Correlation between structural properties and in vivo

biocompatibility of alumina/zirconia bioceramics

Simona CavaluSimona Cavalu ProfessorProfessor Preclinical Sciences DepartmentPreclinical Sciences DepartmentFaculty of Medicine and PharmaceuticsFaculty of Medicine and Pharmaceutics University of OradeaUniversity of Oradea ROMANIAROMANIA

Motivation There is a continuous input from bioengineering for

reaching a high level of comfort, improving reliability, finding new applications.

This development is also a response to the growing number of patients afflicted with traumatic or non-traumatic conditions: the number of implants is continuously growing, due to the increase in persons suffering of arthritis and joint problems.

As the average age of population grows, the need for medical devices to replace damaged or worn tissues increases.

As patients have become more and more demanding regarding esthetic and biocompatibility aspects of their dental restorations

Motivation Al2O3 ZrO2

Excellent hardness and wear properties.

Fracture toughness values are lower than those of the metals used in orthopedic surgery.

Chemical and hydrothermal stability.

It is a brittle material, with low resistance to the propagation of cracks.

Was introduced to overcome the limitations of alumina.

When properly manufactured, zirconia has a higher strength, but only 50% of alumina’s hardness.

Unstable material. The tetragonal phase tends to transform into the monoclinic phase. The addition of stabilizing materials (Y2O3)during manufacture, can control the phase transformation of zirconia.

Al2O3, ZrO2, TiO2 have been considered as bioinert ceramics since they cannot induce apatite formation in SBF. They do however support bone cell attachment, proliferation and differentiation.

The ideal ceramic is a high performance biocomposite that combines the excellent material properties of alumina in terms of chemical stability and low wear and of zirconia with its superior mechanical strength and fracture toughness.

Alumina/zirconia ceramics were successfully used in total hip/knee arthroplasty in the last decades.

For dental application: root canal posts, orthodontic brackets, implant abutments and all- ceramic restaurations.

Goal

An evaluation of the structural and biocompatibility properties of a new zirconia toughened alumina ceramics.

The composition of proposed materials for this study:

90%Al2O3-10%ZrO2 and

90%Al2O3-10%ZrO2+5%TiO2

prepared by using modern processing technologies – spark plasma sintering.

Methods Investigation of the structural changes induced by TiO2

addition to Al2O3/ ZrO2 are made by FTIR spectroscopy and X-ray diffraction (XRD) analysis .

Scanning Electron Microscopy (SEM) and EDX are used for microstructure and morphology investigation of the samples.

In order to perform in vivo tests, the rat model has been applied for biocompatibility evaluation. The rat model has been accepted as a model for the effects of systemic disease on osseointegration.

SEM micrographs are recorded on the rats femur along with the elemental composition of the sheared implant surfaces at different time intervals after the surgery.

Histological examination of the connective tissue is performed to detect any immunological or inflammatory responses.

Results: XRD Spectroscopy

XRD patterns of (a) 90Al2O3∙10ZrO2 and (b) 90Al2O3∙10ZrO2 + 5%TiO2 samples.

0 10 20 30 40 50 60 70 80 90 100

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AA

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A

A

A

A

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(b)

(a)

Inte

nsity

(a

.u.)

2 theta (degrees)

T

The TiO2 addition slightly modifies the relative intensities of XRD peaks. Both samples show similar peak positions, the slight change of relative intensities of XRD peaks could be attributed to weak differences in size and shape of the crystals in these samples

This result suggest that zirconia present in the composite is, therefore, retained in the tetragonal form as alumina particles prevent the tetragonal to monoclinic transformation by matrix constraint.

FTIR Spectroscopy: (a) 90Al2O3∙10ZrO2 and

(b) 90Al2O3∙10ZrO2 + 5%TiO2 samples.

1200 1000 800 600 4000.2

0.3

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518

465

564

614

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797

1088

1168

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nsity

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.u.)

Wavenumber (cm-1)

The large bands around 1088 cm-1 are assigned to stretching vibration of Al–O–Al bonds.

The Al-O stretching vibrations of tetrahedral AlO4 groups are related with the bands in the region 900 – 750 cm-1 and bands in 650 – 460 cm-1 region are associated with stretching modes of AlO6 octahedra.

The absorption bands at 518 to 564 cm-1 correspond to Zr-O vibrations in tetragonal ZrO2 phase.

Upon TiO2 addition to alumina-zirconia matrix, the relative intensity of 660/614 cm-1 band is considerably modified, as a superposition of the characteristics absorption bands occurs in this region.

SEM: Irregular shape of 90%Al2O3-10%ZrO2(a) and 90%Al2O3-10%ZrO2+5%TiO2 (b) granules and their

corresponding microstructure (c, d)

a)

b)

c)

d)

Biocompatibility evaluation: Animal model (Wistar rats)

Surgical procedure

Surgical procedure: filling the critical size

defect created in the femur

Collagen film

Monitoring the osseointegration process at different time intervals (3, 6 weeks).

Radiographic images 90Al2O3∙10ZrO2

90Al2O3∙10ZrO2 + 5%TiO2

SEM images of the sheared implant surfaces:3 weeks

90Al2O3∙10ZrO2

90Al2O3∙10ZrO2 + 5%TiO2

SEM images of the sheared implant surfaces:

6 weeks

90Al2O3∙10ZrO2

90Al2O3∙10ZrO2 + 5%TiO2

Haversian canal details

SEM Analysis reveals: Fibrinous and collagenous matrix extensively interdigitated

with the three-dimensional interconnected porous structure after first 3 weeks.

Distinct gaps between the implant and the bone were observed in a few locations.

After 6 weeks, the matrix around the surface implanted area appeared more densely, well covered and extensively integrated into a mixture of mineralized tissue, osteoid and dense matrix.

As revealed from the EDAX spectra, calcium/phosphate ratio is an indicative of the surface implant coverage for a successful osseointegration, varying from 1.5 (after 3 weeks) to 1.9 (after 6 weeks).

The results suggest that TiO2 presence in the samples favor the osseointegration process.

XRD spectrum of the femoral bone

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AZAZ

AZABA

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AlZr Biocomposite

Bone/AlZr

Bone

AT

Z

B

Histological images: The connective tissue was also examined to detect any

immunological or inflammatory responses

osteoblasts

A network of woven bony trabecular architecture with cellular infiltration was observed

Conclusions Structural investigations of the proposed composites

using XRD and FTIR spectroscopy confirms the stability of the microstructure upon TiO2 addition to alumina/zirconia matrix.

In vivo: both implanted materials in critical size defect of the femur were well integrated in the original bone defects and covered with a layer of soft tissue at 6 weeks after implantation, as demonstrated by SEM images.

As revealed from the EDAX spectra, Ca/P ratio is an indicative of the surface implant coverage for a successful osseointegration, varying from 1.5 (after 3 weeks) to 1.9 (after 6 weeks).

No signs of inflammatory reactions, such as necrosis or reddening suggesting implant rejection, were found upon histological examination.

The team: Prof. dr. Gultekin Goller and dr. Ipek Akin, Istanbul

Technical University, Materials Science Department.

Prof. dr. Viorica Simon and dr. Oana Ponta Babes-Bolyai University, Faculty of Physics & Institute of Interdisciplinary Research in Bio-Nano-Sciences, Cluj-Napoca, Romania.

Assoc. prof. Cristian Ratiu and dr. Ioan Oswald University of Oradea, Faculty of Medicine and Pharmaceutics, Oradea, Romania.

Romania-Turkey Bilateral Cooperation project 385/2010.

Jerry and JimmyLinda

Thank you