Self-Assembly of Matching Molecular Weight Linear and Star-Shaped Polyethylene glycol Molecules for Protein Adsorption Resistance

Fouling properties of materials such as polyethylene glycol (PEG) have been extensively studied over the past decades. Traditionally, the factors believed to result in protein adsorption resistance have included i) steric exclusion arising from the compression of longer chains and ii) grafting density contribution which may provide shielding from the underlying material.

Recent studies have suggested that PEG interaction with water may also play a role in its ability to resist protein adsorption suggesting that steric exclusion may not be the only mechanism occurring during PEG/protein interactions.

Star-shaped PEG polymers have been utilized in protein adsorption studies due to their high PEG segment concentration, which allows to increase the PEG chain grafting density compared to that achieved with linear PEG chains. Most studies that have investigated the interactions of tethered linear and star-shaped PEG layers with proteins have considered linear PEG molecules with molecular weights several orders of magnitude smaller than those considered for star-shaped PEG molecules (i.e. 10 000 g/mol vs. 200 000 g/mol, respectively). Additionally, the star-shaped PEG molecules which have been considered in the literature had up to ~70 arms and were therefore modeled by hard-sphere like structures and low chain densities near the surface due to steric hindrance. This resulted in some difficulties to achieve grafted PEG chain overlap for star molecules.

Here, triethoxysilane end-functionalized linear PEG molecules have been synthesized and utilized to form star-shaped PEG derivatives based on ethoxy hydrolysis and condensation reactions. This resulted in PEG stars with up to ~4 arms, which were found to result in grafted star-shaped PEG chains with significant chain overlap. Linear PEG derivatives were synthesized so that their molecular weight would match the overall molecular weight of the star-shaped PEG molecules. These 2 PEG molecular architectures were covalently self-assembled to hydroxylated silicon wafers and the thickness, grafting density, and conformation of these films were studied. The adsorption of human albumin (serum protein) on linear and star-shaped PEG films was compared to that obtained on control samples, i.e. uncoated silicon wafers. Both film architectures were found to significantly lower albumin adsorption.