Titanium (Ti)-based implants are one of the most commonly used materials in orthopedic surgery. Although Ti-based implants have good biomechanical properties and biocompatibility, their non-antibacterial shortcomings lead to orthopedic implant-related infections that seriously affect the effect of surgery and postoperative recovery. and serious cases need a second operation and increase the pain and cost of patients. Some studies reported metal or antibiotic antibacterial coatings on Ti-based implants, but they have some disadvantages (i.e., heavy metal coatings can cause damage to the human body, and excessive use of antibiotic coatings can lead to drug resistance). It is thus necessary to investigate the preparation of coatings with good antibacterial properties and biological activities on the surface of Ti-based implants, so as to provide an effective solution to the problem of bone implant-related infection in clinic. Magnesium (Mg) is a major element in human body. Some studies reported that Mg and its compounds have good antibacterial and biocompatibility.

Ti sheets were cleaned and immersed in an electrolyte containing sodium chloride and magnesium chloride (pH=9.5) and applied a DC voltage of 3.0 V for 0-12 h to obtain magnesium hydroxide [Mg(OH)₂] coatings. After deposition, Mg(OH)₂ coatings were calcined in a muffle furnace at a heating rate of 2 ℃/min at 650 ℃ for 6 h to obtain magnesium oxide (MgO) coatings. The phases of each group of samples were analyzed by X-ray diffraction (XRD), the surface morphology was analyzed by scanning electron microscopy (SEM) and the composition of surface elements was analyzed by energy dispersive spectroscopy (EDS). The in-vitro antibacterial properties of the samples were evaluated according to the standard ISO22196—2011. The bacterial liquid was resuscitated, diluting it to 1 × 10⁵ cfu/mL (cfu is colony-forming units). The samples were firstly sterilized by drying, then 300 μL bacterial solution (i.e., Staphylococcus aureus and Escherichia coli) was then dropped onto each sample and incubated in a constant temperature incubator (at 37 ℃) for 24 h. After diluting the coating plate, the colony number was analyzed and converted to antibacterial rate. The in-vitro cytotoxicity of each sample was evaluated according to the standard ISO10993.5. After dry heat sterilization, the samples were placed in a 24-well plate (no sample cell suspension in the control group and complete culture medium in the blank group). 1mL mouse osteoblast suspensions (OB-6; 5 000 cell/mL) were dropped onto each sample and then incubated in a cell culture box (5% CO₂ at 37 ℃) for 1 d, 3 d or 5 d. After the completion of culture, the absorbance value was detected by a method named CCK-8 and converted to a cell survival rate.

Mg(OH)₂ coating was prepared on titanium surface by an electrochemical deposition method, and MgO coating was obtained after calcination. Granular matter [Mg(OH)₂ and MgO] are uniformly distributed on the surface of each group, and the particle density and coverage rate increase with deposition time. Mg(OH)₂ and MgO coatings all have a good antibacterial activity against Staphylococcus aureus and Escherichia coli. The antibacterial rates increase with deposition time. When deposited for≤3 h, the antibacterial rate of MgO is higher than that of Mg(OH)₂. After deposited for ≥6 h, the bacteriostatic rate of both is close to 100%. The cytotoxicity of Mg(OH)₂ and MgO coatings increases with the deposition time, and the toxicity of the two groups (i.e., deposited for 0.5 h and 1.0 h) decreases with the culture time, and the toxicity of the other three groups (i.e., deposited for 3 h, 6 h and 12 h) increases with the culture time. At 5 d, the survival rates of Mg(OH)₂ and MgO samples deposited for 0.5 h are 152% and 90%, and the survival rates of the two groups of samples deposited for 12 h are 2% and 6%, respectively.

The surface morphology and thickness of Mg(OH)₂ and MgO coatings changed with the deposition time. The cytotoxicity and antibacterial rate of the coatings were enhanced with the deposition time. It was speculated that there was a dose-effect relationship between them and the coating. The results showed that Mg(OH)₂ coating could be prepared by electrochemical deposition, and the MgO coating could be obtained after calcination. Mg(OH)₂ and MgO coatings deposited for 1 h had good comprehensive properties.