<p>In this work, a gradient of interpenetrating polymer networks, consisting of anionic</p><p>and cationic polymers, has been investigated with respect to protein resistant</p><p>properties and swelling characteristics at different pH and ionic strength</p><p>conditions.</p><p> </p><p>The swelling and protein adsorption have been studied using <em>in situ </em>spectroscopic</p><p>ellipsometry(SE) and imaging surface plasmon resonance(iSPR) respectively.</p><p>It has been shown that, by altering the buffer pH, the region of lowest</p><p>protein adsorption on the surface could be moved laterally. The swelling has</p><p>similarly been shown to respond to both changes in pH and ionic strength. Additionally,</p><p>the arise of surface charge and the polymer swelling in solution, both a</p><p>consequence of the ionisation of fixed charges on the polymer, have been indicated</p><p>to occur at different buffer pH.</p><p> </p><p>The studied polymer systems show promising properties for future applications</p><p>in, for example, the biosensor area, where the surface chemistry can be</p><p>tailor-made to work optimally in a given environment.</p>

We have investigated a series of molecular and polymeric approaches for generating adherent thin films that impart anti-fouling characteristics to oxide surfaces. These films incorporate oligo- or poly(ethylene glycol) moieties that are expressed in high density in the near-surface region. In our molecular approach, oligo(ethylene glycol)-terminated n-alkyl-trichlorosilanes, RO(CH₂CH₂O)₃(CH₂)₁₁SiCl₃, have been designed so to spontaneously adsorb onto oxide surfaces and produce densely packed films. Another strategy uses a surface initiated polymerization to generate reactive anchored polymer chains that are then chemically modified to incorporate oligo(ethylene glycol) units. Lastly, a comb copolymer comprising a poly(acrylic acid) backbone and different grafting ratios of a linear poly(ethylene oxide-r-propylene oxide) chain has been prepared that adsorbs onto surfaces and forms a poly(ethylene glycol)-exposing film in single step. These surface coatings provide varying levels of protein and cellular resistance that can be related to molecular-scale elements of their surface structure. / Singapore-MIT Alliance (SMA)

Previous studies of protein adsorption on silicon have been restricted by the choice of a simple structure or large surface for protein to adsorb on. The aim of this project was to develop an optical model for more complex nanostructures in form of trenches etched in silicon and then examine if a protein would adsorb to the surface. The method used was infrared ellipsometry. The experimental values from measurements on the sample were used to develop an optical model that represent the nanostructure. A three-layered biaxial model proved to be accurate. One sample was then exposed to the protein albumin and then measured upon again. The results before and after protein adsorption were compared and a small optical signature was found were it could be expected for this specific protein. This shows that it is possible to detect adsorption in a complex nanostructure and to develop an accurate optical model for said structure.

Cell adhesion to proteins adsorbed onto implanted surfaces is particularly important to host responses in biomedical and tissue engineering applications. Biomaterial surface properties influence the type, quantity and functional presentation (activity) of proteins adsorbed upon contact with physiological fluids, and modulate subsequent cell response. Cell adhesion to extracellular matrix proteins (e.g. fibronectin) is primarily mediated by the integrin family of cell-surface receptors. Integrins not only anchor cells, supporting cell spreading and migration, but also trigger signals that regulate survival, proliferation and differentiation. A fundamental understanding of the adhesive interactions at the biomaterial interface is critical to the rational design of biomaterial surfaces. Using model surfaces of self-assembled monolayers of alkanethiols on gold presenting well-defined surface chemistries (CH3, OH, COOH, NH2), we investigated the effects of surface chemistry on osteoblastic differentiation. We report that surface chemistry effectively modulates fibronectin adsorption, integrin binding, focal adhesion assembly and signaling to direct the osteoblast cellular functions of adhesion strength, gene expression and matrix mineralization. Specifically, surfaces presenting OH and NH2 functionalities provide enhanced functional presentation of adsorbed fibronectin, promoting specificity of integrin binding as well as elevating focal adhesion assembly and signaling. Furthermore, the OH and NH2 surfaces supported elevated levels of osteoblast differentiation as evidenced by osteoblast-specific gene expression and matrix mineralization. These results contribute to the development of design principles for the engineering of surfaces that direct cell adhesion for biomedical and tissue engineering applications. In particular, the understanding provided by this analysis may be useful in the engineering of surface properties for bone tissue repair and regeneration.

<p>Previous studies of protein adsorption on silicon have been restricted by the choice of a simple structure or large surface for protein to adsorb on. The aim of this project was to develop an optical model for more complex nanostructures in form of trenches etched in silicon and then examine if a protein would adsorb to the surface. The method used was infrared ellipsometry. The experimental values from measurements on the sample were used to develop an optical model that represent the nanostructure. A three-layered biaxial model proved to be accurate. One sample was then exposed to the protein albumin and then measured upon again. The results before and after protein adsorption were compared and a small optical signature was found were it could be expected for this specific protein. This shows that it is possible to detect adsorption in a complex nanostructure and to develop an accurate optical model for said structure.</p>

The behavior of a protein molecule at the solid-liquid interface is a worthy scientific problem for at least three reasons. The main driving force for studying this problem is a practical one, as many areas of bio-related technologies, such as medical implants, biosensing, and drug delivery, require the understanding of protein-surface interactions. In this dissertation, the nature of the precursive weakly adsorbed state of proteins during binding is reviewed. From this perspective, the adsorption and binding of proteins to a solid block copolymer thin film was achieved with regular spacing. Further efforts produced a monolayer of green fluorescent protein (GFP) covalently bound with regular spacing and orientation to a diblock copolymer thin film. This protein could be folded and refolded by changing solvent characteristics. We also explored the binding of DC-SIGN to mannose and mannotriose bearing lipid membranes. While no binding was observed, the usefulness of the lipid-based glycan microarray was proven using the well-studied CTB-GM1 binding motif. / text

Humic-based organic compounds containing phenol or benzoic acid groups strongly compete with phosphates for specific binding sites on the surface of these colloidal particles. To study the interactions between phenol groups and the surface binding sites of unmodified or modified colloidal particles, chemical force spectrometry (CFS) was used as a tool to measure the adhesion force between an atomic force microscopy (AFM) tip terminated with a phenol self-assembled monolayer and colloidal particles under varying pH conditions. Two modification methods, co-precipitation and post-precipitation, were used to simulate the naturally-occurring phosphate and humic-acid adsorption process. The pH dependence of adhesion forces between phenol-terminated tip and colloidal particles could be explained by an interplay of electrostatic forces, the surface loading of the modifying phosphate or humic acid species and ionic hydrogen bonding. Polydimethylsiloxane (PDMS) is a widely-used polymer in microfluidic devices. PDMS surfaces are commonly modified to make it suitable for specific microfluidic devices. We studied the surface modification of PDMS using four perfluoroalkyl-triethoxysilane molecules of differing length of perfluorinated alkyl chain. The results show that the length of fluorinated alkyl chain has important effects on the density of surface modifying molecules, surface topography and surface zeta potential. The perfluorinated overlayer makes PDMS more efficient at supporting electroosmotic flow, which has potential applications in microfluidic devices. The kinetic study of RNase A, lysozyme C, α-lactalbumin and myoglobin at different concentrations adsorbed on the self-assembled monolayers of 1-octanethiol (OT-Au) and 1H, 1H, 2H, 2H-perfluorooctyl-1-thiol (FOT-Au) has been carried out. The results show a positive relationship between the lower protein concentration and the increased adsorption rate constant (ka) on both surfaces. At low concentrations, the protein adsorption on an OT-Au surface has greater ka than it on a FOT-Au surface. Comparing ka values for four proteins on OT-Au and FOT-Au surface demonstrates that hard proteins (lysozyme and RNase A) have larger ka than soft proteins (α-lactalbumin and myoglobin) on both surfaces. The discussion is based on the hydrophobicity of OT-Au and FOT-Au surfaces, as well as average superficial hydrophobicity, flexibility, size, stability, and surface induced conformation change of proteins. / Thesis (Ph.D, Chemistry) -- Queen's University, 2011-10-14 21:08:31.617

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The design of biocompatible synthetic surfaces is an important issue for medical applications. Surface modification techniques provide good approaches to control the interactions between living systems and implanted materials by modifying the surface characteristics. This thesis work demonstrates the feasibility and effectiveness of the novel and low-cost electrostatic self-assembly (ESA) technique for the manufacturing of biocompatible thin film coatings. The ESA process is based on the alternating adsorption of molecular layers of oppositely charged polymers/nanoparticles, and can be applied in the fabrication of well-organized multilayer thin films possessing various biocompatible properties. ESA multilayer assemblies incorporating various biomaterials including metal oxides and polymers were fabricated, the uniformity, thickness, layer-by-layer linearity, and surface morphology of the films were characterized by UV/vis spectroscopy, ellipsometry, and AFM imaging. Preliminary biocompatibility testing was conducted, concentrating on contact angle surface characterization and the in vitro measurements of protein adsorption. The use of Fourier Transform Infrared Reflection-Absorption Spectroscopy (FT-IRAS) for the investigation of the protein adsorption behavior upon the ESA multilayer films is presented. / Master of Science

Combining linear polymers and dendrimers provides numerous advantages such as increased solubility, biodegradability and a large number of functionalizable peripheral moieties. In this work, novel carborane-containing dendronized polymers were designed as potential candidates for Boron Neutron Capture Therapy (BNCT). These polymers were successfully synthesized using two different approaches. The resulting carborane-functionalized polymers were dendronized using a divergent approach to introduce aliphatic polyester dendrons of generation 1-4 grafted from the polymer backbone. Both approaches produced water-soluble dendronized polymers with high molecular weights. The synthetic approach developed in the first part of this work was also applied in the functionalization of poly(ethylene glycol) (PEG)-grafted gold surfaces with hydrophilic dendrons. In this project, the effect of surface dendronization on protein adsorption was investigated. Contrary to our expectation, protein resistance was found to decrease when the surfaces were covalently functionalized with the hydrophilic dendrons despite their improved hydrophilicity. It was postulated that several factors could be responsible for the increased protein adsorption to the dendronized surfaces, including increased surface area, the introduction of hydrogen-bond donor groups, and a decrease in the mobility of the surface-grafted polymers as a result of inter- and intra-molecular hydrogen bonding between the dendrons. To circumvent these confounding phenomena, while maintaining surface hydrophilicity, we have chosen to covalently attach PEG mono-methyl ether (PEG-OMe) chains of various molecular weight to the peripheral hydroxyl groups of first to fourth generation dendronized surfaces. Results showed that protein adsorption was reduced when dendronized surfaces were grafted with PEG-OMe chains. The hydroxyl-terminated G l-G4 dendronized surfaces and PEG-grafted dendronized surfaces were also investigated for cell adhesion and proliferation. These studies showed that little or no cell adhesion occurred on PEG-grafted gold surfaces. However, greater cell affinity for the dendronized surfaces was observed. When dendronized surfaces were coupled with PEG-OMe chains, cell adhesion was significantly diminished. / Thesis / Doctor of Philosophy (PhD)