Reversible shape‐shifting in polymeric materials

Abstract

In recent years, significant progress has been made in polymeric materials, which alter shape upon external stimuli, suggesting potential applications in robotics, biomedical engineering, and optical devices. These stimuli-responsive materials may be categorized into two classes: (i) shapechanging materials in which a specific type of shape-shifting is encoded in the original material structure and (ii) shapememory materials, which do not possess any predetermined shape-shifting as prepared, yet allow programming of complex shape transformations on demand. While shape alterations in shape-changing materials are intrinsically reversible, shape memory is usually a one-way transformation from a metastable (programmed) to an equilibrium (original) state. Recently, different principles for both one-way reversible and two-way reversible shape memory have been developed. These offer a powerful combination of reversibility and programmability, which significantly expands the range of potential applications. The goal of this review is to highlight recent developments in reversible shape-shifting by introducing novel mechanisms, materials, and applications.

Thermally-triggered free-standing shape-memory actuators

“…All of them depend on the incorporation of an internal or external stress-applying component into an already stretched LCN network (microscopic [21,22] or macroscopic [23,24] composites respectively), hindering the recovery of the original shape, but adopting a metastable shape "state-of-ease" after the LCN shrinkage. This state can help to further elongate back to the original shape thanks to the internal stress generated between both the stress-applying component and the LCN [25,26]. In general words, combining a stress-applying component with a shape-shifting component leads to free-standing reversible actuation when compatibility between them is attained.…”

Technological considerations for 4D printing: an overview

“…They morph in response to the stimuli and may return to its permanent shape when the stimuli are removed. Zhou [29] explained that the type of transformation is usually limited to simple affine alterations such as linear volume expansion (stretching) or contraction (shrinking). Homogeneous expansion or contraction (shrinking) in all directions does not lead to a change of geometry.…”

Light‐Responsive Shape‐Changing Polymers

“…Dynamic shape transformations are frequently observed in nature . This biological intelligence has inspired a new class of smart polymer materials that respond to external stimuli by changing their shapes . Such stimuli‐responsive polymer systems are promising candidates to unlock novel types of applications where reconfigurability and adaptability play an important role, including soft robotics, micromachines, and biomedical devices .…”

“…SCPs typically change their shape as long as they are exposed to the stimulus. They recover their initial shape once the stimulus is terminated, resulting in reversible shape changes that can be repeated multiple times . A different shape‐change mechanism is characteristic for shape‐memory polymers (SMPs), which in this review are regarded as a subclass of SCPs.…”