Microalgae-Derived Extracellular Vesicle-Loaded 3D Alginate Hydrogels Promote In Vitro Skin and Bone Repair through Dual Fibroblast and Mesenchymal Stem Cell Modulation

Chronic skin wounds with underlying bone exposure represent a major clinical challenge, characterized by impaired healing and limited tissue regeneration. Sustainable, biologically active biomaterials capable of addressing both cutaneous and bone repair remain highly desirable. Here, we developed three-dimensional (3D) printed sodium alginate (SA) and alginate/hydroxyapatite (SA/HAP) hydrogels incorporating microalgae-derived extracellular vesicles (MdEVs) obtained from<i>Ettlia oleoabundans</i>. The constructs were characterized for their mechanical, structural, and biological properties, and evaluated in vitro using human dermal fibroblasts (hDFs) and mesenchymal stem cells (hMSCs). The printed hydrogels exhibited a well-defined architecture, mechanical stability, and high biocompatibility. Notably, the same bioactive agent, MdEVs, elicited distinct cell-type-specific regenerative programs depending on the material niche in which it was presented. MdEV-loaded SA scaffolds enhanced cell viability and activated AKT/mTOR signaling and extracellular matrix (ECM)-remodeling pathways in hDFs, supporting cutaneous repair. In contrast, MdEV-loaded SA/HAP scaffolds stimulated pro-angiogenic and osteoinductive gene expression in hMSCs, indicative of bone-regenerative potential. This differential bioactivity underscores the sophistication of the platform beyond simply promoting repair, demonstrating how material composition can direct context-dependent cellular responses by using a single, sustainable biological cue. Overall, this in vitro study demonstrates that MdEV-enriched alginate-based scaffolds can differentially guide fibroblast and stem cell responses relevant to skin and bone regeneration. These findings highlight the potential of algae-derived extracellular vesicles as versatile bioactive components in next-generation regenerative biomaterials for complex wounds involving multiple tissue types.