Hydrogel coatings have drawn substantial research interest owing to their great potential in developing advanced flexible devices. However, most of them cannot meet the requirement of large‐scale application on diverse substrates and would lose their functionalities under harsh conditions. In this work, a large‐scale and surface‐independent multifunctional hydrogel coating is developed by directly painting and ultraviolet curing hybrid hydrogel precursor containing acrylamide (AM), branched polyethylenimine (PEI), CaCl2, and glycerol. Such a coating shows superior anti‐fog and anti‐frost properties owing to the hydrophilic nature and freezing‐tolerance of the hydrogel. Besides, the hydrogel coating possesses excellent self‐healing performance at both macro‐ and micro‐ scales because of the dynamic hydrogen bonds prevailing between the polymer chains in a gel network. Moreover, this hydrogel coating also exhibits electric conductivity due to the mobile ions present in the gel network. By patterning the hydrogel coating onto an elastic substrate, a foldable tape sensor is fabricated which can sensitively distinguish short‐time click (≈0.1–0.2 s) from long‐time press (≈1–2 s) and detect electrical signals corresponding to cyclic bending deformation. This work provides practical demonstration of hydrogel coatings for engineering applications where anti‐fog, anti‐frosting, self‐healing, and electrically conductive properties are needed.

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Hydrogel coatings have aroused tremendous research interest due to their excellent biocompatibility, lubricity, and flexibility. However, most hydrogel coatings are limited by their low mechanical strength and large-scale applications on diverse substrates. Herein, a mechanically tunable gelatin methacryloyl-based hydrogel coating is developed via a scalable ultraviolet-curing strategy combined with post-immersion treatment in a sodium citrate–water–glycerol solution. Notably, the hydrogel coating shows mechanically tunable properties by changing the soaking time or the concentration of sodium citrate. The compression modulus of the hydrogel is enhanced by 15 times after 120 min of soaking in sodium citrate–water–glycerol. Besides, the anti-freezing property endows the hydrogel coating with low-temperature (e.g., −40 °C) flexibility. The hydrogel coating is transparent with a transmittance of over 80% within the visible light region and exhibits long-term stability (over 60 days at 25 °C and 40% relative humidity). Moreover, the obtained hydrogel coating shows good lubrication properties with a friction coefficient of less than 0.01. The fabricated hydrogel coating can be potentially used in engineering applications where mechanically tunable properties, anti-freezing, lubrication, and excellent light transmittance are required.

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Hydrogels containing hydrophobic materials have attracted great attention for their potential applications in drug delivery and biosensors. This work presents a kneading-dough-inspired method for dispersing hydrophobic particles (HPs) into water. The kneading process can quickly mix HPs with polyethyleneimine (PEI) polymer solution to form “dough”, which facilitates the formation of stable suspensions in aqueous solutions. Combining with photo or thermal curing processes, one type of HPs incorporated PEI-polyacrylamide (PEI/PAM) composite hydrogel exhibiting good self-healing ability, tunable mechanical property is synthesized. The incorporating of HPs into the gel network results in the decrease in the swelling ratio, as well as the enhancement of the compressive modulus by more than five times. Moreover, the stable mechanism of polyethyleneimine-modified particles has been investigated using surface force apparatus, where the pure repulsion during approaching contributes to the good stability of the suspension. The stabilization time of the suspension is dependent on the molecular weight of PEI: the higher the molecular weight is, the better the stability of the suspension will be. Overall, this work demonstrates a useful strategy to introduce HPs into functional hydrogel networks. Future research can be focused on understanding the strengthening mechanism of HPs in the gel networks.