Air-plasma treatment promotes bone-like nano-hydroxylapatite formation on protein films for enhanced in vivo osteogenesis.

Introducing hydroxylapatite (HAp) into biomolecular materials is a promising approach to improve their bone regenerative capability. Thus a facile method needs to be developed to achieve this goal. Here we show that a simple air-plasma treatment of silk fibroin (SF) films for 5 min induced the formation of bone-like plate-shaped nano-HAp (nHAp) on their surface and the resultant material efficiently enhanced in vivo osteogenesis. The air-plasma-treated SF films (termed A-SF) presented surface nano-pillars and enhanced hydrophilicity compared to the pristine SF films (termed SF), making the A-SF and SF films induce the formation of plate-shaped/more-crystalline and needle-like/less-crystalline nHAp, respectively. The mineralized A-SF and SF films (termed A-SF-nHAp and SF-nHAp, respectively) and their non-mineralized counterparts were seeded with rat mesenchymal stem cells and subcutaneously implanted into the rat models. The A-SF-nHAp and A-SF films exhibited more efficient bone formation than the SF-nHAp and SF films in 4 weeks due to their unique nanotopography, with the A-SF-nHAp films being more efficient than the A-SF films. This work shows that a combination of the air-plasma treatment and the subsequent nHAp mineralization most efficiently promotes bone formation. Our plasma-based method is an attractive approach to enhance the bone regenerative capacity of protein-based biomaterials.