Effect of pH and temperature on swelling Behaviour of tamarind gum

Natural gum tamarind is a plant polysaccharide extracted from seeds endosperm of the plant, Tamarindus indica Linn. Thin film of the gum was prepared by direct compression method. The prepared film was investigated for the effect of pH and temperature on solvent uptake property of film by gravimetric method. Different swelling parameters such as mass swelling ratio (MSR), equilibrium swelling ratio (ESR), equilibrium swelling ratio (ESw) and the equilibrium water content (EWC) were studied. It was found that swelling parameters were influenced by different pH and temperature conditions. The results suggested that the water content in equilibrium state was similar to body fluid. The gum converted to a high viscous gel of pseudo plastic characteristics in different pH conditions and the mechanism of continuous diffusion of solvent molecules into tablet during swelling was a non fickian and followed a second order kinetics.

Preparation of gelatin-based hydrogels with tunable mechanical properties and modulation on cell–matrix interactions

Natural polymer material-based hydrogels normally show inferior mechanical stability and strength to bear large deformation and cyclic loading, therefore their applications in food, biomedical and tissue engineering fields are greatly limited. In this study, gelatin-based hydrogels with remarkable stability, as well as tunable mechanical properties, were prepared via a facile method known as the Hofmeister effect. The higher concentration of potassium sulfatesolution resulted in more dehydration and molecular chain folding, thus the treated hydrogels showed significantly improved tensile and compressive modulus, and decreased equilibrium swelling ratio, as revealed by scanning electron microscopy (SEM), Fourier transform infraredspectroscopy (FTIR), and mechanical tests, etc. Additionally, the reinforced hydrogels were recoverable and biocompatible to modulate the proliferation behavior of human umbilical vein endothelial cells. In conclusion, this paper provides a facile reference for tuning mechanical properties of gelatin-based hydrogels and cell-hydrogel interactions, which show potential capacity in tissue engineering and biomedical fields.

Construction of Cellulose/Carboxymethyl Chitosan Hydrogels for Potential Wound Dressing Application

In this study, novel cellulose/carboxymethyl chitosan (CMCS) composite hydrogels were constructed by blending cellulose and CMCS in LiOH/urea aqueous solutions, and then cross-linking with epichlorohydrin. The structure and morphology of the composite hydrogels were characterized by Fourier transform infrared spectroscopy (FT-IR), wide-angle X-ray diffraction (WXRD), thermo-gravimetric analysis (TGA), and scanning electron microscopy (SEM). The results revealed that the chemical cross-linking reaction between cellulose and CMCS occurred in the hydrogel, and CMCS contributed to the enhancement of pore size, whereas cellulose as a strong backbone in the hydrogel to support the pore wall. The mechanical strength of the composite hydrogels increased with the cellulose content, while the equilibrium swelling ratio and antibacterial activity increased with the CMCS content. The composite hydrogels had no cytotoxicity towards L929 cells, suggesting good biocompatibility. All these results indicate that cellulose/CMCS composite hydrogels can be effectively used as a material in wound dressing.

Superabsorbent hydrogels enhanced by quaternized tunicate cellulose nanocrystals with adjustable strength and swelling ratio

Superabsorbent hydrogels were prepared from biodegradable material, where the matrix was cross-linked cellulose and carboxymethyl cellulose and reinforced by quaternized tunicate cellulose nanocrystals (Q-TCNCs). Due to the large amount of hydrophilic groups on cellulose, carboxymethyl cellulose, and Q-TCNCs, the hydrogels had excellent water absorption capacity. The equilibrium swelling ratio of superabsorbent hydrogels exceeded 500 g/g in deionized water and exceeded 120 g/g even in synthetic urine, which was higher than those of commercial absorbent materials composed of copolymers of acrylic acid and acrylamide. The water absorption performances and mechanical properties of the hydrogels could be adjusted by changing the content of Q-TCNCs. The resultant materials were expected to replace those polyolefin-based materials, thereby reducing environmental pollution.

Effect of 2-(dimethylamino) Ethyl Methacrylate on Nanostructure and Properties of pH and Temperature Sensitive Cellulose-Based Hydrogels

The novel double responsive cellulose/poly 2-(dimethylamino) ethyl methacrylate (PDMAEMA) hydrogel was synthesized via in situ free radical polymerization. The results from light transmittance measurements, scanning electron microscopy (SEM), mechanical property testing as well as swelling experiments demonstrated that DMAEMA played a significant impact on in hydrogel’s nanostructure.With increasing DMAEMA concentration, the transparency of hydrogels dropped and texture became softer. The incorporation of relatively hard cellulose and increase in crosslink density significantly enhanced 3D network structure of hydrogel. The tensile strength, compression and bending capabilities of the composite responsive hydrogels were fine with the DMAEMA in a certain range. When the DMAEMA concentration increased to 6 g/g(cellulose), the mechanical strength decreased noticeably. An increase in DMAEMA concentration resulted in a faster initial swelling rate and higher equilibrium swelling ratio. Further, three-dimensional structure and increase of DMAEMA concentration can also improve pH and temperature response sensitivity of hydrogels. Thus, the mechanical, swelling and responsive properties of hydrogel could be adjusted by the DMAEMA and polymerization modes.

A Recrosslinkable Preformed Particle Gel for Conformance Control in Heterogeneous Reservoirs Containing Linear-Flow Features

Summary Preformed particle gels (PPGs) have been successfully applied to control conformance for mature oil fields because of their advantages over conventional in-situ gels. However, field applications have demonstrated that current particle gels cannot efficiently plug open fractures, fracture-like channels, or conduits that exist in many mature oil fields. The objective of this study is to systematically evaluate a new recrosslinkable-PPG (RPPG) product that can be used to efficiently control the conformance for abnormal features. The RPPG can swell to 38 times its initial volume, and the equilibrium swelling ratio is independent of the brine salinity. Temperature and the particle size showed a gradient effect on the swelling rate of the gel. Additionally, the particle gels can recrosslink to form a rubber-like bulky material in the large-opening features after placement that significantly enhances the plugging efficiency. We systematically evaluated the effect of temperature and RPPG swelling ratio on the recrosslinking time, the gel strength after crosslinking, and the gel thermostability. Coreflooding tests were run to test whether RPPG can significantly improve the fracture-plugging efficiency compared with a traditional PPG that cannot recrosslink after pumping. The RPPG can be customized for mature reservoirs with a temperature from 23 to 80°C with a controllable size from tens of nanometers to a few millimeters. The recrosslinking time can be controlled from 2 to 80 hours, depending on the swelling ratio and temperature. The gel elastic modulus after recrosslinking can achieve from 300 to 10 800 Pa, depending on the swelling ratio and the temperature. Coreflooding tests showed that the breakthrough pressure of the recrosslinked RPPG can reach up to 300 psi/ft for a fracture with a 0.2-cm aperture, which is more than five times higher than that of the conventional PPG.

Preparation and Pharmaco-Mechanical Characterization of Ketoprofen- Polyvinyl Alcohol Cryogel for Medical Applications

Polyvinyl alcohol is a biocompatible polymer used very commonly both in pharmaceutical and medical fields. Being a water-soluble polymer, it is suitable for the manufacture of hydrogels as well as cryogels used for various medical applications. The present work describes the preparation, structural and physico-mechanical characterization of polyvinyl alcohol cryogels loaded with ketoprofen. By cryogenic technique the polymeric solutions are transformed under certain conditions into porous, elastic and very compressible structures. They are able to absorb a large amount of liquids that they give off by gentle compression. The prepared cryogels were evaluated for different physical, chemical and structural properties, as following: internal morphology, equilibrium swelling ratio and mechanical testing. The cryogel structures show good elasticity and optimal swelling at different temperatures. Due to these properties the studied cryogels are suitable for use in various medical applications involving liquid absorption, mechanical resistance and anti-inflammatory effect.

Physical properties of the organic polymeric blend (PVA/PAM) modified with MgO nanofillers

Magnesium oxide/polyvinyl alcohol/polyacrylamide (MgO/PVA/PAM) nanocomposite films were prepared via a solution chemical method. The effect of PVA and MgO nanoparticles (NPs) loading on the physical properties of PAM is discussed. X-ray diffraction reveals that the average MgO crystallite size of the NPs is ∼25 nm, while adding PVA increases the crystallinity of PAM. FTIR spectra confirm the interaction between blend chains and MgO NPs. Differential scanning calorimetry thermograms illustrate the miscibility between the PVA and the PAM. The melting temperature, the glass transition, as well as the equilibrium swelling ratio, depend on the films' composition. PAM showed a transmittance of 87%, that increased to 90% after PVA addition, but decreased to 74% after MgO loading. Meaningful changes are observed in the extinction coefficient and indirect/direct band gap of PAM due to PVA blending and MgO addition. The influence of MgO NPs on the dielectric constant ( ɛ′) of the blend film is reported. The maximum value of AC conductivity of the blend is 4.77 × 10−3 Sm−1, which increased to 8.07 × 10−3 Sm−1 by increasing the MgO loading to 5.0 wt.%. The conduction mechanism changed from the correlated barrier hopping, in the blend, to the large Polaron tunneling with MgO loading. The observed improvements in optical properties and AC conductivity encourage the use of these nanocomposite films in the semiconductors industry.

Continuous Fabrication of Temperature-Responsive Hydrogel Fibers with Bilayer Structure by Microfluidic Spinning

Temperature-responsive hydrogel fibers with bilayer structure were prepared by a microfluidic spinning device with a Y-shaped connector. The bilayer hydrogel fibers include two layer with different chemical composition. One layer is the ionic crosslinking hydrogel of calcium alginate (CA) and the other layer is temperature-responsive hydrogel which is semi-interpenetrating polymer networks (semi-IPN) of linear poly (N-isopropylacrylamide) (PNIPAM) and CA. The bilayer hydrogel fibers were evaluated by morphology observation, tensile stress measurement, temperature-responsive actuation test and equilibrium swelling ratio test. The results show that the prepared hydrogel fibers have obvious double layer structure with different porous structures. The bilayer hydrogel fibers can bend in water at 50 °C and the bending rate is influenced by the diameter of the fiber. Moreover, the diameter of the hydrogel fibers can be controlled by changing the flow rates of spinning fluids.