A shellfish-inspired bionic microstructure design for biological implants: Enhancing protection of antibacterial silver-loaded coatings and promoting osseointegration.

Implants incorporating multi-level micro-nano structures and antibacterial coatings offer a promising approach to overcoming the shortcomings of titanium and its alloys in stimulating bone growth and preventing bacterial infections. Silver ions have been identified as promising antibacterial agents. However, silver-loaded surface coatings are susceptible to damage from direct friction, and excessive release of silver ions can lead to cytotoxicity, thereby limiting their practical application. Inspired by the wear-resistant surface structure of natural shellfish, this study developed a biomimetic micro/nano multi-level structure on the titanium alloy (TC4) surfaces. The structure incorporated a biomimetic microgroove structure (BMS) with alkaline heat treatment (AH) of sodium titanate and chitosan/silver (CS/Ag) micro-nanostructured coatings (BMS/AH/CS/Ag). The microstructural armor effectively reduced external mechanical friction, safeguarding the coatings from damage. Compared to the unstructured sample, the biomimetic micro-groove armor group with a large micro-groove angle (θ) exhibited significantly reduced wear volume and only a marginal decrease of 1.86% in inhibition against Staphylococcus aureus (S. aureus) post-wear, highlighting the protective effect of this microstructure on the coating. The outstanding improvement was primarily attributed to the increased micro-groove angle, which enhanced the stability of the microstructure and effectively mitigated the friction. Additionally, the biomimetic micro-nano multi-level structure and coating have shown a significant ability to improve the bioactivity for the implant, promoting the adhesion, proliferation, collagen secretion, and extracellular matrix mineralization of human mesenchymal stem cells (hMSCs), which suggests the potential for enhanced osteogenic differentiation and indicates that this method can effectively improve the clinical performance of the implant.