The influence of freeze-thawing conditions on swelling and long-term stability properties of poly(vinyl alcohol) hydrogels for controlled drug release

Tough, Stretchable, and Thermoresponsive Smart Hydrogels

Self-healing, thermoresponsive hydrogels with a triple network (TN) were obtained by copolymerizing N-isopropyl acryl amide (NiPAAm) with polyvinyl alkohol (PVA) functionalized with methacrylic acid and N,N'-methylene bis(acryl amide) crosslinker in the presence of low amounts (<1 wt.%) of tannic acid (TA). The final gels were obtained by crystalizing the PVA in a freeze-thaw procedure. XRD, DCS, and SEM imaging indicate that the crystallinity is lower and the size of the PVA crystals is smaller at higher TA concentrations. A gel with 0.5 wt.% TA has an elongation at a break of 880% at a tension of 1.39 MPa. It has the best self-healing efficiency of 81% after cutting and losing the chemical network. Step-sweep strain experiments show that the gel has thixotropic properties, which are related to the TA/PVA part of the triple network. The low amount of TA leaves the gel with good thermal responsiveness (equilibrium swelling ratio of 13.3). Swelling-deswelling loop tests show enhanced dimensional robustness of the hydrogel, with a substantial constancy after two cycles.

Construction of double-network hydrogel based on low methoxy pectin/polyvinyl alcohol and its structure and properties

In this study, an interpenetrating double-network hydrogel (LMP/AA/PVAH) was prepared based on low methoxy pectin (LMP), acrylic acid (AA) and polyvinyl alcohol (PVA). The first rigid network of chemical crosslinking was constructed via free radical polymerization of LMP and AA, and the second of ductile physical crosslinking network was constructed via cyclic freeze-thaw of PVA. The first cycle hardness and elasticity of the LMP/AA/PVAH significantly increased from 13.08 N and 0 to 24.28 N and 0.79, respectively, when the second network structure was constructed in the hydrogel by PVA. Besides, the PVA network might enhance the ductile and limit the swelling of hydrogel. In addition, the adsorption properties of LMP/AA/PVAH were evaluated by adsorption of methylene blue (MB). The adsorption behavior of MB by LMP/AA/PVAH conformed to the pseudo-second-order kinetic model. Besides, after 4 cycles of adsorption, there was no significant difference in adsorption capacity of LMP/AA/PVAH. The results showed that LMP/AA/PVAH had good reusability.

Current Understanding of Hydrogel for Drug Release and Tissue Engineering

Due to their good absorption, satisfactory biocompatibility, and high safety, hydrogels have been widely used in the field of biomedicine, including for drug delivery and tissue regeneration. In this review, we introduce the characteristics and crosslinking methods of natural and synthetic hydrogels. Then, we highlight the design and principle of intelligent hydrogels (i.e., responsive hydrogels) used for drug release. Moreover, we introduce the application of the application of hydrogels in drug release and tissue engineering, and the limitations and research directions of hydrogel in drug release and tissue engineering are also considered. We hope that this review can provide a reference for follow-up studies in related fields.