Controllable Shape Changing and Tristability of Bilayer Composite

Abstract

The programmable shape transition of a two-dimensional sheet to a three-dimensional (3D) structure in response to a variety of external stimuli has recently attracted increasing attention. Among the various shape changing materials, shape memory polymers (SMPs) can fix their temporary shape and/or their length and recover under proper thermal treatment. In this work, we create a bilayer composite by bonding one layer of elastomer with one layer of stretched SMPs, which can undergo a series of shape transitions via the storage and release of internal stresses. The programed shapes are achieved by adjusting the orientation and elongation of the SMPs. Meanwhile, the 3D structures exhibit tristability and can transit between hemihelical, left-handed helical, and right-handed helical shapes. Both theoretical analysis and finite element simulations were conducted to understand the mechanism of shape transformation and used to predict the deformed configuration by adjusting preprogramming parameters. Our work provides a new strategy and design space for fabricating smart reconfigurable structures and paves way for the design and development of bioinspired four-dimensional active matter for a broad range of applications in intelligent materials.

Highly Cross-Linked and Stable Shape-Memory Polyurethanes Containing a Planar Ring Chain Extender

“…Our findings showed that PCHU displayed triple-shape-memory properties. Moreover, we further explored the shape-memory behaviors of the tensile strain of PCAU and orientation angle on its shape-changing procedure. − The shape-memory behavior experiments were done at temperatures of 25, 45, 65, 45, and 25 °C with an external force. In addition, combining the experimental measurement with the theoretical prediction, shapes of the PCAU strips with different orientation angles θ = 0, 45°, 55°, 65°, and 90° are shown in Figure f.…”

Cell‐Laden Multiple‐Step and Reversible 4D Hydrogel Actuators to Mimic Dynamic Tissue Morphogenesis

“…Typically, external stimuli, such as changes in light wavelength, [10,11] media pH, [12] environmental temperature, [13] exogenous chemicals, [14] applied electricity, [15] magnetic fields, [16] and specific biochemical signals, [17] modulate 4D hydrogel swelling and/or shrinking and produce macroscopic actuation. The integration of one or multiple stimuli into such responsive systems, such as gradient hydrogels, [18] single-component hydrogels (unimorph), [19] and bilayer [20] and trilayer [21] hydrogels, can impel the soft actuators to explicitly go through shape evolvement over time either in a preprogrammable fashion, referring to a defined shape morphing in the presence of predefined environmental conditions, or in an "on-demand" manner, referring to a regulated deformation under application of user-controlled external stimulation. Taking advantage of a stimuli responsive systems' programmability and controllability together with a specific geometrical design, hydrogel actuators are cast into 2D or 3D architectures [22] to carry out specific functions (e.g., transporting a cargo, [23] flow control, [24] and grasping [25] ) or locomotion (e.g., swimming [26] , walking [27] , and twisting [28] ).…”

Tough Interfacial Adhesion of Bilayer Hydrogels with Integrated Shape Memory and Elastic Properties for Controlled Shape Deformation

“…Two classes of stimuli-responsive hydrogels are often used as active components for shape-morphing materials, i.e., the stimuli-induced swelling/deswelling hydrogels and shape memory hydrogels. For the first class, hydrogels are usually able to change their volume reversibly via expansion-shrinkage in response to different stimuli, such as pH, temperature, and solvent. − For the second class, shape memory hydrogels (SMHs) are often able to fix temporary shapes and recover to their original shapes through formation–destruction reversible physical interactions or dynamic covalent bonds under external stimuli. − Using the two classes of stimuli-responsive hydrogels as active components, various complex or 3D shapes can be achieved by the combination of active component and passive component via different deformation mechanisms (i.e., bending or buckling). − …”