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Measuring the speed dependence of hydrogel friction helps us understand natural lubricated systems.
SLIDING INTERFACES IN HUMANS AND ANIMALS, either in articulating joints or between the eyelid and the eye, are required to undergo thousands of cycles per day for many years. The contacting materials invariably consist of nanoporous, hydrophilic polymer networks that are permeable to water. Synthetic networks of hydrophilic polymer chains, such as those made from polyacrylamide, have been used as models to study the tribological interfaces encountered in biological systems.
Most of these experiments measured the friction between the hydrogel and hard, Impenetrable counterfaces, while biological interfaces are invariably made from Identical Gemini contacts. The group of professor Greg Sawyer, along with colleague Thomas Angelini from the University of Florida, remedied this deficiency by comparing the friction of a Gemini interface consisting of a polyacrylamide, hydrogel ball sliding against a hydrogel substrate. To gain a deeper understanding of the friction behavior, they compared the results with those for a glass ball sliding against a hydrogel substrate and a hydrogel ball sliding against a glass substrate. In all...