A bioengineering approach to guide non-integrated stem cell-derived embryo model towards yolk sac development and hematopoiesis

Combining stem cell-derived multi-tissue constructs, such as non-integrated embryo models, with bioengineering technologies provide scalable tools for tissue engineering and drug testing. Here, we show the controlled initiation of organogenesis in XEn/EpiCs, a partial chemically-controllable mouse embryo model emulating aspects of E5.5 stage embryo, within milliwells. XEn/EpiCs spontaneously progress to develop a fluid-filled cavity, resembling a yolk sac encasing an embryonic compartment. Locally restricted inner regions of yolk sac-like (YS+) structures undergo cardiogenesis, displaying spontaneous contractions, and outer regions initiate vasculogenesis. Some vascularized YS+ structures develop blood islands composed of primitive erythrocytes, endothelial cells and mesenchyme. Further, we developed a continuous single-step culture using thermoformed milliwell platforms, enabling live tracking, pathway modulation, and in situ visualization of XEn/EpiCs towards organogenesis. Collectively, we demonstrate a multi-tissue vascularized embryo model devoid of trophoblast cells and external stimuli, capable of undergoing post-implantation morphogenesis and amenable to modulation within micro-engineered platforms for diverse applications.