Abstract
Shape memory polymer actuators have attracted great attention in the past few decades for developing soft robots, artificial muscles, and biomedical implants, among others. Herein, under a tutorial perspective, a series of shape memory actuators that display unidirectional movement upon exposure to specific external stimuli is explored. The mechanistic details associated with the movement of each system are also highlighted. In general, an overview of basic design principles, the chemical structure of molecular switches, the strategies used to achieve such controlled and unidirectional movement, as well as key experimental aspects, is provided. The most critical challenges of the existing devices that limit their practical applicability are also discussed. This is of utmost importance because such limitations must be overcome to fabricate micromotors that can generate complex movements, other than simple stretching/contraction or bending, to perform complex tasks.
Highlights
Introduction momentumConsiderable research is being done to investigate the underlying working principles of these materials, and integrate multishape smart materials is to trigger directed motion, which involves interconversion of chemical energy and mechanical energy.[1]Primarily biological systems ranging from unicellular organisms and plants to human beings use anisotropic structures of the memory features as well as multiple functions into a single system.[11,12] Typically, energy derived from various external stimuli such as temperature,[13,14] light,[15] pH,[16,17] and electric[18] and magnetic field[19] is exploited to induce the reversible basic building units to achieve complex motions in response shape transformation in these materials
Biological systems ranging from unicellular organisms and plants to human beings use anisotropic structures of the memory features as well as multiple functions into a single system.[11,12]
We review some recent developments in polymeric actuators focusing on those capable of unidirectional movement
Summary
The ability to sense and respond to environmental conditions is an intrinsic characteristic of some polymeric materials. The response is generated due to specific functional groups present in the polymer and any change in their properties upon exposure to external stimuli. To design polymeric actuators for specific applications, it is important to select an appropriate material as the bulk performance of the actuator originates from its specific stimuli responsiveness at the molecular level. We highlight the most relevant systems and discuss their fabrication strategies, actuation mechanism, and the environmental triggers used in each case. PNIPAM hydrogel PNIPAM/TiNS|| hydrogel Azobenzene-based LC elastomer Graft polymer film. Note: A dash denotes absence of data in the corresponding reference
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