Dry Hydrogels Research Articles

Synthesis and characterization of graft copolymer hydrogel by “grafting from” atom transfer radical polymerization using brominated macro monomeric initiator and investigation of hydrogel properties

In this study, poly(ɛ-caprolactone-g-2-hydroxy ethyl methacrylate) [P(CL-g-HEMA)] graft copolymer hydrogels were successfully synthesized through multi-step reactions. For this purpose, firstly, hydroxyl-terminated poly(ɛ-caprolactone) (PCL-OH) was obtained by ring-opening polymerization (ROP) method of ɛ-caprolactone using 3-chlor-1,2-propanediol initiator, which is suitable for ring-opening polymerization method. Then, from the reaction of synthesized PCL-OH and 3-bromopropionyl chloride, a new brominated poly(ɛ-caprolactone) (PCL-Br) was synthesized for use as a functionalized atom transfer radical polymerization (ATRP) initiator. Poly(ɛ-caprolactone-g-2-hydroxy ethyl methacrylate) [P(CL-g-HEMA)] graft copolymer hydrogels were synthesized by “grafting from” atom transfer radical polymerization (ATRP) of 2-hydroxy ethyl methacrylate (HEMA) presence the new synthesized functionalized ATRP initiator (PCL-Br) and hydrogel properties were investigated. The synthesized functionalized initiators and graft copolymer hydrogel were characterized by spectroscopic methods such as 1H-NMR, FT-IR, TGA, DSC and SEM. The observation of two different decomposition temperatures, respectively, from the TGA analysis results may support the formation of the biblock graft copolymer. A glass transition temperature (Tg) of the graft copolymer hydrogel was found by DSC, and this value is between the Tg values of the homopolymers forming the graft copolymer hydrogel. Water swelling values of graft copolymer hydrogels were measured and calculated every 24 h in pure water with pH = 7 at from + 4 to 65 °C. Considering the weight of dry graft copolymer hydrogels, it was seen that water was absorbed at most at + 4 °C. As the temperature increased, the water absorption or swelling of the hydrogel decreased.

Dry and frost resistance conductive hydrogels based on carbon nanotubes hybrids for use as flexible strain sensor

Dry and frost resistance conductive hydrogels based on carbon nanotubes hybrids for use as flexible strain sensor

Radiation initiated synthesis of (carboxymethyl cellulose/polyacryalmide) hydrogels with polyprotic acid moieties and their utilization in nicotinic acid release

AbstractHydrogels of (carboxymethyl cellulose/polyacrylamide/polyprotic acids) were synthesized via gamma‐irradiation as green initiator. The polyprotic acids were used are oxalic, tartaric, citric and maleic. Effects of irradiation dose and polyprotic acids concentration on gelation (%) and swelling (%) are investigated. The swelling of hydrogels were conducted in the range of pH levels are from 1 to 12 at 37°C. The outcome hydrogels were characterized different techniques of Fourier transform infrared spectroscopy, thermal gravimetric analysis and derivative thermogravimetry, X‐ray diffraction, and scanning electron microscopy. The results confirmed the formation of respective hydrogels. Hydrogels were exploited in release of nicotinic acid as model of drug release. Dry tablets from hydrogels were fabricated as cylindrical discs. Dry hydrogels tablets were subjected to two different pH levels (i) simulated gastric fluid of pH level 1.2 and (ii) simulated intestinal fluid of pH level 7.5. The outcome results showed that there is a difference of nicotinic acid release quantity between the two pH levels. Further, different kinetic models of zero‐order, Korsmeyer–Peppas, Higuchi and Weibull were used to fit the experimental data. Through the results declared that the best fitting model was Weibull.

Evaluation of novel cleaning systems on mock-ups of unvarnished oil paint and chalk-glue ground within the Munch Aula Paintings Project

Low-risk removal of embedded surface soiling on delicate heritage objects can require novel alternatives to traditional cleaning systems. Edvard Munch’s monumental Aula paintings (1911–16) have a long history of exposure to atmospheric pollution and cleaning campaigns that have compromised the appearance and the condition of these important artworks. Soiling removal from porous and water-sensitive, unvarnished oil paintings continues to be a major conservation challenge. This paper presents the approach and results of research into the effect and efficiency of three novel systems used for soiling removal: soft particle blasting, CO2-snow blasting, and Nanorestore Gel® Dry and Peggy series hydrogels. Cleaning tests were performed on accelerated-aged and artificially soiled mock-ups consisting of unvarnished oil paint and chalk-glue grounds. Visual and analytical assessment (magnification using a light microscope and scanning electron microscope, as well as colour- and gloss measurement) was carried out before and after mock-up cleaning tests and the results were compared to those obtained using the dry polyurethane sponges employed in the most recent Aula surface cleaning campaign (2009–11). Although the results varied, the Nanorestore Gel® series proved promising with respect to improved soiling removal efficiency, and reduced pigment loss for the water-sensitive surfaces evaluated, compared to dry sponges.

A biological magnetic nano-hydrogel based on basil seed mucilage: study of swelling ratio and drug delivery

Basil seed with mucilage shell contains carbohydrates (BSG) which can be extracted to produce natural hydrogel compatible with the human body. In this study, a magnetic natural hydrogel was synthesized by copolymerization between the double bonds of vinyl-modified Fe3O4/SiO2 nanoparticles, methacrylic acid (MA) as a monomer, ethylene glycol dimethacrylate (EGDMA) as a crosslinker monomer, and vinylated BSG through free radical addition polymerization for delivery of naproxen (NPX) as a model drug. The product of each reaction step was identified by FTIR technique and the morphology of nanoparticles and magnetic nano-hydrogels was investigated using the SEM technique. SEM image analysis of dry magnetic hydrogels shows the existence of a porous structure with pore size in the range of 100–300 nm. The porosity of the hydrogels used in drug delivery systems can be useful in producing a large surface area, enhancing water absorption, and facilitating drug release. The swelling behavior of nano-hydrogels, a significant feature for drug delivery systems, was investigated at different pHs in buffer solutions. Also, drug loading and delivery experiments were performed by monitoring the concentration of loaded and released NPX by absorption at 245 nm on a UV–Vis spectrophotometer. The cumulative release behavior of hydrogels was investigated and the in vitro NPX release was achieved in the range of 98% at pH 7.4 after 24 h.

Comparative photophysical study of Pt(II) complex-nanoclay hybrid materials as dry powders and hydrogels

Abstract The excited state properties of Pt(II) complexes are strongly influenced by their microenvironment and by intermolecular interactions. In this work, we investigated the photoluminescence of six Pt(II) complexes adsorbed onto a layered nanoclay, namely Laponite® (LAP). The excellent water dispersibility and gel-forming nature of the LAP was exploited to achieve a class of versatile materials. In particular, we report on the comparative photophysics of the dry powders and the hydrogels. Steady-state and time-resolved photoluminescence spectroscopy were used to assess the role of structural features at molecular level on the interaction between the nanodiscs, which in turn affects the intermolecular coupling of the coordination compounds in the excited state.

Role of rheological properties on physical chitosan aerogels obtained by supercritical drying

Chitosan aerogels were obtained after using supercritical carbon dioxide to dry physical hydrogels, studying the effect of the rheological behavior of hydrogels and solutions on the final aerogels properties. An increase on the solutions pseudoplasticity increased the subsequent hydrogels physical entanglement, without showing a significant effect on aerogels morphology (nanoporous) and textural properties (pores of about 10 nm). However, an increase of hydrogel physical entanglement promoted the formation of aerogels with a higher compressive strength (from 0.2 to 0.80 MPa) and higher thermal decomposition range, while decreasing the porosity (from 90 % to 94 %). Aerogels stress-strain responses were also successfully fitted using a hyperelastic equation with three adjustable parameters (Yeoh), showing that this type of models must be taken into account when large stresses are studied.

Turning proteins into hydrophobic floatable materials with multiple potential applications

HypothesisProtein hydrogels are water-rich structure of cross-linked protein networks. The preparation of dry gels is conceptually simple. However, reports on innovative use of dry protein hydrogels are scarce, possibly because water removal would diminish intended properties. Here, an oil-like thiol-organosilane is proposed as a protein hydrogel-promoting agent that mediates the formation of hydrophobic composite gel networks with promising properties upon drying. Experiments3-Mercaptopropyltrimethoxylsilane (MPTMS) was used to transform aqueous albumin solutions into hydrogels. The gelation conditions were systematically investigated and optimized by varying various parameters, including temperature, pH, and the concentrations of MPTMS, albumin, and phosphate. The hydrogels were freeze-dried to obtain dry gel monoliths. The morphology of gel structure was evaluated using FE-SEM. The following properties of the dry monoliths were further evaluated: water uptake, floatability, drug loading and release, water contact angles, bulk densities, and oil adsorption. Mechanistic investigation included FTIR and fluorescence quenching determinations, and the study of emulsion properties. FindingsAn unprecedented protein-organosilane composite hydrogel was synthesized in a one-step reaction, at neutral pH and ambient conditions. Freeze-dried gel monoliths exhibited excellent hydrophobicity and floatability (immediate floating and lasting for >7 days on water). The proposed material may find novel applications in floating drug delivery and environmental clean-up of oil spills.

Influence of the degree of neutralization of acrylic acid and cross-linking agent on optical properties and swelling of sodium polyacrylate

Optical characteristics of polymerization products under variable degrees of neutralization of acrylic acid (AA) and cross-linking agent and at a fixed content of redox components have been studied by IR spectroscopy of frustrated total internal reflection and THz spectroscopy. The results of the analysis show that absorption of IR radiation and dispersion of THz radiation for the samples under study depend on the degree of AA neutralization, which predetermines the mechanism of structure formation of hydrogels, refractive index, and degree of their limited swelling. It is found that the dependences of the refractive index of dry compact hydrogels and the degree of limited swelling of ground polymer samples on the content of neutralizing agent in solutions of the reaction systems have a symbatic character.

Water-Responsive Shape Recovery Induced Buckling in Biodegradable Photo-Cross-Linked Poly(ethylene glycol) (PEG) Hydrogel.

The phenomenon of recovering the permanent shape from a severely deformed temporary shape, but only in the presence of the right stimulus, is known as the shape memory effect (SME). Materials with such an interesting effect are known as shape memory materials (SMMs). Typical stimuli to trigger shape recovery include temperature (heating or cooling), chemical (including water/moisture and pH value), and light. As a SMM is able not only to maintain the temporary shape but also to respond to the right stimulus when it is applied, via shape-shifting, a seamless integration of sensing and actuation functions is achieved within one single piece of material. Hydrogels are defined by their ability to absorb a large amount of water (from 10-20% up to thousands of times their dry weight), which results in significant swelling. On the other hand, dry hydrogels indeed belong to polymers, so they exhibit heat- and chemoresponsive SMEs as most polymers do. While heat-responsive SMEs have been spotted in a handful of wet hydrogels, so far, most dry hydrogels evince the heat and water (moisture)-responsive SMEs. Since water is one of the major components in living biological systems, water-responsive SMMs hold great potential for various implantable applications, including wound healing, intravascular devices, soft tissue reconstruction, and controlled drug delivery. This provides motivation to combine water-activated SMEs and swelling in hydrogels together to enhance the performance. In many applications, such as vascular occlusion via minimally invasive surgery for liver cancer treatment, the operation time (for both start and finish) is required to be well controlled. Due to the gradual and slow manner of water absorption for water-activated SMEs and swelling in hydrogels, even a combination of both effects encounters many difficulties to meet the timerequirements in real procedures of vascular occlusion. Recently, we have reported a bioabsorbable radiopaque water-responsive shape memory embolization plug for temporary vascular occlusion. The plug consists of a composite with a poly(dl-lactide-co-glycolide) (PLGA) core (loaded with radiopaque filler) and cross-linked poly(ethylene glycol) (PEG) hydrogel outer layer. The device can be activated by body fluid (or water) after about 2 min of immersion in water. The whole occlusion process is completed within a few dozens of seconds. The underlying mechanism is water-responsive shape recovery induced buckling, which occurs in an expeditious manner within a short time period and does not require complete hydration of the whole hydrogel. In this paper, we experimentally and analytically investigate the water-activated shape recovery induced buckling in this biodegradable PEG hydrogel to understand the fundamentals in precisely controlling the buckling time. The molecular mechanism responsible for the water-induced SME in PEG hydrogel is also elucidated. The original diameter and amount of prestretching are identified as two influential parameters to tailor the buckling time between 1 and 4 min as confirmed by both experiments and simulation. The phenomenon reported here, chemically induced buckling via a combination of the SME and swelling, is generic, and the study reported here should be applicable to other water- and non-water-responsive gels.

Superabsorbent, High Porosity, PAMPS-Based Hydrogels through Emulsion Templating.

Swell! Superabsorbent, mechanically robust, high-porosity hydrogels based on poly(2-acrylamido-2-methyl-1-propanesulfonic acid) have been successfully synthesized by templating within high internal phase emulsions (HIPEs). These hydrogel polyHIPEs (HG-PHs) exhibit unusually high uptakes of water and of artificial urine through structure- and crosslinking-dependent hydrogel-swelling-driven void expansion. An HG-PH with 3.1 mmol g-1 of highly accessible sulfonic acid groups exhibits a 7 meq NaOH ion exchange capacity per gram polymer and rapid dye absorption. The highly swollen HG-PHs do not fail at compressive strains of up to 60%, they retain water and recover their shapes upon the removal of stress. Unusually, the dry hydrogels have relatively high compressive moduli and achieve relatively high stresses at 70% strain.

Preparation of microgel/sodium alginate composite granular hydrogels and their Cu2+adsorption properties

Schematic diagram of microgel/SA composite spherical granular hydrogel formation.

Softening of seawater and desalination brines using grafted polysaccharide hydrogels

This paper investigates the potential of using polysaccharide hydrogels as softeners for saline solutions of seawater and reverse osmosis desalination brine. Grafting of acrylamide onto alginate and chitosan was conducted using microwave (MW) and ultraviolet (UV) irradiation techniques. The produced hydrogels: alginate (Alg-UV and Alg-MW) and chitosan (Ch-UV and Ch-MW) were characterized using X-ray diffraction and scanning electron microscopy. Hydrogel products were tested for their swelling behavior in distilled water and saline solutions, and their calcium and magnesium adsorption capacities in the pre-swollen and dry forms were measured in saline solutions. Swelling in distilled water was found to exceed that in saline solutions by 16.7–21-fold. Maximum attained swelling ratios in distilled water were 168 and 173 g/g for Alg-UV and Ch-MW grafted acrylamide hydrogels, respectively. Dry hydrogels had relative selectivity toward calcium adsorption in seawater and magnesium adsorption in brine. Furthermore, pre-swollen hydrogel manifested favorable adsorption for calcium and magnesium when compared to dry hydrogel at the same adsorbate volume. For both dry and pre-swollen hydrogels, maximum calcium adsorption capacities were 54 and 34 mg/g from seawater using Alg-MW and UV-prepared alginate and chitosan hydrogels, respectively. Maximum magnesium adsorption capacities from brine were 280 and 316 mg/g using dry alginate and chitosan hydrogels, respectively, prepared by MW technique. Magnesium adsorption capacities of the prepared hydrogels in brine were higher than those of tested commercial resins. It is concluded that alginate- and chitosan-grafted acrylamide hydrogels are promising softeners for saline solutions.

Synthesis of oxidized glycerol monooleate-chitosan polymer and its hydrogel formation for sustained release of trimetazidine hydrochloride

In this paper, a lipid material glycerol monooleate was used as the starting material to synthesize the oxidized glycerol monooleate (OGMO). OGMO was subsequently linked to chitosan (CS) via imine bonds (-C=N-) to obtain a new chitosan-based polymer (OGMO-CS), which can form hydrogels rapidly in aqueous media. Scanning electron microscopy, swelling behavior studies and degradation kinetics studies were performed to demonstrate the effect of this synthetic modification on the hydrogels formation of chitosan network and in vitro drug release. The effects of OGMO-CS type, dry hydrogels percentage, release media and drug loading on the sustained release of the model drug trimetazidine hydrochloride were evaluated. The release profiles of the hydrogels could be described by the Peppas-Sahlin mechanism, a combination of Fickian diffusion and Case-II relaxation. Based on the fact that numerous pharmaceutical lipids are available, the present study may pave the way for other lipids to be employed as modifiers of chitosan for more innovative chitosan derivatives with versatile properties and pharmaceutical applications.

Emulsion-templated macroporous polymer/polymer composites with switchable stiffness

Abstract Emulsion templates containing monomers in both emulsion phases were used to manufacture polystyrene-co-divinylbenzene based polymerized high internal phase emulsions (polyHIPEs) which have been reinforced by poly(methacrylic acid) (polyMAA) and poly(dimethyl aminoethyl methacrylate) (polyDMAEMA). The morphology of the hydrogel-filled polyHIPEs is affected by the hydrogels synthesized in the aqueous emulsion phase. The pore structure of polyMAA-filled polyHIPEs is highly interconnected indicating the formation of a methacrylic acid-co-styrene copolymer at the oil/water interface of the emulsion templates during synthesis. However, polyDMAEMA-filled polyHIPEs are predominately closed celled and the pore walls are covered by grafted hydrogel. The ability of the hydrogel-filled polyHIPEs to absorb water decreased with increasing crosslinking density of the hydrogels. The dry hydrogel reinforced the polyHIPE scaffolds possessed higher elastic moduli and crush strengths than the control polyHIPEs. The reinforcing ability of the dry hydrogels was further enhanced by increasing their degree of crosslinking. However, the reinforcement could be “switched off” simply by hydrating the hydrogels. The switchable mechanical properties of the hydrogel-filled polyHIPEs could potentially be utilized in smart humidity sensor technology.

Electric and Magnetic Properties of Hydrogels Doped with Cu Ions

The electric and magnetic properties of Cu doped and pure/undoped hydrogels were investigated by impedance spectroscopy and electron spin resonance techniques, respectively. The capacitance and dissipation factor (tan δ) were measured in the frequency range of 100 Hz 10 MHz at room temperature. The Cole Cole plots for the Cu doped dry and pure dry hydrogels have been used to describe the characteristic change of electrical properties in mentioned temperature interval. The comparison between Cu ions doped and pure/undoped samples is done using the impedance spectroscopy and the electron spin resonance techniques. Electron spin resonance signal for pure, Cu doped wet and Cu doped dry samples are not any power absorption signal, near the symmetric with respect to the resonance eld values according to the dry sample and asymmetric for resonance eld/base line, respectively.

Characterization of superabsorbent carboxymethylcellulose/clay hydrogel prepared by electron beam irradiation

Hydrogels for this study were prepared from a mixture of carboxymethyl cellulose (CMC) and different concentration of clay using freezing and thawing cycles followed by electron beam irradiation. The introduction of montmorillonite (MMT) up to 4% leads to an increase in the gel fraction and an improvement in water resistance indicating that the clay is well dispersed within the polymer matrix. Their swelling (%) of the hydrogel in distilled water and different physiological fluids, such as physiological saline water and synthetic urine, were evaluated. These results suggest that the maximum swelling (%) in water reached 3559% compared to the dry hydrogels but still maintained its steady appearance. Moreover, the hydrogels exhibited smart swelling and shrinking in NaCl and synthetic urine. The surface morphology and thermal properties of these hydrogels were characterized by scanning electron microscopy and thermogravimetric analysis (TGA). The ability of the prepared hydrogel to absorb and retain a large amount of water and simulated urine was measured. The results suggested the possible use of CMC/MMT composite hydrogels in the personal care product industry.

Synthesis and characterization of temperature-sensitive and biodegradable hydrogel based on N-isopropylacrylamide

Abstract Based on a biodegradable cross-linker, N-maleyl chitosan (N-MACH), a series of Poly(N-isopropylacrylamide) (PNIPAAm) and Poly(N-isopropylacrylamide-co-acrylamide) [P(NIPAAm-co-Am)] hydrogels were prepared, and their lower critical solution temperature (LCST), swelling kinetics, equilibrium swelling ratio in NaCl solution, and enzymatic degradation behavior in simulated gastric fluids (SGF) were discussed. The LCST did not change with different cross-linker contents. By altering the NIPAAm/Am molar ratio of P(NIPAAm-co-Am) hydrogels, the LCST could be increased to 39°C. The LCST of the hydrogel was significantly influenced by the monomer ratio of the NIPAAm/Am but not by the cross-linker content. In the swelling kinetics, all the dry hydrogels exhibited fast swelling behavior, and the swelling ratios were influenced by the cross-linker content and NIPAAm/Am molar ratios. Equilibrium swelling ratio of all the hydrogels decreased with increasing NaCl solution concentration. In enzymatic degradation tests, the weight loss of hydrogels was dependent on the cross-linker contents and the enzyme concentration.

Properties of a poly(acrylamide‐co‐diallyl dimethyl ammonium chloride) hydrogel synthesized in a water–ionic liquid binary system

AbstractA novel copolymer hydrogel, poly(acrylamide‐co‐diallyl dimethyl ammonium chloride), was prepared by the radical copolymerization of acrylamide and diallyl dimethyl ammonium chloride in an ionic liquid (IL)–water binary system in the presence of the crosslinker N,N′‐methylene bisacrylamide. The equilibrium swelling ratios of the hydrogels synthesized in the IL–water binary system increased with the content of IL and were remarkably higher than that of the gel synthesized in water. Differential scanning calorimetry measurements showed that the glass‐transition temperatures of the dry hydrogels that were synthesized in the IL–water binary system were remarkably lower than that of the gel synthesized in pure water. The mechanical properties of the gels synthesized in both water and the IL–water binary system were characterized with a universal material‐testing machine. The results show that fracture toughness of the hydrogels was improved when they were synthesized in the IL–water binary system. The gel shrank under a direct‐current electric field. The response rates of the gels that were synthesized with the IL–water binary system were faster than that of the gel synthesized in water. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Effect of the cross-linking degree on the morphology of poly(NIPAAm- co-AAc) hydrogels

Hydrogels of poly( N-isopropylacrylamide) co-polymerized with acrylic acid [P(NIPAAm- co-AAc)] were synthesized with cross-linking degrees of 2–7% using ( N, N′-methylenebisacrylamide). SEM micrographs revealed that the morphology of dry hydrogels changes from interconnected spherical pores to channel-like pores, with the change in the cross-linking degrees from 3 to 5%. The change in morphology is associated with a significant change in the swelling ratio. It was found that the diffusion rates and permeabilities of methylene blue (MB) through the hydrogel with channel-like pores are significantly higher if the main axes of the pores are oriented parallel to the flow of MB molecules, than if it is oriented perpendicularly. These results show that different morphologies can be obtained by controlling the cross-linking degree of P(NIPAAm- co-AAc) hydrogels in a narrow range around 5% and by performing the polymerization reaction in moulds placed in horizontal and vertical positions, opening a new perspective for modulating their properties in applications as matrices for controlled release of drugs or as membranes for separation processes.