Fabrication Of Porous Calcium Phosphate Bioceramics For Bone Defect Repair By Extrusion

To solve the problem of among porosity and mechanical strength of the porous calcium phosphate bioceramics for bone defect repair, the extrusion molding was first used to fabricate porousβ-tricalcium phosphate (β-TCP) bioceramics with honeycomb structure in this study. The porousβ-TCP bioceramics with high porosity and mechanical property can be obtained by forming more mesopores on pore wall by the addition of porogen before extrusion, and altering the composition of raw material, respectively. In addition, the size, shape of the macropores (the tunnels formed by extrusion) of the porousβ-TCP bioceramics were adjusted by means of slip-casting.A mould suitable for plunger-typed extrusion was designed to fabricate porousβ-tricalcium phosphate (β-TCP) bioceramics with honeycomb structure, high porosity, uniform and controllable pore size and excellent mechanical property. This technology would be feasible for industrial production.β-TCP powders were synthetised by wet ball-milling, experimental results showed that theβ-TCP powders can be suitable for extrusion. Powders and additives (methylcellulose M450, liquid paraffin, and deionized water) were mixed in the right order, and a paste with good plasticity was formed. According to the method of orthogonal experiment the optimal mass ratio of additive methylcellulose M450, liquid paraffin, and deionized water was 8%, 10%, and 32%, respectively. The effects of extrusion pressure, drying method, sintering temperature and time, mould structure, et al. on the structure and properties of porous materials were studied, and the proper process parameters and related equipments are fixed, and the porous materials with ideal structure and properties were obtained. The porous materials fabricated by extrusion exhibited square macropore with uniform pore size of 850μm approximately, The porosity and compressive strength was about 74% and 17 MPa, respectively.On the basis of previous study, in order to improve the porosity of the pore wall's mesopores, the potato starch as porogen was introduced to the raw materials for extrusion. And when the amount of potato starch was 30%, the porosity of the porous materials was increased from 74% to 85%, the potato starch distributed uniformly in the green body, so the pore distributed uniformly in the porous materials. But the compressive strength was decreased from 17 MPa to 4.5 MPa approxiamately, which still can basically satisfy the requirements as tissue engineering scaffold or bone defect repair material at non weight-bearing sites. The phase composition and calcining system are the main factors that influence the properties of porous material. In order to improve the mechanical properties of the cellular structured material. The calcium pyrophosphate (CPP)/β-TCP mixed powders were synthesized, and the calcining system was optimized. The experimental results showed that the compressive strength of porous materials was increased from 4.5 MPa to 6.5 MPa approximately, whenβ-TCP powders contain 5% CPP, and the materials were sintered for 1 hour at 1200℃. This indicated that the addition of CPP can improve the compressive strength of cellular structured materials remarkably.In order to study the effects of the structure and phase composition on the degradation performance of the porous bioceramics, pristineβ-TCP porous materials (β-TCP),β-TCP porous materials treated by 30% porogen (β-TCP-30%P) and CPP/β-TCP porous materials treated by 30% porogen (CPP/β-TCP-30%P) were prepared for evaluation of degradation performance. The results showed that dissolution and recrystallization of the porous calcium phosphate materials occured simultaneously in the PBS solution.In the surface of theβ-TCP porous materials precipitated needle crystal, but in the surface ofβ-TCP-30%P and CPP/β-TCP-30%P porous materials aren't find crycal clearly.β-TCP-30%P porous materials with a higher weightlessness rate contrast otβ-TCP porous materials. And CPP/β-TCP-30%P porous materials with a higher weightlessness rate contrast otβ-TCP-30%P porous materials.In addition, pore size of porous materials which is suitable for bone ingrowth is on the controversy. In this article, the pore size and shape of the porous materials were modified by slip casting. After modification by slip casting, the pore size became smaller, the pore shape changed from square to circular arc, which were beneficial for cell migration. In addition, the compressive strength of the porous materials significantly increased after treatment of casting.Cell experiments showed that the caiclum phosphate porous materials had good biocompatibility. The cell spread well on the surface of porous calcium phosphate materials. Moreover, the cell proliferated fine on the porous materials.