’s

health. Advances in biomaterials, will eradicate problems related with bad bone healing, and

better integration machine-human in terms of creating new technology biocompatible that will

not harm human physiology.

As environment impact, it does not make a huge impact; we could say that, as in every manu-

facturing process, there are residues, chemical residues. It will follow the process of chemical

laboratories and main objective will be reducing these residues.

I my opinion, Society is evolving hand by hand with technology, this fact is unstoppable just

because it is within the nature of human being. Then, thinking big, best choice we can make is

choose our path to keep developing our specie in terms of nature, health, knowledge. Put aside

new discoveries just related with control of the markets, and combine it with doing thing right,

things that will change the world.

I encourage all who want to create, to innovate, to do something great in this world, to choose

a path of social development, and improvements in human quality without big bad impacts. The

world is moved by us, and every little part of the puzzle is as much important and the complete

puzzle.

CORPORATE SOCIAL RESPONSIBILITY




8. TIMING AND BUDGET

Table 8.1. Budget covering the entire thesis

BUDGET Unit const Unit Quantity TOTAL

Master Student 12 €/h 900 € 10,800.00

PhD assistant 20 €/h 100 € 2,000.00

Supervisor 80 €/h 70 € 5,600.00

IT material 300 € 1 € 300.00

Chemicals 100 € 1 € 100.00

Lab material 2500 € 1 € 2,500.00

TOTAL € 21,300.00

TIMING AND BUDGET


Figure 8.1Gantt chart of all the thesis duration



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REFERENCES




LIST OF FIGURES

Figure 3.1 Hydroxyapatite structure [6] .................................................................................... 6

Figure 3.2. Stress-strain curves of human femoral bone. Adapted from Evans (1969).

[8] ....................................................................................................................... 7

Figure 3.3. Phosphate and silica tetrahedron. ........................................................................... 8

Figure 3.4.Glass characterization examples [10] ..................................................................... 8

Figure 3.5. Phosphate tetrahedral units. Oxygen atoms (pink) connected to phosphorus

atoms (blue). Q3 crosslinking units; Q2 middle units; Q1 end units; Q0

isolated units. [13] .............................................................................................. 8

Figure 3.6. Structure of a DTA instrument. ............................................................................... 9

Figure 3.7. FTIR, main principle of who it works [18]. .......................................................... 11

Figure 3.8. Vibrational modes of a molecule. [20] .................................................................. 12

Figure 3.9. Infrared spectrum of methanol, which shows O-H, C-H and C-O stretching

absorptions from several bending modes. [20] ................................................ 12

Figure 3.10. Typical FTIR spectrum of hydroxyapatite (Ratner, 2004). [19] ......................... 13

Figure 3.11. Structure of AAS instrument. [23] ....................................................................... 14

Figure 3.12. Young’s Modulus ................................................................................................. 15

Figure 4.1. Heating program for preparing Ca(PO3)2 and Sr(PO3)2. ..................................... 17

Figure 4.2. Ti5 glass disc after melting process. ..................................................................... 19

Figure 4.3. Ti5 glass during the crushing process ................................................................... 20

Figure 4.4. Structure of the furnace used for drawing fibers from melting ............................. 20

Figure 4.5. Average values of different diameters depending on immersion time for Sc2

and Cc2 250 micron fibers. .............................................................................. 24

Figure 4.6. Average values of different diameters depending on immersion time for Sc2,

Cc2 and Sr5 125 micron fibers. ........................................................................ 25

Figure 4.7. Stress-strain curve of Sc2 125 fiber, 6h immersion time, specimen 1. .................. 26

Figure 5.1. DTA comparison between 5 different glasses; Sr50, Ti5, Si5, Mg5 and Cu5. ...... 29

Figure 5.2. PH measured in SBF solution as a function of immersion time for Sc2 and

Cc2. ................................................................................................................... 30

Figure 5.3. PH measured in SBF solution as a function of immersion time for Sr5. .............. 31

Figure 5.4. Measured calcium ion concentration of SBF plotted as a function of

immersion time for Sc2 and Cc2. ...................................................................... 31

Figure 5.5. Measured calcium ion concentration of SBF plotted as a function of

immersion time for Sr5. .................................................................................... 32

Figure 5.6.Average of Young’s modulus in function of the immersion time for Sc2 and

Cc2 250 micrometers. ....................................................................................... 33

Figure 5.7. Average of Young’s modulus in function of the immersion time for Sc2 and

Cc2 125 micrometers. ....................................................................................... 33

Figure 5.8. Average of Young’s modulus in function of the immersion time for Sr50. ............ 34

Figure 5.9. Average of Young’s modulus in function of the immersion time for Sr5. .............. 34

LIST OF FIGURES AND TABLES


Figure 5.10. Average stresses at maximum load before the break of the fiber in function

of the immersion time for Sc2 and Cc2 250 micrometers. ................................ 35


of the immersion time for Sc2 and Cc2 125 micrometers. ................................ 35


of the immersion time for Sr50. ........................................................................ 36


of the immersion time for Sr5. .......................................................................... 36

Figure 5.14. FTIR spectra of Sr50 glass fibers as function of the immersion time. ................ 37

Figure 5.15. Infra red spectra: (a) P40B10Na50, (b) P40B15Na45, (c) P40B20Na40,

(d) P40B25Na35, (e) P40B30Na30. [27] ......................................................... 38

Figure 5.16. FTIR spectra of Sc2 glass fibers, 125 micrometer diameter, as function of

the immersion time. ........................................................................................... 39

Figure 5.17. FTIR spectra of Sc2 glass fibers, 250 micrometer diameter, as function of


Figure 5.18. FTIR spectra of Cc2 glass fibers, 125 micrometer diameter, as function of


Figure 5.19. FTIR spectra of Cc2 glass fibers, 250 micrometer diameter, as function of


Figure 5.20. FTIR spectra of Sr5 glass fibers, as function of the immersion time. ................. 42

Figure 8.1Gantt chart of all the thesis duration ...................................................................... 48



LIST OF TABLES

Table 3.1. Ion concentration of SBF comparing with human blood plasma according to

the ISO standard [16] ....................................................................................... 10

Table 4.1. Amount in grams of the raw materials needed for making Ca(PO3)2 and

Sr(PO3)2 ............................................................................................................ 17

Table 4.2. Raw material quantities for each glass composition .............................................. 18

Table 4.3. Raw material quantities for B50 ............................................................................. 19

Table 4.4. Composition of Sc2 and Cc2.Phosphate glass fibers under investigation .............. 22

Table 4.5. Fiber diameters corresponding for each immersion time period for Sc2 and

Cc2. ................................................................................................................... 23

Table 4.6. Fiber diameters corresponding for each immersion time period for Sr5 and

Sr50. .................................................................................................................. 24

Table 8.1. Budget covering the entire thesis ............................................................................ 47

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