Molecular Dynamics Study on the Water Mobility and Side-Chain Flexibility of Hydrated Poly(ω-methoxyalkyl acrylate)s

Intermediate water (IW) is known to play an important role in the antifouling property of biocompatible polymers. However, how IW prevents protein adsorption is still unclear. To understand the role of IW in the antifouling mechanism, molecular dynamics simulation was used to investigate the dynamic properties of water and side-chains for hydrated poly(ω-methoxyalkyl acrylate)s (PMCxA, where x indicates the number of methylene carbons) with x = 1-6 and poly(n-butyl acrylate) (PBA) in this study. Since the polymers uptake more water than their equilibrium water content (EWC) at the polymer/water interface, we analyzed the hydrated polymers at a water content higher than that of EWC. It was found that the water molecules interacting with one polymer oxygen atom (BW1), of which most are IW molecules, in PMC2A exhibit the lowest mobility, while those in PBA and PMC1A show a higher mobility. The result was consistent with the expectation that the biocompatible polymer with a long-resident hydration layer possesses good antifouling property. Through the detailed analysis of side-chain binding with three different types of BW1 molecules, we found that the amount of side-chains simultaneously interacting with two BW1 molecules, which exhibit the highest flexibility among the three kinds of side-chains, is the lowest for PMC1A. The high mobility of BW1 is thus suggested as the main factor for the poor protein adsorption resistance of PMC1A even though it possesses enough IW content and relatively flexible side-chains. Contrarily, a maximum amount of side-chains simultaneously interacting with two BW1 molecules was found in the hydrated PMC3A. The moderate side-chain length of PMC3A allows side-chains to simultaneously interact with two BW1 molecules and minimizes the hydrophobic part attractively interacting with a protein at the polymer/water interface. The unique structure of PMC3A may be the reason causing the best protein adsorption resistance among the PMCxAs.