Materials surfaces exposed to biofluids acquire biopolymer layers that undergo dynamic changes during time. The biomolecules adsorb, desorb and displace each other and may become subject to structural (conformational) changes caused by the altered local environment. Cells respond to the molecular characteristics of the biointerfacial layers by adhesion, motility

Tilo Pompe, Lars Renner, Carsten Werner: Leibniz Institute of Polymer Research Dresden, Max Bergmann Center of Biomaterials Dresden, Hohe Str. 6, 01069 Dresden, Germany, E-mail: [email protected]

Principles and Practice Proteins at Solid-Liquid Interfaces Philippe Dejardin (Ed.) © Springer-Verlag Berlin Heidelberg 2006

and the attainment of certain activities or functions. Among the secondary cellular processes, the secretion and degradation of matrix biopolymers and the reorganisation of these molecules into complex structures play a prominent role and determine the patterns of interaction between living and non-living matter at a vast majority of interfaces.

The very complex and dynamic nature of the biomolecular adlayers of materials arises from the complex composition of the biofluids and the biomolecules contained therein, their conformational changes during adsorption and the different interactions involved in the adsorption process. Therefore, and despite of a wealth of detailed investigations of various systems, a comprehensive model of protein adsorption at solid-liquid interfaces is still missing. Haynes and Norde (1994) pointed out that the interplay of hydrophobic and polar interactions, hydrogen bonds, van der Waals interaction, and entropic and structural forces determines protein adsorption in almost any setting.

The dynamics of the protein adsorption process onto solid surfaces and the involved conformational changes have been unravelled and modelled for various single-protein systems (Calonder and Van Tassel 2001; Haynes and Norde 1994; Huetz et al. 1995; Wertz and Santore 2002). Despite the complexity of interlinked processes involved even in the adsorption of a single protein, several investigations could establish general ideas on adsorption, desorption, and exchange from complex protein solutions. An early and widely known finding is referred to as the "Vroman effect" (Bamford et al. 1992), stating a sequential displacement of proteins from surfaces in a size-dependent manner with large proteins exhibiting the highest surface affinity due to the higher number of interacting segments. While convincingly explaining some systems, this simple picture cannot hold true for protein displacement processes in general. However, protein exchange experiments provide a valuable and realistic measure of the interaction strength of proteins with solid substrates, as was demonstrated byGrinell and Feld(1981).

Starting from these findings we analysed the impact ofprotein-substrate anchorage in the context of cell culture experiments to determine the environmental signals that trigger the fate decisions of adherent endothelial cells. We focussed on fibronectin (FN) as a key protein of the extracellular matrix that enables cell adhesion. A set of polymer surfaces was used as substrates; these were established from different alternating maleic anhydride copolymers. Covalently attached thin films of these copolymers allowed us to create a platform of substrates with graduated surface physic-ochemistry that was thoroughly characterised (Pompe et al. 2003b). In detailed protein adsorption and exchange studies, the adsorption kinetics and binding strength were studied and correlated to the protein surface concentration, protein conformation and surface interaction parameters

(Renner et al. 2004, 2005). Finally, the corresponding cellular interaction was investigated in cell adhesion and protein reorganisation experiments using endothelial cells (Pompe et al. 2003a, 2005a).

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