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From the liquid–liquid equilibrium (LLE) data of a linear polymer, an investigation of the Sanchez and Lacombe equation of state (SL-EOS) is performed with the goal of describing the swelling of th...

The development of in situ-gelling hydrogels that can enable prolonged protein release is increasingly important due to the emergence of a growing number of protein-based therapeutics. Herein, we describe a high-throughput strategy to fabricate, characterize, and subsequently optimize hydrazone-cross-linked in situ-gelling hydrogels for protein delivery. Hydrogels are fabricated using an automated high-throughput robot to mix a variety of thermoresponsive, nonthermoresponsive, charged, neutral, naturally sourced, and synthetic polymers functionalized with hydrazide or aldehyde groups, generating in situ-gelling hydrogels with well-defined compositions within a 96-well plate. High-throughput characterization strategies are subsequently developed to enable on-plate analysis of hydrogel swelling, mechanics, degradation, transparency, and protein (ovalbumin) release kinetics that yield results consistent with those collected using traditional bulk hydrogel analysis techniques. Dynamic regression and latent variable modeling are then applied to fit performance statistics to the collected data set; subsequently, numerical optimization is used to identify mixtures of precursor polymers that exhibit targeted combinations of minimal burst release, maximum total protein release, minimum release rate, and maximum transparency (the latter of particular relevance for ophthalmic protein delivery applications). Given the rapid throughput of the protocols developed (i.e., 126 hydrogels can be synthesized and screened in quadruplicate within hours), this approach offers particular promise for accelerating the identification of injectable hydrogel compositions relevant for both protein delivery as well as other biomedical applications for which clearly predefined materials properties are required.

When inflating a rubber balloon, it is commonly concluded that a sudden expansion in balloon size (i.e., the burst) occurs once the inner pressure reaches a critical threshold, the instantaneous burst pressure. Such burst phenomena are usually attributed to the snap-through instability. In this work, we demonstrate that when a hydrogel balloon is subject to a subcritical pressure lower than the instantaneous burst pressure, the hydrogel balloon may remain stable for a span of time, and then burst suddenly. We refer to such burst phenomena as the delayed burst of the gel balloon. When subject to such a subcritical inner pressure, a hydrogel balloon slowly and continuously absorbs solvent and swells. We find the instantaneous burst pressure of the hydrogel balloon to be a decreasing function of swelling ratio. The criterion for the onset of burst is that the swelling-related instantaneous burst pressure drops to the applied inner pressure. The delayed burst can, therefore, be attributed to the time needed for the hydrogel swelling to reduce the instantaneous burst pressure to the level of applied pressure. We further delineate a map indicating three distinct deformation modes of gel balloons, i.e., instantaneous burst, delayed burst, and steady deformation without burst (safe mode), in the parameter space of applied pressure and mechanical properties of the hydrogel. The delayed burst of a hydrogel balloon is counterintuitive and a crucial aspect in developing hydrogel-shell-based soft actuators and soft machines. The research findings may shed light on the understanding of the complex failure mechanisms of hydrogel actuators and also facilitate the design of hydrogel-based tissue delivery capsules.

Visualization reveals that confinement in a granular medium hinders hydrogel swelling, with implications for agriculture., Hydrogels hold promise in agriculture as reservoirs of water in dry soil, potentially alleviating the burden of irrigation. However, confinement in soil can markedly reduce the ability of hydrogels to absorb water and swell, limiting their widespread adoption. Unfortunately, the underlying reason remains unknown. By directly visualizing the swelling of hydrogels confined in three-dimensional granular media, we demonstrate that the extent of hydrogel swelling is determined by the competition between the force exerted by the hydrogel due to osmotic swelling and the confining force transmitted by the surrounding grains. Furthermore, the medium can itself be restructured by hydrogel swelling, as set by the balance between the osmotic swelling force, the confining force, and intergrain friction. Together, our results provide quantitative principles to predict how hydrogels behave in confinement, potentially improving their use in agriculture as well as informing other applications such as oil recovery, construction, mechanobiology, and filtration.

Gout is a condition that affects over 8 million Americans. This condition is characterized by severe pain, and in more advanced cases, bone erosion and joint destruction. This study explores the fabrication and characterization of an optical, enzymatic urate biosensor for gout management, and the optimization of the biosensor response through the tuning of hydrogel matrix properties. Sensors were fabricated through the co-immobilization of oxygen-quenched phosphorescent probes with an oxidoreductase within a biocompatible copolymer hydrogel matrix. Characterization of the spectral properties and hydrogel swelling was conducted, as well as evaluation of the response sensitivity and long-term stability of the urate biosensor. The findings indicate that increased acrylamide concentration improved the biosensor response by yielding an increased sensitivity and reduced lower limit of detection. However, the repeatability and stability tests highlighted some possible areas of improvement, with a consistent response drift observed during repeatability testing and a reduction in response seen after long-term storage tests. Overall, this study demonstrates the potential of an on-demand, patient-friendly gout management tool, while paving the way for a future multi-analyte biosensor based on this sensing platform.

Purpose The purpose is to target model drug particles to the posterior region of the suprachoroidal space (SCS) of the eye controlled via pushing by hydrogel swelling. Methods A particle formulation containing 1% hyaluronic acid (HA) with fluorescent polymer particles and a hydrogel formulation containing 4% HA were introduced in a single syringe as two layers without mixing, and injected sequentially into the SCS of the rabbit eye ex vivo and in vivo using a microneedle. Distribution of particles in the eye was determined by microscopy. Results During injection, the particle formulation was pushed toward the middle of the SCS by the viscous hydrogel formulation, but less than 12% of particles reached the posterior SCS. After injection, the particle formulation was pushed further toward the macula and optic nerve in the posterior SCS by hydrogel swelling and spreading. Heating the eye to 37°C, or injecting in vivo decreased viscosity and mechanical strength of the hydrogel, thereby allowing it to swell and flow further in the SCS. A high salt concentration (9% NaCl) in the hydrogel formulation further increased hydrogel swelling due to osmotic flow into the hydrogel. In this way, up to 76% of particles were delivered to the posterior SCS from an injection made near the limbus. Conclusions This study shows that model drug particles can be targeted to the posterior SCS by HA hydrogel swelling and pushing without particle functionalization or administering external driving forces.

The inline monitoring of ethanol concentrations in liquids is a crucial part of process monitoring in breweries and distilleries. Current methods are based on infrared spectroscopy which are bulky and costly making them non-affordable for small and middle-sized companies. To overcome these problems, we present a small, compact and cost-effective sensing method, based on a nanostructured, plasmonically active sensor substrate. The sensor substrate is coated with a microstructured ethanol-sensitive acrylamide-bisacrylamide hydrogel which induces a change of the hydrogel’s refractive index in conjugation with the hydrogel swelling and shrinking. With such an approach, the ethanol concentration in liquids can be determined in a simple optical transmittance setup. In our study, we demonstrate the capability of the sensor principle for the detection of ethanol concentration ranging from 0 to 30 vol%. Furthermore, we determined the response time of the sensor substrate to be less than 10 seconds, which shows an enormous improvement compared to other hydrogel-based sensing methods. Finally, initial results for real sample measurements are presented.

A biomedical sensor was developed to measure local pH near orthopedic implants to detect and study implant-associated infection. The sensor is read using plain radiography, a technique which is noninvasive, inexpensive, ubiquitously available in medical facilities, and routinely used in diagnosis and follow-up. The sensor comprises a radiopaque tungsten indicator pin embedded within a chemically responsive hydrogel that exhibits a pH-dependent swelling. A stainless steel well holds this hydrogel and attaches to an orthopedic plate. The local pH may be determined from the extent of hydrogel swelling by radiographically measuring the indicator position relative to the well. We calibrated the sensor in a series of standard pH buffers and tested it during bacterial growth in culture. The sensor was robust: its response was negligibly affected by changes in temperature, ionic strength within the normal physiological range, or long-term incubation with reactive oxygen species generated from hydrogen peroxide and copper. Pooled data from several sensors fabricated at different times and tested in different conditions had a root-mean-square deviation from a pH electrode reading of 0.24 pH units. Radiographic measurements were also performed in cadaveric tissue with the sensor attached to an orthopedic plate fixed to a tibia. Pin position readings varied by 100 μm between observers surveying the same radiographs, corresponding to 0.065 pH units precision in the range pH 4-8. The sensor was designed to augment standard radiographs of tissue, bony anatomy, and hardware by also indicating local chemical concentrations.

The potential to develop materials with antibody-like molecular recognition properties has helped sustain interest in protein-imprinted polymers over the past several decades. Unfortunately, despite persistent research, the field of noncovalent protein imprinting has seen limited success in terms of achieving materials with high selectivity and high affinity. In this Perspective, important yet sometimes overlooked aspects of the imprinting and binding processes are reviewed to help understand why there has been limited success. In particular, the imprinting and binding processes are viewed through the scope of free radical polymerization and hydrogel swelling theories to underscore the complexity of the synthesis and behavior of protein-imprinted polymers. Additionally, we review the metrics of success commonly used in protein imprinting literature (i.e., adsorption capacity, imprinting factor, and selectivity factor) and consider the relevance of each to the characterization of an imprinted polymer’s recognition characteristics. Throughout, common shortcomings are highlighted, and experiments that could help verify or disprove the efficacy of noncovalent protein imprinting are discussed.

Permeation through polymeric membranes can be controlled by surface coating of a polyethylene terephthalate (PET) membrane with poly(N-isopropylacrylamide) (PNIPAAm) and inserting pores of defined geometry. When the temperature of the system rises above the volume phase transition temperature, the pores open, which allows permeation of formerly blocked particles. The exact control of the temperature allows defined change of the pore size and therefore enables separation abilities. Free swelling experiments are conducted to obtain the swelling behaviour of PNIPAAm. Then, a temperature expansion model is derived in order to simulate this behaviour with the finite element tool ABAQUS. The gained results are in excellent agreement with the observed shape change. Membranes with permeation control of particles can be used for biomedical application in microfluidics to analyse the size distribution of cells or in chemical information processing as a transistor-like component for an information-bearing chemical species. The possibility to simulate the behaviour of such permeation systems allows computer aided design and prediction of permeation abilities in these areas.

In this focused progress review, the recent developments and trends of hydrogel-forming microneedles (HFMs) and potential future directions are presented. Previously, microneedles (solid, hollow, coated, and dissolving microneedles) have primarily been used to enhance the effectiveness of transdermal drug delivery to facilitate a wide range of applications such as vaccinations and antibiotic delivery. However, the recent trend in microneedle development has resulted in microneedles formed from hydrogels which have the ability to offer transdermal drug delivery and, due to the hydrogel swelling nature, passively extract interstitial fluid from the skin, meaning they have the potential to be used for biocompatible minimally invasive monitoring devices. Thus, in this review, these recent trends are highlighted, which consolidate microneedle design considerations, hydrogel formulations, fabrication processes, applications of HFMs and the potential future opportunities for utilizing HFMs for personalized healthcare monitoring and treatment.

The introduction of the work Makromolekule by Herman Staudinger in 1919 brings back an understanding of the very early days of polymer science when characterizing the molecular structure of exact networks was a main goal of research. Here, we present updates to a swollen polymer network hypothesis with a focus on hydrogel physical properties. We discuss the connections between hydrogel structure, swelling behavior, mechanical properties, and transport properties, including the most substantial developments since the original Flory-Rehner model (1944) of swollen polymer networks. In addition to analyzing well-established and recent contributions to the swollen polymer network hypothesis, we introduce novel amendments that combine the insights of existing models. We suggest that coordinating rubberlike elasticity theory, equilibrium swelling theory, and mesh size theory will help to develop a universal predictive model for swelling, stiffness, and solute diffusivities in a diverse array of hydrogel formulations.

Long and short path length differences interferometric sensing modalities have been combined based on immobilizing hydrogel on thin-core optical fiber end face. Dual parameter sensing of hydrogel swelling and refractive index was demonstrated.

Reliable cerebrospinal fluid (CSF) draining methods are needed to treat hydrocephalus, a chronic debilitating brain disorder. Current shunt implant treatments are characterized by high failure rates that are to some extent attributed to their length and multiple components. The designed valve, made of hydrogel, steers away from such protracted schemes and intends to provide a direct substitute for faulty arachnoid granulations, the brain's natural CSF draining valves, and restore CSF draining operations within the cranium. The valve relies on innate hydrogel swelling phenomena to strengthen reverse flow sealing at idle and negative pressures thereby alleviating common valve failure mechanisms. In vitro measurements display operation in range of natural CSF draining (cracking pressure, PT ~ 1-110 mmH2O and outflow hydraulic resistance, Rh ~ 24-152 mmH2O/mL/min), with negligible reverse flow leakage (flow, QO > -10 µL/min). Hydrodynamic measurements and over-time tests under physically relevant conditions further demonstrate the valve's operationally-reproducible properties and strengthen its validity for use as a chronic implant.

In this paper, we demonstrate a low-cost and tunable pH-triggered smart switch which is based on the deflection of a conductive elastic membrane induced by the swelling of a pH-responsive hydrogel. The described switch comprises of a porous plate, a gel chamber, a deflectable conductive membrane, and an electrical isolation cell. The switching action is initiated through a sudden pH change (e.g., transition from acidic stomach to basic small intestine) which in turn results in diffusion/time controlled hydrogel swelling, making it suitable for ingestible capsules targeted for pH-controlled localized drug release in the gastrointestinal (GI) tract. A typical prototype (9 mm in diameter and 3.2 mm in thickness) responds to pH changes from 2 to 7 (transition from stomach to small intestine) with a response time of one hour.

The article are outlined the medicinal use of polymer materials and characteristics and described its preparation method and application for controlled drug release from polymer, polymer drugs, pharmaceutical formulations and packaging polymer materials three aspects. Meanwhile elaborates a novel well dispersed MWCNTs PMAA/MWCNTs nanohybrid hydrogels. The introduction of MWCNTs significantly improved pH-responsive hydrogels and mechanical strength, and which depending on the composition ratio of MWCNTs, particle size and concentration of crosslinker. Study found that hybrid hydrogel swelling rate significantly faster than the pure PMAA hydrogel swelling behavior and this is explained. Compressive stress - strain was found, MWCNTs load transfer heterozygous for improving mechanical properties of the hydrogel network compression plays an important role. MTT cell compatibility evaluation proves that this astute hydrogel biomedical research in particular has potential application value.

This review highlights recent developments in the field of stimuli-responsive hydrogels, focusing primarily on thin films, with a thickness range between 100 nm to 10 μm. The theory and dynamics of hydrogel swelling is reviewed, followed by specific applications. Gels are classified based on the active stimulus—mechanical, chemical, pH, heat, and light—and fabrication methods, design constraints, and novel stimuli-responses are discussed. Often, these materials display large physiochemical reactions to a relatively small stimulus. Noteworthy materials larger than 10 μm, but with response times on the order of seconds to minutes are also discussed. Hydrogels have the potential to advance the fields of medicine and polymer science as useful substrates for “smart” devices. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1084–1099

Biodegradable polymeric microneedles were developed as a method for achieving sustained transdermal drug release. These microneedles have potential as a patient-friendly substitute for conventional sustained release methods. However, they have limitations related to the difficulty of achieving separation of the needles into the skin. We demonstrated that microneedle separation into the skin was mediated by hydrogel swelling in response to contact with body fluid after the needles were inserted into the skin. The hydrogel microparticles were synthesized by an emulsification method using poly-N-isopropylacrylamide (PNIPAAm). The microneedles were fabricated by micromolding poly-lactic-co-glycolic acid (PLGA) after filling the cavities of the mold with the hydrogel microparticles. The failure of microneedle tips caused by hydrogel swelling was studied in regard to contact with water, insertion of microneedles into porcine cadaver skin in vitro, stress-strain behavior, and insertion into the back skin of a hairless mouse in vivo. The drug delivery property of the hydrogel particles was investigated qualitatively by inserting polymer microneedles into porcine cadaver skin in vitro, and the sustained release property of PLGA microneedles containing hydrogel microparticles was studied quantitatively using the Franz cell model. The hydrogel particles absorbed water quickly, resulting in the cracking of the microneedles due to the difference in volume expansion between the needle matrix polymer and the hydrogel particles. The swollen particles caused the microneedles to totally breakdown, leaving the microneedle tips in the porcine cadaver skin in vitro and in the hairless mouse skin in vivo. Model drugs encapsulated in biodegradable polymer microneedles and hydrogel microparticles were successfully delivered by releasing microneedles into the skin.

In this research, an antibiotic was loaded in the composites of polyethylene glycol (PEG), acrylamide (AAm) and acrylic acid (AAc) hydrogels matrices and their drug deliveries were tested. Effect of some parameters on the drug delivery was checked by UV-spectrophotometer. Temperature enhancement considerably increased hydrogel swelling and the drug release in the AAc and AAm. A dynamic model based on the Maxwell–Stefan equation was developed to model the drug delivery of hydrogels. COMSOL software was also applied to simulate buffer diffusion inside the hydrogels.

The objective of presented work is to simulate the response of 2D hydrogel when subjected to the varying pH of buffer solution and initial fixed-charge concentration inside the hydrogel. The novelty of the work is that this is the first attempt to perform the 2D simulation of pH-responsive hydrogel by novel strong-form meshless method, such as random differential quadrature (RDQ) method. The analytical equations, derived for the hydrogel deformation in the x and y directions, are numerically verified by the square shaped hydrogel disc. The jumps in the distributions of ionic concentrations and electrical potential, across the interface between solution and hydrogel, are effectively captured by the RDQ method. A novel approach is proposed to correctly impose natural boundary conditions for non-uniform boundary. The effects of solution pH and initial fixed-charge concentration on the hydrogel swelling are also successfully investigated.

Polyacrylamide (PAAm) hydrogels are commonly employed to ensure soil hydration in horticulture, but studies have shown that they have a minimal effect on crop life and quality. The reasons for this poor performance are not understood since the commercial hydrogels have not been adequately characterized. PAAm hydrogels were synthesized and their properties were measured along with those of commercial hydrogels. Hydrogel swelling, density, and SEM analyses showed that the commercial hydrogels were most likely a derivative of PAAm with ionic groups and they were able to retain moisture for only a few hours.

The preliminary results of gel swelling experiments are reported, and then compared to predictions made by a recently-developed finite element model (FEM). This model utilises energy transport between different energy domains, and is being used to simulate gel swelling dynamics. Initial experiments have revealed the model does capture the general behaviour of polymer hydrogel swelling dynamics and further improvements are necessary for better accuracy.

Hydrogels, polymers and various other composite materials may be used in sensing applications in which the swelling or de-swelling of the material in response to some analyte is converted via a transducer to a measurable signal. In this paper, we analyze models used to predict the swelling behavior of hydrogels that may be used in applications related to hydration monitoring in humans. Preliminary experimental data related to osmolality changes in fluids is presented to compare to the theoretical models. Overall, good experimental agreement with the models is achieved.

Corrosion on steel and copper pipes in industry can trigger pollution and weakness due to undesired chemical and biochemical reactions. Too much or too little inhibitor can decrease its efficiency, even causing waste and pollution. In this contribution, an innovative delivery device driven by hydrogel swelling, mainly consisting of a semi-permeable membrane, a hydrogel-swelling force drive and a release orifice, was developed to control the release of inhibitor in a water system at a constant rate, leading the amount of inhibitor to maintain a proper concentration. The effects of hydrogel mass and orifice dimension on release property were studied for controlling release rate. Moreover, a weight loss experiment on carbon steels was carried out to show the incredible anti-corrosion function of the system.

DNA-polyacrylamide hybrid hydrogels designed with covalent and double-stranded (dsDNA) crosslinks respond to specific single-stranded DNA (ssDNA) probes by adapting new equilibrium swelling volume. The ssDNA probes need to be designed with a base pair sequence that is complementary to one of the strands in a dsDNA supported network junction. This work focuses on tuning the hydrogel swelling kinetics by introducing polyethylene glycol (PEG) as a pore-forming agent. Adding PEG during the preparation of hydrogels, followed by removal after polymerization, has been shown to improve the swelling dynamics of DNA hybrid hydrogels upon specific ssDNA probe recognition. The presence of porogen did not influence the kinetics of osmotic pressure-driven (2-acrylamido-2-methylpropane sulfonic acid)-co-acrylamide (AMPSA-co-AAm) hydrogels’ swelling, which is in contrast to the DNA-sensitive hydrogels. The difference in the effect of using PEG as a porogen in these two cases is discussed in view of processes leading to the swelling of the gels. © 2015 by the authors; license MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/4.0/).

In this paper, a three-dimensional dynamic model describing drug delivery and swelling behavior of polyelectrolyte gels was developed based on the Maxwell-Stefan equation and Bio-heat equation. COMSOL software was employed to simulate hydrogel swelling and the transportation of created automatically by COMSOL, and it had 78035 elements, which was unconcerned with the results. The results showed that Maxwell-Stefan equation and Bio-heat equation were suitable for modeling hydrogel behavior of swelling with temperature change. In addition, when temperature increased, the hydrogel swelling increased which also intensified drug release.Copyright © 2013 by ASME

This paper present the modeling and simulation of the hydrogel coated FBG for pH sensor application. The hydrogel swelling was modeled by using Poisson-Nernst-Planck equation and mechanical equilibrium equation. The simulation was done by assuming that the hydrogel was coated on unetched fiber and etched fiber. The strain induced at the fiber core was analyzed using finite element method. It was found that at the region near the jacketed fiber, the strain is distributed nonuniformly. The non uniform area for etched fiber is shorter than that of unetched fiber. The Bragg wavelength shift due to strain of the etched fiber is much larger than that of the unetched fiber.

To achieve pH detection of multi-points, a new pH sensor based on pH sensitive hydrogel swelling detection by a fiber Bragg grating is proposed. The deflection of a silica membrane due to pH value change induced hydrogel swelling is measured by the center wavelength shifts of a fiber Bragg grating epoxied on the membrane. The relation between center wavelength shifts of the fiber Bragg grating with the hydrogel swelling behavior was studied experimentally. Around 100pm shift of the fiber Bragg grating center wavelength was observed when the pH value was changed from 4 to 7 or from 7 to 10 by using pH standard solutions, which fundamentally proved the feasibility of this method for pH detection.

The ability of hydrogels to respond to relatively small changes in stimuli with relatively large changes in volume allows a wide variety of applications. This chapter addresses hydrogels with regard to the chemical identity of hydrophilic polymers and copolymers, polymer synthesis, the degree of crosslinking and hydrogel porosity, and bulk geometry of hydrogels in the form of matrix, membrane and erodible systems. The relationships between these features and hydrogel swelling behavior upon stimulation are also described. Finally, various exploitations of hydrogel swelling behavior in developing highly sensitive, real-time biosensors are discussed.

A method for hydrogel swelling kinetics measurement has been demonstrated by working with impedance analyzing technique.

In this paper a sensor is presented for the detection of carbon dioxide gas inside the stomach in order to diagnose gastrointestinal ischemia. The operational principle of the sensor is measuring the CO/sub 2/ induced pressure generation of a confined pH-sensitive hydrogel by means of a micro pressure sensor. The sensor is capable of measuring CO/sub 2/ with a response time between 2 and 4 minutes and a maximum pressure of 0.29/spl times/10/sup 5/ Pa at 20 kPa CO/sub 2/. The sensor is able to resist up to 1 M HCl acid as can be present inside the stomach. The results are very promising for real application and clinical trials are planned.

We study the configuration of atomically-thin graphene membranes on tunable microhydrogel patterns. The polyethylene oxide microhydrogel structures patterned by electron-beam lithography show increase in height, with a persistent swelling ratio up to ?10, upon exposure to vapors of an organic solvent. We demonstrate that modifying the height fluctuations of the microhydrogel affects the strain and morphology of ultrathin graphene membrane over-layer. Raman spectroscopic investigations indicate that small lattice strains can be switched on in mechanically exfoliated few-layer graphene membranes that span these microhydrogel structures. In case of chemical-vapor deposited single-layer graphene, we observe Raman signatures of local depinning of the membranes upon swelling of microhydrogel pillars. We attribute this depinning transition to the competition between membrane-substrate adhesion energy and membrane strain energy, where the latter is tuned by hydrogel swelling. � 2014 AIP Publishing LLC.

In this paper, 2D simulation of a pH-sensitive hydrogel is performed by a novel strong-form meshless method called the random differential quadrature (RDQ) method. So far the simulations of pH-responsive hydrogels have been performed over 1D hydrogel domains by simplification, where the hydrogel is allowed to deform in one direction only with a constant axis-symmetric cross-section. However, for an irregular cross-section, in which the hydrogel swells unevenly in different directions, it truly becomes the 2D problem. The RDQ method is a novel meshless technique based on the fixed reproducing kernel particle method and the differential quadrature method.The diffusion of mobile ionic species between the hydrogel and solution is simulated by the system of the Poisson–Nernst–Planck equations, and the hydrogel swelling is captured by mechanical equilibrium equations. The analytical expressions of displacements in the x and y directions are derived for a constant osmotic pressure at field nodes located along the interface between the hydrogel and solution domains. The numerical values of the displacements are verified with the corresponding analytical values obtained from the derived expressions for a hydrogel with square geometry. It is shown from the simulation results that the RDQ method is capable of capturing the jumps in the values of field variables across the interface between the multiple domains. The hydrogel swelling is studied by changing Young's modulus and the geometrical shape, and the simulation results are found qualitatively in good agreement with the physics of the problem.

Within this work we present the synthesis and characterization of a pH-sensitive macroporous p(AAm-co-AA) hydrogel with an interconnected channel structure to enhance diffusion of aqueous solutions. The hydrogel is characterized by SEM and mercury porosimetry. Furthermore, the hydrogel is successfully integrated into piezoresistive microsensors measuring the hydrogel swelling due to pH changes. A response time reduction of about 80% compared to sensors with conventional non-porous hydrogels is accomplished.