(200e) Choline and Phosphoryl Contributions to Hydration Structure and Dynamics of Poly(2-methacryloyloxyethyl phosphorylcholine)

We explore the hydration structure and dynamics of poly(2-methacryloyloxyethyl phosphorylcholine)50, or pMPC50, in solution using molecular dynamics simulations with an emphasis on isolating the contributions of the key chemical moieties. Surface bound films of this biocompatible polymer have been shown experimentally to produce tribological properties that surpass those of the human synovial joint [1] and are being developed for use in artificial joints [2]. The mechanism by which such materials are thought to provide ultra-low friction coefficients has been termed â??hydration lubricationâ? [3]. Here, we further characterize the molecular level structure and dynamics of this hydration water around pMPC molecules that are experimentally grafted onto substrates for biomimetic lubrication. Previous results [4] showed that the charged choline groups of individual monomers tend to fold onto neighboring monomers yielding solvent facing, highly hydrated phosphoryl groups. Here, we further analyze the effect of the two outer chemical moieties, the choline and phosphoryl groups, by removing them and comparing the behavior of pMPC to poly(2-methacryloyloxyethyl phosphate) and poly(ethyl methacrylate). Preliminary results strengthen the previous hypothesis [4] that the choline moiety is responsible for stabilizing the polymer.

[1]  M. Chen et al., â??Lubrication at Physiological Pressures by Polyzwitterionic Brushes.â? Science 2009, 323, 1698â??1701.

[2]  M. Kyomoto et al., â??Biomimetic hydration lubrication with various polyelectrolyte layers on cross-linked polyethylene orthopedic bearing materials.â? Biomaterials 2012, 33, 4451-9.

[3] J. Klein, â??Hydration lubrication.â? Friction 2013, 1, 1â??23.

[4]  W.L. Roussell, C. Klein, C.R. Iacovella, P.T. Cummings, C. McCabe, â??Molecular Origins of the Ultra-Low Friction Exhibited by Biocompatible Zwitterionic Polymer Brushesâ? accepted at Young Scientist