Multiphysics modeling of responsive characteristics of ionic-strength-sensitive hydrogel

Abstract

A multiphysics model is developed in this paper for simulation of the volume transition mechanism of the smart hydrogel in response to the changes in the ionic strength of bathing solution as an important measure of the ionic concentration of that solution, which is termed the multi-effect-coupling ionic-strength-stimulus (MECis) model. In the present works, the ionic strength is treated as a main stimulus and incorporated into both the ionic convection-diffusion system in the Nernst-Planck flux and the fixed charge density equation characterized by Langmuir isotherm theory. Due to the diffusion and convection, the osmotic pressure is produced by the difference in the ionic concentration between the interior hydrogel and exterior solution, which drives the swelling of the smart hydrogel. The deformation of the ionic-strength-sensitive hydrogel is described by the momentum conservation law, in which the osmotic pressure is a main driving source. Apart from osmotic pressure, however, the repulsive force between the fixed charges is also considered in the mechanical equilibrium equation as another driving source for the swelling of the hydrogel. The simulation is conducted for one-dimensional steady-state problem, and then compared with the experimental data and other theories from open literature. The comparisons demonstrate that the MECis model can simulate well the swelling behavior of the ionic-strength-sensitive hydrogel qualitatively and quantitatively. Probably it is able to predict the responsive characteristics of the bathing solution including the distribution of diffusive ionic concentrations and electrical potential.

Chemically Responsive Hydrogel Deformation Mechanics: A Review

“…However, when delving into the micro-structural effects on the ionic energy, alternative descriptions can be used [21]. Due to the difficulty of generating a correct model of the micro-structure of the material, as well as defining experimental values for those models (e.g., ionized groups per chain, number of monomer chains, electrostatic repulsion between chains, and so on), significant retro-engineering is necessary to describe the condition being assessed [24,33,34,35,36,37]. Although significant variation occurs between the models, even in non-equilibrium transient states of swelling, Donnan equilibrium is acceptable for gels, as the characteristic times of ionic diffusion, h2/D+ and h2/D−, is generally much smaller than the characteristic time of hydraulic pressure diffusion of the solvent, h2/KE ( h = characteristic distance, K = hydraulic permeability, and E = Young’s modulus) [11].…”

A review on swelling theories of pH-sensitive hydrogels

“…One of the critical parameters in the classification of hydrogels is their responsiveness. The material characteristics of a hydrogel such as the swelling ratio, permeability, and shear modulus, change in response to the external stimuli like pH (De et al, 2002; De and Aluru, 2004; Hu et al, 2012; Marcombe et al, 2010), temperature (Mazaheri et al, 2016), electrostatic field (Wallmersperger et al, 2004; Yamaue et al, 2005), and ionic strength of the surrounding solution (Hong et al 2010; Li and Lai, 2010). This exciting property classifies hydrogels as smart materials and makes them attractive for applications such as in drug delivery (Gupta et al, 2002; Rizwan et al, 2017), tissue engineering (Strehin et al, 2010), soft actuators (Bayat and Baghani, 2018), and chemical micro-valves (Beebe et al, 2000).…”

Recent Advances of the Constitutive Models of Smart Materials — Hydrogels and Shape Memory Polymers

“…For the solvent mixture, developed a constitutive model to describe the equilibrium swelling behaviors of gels in solvent mixtures, which successfully captures experimentally observed cosolvency and cononsolvency effects in different gel-solvent systems. For multiphysics modeling of smart hydrogels, [Li and Lai, 2010;Li et al, 2007a,b,c,d] have theoretically developed several multiphysics models that are able to numerically simulate the multiphase smart soft hydrogels in continuous multi-domain, where the three different phases of hydrogels are considered simultaneously. The multiphysics (coupled chemo-electro-mechanical or higher complexity) fields are included and the performance of the polymeric network solid matrices with flow of ions and interstitial fluid being characterized.…”