Titanium oxide (TiO₂) has been widely used as implant materials for bone tissue engineering in orthopaedic and dental fields due to its various advantages such as good biocompatibility and suitable mechanical strength. However, one of the main concerns of TiO₂ implants is lack of biological activities which can lead to failure of implantation by not integrating well with surrounding bone tissues. In this study, we report a novel surface modification method using an enzymatic reaction to develop bioactive TiO₂ implants. Tyramine (TA) was conjugated to poly(ethylene glycol) (PEG) as a hydrophilic linker and then the resulting material (PTA) was chemically immobilized onto the TiO₂ substrates via a Tyrosinase-mediated reaction. Bone morphogenetic protein-2 (BMP-2), which is known to enhance bone regeneration, was subsequently immobilized onto the PTA-modified TiO₂ substrates via Schiff base and Michael-type addition reaction. The changes in atomic compositions and hydrophilicity of the BMP-2 immobilized TiO₂ were monitored by X−ray photoelectron spectroscopy (XPS) analysis and contact angle measurement. The immobilized amounts of BMP-2 on TiO₂ quantified by a Sandwich-ELISA assay were found to be 30−170 ng/cm2, depending on the feed amounts of PTA and BMP-2. The obtained results demonstrate that this facile BMP-2 immobilization method onto TiO₂ via an enzymatic reaction can be employed as a versatile surface modification technique to improve bioactivity of the metallic implants for efficient bone tissue regeneration.
