Swelling Characteristics Of Hydrogels Research Articles

Three-phase soft mechanical metamaterials for tunable negative expansion deformation and bandgaps

As the new artificial composite structures combing the smart materials and extensible topologies, the mechanical negative-expansion metamaterials deformation are promising in the fields of aerospace, robotics, medical devices, and flexible electronics. Based on the swelling characteristics of hydrogels, this work develops 2D and 3D soft mechanical metamaterials suitable for super large negative expansion deformations. The 2D and 3D metamaterials are fabricated by the multi-material 4D printing, and characterized by the experiments of self-driven negative expansion deformation and recovery. To accurately and quickly predict the deformation behavior of negative expansion response, a large-deformation theoretical model is developed based on finite element method and verified by the experimental characterizations. The influence of lattice parameters on the negative expansion response deformation and the corresponding adjustability are characterized and demonstrated through the theory, simulations and experiments. The 2D and 3D soft mechanical metamaterials show that their elastic wave bandgaps can be regulated actively and flexibly using the evolution of the lattice during the negative expansion deformation process. The present metamaterials can be used to design and manufacture instruments with adjustable negative expansion deformation and acoustic functionalities, showing the potential applications in the fields of smart soft robots and active metamaterial devices.

PH-Sensitive Dairy-Derived Hydrogels with a Prolonged Drug Release Profile for Cancer Treatment.

A novel versatile biocompatible hydrogel of whey protein isolate (WPI) and two types of tannic acid (TAs) was prepared by crosslinking of WPI with TAs in a one-step method at high temperature for 30 min. WPI is one common protein-based preparation which is used for hydrogel formation. The obtained WPI-TA hydrogels were in disc form and retained their integrity after sterilization by autoclaving. Two TA preparations of differing molecular weight and chemical structure were compared, namely a polygalloyl glucose-rich extract-ALSOK 02-and a polygalloyl quinic acid-rich extract-ALSOK 04. Hydrogel formation was observed for WPI solutions containing both preparations. The swelling characteristics of hydrogels were investigated at room temperature at different pH values, namely 5, 7, and 9. The swelling ability of hydrogels was independent of the chemical structure of the added TAs. A trend of decrease of mass increase (MI) in hydrogels was observed with an increase in the TA/WPI ratio compared to the control WPI hydrogel without TA. This dependence (a MI decrease-TA/WPI ratio) was observed for hydrogels with different types of TA both in neutral and acidic conditions (pH 5.7). Under alkaline conditions (pH 9), negative values of swelling were observed for all hydrogels with a high content of TAs and were accompanied by a significant release of TAs from the hydrogel network. Our studies have shown that the release of TA from hydrogels containing ALSOK04 is higher than from hydrogels containing ALSOK 02. Moreover, the addition of TAs, which display a strong anti-cancer effect, increases the cytotoxicity of WPI-TAs hydrogels against the Hep-2 human laryngeal squamous carcinoma (Hep-2 cells) cell line. Thus, WPI-TA hydrogels with prolonged drug release properties and cytotoxicity effect can be used as anti-cancer scaffolds.

A Study on the Correlation Between Adsorption and Swelling for Poly(Hydroxamic Acid) Hydrogels-Triarylmethane Dyes Systems

The influence of crosslinker and dye type on the swelling and adsorption characteristics of poly(hydroxamic acid) (PHA) hydrogels have been investigated. PHA hydrogels with crosslinker such as N,N′-methylenebisacrylamide or ethylene glycol dimethacrylate were used in experiments on swelling, diffusion and adsorption of the triarylmethane dye such as Malachite Green, Methyl Violet 6B and Crystal Violet. The equilibrium swelling (Se) values of PHA hydrogels in the dye solutions were calculated as 2.26–21.57 g g−1. Some swelling, swelling kinetics, diffusional behavior and diffusional kinetics parameters were found. Diffusional behavior of the triarylmethane dye solutions was investigated. Diffusion behavior analyses determined that dye solution diffusion into hydrogels followed the anomalous Fickian behavior. It was observed that swelling characteristics of hydrogels are highly affected by the by the crosslinker type. Sorption of the triarylmethane dyes onto PHA hydrogels were studied by batch sorption technique at 25 °C. PHA hydrogels in the triarylmethane dye solutions showed the dark coloration. In the experiments of the adsorption, S type adsorption in the Giles classification system were found with an adsorption mechanism well represented by the Freundlich model. It has been found that there is an increasing linear correlation between swelling and adsorption values. The adsorbed amounts of the dyes by PHA–EGM hydrogels were very high (95% of the total concentration of the dyes), whereas the dyes were adsorbed in smaller (77%) amounts by PHA–NBis hydrogels. At the end of this study, it can be said that PHA hydrogels may be used a sorbent for removal of some agents (such as organic molecules) and dye molecules.

Remazol red dye removal using poly(acrylamide-co-acrylic acid) hydrogels and water absorbency studies

Acrylamide (AAm) and acrylic acid (AAc) were copolymerized in aqueous solution using 2,2-azobis(2-amidinopropane) hydrochloride (V-50) as initiator and N,N′-methylenebisacrylamide (NMBAM) as cross-linking agent to obtain high swelling hydrogels. The effects of AAm/AAc ratio and the amount of cross-linking agent on the swelling properties were studied. It was observed that swelling characteristics of hydrogels are highly affected by the presence of carboxylic groups of AAc units in the hydrogels and by the cross-linking amount in the polymer chains. Hydrogel with 70/30 ratio of AAm/AAc showed the highest swelling degree, until 69.2 g of water/g of dried hydrogel, which represents approximately 7000% of swelling. Swelling kinetic was well represented by a second-order kinetic model for all the AAm/AAc compositions with maximum weight swelling ratio between 20.4 and 82.6 g/g for the hydrogels synthesized using 1% of NMBAM. Diffusion behavior analyses determined that water diffusion into hydrogels followed the anomalous Fickian behavior. The as synthesized hydrogels were used in the removal of Remazol Red 3BS (RR3BS) dye from aqueous solutions, finding that the maximum dye adsorption capacity for an equilibrium aqueous concentration of 130 mg/L of RR3BS was 44.19 mg of RR3BS/g of dried hydrogel with 1% of NMBAM, with an adsorption mechanism well represented by the Langmuir model.

Swelling behavior and structural characteristics of polyvinyl alcohol/montmorillonite nanocomposite hydrogels

AbstractA series of nanocomposite hydrogels based on polyvinyl alcohol containing 0–10 wt % of the organically modified montmorillonite clay were prepared by freezing‐thawing cyclic method. The morphology of the nanocomposite hydrogels was observed by the scanning electron microscopy technique. The structural properties were determined by measuring the network mesh size, crosslinking density, and average molecular weight of polymer chains between crosslinks. The swelling behavior and the effect of swelling medium temperature on the swelling kinetics and characteristics of the nanocomposite hydrogels were also investigated. The results showed that two structural characteristics i.e., network mesh size and average molecular weight of polymer chains between crosslinks have inverse dependence on the clay loading level in the nanocomposite hydrogel, while crosslinking density shows completely direct dependence. Swelling measurements demonstrated a linear relation between the degree of swelling and the square root of immersion time at all swelling medium temperatures. The results indicated that the swelling characteristics of the nanocomposite hydrogels including the equilibrium degree of weight and volume swelling and the equilibrium water content were decreased by increasing the quantity of the clay incorporated into the hydrogel as well as by decreasing the temperature of swelling medium. While, the time required to reach to the equilibrium condition, as another swelling characteristic of the hydrogels, exhibited a completely opposite behavior. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.