Study On The Preparation Of β-TCP Powder And The Performance Of β-TCP/PLLA Porous Scaffold

It is necessary that the scaffold materials for bone tissue-engineering, acting as the carrier materials of bone tissue cells, possessed good biocompatibility, controllable biodegrade speed, proper pore size and porosity, suitable mechanical strength and suitable interface of the materials and cells. Therefore, β-tricalcium phosphate (β-TCP) and polylatic acid (PLLA) which possessed good biocompatibility and biodegradability have been selected for preparing composite material, and subsequently preparing β-TCP/PLLA porous scaffold, and the mechanical and biological performances of β-TCP/ PLLA porous scaffold have been studied in the present research.First of all, three processes of preparing β-TCP powders, Ca(NO3)2/(NH4)2HPO4 process, Ca(OH)2/H3PO4 process, and CaCO3/H3PO4 process, have been compared. It was found that the uniform, ultra-fine, crystal β-TCP powder(d50=0.5~2μm)could be obtained after calcining the precursor with CaCO3/H3PO4 process at 950℃ for 2hrs. Compared with other processes, it is obvious that with CaCO3/H3PO4 process, the reaction rate to be fast, the operation to be simple, the precursor to be easily filtrate, and no impurity to be introduced. So, the CaCO3/H3PO4 process was chosen to preparing β-TCP powders for subsequent β-TCP/PLLA porous scaffold. Secondly, the detail researches have been carried out with CaCO3/H3PO4 process. The thermodynamic analysis showed that the precursor would be octacalcium phosphate [Ca8H2(PO4)6·5H2O, OCP] under the experimental conditions. The effects of different reaction conditions, such as raw materials addition method, reactants concentration, washing method, calcining temperature, cooling method and ultrasonic field etc, on the particle diameter were studied, then the optimum process conditions were determined.β-TCP powders and palmy acid modified β-TCP powders were composited respectively with PLLA in proportion as 2:1, 1:1, and 1:2, and β-TCP/PLLA porous scaffold with the pore size from 100μm to 400μm , porosity rate above 50% was prepared which compressive strength was 4~10MPa and bending strength was 1~4 MPa. Then the biodegradation test in vitro was carried through immersing the composited scaffold in stimulated body fluid (SBF) at 37℃, and sampling respectively after 3, 7, 14, 21, 35, and 42 days. PLLA molecular weight, water absorption, weight loss, mechanical strengths, and microstructure changes were measured, and the samples were characterized by SEM, IR, and XRD spectrum. The results showed that all β-TCP/PLLA porous scaffolds could maintain their shape and keep partially mechanical strength after degradation for 42 days. Bone-like apatite could be formed on the surfaces of all β-TCP/PLLA porous scaffolds. And different degrade characteristics appeared in different samples, so the degradation speed could be controlled by the ratio of β-TCP and PLLA. Osteo-induced rat bone marrow mesenchymal stem cells were cocultured with β-TCP/ PLLA porous scaffolds. The results showed that BMCs could attach, proliferate on scaffold, and cell configuration was normal. So it was indicated that the scaffold could not disturb BMCs' biological behavior. It also showed that the scaffold of β-TCP/PLLA=2∶1 possessed the best biocompatibility.