While 3D organoids provide highly promising tools for iPSC-based disease modeling, the organoid technology has limitations. One challenge is to create an organoid platform with increased efficiency and reproducibility as compared to traditional two dimensional cultures115. The recent application of miniaturized spinning bioreactors with 3D design has allowed the generation of forebrain organoids with high reproducibility110. The development of more standardized organoid culture medium, together with a more defined extracellular matrix, would further facilitate the generation of a highly reproducible organoid system that is more applicable for accurate disease modeling, drug discovery, and therapeutic development116. Another challenge is the lack of vascularization in the current organoid system97. Accordingly, organoids exhibit limited growth and maturation due to the lack of continuous nutrient supply. Spinning bioreactors and shaking culture platforms have been shown to provide better nutrient supply and improve the growth of organoids110,117. Co-culture with endothelial cells has allowed generation of vascular-like network in organoids99. Moreover, transplantation of in vitro generated human organoids into relevant sites of animal hosts facilitates vascularization and maturation of organoids. This transplantation approach may be applied when organoids with increased size and improved maturation are needed for the study.
