<title>Design and modeling of a novel spring-loaded ionic polymeric gel actuator</title>

Abstract

Presented is a novel design for a helical spring-loaded ionic polymeric gel actuator and in particular an encapsulated hermetically sealed, helical compression spring-loaded cylindrical linear actuator containing a counterionic solution or electrolyte such as water+acetone, a cylindrical helical compression spring and a collection of polymeric gel fibers (polyelectrolytes) such as polyvinyl alcohol (PVA) polyacrylic acid (PAA) or polyacrylamide fibers. Furthermore, the proposed design is such that the helical spring not only acts as a compression spring between the two hermetically sealed circular end caps but contains snugly the polymeric gel fiber bundle and also acts as the cathode (anode) electrode while the two actuator caps act as the anode (cathode) electrodes. In this fashion, a DC electric field of a few volts per centimeter can cause the polymer gel fiber bundle to contract (expand). This causes the compression spring to contract and pull the two end caps closer to each other against the elastic resistance of the helical spring. By reversing the action by means of reversing the electric field polarities the gel is allowed to expand while the compression spring is also expanding and helping the linear expansion of the actuator since the polymeric gel muscle expands due to the induced alkalinity along the helical spring. Thus, electrical control of the expansion and the contraction of the linear actuator will be possible.A mathematical model is finally presented for the dynamic response of contractile fiber bundles embedded in or around elastic springs that are either linear helical compression springs or hyperelastic springs such as rubber-like materials. The fiber bundle is assumed to consist of a parallel array of contractile fibers made form contractile polymeric muscles such as polyacrylic acid plus sodium acrylate cross-linked with bisacrylamide (PAAM) or polyacrylonitrile (PAN) fibers. The proposed model considers the electrically or p11-induced contraction of the fibers for the computer-controlled dynamic performance of the actuator.