Table 1.

Some representative microtissues in heart-on-a-chip

Features	Fabrication methods	Cells	Materials	Functionalities
Patterned microtissues	Soft lithography[22,27] Microcontact printing[22-25] Electrospinning[44] 3D bioprinting[28]	HUVECs[22] Rat CMs[24,25,2828] Fibroblasts[24]	PAAm[22] Collagen[24] GelMA[28] MeTro[25]	To study the influence of stiffness on cell morphology[22] To promote the attachment, spreading, alignment, and intercellular communication[24,25,28]
Vascularized microtissues	3D bioprinting[30,34,100] Photocuring[32] Lithography[34]	HUVECs[30,34,98] iPSC-CMs[30] Rat CMs[32]	Alginate[30] GelMA[30,98] PEGDA[98], hydroxybutyl chitosan (HBC)[34]	To align cardiomyocytes that can contract synchronously[30,32]
Microtissues with multiple cells	3D bioprinting[31,33]	NIH/3T3[33], C2C12[33] iPSC-CMs[29,31] Endothelial cells[29]	GelMA[31,33] Alginate[31] Gelatin, Fibrinogen[29]	Biomimetic heterogeneous tissues[31,33] Multiple-organs-on-a-chip[29]