This thesis includes two projects. The first one is a study of organic molecular self assembled monolayers designed to promote selective protein adsorption processes. The second one describes a high quality, freestanding films based on biodegradable chitosan obtained through a controlled preparation process and investigated as a promising system for many applications including biomaterials.
Within the first part of this work it was explored selective adsorbates for molecular recognition based on positively charged peptide and it has studied how the biomolecules are expressed when adsorbed to the surface. The design and the preparation of a peptide modified surface were done to investigate G-protein interactions. Pure and mixed monolayers of a synthetic peptide, GPR-i3n, derived from the 3rd intracellular loop of the α2 Adrenergic Receptor and a smaller inactive oligopeptide, N-formyi-(Gly) 3- (Cys) called 3GC, were prepared. In this study, 3GC is chosen as a co-adsorbent, with the aim to induce molecular conformational changes of GPR-i3n during the monolayer formation to improve the G-protein adsorption to the functionalized surface.
The formation and the chemical composition of the peptide monolayers on the surface were investigated as well as the monolayers thickness and the mass related surface coverage. The interaction between the mixed monolayers and G-proteins was investigated by means of real time Surface Plasmon Resonance (SPR). There is a higher protein binding capacity to the monolayer when the GPR-i3n peptide is intermixed with the 3GC coadsorbent, despite the fact that the 3GC itself has a very low G-protein binding capability. This supports our theory that a molecular reorientation of the GPR-i3n peptide occurs on the surface when 3GC is intermixed with GPR-i3n.
The formation of SAMs is described in chapter 4 and a full characterization of the mixed monolayers is reported as well as a G-protein interaction study.
In terms of biomaterials, a fundamental understanding of the structure and the composition of the surfaces is necessary for a successful design or when interacting with human body.
The objective of the second study was to thoroughly investigate the properties of free standing chitosan films, prepared by dry phase inversion from chitosan solutions in acetic acid. The films of chitosan were transparent with very good flexibility, while thicker films were fragile, showing an increase of internal tension with thickness. Structural analysis by X-ray diffraction (XRD) proved that the films as initially prepared are almost amorphous. Subsequent annealing converted the amorphous films into a mixture of amorphous and crystalline phases. The investigations by thermogravimetry (TG), the derivative (DTG) and the differential thermal curves (DTA) showed that the thermal degradation of chitosan films as initially prepared proceeds in two stages. The first decomposition stage corresponds to a complex series of processes including dehydration of saccharide rings, depolymerization and decomposition of the acetylated and deacetylated units of the polymers.
The methods used for surface analysis can provide information about the biomaterials, information that can be used to ensure the surface reproducibility and the fundamental aspects toward the interaction of biological systems with living systems.
Linköping: Linköping University , 2006. , 42 p.