*Article* **Supramolecular Structure and Mechanical Performance of** κ**-Carrageenan–Gelatin Gel**

**Anastasiya O. Makarova <sup>1</sup> , Svetlana R. Derkach <sup>2</sup> , Aidar I. Kadyirov <sup>3</sup> , Sufia A. Ziganshina <sup>4</sup> , Mariia A. Kazantseva 1,5, Olga S. Zueva <sup>6</sup> , Aidar T. Gubaidullin 7,8 and Yuriy F. Zuev 1,8,\***


**Abstract:** In this work, by means of complex physicochemical methods the structural features of a composite κ-carrageenan–gelatin system were studied in comparison with initial protein gel. The correlation between the morphology of hydrogels and their mechanical properties was demonstrated through the example of changes in their rheological characteristics. The experiments carried out with PXRD, SAXS, AFM and rheology approaches gave new information on the structure and mechanical performance of κ-carrageenan–gelatin hydrogel. The combination of PXRD, SAXS and AFM results showed that the morphological structures of individual components were not observed in the composite protein–polysaccharide hydrogels. The results of the mechanical testing of initial gelatin and engineered κ-carrageenan–gelatin gel showed the substantially denser parking of polymer chains in the composite system due to a significant increase in intermolecular protein–polysaccharide contacts. Close results were indirectly followed from the SAXS estimations—the driving force for the formation of the common supramolecular structural arrangement of proteins and polysaccharides was the increase in the density of network of macromolecular chains entanglements; therefore, an increase in the energy costs was necessary to change the conformational rearrangements of the studied system. This increase in the macromolecular arrangement led to the growth of the supramolecular associate size and the growth of interchain physical bonds. This led to an increase in the composite gel plasticity, whereas the enlargement of scattering particles made the novel gel system not only more rigid, but also more fragile.

**Keywords:** κ-carrageenan–gelatin hydrogel; supramolecular structure; mechanical performance
