Titania versus ceria addition to alumina/zirconia composites: structural aspects and biological tolerance

Simona Cavalu Professor

Preclinical Sciences DepartmentFaculty of Medicine and Pharmaceutics University of Oradea ROMANIA

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

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.

Al2O3ZrO2

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:

80Al2O3-20YSZ (vol%) 80Al2O3-20YSZ (vol%) with 5 wt% TiO2

80Al2O3-20YSZ (vol%) with 5 wt% CeO2 prepared by using modern processing

technologies – spark plasma sintering.

METHODS

Investigation of the structural changes induced by TiO2 (CeO2) addition to Al2O3/ ZrO2 are made by FTIR spectroscopy and X-ray diffraction (XRD) analysis .

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

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

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

XPS - surface modifications of the proposed alumina/zirconia ceramics upon different fluoride treatments (NaBF4 and SnF2) .

RESULTS- SEM80Al2O3-20YSZ (vol%)

80Al2O3-20YSZ (vol%) with 5 wt% TiO2

80Al2O3-20YSZ (vol%) with 5 wt% CeO2 . Formation of elongated grains of CeAl11O18

due to the reduction of CeO2 Ce2O3 in reaction with Al2O3 at high temperature.

RESULTS: XRD

I. Akin& all, Ceramic Int. 37 (2011) 3273- 3280

RESULTS- FTIRSPECTROSCOPY

1200 1000 800 600 400

0

3

5

x

Al2O

3

(100-x)[90Al2O

3·10ZrO

2]·xTiO

2

Inte

nsity

/ a.u

.

Wavenumbers (cm-1)

648

617 465

Fig.2 FTIR spectra of (100-x)[90Al2O3·10ZrO2]

.xTiO2 composites.

1200 1000 800 600 400

0

5

3

x

Al2O

3

(100-x)[90Al2O

3·10ZrO

2]·xCeO

2

Inte

nsity

/ a.u

.

Wavenumber (cm-1)

648 617 46

5

1400 1200 1000 800 600 400

x

560

1168

1088

797

780

485

515

465

693

648

617

10

20

30

0

Inte

nsity

(a

.u.)

Wavenumber (cm-1)

Fig. 1 FTIR spectra of (100-x)Al2O3·xZrO2 ceramic composites. • Al-O stretching vibration of AlO4 group (tetrahedral) at 1088 , 1168 cm-1, 780/797 cm-1.•Al O6 group (octahedral) at 617/648 cm-1 and 465 cm-1.

Fig. 3 FTIR spectra of (100-x)[90Al2O3·10ZrO2].xCeO2 ceramic composites

MACHINED ALUMINA/ZIRCONIA CERAMICS - CYLINDRICAL SHAPE, SUITABLE FOR ANIMAL MODEL (RABBIT)

Biomedical coatingsThe use of surface covering layers (i.e. coatings) provides methods to control the biological response to materials and material devices including implants and prostheses (Figure 1). Depending on implant location and function, implants require specific biological responses. For instance, bone implants require fast integration with native bone tissue. On the other hand, soft tissue implant functionality is improved by the absence of a contractile fibrous tissue capsule. The aim of our research on biomaterial coatings is to optimize the biological response for specific applications of biomedical implants.Organic coatingsSeveral types of organic materials can be used to generate a coating with specific modulatory effects on the biological response. Examples include proteins, DNA, sugars, etc. Specific biological responses that can be controlled are cell attachement and behavior. Organic coatings consisting of proteins are generally based on the presence of these proteins at the implant location. Members of the extracellular matrix (ECM) are the most commonly used proteins. DNA is interesting as a structural molecule, as it is homogeous within all vertebrate species. Consequently, as an implant coating, it masks the implant from being recognized as a foreign body.

Alumina/zirconia ceramics are bioinert materials: once placed in the natural tissue, it has a minimal interaction with the surrounding tissue, generally a fibrous capsule might form around the implants.

Surface properties control the amount and quality of cells adhered on the implant and consequently, the tissue growth. Surface treatment techniques: sandblasting, acid-etched, organic (protein) or inorganic (Ca/P) coating.

BIOTOLERANCE - ANIMAL MODEL

HISTOLOGICAL SECTIONS

osteoblastsH& E tests

A network of woven bony trabecular architecture with cellular infiltration was observed. The periosteal regions were completely closed with new blood capillaries around the implant site. No signs of inflammatory reaction such as necrosis or reddening suggesting implant rejection were found upon histological examination.

HISTOLOGY: IMPLANT- BONE MARROW CELLS INTERACTION

Goldner’s Trichrome stain: alumina zirconia specimens with ceria addition may cause some problems due to small vascular congestion occurring concomitant with the proliferation of the new bone in the contact area.

HISTOLOGY: IMPLANT- HOST BONE INTERACTION

Goldner’s Trichrome stain:The details reveals the new bone proliferation and and young trabecular bone at the interface and the periost (d).

IMPROVING THE BIOLOGICAL TOLERANCE The surfaces modifications and post-

synthesis treatment also influences the performances of the bioceramics designed to dental and orthopedic applications.

In order to improve the biological tolerance of the proposed ceramics, the surface modifications of alumina and alumina/zirconia bioceramics are investigated upon different treatments with sodium tetrafluoroborate and stannous fluoride respectively.

XPS AFTER FLUORIDE TREATMENT

By comparing the results we can notice that both specimens presents a high sensitivity to the SnF2 treatment. The effectiveness of surface treatment is more evident on the sample with TiO2 addition. Further in vitro tests are required to be performed in order to establish a correlation between the effectiveness of surface treatment in improving the bioactivity of alumina/zirconia composites.

CONCLUSIONS Ceramics with the composition 80Al2O3-20YSZ (vol%) +

with 5 wt% TiO2 (CeO2) were prepared by Spark Plasma Sintering.

XRD pattern show characteristic peaks of tetragonal zirconia with different intensities. No monoclinic phase was detected.

FTIR spectra presents a special behavior with respect to the evolution of the structural units related to Al-O and Zr-O stretching vibrations .

SEM images show the details including the size and shape of the alumina and zirconia grains demonstrating that Spark Plasma Sintering makes possible the densification of the composites.

CONCLUSIONS Based on the histological analysis, one can conclude

that both specimens (with TiO2 and CeO2) present a satisfactory tolerance toward the host bone. With respect to the bone marrow, we observed that alumina zirconia specimens with ceria addition may cause some problems due to small vascular congestion occurring concomitant with the proliferation of the new bone in the contact area.

Fluoride-based treatment is proposed to condition the surfaces improving the bioactivity of alumina/zirconia composites.

THE TEAM:•Prof. dr. Viorica Simon Babes-Bolyai University, Faculty of Physics & Institute of Interdisciplinary Research in Bio-Nano-Sciences, Cluj-Napoca, Romania.

•*Assist. prof. Cristian Ratiu , University of Oradea, Faculty of Medicine and Pharmaceutics, Oradea, Romania.

*Prof. dr. Gultekin Goller and assist. prof. Ipek Akin, Istanbul Technical University, Materials Science Department.

Romania-Turkey Bilateral Cooperation 2011-2012 and CNCS-UEFISCDI project PNII-ID-PCE 2011-3-0441 contract nr. 237/2011 .