Hydrogels are often used as model systems for articular cartilage due to similarities in their tribological properties. However, neither the structures nor the friction mechanisms of either system are fully understood. A key aspect of hydrogel lubrication is the nature of the polymeric structure at the surface, and the lubricating water film. A combination of neutron reflectometry and infrared spectroscopy is used to probe polymer volume fraction from the interface into the bulk hydrogel and its dependence on the molding material. The depth dependence of the polymer‐network density influences the compressibility of the hydrogel surfaces, as demonstrated by both atomic force microscopy (AFM)‐ and micro indentation. By changing molding materials, substantial differences in the gradient of polymer‐network density are observed with depth. The lower the volume fraction of polymer at the hydrogel surface, the more water it can maintain at its interface as a substantial water film that is stable even under static conditions. Such films render the hydrogel highly lubricious, with a speed‐independent friction coefficient of μ = 0.01, measured in gemini contact. This result provides experimental evidence that the presence of these highly lubricious water films is strongly dependent on the polymer‐network structure at the surface.
The polymeric structure of hydrogels is commonly presented in the literature as resembling a fishing net. However, this simple view cannot fully capture all the unique properties of these materials....
Molecular dynamics (MD) simulations present a data-mining challenge, given that they can generate a considerable amount of data but often rely on limited or biased human interpretation to examine their...
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