Sheath-Inspired Durable Semi-Convertible Hydrogel Enabled Controllable Lubrication and Contractibility

The dynamic lubrication of sheath surrounding the tendon is significant to the motion of limbs. The sheath-inspired hydrogels for soft actuator and transplantable substitutes primarily focus on high toughness and intrinsic lubricating ability, it remains a significant challenge to design the hydrogels with secreting lubricants capability for continuous lubrication like sheath. In this work, a sheath-inspired semi-convertible hydrogel is designed by cooperating responsive supramolecular networks (gelatin and polydopamine particles) into covalent polymer network (polyvinyl alcohol/poly(N-isopropylacrylamide)). The interpenetrating covalent networks provide the high mechanical strength of 1.73 MPa and reversible contracting capability. The non-covalent disassembly of gelatin network under near-infrared light irradiation endows photothermal-responsive dynamic lubricating function, which could reach superlubricity level (coefficient of friction of 0.007) by introducing hydrophosphatidylcholine in the hydrogel. The synergy of well-lubricating capability and mechanical property of the hydrogel endows excellent durable property, which presents well elasticity after 15 000 compression cycles; and extreme low wear even after 100 000 shearing cycles. The developed hydrogel in this work is further processed into smart lubrication platform and photothermal regulation switch, which can broaden the application of smart responsive and interfacial lubricating materials.