Abstract
In nature, hydrostatic, endo- and exo-skeletons are widely observed, and provide essential rigidity and anchoring points for the application of muscular forces. The efficient interface between a hard skeleton and soft muscle in biology is made possible by a complex hierarchy of structures and composite materials, extending from the nano- to the meso-scale. In contrast, artificial constructs which aim to bridge this hard-soft interface are prone to failure due to local discontinuities and concentrations in stress and strain which lead to material ruptures, delamination and tearing. In this article, the concept of a stiffness-graded electroactive material (SGEM) is proposed which emulates the soft-rigid interface in the nature biological systems and provides both electromechanical activity and the smooth stiffness gradient needed to bridge these two extreme states. This is achieved by programming the diffusion of a rigid filler material (polyvinyl chloride) in a liquid plasticizer (diisodecyl adipate). It is shown that the resulting stiffness gradient can match that of biological tissues such as smooth and skeletal muscles, and that the distal rigid region can be drilled and bonded and significant loads can be safely applied. Additionally, the resulting composite shows electroactive capability through graded anodophilic actuation characteristics. This protocol can be extended to numerous morphologies such as vertical or radial gradients depending on the deployment of two precursor ingredients. Finally, example applications including surface morphing and motion generation are demonstrated. The embodied stiffness gradient and electroactivity make this concept suitable for the development of bio-integrating and wearable artificial muscles systems and more effective soft robots.
Original language | English |
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Article number | 2200994 |
Number of pages | 12 |
Journal | Advanced Functional Materials |
Volume | 32 |
Issue number | 39 |
Early online date | 14 Jul 2022 |
DOIs | |
Publication status | Published - 26 Sept 2022 |
Bibliographical note
Funding Information:M.T. and H.Y.C. contributed equally to this work. This work was supported by Engineering and Physical Sciences Research Council (EPSRC) grant EP/R02961X/1. J.R. was also supported by EPSRC grants EP/L015293/1, EP/M020460/1, EP/V026518/1, EP/T020792/1, and EP/S026096/1, the Royal Academy of Engineering through the Chair in Emerging Technologies scheme, and Royal Society ‐ ERA Foundation Translation Award TA/R1/170060.
Publisher Copyright:
© 2022 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH.
Keywords
- artificial muscle
- electroactive polymer
- stiffness gradient
- PVC gel
- soft robotics