Porous silicon nitride for scaffold material by direct forming with protective gelling

Porous Si₃N₄ substrate for scaffold is prepared by the direct foaming process that is modified by introducing a protective gelling agent (PGA) combined with quench-freezing technique in this work. Nano-hydroxyapatite (nHA) is deposited onto the as-prepared substrate. The adhesion strength of the deposited nHA is evaluated with ultrasonic vibration method and the bioactivity of the pristine porous silicon nitride and that with nHA coating (nHA-coated Si₃N₄) are assessed by simulated body fluid (SBF) treatment along with in vitro cell culture experiments. The results indicate that compared with conventional direct foaming method, the introducing of PGA combined with quench-freezing significantly enhances the stability of foams and lowers the standard deviation of pore size distribution, leading to improved strength and reliability of the porous Si₃N₄ substrates. It is also found that the adhesion strength of the nHA coating is relatively low as shown by mass loss experiment with an ultrasonic cleaning device. The results of SBF treatment and in vitro cell culture experiment demonstrate that the pristine porous silicon nitride exhibits considerable bioactivity comparable to that with nHA coating.