Antioxidant and ion-induced gelation functions of pectins enabled by polyphenol conjugation.

The development of antioxidant polymers through the chemical conjugation of natural polyphenols onto polysaccharides has important applications in biomedical, pharmaceutical, food, and cosmetic fields. Due to their labile characteristics, the covalent conjugation of polyphenols while retaining antioxidant properties has been a challenging task. Herein, four structurally different polyphenols, three with and one without a catechol group, were conjugated onto pectin macromolecules via a simple and efficient preparation method involving epichlorohydrin chemistry. The conjugation reactions were confirmed by FT-IR and UV-vis characterization, and the free radical scavenging assay confirmed that the polyphenols maintained their antioxidant activity after the reaction. The conventional structure-antioxidant property relationship can be applied to the assay results, and hesperidin without a catechol group showed the lowest antioxidant capability. The coordination of multivalent metal ions with polyphenols enabled ionic crosslinking and the moduli of hydrogels depend on the type of polyphenols and their molecular interactions with metal ions. The simplicity of preparation and the resulting unique properties could make the pectin conjugates useful in a wide range of application areas.

Superporous thermo-responsive hydrogels by combination of cellulose fibers and aligned micropores.

In the area of artificial hydrogels, simultaneous engineering of the volume transition characteristics and mechanical properties of stimuli-responsive hydrogels is an important subject. By unrestricted architecting of hierarchical structures, natural hydrogels are able to provide a wide range of swelling and mechanical properties, beyond the limits of artificial hydrogels. Herein, a combination of nanostructures and microstructures was developed to construct superporous hydrogels. Fibers of microfibrillated cellulose (MFC), an eco-friendly reinforcing material, were used as nanostructures, aligned micropores were used as microstructures, and in situ photopolymerization was used to immobilize the two structures together within the gel networks of poly(N-isopropyl acrylamide) (PNIPAm). The introduction of MFC distinctly enhanced volume transition, mainly by decreasing the swelling ratios above the transition. The introduction of directional micropores increased the swelling ratio below the transition and decreased the swelling ratio above the transition, thereby also enhancing the volume transition. Additionally, the formation of aligned micropores achieved fast water infiltration, which is beneficial for superabsorbent applications. The introduction of aligned micropores reduced the elastic modulus, but this could partially be compensated for by reinforcement with MFC. This combination of crystalline nanofibers and aligned micropores has great potential for the development of stimuli-responsive superporous hydrogels outperforming current artificial hydrogels.