Recent progress in fabrications and applications of functional hydrogel films

Abstract

Hydrogels are a class of soft and wet materials that typically consist of a three‐dimensional polymer network that swells yet does not dissolve in water. There are extensive research and development of hydrogel materials for diverse applications over the past two decades. More recently, hydrogel films with controlled thickness have been fabricated based on crosslinked natural or synthetic polymer networks. These films not only show the chemical/physical properties of bulk gels, such as biocompatibility and stimuli responsiveness, but also exhibit faster response speed and high flexibility/adaptivity, allowing for new functions and applications. In this minireview, we summarize the recent advances in hydrogel films with focuses on two aspects: (i) methods for facile fabrication of hydrogel films, and (ii) versatile applications of hydrogel films in biomedical and emerging fields. Hydrogel films with controllable thickness, fast response, good compliance, and tunable mechanical properties are ideal materials as artificial muscles and wound dressing, and to construct soft actuators, flexible electronics, and so forth. Current challenges and future perspectives of hydrogel films are also given at the end of this minireview.

Hydrogels for active photonics

“…These interactions cause the polymer chains to expand and swell, resulting in the characteristic soft and rubbery texture of hydrogels 53 . The deformable behavior of hydrogels can be controlled by adjusting the chemical composition of the polymer chains, the degree of crosslinking, and environmental conditions, such as pH and temperature [62][63][64] . The deformable mechanism of the stimuli-responsive hydrogels is based on the reversible formation or disruption of crosslinks between the polymer chains 65 .…”

Recent Progress in 3D Printing of Polymer Materials as Soft Actuators and Robots

“…Hydrogel is a three-dimensional polymer network containing a large amount of water. − Due to its similarities to soft biological tissues, good biocompatibility, and operational capabilities in moist or wet environments, hydrogels hold significant potential in biomedical and underwater engineering fields. , Hydrogels offer a versatile design space, allowing the incorporation of various functional components to meet diverse requirements. ,, More importantly, hydrogels exhibit rich responsivenesses to external stimuli and have been recognized as an ideal candidate to devise soft actuators and robots. , Especially, the developments of various tough hydrogels with remarkable strength and stretchability significantly expand the application scope of hydrogels as soft robots and actuators . Hydrogels can be engineered through extrusion-based printing and photocuring printing techniques .…”

“…This gripper successfully captured live goldfish underwater. Shape morphing can also be realized in a single hydrogel with regions of different swelling capacities, due to different cross-linking densities or different alignments of nanofillers. ,, For example, Gladman et al developed a morphing hydrogel by extrusion-based printing of an ink containing nanocellulose fibers that are oriented during the extrusion process. The resultant gel fibers had anisotropic stiffness and anisotropic swelling, enabling the printed constructs to morph and form complex configurations.…”

Liquid metal–hydrogel composites for flexible electronics

“…Hydrogels are a class of polymeric materials with a 3D crosslinked network structure. 37 Due to the hydrophilicity of their polymer chains, hydrogels can absorb large amounts of water without dissolving, and therefore they typically have a high water content (>80 wt%). 38 Thanks to this, hydrogels are highly biocompatible and have a Young's modulus similar to biological tissue (Fig.…”