Physical-mechanical properties of fucoidan-alginate composite hydrogels

Fucoidan, a sulfated polysaccharide from kelp, is gaining attention for its bioactive properties. Alginate is well established as a hydrogel forming biomaterial. While alginate hydrogels have been extensively studied, the effects of fucoidan inclusion remain underexplored. This study examines the effects of fucoidan on alginate hydrogels, focusing on mechanics, ion binding, stability, and leakage. Compression revealed a slightly lower Young's modulus in composite gels compared to pure alginate hydrogels. Composite fucoidan-alginate hydrogels exhibited greatly increased compressibility, tolerating ~90% strain before fracture and requiring 3- to 4-fold greater compressive force. Furthermore, fucoidan yielded fundamental differences in compressive behavior, with pronounced strain stiffening at higher strains and greatly increased total work required for gel rupture. Ion binding, measured by ICP-MS, as well as stability in saline were similar in hydrogels irrespective of fucoidan inclusion. Increased stability was observed when a small fraction of alginate was substituted with fucoidan in microspheres produced by calcium diffusion gelation. NMR analysis of leaked polymeric material from hydrogels indicated an initial release of low-molecular-weight fucoidan, followed by higher-molecular-weight fucoidan with prolonged exposure. These findings demonstrate that fucoidan fundamentally alters the deformation mechanics of alginate hydrogels while maintaining stability, enabling the design of highly compressible hydrogels.