Science ( IF 41.845 ) Pub Date : 2020-10-16 , DOI: 10.1126/science.abd3831 Tannin A. Schmidt
Hydrogels are hydrophilic polymer chain networks that can absorb large quantities of water or biological fluids. In many of their biomedical and other applications (1), hydrogels slide against another surface and must be well lubricated. Hydrogel lubrication is normally provided by fluid interfacial layers (2), but the long-lasting lubrication of articular cartilage in our joints (3–5) is partially the result of nonfluid, highly hydrated head groups of exposed phosphatidylcholine lipids (6). On page 335 of this issue, Lin et al. (7) mimic and modify this mechanism in various synthetic hydrogels by incorporating small concentrations of lipids to create a self-renewing, molecularly thin lipid-based boundary layer. The results are striking, with substantial reduction of friction (and wear) observed by as much as a factor of 100 relative to lipid-free hydrogels. Moreover, the effect remained even when gels were dried and rehydrated.