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TECHNICAL PAPERS: Cell

Effects of Initial-Fixed Charge Density on pH-Sensitive Hydrogels Subjected to Coupled pH and Electric Field Stimuli: A Meshless Analysis

[+] Author and Article Information
T. Y. Ng

School of Mechanical & Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798mtyng@ntu.edu.sg

Hua Li, Y. K. Yew

Institute of High Performance Computing, National University of Singapore, 1 Science Park Road, #01-01 The Capricorn, Singapore Science Park II, Singapore 117528

K. Y. Lam

School of Mechanical & Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798

J Biomech Eng 129(2), 148-155 (Sep 04, 2006) (8 pages) doi:10.1115/1.2472370 History: Received March 11, 2006; Revised September 04, 2006

In this paper, we study the effects of initial fixed-charge density on the response behavior of pH-sensitive hydrogels subjected to coupled stimuli, namely, solution pH and externally applied electric field. This is the first instance in which a coupled stimuli numerical analysis has been carried out for these polymer gels, which are used as active sensing/actuating elements in advanced biomicroelectromechanical systems devices. In this work, a chemo-electro-mechanical formulation, termed the multi-effect-coupling pH-stimulus (MECpH) model, is first presented. This mathematical model takes into account the ionic species diffusion, electric potential coupling, and large mechanical deformation. In addition, a correlation between the diffusive hydrogen ions and fixed-charge groups on the hydrogel polymeric chains is established based on the Langmuir absorption isotherm, and incorporated accordingly into the MECpH model. To solve the resulting highly nonlinear and highly coupled partial differential equations of this mathematical model, the Hermite-Cloud method, a novel true meshless technique, is employed. To demonstrate the accuracy and robustness the MECpH model, computed numerical results are compared with experimental data available from literature. Following this validation, several numerical studies are carried out to investigate the effects of initial fixed-charge density on the volumetric variations of these pH-stimulus-responsive hydrogels when immersed in buffered solutions.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of a triphasic hydrogel

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Figure 2

Experimental setup of the immersed hydrogel strip fixed at the center and placed between two electrodes

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Figure 3

Comparison of simulation results with experimental data of Kim (46) for equilibrium bending angle of PMAA/PVA IPN hydrogel in various pH environments, when a constant voltage of 15V is applied across the hydrogel strip

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Figure 4

Comparison of simulation results with experimental data of Kim (46) for swelling ratio of PMAA/PVA IPN hydrogel in various pH environments

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Figure 5

Effects of pH environment with varying fixed charge concentration cm0s on (a) swelling equilibrium and (b) average bending curvature of the hydrogel under the influence of 0.5V applied voltage

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Figure 6

Effects of externally applied voltage with varying fixed charge concentration cm0s on (a) swelling equilibrium and (b) average bending curvature of the hydrogel in acidic swelling medium of pH=3

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Figure 7

Effects of externally applied voltage with varying fixed charge concentration cm0s on (a) swelling equilibrium and (b) average bending curvature of the hydrogel in alkaline swelling medium of pH=12

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Figure 8

Effects of fixed-charge concentration cm0s with varying applied voltage on (a) swelling equilibrium and (b) average bending curvature of the hydrogel in acidic swelling medium of pH=3

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Figure 9

Effects of fixed-charge concentration cm0s with varying applied voltage on (a) swelling equilibrium and (b) average bending curvature of the hydrogel in alkaline swelling medium of pH=12

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