Multiscale design of core-shell GelMA-alginate composite microspheres enabling spatially compartmentalized co-culture of skin cells

Biomaterial-based hydrogels are widely used in skin regeneration as wound dressings and cell delivery vehicles owing to their biocompatibility and ability to mimic native skin microenvironments. However, most strategies rely on encapsulating a single cell type within homogeneous hydrogel matrices, which fail to recapitulate the fibroblast-keratinocyte crosstalk essential for wound healing. This limitation arises from the absence of spatial compartmentalization required to balance the disparate proliferation kinetics and functional roles of dermal fibroblasts and epidermal keratinocytes. Therefore, there is a need for platforms that enable spatially defined multicellular organization and controlled intercellular interactions. Herein, we report a multiscale-engineered core-shell gelatin methacryloyl (GelMA)-alginate composite microsphere platform fabricated via coaxial electrospray for spatially organized co-culture of fibroblasts and keratinocytes within compartmentalized microenvironments. By tuning GelMA molecular properties and electrospray parameters, monodisperse core-shell microspheres were fabricated to support robust compartmentalized cell encapsulation. At the microscale, controlled electrospraying, together with an ionically crosslinked alginate-reinforced shell, governs the core-shell geometry and structural integrity. The resulting microspheres exhibit high post-encapsulation viability, enable precise spatial compartmentalization of heterotypic cell populations and significantly enhanced early keratinocyte proliferation under co-culture conditions. Gradual microsphere degradation facilitates cell release and reorganization into confluent sheet-like assemblies in vitro , while high-yield fabrication demonstrates the scalability of the coaxial electrospray approach. Collectively, this work establishes spatial compartmentalization as a multiscale design principle for enabling spatially regulated heterotypic cell interactions, preventing fibroblast overgrowth and enabling modular, directly deployable multicellular platforms for spatially controlled skin cell delivery and tissue engineering.