Hydrogels, because of their water-rich nature and soft mechanical characteristics that resemble those of skin tissues, are promising materials for artificial skin. Existing piezoresistive hydrogels combine unique tissue-like and sensory properties, but these materials are often plagued by problems such as poor mechanical properties and the requirement of an external power supply or batteries. Here, a tough and self-powered hydrogel based on a tough polyacrylonitrile hydrogel incorporating ferroelectric poly(vinylidene fluoride) (PAN-PVDF) is reported. The dipolar interactions between the PVDF and PAN chains cause an increase in the best electroactive β-phase PVDF percentage in the composites from 0 to 91.3%; thus, a maximum piezoelectric coefficient d 33 , 30 pC N −1 , was achieved for the hydrogels. Skin-like Young's modulus values (1.33− 4.24 MPa), stretchability (90−175%), and high toughness (1.23 MJ/m 2 ) were achieved simultaneously for the hydrogels. This tough gel is capable of generating an electrical signal output (≈30 mV and ≈2.8 μA) with a rapid response (≈31 ms) due to the stress-induced poling effect. Moreover, the gel can also precisely detect physiological signals (e.g., gesture, pulse, and words). This study provides a simple and efficient method for artificial skin with high toughness, self-power generation capability, fast response, low cost, and tissue-like properties.

Biopolymer based hydrogels are characteristic of their biocompatibility and capability of mimicking extracellular matrix structure to support cellular behavior. However, these hydrogels suffer from low mechanical properties, uncontrolled degradation, and insufficient osteogenic activity, which limits their applications in bone regeneration. In this study, we developed hybrid gelatin (Gel)/oxidized chondroitin sulfate (OCS) hydrogels that incorporated mesoporous bioactive glass nanoparticles (MBGNs) as bioactive fillers for bone regeneration. Gel-OCS hydrogels could be self-crosslinked in situ under physiological conditions in the presence of borax. The incorporation of MBGNs enhanced the crosslinking and accelerated the gelation. The gelation time decreased with increasing the concentration of MBGNs added. Incorporation of MBGNs in the hydrogels significantly improved the mechanical properties in terms of enhanced storage modulus and compressive strength. The injectability of the hydrogels was not significantly affected by the MBGN incorporation. Also, the proliferation and osteogenic differentiation of rat bone marrow mesenchymal stem cells in vitro and rat cranial defect restoration in vivo were significantly promoted by the hydrogels in the presence of MBGNs. The hybrid Gel-OCS/MBGN hydrogels show promising potential as injectable biomaterials or scaffolds for bone regeneration/repair applications given their tunable degradation and gelation behavior as well as favorable mechanical behavior and osteogenic activities.

The DA–PPy–GP ECHs with continuous conductive networks show high force and strain sensitivity.

The vulnerability of hydrogel electronic materials to mechanical damage due to their soft nature has necessitated the development of self‐repairing hydrogel electronics. However, the development of such material with underwater self‐repairing capability as well as excellent mechanical properties for application in aquatic environments is highly challenging and has not yet been fully realized. This study designs a tough and highly efficient underwater self‐repairing supramolecular hydrogel by synergistically combining weak hydrogen bonds (H‐bonds) and strong dipole–dipole interactions. The resultant hydrogel has high stretchability (up to 700%) and toughness (4.45 MJ m−3), and an almost 100% fast strain self‐recovery (10 min). The underwater healing process is rapid and autonomous (98% self‐repair efficiency after 1 h of healing). Supramolecular hydrogels can be developed as soft electronic sensors for physiological signal detection (gestures, breathing, microexpression, and vocalization) and real‐time underwater communication (Morse code). Importantly, the hydrogel sensor can function underwater after mechanical damage because of its highly efficient underwater self‐repairing capability.

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Imitating the physiological microenvironment of living cell and tissues opens new avenues of research into the application of electricity to medical therapies. In this study, dynamic piezoelectric stimulation is generated in a dynamic culture because of the piezoelectric effect of the poly(vinylidene fluoride)−polypyrrole (PVDF−PPy) electroactive composite. Combined with PPy nanocones, dynamic piezoelectric signals are effectively and continuously provided to cells. In the presence of dynamic piezoelectric stimulation and PPy nanocones, PPy-PVDF NS samples show promoted bone mesenchymal stem cell (BMSCs) adhesion, spreadin, and osteogenic differentiation. On the basis of the results of this study, PPy nanocones and dynamic piezoelectric stimulation can be administered to modulate cell behavior, paving the way for the exploration of cellular responses to dynamic electrical stimulation.

Piezoelectric sensors are widely used in wearable devices to mimic the functions of human skin. However, it is considerably challenging to develop soft piezoelectric materials that can exhibit high sensitivity, stretchability, super elasticity, and suitable modulus. In this study, a soft skin-like piezoelectric polymer elastomer composed of poly(vinylidene fluoride) (PVDF) and a novel elastic substrate polyacrylonitrile is prepared by combining the radical polymerization and freeze-drying processes. Dipole−dipole interaction results in the phase transition of PVDF (α phase to β phase), which enhances the electrical and mechanical performances. Thus, we achieve a high piezoelectric coefficient (d 33max = 63 pC/N), good stretchability (211.3−259.3%), super compressibility (subjected to 99% compression strain without cracking), and super elasticity (100% recovery after extreme compression) simultaneously for the elastomer. The soft composite elastomer produces excellent electrical signal output (V ocmax = 253 mV) and responds rapidly (15 ms) to stress-induced polarization effects. In addition, the elastomer-based sensor accurately detects various physiological signals such as gestures, throat vibrations, and pulse waves. The developed elastomers exhibit excellent mechanical properties and high sensitivity, which helps facilitate their application as artificial electronic skin to sense subtle external pressure in real time.

Multifunctional hydrogel bioadhesives have great prospects in biomedical applications, but their design still faces great challenges, such as multiple and tedious chemical modifications. However, it is difficult to integrate injectable, self‐healing, and stimulus‐responsive properties together. A facile approach based on dynamic metal‐ligand coordination chemistry between chondroitin sulfate (CS) and Fe3+ in the design and synthesis of novel multifunctional metallohydrogel bioadhesives is reported. This CS‐based hydrogel not only has strong tissue adhesion superior to that of commercial fibrin glue, but also exhibits an excellent self‐healing ability and injectability, which are beneficial in the field of bioadhesives. Moreover, the hydrogels undergo a rapid gel–sol transformation in response to multiple external stimuli, including pH, ions, neutral molecules, and chemical redox reactions enabling the rapid removal of the bioadhesive. In addition, metallohydrogels are rapidly formed within 10 s, quick enough to promptly seal the tissue. Importantly, the multifunctional CS‐based bioadhesives are shown to exhibit good biocompatibility, thus allowing the developed materials to meet key requirements for next‐generation tissue adhesives.