Studies On Porous Hydroxyapatite Bioceramics By Gel-casting Method

Hydroxyapatite (HA) ceramics has chemical compositions closely resembling that of mineral phase of natural bone. Many in-vivo experiments have confirmed the HA as a potential implant material for biomedical applications. To fabricate a bioceramic with porous configuration, the evidence of tissues ingrowth and biological responses provide obvious advantages in tissue-implant fixation and controlled biodegradation rate. The pore size or pore size distribution is directly related to the particle size or particle size distribution of introduced polymeric powders by traditional methods. This leads to the poor mechanical properties for the porous ceramics. Several advantages can usually be obtained for gel-casting route such as controlled pore geometry, structural uniformity, and minimum defects/defect size, etc, and which methodology has long been considered as a major processing for production of ceramics with a more uniform microstructure.First, the properties and the crystal structure of hydroxyapatite were introduced, and the domestic and foreign situations of the research about hydroxyapatite ceramics were reviewed. Then, the ultrafine hydroxyapatite powder was prepared by low-temperature combustion synthesis (LCS). Using the powder, the hydroxyapatite porous ceramics was prepared by gel-casting route. Characters of the powders and porous ceramics were studied by XRD, TEM, and SEM. The results show that the diameters of hydroxyapatite powders prepared by LCS are 20～80 nm. The porous ceramic sintered at 1200℃with a successful control of pore size and porosity characters can be obtain by controlling holding time. The strength of the porous hydroxyapatite ceramic decreased with increased pore size and porosity. The flexural and compression strength of specimen sintered at 1200℃for 2h showed a value of 0.0626MPa and 83.62 MPa, with a porosity of 39.59vol%.Finally, the effect of technological parameters on the size of powders, fluidity of the ceramic slips and microstructure of the porous ceramic were investigated, and many optimum parameters were obtained, which is that the optimum n(glycol)/Ca²⁺ is 1/1, the n(H2O)/n(Ca²⁺) is 30,the value of pH is 2～3, the temperature to calcine is 800℃at the phase of the powder was created; the optimum m(H₂O)/m(powder) is 1.5/1, the time of milling is 5h, the concentration of dispersant is 2wt%, the value of pH is 10 when the slurry was cranked out. The waterish ceramicembryoes must be dried under a series of system from the humidity of 90% and the temperature of 25℃to the low humidity and the temperature of 80℃.