Behaviour of Anionic and Cationic Hydrogels (original) (raw)
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Swelling characteristics of acrylic acid polyelectrolyte hydrogel in a dc electric field
Smart Materials and Structures, 2007
A novel application of environmentally sensitive polyelectrolytes is in the fabrication of BioMEMS devices as sensors and actuators. Poly(acrylic acid) (PAA) gels are anionic polyelectrolyte networks that exhibit volume expansion in aqueous physiological environments. When an electric field is applied to PAA polyelectrolyte gels, the fixed anionic polyelectrolyte charges and the requirement of electro-neutrality in the network generate an osmotic pressure, above that in the absence of the electric field, to expand the network. The objective of this research was to investigate the effect of an externally applied dc electric field on the volume expansion of the PAA polyelectrolyte gel in a simulated physiological solution of phosphate buffer saline (PBS). For swelling studies in the electric field, two platinum-coated plates, as electrodes, were wrapped in a polyethylene sheet to protect the plates from corrosion and placed vertically in a vessel filled with PBS. The plates were placed on a rail such that the distance between the two plates could be adjusted. The PAA gel was synthesized by free radical crosslinking of acrylic acid monomer with ethylene glycol dimethacrylate (EGDMA) crosslinker. Our results demonstrate that volume expansion depends on the intensity of the electric field, the PAA network density, network homogeneity, and the position of the gel in the field relative to positive/negative electrodes. Our model predictions for PAA volume expansion, based on the dilute electrolyte concentration in the gel network, is in excellent agreement with the experimental findings in the high-electric-field regime (250-300 Newton/Coulomb). with biologically active peptides to fabricate smart environmentally responsive hydrogels . Hydrogels exhibit large volume changes to many environmental factors including solvent composition, pH, salt concentration, temperature, light intensity, glucose concentration, antigens, and the application of an external electric field . Polyelectrolyte gels are used extensively in medicine and pharmacy as drug delivery systems, contact lenses, catheters, wound dressings, and biosensors [9, 10].
Journal of Applied Polymer Science, 2014
Hydrogels with electric responsive properties are gaining research focus due to increasing demand for miniaturized devices that can be precisely controlled using an external stimulus. Such systems are well suited due to their ability to expand and contract when in contact with different types of fluid. This study reports on the synthesis of a "smart" electroresponsive network, using a neutral, "non-smart," biocompatible hydrogel forming building block, Pluronic F127 (PF127), as a starting molecule. The PEO-PPO-PEO copolymer was modified with telechelic methacrylic end functionalities to form a triblock linear prepolymer with crosslinkable end groups (crosslinker). This bifunctional prepolymer, PF127 bismethacrylate (PF127BMA), was copolymerized covalently with anionic methacrylic acid sodium salt groups into a nonsoluble 3D hydrogel network in the presence of redox initiators. The polyelectrolyte domains in the pluronic hydrogel afforded controllable swelling capabilities with volumetric expansion exceeding 8500% in deionized water or 1400% in Krebs solution. The hydrogels were further assessed for their mechanical and electroactive response as a function of increasing acid salt content.
Swelling characterization of anionic acrylic acid Hydrogel in an external electric field
2006
A polymer gel is a cross-linked polymer which undergoes a reversible volume and/or sol-gel phase transition in response to physiological (temperature, pH and presence of ion in organism fluids) or other external (electric field, light) stimuli. In structurally soft gels, the motion of polymer network and the diffusion of ions easily take place by an external stimulus. A typical function of gel containing ionic groups is to swell under the influence of an electric field, making it useful for wide biomedical applications. In this study, poly(acrylic acid) (PAA) hydrogel network was prepared by free radical polymerization whose average molecular weight between crosslinkes was calculated as 18500 g/mol and its homogeneity assessment evaluated by comparing 30 samples swelling ratios after 48 h soaking in distilled deionized water. The swelling behaviour of PAA under an electric field application was also investigated as a function of cross-linking agent and electric field intensity variation. It is seen that equilibrium swelling ratio of PAA gel increases from 16 (no electric field) to 30 (by application of 300 V/m electric field), however this variation is dependent on the sample location relative to electrodes. The normalized swelling ratio of sample changes by 4.8 to 0.9 relative to its distance from positive electrode. Increasing the concentration of cross-linking agent (EGDMA) from 0.14 to 0.71 molar percent of monomer resulted in 45% decrease of gel volume fraction. It is proven that applying an external electric field can make an improvement in the time-response of the hydrogel expansion phase and swelling behaviour.
Biosensors & Bioelectronics, 2004
Based on a multi-phasic mixture theory with consideration of ionic diffusion and convection, a multi-physic model, called the multi-effectcoupling 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.
Electroactive Polymer Actuators and Devices (EAPAD) 2009, 2009
Environmental responsive or smart hydrogels show a volume phase transition due to changes of external stimuli such as pH or ionic strength of an ambient solution. Thus, they are able to convert reversibly chemical energy into mechanical energy and therefore they are suitable as sensitive material for integration in biochemical microsensors and MEMS devices. In this work, microfabricated silicon pressure sensor chips with integrated piezoresistors were used as transducers for the conversion of mechanical work into an appropriate electrical output signal due to the deflection of a thin silicon bending plate. Within this work two different sensor designs have been studied. The biocompatible poly(hydroxypropyl methacrylate-N,N-dimethylaminoethyl methacrylate-tetra-ethyleneglycol dimethacrylate) (HPMA-DMA-TEGDMA) was used as an environmental sensitive element in piezoresistive biochemical sensors. This polyelectrolytic hydrogel shows a very sharp volume phase transition at pH values below about 7.4 which is in the range of the physiological pH. The sensor's characteristic response was measured in-vitro for changes in pH of PBS buffer solution at fixed ionic strength. The experimental data was applied to the Hill equation and the sensor sensitivity as a function of pH was calculated out of it. The timedependent sensor response was measured for small changes in pH, whereas different time constants have been observed. The same sensor principal was used for sensing of ionic strength. The time-dependent electrical sensor signal of both sensors was measured for variations in ionic strength at fixed pH value using PBS buffer solution. Both sensor types showed an asymmetric swelling behavior between the swelling and the deswelling cycle as well as different time constants, which was attributed to the different nature of mechanical hydrogel-confinement inside the sensor.
Sensors and Actuators B: Chemical, 2014
A novel Pluronic-based hydrogel copolymer was synthesized and actuated. The combined properties of improved biocompatability and response to electrical excitation of this cross-linked gel make it a potential candidate for actuators such as electrically controllable occlusion devices and non-surgical implants. The electrical response of the copolymer was verified using bending tests performed in potassium chloride (KCl) solutions of different concentrations and the novel material was characterized using equilibrium swelling experiments, environmental scanning microscopy (ESEM) imaging, and a potentiometric method for estimating the fixed charge. We considered the influence of current, pH and concentration on the hydrogel actuator behavior, which was manifested in the degree of bending and in direction of bending. A reversal of the bending direction was observed twice in a single system under DC bias (without reversal of electric field polarity). We described this phenomenon as representing several different types of electric-responsive behavior that become dominant at different actuation stages of the polymer system. The distinction between the different actuation effects is important for the development of hydrogel actuators.
Electrochemistry Communications, 2009
Poly(acrylic acid) gels are known to swell to different extent (measured by the swelling ratio) depending on pH and ionic strength of the solution. The experimental method employed by us to monitor the concentration and diffusion coefficient of the probes allows the simultaneous determination of their concentration and diffusion coefficient for any value of the ionic strength and pH of the solution trapped in the polymeric network. Two different electroactive probe systems, 1,1 0 -ferrocenedimethanol and 2,2,6,6-tetramethylpiperidine 1-oxyl, were selected for the examination. Small values of the swelling ratio, obtained either by application of a high ionic strength or a low pH, result in an unexpected high concentration of both probes in the gel samples. Correspondingly, the probes diffusion coefficients were much smaller compared to their values in the swollen gels.
Theory and application of electrically controlled polymeric gels
Smart Materials and Structures, 1992
This paper presents several applications of ionizable polymeric gels that are capable of undergoing substantial expansions and contractions when subjected to changing pH environments. temperature, electric field or solvent. Conceptual designs for smart, electrically activated devices exploiting this phenomenon are discussed. These devices have the possibility of being manipulated via active computer control as large-displacement actuators for use in adaptive structures.
Development and modeling of electrically triggered hydrogels for microfluidic applications
Journal of Microelectromechanical Systems, 2000
In this paper, we present progress in the development of electrically triggered hydrogels as components in microfluidic systems. Stimuli-responsive hydrogels are fabricated using liquidphase photopolymerization techniques and are subjected to different voltage signals in order to determine their volume change response characteristics. A chemoelectromechanical model has been developed to predict the swelling and deswelling kinetics of these hydrogels. The Nernst-Planck equation, Poisson equation, and mechanical equations are the basic governing relationships, and these are solved in an iterative manner to compute the deformation of the hydrogel in response to varied electrical input.