Deformation Of Hydrogels Research Articles

A novel optical coherence tomography-based micro-indentation technique for mechanical characterization of hydrogels

Depth-sensing micro-indentation has been well recognized as a powerful tool for characterizing mechanical properties of solid materials due to its non-destructive approach. Based on the depth-sensing principle, we have developed a new indentation method combined with a high-resolution imaging technique, optical coherence tomography, which can accurately measure the deformation of hydrogels under a spherical indenter at constant force. The Hertz contact theory has been applied for quantitatively correlating the indentation force and the deformation with the mechanical properties of the materials. Young's moduli of hydrogels estimated by the new method are comparable with those measured by conventional depth-sensing micro-indentation. The advantages of this new method include its capability to characterize mechanical properties of bulk soft materials and amenability to perform creeping tests. More importantly, the measurement can be performed under sterile conditions allowing non-destructive, in situ and real-time investigations on the changes in mechanical properties of soft materials (e.g. hydrogel). This unique character can be applied for various biomechanical investigations such as monitoring reconstruction of engineered tissues.

Modeling and simulation of the deformation of multi-state hydrogels subjected to electrical stimuli

In this paper, a mathematical model capable of simulating pH-sensitive hydrogels is refined to extend its application to electric-sensitive hydrogels. This is achieved by consideration for large deformation as well as the reformulation of the fixed charge density. The present model, termed the refined multi-effect-coupling electric-stimulus (rMECe) model, consists of nonlinear partial differential governing equations with chemo-electro-mechanical coupling effects and the fixed charge density, which includes the effect of externally applied electric field. A comparison between simulation results and experimental data is carried out so as to validate the rMECe model, and very good agreement is observed. The multi-state rMECe model accurately predicts the responsive deformation of the hydrogels when placed in a bath solution, which is subjected to externally applied electric field. The influences of several physical parameters, such as the applied voltage, initial fixed charge density and ionic concentration of surrounding solution, are examined and discussed in detail.

Transient simulation of kinetics of electric-sensitive hydrogels

Kinetics of the hydrogels responsive to electric stimulus due to an externally applied electric field is modeled for the first time through transient simulation. The mathematical model employed is called the multi-effect-coupling electric-stimulus (MECe) model, which is developed with consideration of multi-phases and multi-physics. Transient simulation by the MECe model is examined with available experimental data and good agreement is achieved. The kinetics of ionic concentration of diffusive species is simulated. The simulation also predicts the influences of several important parameters on the hydrogel deformation, including the externally applied electric voltage, initially fixed charge density and surrounding bath solution concentration.

Modeling and simulation of deformation of hydrogels responding to electric stimulus

A model for simulation of pH-sensitive hydrogels is refined in this paper to extend its application to electric-sensitive hydrogels, termed the refined multi-effect-coupling electric-stimulus (rMECe) model. By reformulation of the fixed-charge density and consideration of finite deformation, the rMECe model is able to predict the responsive deformations of the hydrogels when they are immersed in a bath solution subject to externally applied electric field. The rMECe model consists of nonlinear partial differential governing equations with chemo-electro-mechanical coupling effects and the fixed-charge density with electric-field effect. By comparison between simulation and experiment extracted from literature, the model is verified to be accurate and stable. The rMECe model performs quantitatively for deformation analysis of the electric-sensitive hydrogels. The influences of several physical parameters, including the externally applied electric voltage, initial fixed-charge density, hydrogel strip thickness, ionic strength and valence of surrounding solution, are discussed in detail on the displacement and average curvature of the hydrogels.

Transient simulation for kinetic responsive behaviors of electric-sensitive hydrogels subject to applied electric field

In this paper, the kinetics of polymer-based electric-stimulus-responsive hydrogels is investigated numerically. The studied hydrogels are mainly composed of three phases, i.e. the interstitial water, mobile ions and a three-dimensional networked structure of hydrophilic polymer-chains crosslinked to each other. With consideration of the chemo-electro-mechanical coupling effect and the multi-phasic (water, ion and polymer-based solid phases) interactions, a newly developed mathematical model, called the multi-effect-coupling electric-stimulus (MECe) model, is briefly presented to simulate the responsive behaviors of electric-sensitive hydrogels immersed into a bath solution under an externally applied electric field. The full formulation of the MECe model is expressed by a set of nonlinear partial differential equations, consisting of the Nernst–Plank equations for the concentration distributions of diffusive ionic species, the Poisson equation for the pattern of electric potential, and the continuum mechanical equation for the mechanical deformation of hydrogels. In order to solve the complex MECe model, a novel meshless Hermite-Cloud method is used in numerical implementations. The simulations in this paper focus on the one-dimensional transient analysis for the kinetics of the hydrogels. After the validation of the developed MECe model by comparing the steady-state numerical results with the experiments, this paper presents the transient simulations for variations of the ionic concentration and average curvature of hydrogels. The simulating results of the kinetic hydrogel indicate that the electric-sensitive hydrogels respond rapidly to the external electric-stimulus before a critical time and then no significant further response occurs after the critical time.

Model development and numerical simulation of electric-stimulus-responsive hydrogels subject to an externally applied electric field

Based on a multi-phasic mixture theory with consideration of ionic diffusion and convection, a multi-physic model, called the multi-effect-coupling electric-stimulus (MECe) model, is developed for simulation of responsive behavior of the electric-sensitive hydrogels when they are immersed into a bathing solution subject to an externally applied electric field. In the developed model, with chemo-electro-mechanical coupling effects, the convection–diffusion equations for concentration distribution of diffusive ions incorporate the influence of electric potential. The electroneutrality condition is replaced by the Poisson equation for distribution of electric potential. The steady and transient analyses of hydrogel deformation are easily carried out by the continuity and momentum equations of the mixture phase. Further, the computational domain of the present model covers both the hydrogel and the surrounding solution. In order to solve the present mathematical model consisting of multi-field coupled nonlinear partial differential governing equations, a hierarchical iteration technique is proposed and a meshless Hermite–Cloud method (HCM) is employed. The steady-state simulation of the electric-stimulus responsive hydrogel is numerically conducted when it is subjected to an externally applied electric field. The hydrogel deformation and the ionic concentrations as well as electric potentials of both the hydrogel and external solution are investigated. The parameter influences on the swelling behaviors of the hydrogel are also discussed in detail. The simulating results are in good agreement with the experimental data and they validate the presently developed model.