Table 5.

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

Surface modification method		Substrate	Techniques and modified layer	Main layer structure	Layer thickness	In vitro corrosion rate (mm/y)			In vitro biocompatibility			In vivo Biocompatibility	Ref.
						Corrosion medium	Electrochemical test	Immersion test	Cell line	Cytocompatibility	Hemocompatibility
chemical method	Phosphate conversion coating	Pure Zn (99.99+%)	Immersing in 0.07 M Zn(NO3)2 and 0.15 M H3PO4 solution, pH 2-3	Zinc phosphate	5–6 μm	Hank's solution	0.004 ± 0.001		i. Murine calvarial pre-osteoblast (MC3T3-E1)	Improved cell adhesion, proliferation and differentiation	Both platelets adhesion and hemolysis tests showed good hemocompatibility with no sign of thrombogenicity		[136]
									ii. Human endothelial cell (EA.hy926)	Improved cell adhesion and proliferation
		Pure Zn (99.99%)	Immersion in the mix solution of 0.07 M Zn(NO3)2, 0.15 M H3PO4 and 1 g/L graphene oxide, pH 2.5	Graphene oxide (GO)-containing zinc phosphate	4.65 ± 0.45 μm	Hank's solution	0.0685 ± 0.003						[190]
	Organic and polymer coating	Pure Zn (99.99+%)	Dip-coating in the 1 mg/ml rat tail type I collagen solution for 20 min at room temperature	Rat tail type I collagen	2.5 μm	Hank's solution	0.085 ± 0.009		i. Murine calvarial pre-osteoblast (MC3T3-E1)	Improved cell proliferation and differentiation	Platelets activation on the surface with hemolysis rate below 5%		[136]
									ii. Human endothelial cell (EA.hy926)	Improved cell proliferation
	Biomimetic deposition	Zn-1.5Mg	Immersing in SBF for two weeks	Calcium phosphate		MEM cultivation medium with 5% fetal bovine serum		0.019 ± 0.011 (mg cm−2 day−1, with CO2 atmosphere); 0.004 ± 0.002 (mg cm−2 day−1, without CO2 atmosphere);	i. Murine fibroblast (L929)	Improved cell viability			[155]
									ii. Human osteosarcoma cell (U-2 OS)	Improved cell adhesion number with more spreading
		Zn–3Cu–1Mg	Immersing in Ca(H2PO4) ·H2O, sodium nitrate and hydrogen peroxide mixture solution for 1d at 20 °C	CaHPO4·2H2O					Bone marrow mesenchymal stem cell (BMSC)	Improved cell proliferation, osteogenic differentiation and calcium deposition			[191]
	Stabilization treatment	Zn–1Mg	Immersing in Dulbecco's Modified Eagle's Medium for 1 day under a humidified atmosphere with 5% CO2 at 37 °C	ZnO and Zn(OH)2					Murine mesenchymal stem cell (MSC)	Improved cell adhesion and proliferation			[192]
		Zn–1Mg-0.5Ca								Improved cell adhesion and proliferation
Electrochemical method	Microarc oxidation	Pure Zn (99.999%)	400 V, 3 min, electrolyte: 2.5 g/L sodium hydroxide and 0.02 mol/L calcium glycerophosphate hydrate dissolved in deionized water	Zn and amorphous Ca3(PO4)2	~25 μm	Hank's solution	1.361 ± 0.124		Human osteoblast-like cell (MG63 )	Decreased cell proliferation and improved cell adhesion.			[137]
Physical method	Atomic layer deposition	Zn-0.1Li	Tetrakis (dimethylamino) zirconium (TDMAZ) as Zr precursor (heated to 120 °C), deionized water as O precursor (heated to 35 °C), 500 deposition cycles	Amorphous ZrO2	~120 nm	Hank's solution	0.054 ± 0.014		Murine osteoblast precursor cell (MC3T3-E1)	Improved cell adhesion and proliferation		Improved in vivo osseointegration	[135]
	Magnetron sputtering	Pure Zn (≥99.995%)	Target: high purity C, chamber pressure: 8 mTorr, Ar flow rate: 20 sccm, direct-current power: 90 V, deposition time:60 min	Diamond-like carbon	~100 nm				Murine osteoblast precursor cell (MC3T3-E1)	Decreased cell proliferation	Hemolysis rate was below 5%		[193]
Mechanical method	Sandblasting	Pure Zn	Abrasive: Al2O3 (250 μm particle size), distance between jet and sample surface: 10 mm, pressure: 2 bar, time: 20 s			DMEM/F-12		~0.035	Human osteosarcoma cell (Saos-2)	Decreased cell proliferatiom			[194]