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Cartilage is a complex material composed of many biomolecules including glycoproteins. Scott S. Perry, an associate professor of chemistry at the University of Houston, explained that these biopolymers form brush structures in which numerous polymer side chains extend like bristles from a polymer backbone. Importantly, the polymers support large concentrations of water through complexation interactions. NATURE'S WAY University of Houston chemists Yan (left) and Perry explore bio-inspired lubricants. FOLLOWING nature's lead, Perry and other scientists, including Nicholas D. Spencer, a professor of materials at the Swiss Federal Institute of Technology, Zurich, are investigating the tribological properties of synthetic water-absorbing, brush-type polymers in which poly(ethylene glycol) (PEG) side chains are grafted onto a poly(l-lysine) backbone. To judge the polymer's lubricating potential, Perry and postdoctoral associate Xiaoping Yan measured the friction generated by sliding an oxide AFM tip across an oxide surface under aqueous conditions. They found that coating both surfaces with polymer reduced the friction to a tiny fraction of the force measured when the bare oxide surfaces were rubbed. With encouraging results in hand, Perry's group and Spencer's group, which work collaboratively, systematically investigated the influence of polymer structure on friction by varying the number of side chains per molecule and the side-chain molecular weight. Perry reported that increasing the length and concentration of PEG side chains reduces frictional forces. |
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