| DISCOVERY |
that for a given chemical structure, a hydrogel that is synthesized by polymerizing a monomer on a hydrophobic substrate such as polytetrafluoroethylene or polystyrene exhibits much lower surface friction than when the hydrogel is prepared on a hydrophilic substrate such as glass. The results suggest that the polymerization that normally leads to a fully cross-linked gel is suppressed near the hydrophobic surface, producing branched, dangling polymer chains on the edge of the cross-linked network. These "polymer brushes" reduce the already low friction at the surface, although the mechanism is still unclear.
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