Table 1.

Approaches in the establishment of 3D brain organoids

Approaches	Organoid type	Tissue structure	PROS	CONS	References
Xenotransplantation	Forebrain	Axonal projections, synaptogenesis mapping	Long-term culturing	Lack of vascular bed	Mansour et al., 2018 [6], Cakir, B. et al., 2019 [7], Wang, Z et al., 2020 [8]
Air–liquid interface-cerebral organoids (ALI-COs)	Whole brain organoid	Axonal tracts	Proper neural tract formation, long-term culturing	Devoid of vascularity	Giandomenico et al., 2019 [9]
Miniaturized spinning bioreactors	Forebrain, midbrain and hypothalamus	Defined oSVZ, and human oRGC-like NPCs, hypothalamic neurons	Patterning into different brain-like subregions, smaller volume of medium required, high reproducibility	Expensive for mass production and lacks vascularization	Qian, X et al., 2018 [10], Romero-Morales et al., 2019 [11]
Assembloids	Dorsal and ventral forebrain	Dorsal-ventral axis	Robust directional GABAergic interneuron migration, rough organization into cortical layers	Lack of output and input systems	Bagley et al., 2017 [3], Xiang, Y et al., 2019 [12]
Bioengineered scaffolds	Forebrain	Polarized cortical plate and radial units	Enhance tissue identity and architecture, and establish organoid models for teratogenic compounds Generation of patients’ specific disease-relevant cell types	Poor spatial orientation	Lancaster et al., 2016 [13], Sood et al., 2019 [14], Zafeiriou, et al., 2020 [15]