Phenol-grafted Aphanothece sacrum polysaccharide hydrogels with intrinsic angiogenic activity and enhanced in vivo...

Sulfated polysaccharides are attractive biomaterials owing to their biocompatibility and strong affinity for cells and growth factors. Aphanothece sacrum polysaccharide (ASP), a supergiant sulfated polysaccharide, exhibits excellent hydration as well as anti-inflammatory and antioxidant properties. However, its ability to form hydrogels under mild, cell-compatible conditions remains limited. In this study, we developed phenol-grafted ASP (ASP-Ph), which undergoes enzymatic crosslinking via horseradish peroxidase (HRP) in the presence of hydrogen peroxide (H₂O₂) to form stable hydrogels directly from aqueous solutions. Increasing the phenol content reduced solution viscosity, accelerated gelation, and enhanced hydrogel mechanical strength. ASP-Ph hydrogels strongly retained fibroblast growth factor-2 (FGF-2) via electrostatic interactions with sulfate groups, enabling sustained release while maintaining bioactivity. The hydrogels supported fibroblast viability at levels comparable to standard tissue-culture substrates. Notably, in a chick embryo chorioallantoic membrane assay, ASP-Ph hydrogels induced more pronounced angiogenesis than hyaluronic acid-based hydrogels, even without FGF-2, demonstrating intrinsic angiogenic activity. Subcutaneous implantation in mice further confirmed excellent biocompatibility and enhanced vascularization. Collectively, these results identify ASP-Ph hydrogels as promising sulfated biomaterials for localized growth factor delivery and angiogenesis-driven tissue regeneration.