Hydrogel lubrication modification of hard polymer surfaces shows broad application prospects in soft robotics, tissue engineering, and biomedical devices. However, orders-of-magnitude differences in modulus can easily lead to stress concentrations at the interface between soft and hard materials, increasing material failure, especially in the field of artificial joint replacement, which involves high-load service. Herein, we propose a robust hydrogel lubricating modification strategy for high-modulus polymer surfaces via gradient-structured stress-transfer dissipation and interfacial polymer chain interpenetrating anchoring. The material modulus of the entire lubrication system increases sequentially from the outside in-the modulus of the hydrogel portion increases by more than two orders of magnitude, from hundreds of kilopascals to megapascals, and then to 10 megapascals, at which point the hydrogel modulus matches the high-modulus polymer (polydimethylsiloxane). The surface of the high-modulus polymer and the hydrogel are anchored together through the interpenetration of polymer chains (anchoring force of 250 N·m-1). What's more, this nonhomogeneous surface structure construction achieves high load-bearing and ultra-low friction simultaneously, which are inherently in conflict, with one raised at the expense of the other. This unique approach provides the high-modulus polymer surface with robust lubricating capacity with a low coefficient of friction (COF: ∼0.03) and maintains stable lubricity under ultimate-load and long-term shear conditions (contact stress: ∼12 MPa, friction 5000 cycles). This strategy provides a reference for surface modification of medical interventional devices.
Ma et al. (Fri,) studied this question.