Surface functionalization of nanoporous alumina with bone morphogenetic protein 2 for inducing osteogenic differentiation of mesenchymal stem cells

Many studies have demonstrated the possibility to regulate cellular behavior by manipulating the specific characteristics of biomaterials including the physical features and chemical properties. To investigate the synergistic effect of chemical factors and surface topography on the growth behavior of mesenchymal stem cells (MSCs), bone morphorgenic protein 2 (BMP2) was immobilized onto porous alumina substrates with different pore sizes. The BMP2-immobilized alumina substrates were characterized with scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Growth behavior and osteogenic differentiation of MSCs cultured on the different substrates were investigated. Cell adhesion and morphological changes were observed with SEM, and the results showed that the BMP2-immobilized alumina substrate was able to promote adhesion and spreading of MSCs. MTT assay and immunofluorescence staining of integrin β1 revealed that the BMP2-immobilized alumina substrates were favorable for cell growth. To evaluate the differentiation of MSCs, osteoblastic differentiation markers, such as alkaline phosphatase (ALP) activity and mineralization, were investigated. Compared with those of untreated alumina substrates, significantly higher ALP activities and mineralization were detected in cells cultured on BMP2-immobilized alumina substrates. The results suggested that surface functionalization of nanoporous alumina substrates with BMP2 was beneficial for cell growth and osteogenic differentiation. With the approach of immobilizing growth factors onto material substrates, it provided a new insight to exploit novel biofunctional materials for tissue engineering.