Control of Protein Adhesion

Fundamentally, surfaces can interact with proteins in a nonspecific or a specific way. Although nonspecific interaction of proteins with surfaces is undesirable in most cases, it can be of interest to switch the capability of adsorption using an external stimulus. Alternatively, it might be advantageous to switch the specific interaction of a surface with a distinct protein, while keeping it repellent for all other biological species under all conditions. For either approach, polymers are important building blocks that can mediate the stimuli-responsive properties. 

There are several recent examples of the switching of nonspecific protein binding on polymer surfaces by application of an external stimulus. Alexander and coworkers demonstrated that protein adhesion can be controlled on PNIPAM surface brushes [14, 181]. For instance, it was reported that the adsorption of FITC-labeled bovine serum albumin (FITC-BSA) on PNIPAM/hexadecanethiol micropatterned surfaces could be tuned by LCST. However, this effect was found to be less pronounced after prolonged incubation times or repeated heating/cooling cycles. The authors suggested that this behavior could be due to unspecific PNIPAM-protein interactions [14], 

In contrast to these approaches based on nonspecific interactions, Zhang and coworkers described a molecularly imprinted hydrogel based on the ther-moresponsive PNIPAM [184], This hydrogel was prepared by copolymerization of a metal chelate monomer iV-(4-vinyl)-benzyl iminodiacetic acid, which formed a coordination complex with the template protein in the presence of Cu ions, A-isopropylacrylamide, acrylamide, and IV.lV-methylenebisacrylamide as crosslinker. The interaction of the imprinted thermoresponsive hydrogel with the protein could be switched between coordination effects and electrostatic attraction by addition or omission of Cu ions. Furthermore, this imprinted hydrogel allowed switching of lysozyme adsorption by changing the temperature. 

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