Lubrication and Wear Protection of Micro-Structured Hydrogels using Bioinspired Fluids.

We report the fabrication and the use of a bioinspired synovial fluid acting as a lubricant fluid and anti-wear agent at soft and porous chitosan hydrogel tribopairs. This synthetic synovial fluid is composed of sodium hyaluronate (HA) and a bottle-brush polymer (BB) having a polycationic attachment group and polyzwitterionic pendant chains. 2.5 %w/w chitosan hydrogel plugs are organized in a bilayered structure exposing a thin and dense superficial zone (SZ), covering a porous deep zone (DZ) and exhibiting microchannels perpendicularly aligned to the SZ. Using a low-load tribometer, the addition of HA lubricating solution at the hydrogel-hydrogel rubbing contact drastically decreased the coefficient of friction (CoF) from µ = 0.20 ± 0.01 to µ = 0.04 ± 0.01 on the DZ configuration and from µ = 0.31 ± 0.01 to µ = 0.08 ± 0.01 on the SZ surface when increasing HA concentration from 0 to 1000 µg/mL and its molecular mass from 10 to 1500 kDa, similar to what was found when using BB polymer alone. When combining the BB polymer and the 1500 kDa HA, the CoF remained stable at µ = 0.04 ± 0.01 for both studied contact configurations, highlighting the synergistic interaction of the two macromolecules independently of the gel surface topography. Hydrogel wear was characterized by assessing the final gel surface roughness by the means of an interferometer. Increasing HA concentration and molecular weight plus the addition of BB polymer lead to a dramatic surface wear protection with a final gel surface roughness of the hydrogels similar to the untested gels. In brief, BB polymer in combination with high molecular weight HA is a potential lubricating fluid as well as a wear resistant agent for soft materials lubrication and wear protection.