| Understanding the mechanisms and dynamics of the forces and interactions involved in biological systems is essential for predicting and controlling these systems. Developing a fundamental understanding of the interactions at the molecular-level is needed to develop further bioengineering techniques.; The aim of my research was to study the physical interactions, both non-specific and specific, between biomolecules and biosurfaces. In this dissertation, the interactions in four biological systems, which involve different surfactants/lipids, proteins and polysaccharides, were studied. Normal and lateral forces were directly measured using the surface forces apparatus (SFA), and atomic force microscopy (AFM) was used for surface characterization.; Long- and short-ranged hydrophobic interactions were measured between two physisorbed surfactant-coated surfaces using a dynamic force-measuring technique. AFM images showed that, on being immersed in water, the initially hydrophobic monolayer overturns and transforms into patchy hydrophilic bilayers, suggesting an electrostatic origin for the subsequently observed long-range attraction.; In the second project, the adhesion properties of two mussel foot proteins, mefp-1 and mefp-3, binding on mica were studied. The results are consistent with the different biological functions of those molecules, showing that mefp-1 behaves as a protective protein and mefp-3 as the real adhesive protein.; In the third, related project, the lubrication properties of a polysaccharide extracted from red alga was investigated. It showed good adsorption on mica and maintained low friction even under high loads and large shearing distances, all of which make it a good candidate for biolubrication systems.; Finally, a model system was constructed for directly measuring the specific interactions between selectins and their ligands. Adhesion was measured but may have been due to other mechanisms rather than to a specific selectin-ligand interaction.; The systems studied shared some major similarities: apart from involving biological molecules, all the interactions involved large molecular rearrangements. The dependence of the different types of interactions on various parameters was explored. In most of the cases, the interactions between adjacent molecules were correlated, which affected the whole system in ways that are more complex than simply adding the forces between two individual entities. |
