Multifunctional gelatin/PVA hydrogels chemically crosslinked with grape pomace extract for controlled transdermal delivery of polyphenolic compounds

Multifunctional and environmentally friendly hydrogel materials were developed through the reaction of chemically crosslinking biocompatible polymers and natural crosslinkers present in grape pomace, a waste product left over during the wine making process. This interesting approach to designing hydrogels, especially considering that many synthetic crosslinking agents, such as N, N’-methylenebisacrylamide, epichlorohydrin, and glutaraldehyde, all of which are harmful and toxic. It turns out that not only fresh grape berries but also grape pomace constitute a source of many beneficial active substances including anthocyanins, flavanols, flavonols, stilbenes, and phenolic acids. The application of grape pomace extract to obtain hydrogels not only enables chemical crosslinking of polymers, but also provides therapeutic properties to the final matrix. The obtained hydrogels were characterized using Scanning Electron Microscopy and Fourier-Transform Infrared Spectroscopy analysis as well as physicochemical (gel fraction, swelling ability, degradation) and thermal properties. Results confirm clearly that only some of the compounds from the grape pomace extract (malvidin-3-O-glucoside; catechin; epicatechin; citric acid; L-phenylalanine; procyanidins B1 and B2) participate in the polymer cross-linking reaction. The remaining active substances (mainly L-phenylalanine, malvidin-3,5-O-diglucoside, and catechin) are released in a controlled manner and penetrate the skin, which indicates the high therapeutic potential of the obtained hydrogels.