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Cartilage-inspired, lipid-based boundary-lubricated hydrogels

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Science  16 Oct 2020:
Vol. 370, Issue 6514, pp. 335-338
DOI: 10.1126/science.aay8276

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Slippery surfaces using lipids

In engineered systems, a reduction in friction can come from the use of lubricants or through surface coatings that are inherently slippery. For most hydrogels, which are cross-linked polymers heavily swelled with water, surface lubrication typically comes from trapped liquids that help to form a slippery surface. Drawing inspiration from articular cartilage that in part uses a lipid boundary layer, Lin et al. designed hydrogels with small concentrations of lipids that are continuously exuded toward the surface to make a slippery layer (see the Perspective by Schmidt). Friction and wear of the hydrogels was reduced by up to a factor of 100, and the effect was observed even after the hydrogels were dried and rehydrated.

Science, this issue p. 335; see also p. 288

Abstract

The lubrication of hydrogels arises from fluid or solvated surface phases. By contrast, the lubricity of articular cartilage, a complex biohydrogel, has been at least partially attributed to nonfluid, lipid-exposing boundary layers. We emulated this behavior in synthetic hydrogels by incorporating trace lipid concentrations to create a molecularly thin, lipid-based boundary layer that renews continuously. We observed a 80% to 99.3% reduction in friction and wear relative to the lipid-free gel, over a wide range of conditions. This effect persists when the gels are dried and then rehydrated. Our approach may provide a method for sustained, extreme lubrication of hydrogels in applications from tissue engineering to clinical diagnostics.

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