Silk fibroin film-coated MgZnCa alloy with enhanced in vitro and in vivo performance prepared using surface activation.

Magnesium and its alloys have generated considerable interest as one of the most promising biodegradable metals for biomedical bone implants. However, the enormous challenges are to improve their rapid corrosion excessively as well as to endow them with biocompatibility and biosafety. Herein, we introduce a natural silk fibroin protein coating to control the corrosion resistance and enhance the biocompatibility of MgZnCa alloy. To obtain a robust and reliable coated structure, different surface-activation processes are employed to increase the available functional groups on MgZnCa surfaces before coating. Compared to oxygen plasma activation, our unique vacuum ultraviolet-ozone (VUV/O3) activation method is effective in realizing uniform silk fibroin films as a protective barrier on MgZnCa alloy surfaces, and the nanoscratch test verified the superior adhesion strength of the silk fibroin-coated magnesium alloy structure. Long-term immersion results combined with electrochemical tests showed the preferable in vitro anticorrosion behavior and a low degradation rate of coated Mg alloy (1/8 times that of uncoated Mg alloy). Cell adhesion and cytotoxicity tests demonstrated that silk fibroin-coated MgZnCa presented improved biocompatibility with bone marrow mesenchymal stem cells. An animal study involving silk fibroin-coated MgZnCa implanted on one side of a rabbit spine for 180 days showed remarkably improved in vivo corrosion resistance, with 1/18 times the degradation rate of uncoated MgZnCa. These results not only comprehensively confirmed the validity of the VUV/O3-activation method as a coating strategy but also implied the tremendous potential of the modified Mg alloy for application as a degradable biomedical implant material. STATEMENT OF SIGNIFICANCE: MgZnCa alloy is a promising material in clinical implantation. Silk fibroin (SF) is a natural organic material with biocompatibility and biodegradability. To date, the combination of SF and MgZnCa alloy has exhibited considerable prospects for orthopedic applications. The realization of a direct coating is an enormous challenge because strong chemical bonds cannot be easily formed between organic and inorganic materials. To solve this bottleneck, we proposed a unique vacuum ultraviolet-ozone (VUV/O3) surface-activation method for the first time to modify the Mg alloy surface before SF coating, which significantly enhanced both in vitro and in vivo performance, such as superior biocompatibility and remarkably improved corrosion resistance of magnesium alloys (∼1/18 the in vivo degradation rate of uncoated MgZnCa).