Preparation And Properties Of Silica Modified Hydroxyapatite Whisker Porous Ceramic Materials

The porous ceramic scaffolds which are made of hydroxyapatite whiskers are considered to be an excellent bone graft material because of their excellent features, such as biocompatibility, bioactivity, osteoconduction and designable in the three-dimensional pore structure, and so on. Meanwhile, there are two problems for the scaffolds which limit their applications, the hydroxyapatite whiskers themselves own a longer degradation, leading the porous ceramic material possessed of poor degradation in body environment; on the other hand, for porous ceramic scaffolds, compressive strength is inversely proportional to its porosity, the higher porosity brings about the lower compressive strength. Based on those mentioned, this article is attempted to induce the nanoscale silica spheres depositing on the surface of the hydroxyapatite whiskers. The presence of nano-silica spheres can not only provide a degradation site for accelerating the biodegradation rate of porous ceramic material, but also enhance the surface roughness of the whiskers, further leading to the improvements of the mechanical strengths. Meanwhile, the honeycomb-shaped structure is apt to be fashioned by the methods of extrusion and foaming, and the straight-through holes and side-wall holes within the honeycomb structure are facilitated the adhesion, growth and proliferation of cells.The modifier of Tetraethoxysilane (TEOS) and the solvent of ethanol were adopted to synthesize the silica modified hydroxyapatite whiskers material according to the principles of Stober law. The nano silica spheres adhering to the surface of the hydroxyapatite whiskers relied on the two-phase titration process under the constant temperature condition combined with the stepped low temperature sintering. The orthogonal experimental design was built to investigate the efforts of designed parameters on the amounts and the distribution of silica particles, the adhesion degree between silica particles and hydroxyapatite whiskers. The phase composition, morphology and structure of obtained silica-modified hydroxyapatite whiskers material were characterized via SEM, XRD and FT-IR etc.The results showed that, the silica modified hydroxyapatite with suitable distribution could be effectively prepared by this method. According to the orthogonal experiment design, the content of tetraethoxysilane should be the most important factor, and the stirring time, calcining temperature, holding time was minimized. The best experimental scheme was A2B1C2D3, which was 15ml of TEOS as modifier dosage, stirring time for AB mixture at 14h, drying powder calcination temperature at 650℃ and holding time for 4h. In addition, the bonding mechansm between silica microspheres and the hydroxyapatite whiskers were not a simple surface attachment. Because of the nanometer effects, there was a strong atomic bonding between microspheres and whiskers.Using Laurie acid potassium as a foaming agent, carboxymethyl cellulose as a foam stabilizer and the modified hydroxyapatite whiskers as the main raw material, the foam slurry composed of mentioned materials was extrused by the mold, and the mold equipped with close-packed hole structure in the pore size of less than 500μm was designed by Laser cutting. The initial scaffolds were cured by heating in the preliminary microwave process, after drying and sintering, the samples were further treated to enhance the mechanical strength by silica gel immersion and stepped calcination. Obtained samples were characterized via SEM, XRD, EDS and FT-IR etc. by examining the structure of the holes, morphology, pore size, phase composition and mechanical properties. In order to evaluate the biodegradation and biotoxicity, in vitro degradation experiments and cytotoxicity experiments were carried out simultaneously.The results show that, the honeycomb-shaped structure showed the straight-through holes and side-wall holes whose cell pore diameter were about 500μn and 10 to 80μm, respectively.The modified hydroxyapatite whisker porous ceramic material showed the top average compressive strength of 1.0 MPa the above, the highest average porosity of sample was 80%. The results of cell toxicity were grade 1 showed that the materials were the qualified biomaterials.