4D Printing of Surface Morphing Hydrogels

Abstract

Polymeric systems displaying spontaneous formation of surface wrinkling patterns are useful for a wide range of applications, such as diffraction gratings, flexible electronics, smart adhesives, optical devices, and cell culture platforms. Conventional fabrication techniques for wrinkling patterns involves multitude of processing steps and impose significant limitations on fabrication of hierarchical patterns, creating wrinkles on 3D and nonplanar structures, the scalability of the manufacturing process, and the integration of wrinkle fabrication process into a continuous manufacturing process. In this work, 4D printing of surface morphing hydrogels enabling direct fabrication of wrinkling patterns on curved and/or 3D structures with user‐defined and spatially controlled pattern geometry and size is reported. The key to successful printing is to tailor the photopolymerization time and partial crosslinking time of the hydrogel inks. The interplay between crosslinker concentration and postprinting crosslinking time allow for the control over wrinkling morphology and the characteristic size of the patterns. The pattern alignment is controlled by the print strut size—the size of the solid material extruded from the print nozzle in the form of a line. To demonstrate the utility of the approach, tunable optical devices, a solvent/humidity sensor for microchips, and cell culture platforms to control stem cell shape are fabricated.

4D printing for biomedical applications

“…These mechanisms underpin 4D printing strategies to generate surface patterns on printed hydrogels. [228][229][230] Recent findings, however, suggest that the fingerprint patterning is better described by Turing reaction-diffusion mechanisms during developmental processes, 231 the same mechanism that determines hair follicle spacing, 232 lends cheetah its spots, 233 or an Ornate Boxfish its hexagon/stripe patterns. 234 Patterned surfaces governed by Turing reaction-diffusion mechanisms will represent a new direction in 4D surface morphing.…”

Wrinkled Structure and Morphology Transition of Poly(vinylidene Fluoride Cohexafluoropropylene) Films for Smart Windows

“…The current methods for the preparation of wrinkled structure mainly include mechanical stretching or relaxation ,− and PDMS surface modification, − which usually requires a bilayer system pretreatment of the material . Otherwise, the solvent swelling method − also was used for the fabrication of wrinkle structure, which can induce uniform wrinkle on nonplanar soft substrates, but it is difficult for the fabrication of a large area sample and the wrinkle morphology cannot be regulated . Many researchers have achieved the transformation and modulation of wrinkle morphology by adjusting the magnitude and direction of mechanical forces , and the substrate material properties (thickness, stiffness, and cross-linking gradients).…”

“…43 Otherwise, the solvent swelling method 19−21 also was used for the fabrication of wrinkle structure, which can induce uniform wrinkle on nonplanar soft substrates, but it is difficult for the fabrication of a large area sample and the wrinkle morphology cannot be regulated. 44 Many researchers have achieved the transformation and modulation of wrinkle morphology by adjusting the magnitude and direction of mechanical forces 45,46 and the substrate material properties (thickness, stiffness, 47 and cross-linking gradients 48 ). In addition, the formation/elimination of wrinkles with responsive surface morphology can be modulated by external stimuli (light, 27,49,50 solvent, 21,51 heat).…”

Self‐Powered All‐Optical Tactile Sensing Platform for User‐Interactive Interface

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sensing represents one of the most promising schemes to such sHMI, owning to its mechanical compliance, physical imperception, and multifunction. [4][5][6][7][8] Thus, emerging materials such as nanowires/ fibers, [9][10][11][12] nanomembranes, [13,14] conductive polymers, [15][16][17] organohydrogels, [18][19][20] liquid metals, [21] and MXenes, [22][23][24][25][26] combined with novel constructions including mesh, [27,28] serpentine, [29] textile, [30][31][32][33] wrinkle, [23] and micropattern, [34][35][36] assisted with the emerging fabrication methods such as 3D printing, [37] 4D printing, [38] and transfer printing, [39] have been developed for contact/noncontact interactive electronic skin, on the basis of different mechanisms of piezoresistive, [27] capacitive, [40] piezoelectric, [41] and triboelectric. [42][43][44][45] Despite the thriving progress, the la...

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