Hydrophilic-Hydrophobic Network Hydrogels Achieving Optimal Strength and Hysteresis Balance.

The biocompatibility and adaptability of hydrogels make them ideal candidates for use as artificial tendons and muscles in clinical applications, where both muscle-like strength and low hysteresis are essential. However, achieving a balance between a high strength and low hysteresis in hydrogels remains a significant challenge. Herein, we demonstrated a self-assembly process of heterogeneous hydrogels to meet the dilemma. And the hydrogels are composed of both hydrophilic and hydrophobic polymers. The hydrophilic network absorbs water, causing phase separation into a water-rich phase and a water-poor phase, while hydrophobic polymers and entanglement of the network arrest phase separation. Our results demonstrated that these hydrogels achieve remarkable mechanical properties, with a strength of 848.8 kPa, a low energy loss of 19.6 kJ/m, and minimal hysteresis (0.046) during loading-unloading cycles. The reinforcing mechanisms underlying these properties are attributed to crystallization, molecular entanglement, and chain rearrangement induced by stretching. Furthermore, the combination of hydrophilic and hydrophobic networks is exceedingly rare in reported hydrogels.