Molecular composition and mechanical properties of biopolymer interfaces studied by sum frequency generation vibrational spectroscopy and atomic force microscopy

Sum frequency generation (SFG) vibrational spectroscopy and atomic force microscopy (AFM) have been used to study the surface structure and surface mechanical behavior of biologically-relevant polymer systems. These techniques have emerged as powerful surface analytical tools to deduce structure/property relationships in situ, at both air/solid and air/liquid interfaces. SFG and AFM studies have been performed to understand how the surface properties of polymers are linked to polymer bulk compositions, changes in the ambient environment, or the degree of mechanical strain. Specifically, this review discusses (1) the macroscopic- and molecular-level tracking of small end groups attached to polyurethane blends, engineered to reduce blood clotting; (2) the role of ambient humidity on the surface mechanics of soft contact lenses possessing different water content in the bulk; (3) the affect of cyclic stretch on the molecular surface structure of polyurethane films, designed to mimic the mechanical deformation caused by heartbeat; and (4) the molecular ordering of functional groups at the polystyrene-protein interface. The correlation of spectroscopic and mechanical data by SFG and AFM is a powerful methodology to study and design materials with tailored surface properties.