Search

Hydrogels are attractive materials for stimulating 3D cell growth and tissue regeneration, and they provide mechanical support and physical cues to guide cell behavior. Herein, we developed a robust methodology to increase the stiffness of polyethylene glycol (PEG) hydrogels by successfully incorporating carbon nanotubes (CNTs) within the polymer matrix. Interestingly, hydrogels containing pristine CNTs showed a higher stiffness (1915 ± 102 Pa) than both hydrogels without CNTs (1197 ± 125 Pa) and hydrogels incorporating PEG-grafted CNTs (867 ± 103 Pa) (p < 0.005). The swelling ratio was lower for hydrogels with pristine CNTs (45.4 ± 3.5) and hydrogels without CNTs (46.7 ± 5.1) compared to the hydrogels with PEG-grafted CNTs (62.8 ± 2.6). To confirm that the CNT-reinforced hydrogels were cytocompatible, the viability, proliferation, and morphology of encapsulated L929 fibroblasts was investigated. All hydrogel formulations supported cell proliferation, and the addition of pristine CNTs increased initial cell viability (83.3 ± 10.7%) compared to both pure PEG hydrogels (51.9 ± 8.3%) and hydrogels with PEG-CNTs (63.1 ± 10.9%) (p < 0.005). Altogether, these results demonstrate that incorporation of CNTs could effectively reinforce PEG hydrogels and that the resulting cytocompatible nanocomposites are promising scaffolds for tissue engineering., (Copyright © 2019 Elsevier B.V. All rights reserved.)

In the present study, we have developed a mathematical model of drug release from a film of highly swellable gelatin based hydrogel mixed with graphene. The model considers the hydrogel volume expansion because of the swelling as well as the non-linear concentration dependence of the diffusion coefficients for the solvent and the drug. An additionl term is considered for the drug diffusion coefficient enabling the model to predict the drug maximum release from the hydrogel. The model parameters are estimated by genetic algorithem and the model resutls are validated using data sets obtained from experiments on Zoledronic acid, the model drug, loaded hydrogel samples made from several weigth ratios of gelatin to graphene crosslinked with different amounts of glutaraldehyde. The model is further developed to mathematically predict the drug conrolled release into in vivo environment and the impact of several factors influencing the release rate into the surrounding environment is investigated., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Hydrogels were prepared from guar gum (GG) via esterification with 1,2,3,4-butanetetracarboxylic dianhydride (BTCA). Detailed spectroscopic analysis using FTIR and solid-state NMR revealed that an increase in the BTCA feed amount in the preparation mixture led to an increased degree of crosslinking, which affected the swelling behavior and rheological properties of the hydrogels. The hydrogels exhibited enzyme degradability, and after incubation with β-mannanase and α-galactosidase, 30-57% of the hydrogels were degraded. In addition, the hydrogels adsorbed bovine serum albumin and hen egg white lysozyme thorough electrostatic and hydrophobic interactions. The protein-adsorbed GG hydrogels exhibited a slow and steady release of the proteins over a 24h period in buffer solutions after a fast release of proteins in the first hour. As such, GG hydrogels are expected to be efficient drug delivery carriers for protein-based drugs., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

In the field of material informatics, artificial neural networks (ANNs) contribute to the investigation of the processing‐structure‐properties‐performance relationship of materials. This inspires us to leverage the capabilities of ANNs to decode properties of hydrogels, thereby customizing these active materials for sensors or actuators. In the current work, we introduce an approach to predict discrete swelling states of temperature‐responsive hydrogels, especially PNIPAAm, based on their synthesis parameters, utilizing ANN models. To build the database, we analyze literature on temperature‐responsive hydrogels and compile essential synthesis parameters. The corresponding data points related to these synthesis parameters are then extracted. We propose different variants of ANN models and compare their accuracy on the acquired dataset. The selected model can predict the swelling states of hydrogel samples within the test dataset with relative prediction error of 0.11. This approach is applied to predict the expected properties. Subsequently, the hydrogels can be synthesized, and their properties can be experimentally verified. Our approach can be extended to other types of hydrogels and in the prediction of additional properties. The identified synthesis parameters serve as a valuable foundation for the expansion of the database with further literature resources. An enriched database will enhance the performance of the data‐driven model, thereby improving its predictive capabilities. [ABSTRACT FROM AUTHOR]

Polyacrylamide hydrogel was investigated to improve its water retention capacity. Among the several hydrogel samples prepared, a sample with ∼0.55 % cross-linker was found sufficiently rigid with high water content. The drying and rehydration cycles induced the appearance and disappearance of cracks respectively within the hydrogel and were confirmed by FESEM analysis. The effect of mili-patterns on hydrogel surface was studied and was found that the patterns enhanced the duration of water retention by ∼60 %. Even after 100 h of drying of a swelled hydrogel, the one with the pattern retained sufficient water so that its length remained ∼35 % longer compared to a non-patterned flat hydrogel. These findings were discussed in light of the Kelvin equation and were supported by the time-resolved Raman spectra that ensured the presence of the bound water for a longer duration. Based on the intensity of O–H stretching, it was inferred that patterned hydrogel exhibited water retention efficiency (RE) of ∼97 %, whereas, a flat non-patterned hydrogel had RE merely of ∼70 % after 3 cycles of drying and rehydration. [Display omitted] • Milli-patterns on PAAm hydrogel surface enhanced water retention duration by ∼60 %. • Length of patterned hydrogel remains 35 % longer than flat hydrogel while drying. • Kelvin eq. and Raman spectra support higher water retention by patterned hydrogel. • Patterned hydrogel showed retention efficiency (RE) of ∼97 %. [ABSTRACT FROM AUTHOR]

To prepare superabsorbent hydrogels, starch-graft-poly(acrylic acid) reinforced by cellulose nanofibers (CNF), was synthesized through free radical graft polymerization. The results of its biocompatibility tests exhibited that by increasing incubation time from 1 to 5 days, the numbers of living cells were increased on both reinforced and unreinforced hydrogels. However, the fraction of cells on the surfaces of the reinforced hydrogel is comparable to unreinforced samples. The swelling amounts in NaCl, CaCl2, and AlCl3 solutions were 193 ± 9, 110 ± 8, and 99 ± 7 (gwater/gabsorbent) for 5 wt% CNF-reinforced hydrogels and 109 ± 8, 62 ± 7, and 56 ± 6 (gwater/gabsorbent) for unreinforced hydrogels, respectively. Compressive strength and Young's modulus of 5 wt% CNF-assisted hydrogels were also 63.3 and 31.6 kPa corresponding to 69% and 140% improvements compared with unreinforced one. The graft polymerization of acrylic acid monomer was controlled by monomer content and cross-linking percentage, in order to achieve the highest swelling capacity for hydrogels. Hydrogel swelling in water was 312 gwater/gabsorbent for unreinforced hydrogel and 523 gwater/gabsorbent for 5 wt% CNF-reinforced sample and water absorption kinetics results was in agreement with the pseudo-second-order model. The prepared CNF-reinforced starch-graft-poly(acrylic acid) hydrogels can be used in a wide range of medical application due to the enhanced hydrophilicity, mechanical strength, and biocompatibility. [ABSTRACT FROM AUTHOR]

A main characteristic of hydrogels is their multisensitivity, i.e., the material's capability to respond to multiple stimuli such as temperature, chemical concentration or light. Most modeling approaches to swelling in the literature deal with the monosensitive behavior of hydrogels. Herein, two approaches to the modeling of multisensitive sensors and actuators are proposed: the N‐field method and the trajectory method. They are derived using experimental data of the bisensitive hydrogel [net‐P(AMPS‐co‐NiPAAm)]‐sipn‐PAMPS. It is sensitive to sodium salt concentration and temperature. For the trajectory method, the procedure for the generalized representation of the material behavior is presented. Applying the Temperature Expansion Model, this is implemented in Abaqus and the results of verification simulations are given. The trajectory method is capable of representing the multisensitive behavior of hydrogels. The method is easy to implement in commercial Finite Element tools based on the free‐swelling data of the material. Simulation results of the free swelling are in excellent agreement with the given calibration data. The obtained swelling behavior can be combined with mechanical loads and arbitrary boundary conditions to form more complex setups. The current work allows a deeper understanding of complex multifunctional materials, such as hydrogels, and their application in sensor or actuator devices. [ABSTRACT FROM AUTHOR]

Hydrogels can be used for sensor or actuator applications depending on their swelling behavior: highly sensitive hydrogels are better suited for sensors while hydrogels with lower sensitivity are more suitable for precision actuators. The identification of an appropriate material for a specific application is however tedious, since different measures for swelling are used in literature. To overcome this drawback, an approach for the generalization of hydrogel swelling is presented in the current research. In order to obtain the normalized form of swelling data, the reference point is extracted from the stimulus-swelling-curve. For isotropic swelling of different hydrogel materials, the Hencky strain is applied as generalized swelling parameter. Together with the stimulus ratio, a normalized sensitivity parameter is derived. In the present work, different kinds of stimuli such as temperature, pH, ions and light with their respective swelling mechanisms are considered. The Temperature Expansion Model allows Finite Element simulation of hydrogels with the described responsivenesses in their normalized forms. It is shown that the normalized swelling and the derived sensitivities can be used to assess hydrogels in their suitability for the application in sensors or actuators. The normalized forms can also be used in the design process to choose adequate materials for an envisioned application. [ABSTRACT FROM AUTHOR]

Membranes act as smart structures in respect to their permeation abilities. Control of particle and fluid permeation through a synthetic membrane can be achieved by using different effects like size-exclusion or electromagnetic interactions that occur between the particles and membrane pores. The simulation of controlled permeability provides an insight into the smart behavior of membranes for chemical signal processing, sensing interfaces or lab-on-a-chip devices. In the current work, we model the underlying physical processes on a microfluidic level using the engineer’s approach of laminar flow through pipes. Different pore geometries inside a composite membrane system consisting of a polyethylene terephthalate support membrane and a poly(N-isopropylacrylamide) hydrogel-layer are investigated. Simulations for different states of thermally induced pore opening are performed for free and blocked states. From the results we derive paradigms for the design of a membrane system for microfluidic cell-size profiling considering stimulus-range, pore shape and measurement setup. [ABSTRACT FROM AUTHOR]

Background and aims: Interactions between soil constituents define soil microstructural stability and are enhanced by swellable organic substances (hydrogels) such as extracellular polymeric substances (EPS), root mucilage or synthetic polymers. This study aims to identify the still largely unknown mechanisms behind hydrogel-induced soil microstructural stability. We hypothesized that soil microstructural stability increased with increasing limitation of hydrogel swelling between soil particles. Methods: One- and two-dimensional H proton nuclear magnetic resonance relaxometry (H-NMR relaxometry) measurements were performed with untreated and polyacrylic-acid (PAA) treated artificial soils at various clay content and PAA concentrations. The results on the water distribution and water mobility in the artificial soils were related to their microstructural stability as measured by rheology. Results: PAA treatment significantly increased soil microstructural stability up to five times, especially at high clay content. Soil microstructural stability increased with decreasing rotational mobility of water in the PAA-treated artificial. At the two highest PAA concentrations, the microstructural stability was the highest, although the mobility of water molecules was not further restricted. Conclusion: In artificial soils, the viscosity of hydrogel structures between mineral particles and the additional formation of an external network by polymer-clay interactions such as polyvalent cation bridging seem to promote microstructural stability. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

To improve gel toughness, surface cross-linking of partiallyneutralized acrylic acid based superabsorbent polymers (superabsorbent polymers, prepared by solution polymerization) was performed by diethylene glycol diglycidyl ether. Considering effective factors (treatment solution, surface cross-linker content, post-treatment temperature, and duration), a two-step surface modification procedure was performed on dried superabsorbent polymers particles. Attenuated total reflection–Fourier transform infrared spectroscopy has proved chemical cross-linking reaction. Mechanical properties have also been investigated. Besides, the modified rubber elasticity theory and Flory–Rehner equations have been used to investigate how they work in core–shell-like structure. The optimum condition provides at least a 100% raise in gel strength and appropriate absorbency. [ABSTRACT FROM AUTHOR]

Polymeric hydrogel systems based on poly(2-hydroxyethyl methacrylate), poly(ε-caprolactone), and poly(ethylene glycol) were prepared by photopolymerization using 2,4,6-trimethyl benzoyl diphenyl phosphine oxide as the photoinitiator. The structural details, morphology, and crystallinity were evaluated by Fourier transform infrared, scanning electron microscope, and X-ray diffraction analysis. The fluid uptake of the hydrogels was measured using swelling analysis. Based on a hemolysis assay, the prepared hydrogels were non-hemolytic. No attachment of fibroblasts to the hydrogel systems was observed. Stress–strain results indicated that the poly(2-hydroxyethyl methacrylate), poly(ε-caprolactone), and poly(ethylene glycol) hydrogel system (85:10:5) possessed better mechanical properties. Cytotoxic assessment by direct contact method of 85:10:5 systems found that the hydrogel was non-cytotoxic to L929 fibroblasts. This hydrophilic polymer system has a potential for wound dressing applications. [ABSTRACT FROM PUBLISHER]

Hydrogels were prepared from guar gum (GG) via esterification with 1,2,3,4-butanetetracarboxylic dianhydride (BTCA). Detailed spectroscopic analysis using FTIR and solid-state NMR revealed that an increase in the BTCA feed amount in the preparation mixture led to an increased degree of crosslinking, which affected the swelling behavior and rheological properties of the hydrogels. The hydrogels exhibited enzyme degradability, and after incubation with β-mannanase and α-galactosidase, 30-57% of the hydrogels were degraded. In addition, the hydrogels adsorbed bovine serum albumin and hen egg white lysozyme thorough electrostatic and hydrophobic interactions. The protein-adsorbed GG hydrogels exhibited a slow and steady release of the proteins over a 24 h period in buffer solutions after a fast release of proteins in the first hour. As such, GG hydrogels are expected to be efficient drug delivery carriers for protein-based drugs. [ABSTRACT FROM AUTHOR]

Highlights: [•] Polyampholyte and polyzwitterionic hydrogels are synthesized at optical fiber tip. [•] Hydrogels contain balanced and non-balanced charges copolymerized in the network. [•] Hydrogel swelling is followed using high resolution interferometry. [•] Swelling of polyelectrolyte and zwitterionic hydrogels is not always additive. [Copyright &y& Elsevier]

[Display omitted] • The drug release rate can be enhanced up to 10 times through ultrasound stimulation over a non-stimulated release. • The drug release rate increases with ultrasound power and induction time until their peak, but decreases then. • Increasing exposure time can reach the peak release rates with lower power values. • The maximum cell death rate of Wilms tumor is at an ultrasound power of 1 W for 20 s. • Multiphysics simulation is a helpful tool for future potential predictions. In this study, silk fibroin hydrogel is employed as a carrier for vincristine and ultrasound as a method to accelerate the drug release. The Acoustic, deformation, swelling, and diffusion fields are coupled in a multi-physics model to optimize the drug delivery. A transient acoustic structure model and a chemically controlled mechanism are implemented, while a coupled model of deformation and diffusion takes the impact of mechanical forces into account. An evaluation of the model is made through experiments. To monitor the drug release rate over 40 days following injection of silk hydrogel syringes containing vincristine, they were triggered by ultrasound in some selected time intervals. Drug release rates were determined using different power intensities and induction times. Computed simulation results and laboratory experiments revealed that ultrasound could cause a significant improvement in drug release rate, with an increase of up to 10 times over a release without ultrasound stimulation. By increasing the ultrasound power and induction time up to their peak value, the drug release rate rises and drops then. Predictions of the drug release rate by the model were in good agreement with those observed in experiments. This makes the model a valuable tool for potential predictions. Results showed that the ultrasound triggers the increased cell death rates, but the Wilms tumor cells were resistant to higher concentrations of released drugs. [ABSTRACT FROM AUTHOR]

• An eNRTL activity coefficient model is presented for poly (n-isopropyl acrylamide) (IPAAm) hydrogel-water-NaCl systems. • The hydrogel swelling and NaCl salt partitioning data are investigated for four IPAAm hydrogels. • The hydrogel swelling is controlled by the NaCl-water attractive interactions due to NaCl hydration. • The salt partitioning is controlled by the NaCl-IPAAm segment repulsive interactions. A comprehensive thermodynamic model is presented for swelling and salt partitioning of poly (n-isopropyl acrylamide) hydrogels in aqueous sodium chloride (NaCl) solutions at 298 K. Together with a Helmholtz energy expression for network elastic energy, a modified electrolyte Nonradom Two-Liquid activity coefficient model is used to represent both the long-range electrostatic interactions and the short-range van der Waals interactions present in the gel phase. The model parameters include one network parameter per hydrogel system plus two binary parameters per interaction pair in the polymer–solvent-salt systems. With semiquantitave agreement with experimental data for both hydrogel swelling and salt partitioning up to salt saturation, the analysis suggests the ion hydration between NaCl and water is the root cause for hydrogel deswelling in aqueous NaCl solution at high NaCl concentrations, i.e., NaCl weight fraction >0.03. On the other hand, the strong repulsive interaction between NaCl and hydrogel polymer is the dominant factor for salt partitioning. [ABSTRACT FROM AUTHOR]

Poly(acrylamide-co-crotonic acid) (PAAmCA), poly(acrylic acid- co-crotonic acid) (PAACA), PAA and PAAm hydrogels were prepared by free radical polymerization and ethylene glycol dimethacrylate (EGDMA) as a cross- linker. The variations of swelling values (%) with time, temperature, and pH were determined for four types of hydrogels. The PAACA hydrogel was swollen 2300% at pH = 7.4 and 37°C. The drug release from pantoprazole-Na loaded PAACA and PAAmCA hydrogels was followed at pH = 7.4, 37°C for 30 h. The release from PAACA hydrogel was faster than that from PAAmCA hydrogel; therapeutic levels for both hydrogels are obtained within 1 hour. Non-Fickian diffusion was determined for both hydrogels. [ABSTRACT FROM AUTHOR]

[Display omitted] • Vincristine is released dramatically within the first hour from silk fibroin hydrogel. • Drug concentration is higher on the larger sides of the matrix and minimum at the corners. • The release of drugs in enzyme solution is ten times faster than in PBS solution. • It is possible to adjust the concentration in specific distances from the hydrogel. • Multiphysics simulation predicts optimal time and coordination for multi-injections. • Considering the swelling behavior of hydrogel results in a precise prediction of drug release. In this paper, silk fibroin hydrogel is used as a drug carrier for vincristine. To optimize drug delivery, a multi-physics model is proposed that couples the deformation and diffusion fields. We applied inverse analysis and general continuum mechanics to define material parameters and mechanical properties. To examine the mass transport and chemical behavior, an affinity-based diffusion and degradation of a drug-loaded polymer matrix is employed. Some experiments are carried out to examine the capability of the presented model. After preparing the vincristine loaded silk hydrogel syringes, they were injected into PBS and enzyme solutions to monitor the drug release rate for 40 days. Obtained results from the computational simulation and laboratory tests showed that the silk fibroin hydrogel was deswelled after about 40 days in enzyme solution. Degradation led to faster and higher doses of vincristine drug release in comparison to the case of PBS solution. Results revealed that more than 80% of the drug was released in the first 5 days in the enzyme solution, but in PBS solution only 10% of the drug was released during 40 days. The model predictions of deswelling behavior and drug release rate were in good agreement with those of experimental results. Therefore, it can be employed as a reliable tool for further predictions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Solvent – hydrogel interactions are the dominant driving force for hydrogel swelling. • Polymer NRTL activity coefficient model accounts for the solvent – hydrogel interactions. • The model correlates data for both swelling and equilibrium phase compositions. • Hydrogels deswell if the hydrogel – solvent mixture forms an ideal solution. Hydrogel, a three-dimensional elastic structure of cross-linked polymer chains, swells or deswells when immersed in aqueous organic solutions. The swelling of hydrogels depends on temperature, solvent composition, and hydrogel structure as the thermodynamic driving forces for hydrogel swelling are due to solvent – hydrogel interactions and expansion of elastic network. In this work, polymer Nonrandom Two-Liquid activity coefficient model is used to account for the solvent – hydrogel interactions and a semi-empirical expression for rubber elasticity is used to describe the expansion of elastic network. The model successfully correlates data for both swelling and equilibrium phase compositions for n -isopropyl acrylamide hydrogels in water – ethanol, water – acetone, water – n -butanol, and water – methyl isobutyl ketone mixed solvents. [ABSTRACT FROM AUTHOR]

The in-line monitoring of ethanol concentration in liquids is a crucial part of process monitoring in breweries and distilleries. Current methods are based on infrared spectroscopy, which is time-consuming and costly, making these methods unaffordable for small and middle-sized companies. To overcome these problems, we presented a small, compact, and cost-effective sensing method for the ethanol content, based on a nanostructured, plasmonically active sensor substrate. The sensor substrate is coated with an ethanol-sensitive hydrogel, based on polyacrylamide and bisacrylamide, which induces a change in the refractive index of the substrate surface. The swelling and shrinking of such hydrogels offer a means to measure the ethanol content in liquids, which can be determined in a simple transmittance setup. In our study, we demonstrated the capability of the sensor principle for the detection of ethanol content ranging from 0 to 30 vol% ethanol. Furthermore, we determined the response time of the sensor substrate to be 5.2 min, which shows an improvement by a factor of four compared to other hydrogel-based sensing methods. Finally, initial results for the sensor's lifetime are presented. [ABSTRACT FROM AUTHOR]