Surface Functionalization of Titanium with Carboxymethyl Chitosan and Immobilized Bone Morphogenetic Protein-2 for Enhanced Osseointegration

Orthopedic implant failure has been attributed mainly to loosening of the implant from host bone, which may be due to poor bonding of the implant material to bone tissue, as well as to bacterial infection. One promising strategy to enhance tissue integration is to develop a selective biointeractive surface that simultaneously enhances bone cell function while decreasing bacterial adhesion. In this in vitro study, the surfaces of titanium alloy substrates were functionalized by first covalently grafting carboxymethyl chitosan (CMCS), followed by the conjugation of bone morphogenetic protein-2 (BMP-2) to the CMCS-grafted surface. Bacterial adhesion on the substrates was assayed with Staphylococcus aureus and Staphylococcus epidermidis. Cell functions were investigated using osteoblasts and human bone marrow-derived mesenchymal stem cells. The results showed that bacterial adhesion on both the CMCS and CMCS-BMP-2 functionalized surfaces was significantly reduced compared to that on the pristine substrates. In addition, the CMCS-BMP-2 modified substrates significantly promoted attachment, alkaline phosphatase activity, and calcium mineral deposition of both osteoblast and human bone marrow-derived mesenchymal stem cells. The achievement of the dual functions of bacterial adhesion reduction and cell function promotion by the CMCS-BMP-2 modified titanium substrates illustrates the good potential of such surfaces for enhancement of tissue integration and implant longevity.