Microwave Plasma Sintering Of Porous β-TCP/HA Biphasic Bioceramics

Synthetically produced porous -TCP/HA biphasic bioceramics have an important role among other biomaterials, because they are considered to be osteoconduction and osteoinduction, and the rate of biodegradation can be controlled by varying HA/TCP ratio. But there are some problems on them with conventional sintering, such as long holding time, high sintering temperature, large grain size and great difficulty to enhance the bioactivity and the mechanical strength simultaneously.In this paper, microwave plasma sintering was introduced to prepare the porous -TCP/HA biphasic bioceramics. Scanning electron microscopy, X-ray diffraction, Material test machine and Atomic absorption spectrophotometer were used to characterize sintered samples. The results show that when samples were placed on a dense Al2O3 substrate, sintering with a constant heating rate of 45C/min, the rate of O2 flowing 75ml/min, the pressure of plasma 1.3kPa, holding 15min at 1100C, the plasma-sintered samples exhibit a higher densification rate, smaller grain size and higher compressive strength compared to those of conventional sintered samples. Porous -TCP/HA biphasic bioceramics with average grain size of 400nm and compressive strength of 2.31MPa were obtained compared to those sintered by a conventional furnace with average grain size of 600nm and compressive strength of 2.00 MPa.. The [Ca2+] concentration and the dissolution rate of plasma-sintered samples are higher than those of conventional sintered samples in physiological saline. After immersed in swaying or dynamic simulated body fluid (SBF) and insimulated inflammation body fluid, the plasma-sintered samples are formed on more bone-like apatite than that conventional sintered samples formed on. The results indicate that plasma-sintered porous -TCP/HA biphasic bioceramics have better mechanical properties and may also have better biological properties.On the other hand, bone-like apatite was found formed on the edge of samples in swaying SBF, but the center area of samples was not discovered, which may mean that physiological micro-circulation benefits to form bone-like apatite on the edge of implanted porous Ca-P materials, but not benefits in the center area of implanted porous Ca-P materials. There was some bone-like apatite formed on the center area of samples besides the edge area in dynamic SBF, which may mean that the physiological through circulation benefits to form bone-like apatite not only on the edge area, but also in the center area of implanted porous Ca-P materials.The surface of samples that underwent a simulated inflammation procedure is smoother and the amount of bone-like apatite formed on them is less than that formed on the samples immersed in normal SBF all the duration, which may indicate that the light acid in an inflammation response would affect the bone reconstruction when Ca-P bioceramics implanted in living body.The dense HA and -TCP/HA biphasic bioceramics prepared by microwave plasma also exhibit a higher densification rate, smaller grain size and higher indentation hardness compared to those of conventional sintered samples. But the sintering behaviors of dense material are significantly different from those of porous -TCP/HA biphasic bioceramics. The sintering efficiency of dense HA and -TCP/HA biphasic bioceramics is lower than that of porous ones.In addition, aimed at solving some problems on a conventional co-precipitation method of preparing biphasic bioceramic powders, a modified co-precipitation method was introduced. The effect of reacting temperature, pH value, reacting time and the initial ratio of Ca/P on final precipitates were discussed. The results indicate that the final precipitates are calcium deficient hydroxyapatite. The biphasic bioceramic powders with different Ca/P ratios can been synthesized by fixing the initial ratio of Ca/P less than 1.5, heating the reacting solution and adjusting the pH.The modified co-precipitation method has a good repetition and requires a shorter ageing time. In this paper, the crystallization mechanism...