Polydopamine-assisted BMP-2 immobilization on titanium surface enhances the osteogenic potential of periodontal ligament stem cells via integrin-mediated cell-matrix adhesion

A mussel-inspired polydopamine (PDA), resulting from the oxidative polymerization of dopamine, was reported to be an attractive substrate for advancing biomaterial applications. Thus, this study determined the osteoconductive/osteoinductive properties of titanium (Ti) surfaces coated with PDA and the facilitation of the PDA layer to immobilize bone morphogenetic protein-2 (BMP-2) on Ti substrates. The surface chemistry of PDA or PDA/BMP-2-coated Ti was confirmed by contact angle measurement, scanning electron microscopy (SEM), immunofluorescence staining, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). We verified the osteogenic potential of periodontal ligament stem cells (PDLSCs) cultured on the PDA or PDA/BMP-2-Ti surfaces. The osteogenic differentiation of the PDLSCs was assessed by measuring alkaline phosphatase (ALP) activity, intracellular calcium levels, as well as by evaluating osteocalcin (OCN), osterix (OSX), and runt-related transcription factor 2 (RUNX2) protein levels. The PDLSCs cultured on PDA/BMP-2-Ti showed the highest osteogenic activity compared with those on the control Ti and PDA-coated Ti surfaces. Moreover, PDLSCs on PDA and PDA/BMP-2-Ti expressed increased levels of integrin β1 and actin molecules compared to cells on control Ti. Blocking integrin β1 significantly decreased the osteogenic activity of PDLSCs on PDA/BMP-2 surfaces. This study suggests that the PDA coating can efficiently encourage the immobilization of BMP-2 on Ti surfaces and that this modified Ti substrate highly enhanced the osteogenic differentiation of PDLSCs by integrin-mediated cell-matrix adhesion mechanisms.