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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.

An impregnation of soft contact lenses with salicylic acid in supercritical CO 2 was enhanced by addition of water. The supercritical CO 2 impregnations including water were conducted at 40 °C and 11 MPa with 0.34–2.18 g L −1 of water amount. The contact lenses impregnated in supercritical CO 2 including water result in the high loading-amount of salicylic acid compared with those without water. The higher amount of water in supercritical CO 2 impregnation gives the slower release of salicylic acid from the lenses. The impregnation efficiency of the contact lenses with salicylic acid in supercritical CO 2 including water was evaluated from the loading-amount in the lenses and the concentration in the supercritical CO 2 phase. The efficiencies of supercritical CO 2 impregnation including water are higher than aqueous solution impregnation. The impregnation efficiency of the lenses increases with the water amount in the supercritical CO 2 impregnation processes. The amount of salicylic acid loaded in the lenses also increases with the amount of water dissolved in supercritical CO 2 . A release model using kinetic constant and exponent parameter was applied for modeling the release profile of salicylic acid from the contact lenses. The release modeling suggested that the release from the contact lenses resulted from the superimposition of Fickian controlled and hydrogel swelling controlled releases.

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 purpose of this study was to formulate a superporous hydrogel (SPH) containing carvedilol self-nanoemulsifying drug delivery system. Effects of formulation parameters (amount of SPH and 0.1 N HCl used during drug loading) were studied in 3(2) factorial design. Response surface plots showed significant effect of the parameters on hydrogel swelling, carvedilol content, and carvedilol in vitro release. Regression equations were generated to calculate the desirable responses.

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.

A facile method for the characterization of hydrogel swelling is described which is based on the determination of changes in the liquid phase concentration of an excluded tracer as gel swells in a constant volume system. The utility of this approach is demonstrated with two responsive hydrogel preparations, one where swelling is influenced by system pH, the other by changes in specific solute concentration.

Although studies of charged hydrogel swelling focus on the swelling transition, hydrogels display pre‐transition swelling which may affect their performance in applications such as sensors. In this paper we investigate the effect of system parameters on the pre‐transition swelling of charged poly methacrylic acid (PMAA) hydrogels. We find that the pre‐transition swelling can be quite significant in magnitude (in our case ∼40% of the maximal swelling). Increasing the sub‐chain molecular weight increases swelling in the pre‐transition region only in the case where no salt is added; Contrary to expectation, in moderate ionic strength solutions the degree of swelling of longer chains is lower than that of shorter sub‐chains. Also contrary to expectation, in the case of longer sub‐chains the addition of salt decreases the gel volume in the pre‐transition region, thereby indicating that in this system a significant number of charges are dissociated. These trends can be understood by accounting for the ...

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.

Hydrogels have found wide application in biosensors due to their versatile nature. This family of materials is applied in biosensing either to increase the loading capacity compared to two-dimensional surfaces, or to support biospecific hydrogel swelling occurring subsequent to specific recognition of an analyte. This review focuses on various principles underpinning the design of biospecific hydrogels acting through various molecular mechanisms in transducing the recognition event of label-free analytes. Towards this end, we describe several promising hydrogel systems that when combined with the appropriate readout platform and quantitative approach could lead to future real-life applications. This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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.

Hydrogels containing benzo-18-crown-6 were used to modify microcantilevers for measurements of the concentration of Pb2+ in aqueous solutions. These microcantilevers undergo bending deflection upon exposure to solutions containing various Pb2+ concentrations as the result of a swelling of the hydrogels. It was found that a concentration of 10(-6) M Pb2+ can be detected using this technology. Other cations, such as Na+, have no effect on the deflection of this cantilever. The cation K+, which also complexes with benzo-18-crown-6, could interfere with Pb2+ detection, but only at high concentrations (> 10(-4) M).

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.

An oligonucleotide–polymer hybrid hydrogel displaying swelling response in a logical AND and OR fashion depending on specific stimuli by probe oligonucleotides was prepared. The hydrogel acts as a transducer of the specific recognition of DNA sequences into micro- and macroscale mechanics. Input oligonucleotide probes induce hydrogel swelling ratio at two signal levels.

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.