Hydroxyapatite Zirconia Research Articles

Silver catalytic effect on flash sintering of ceramics

We investigated the use of metallic silver as a catalyst for flash sintering on hydroxyapatite/zirconia (HZ) composites. Adding 3 wt% of silver to the ceramic powder reduced the flash onset temperature (from 1084 °C to 925 °C) and also the electric field (from 300 V cm−1 to 150 V cm−1) used in the process. We attribute this behaviour to the formation of a silver percolation path that acts as a heat source, accelerating the thermal runaway. As a result, both the flash temperature and the required electric field were reduced. Furthermore, the results suggest that the temperatures along the percolation paths are high enough to reach the boiling point of silver, forming a gaseous phase that leaves the sample.

Electrochemical characterization of surface modification for Ti6Al7Nb implants with hydroxyapatite-zirconia nanoparticles synthesis by ultrasound irradiations

Ultrasound irradiation is an effective means of obtaining nanoparticles. Hydroxyapatite–zirconia (HA–ZrO2) synthesized by ultrasound irradiation was coated on Ti6Al7Nb implant alloy by electrophoretic deposition. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) were used to evaluate the morphology and composition of HA–ZrO2 coatings. The electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves were used to characterize the corrosion performance of HA–ZrO2 coated sample in simulated body fluid (pH 3.9) at 37 °C. The EIS interpretation was performed in two-layer model of the coated sample. It was found that the nanoparticles of HA–ZrO2 coated on Ti6Al7Nb alloy showed a good corrosion resistance after a short-time immersion in simulated body fluid (pH 3.9).

A Review: Effect of Sintering Method on the Decomposition of Hydroxyapatite and Density of Hydroxyapatite Zirconia Composites

Hydroxyapatite (HA) is a biomaterial with excellent biocompatibility. However, the brittleness and low fracture toughness of HA have limited its biomedical applications. As such, HA has been incorporated with zirconia (ZrO2) to enhance its mechanical strength. However, ZrO2 addition decreases the phase stability of HA. HA decomposition is not favored because it decreases the mechanical strength of HA/ZrO2. In this paper, the effect of sintering on HA decomposition is reviewed. Experimental results show that hot isostatic pressing of HA/ZrO2 is one of the most effective methods to suppress HA decomposition, yielding the highest relative density compared with other sintering methods.

Microstructural and mechanical investigation of hydroxyapatite–zirconia nanocomposites prepared by spark plasma sintering

Nano hydroxyapatite (nHA)–zirconia (ZrO2) composites have been produced by spark plasma sintering (SPS). During the SPS process low temperatures (600–950 °C) and short dwelling time (5 min) have been applied to avoid the decomposition of nHA as well as the reaction between nHA and ZrO2. The grain size of the sintered composites was between 200 and 1000 nm. Carbon diffusion was induced from the graphite die and layered composite structure was formed. These observations might be related to the spark plasma sintering side effects. The microstructure and mechanical properties of high hydroxyapatite content zirconia composites have been found to be influenced and strongly correlated with the specialties of SPS method.

Novel Layered Hydroxyapatite/Tri‐Calcium Phosphate–Zirconia Scaffold Composite with High Bending Strength for Load‐Bearing Bone Implant Application

The integration of biological and mechanical requirements remains a challenge in developing porous hydroxyapatite (HA) and tri‐calcium phosphate (TCP) scaffolds for load‐bearing bone implant application. With the newly developed slip‐deposition and coating‐substrate co‐sintering technique, a strong layered HA/TCP‐zirconia scaffold composite structure was successfully fabricated. The bending strength (321 MPa) of this composite can match upper strength limit of the natural compact bone. The HA‐based scaffold coating has multiple scale porous structures with pore size ranging 1–10 and 20–50 μm. The zirconia‐based substrate is also porous with submicropores. Focus ion beam micrographs show most of the micropores in the coating are interconnected. Microindentation and primarily adhesive strength tests demonstrate that the scaffold coating strongly bonds with the zirconia based substrate. In vitro cell culture study indicates that the coatings have no cytotoxicity. It is evident that the strong layered HA–zirconia scaffold composite offers new implant options for bone repairs requiring immediate load bearing capacity.

Phase stability and rapid consolidation of hydroxyapatite–zirconia nano-coprecipitates made using continuous hydrothermal flow synthesis

A rapid and continuous hydrothermal route for the synthesis of nano-sized hydroxyapatite rods co-precipitated with calcium-doped zirconia nanoparticles using a superheated water flow at 450°C and 24.1 MPa as a crystallizing medium is described. Hydroxyapatite and calcium-doped zirconia phases in the powder mixtures could be clearly identified based on particle size and morphology under transmission electron microscopy. Retention of a nanostructure after sintering is crucial to load-bearing applications of hydroxyapatite-based ceramics. Therefore, rapid consolidation of the co-precipitates was investigated using a spark plasma sintering furnace under a range of processing conditions. Samples nominally containing 5 and 10 wt% calcium-doped zirconia and hydroxyapatite made with Ca:P solution molar ratio 2.5 showed excellent thermal stability (investigated using in situ variable temperature X-ray diffraction) and were sintered via spark plasma sintering to >96% sintered densities at 1000°C resulting in hydroxyapatite and calcium-doped zirconia as the only two phases. Mechanical tests of spark plasma sintering sintered samples (containing 10 wt% calcium-doped zirconia) revealed a three-pt flexural strength of 107.7 MPa and Weibull modulus of 9.9. The complementary nature of the spark plasma sintering technique and continuous hydrothermal flow synthesis (which results in retention of a nanostructure even after sintering at elevated temperatures) was hence showcased.

Porous Hydroxyapatite–Zirconia Composites Prepared by Powder Deposition and Pressureless Sintering

In the present study, hydroxyapatite was synthesized from local gypsum by microwave-hydrothermal method. Different percentage amounts of zirconia (0, 20, 30 and 40 wt.%) and poly-methyl methacrylate (40, 50 and 60 wt.%) mixed with hydroxyapatite (HA) for six hours. These powder mixture were deposited using deposition machine to produce specimens. These specimens were sintered at a temperature of 140°C with holding time for 1 hour into the green parts. These green parts were sintered at temperature of 1450°C with holding time for 2 hours. This process produces porous hydroxyapatite-zirconia composites with porosity between 62.76-73.92 percent. These composites were examined by XRD, XRF, SEM-EDX, BET analysis and compressive strength testing. Compressive strength of porous hidroxyapatite-zirconia composite decreased from 3.706 to 0.039 MPa when percentage amounts of zirconia increased up to 40 wt.%. This caused by several factors i.e. increased porosity, grain zirconia cracked, zirconia reacted with HA to produce CaZrO3, β-TCP and α-TCP, HA matrix cracks because of the phase change of tetragonal-zirconia into monoclinic-zirconia.

Porous Hydroxyapatite–Zirconia Composites Prepared by Powder Deposition and Pressureless Sintering

In the present study, hydroxyapatite was synthesized from local gypsum by microwave-hydrothermal method. Different percentage amounts of zirconia (0, 20, 30 and 40 wt.%) and poly-methyl methacrylate (40, 50 and 60 wt.%) mixed with hydroxyapatite (HA) for six hours. These powder mixture were deposited using deposition machine to produce specimens. These specimens were sintered at a temperature of 140°C with holding time for 1 hour into the green parts. These green parts were sintered at temperature of 1450°C with holding time for 2 hours. This process produces porous hydroxyapatite-zirconia composites with porosity between 62.76-73.92 percent. These composites were examined by XRD, XRF, SEM-EDX, BET analysis and compressive strength testing. Compressive strength of porous hidroxyapatite-zirconia composite decreased from 3.706 to 0.039 MPa when percentage amounts of zirconia increased up to 40 wt.%. This caused by several factors i.e. increased porosity, grain zirconia cracked, zirconia reacted with HA to produce CaZrO3, β-TCP and α-TCP, HA matrix cracks because of the phase change of tetragonal-zirconia into monoclinic-zirconia.

Biological evaluation of nano-hydroxyapatite–zirconia (HA–ZrO2) composites and strontium–hydroxyapatite (Sr–HA) for load-bearing applications

The biological response of strontium (Sr) doped hydroxyapatite (HA) and hydroxyapatite-zirconia (HA-ZrO₂) composites produced by employing sol-gel technology, minimal ZrO₂ loadings, and novel microwave-sintering regimes thereby retarding decomposition, is reported. In vitro evaluations indicate that all materials induce a favorable response from rat osteosarcoma cells. In vivo evaluations show osteoconductivity and biocompatibility for both the Sr-HA and HA-ZrO₂. The materials did not cause any inflammatory response in bone. The Sr-HA displays better biocompatibility which may be due to the incorporation of Sr and the formation of a surface apatite layer.

Mechanical properties of hydroxyapatite–zirconia compacts sintered by two different sintering methods

Microwave sintering is traditionally employed to reduce the sintering temperature required to densify powder compacts. The effect of microwave heating on hydroxyapatite (HA)-zirconia (ZrO2) green bodies has been investigated in order to understand how microwave energy may affect the physical and mechanical properties of the resultant densified composites. Laboratory synthesised nano-sized HA and a commercial nano-sized ZrO2 powder have been ball milled to create mixtures containing 0-5 wt% ZrO2 loadings. Compacts were microwave sintered at either 700, 1000 or 1200 degrees C with a 1 h hold time. Comparative firings were also performed in a resistive element furnace using the same heating profile in order to assess the differences between conventional and microwave heating on the physical, mechanical and microstructural properties of the composites. Samples sintered at 700 degrees C show little sign of densification with open porosities of approximately 50%. Composites conventionally sintered at 1000 degrees C were between 65 and 75% dense, whereas the samples microwave sintered at this temperature were between 55 and 65% dense. Samples sintered at 1200 degreesbC showed the greatest degree of densification (>80%) with a corresponding reduction in open porosities. TCP generation occurred as a consequence of sintering at 1200 degrees C, even with 0 wt% ZrO2, and increased degradation of the HA phase to form significant amounts of TCP occurred with increasing additions of ZrO2, along with increasing open porosity. Nanosized ZrO2 prevents the densification of the HA matrix by effectively pinning grain boundaries and this effect is more pronounced in the MS materials. Similar strengths are achieved between the microwave and conventionally sintered samples. Greater amount of open porosity and pore interconnectivity are seen in the MS samples, which are considered to be useful for biomedical applications as they can promote osteo-integration.

In vitro and in vivo biocompatibility of graded hydroxyapatite–zirconia composite bioceramic

To obtain bioceramics with good osteoinductive ability and mechanical strength, graded hydroxyapatite-zirconia (HA-ZrO(2)) composite bioceramics were prepared in this work. The biocompatibility of the bioceramics was investigated in vitro based on acute toxicity and cytotoxicity tests and hemolysis assay. Results showed the studied graded HA-ZrO(2) had little toxicity to mouse and L929 mouse fibroblasts. Also, hemolysis assay indicated a good blood compatibility of the bioceramics. Based on the results of in vitro tests, animal experiments were performed on white New Zealand rabbits by implantation into hip muscles and femur. It was found that the graded HA-ZrO(2) composite bioceramics exhibited superior osteoinductive ability, which may be a promising bioceramics implant.

Fabrication of Hydroxyapatite–Zirconia Composites for Orthopedic Applications

Dense hydroxyapatite–zirconia (HAp–ZrO2) composites are expected to have desired mechanical and biological properties for orthopedic applications. However, due to some processing problems, to date, this material can only be prepared by special techniques. In this paper, we report for the first time a facile route to prepare HAp–ZrO2 composites. Initially, HAp and ZrO2 powders were dispersed in aqueous media with polyacrylic acid and glutamic acid as the dispersants. The slurries exhibited a well‐stabilized state at a high solid content (>50 vol%) and therefore green samples with high density (>60%) can be obtained after slip casting. These HAp–ZrO2 green samples can be easily densified by pressureless sintering at 1450°C with 2 h holding. After sintering, only hydroxyoxyapatite Ca10(PO4)6Ox (OH)2(1−x) (HOA), ZrO2, and trace amounts of α‐tricalcium phosphate phases were detected. No obvious reactions between HAp and ZrO2 phase were observed. The HAp–ZrO2 samples showed excellent mechanical and biological properties. For 40 vol% HAp–60 vol% ZrO2 samples sintered at 1450°C, the flexural strength and toughness were 220 MPa and 4.37 MPa·m1/2, respectively. In addition, we observed the attachment, spreading, and proliferation of mesenchymal stem cells on the HAp–ZrO2 samples' surface. The results showed that the proposed colloidal processing and pressureless sintering process is feasible for preparing HAp–ZrO2 composites with high mechanical properties and promising bioactivity for orthopedic applications.

Phase stability of hydroxyapatite–zirconia (HAp–ZrO 2) composites for bone replacement

During the production of biomedical hydroxyapatite–zirconia (HAp–ZrO 2) composites new phases which determine the biocompatibility of implant materials may occur in the system. These phenomena may be associated both with the phase decomposition of hydroxyapatite itself and the interactions between the matrix material and particles of reinforcing zirconia phase. The work deals with the investigations of phase stability of HAp–ZrO 2 composites at high temperature. The composites studied have been in the form of dense sinters obtained by the hot pressing process.

Phase stability of hydroxyapatite?zirconia (HAp?ZrO2) composites for bone replacement

During the production of biomedical hydroxyapatite–zirconia (HAp–ZrO2) composites new phases which determine the biocompatibility of implant materials may occur in the system. These phenomena may be associated both with the phase decomposition of hydroxyapatite itself and the interactions between the matrix material and particles of reinforcing zirconia phase. The work deals with the investigations of phase stability of HAp–ZrO2 composites at high temperature. The composites studied have been in the form of dense sinters obtained by the hot pressing process.

Reaction Sintering and Mechanical Properties of Hydroxyapatite–Zirconia Composites with Calcium Fluoride Additions

The effects of calcium fluoride (CaF2) additions on the densification and mechanical properties of hydroxyapatite–zirconia composites (HA–ZrO2) were investigated. When small amount of CaF2 was added, the density of the composites was markedly enhanced. The reactions of HA with CaF2, which led to the formation of fluorapatite (FA), were attributed to the observed improvements in densification. When HA–20‐vol%‐ZrO2 composites were sintered, with the addition of 5 vol% of CaF2, in air at 1300°C, the density of the specimen approached 98% of the theoretical value. The flexural strength and fracture toughness of the composites were also improved, as a result of the enhanced densification.

Effect of CaF 2 on densification and properties of hydroxyapatite–zirconia composites for biomedical applications

Hydroxyapatite (HA) composites with zirconia (ZrO 2) up to 40 vol% were fabricated with the addition of CaF 2. The sinterability of the composites was found to be enhanced markedly by the addition of small amounts of CaF 2 (<5 vol%). Decomposition of HA to β-TCP was suppressed due to the substitution of F − for OH −, consequently forming fluor-hydroxyapatite (FHA) solid solution. This suppression of decomposition allowed the production of a fully dense body, which retained both high flexural strength and fracture toughness. The osteoblast-like cell (MG63) response to these F − ion-containing composites displayed comparable cell viability to pure-HA by in vitro proliferation test.

Synthesis and sintering of hydroxyapatite–zirconia composites

Hydroxyapatite (HA) has been synthesised in presence of 10–30 wt.% of m-ZrO 2 by solid state reaction between tricalcium phosphate (TCP) and Ca(OH) 2 at 1000 °C for 8 h. The m-ZrO 2 was partly converted into t-ZrO 2 by partial consumption of CaO which in turn resulted in a mixture of β-TCP and HA. On sintering these HA–β-TCP–ZrO 2 composite powders at 1100–1400 °C for 2 h, the HA is further decomposed into β-TCP and CaO. The CaO so produced reacts further with m-ZrO 2/ t-ZrO 2 generating a mixture of t-ZrO 2 and CaZrO 3 in different proportions. These various phases formed interfere with the sinterability of the composites due to their differential shrinkages leading to a overall reduced density as compared to that of pure HA. The composites show a T-onset of decomposition at around 1150 °C and a 40% HA yield was obtained at the highest sintering temperature of 1400 °C. The products were subjected to XRD for phase analysis and the microstructural features were studied by SEM.

ChemInform Abstract: Dense Hydroxyapatite—Zirconia Ceramic Composites with High Strength for Biological Applications.

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Hydroxyapatite–zirconia composite coatings via the plasma spraying process

Abstract Hydroxyapatite (HA) coatings have been deposited on artificial hip prosthesis as a bioactive surface to induce a direct chemical bond with natural bones and hence achieve a biological fixation onto implants. However, its intrinsic weak mechanical properties have always been the main obstacle to its applications, especially in the area of orthopedic applications, where implants have to withstand medium–high loading. In this study, HA and yttria-stabilized zirconia (YSZ) powders were ball-milled and then sprayed onto Ti–6Al–4V alloy substrates. The effect of plasma arc current on the phase composition was investigated. The amount of decomposition of HA increases with the increase of plasma arc current from 600 to 1000 A. The impurities, as a result of the decomposition, were α-TCP (alpha-tricalcium phosphate) and CaO, although a small amount of TTCP (tetra-calcium phosphate) was also detected. The influence of ZrO2 on the decomposition of HA was also studied. The results show that ZrO2 reacts with CaO in HA to form CaZrO3. This reaction caused an increase in the decomposition of the CaO-poor HA.