| Biomaterials must meet diverse property demands in many applications. A coating approach---whereby a thin film is chosen based on its (bio)chemical and micro-mechanical properties, and a bulk material is chosen based on its structural, macro-mechanical, and degradation properties---allows for the effective decoupling of surface and bulk effects. We investigate here multilayer thin film assemblies, formed from charged macromolecules, as biomaterials of thickness ca. 10-100 nm (i.e. "nanofilms"). Employing the layer-by-layer method, we form multilayer films from polypeptide, polysaccharide, and protein building blocks. We focus on three questions. The first involves the importance of formation history on adsorbed layer structure. By considering a monolayer of fibronectin (a matrix protein known to enhance cell attachment and growth), we show formation history to significantly influence protein orientation, thereby suggesting its importance as a control variable in directing nanofilm assembly. We demonstrate that post-adsorption structural changes can either increase or decrease the number of cell binding sites available depending on the choice of the formation path. The second question involves the simultaneous influence of several important multilayer film variables: rigidity, charge, degree of hydration, and biofunctionality. By considering the influence of a model polypeptide-polysaccharide film on human umbilical vein endothelial cells, we elucidate the effects of these four important properties on the morphological response of contacting cells. We find cells spread on biofunctional films to remain spread on rigid films, and to retract somewhat on softer films. The third question concerns the extension of multilayer film biomaterials to the realm of tissue engineering. Within a human liver application, we determine film properties (composition, charge, rigidity, and biofunctionality) most suitable to promote hepatocyte growth, and thereby uncover best candidate systems for subsequent in vivo applications. We find composition and rigidity to be key for cell growth and attachment, biofunctionalization using collagen to be necessary only for certain films, and terminal layer charge to be fairly unimportant. Throughout, we exploit optical waveguide lightmode spectroscopy (OWLS) as a sensitive and precise means of measuring adsorption/film formation kinetics in situ. |
