Artificial skin-like materials have wide applications, particularly in flexible electronics. However, developing intelligent skin-like soft materials with a remarkable range of properties is still a challenge. Herein, a versatile biomimetic hydrogel inspired by natural skin was fabricated based on Ag/TA@CNC (cellulose nanocrystals (CNCs) decorated with tannic acid (TA) and Ag nanoparticles) nanohybrids and polyvinyl alcohol via dynamic borate ester bond crosslinking, which realized the combination of superstretchability (>4000%), efficient (within 10 min, 98.6%) and repeatable self-healing property, conformability and mechano-stimuli sensitivity within a single structure. This skin-inspired hydrogel can be assembled as a self-healing flexible capacitive sensor to track human body motions with a relatively broad sensible range of strain (up to 400%). Meanwhile, the hydrogel can be further used for repairing circuits, constructing switches, programmed electrical circuit assembly, as electronic skin, and in touch screen pens. Moreover, the modified CNCs could be used as a functional trigger to endow the nanocomposite hydrogels with excellent antibacterial properties and repeatable self-adhesiveness, which also play an important role in bionic skin materials. Compared with previous skin-like materials, these nanocellulose biomimetic hydrogels achieve more favorable functionalities in mimicking natural skin, which can meet versatile application needs ranging from flexible/wearable/self-healable electronic devices to artificial electronic skin.

Developing physical hydrogels with advanced mechanical performance and multi-functionalities as alterative materials for load-bearing soft tissues remains a great challenge. Biological protein-based materials generally exhibit superior strength and toughness owing to their hierarchical structures via hydrogen-bonding assembly. Inspired by natural biological protein materials, tannic acid (TA) is exploited as a molecular coupling bridge between cellulose nanocrystals (CNCs) and poly(vinyl alcohol) (PVA) chains for the fabrication of a bio-based advanced physical hydrogel via strong multiple H-bonds. When exposed to mechanical stress, the sacrificial H-bonds can dissipate energy effectively on the molecular scale via dynamic rupture and reformation, endowing these biomimetic hydrogels with remarkable toughness, ultrahigh strength, large elongation, and good self-recoverability, which are much superior to those of most hydrogen bond-based hydrogels. Moreover, the characteristics of TA endow these biomimetic hydrogels with versatile adhesiveness and good antibacterial properties. This work presents an innovative biomimetic strategy for robust biocompatible hydrogels with superior mechanical strength and functionalities, which holds great promise for applications in tissue engineering and biomedical fields.

Integrating superior mechanical performance, anisotropic conductivity, and biocompatibility into conductive hydrogels as all‐in‐one human‐machine interaction device remains challenging. Herein, by mimicking the anisotropic structures of human muscles, a robust anisotropic conductive hydrogel is developed by initially aligning polyvinyl alcohol with polypyrrole decorated cellulose nanofibrils to form an anisotropically oriented polymer networks, followed by post‐crosslinking with tannic acid (TA). Introducing TA into hydrogel network permanently secures its hierarchically anisotropic structure through multiple hydrogen bonds, thus endowing the hydrogel with exceptional mechanical properties (tensile strength of 11.41 MPa, toughness of 12.44 MJ m⁻³), anisotropic adhesive property, and direction‐dependent conductivity. With these attributes, a hydrogel strain sensor with excellent multidirectional sensitivity is developed, enabling stable monitoring of multi‐degrees of freedom joint movements in the human body and facilitating the control of a multiaxial virtual robot manipulator. Moreover, the in vitro/vivo tests demonstrate exceptional biocompatibility and anti‐biofouling properties of the as‐prepared hydrogel sensor, maintaining stable electronic response signals for over 14 days after successful implantation into the Achilles tendon of mice. Overall, this study presents a promising approach for designing conductive hydrogels with superior mechanical properties and anisotropic functionality for emerging applications in both in vitro and in vivo human‐machine interface materials.