Development of macro/micro porous silk fibroin scaffolds with nano-sized calcium phosphate particles for bone tissue engineering

Macro/micro porous silk scaffolds with nano-sized calcium phosphate (CaP) particles were developed for bone tissue engineering. Different amounts of nano-sized CaP particles 4, 8, 16 and 25% (CaP:silk fibroin, wt/wt) were generated into the highly concentrated aqueous silk fibroin solutions via an in-situ approach. Afterwards, the pure silk and silk/nano-CaP porous scaffolds were produced by a combination of salt-leaching/freeze-drying methods. Thermal gravimetric analysis results were able to demonstrated that the silk/nano-CaP scaffolds maintained 64–87% of incorporated CaP after salt-leaching. Dynamic mechanical analysis showed that storage modulus of the 16% formulation was significantly higher than all remaining groups. The porosity of silk/nano-CaP scaffolds assessed using Micro-Computed Tomography decreased from 79.8% to 63.6% with increasing CaP incorporated until 16%. By soaking the scaffolds in Simulated Body Fluid for 7 days, cauliflower-like apatite clusters were observed on the surface of both macro and micro pores of 16% and 25% formulations, which was not observed in 4 and 8% formulations. 16% silk/nano-CaP scaffolds were further chosen for in vitro cytotoxicity and biocompatibility assays. Both silk and 16% silk/nano-CaP scaffolds were non-cytotoxic and promoted cell adhesion and proliferation to a similar extent. These results indicated that the 16% silk/ nano-CaP scaffolds could be a good candidate for bone tissue engineering