Three dimensional co-cultures in Janus-like hydrogel microcapsules

Most natural tissues, including bone, consist of multi-cellular systems of two or more cell types, which interact with each other to maintain homeostasis. Moreover, tissue regeneration involves the straight coordination and organization of different populations of cells. The design of co-cultures that serve as a mimic of in vivo tissue niche in terms of local biophysical and humoral cues, cell ratio and inductive microenvironment has been of major importance to reach improved tissue engineering approaches. This is also true for bone tissue engineering in which osteoblastic and endothelial cells crosstalk are critical.

In this work, we aimed at developing three dimensional co-culture systems in hydrogel microcapsules for human adipose stem cells (hASCs) derived-osteoblasts and human Umbilical Vein Endothelial Cells (HUVECs) using droplet-based microfluidics co-flow system. We hypothesized that such compartmentalized systems could be used as a prototype in the high-throughput screening of cell-biomaterials interactions. The microfluidics droplet generator chip comprised two parallel streams of precursor polymers (methacrylated-gellan gum and collagen in which cells were resuspended), that were then co-emulsified into a continuous phase at a junction while maintaining two distinct domains. Monodisperse droplets were formed and cross-linked in a calcium chloride solution to form microcapsules with two separate compartments (Janus-like microcapsules) amenable to co-encapsulate the two different cell types. The generated microcapsules-based co-culture system was optimized regarding the cell number, cell ratio and culture media specific for concomitant maintenance of the two cell types. Segregated co-culture and mixed co-culture within microcapsule permitted to assess the indirect and direct effects of co-culture, respectively.