Physicochemical aspects of hydrogel preparation from algal cellulose

Brown algae represent a valuable and promising source of cellulosic materials due to their high productivity and widespread, low cultivation cost and ease of processing, attributable to the absence of lignin. The aforementioned advantages are accompanied by the unique properties of algal cellulose (low degree of polymerization and an Iα-type crystal cell structure) due to the peculiarities of biosynthesis. These properties render algae superior to higher plants in terms of producing pure, mesoporous cellulosic materials, e.g. gels. The aim of this study is to first time evaluate the hydration capacity of algal cellulose and nanocellulose during hydrogel formation. Employing FTIR spectroscopy, calorimetry, and nuclear magnetic resonance relaxometry, we explored the interaction of algal cellulose and nanocellulose with water. Nanocellulose has a higher content of free water owing to its developed mesoporous structure. The interaction between cellulose and water is exothermic, liberating heat at 7.2-29.2 J/g d.w. The high moisture retention capacity (37 g/g), coupled with the small size of nanocrystals, facilitates the formation of a stable homogeneous algal nanocellulose hydrogel, which remains stable over extended storage periods. This resultant hydrogel has promising applications in biomedical material production, including wound dressings, anti-adhesive films, and abdominal surgery gels.