Biomimetic Ca, Sr/P-Doped Silk Fibroin Films on Mg-1Ca Alloy with Dramatic Corrosion Resistance and Osteogenic Activities

Magnesium and its alloys have emerged as some of the most promising biodegradable metals for temporary bone implants, but challenges remain in controlling their corrosion and biocompatibility and endowing them with bioactivity and osteogenic functionality. Herein, we presented newly developed bioactive Ca, Sr/P-containing silk fibroin films (the Ca, Sr/P silk) on top of Mg-1Ca alloy to simultaneously improve the corrosion resistance, osteocompatibility, and osteogenic activities important in maintaining mechanical integrity and stimulating bone formation, respectively. Briefly, extracellular matrix (ECM) mimicking Ca, Sr/P silk fibroin films were constructed layer upon layer on fluoridized Mg-1Ca alloy via simple spinning assembly. The corrosion resistance property of different samples was studied in vitro by immersion experiments and electrochemistry measurements in Hanks' solution, with the silk-coated ones showing over 1 order of magnitude increase in corrosion resistance compared to the uncoated. Particularly, the Ca, Sr/P silk had the best anticorrosion performance, presumably because of better retaining of the β-sheet silk conformation and ion-induced structural conversion from random coils to silk I and α-helices. Furthermore, the preliminary study of the corrosion behavior of the Ca, Sr/P silk was confirmed the availability of the films for corrosion resistance improvement. The osteocompatibility and osteogenic activities were evaluated by the multiple osteoblast (MC3T3-E1) responses, i.e., proliferation, adherence, spreading, and differentiation in vitro. The Ca, Sr/P silk exhibited the optimal osteogenic activity among all experimental groups. These preliminary results comprehensively confirmed the validity of the coating strategy and they implicated the great potential of the modified Mg alloys as degradable bone implants.