Reconstructable Gradient Structures and Reprogrammable 3D Deformations of Hydrogels with Coumarin Units as the Photolabile Crosslinks

Abstract

Morphing hydrogels have versatile applications in soft robotics, flexible electronics, and biomedical devices. Controlling component distribution and internal stress within a hydrogel is crucial for shape‐changing. However, existing gradient structures of hydrogels are usually non‐reconstructable, once encoded by chemical reactions and covalent bonds. Fabricating hydrogels with distinct gradient structures is inevitable for every new configuration, resulting in poor reusability, adaptability, and sustainability that are disadvantageous for diverse applications. Herein, a hydrogel containing reversible photo‐crosslinks that enable reprogramming of the gradient structures and 3D deformations into various configurations is reported. The hydrogel is prepared by micellar polymerization of hydrophobic coumarin monomer and hydrophilic acrylic acid. The presence of hexadecyltrimethylammonium chloride micelles increases the local concentration of coumarin units and also improves the mechanical properties of the hydrogel by forming robust polyelectrolyte/surfactant complexes that serve as the physical crosslinks. High‐efficiency photodimerization and photocleavage reactions of coumarins are realized under 365 and 254 nm light irradiation, respectively, affording reversible tuning of the network structure of the hydrogel. Through photolithography, different gradient structures are sequentially patterned in one hydrogel that direct the deformations into distinct configurations. Such a strategy should be applicable for other photolabile hydrogels toward reprogrammable control of network structures and versatile functions.

Controlling Properties and Functions of Polymer Gels Using Photochemical Reactions

“…Photoresponsive polymer gels have shown potential applications in the fields of self‐healing materials, actuators, drug release, and extracellular matrices. In addition, there are some other applications that are not mentioned: programmed materials, [ 116 ] tissue printing, [ 117 ] and adaptive surfaces. [ 118 ]…”

Self‐Shaping Soft Electronics Based on Patterned Hydrogel with Stencil‐Printed Liquid Metal

“…We address this issue by affording the hydrogel substrate with shape-morphing ability, which is realized by creating gradient structure to program the internal stress under external stimuli. [50][51][52][53][54] The active morphing of the hydrogel substrate leads to wrapping of the HSE on the objects/organs with good fixation and interfacial contact. A proof-of-concept example is shown in Figure 3a-i.…”

Multi-level encryption of information in morphing hydrogels with patterned fluorescence

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