Table 1.

List of recent progress of 3D bioprinting for cardiac tissue engineering.

Bioprinting method	Printer hardware	Bioink hydrogel	Bioink cell	Bioink cofactor	Application condition	Outcome of the effect	Reference
Inkjet-based 3D bioprinting	One-head operation	Fbronectin & gelatin	hiPS-CM & fibroblast	dECM	Following the 3D-engineered cardiac muscle fiber unit, co-culture with human cardiac microvascular endothelial cell (HMVEC) was then utilized for tests on functional properties in vitro.	Vascularization and contractility of the fabricated unit can be simultaneously possessed.	[69]
	Needle-arrayed system	None	Sphere-like cell population composed of human iPSC-derived CM, fibroblast and umbilical vein endothelial cell (HUVEC)	Wnt signaling activator	The direct-write bioprinted cardiac patch was cultured in vitro with shaking for 72 h to obtain synchronized beating function, followed by being implanted to the infarcted area with pull-up omentum as a fixture of nude mice.	Compared with the control group, the infarct area in the myocardial infarction area decreased, while its angiogenesis and cardiac ejection fraction increased.	[73]
Extrusion-based 3D bioprinting	One-headed operation	GelMA, fibronectin, laminin-111, & collagen methacrylate (MeCol)	hiPSC	None	iPSC was first printed and proliferated, and was subsequently differentiated into cardiomyocyte for testing long-term viability and function in vitro.	The heart organoid built sequentially could be endowed with contractility and pump functions.	[90]
	Two-headed operation	Polyvinyl alcohol (PVA), agarose & alginate	H9c2 & HUVEC	Platelet-rich plasma	Heart-shaped PVA scaffold was first printed, followed by cell-hydrogel 3D bioprinting along the structure, so as to check heart-oriented biological properties in vitro.	Complex functional heart might be well engineered by an appropriate cell-hydrogel ratio.	[68]
		Fibrin	iPS-CM	None	The cell ink was firstly printed as a path, which the structural ink closely followed, so as to engineered a 3D cardiac chip for in vitro biological evaluation.	The engineered body showed excellent myocardial tissue-like functions.	[148]
		Gelatin	hiPS-CM & endothelial cell (EC)	Decellularized porcine omentum	A complete, thick vascularized cardiac patch and heart were printed of in one step, and were tested in vitro.	The realistic heart-like active structure with vascularization presented human affinity and could potentially be suitable for future clinical use.	[117]
		Collagen composited freeform reversible embedding of suspended hydrogels (FRESH)	Human CM and EC	Vascular endothelial growth factor (VEGF)	The highly simulated heart model with its own vascularization system was 3D bioprinted, and was tested in vitro.	In addition to the retractable heart, FRESH v2.0 system might engineer many other complex tissue scaffolds.	[102]
	Three-headed operation	Fibrinogen, gelatin, aprotinin, glycerol, hyaluronic acid, sacrificial hydrogel, & polycaprolactone (PCL)	Primary CM from rat ventricular	None	Cell-laden hydrogel, sacrificial hydrogel, and PCL polymer were 3D bioprinted in order to produce an engineered cardiac patch for testing of electrophysiology and biomechanics in vitro, especially the Notch signaling pathway.	Micro-sensing and controlling of the printed cardiomyocyte might be necessary for the creation of functional heart tissues, and Notch inhibitor can improve the maturity level.	[87]
	Multi-headed operation	Type-1 atelo-collagen, & polyethylene-vinyl acetate (PEVA)	Cardiomyocyte (CM) of left ventricle of neonatal rat	Porcine left ventricular dECM	Living cells were added after scaffold formation in vitro.	Cardiomyocyte behaved differently in respond to bioink composition and culture conditions.	[70]
		GelMA & fibronectin	CM & cardiac fibroblast	None	Mechanical force and biological activity were quantified to clarify how the printing process affected the two main types of heart cells in vitro after the heart cross-sectional shape was printed.	Adding extra molecules, using two-cell bio-ink, and lowering the concentration of GelMA might improve cell survival and network formation.	[89]
		Alginate & PEG-Fibrinogen (PF)	Mice iPS-CM & HUVEC	None	The scaffold and cells are printed one after another, and then the organizations were evaluated both in vitro and in vivo.	The transplanted engineered tissue can merge well with the host's heart by vasculature.	[71]
	Visible lihgt-assisted system	GelMA	Neonatal human cardiac progenitor cell	Cardiac dECM	The myocardial patch was subjected to in vitro biological testing and transplanted into the heart of healthy rats to evaluate the effect in vivo.	The patches attached effectively to rat hearts for 14 d and showed microangiogenesis.	[84]
		Fibrin & furfuryl-gelatin	iPS-CM & cardiac fibroblast	None	3D herringbone construct was printed for identifying the bioink feasibility of combination of cardiomyocyte and cardiac fibroblast in Vitro.	Connexin-43 might be important for the communications between cardiomyocyte and cardiac fibroblast in 3D-engineered tissue.	[119]
	Rapid digital light processing (DLP)-based 3D bioprinting	GelMA	Human iPSC-derived CM (hiPSC-CM)	Porcine left ventricular dECM	After the cells are mixed with the hydrogel, the stripe-like micro-structure is printed and cultured in vitro.	A myocardial microstructure with complex geometry was produced in just a few seconds, and its controllable resolution was as fine as 30 μm.	[85]
UV-assisted 3D bioprinting	One-headed operation	GelMA & methacrylated hyaluronic acid (HAMA)	Valvular interstitial cell	None	The 3D layered structure of heart valve tissue were reproduced for the test of mechanical properties and biomechanics in vitro.	The nature and patient delicate hierarchical structure of heart valve tissues can be engineered.	[88]
		GelMA	Human embryonic stem cell-derived CM	Green Fluorescent Protein/Calmodulin/M13 Peptide (GCaMP 3)	The block-patterned multicellular cardiac element was rapidly created and long-term cultured for the valuation of calcium transients and mechanical forces in vitro.	Connexin-43 might serve as another critical bio-marker of electrical signal transmission for quality control of bioprinted myocrdium.	[86]
	Two-headed operation	Alginate, MeCol, & arboxyl functionalized carbon nanotubes (CNTs)	Human coronary artery endothelial cell (HCAEC)	None	Alginate (with or without CNTs) was printed as a net-like scaffold, and the MeCol filled with cells was then printed alongside to yield cytological features.	Proliferation, differentiation, and lumen-like organization of HCAEC got short-term improved by the additive CNTs in vitro.	[67]
	Sequential	None	Cardiac progenitor derived from hiPSC	Wnt signaling activator	Functional pacemaker-like tissue was created in a hydrogel-free manner, and cardiac gene expression was tested in vitro.	Wnt5b activated a conserved canonical Wnt signaling pathway to guide the differentiation of Nkx2.5+ cardiac progenitors into primary pacemakers.	[72]