Strontium-calcium doped titanium dioxide nanotubes loaded with GL13K for promotion of antibacterial activity, anti-Inflammation, and vascularized bone regeneration

Poor osseointegration and postoperative bacterial infections are the main causes of clinical failure of titanium (Ti) based implants. In this study, calcium (Ca) and strontium (Sr), which have osteogenic activity, were simultaneously introduced into titanium dioxide nanotubes (TN) in order to balance the potential cytotoxicity of GL13K (Antibacterial peptides), and a multifunctional Sr, Ca and GL13K-doped TN (SrCaTN-GL13K) coating was successfully constructed. The results showed that the SrCaTN-GL13K coating exhibited good mechanical properties, hydrophilicity, corrosion resistance and bioactivity. Sr2+, Ca2+ and GL13K could be continuously released from the coating and was pH-responsive. In addition, SrCaTN-GL13K showed good antibacterial properties against E. coli and S. aureus with antibacterial rates of approximately 70.32% and 70.78%, respectively. Cellular assays showed that RAW264.7 (immune), human umbilical vein endothelial cell (HUVEC, angiogenic) and mouse embryo osteoblast precursor cell (MC3T3-E1, osteogenic) exhibited good adhesion, survival and proliferation activities on the SrCaTN-GL13K coated surface. At both gene level and protein level, expression of anti-inflammatory markers (Interleukin-10, IL-10; mannose receptor, CD206), angiogenic markers (vascular endothelial growth factor, VEGF; platelet endothelial cell adhesion molecule-1, CD31) and osteogenic markers (alkaline phosphatase, ALP; runt-related transcription factor 2, RUNX2; human collagen type I, COL1a1; osteocalcin, OCN) were significantly upregulated in SrCaTN-GL13K coating. At the cellular and molecular level, SrCaTN-GL13K possessed the ability to induce RAW264.7 towards M2 polarization and it possessed the ability to induce HUVEC tube-formation; meanwhile, it exhibited the ability to induce MC3T3-E1 towards osteogenic differentiation. In conclusion, Ti implants exhibited improved antibacterial, anti-inflammatory, angiogenic, and osteoinductive capabilities by loading Sr, Ca, and GL13K to alter TN. In this study, a multifunctional modification of Ti surface was achieved by an economical and efficient method, which provides a new idea for the design of antimicrobial implantable devices with immunomodulatory functions in the clinic.