Bi‐Directional Shape Morphing in 4D‐Bioprinted Hydrogels on a Single Stimulation

Abstract

AbstractA generalizable 4D bioprinting technique utilizing graded semi‐interpenetrating network (IPN) hydrogels is introduced with versatile ink design, which exhibits rapid, sequential shape‐morphing transformations in two opposite directions on a single stimulation (immersion in water). The bi‐directional shape morphing behavior is governed by the sequential activation of two distinct actuation mechanisms, namely, anisotropic water uptake due to photocrosslinking gradient and subsequent temporal water redistribution as a consequence of differential swelling‐induced osmolarity gradient. This study demonstrates that the spatiotemporal characteristics of these bi‐directional shape‐morphing hydrogels can be precisely programmed according to desired part specifications by rationally designing dual‐component hydrogel systems based on a mechanistic understanding of the underlying phenomena. Additionally, a proof‐of‐concept demonstration is provided where the bi‐directional, shape‐morphing behavior is leveraged for the design of soft, deployable hydrogel devices. Lastly, a systematic guideline is proposed facilitating the selection of the second hydrogel component for tuning the extent and pace of shape changes. Owing to their excellent biocompatibility and mild enabling conditions, these hydrogels stand to transform the capacity to precisely design soft, deployable devices for the delivery of therapeutic agents in a minimally invasive manner inside the human body, among other potential applications.