Reinforced Gels and Elastomers for Biomedical and Soft Robotics Applications

Abstract

Natural tissues possess a so-called J-shaped strain-stiffening behavior, being soft and compliant at small strains followed by a rapid stiffening at higher strains to prevent tissue damage. In addition, they have significant anisotropy and local variations of mechanical properties that are difficult to reproduce with homogeneous materials. Inspired by many biological organisms, biomimetic and soft robotics research has been focusing on composites of soft components being reinforced by structured stiff components. Especially, structures from mature textile technology and recently emerging additive manufacturing techniques are effective in achieving complex biomimetic structures in a deterministic manner. This review focuses on composites of soft elastomers and gels reinforced by woven or knitted fibers and 3D printed structures, often with conductive or magnetic functionalities for active actuation. Discussions include describing the property requirements from biomedical and soft robotics applications with examples of specific cases, followed by a summary of a few technical solutions that have been suggested. For soft matrix materials, we focus on silicone elastomers because they are the most widely used for biomedical and soft robotics applications. Among reinforcements, knitted/woven fabrics, kirigami/origami structures, and 3D printed metamaterial reinforcements are the topics of interest because their local and global structure can be designed to govern properties of the composites and direct complex motions of soft robots in a deterministic manner. Then, application examples in the fields of biomimetic materials, soft robotics, and tissue engineering are reviewed. Finally, we emphasize the importance of advancing numerical modeling and simulation tools to predict the mechanical properties and actuation behavior of the designed composite materials.

Magnetically Controlled Soft Robotics Utilizing Elastomers and Gels in Actuation: A Review

“…Our recent Review provides summaries on the macromolecular origin of the toughness of elastomer and gels, as well as on the key material properties that are important in soft robotics applications. [8] Elastomers and gels can become magnetically responsive by attaching/incorporating permanent magnets [33] or magnetic coils [34] or by dispersing magnetic particles and/or ferrofluid in the material. [35] The former method is simpler and resulting magnetism is more straightforward to analyze, but both permanent magnets and magnetic coils are considerably stiffer and more brittle in nature compared with elastomers and gels.…”

“…Smart functionalities include, but are not limited to, controllable modulations of dimension, shape, and stiffness that enable actuation of soft robotics with respect to nonpneumatic or nonhydraulic external stimuli, which may be of electric, magnetic, chemical, thermal, or photonic origin. [5][6][7][8] The motions of soft robotics are driven by soft actuators. Traditional actuators, that most of the conventional robots employ, are gearmotor driven with precision linkages regulated by proportional-integralderivative (PID) controllers.…”

“…Gels are swollen polymers that can incorporate solutions with various additives. [8,17] To enable magnetism to steer the translational and rotational motion of the soft actuator, the most popular approach is to blend microor nanosized magnetic materials into the elastomers and gels. [18] The control of motion can become more deterministic by distributing local magnetic susceptibility within the elastomeric composites.…”

“…Recently emerging fabrication strategies of 3D printing, origami, and kirigami are instrumental in applying these concepts in developing new materials for soft actuators. [8,22] In this Review, we intend to summarize the vibrant field of magnetically responsive soft actuators and magnetically controlled soft robotics. In Section 2, a broad overview on the historical background and the recent trends of magnetic soft actuators is provided from materials researchers' perspective.…”

Large-Scale Shape Transformations of a Sphere Made of a Magnetoactive Elastomer

“…Due to their macroscopically significant shape and force response to applied magnetic fields and, reciprocally, considerable change of magnetic properties under mechanical loads, MAEs display a diversity of unique magnetomechanical effects. Recent fascinating examples of MAEs use as active elements in micron-scale technical device and medical engineering—field-tuned acoustic metamaterials [ 1 ], microfluidic transportation systems [ 2 , 3 ], remotely controlled grippers and microrobots [ 4 , 5 , 6 , 7 ]—make it utterly important to fundamentally understand the physics and mechanics underlying the functional properties of these composites.…”