Table 6.

Summary of different surface modification methods of biodegradable Zn-based BMs for cardiovascular applications.

Surface modification method	Substrate	Techniques and modified layer	Main layer structure	Layer thickness	Efficiency of the coating	Ref.
Organic coating	Pure Zn (99.9%)	Immersing in MPS for 30 min followed by dip-coating in PLLA solution at room temperature.	PLLA	1–12 μm	Increased corrosion resistance in vitro and in vivo. Decreased cytocompatibility with signs of toxicity and active neointima.	[222]
	Pure Zn foil (99.9%)	Immersing in the 2 mg/ml dopamine solution for 12 h.	Polydopamine		Improved cell viability of human dermal fibroblasts, human aortic smooth muscle cells and human aortic endothelial cells.	[221]
	Pure Zn foil (99.9%)	Zn foils were incubated in the 2 mg/ml dopamine solution for 12 h. A 100 μm-thickness section of gelatin was produced, and affixed to the dopamine-coated Zn foil by bringing them into contact. Gelatin-covered foils were then immersed in 10 mM EDC in 90% ethanol for 20 min to cross-link the gelatin.	Polydopamine/gelatin		Improved cell viability of human dermal fibroblasts, human aortic smooth muscle cells and human aortic endothelial cells.	[221]
	Zn–1Mg	Zn–1Mg plates were immersed in 1 mol/L NaOH solution for 0.5 h at 60 °C. Then, they were immersed in 2 mL silane hydrolysate solution for 12 h at 37 °C. Next, the samples were immersed in 2 mL of 1 mol/L glutaraldehyde for 12 h at 37 °C. Finally, they were immersed in 2 mg/ml phosphorylcholine chitosan copolymer solution for 12 h.	APTES/phosphorylcholine chitosan copolymer		Increased corrosion resistance. Excellent hemocompatibility with hemolysis rate below 0.2%. Improved cell attachment and proliferation of human umbilical vein endothelial cells.	[225]
Air oxidation	Pure Zn wire (>99.99%)	350 °C for 1 and 2 h in a regular furnace in air.	ZnO	0.3–1.4 μm		[223]
Electropolishing	Pure Zn wire (>99.99%)	0.25 A/cm2, 10 V, 2 min, electrolyte: 885 ml ethanol, 100 ml butanol, 109 g AlCl3·6H2O, 250 g ZnCl2, 120 ml H2O.		0.06–0.08 (+0.05–0.15) μm		[223]
	Pure Zn (99.99%)	0.45 A, ~90s, electrolyte: 885 m L C2H5OH, 100 mL C4H9OH, 109 g AlCl3·6H2O , 250 g ZnCl2.			A 22% failure rate in vivo (2 out of 9 samples), with 44% of the observations meeting the full biocompatibility benchmarks.	[226]
Anodization	Pure Zn wire (>99.99%)	I. Electropolishing: 0.25 A/cm2, 10 V, 2 min, electrolyte: 885 ml ethanol, 100 ml butanol, 109 g AlCl3·6H2O, 250 g ZnCl2, 120 ml H2O. II. Anodization ~4 A, 10 V, 1 min, electrolyte: 1 L oxalic acid (0.1, 0.3 or 0.5 M) solution.	ZnO	5–10 μm		[223]
	Pure Zn (99.99%)	I. Electropolishing: 0.45 A, ~90s, electrolyte: 885 m L C2H5OH, 100 mL C4H9OH, 109 g AlCl3·6H2O, 250 g ZnCl2. II. Anodization: ~4 A, 1min, electrolyte: 0.5 M (COOH)2.			100% of the treated samples (9 out of 9) met the full biocompatibility benchmarks in vivo, leading to a failure rate of 0% (0 out of 9).	[226]
Microarc oxidation	Zn-0.1Mg	300 V, 120 s, electrolyte: 14 g/L Na2SiO3, 2 g/L KOH, 15 ml/L glycol and 10 ml/L glycerol.	ZnO and Zn2SiO4	28.6 ± 2 μm	Improved blood compatibility with decreased hemolysis rate, lower lytic activity against red blood cells and lower platelet adhesion. Improved adhesion and viability of human umbilical vein endothelial cells.	[224]