Modeling and simulation of hydrogels for the application as finger grippers

2021

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Crosslinked polyelectrolytic polymers embedded in an aqueous solution, so-called hydrogels, show stimuli-responsive behaviour under various kinds of stimulation. These "smart" reactions can be triggered by e.g. chemical, electrical, mechanical or thermal stimuli. The hydrogels react via uptake or delivery of mobile ions and solvent, and show enormous swelling capabilities. This behaviour can be used for chemo-electro-mechanical energy converters or as an actuator or sensor. The presented research investigates anionic hydrogels in the framework of a sensitivity analysis, by a design of experiment (DOE) with the use of ANSYS optiSLang. The hydrogel itself is modelled within a finite element code (Abaqus Unified FEA) as a user element. The applied stimuli are of different nature: chemical, electrical, mechanical and thermal. On the one hand, the stimulus is applied by the change of boundary conditions, e.g. for chemical stimulation by a change of the concentrations of the constituents themselves (N a + and Cl −). For electrically stimulated hydrogels, two electrodes are incorporated at the boundaries and the electric potential is changed. On the other hand, the mechanical stimulus is defined by prescribed displacements at a boundary of the fixed hydrogel. The thermal stimulus is applied over the whole domain in the form of transient temperature changes with temperature-dependent material parameters. The reactions of the hydrogel differ-depending on the type of hydrogel and the stronger or weaker sensitivity-on the applied stimulus. The fully coupled three-field description of the chemo-electro-mechanical model enhanced with thermal dependencies is capable of giving local concentrations, electric potential and displacements.

“…The coupled three field approach -the chemo-electro-mechanical model with thermal dependencies -according to Attaran et al [7] is applied. Only infinitesimal deformations are assumed.…”

Section: Modelingmentioning

confidence: 99%

Sensitivity Analysis of a Simulated Hydrogel

2021

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“…For more details on electrical stimulation, please refer to [1]. The investigated finger gripper consists of a cationic and an anionic gel strip, fixed at their right ends.…”

Section: Electrical Stimulationmentioning

confidence: 99%

“…The applied electric field yields to hyperor depolarization, leading to swelling on one and deswelling on the other side, which results in bending of the gripper arms. For more details on electrical stimulation, please refer to [1].…”

Section: Electrical Stimulationmentioning

confidence: 99%

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An Overview of Simulated Hydrogel Behaviour under Various Kinds of Stimulation

2019

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Polyelectrolytic gels placed in aqueous solution show effects under various kinds of stimulation. The stimuli could be e.g. of chemical, electrical, mechanical or thermal nature. The hydrogels react via uptake or delivery of mobile ions and solvent, and they show enormous swelling capabilities. This multifunctional behaviour is potentially attractive for chemo-electromechanical energy converters or for the use as actuators or sensors. In the present research, anionic and cationic hydrogels are investigated, which means that the polymer network contains anionic or cationic bound charged groups. The chemical stimulation is applied by a change of boundary conditions in the solution bath for the salt concentrations. The electrical stimulus is realized by incorporating electrodes between which an electric potential difference is applied. The mechanical stimulus is realized by prescribed displacements at a boundary of the hydrogel itself. The thermal stimulus is applied as transient temperature change over the whole domain, incorporating temperature-dependent material parameters and osmotic pressure differences. The reactions of the hydrogel differ depending on the sensitivity of the gel to the applied stimulus. The incorporated chemo-electro-mechanical model enhanced with thermal dependencies is capable of giving local concentrations, electric potential and mechanical displacements.

“…Only infinitesimal deformations are assumed in this research, with negligible differences between current and reference configuration. For a more detailed derivation of the governing PDEs and the discretization please refer to Attaran and Wallmersperger et al [1,2,9].…”

Section: Modelingmentioning

confidence: 99%

Behaviour of Anionic and Cationic Hydrogels

2018

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Ionic polyelectrolytic gels in an aqueous solution, i.e. hydrogels -also known as smart materials -react to different kinds of environmental changes, e.g. chemical, electrical, mechanical, and thermal stimulation. As a reaction, they show enormous swelling capabilities resulting from the delivery or uptake of ions and solvent. These properties make them attractive for chemo-electro-mechanical energy converters and for the application as actuators or sensors. The applied multi-field formulation consists of the chemical, electrical, and mechanical field and is capable of giving local concentrations, electric potential distributions and displacements. In this excerpt the reaction of a modelled hydrogel finger gripper under electrical stimulation is shown. The swelling ratio is assumed to be in the regime of small volume changes and corresponding displacements.