Fig. 2.

Challenges of existing hPDBOs: 1. Limited reproducibility: attempt to develop homogenous hPDBOs by introducing new biomaterials or combining with microfabrication techniques; 2. Lack of vascular system: different attempts to realize organoid vascularization, including hPDBOs co-culture with endothelial cells, or co-differentiation with VEGF administration or co-overexpression with hETV2; 3. Deficiency of immune responses: attempt to develop microglia-containing brain organoids by co-culture of hPDBOs with microglial cells