Swelling kinetics of poly(N-vinylimidazole-co-sodium styrenesulfonate) hydrogels

Stabilizing interactions of casein microparticles after a thermal post-treatment

Casein microparticles from milk are important carrier materials for bioactive substances with stability and swelling properties that can be influenced by heat treatment. Microparticles produced by depletion flocculation and film drying remain stable in acidic media but swell and disintegrate under slightly alkaline conditions. Heat treatment after formation can stabilize the microparticles via a disulfide bridge network and newly formed hydrophobic contacts. Temperatures >60 °C are required so that denatured whey protein initiate formation of disulfide bridges via thiol exchange reactions. The particles then swell in a two-step process and exhibit an overshooting effect. If formation of disulphide bridges is prevented during heat treatment by adding N-methylmaleimide, overshooting swelling disappears and microparticles continue to expand instead. The analysis with parallel system dynamics models is based on the swelling of uncross-linked caseins, which is limited by the expansion capacity of cross-linked caseins.

Structure Effects on Swelling Properties of Hydrogels Based on Sodium Alginate and Acrylic Polymers

Hydrogels based on sodium alginate (SA) and partially neutralised poly(acrylic acid) were obtained by radical polymerisation. The hydrogels were cross-linked with N,N'-methylenebisacrylamide (MBA), simultaneously grafting the resulting polymer onto SA. The findings of the FTIR spectroscopy showed that all of the hydrogels were effectively synthesized and sodium alginate was chemically bonded with the poly(sodium acrylate) matrix. DSC analysis of the melting heat and glass transition parameters indicated that the hydrogel structure had changed as a result of the cross-linking process. Sodium alginate and MBA were tested at different concentrations to determine how they affected the hydrogel properties. A very high content of the biopolymer, i.e., sodium alginate, was used in our research, up to 33 wt%. This resulted in durable and stable hydrogels with a very high ability to uptake water, comparable to hydrogels based on synthetic polymers only. The ability to swell is inversely proportional to the quantity of MBA present. By increasing the amount of sodium alginate in the hydrogel, the ability of the hydrogel to absorb water is reduced. However, water uptake remains relatively high at 350 g·g-1, even for the hydrogel with the highest SA content.

Manufacturing of Zinc Oxide Nanoparticle (ZnO NP)-Loaded Polyvinyl Alcohol (PVA) Nanostructured Mats Using Ginger Extract for Tissue Engineering Applications

In this research, as an alternative to chemical and physical methods, environmentally and cost-effective antimicrobial zinc oxide nanoparticles (ZnO NP) were produced by the green synthesis method. The current study focuses on the production of ZnO NP starting from adequate precursor and Zingiber officinale aqueous root extracts (ginger). The produced ZnO NP was loaded into electrospun nanofibers at different concentrations for various tissue engineering applications such as wound dressings. The produced ZnO NPs and ZnO NP-loaded nanofibers were examined by Scanning Electron Microscopy (SEM) for morphological assessments and Fourier-transform infrared spectrum (FT-IR) for chemical assessments. The disc diffusion method was used to test the antimicrobial activity of ZnO NP and ZnO NP-loaded nanofibers against three representatives strains, Escherichia coli (Gram-negative bacteria), Staphylococcus aureus (Gram-positive bacteria), and Candida albicans (fungi) microorganisms. The strength and stretching of the produced fibers were assessed using tensile tests. Since water absorption and weight loss behaviors are very important in tissue engineering applications, swelling and degradation analyses were applied to the produced nanofibers. Finally, the MTT test was applied to analyze biocompatibility. According to the findings, ZnO NP-loaded nanofibers were successfully synthesized using a green precipitation approach and can be employed in tissue engineering applications such as wound dressing.

Multi-responsive hydrogels with UCST- and LCST-induced shrinking and controlled release behaviors of rhodamine B

By using a disulfide-functionalized crosslinker, a pH- and thermo-responsive 2-(dimethylamino) ethyl methacrylate (DMAEMA) monomer and a zwitterionic sulfobetaine methacrylate (SBMA) monomer were conjugated to fabricate a multi-responsive P(DMAEMA-SS-SBMA) copolymeric hydrogel. Apparent UCST and LCST volume transitions were observed in the P(DMAEMA-SS-SBMA) hydrogels with equivalent weight fractions of monomers. Different pore size and response sensitivity of shrunken structures below UCST and above LCST were visualized by SEM images. The hydrogel exhibited a highly swollen state with a swelling ratio of 17.8 and a pore size of 106μm at 45°C, they deswelled unequally at 5°C with a compact surface with pore size of 30μm and a loose bulk with pore size of 83μm, while they deswelled uniformly at 65°C with dense shrunken structure with small pore size of 12μm. The dual-thermoresponsive hydrogel was promising in controlled drug release. The initial drug release was predominantly controlled by diffusion, and the long-term release was influenced by the swelling ratio. Below UCST, the relatively hydrophilic shrunken structure and slow diffusion had a synergistic effect on the sustained release. Above LCST, the fast diffusion and the rapid "off" effect of hydrophobic skin layer resulted in a burst release. Additionally, pH-tunable swelling and redox-sensitive degradation were also observed.

Spontaneous volume transition of polyampholyte nanocomposite hydrogels based on pure electrostatic interaction

A circular system is employed in this paper to investigate the swelling behaviors of polyampholyte hydrogels; this circular system can effectively eliminate the disturbance of various factors and keep the surrounding environment constant. It is found that there exists a spontaneous volume transition to the collapsed state of polyampholyte hydrogels, which is attributed to the overshooting effect, and the transition can occur repeatedly under certain conditions. (13)C NMR is employed to investigate the swelling behavior of polyampholyte hydrogels. The swelling kinetics of polyampholyte hydrogels under various circular media and various circular runs are also investigated in this paper. All the results suggest that the spontaneous volume transition to the collapsed state of polyampholyte hydrogels is dominated by pure electrostatic interaction between different charges in polymer chains.

Hydrogel-based reconfigurable components for microfluidic devices

In situ liquid-phase photopolymerization (LP(3)) has been applied to the field of microfluidics to create components within integrated systems. As an extension of LP(3) technology, we present reconfigurable components that utilize the swelling of hydrogels. These components can be conveniently used to enhance microfluidic functions and applications. In order to utilize the swelling characteristic of hydrogels to the fullest, we demonstrate strategies to increase the swelling performance temporally and spatially. To this end, two successful applications using the reconfigurable components were tested: (1) active walls to block or divert flow at different steps in the fabrication or assay process, and (2) delivery pistons to move objects to specific locations within the microchannels after device fabrication.