Protein adsorption is a critical biological event taking place whenever a foreign body is introduced to the human body, playing a key role in deciding subsequent cellular responses. It is also an important indicator of a material’s biocompatibility. However, protein adsorption on bioactive glasses, which are a special class of biomaterials due to their peculiar biocompatibility and dissolution mechanisms, has not been fully understood.
The ability to immobilize two model proteins, i.e. bovine serum albumin (BSA) and fibronectin, of several bioactive glass compositions were assessed and improved by different surface treatments, namely washing in buffer solutions with varied pH values and functionalization with a silane coupling agent – (3-aminopropyl)triethoxysilane (APTES). The purposes of surface treatments were to improve the APTES grafting and glass surface charge for BSA and fibronectin grafting. The effects of surface treatments on wettability and surface chemistry were investigated using contact angle measurements and Fourier-transform infrared spectroscopy (FTIR), respectively. The presence of proteins on glass surface were evidenced by fluorescence imaging and were later correlated to fibroblasts adhesion.
Contact angle data show that the washing treatments slightly raised the wettability of bioactive glasses, thus modestly facilitating the adsorption of protein. A remarkable increase of the contact angle in APTES coated samples was the evidence of a successful silanization, which was expected to significantly enhance the protein adsorption via interaction between functional groups of proteins and APTES. Imaging of fluorescently-tagged proteins confirmed that APTES coated surface immobilized a greater amount of proteins and featured a more uniform protein layer. Subsequent cell culture tests showed that the improved protein adsorption by the surface treatments did support cell adhesion and spreading with larger cells and multiple focal adhesions detected. The results of this study propose a potential pathway to improve protein adsorption on both new and traditional bioactive glass compositions, which is promising toward the expansion their current application range
