Titania or ceria effects on alumina/zirconia composites
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Titania vs. ceria addition to alumina / zirconia composites: structural aspects and biological tolerance.
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Titania or ceria effects on alumina/zirconia composites
- 1. Titania versus ceria addition to alumina/zirconia composites: structural aspects and biological tolerance Simona Cavalu Professor Preclinical Sciences Department Faculty of Medicine and Pharmaceutics University of Oradea ROMANIA
- 2. 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
- 3. MOTIVATION Al2O3 ZrO2 Excellent hardness and wear Was introduced to overcome the properties. limitations of alumina. Fracture toughness values are When properly manufactured, lower than those of the metals zirconia has a higher strength, but used in orthopedic surgery. only 50% of alumina’s hardness. Chemical and hydrothermal Unstable material. The tetragonal stability. phase tends to transform into the monoclinic phase. The addition of It is a brittle material, with low stabilizing materials (Y2O3)during resistance to the propagation manufacture, can control the phase of cracks. 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.
- 4. 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.
- 5. 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.
- 6. 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) .
- 7. RESULTS- SEM 80Al2O3-20YSZ (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.
- 8. RESULTS: XRD I. Akin& all, Ceramic Int. 37 (2011) 3273- 3280
- 9. 1088 x 465 RESULTS- FTIR 797 1168 780 515 617 693 648 30 Intensity (a.u.) SPECTROSCOPY 20 Fig. 1 FTIR spectra of (100-x)Al2O3·xZrO2 10 ceramic composites. • Al-O stretching vibration of AlO4 group (tetrahedral) at 1088 , 1168 cm-1, 780/797 cm-1. 0 •Al O6 group (octahedral) at 617/648 cm-1 and 560 485 465 cm-1. 1400 1200 1000 800 600 400 -1 Wavenumber (cm ) 465 648 (100-x)[90Al2O3·10ZrO2]·xTiO2 465 617 x 617 (100-x)[90Al2O3·10ZrO2]·xCeO2 648 x Intensity/ a.u. 5 5 Intensity/ a.u. 3 3 0 0 Al2O3 Al2O3 1200 1000 800 600 400 -1 Wavenumbers (cm ) 1200 1000 800 600 400 -1 Wavenumber (cm ) Fig.2 FTIR spectra of Fig. 3 FTIR spectra of (100- (100-x)[90Al2O3·10ZrO2].xTiO2 composites. x)[90Al2O3·10ZrO2].xCeO2 ceramic composites
- 10. MACHINED ALUMINA/ZIRCONIA CERAMICS - CYLINDRICAL SHAPE, SUITABLE FOR ANIMAL MODEL (RABBIT) 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.
- 11. BIOTOLERANCE - ANIMAL MODEL
- 12. HISTOLOGICAL SECTIONS H& E tests osteoblasts 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.
- 13. 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.
- 14. 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).
- 15. 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.
- 16. 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.
- 17. 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.
- 18. 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.
- 19. 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 .
Editor's Notes
- The details including the size and shape of the alumina (micron size, grey) and zirconia (sub micron, bright white) grains clearly demonstrates that Spark Plasma Sintering makes possible the densification of Al2O3 based composites at a lower temperature and in a shorter time compared with some other conventional techniques [9,11, 19]. Furthermore, the microstructure can be controlled by a fast heating rate and shorter processing time. The details presented in Fig.1 demonstrate that the presence of zirconia as a second phase is beneficial with respect to the inhibition of grain growth. Alumina grain size as a matrix has an important effect on the hardness and fracture toughness. Fine zirconia particles located on the boundaries inhibit the movement and prevent the grain growth of alumina. It has been previously demonstrated that the zirconia addition to alumina matrix promotes composites with higher densities, higher flexural strength and fracture toughness [11, 19]. Moreover, as shown in Fig. 1 (e,f), adding TiO2 particles is more effective, as the size of alumina grains is reduced by comparison with Fig.1 (c,d). The formation of well-elongated grains of CeAl11O18 in amatrix of fine grained alumina was observed in the compositescontaining 3 and 5 mass% CeO2 sintered at 1400 8C. The sizeof elongated CeAl11O18 grains were 5–7 mm in length and 0.8–1 mm in width, and 10–12 mm in length and 1.8–2 mm in widthfor 90A10Z3C and 90A10Z5C samples, respectively. Theaverage length of elongated grains increased with increasingCeO2 content from 3 to 5 mass% (Fig. 4(c) and (d)). It is knownthat, CeO2 exhibits sensitivity to the sintering atmosphere andcan form nonstoichiometric oxides such as Ce2O3 whensintering in vacuum, reducing or at low oxygen pressureatmosphere [22]
- Cu TiO2:Characteristic peaks of Al2O3 (JCPDS: 71-1683), tetragonal zirconia (t-ZrO2, JCPDS: 42-1164) and ZrTiO4 (JCPDS: 30-0415) were identified . XRD analysis revealed thatAl2O3-YSZ composites containing 5 vol% YSZ with and without TiO2 showed high tetragonal intensities of (111) planes at 2θ=31° and (220) planes at 2θ=51°, and lowertetragonal intensities of (113) and (311) planes at approximately 2θ=60°. No monoclinicphase of ZrO2 was detected from the XRD results.Cu CeO2:Characteristic peaks of Al2O3 (JCPDS: 71-1683), tetragonalzirconia (t-ZrO2, JCPDS: 42-1164) and CeAl11O18 (JCPDS:48-0055) were identified. XRD analysis revealed that Al2O3–YSZ composites containing 10 vol% YSZ with and withoutCeO2 showed high tetragonal intensities of (1 1 1) planes at2u = 31 and (2 2 0) planes at 2u = 51, and lower tetragonalintensities of (1 1 3) and (3 1 1) planes at approximately2u = 60. Also, the presence of low intensity (4 0 0) crystaldiffraction at 2u = 748 confirmed the existence of cubic zirconia(c-ZrO2) phase [15]. No monoclinic phase of ZrO2 was detectedfrom the XRD results.Since CeO2 is easily reduced to the trivalent Ce2O3,formation of CeAlO3 (cerium monoaluminate) and CeAl11O18phases is possible in a reductive atmosphere. CeAlO3 formationoccurs by occupation of Al3+ cations sites Ce3+ after thecomplete reduction of CeO2. Damyanova et al. havecharacterized the CeO2–Al2O3 mixed oxides using differenttechniques and found that CeAlO3 phase appears only at highreduction temperatures [16]. The characteristic peaks ofCeAlO3 locate at 2u = 33.58, 418 and 608. According to theXRD analysis (Fig. 3), peak formation was not observed atforesaid values. The other possible phase, CeAl11O18, wasidentified from its characteristics peaks at 2u = 34.18 and 36.38
- The absorption bands and shoulders recorded in the spectral region between 465 and 650 cm-1 are assigned to six coordinated aluminium which are associated with stretching modes of AlO6 octahedra. The Al-O stretching vibrations of tetrahedral AlO4 groups are related to the broad band at 1088 cm-1 and shoulder at 1168 cm-1, and to the doublet at 780 and 797 cm-1. By addition of ZrO2, the weak absorption band at 515 cm-1 increases in intensity because the Zr-O vibrations in tetragonal ZrO2 phase, evidenced by XRD analysis, contributes to this IR band [3, 4]. At the same time, the 485 cm-1 shoulder disappears as x ≥ 20 ZrO2vol%. The most pronounced effect is observed on the 617 and 648 cm-1 absorption bands which nearby disappear. The sole new IR absorption band recorded from ZTA composites is at 693 cm-1, and it is typical for penta-coordinated aluminium atoms [5]. The increasing content of zirconia diminishes the intensity of 465 cm-1 band that denotes that this band occurs from vibrations of aluminium bonds. At the same time the shoulder at 485 cm-1 disappears. No changes are observed with respect to Al-O stretching vibrations of tetrahedral AlO4 groups, or if there were any, they could be compensated by the contribution introduced in the same spectral range by the vibration bands of zirconia.The pronounced attenuation up to suppression of 617 and 648 cm-1 IR absorption bands recorded from pure alumina sample, caused by increasing content of zirconia in spark plasma sintered ZTA composites, is attributed to structural changes that affect bond vibrations of the six coordinated aluminium atoms in AlO6 octahedra. At the same time, the weak IR absorption line at 693 cm-1, that is not present in the spectrum of pure alumina sample, denotes the occurrence of penta-coordinated aluminium species only in alumina-zirconia composite samples.Moreover, upon TiO2 (respectively CeO2) addition to alumina zirconia matrix, the relative intensity of 648/617 cm-1 band is considerably modified, as a superposition of the characteristics absorption bands occurs in this region (fig. 2 and fig. 3).
- 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.