Bioactuators based on stimulus-responsive hydrogels and their emerging biomedical applications

Abstract

The increasingly intimate bond connecting soft actuation devices and emerging biomedical applications is triggering the development of novel materials with superb biocompatibility and a sensitive actuation capability that can reliably function as bio-use-oriented actuators in a human-friendly manner. Stimulus-responsive hydrogels are biocompatible with human tissues/organs, have sufficient water content, are similar to extracellular matrices in structure and chemophysical properties, and are responsive to external environmental stimuli, and these materials have recently attracted massive research interest for fabricating bioactuators. The great potential of employing such hydrogels that respond to various stimuli (e.g., pH, temperature, light, electricity, and magnetic fields) for actuation purposes has been revealed by their performances in real-time biosensing systems, targeted drug delivery, artificial muscle reconstruction, and cell microenvironment engineering. In this review, the material selection of hydrogels with multiple stimulusresponsive mechanisms for actuator fabrication is first introduced, followed by a detailed introduction to and discussion of the most recent progress in emerging biomedical applications of hydrogel-based bioactuators. Final conclusions, existing challenges, and upcoming development prospects are noted in light of the status quo of bioactuators based on stimulus-responsive hydrogels.

A Macroporous Hydrogel Dressing with Enhanced Antibacterial and Anti‐Inflammatory Capabilities for Accelerated Wound Healing

“…Generally, hydrogels composed of polyacidic polymers tend to swell more at basic pH because of the charge repulsion between the polymer chains caused by deprotonation. [ 13,17 ] In addition, acidic conditions increase protonation of the CMA, thus increasing the intermolecular hydrogen bonding between CMA chains and resulting in shrinkage of the hydrogels. However, the CMA–Ag hydrogel, which is cross‐linked by Ag + ions that form complexes with the hydroxy groups in the CMA molecular chains, swells more at acidic pH because acidic conditions are likely to disrupt the complexation between Ag + ions and hydroxy groups.…”

Hydrogel‐Based Artificial Muscles: Overview and Recent Progress

“…Including aforementioned examples, several researches demonstrated considerable performance and applications of hydrogel‐based artificial muscles . Although hydrogels have shortcomings in mechanical performance, there are several differentiated advantages and corresponding promising applications.…”

“…Incorporating functional nanomaterials is a promising approach to be investigated in the future. Biological applications, including work‐providing exoskeletons and implantable artificial muscle, may be potential applications . Although biocompatibility, primary advantage of hydrogels makes them promising material for biological applications, plenty of issues such as biodegradability, delivery of stimuli, integration into human body, and lifetime should be addressed for practical application, especially in vivo application.…”

Design Rationale for Stimuli‐Responsive, Semi‐interpenetrating Polymer Network Hydrogels–A Quantitative Approach

“…[ 1 ] To enable specific functions, hydrogels can be designed to be responsive to stimuli, e.g., pH, temperature, ionic strength, etc. [ 2 ] Such stimuli‐responsive hydrogels have found wide applications in drug delivery and tissue engineering, [ 3–7 ] wound dressing, [ 8 ] bio actuators, [ 9,10 ] microsensors [ 11–13 ] and as osmotic agents. [ 14,15 ] The most intriguing properties of stimuli‐responsive hydrogels, also highly relevant for the abovementioned applications is the high reversibility of physicochemical changes.…”