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Numerical Modelling and Simulation of Volume Variation of pH Sensitive Anionic Hydrogels

Lookup NU author(s): Dr Nsidibe-Obong Moses, Dr Vladimir Zivkovic, Dr Francis Franklin, Dr Katarina Novakovic


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Over the years, smart hydrogels have received significant attention in pharmaceutical and biomedical disciplines. Main reason is their potential use in drug delivery devices and tissue scaffolds, of particular interest due to their ability to respond to external triggers, such as pH variations in the body, and alter their conformation (swell and/or collapse) accordingly. To modulate smart hydrogel properties, a broader understanding of the underlying mechanism yielding their behaviour is required. To achieve this, mathematical modelling and simulation studies were pursued in place of expensive empirical approach. The classical Poisson-Nernst-Planck (PNP) equations and equilibrium mechanical equation, can mathematically model the interplay of chemo-electro-mechanical fields for hydrogels exposed to ionic environment. However, this continuum model is not amenable to analytical solutions, and the complex geometry involved makes finite difference method unsuitable for the numerical simulation. Therefore, finite element approach is employed to develop a numerical model that approximates the earlier mentioned mathematical model.In this modelling study, a cylindrically shaped anionic hydrogel immersed in a buffer solution has been used as a case study. All relevant information, defining hydrogel and its environment, was obtained from the literature. A two-dimensional axial symmetrical domain using Finite Element Method implemented in COMSOL Multiphysics software was employed. In the software, the transport of diluted species interface representing the Nernst Planck equation (captures the diffusion and migration of ionic species), electrostatics interface under AC/DC module (represents the Poisson equation, which describes the distribution of the electrical potential in the subdomains) and the solid mechanics interface (describing the deformation of the gel) were all coupled and solved using Direct-PARADISO linear system solver.Parametric studies for transient and equilibrium simulations were performed to determine the effects of material properties (such as concentration of the fixed charge group at the backbone of the hydrogel, modulus of elasticity, and initial dimensions of the hydrogel) and the surrounding external conditions (such as ionic strength, composition and pH value of the buffer solution) on the volume change of the pH responsive hydrogel.The results obtained from the simulation were compared with experimental work in the literature for hydrogels fabricated in a microchannel, confined to deform only in the radial direction. The predictions are in good agreement; hence, the model has the potential to offer predictions for volume changes as a function of pH changes in the surrounding medium.

Publication metadata

Author(s): Moses N, Zivkovic V, Franklin F, Novakovic K

Publication type: Conference Proceedings (inc. Abstract)

Publication status: Published

Conference Name: Chemical Engineering Day UK 2021

Year of Conference: 2021

Print publication date: 07/04/2021

Acceptance date: 08/01/2020