AVS2001 Session BI-ThM: Protein Surface Interaction

Thursday, November 1, 2001 8:20 AM in Room 102

Thursday Morning

Start	Invited?	Item
8:20 AM	Invited	BI-ThM-1 Physicochemical Properties of Polysaccharide Coatings as Determinants of Protein Adsorption P.G. Hartley (CSIRO Molecular Science, Australia); S.L. McArthur (University of Washington); K.M. McLean (CSIRO Molecular Science, Australia); S. Oiseth (Chalmers University of Technology, Sweden); G. Johnson, H.J. Griesser (CSIRO Molecular Science, Australia) The use of protein resistant coatings has long been seen as a means of controlling the biological response to implanted materials. Whilst many such surfaces have been produced, the properties which give rise to their protein resistant character are often poorly elucidated. Polysaccharides have been frequently employed as surface modification agents in the biomaterials area by virtue of their ready availability and apparent protein repellancy. The ability to chemically derivatize polysaccharides is a further key feature which suits them to studies of the relationship between surface chemistry and protein adsorption. In our studies we have utilized this ability to produce a range of derivatized dextran coatings with variable physico-chemical properties. These properties have been characterized in detail using both aqueous and high vacuum surface analytical techniques. These results have then been correlated with the protein adsorption behaviour of the surfaces. The results highlight the interplay between surface charge and steric interactions in determining the protein selectivity and/or repellency of the polysaccharide surfaces. In addition, we have further correlated the surface properties with biological responses using in vitro cell adhesion and growth studies. These studies demonstrate that control over cellular responses may be achieved to a large extent by the manipulation of non-specific interactions between polysaccharide surfaces and extracellular matrix proteins.
9:00 AM		BI-ThM-3 Effect of Adsorbate Alkyl Chain Length and Terminal Group Chemistry on the Adsorption of Fibronectin and Albumin on Self-assembled Monolayers C.M.-J. Fauroux, C.C. Dupont-Gillain, R.W. Manning, G.J. Leggett (UMIST, U.K.) Recent studies of the responses of mammalian cells to self-assembled monolayers (SAMs) have provided important insights into the relationship between surface chemical structure and cell attachment to artificial surfaces. Our hypothesis is that a mechanistic explanation of the correlations we have observed depends upon a detailed knowledge of the composition of the protein layer that coats the SAM prior to cell attachment and the conformations of the molecules of which it is composed. Of particular importance are fibronectin (fn), which interacts with membrane receptors (integrins) involved in cell attachment, and albumin (alb), the must abundant component of serum but thought to inhibit attachment. We have studied the adsorption of these proteins onto a range of SAMs to determine whether there is a correlation between the results of our earlier studies and the kinetics of adsorption of these proteins. The kinetics of adsorption of single proteins (human alb and human fn) have been studied for methyl, hydroxyl and carboxylic acid terminated SAMs with short and long alkyl chains. Two complementary techniques have been used. Using ³H-radiolabelling, the mass of adsorbed molecules per unit area may be determined. Measurement of the amide band intensity in Fourier transform infra-red spectroscopy (FTIR) also provides a measure of the amount of adsorbed protein. Data obtained by the two methods have been found to be in close agreement. It has been found that more alb adsorbed to methyl terminated SAMs than to carboxylic acid terminated SAMs, while the smallest amounts of adsorbed protein were observed for the hydroxyl terminated surfaces.
9:20 AM		BI-ThM-4 Deformation of Proteins Adsorbed on Glass Surfaces as Characterized by XAS H.E. Canavan (George Washington University); J.J. Hickman (Clemson University); W.E. O'Grady (U.S. Naval Research Laboratory); D.E. Ramaker (George Washington University) The interaction of proteins with artificial surfaces is of interest to many in the fields of medicine, biotechnology, and surface science. It is known that certain proteins experience considerable conformational deformation upon adsorption onto surfaces. In contrast, some proteins are described as colloidal or "hard," and experience little if any deformation upon adsorption. In the work presented here, the biomolecular interaction is characterized by X-Ray Absorption Spectroscopy (XAS). Sulfur K-edge XAS will be used to analyze the S-S, S-C and S-O bonds to monitor the extent to which the sulfur bond character is changed in both "hard" and "soft" proteins such as BSA, lysozyme, and cytochrome C upon their adsorption onto a glass surface. In addition, X-ray Photoelectron Spectroscopy (XPS) is used to characterize the glass surfaces both prior and subsequent to protein deposition.
10:00 AM		BI-ThM-6 Reversible Adsorption/Desorption of Proteins from a Thermally Switching Polymer Monolayer D.L. Huber, M.A. Samara, B.C. Bunker, R.A. Manginell, C.M. Matzke, G. Dulleck (Sandia National Laboratories) The phase transitions of poly(N-isopropyl acrylamide) (poly NIPAM) hydrogels have been studied extensively for a number of years. We have investigated the thermal transitions of the linear polymer bound to silicon oxide surfaces. The poly NIPAM monolayers are grown from a self assembled monolayer of free radical initiators, and their properties towards protein adsorption are studied as a function of temperature using IR and UV-visible spectroscopies, as well as ellipsometry and fluorescence microscopy. At room temperature, the monolayers are swollen with water and are extremely resistant to protein adhesion, but at elevated temperatures ( above 35C) the polymer collapses and expels a large portion of the water. The collapsed polymer monolayers are capable of quickly adsorbing a protein monolayer. The layer of adsorbed protein can be completely desorbed by cooling the polymer to below its transition temperature. A well prepared monolayer has been shown to be capable of repeated adsorption and desorption cycles with no degradation of the effect. Poly NIPAM monolayers have been grown onto a microchip based platform containing micron scale resistive heaters capable of precisely controlling the surface temperature, and the adsorption and desorption of fluorescently labelled proteins monitored using flurorescence microscopy. Possible applications of on chip structures, as well as the adsorption/desorption kinetics will be discussed.
10:40 AM		BI-ThM-8 Polyelectrolyte Multilayers : A New Tool to Design Targeted Biofilms P. Schaaf (Institut Charles Sadron / Universite Louis Pasteur Strasbourg, France); L. Szyk (Unite INSERM U424 Strasbourg, France); B. Tinland (Institut Charles Sadron (CNRS) Strasbourg, France); F. Cuisinier, P. Schwinte, J.C. Voegel (Unite INSERM U424 Strasbourg, France) The alternate deposition of polycations and polyanions on a solid surface allows to build a polyelectrolyte multilayer film. This method whose driving force is the charge overcompensation at each adsorption step, offers a simple and elegand way to design new types of films with applications ranging from non linear optics to nanoreactors. The buildup procedure also offers the possibility to develop new bioactive films with multiple functionalities. One can, for example, easily embed proteins into these films. We will present results relative to this later aspect and in particular to the structure and the diffusion of proteins embedded in multilayers. It will be shown that proteins embedded in multilayers are not irreversibly fixed but can diffuse along the film. The diffusion coefficient depends upon the polyelectrolytes in contact with the protein. Such films seem also to preserve the secondary structure of the adsorbed and embedded proteins an even to enhance their thermal stability. Polyelectrolyte multilayers appear also to inhibit the formation of intermolecular beta-sheets frequently observed during the heating of protein solutions. Some new perspectives of these films for the coating of biomaterials will finally be presented.
11:00 AM	Invited	BI-ThM-9 Design of Bioadhesive Polymers for Use at Mucosal Interfaces A. Hoffman (University of Washington) Mucosal surfaces of the body include "wet" surfaces such as the eye, nose, mouth, GI-tract, vagina and lungs. They represent a large surface area of the body and thus may be an attractive route for delivery of drugs. When a drug formulation is applied to those surfaces, it may resist being washed away due to a combination of its own viscosity plus its intermolecular interactions with the mucous polymer coating. Two typical bioadhesive polymers that have been most often applied for mucosal drug delivery are polyacrylic acid and chitosan. This talk will describe drug delivery formulations containing PAA or chitosan or their derivatives that may provide better control over drug release rate and duration.
11:40 AM		BI-ThM-11 The Role of Protein-surface Interactions in Implanted Joints M.R. Widmer, M. Heuberger, J. Voros, N.D. Spencer (ETH-Zurich, Switzerland) Proteins appear to play an important role in the boundary lubrication of both natural and implanted hip and knee joints. However, the nature of the interaction of proteins in synovial fluid with the prosthetic tribosurface appears to influence the effectiveness of boundary lubrication significantly. Protein adsorption (waveguide and fluorescence experiments) and tribological (pin-on-disk) studies have been carried out on a number of polymer and model surfaces in order to determine the tribological role and nature of such interactions.