Control hydrogel-hyaluronic acid aggregation toward the design of biomimetic superlubricants.

Healthy synovial fluids (SFs) are complex fluids consisting of biopolymers, globule proteins, and lipids and regarded as superlubricants to provide nearly life-long low friction and wear protection of synovial joints in mammals. In this paper, we report that the intricate lubricious mixture can be simulated by the aggregation of hyaluronic acid (HA) and hydrogel particles in aqueous suspensions. In the HA aqueous suspensions added with synthetic polymer microgels, we have effectively captured the bulk rheological properties of healthy SFs. It is also confirmed by light scattering and fluorescence microscopic characterization that added hydrogel particles can enhance the HA network by hydrogel-mediated hydrogen bonding, leading to the fractal HA-hydrogel aggregating networks in aqueous suspensions. The potential application of HA-hydrogel particle aggregates as biomimetic superlubricants is supported by the comparable low friction at high load to that of healthy SFs.