Table 2.

Various OCCs with subsequent pre/post coating treatment details for biodegradable Mg alloys.

Coating	Bath Composition	pH	Temp, °C	Duration, mins	Adhesion strength (MPa)	Ecorr (V/SCE)		Icorr (A/cm2)		Corrosion rate (mm/year)	Pre/post treatment	Ref.
						Uncoated	Coated	Uncoated	Coated
PA-HA composite	0.70 wt % PA Soln, 35–50% (wt/wt) HA	4.5	40	20	–	−1.60	−1.41	40.20 × 10−6	2.28 × 10−6	–	–	[116]
PA-Ce(III) nanocomposite	5 mM PA, 20 mM CeCl3	–	–	3	5B	−1.46	−1.37	3.47 × 10−3	4.71 × 10−8	–	Coated sample treated in ethanol/HDMS (10μl/10 ml) solution for 6 h to obtain superhydrophobicity with contact angle (167.3°).	[117]
Vanillic acid	1.0 mmol/L Vanillic acid soln.	–	20	1440	–	−1.53	−1.40	56.9 × 10−6	0.58 × 10−6	–	Pre-treatment of uncoated substrate in 1 M NaOH for 24 h.	[110]
Vanillic acid	1.0 mmol/L Vanillic acid soln.	–	20	1440	–	−1.41	−1.25	–	–	–	Pre-treatment of uncoated substrate in NaOH for 1.5 h	[118]
PA-Stannic acid multilayer	2 g/L Ce(NO3)3, 10 ml/L H2O2) (Step-1)	6	40	20	–	−1.42	−1.28	1.81 × 10−4	2.12 × 10−7	–	MAO Pre-treatment in 10 g/L Na2SiO3, 3 g/L NaOH, and 10 ml/L triethanolamine.	[119]
	20 g/L Na2SnO3, 4 g/L NaF, 3 g/L NaOH (Step-2)	12.5	60	60						–
PA/Silane hybrid	PA and γ-APS Soln. with molar ratios (1:1, 1:2, 2:1), mixed with 40 ml EtOH/H2O soln.	8	20	30	–	−1.70	−1.61	49.41 × 10−6	3.95 × 10−6	–	Pre-treatment of uncoated substrate in 3 M NaOH at 80 °C for 24 h	[120]
CaP/Collagen	23.6 g/L Ca(NO3)2·4H2O, 34.2 ml/L H3PO4, 7 mg/ml Col-I Soln prepared in 0.005 acetic acid.	2.8	37	10	–	−1.47	−1.23	27 × 10−6	87 × 10−8	–	Post treatment of Ca–P converted sample by dipping in Col soln. for 15 min.	[121]
HA/Tannic acid	0.05 g Na3PO4, 0.25 g Na2B7O4, 0.04 g C76H52O46, 0.05 g NH4VO3, 0.055 g K2ZrF6, and 0.02 g HNO3 in 50 ml DI H2O (Step-1)	4	37	540	–	−1.46	−1.30	4.89 × 10−6	5.64 × 10−8	–	Pre-treatment of uncoated substrate in 1 M NaOH for 24 h followed by heating at 150 °C for 24 h.	[122]
	14 mmol/L Ca(NO3)2, 8.4 mmol/L NaH2PO4, 4 mmol/L NaHCO3 (Step-2)	–	37	2880						–
MgF-Tannic acid	40% HF (v/v) soln., TA was dissolved in 2 mg/mL Tris–HCl soln to obtain 2 mg/mL final conc.	10	25	1440 (HF)	–	–	–	–	0.24 × 10−6	–	Pre-treatment of uncoated substrate in 5 M in boiled NaOH for 3 h	[123]
				180 (Ta)
Chitosan-Tannic acid	Chitosan (Mw 1.8 × 106) and tannic acid (Mw 1701.2 g/mol) were dissolved (50:50, 50:80) in 0.1 M acetic acid with 2% conc.	–	–	–	σmax (UTS) of coating after 0, 24 and 48 h of immersion in PBS was 3.5, 7.5 and 5.5 MPa	–	–	–	–	–	To analyse tannic acid release profile coated sample immersed in SBF (pH 7.4), SGF (pH 1.2), SIF (pH 6.8) and found suitable for pH around 7.	[124]
Chitosan (CHI)/Bioactive glass(BG)	1.5–6.0 g/L CHI soln. in 1% vol acetic acid, 6 g/L BG	3.31–3.62	75	15–120	–	–	–	–	–	–	–	[125]
Gallic acid (GA)- hexamethylenediamine (HD)	GA and HD were mixed (wt % 1:3, 1:1 and 2:1)	–	37	360	–	−1.59	−1.61	54.0 × 10−5	8.0 × 10−7	–	An in-situ MgO/Mg(OH)2 layer chelated beneath coating layers, obtained from 1:1 and 2:1 bath soln.	[126]
Catechol (CA)/polyethyleneimine (PEI)	2 mg/ml CA, 4 mg/ml PEI	8.5	22	720	5B	−1.59	−1.37	Log (−4.19)	Log (−7.34)	0.01	Heparinization treatment was given to coated samples by immersion in 4 mg/ml Heparin dissolved in water-soluble carbodiimide and a mixed solution of 1 mg/ml 1-ethyl-3-(3-(dimethylamino)propyl) carbodiimide hydrochloride (EDC) and 9.8 mg/ml 2- morpholino ethanesulfonic acid (MES).	[127]
Epigallocatechin gallate (EGCG)/polyethyleneimine (PEI) multilayer	1 mg/ml EGCG and 1 mg/ml PEI Soln in Tris-buffer.	7.4	37	30	5B	−1.33	−1.25	Log (−4.46)	Log (−6.65)	0.05	–	[128]
CaF2- Stearic acid (SA)	Saturated Ca(OH)2 and 0.05 M/L SA ethanol soln.	–	70	240	5B	−1.57	−1.10	4.25 × 10−6	4.13 × 10−8	0.94	Pre-treatment in 40 wt% HF soln. for 5 days	[109]
MnO2 – Stearic acid (SA)	0.1 M MnSO4, 0.02 M SA in ethanol soln.	–	22	240 (MnO2)	5B	−1.61*	−1.32*	*6.84 × 10−7	2.70 × 10−8	–	Pre-treatment in 0.01 M MnSO4 soln. for 1 h.	[129]
				300 (SA)