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 fromEttlia oleoabundans. 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.