Hydrogel-Forming Ability and Characterization of Exopolysaccharide (EPS) from Porphyridium cruentum for Wound Healing Applications

Marine exopolysaccharides (EPS) are emerging as sustainable bioactive polymers for biomedical hydrogels. Here, we report hydrogels from sulfated EPS produced by Porphyridium cruentum and ionically crosslinked with Ca²⁺, Ce³⁺, or Cu²⁺ to generate tunable networks for wound-healing applications. Rheological analysis showed that viscoelastic behavior was primarily governed by cation nature and accessible binding-site density, with diminishing gains above 2.5 wt% EPS and limited benefit beyond 10 wt% crosslinker. Ce³⁺ produced the most solid-like gel, Ca²⁺ yielded more thixotropic networks, and Cu²⁺ promoted rapid, heterogeneous crosslinking consistent with fast surface complexation. These network signatures translated into distinct in vitro performances. Cation selection tuned antibacterial activity against Staphylococcus aureus and Escherichia coli, with Cu²⁺ achieving rapid bactericidal effects and Ce³⁺ enabling an 8-log reduction after 24 h. Antioxidant capacity was assay-dependent (ABTS vs DPPH), reflecting combined EPS radical-quenching and metal-associated redox contributions. Conditioned-media assays using human dermal fibroblasts and keratinocytes indicated the most favorable cytocompatibility balance for Ce³⁺-crosslinked gels, whereas Cu²⁺ gels were limited by cytotoxicity. Macrophage cytokine readouts (TNF-α, IL-6) further supported formulation-dependent immunobiological activity. This work establishes microalgal EPS as a versatile polymer platform and links ionic crosslinking chemistry to rheological control and multifunctional biomedical performance.