Study of collagen/γ-PGA polyelectrolyte multilayers coating on plasma treated 316 L stainless steel substrates

316 L stainless steel has been widely used in orthopaedic and dental implants due to its good corrosion resistance, good biocompatibility and strong mechanical strength. However, limited cell attachment, osseointegration failure and bacterial infection of 316 L stainless steel are the main challenges for its clinical application, and these problems can lead to severe implant failure. Among all solutions, surface modification is one of the most promising techniques without damaging the structural integrity of the base metal. In this research, poly electrolyte multilayers (PEM) coating was applied on plasma treated 316 L stainless steel. PEM coating was fabricated composing two biocompatible materials: collagen and gamma-poly-glutamic acid. In addition, a chitosan barrier was applied at the 11th layer to seal and control the drug release rate. Bone morphogenetic protein 2 (BMP-2) and basic fibroblast growth factor 2 (FGF-2) were loaded at the 1st and 11th layers of PEM. Plasma treatment was found to enhance the hydrophilicity and adhesion of PEM coating on 316 L stainless steel. The degradation rate of PEM was similar to 80% on day 70. Releases of FGF-2 and BMP-2 from PEM were 58% and 50% after 768 h. PEM coating with dual growth factors was demonstrated with good biocompatibility and promoted cell proliferation of rat bone mesenchymal stem cells (rBMSCs). Furthermore, alkaline phosphatase activity and mineralization of rBMSCs were also enhanced with the addition of BMP-2 and FGF-2. In conclusion, the extreme mechanical properties of 316 L stainless steel was greatly reduced by PEM coating while the BMP-2 and FGF-2 loaded further endowed osteoconductivity and osteoinductivity of the metal substrate.