Polymers, surfactants, and proteins at biomaterial interfaces: Observation, manipulation, and measurement of surface interactions using atomic force microscopy

Biomaterials science has a large stake in cellular and molecular interactions at the blood-biomaterial interface. The efficacy of cardiovascular implants is largely dependent on responses of the body, which are mediated by the biomaterial surface. In this work, the observation of blood plasma protein adsorbed to biomaterial surfaces, the manipulation of surface properties of biomaterials to inhibit protein adsorption, and an attempt to measure specific interactions at platelet surfaces are presented.; Fibrinogen, a plasma protein important in coagulation, is adsorbed to three relevant biomaterial surfaces: polydimethylsiloxane, low-density polyethylene, and extended polytetrafluoroethylene. Phase contrast atomic force microscopy (AFM) is utilized to distinguish the protein from the biomaterial topography.; The manipulation of surface properties is based on the hypothesis that modifying biomaterial surface to mimic the cell glycocalyx will render a protein resistant, and therefore less thrombogenic, surface. Biomimetic surface modifications are prepared by physisorption of oligosaccharide surfactants. It is the primary work of this thesis to investigate the adsorption structure of such modifications. Oligosaccharide diblock surfactants are the simplest of such a modifications. N-alkylmaltonamide surfactants of varying hydrophobic segment lengths were observed to form a saccharide layer at a graphite substrate. Oligosaccharide surfactant polymers, which are intended to provide a higher density of saccharides at the surface and to form a more stable surface than the diblock surfactants, also were characterized at the graphite surface. The effect of the hydrophilic side chains and the hydrophobic-hydrophilic balance were investigated. Polymer surfactants with appropriate side chains were capable of forming a confluent layer of polysaccharides. These layers inhibit plasma protein and fibrinogen adsorption as compared to a graphite substrate.; The measurement and mapping of specific receptor-ligand interactions across a platelet surface was attempted using AFM. It was found that modifications of the AFM instrumentation are needed to appropriately make the measurement. The AFM is sensitive enough to make such measurements, but the resolution of the force measurements and the time required to measure forces prohibits the mapping of adhesion forces at the level of receptor-ligand bonds.