Preparation and characterization of superabsorbent polymers (SAPs) surface-crosslinked with polycations

Research Advances in Superabsorbent Polymers

Superabsorbent polymers are new functional polymeric materials that can absorb and retain liquids thousands of times their masses. This paper reviews the synthesis and modification methods of different superabsorbent polymers, summarizes the processing methods for different forms of superabsorbent polymers, and organizes the applications and research progress of superabsorbent polymers in industrial, agricultural, and biomedical industries. Synthetic polymers like polyacrylic acid, polyacrylamide, polyacrylonitrile, and polyvinyl alcohol exhibit superior water absorption properties compared to natural polymers such as cellulose, chitosan, and starch, but they also do not degrade easily. Consequently, it is often necessary to modify synthetic polymers or graft superabsorbent functional groups onto natural polymers, and then crosslink them to balance the properties of material. Compared to the widely used superabsorbent nanoparticles, research on superabsorbent fibers and gels is on the rise, and they are particularly notable in biomedical fields like drug delivery, wound dressing, and tissue engineering.

Preparation of fast-swelling porous superabsorbent hydrogels with high saline water absorbency under pressure by foaming and post surface crosslinking

Superabsorbent hydrogels have wide applications in many fields because of their unique water absorbing performance. In spite of decades of research about superabsorbent hydrogels, high water absorbency under pressure and fast-swelling are still challenging and highly desired for their applications in hygienic products and others. Here, we report preparation of fast-swelling porous starch-g-poly(acrylic acid)/poly(vinyl alcohol) superabsorbent hydrogels with high saline water absorbency under pressure by foaming and post surface crosslinking. 2,2'-Azobis(2-amidinopropane) dihydrochloride (AIBA) was used as a new porogen instead of conventional porogens like NaHCO3. Post surface crosslinking of the hydrogel was achieved using glycerol via the esterification reaction. AIBA is a better porogen than NaHCO3 regarding porosity and swelling performance of the hydrogels, and its content has great influences on structure and swelling performance of the hydrogels including water absorbency and swelling rate. Also, the surface crosslinking using glycerol can significantly enhance the saline water absorbency under pressure (2 kPa) but at the sacrifice of the swelling rate. Consequently, the hydrogels show high water absorbencies for deionized water (560 g/g), 0.9 wt% NaCl solution (58 g/g), 0.9 wt% NaCl solution under 2 kPa pressure (28 g/g) and fast-swelling (31 s to achieve a highly swelling state).

Matrix Stiffening Enhances DNCB-Induced IL-6 Secretion in Keratinocytes Through Activation of ERK and PI3K/Akt Pathway

Matrix stiffness, a critical physical property of the cellular environment, is implicated in epidermal homeostasis. In particular, matrix stiffening during the pathological progression of skin diseases appears to contribute to cellular responses of keratinocytes. However, it has not yet elucidated the molecular mechanism underlying matrix-stiffness-mediated signaling in coordination with chemical stimuli during inflammation and its effect on proinflammatory cytokine production. In this study, we demonstrated that keratinocytes adapt to matrix stiffening by increasing cell–matrix adhesion via actin cytoskeleton remodeling. Specifically, mechanosensing and signal transduction are coupled with chemical stimuli to regulate cytokine production, and interleukin-6 (IL-6) production is elevated in keratinocytes on stiffer substrates in response to 2,4-dinitrochlorobenzene. We demonstrated that β1 integrin and focal adhesion kinase (FAK) expression were enhanced with increasing stiffness and activation of ERK and the PI3K/Akt pathway was involved in stiffening-mediated IL-6 production. Collectively, our results reveal the critical role of matrix stiffening in modulating the proinflammatory response of keratinocytes, with important clinical implications for skin diseases accompanied by pathological matrix stiffening.

Effective Enhancement of Water Absorbency of Itaconic Acid Based-Superabsorbent Polymer via Tunable Surface-Crosslinking

A superabsorbent polymer (SAP) was synthesized by copolymerizing itaconic acid and vinyl sulfonic acid. The typically low absorbency of itaconic acid-based SAPs under mechanical loads was improved by introducing surface crosslinking. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to characterize the synthesis and surface-crosslinking reactions in the SAP. Various conditions for surface-crosslinking reactions, such as the surface-crosslinking solution, content of surface-crosslinking agent, and reaction temperature, were explored and correlated with the gel strength and absorption characteristics of the resulting SAP particles. The distilled water content in the surface-crosslinking solution strongly influenced the absorption capacity of the SAP, but this sensitivity decreased when acetone was used as a co-solvent. Itaconic acid-based SAP that was crosslinked under optimal conditions exhibited centrifuge retention capacity and absorbency under a load of 31.1 and 20.2, respectively.

The Influence of Monomer Composition and Surface-CrossLinking Condition on Biodegradation and Gel Strength of Super Absorbent Polymer

In this study, a superabsorbent polymer (SAP) comprising poly (IA-co-cellulose-co-VSA-co-AA; ICVA) core-SAP (CSAP) was synthesized through radical polymerization using itaconic acid (IA), acrylic acid (AA), cellulose, and vinyl sulfonic acid (VSA) as monomers. The absorption performances and relative biodegradability of various compositions prepared by adjusting the amounts of cellulose and VSA with constant IA and AA content were compared. Increasing the cellulose content in CSAP contributed to improved biodegradation of the surface-crosslinked SAP (SSAP) and gel strength, although the free absorbency (FA) and centrifuge retention capacity (CRC) decreased. Increasing the VSA content resulted in strong anionicity, which enables the absorption of large amounts of water. Surface-crosslinking technology was applied to the CSAP synthesized with the optimal composition ratio to increase its absorption performance and gel strength. Improved performance of the synthesized SSAP (a CRC of 30.4 g/g, absorbency under load (AUL) of 23.3 g/g, and permeability of 55 s) was achieved by selecting the optimal surface-crosslinking treatment time and the amount of distilled water in the surface-crosslinking solution: as the latter was increased in the surface-crosslinking solution, the AUL and permeability of the SSAP were improved, and its biodegradability was found to be 54% compared to the 100% biodegradable cellulose hydrogel in the control group.