Cell-laden hydrogel microspheres as functional 3D cellular units.

Engineering three-dimensional cellular systems with controlled size, matrix composition and cellular organization is central to disease modelling, drug evaluation and regenerative medicine. In this context, cell-laden hydrogel microspheres have emerged as a platform for constructing microscale living units. Their structure facilitates local cell-matrix interactions and cell-cell communication, while the hydrogel phase provides a tunable microenvironment for cell culture and function. Droplet microfluidics offers a powerful route to produce these microspheres with defined size, composition, architecture and cellular input, allowing fabrication parameters to be linked directly with biological outcomes. In this review, we focus on how droplet microfluidics, hydrogel matrix design and cellular organization converge to transform cell encapsulation into the construction of functional 3D cellular units. We outline the principles of microsphere fabrication, including droplet generation, gelation and post-generation recovery, and discuss how hydrogel matrices regulate processability, bioactivity and reproducibility. We then examine how cell loading, spatial architecture and organoid-centered organization determine microsphere function. Finally, we discuss applications in bioanalysis, drug testing, therapeutic delivery and tissue assembly, and highlight key challenges in cytocompatible processing, recovery, reproducibility, standardization and functional validation. This review aims to provide design principles for transforming cell encapsulation into interpretable and deployable microscale living systems.