The adsorption of proteins from a solution to solid surfaces is one of the most extensively studied topics due to its significant scientific interests and widespread applications. On the one hand, uncontrolled adsorption of proteins on an implant surface, such as catheters, stents, or pacemakers, can result in encapsulation and ultimate deterioration of the device or surface-induced thrombosis. On the other hand, to realize commercial success in tissue-engineered products there must be precise tuning of protein and cell adhesion to the synthetic scaffolds.

Surface-bound polymer gradients provide a novel platform for systematically evaluating the parameters affecting protein adsorption on man-made surfaces. We chose to use poly(2-hydroxylethyl methacrylate) (PHEMA) brushes in our study due to its ease of synthesis on surfaces at high grafting density by controlled radical polymerization. Moreover, it offers a rather broad range of chain length and/or grafting density that can be varied to manipulate protein adsorption. Additionally, it is possible to attach molecules with different functionality to PHEMA via its hydroxyl groups. This chemical tailoring will help PHEMA surfaces satisfy the growing demands of many complex biomedical applications. We employed a linear gradient in MW of grafted PHEMA and silane coupling agents to modify the OH groups in our study.

It has been well known for decades that alkylchlorosilanes in solution react with hydroxylated surface to produce a surface modified by SAMs. The end-functionality of adsorbed organosilane subsequently dictates the functionality of the surface. In our experiments we used fluorine-containing organosilane coupling agents 1H,1H,2H,2H - perfluorodecyldimethyl-chlorosilane (mF8H2) and 1H,1H,2H,2H-perfluoro-decyltrichlorosilane (tF8H2) and optimized solvent conditions for silane attachment. The substrates were characterized by a battery of analytical tools, including, ellipsometry for thickness measurement, contact angle goniometer for surface energy estimation, near-edge x-ray absorption fine structure (NEXAFS) spectroscopy for the identification of chemical bonds and determination of their relative population density within the sample, and a relative measurement of the concentration of the F8H2 groups on the substrate and their possible orientation. Our experimental results indicate that the highest amount of fluorinated material on the PHEMA polymer brush occurs when the deposition is done in cyclohexhene with dibutyl dilauryl tin as a catalyst. These results open up a new venue in preparing novel materials with varying functionality using silane coupling agents. By utilizing these systems we can systematically vary the surface property of polymer brush and study their effect on protein adsorption.