Tough Engineering Hydrogels Based on Swelling–Freeze–Thaw Method for Artificial Cartilage

Articular cartilage, which exhibits toughness and ultralow friction even under high squeezing pressures, plays an important role in the daily movement of joints. However, joint soft tissue lesions or injuries caused by diseases, trauma, or human functional decline are inevitable. Poly(vinyl alcohol) (PVA) hydrogels, which have a water content and compressive strength similar to those of many tissues and organs, have the potential to replace tough connective tissues, including cartilage. However, currently, PVA hydrogels are not suitable for complex dynamic environments and lack rebound resilience, especially under long-term or multicycle mechanical loads. Inspired by biological tissues that exhibit increased mechanical strength after swelling, we report a tough engineered hydrogel (TEHy) fabricated by swelling and freeze-thaw methods with a high compressive strength (31 MPa), high toughness (1.17 MJ m^-3), a low friction coefficient (0.01), and a low energy loss factor (0.22). Notably, the TEHy remained remarkably resilient after 100 000 cycles of contact extrusion and remains intact after being compressed by an automobile with a weight of approximately 1600 kg. The TEHy also exhibited excellent water swelling resistance (volume and weight changes less than 5%). Moreover, skeletal muscle cells were able to readily attach and proliferate on the surface of TEHy-6, suggesting its outstanding biocompatibility. Overall, this swelling and freeze-thaw strategy solves the antifatigue and stability problems of PVA hydrogels under large static loads (>10 000 N) and provides an avenue to fabricate engineering hydrogels with strong antifatigue and antiswelling properties and ultralow friction for potential use as biomaterials in tissue engineering.