Bioinspired 3D structures with programmable morphologies and motions

Abstract

Living organisms use spatially controlled expansion and contraction of soft tissues to achieve complex three-dimensional (3D) morphologies and movements and thereby functions. However, replicating such features in man-made materials remains a challenge. Here we report an approach that encodes 2D hydrogels with spatially and temporally controlled growth (expansion and contraction) to create 3D structures with programmed morphologies and motions. This approach uses temperature-responsive hydrogels with locally programmable degrees and rates of swelling and shrinking. This method simultaneously prints multiple 3D structures with custom design from a single precursor in a one-step process within 60 s. We suggest simple yet versatile design rules for creating complex 3D structures and a theoretical model for predicting their motions. We reveal that the spatially nonuniform rates of swelling and shrinking of growth-induced 3D structures determine their dynamic shape changes. We demonstrate shape-morphing 3D structures with diverse morphologies, including bioinspired structures with programmed sequential motions.

Transformer Hydrogels: A Review

“…Researchers have created hydrogels with gradients by mixing varying concentrations of monomers or cross‐linkers, applying mechanical forces during polymerization, exposing the materials to magnetic and electric fields, and spatially controlling polymerization . Klein et al were able to create lateral radial cross‐link gradients by varying the concentration of NIPAM monomers injected into a Hele‐Shaw cell to form unique shape change gels that showed an asymmetric distribution of Gaussian curvature ( Figure a) .…”

“…d) 2D thermoresponsive hydrogels programmed to transform into 3D structures based on gradients created with digital light projection grayscale lithography. Adapted under the terms of the Creative Commons Attribution 4.0 International License . Copyright 2018, The Authors.…”

“…The monomer precursor was inserted between two glass slides and cross‐linked continuously as a function of the spatial location and the exposure time which controlled the stiffness and swelling characteristics of the hydrogels. Nojoomi et al also adopted a similar strategy to achieve spatially and temporally controlled bioinspired movements using hydrogels . Their resulting structures were able to undergo complex programmable shape transformations due to the swelling gradients created during the photopolymerization (Figure d).…”

Materials as Machines

“…Accordingly, upon exposure to thermal stimuli, axisymmetric and nonaxisymmetric Gaussian curvature can be achieved, plainly evident in a hydrogel that swells to a near spherical shape ( Figure a). Yum and co‐workers have since demonstrated that the formation of Gaussian curvature is dynamic and may be programmed by controlling the rate at which given regions of a hydrogel swell, resulting in spatially controlled, sequential deformation in a thermoresponsive hydrogel 463…”

3D printing and growth induced bending based on PET-RAFT polymerization

“…4D movement allows for the creation of highly customizable devices such as; medical implants which move and grow within the body [35][36][37] , sensors which move upon stimulation 38,39 , and various soft robotics applications 40,41 . There are many different pathways to achieving such movement in 3D printed objects, common examples include; solvent swelling and expansion [42][43][44][45] , thermally induced contraction [46][47][48][49][50] , pneumatic force through printed channels 38,41,51 , photochemical changes (cis-trans isomerization, reversible ring opening, cycloaddition, and bond-exchange) [52][53][54] , and spatioselective printing of areas of high and low stress 55,56 . Of all these techniques, the least explored is the use of non-uniform stress to induce movement to a more "comfortable" position.…”