In Vitro And In Vivo Studies Of Novel CaP-Mg Bi-layer Coated Titanium

Objective: A novel of Calcium phosphate-Magnesium(Ca P-Mg)bi-layer coating was fabricated on the surface of titanium,the degradation behavior and antibacterial ability in vitro were studied,and osteogenesis of bi-layer coating in vivo was characterized.Method:1.A uniform calcium phosphate(Ca P)coating was firstly constructed on the pure titanium surface by alkali heat treatment combined with biomimetic method.The pure magnesium(Mg)coating was then deposited on its surface by physical vapor deposition(PVD).The surface morphology,thickness and composition of coatings were detected by scanning electron microscope(SEM)and X-ray diffraction(XRD).2.In vitro degradation of Ca P-Mg bi-layer coating was tested,the p H-time curve of different coatings and the curve of the amount of Mg ions releasing over time were studied.Scanning electron microscopy(SEM)and Energy dispersive X-ray spectroscopy(EDS)were applied to characterize the coating surface morphology,thickness and the elements composition changes after immersion for 3,7,14 days.3.In vitro degradation behavior and mechanism of coating was checked by electrochemical experiments.4.The antibacterial performance of the experimental group(Ca P-Mg bi-layer coating group),the control group(blank control group),the Ca P coating group,the pure magnesium coating group,and the pure titanium control group were evaluated by in vitro antibacterial test.5.The Ca P-Mg bi-layer coated titanium rods was implanted into the mandible of 12 New Zealand white rabbits,the CBCT detection,HE staining and Mason staining were performed in the first and the third month,and histological observation was conducted.Results:1.The SEM showed needle-like and plate-like morphologies of calcium phosphate(Ca P)coating.The grain size of the pure magnesium coating is about 10μm.Ca P-Mg bilayer coating surface morphology showed that the thickness of the outermost magnesium layer ranged from 50μm to 70μm.The interface between Mg and Ca P coating was in close contact.The connecting way of Ca P coating and the magnesium coating was mechanical setting.The results of XRD analysis showed that the surface of Ca P-Mg bi-layer coating samples only detected magnesium,and no other phase components were checked.2.In vitro immersion test showed that the p H value of magnesium coating and Ca P-Mg bi-layer coating increased quickly at the initial stage,and the p H value peaked at the third hour at11.3 and 11.8 respectively.After immersion for 1 day,the magnesium coating on the titanium matrix has been mostly cracked due to the electrochemical corrosion.the Ca PMg bi-layer coating did not peeled off after immersion for 3,7,14 days.This is because the Ca P coating inhibits the detachment of magnesium from the titanium substrate.And the p H value kept at around 10.3 for extending immersion time.Obtained results of the electrochemical experiment showed the corrosion rate of Ca P-Mg is higher than Mg coating.This is because the rougher surface of Ca P-Mg bi-layer coating which caused the faster degradation.4.In vitro antibacterial assays proved that Ca P-Mg coating strongly reduced the viability of S.aureus and performed an about 98% antibacterial efficacy(ABE)in 12 hours.5.CBCT detection,HE staining and Mason staining showed that Cap-Mg bilayer coating can effectively enhance osteoblast capacity and promote bone cell growth.Conclusion: 1.A novel Ca P-Mg bi-layer coating was fabricated using biomimetic method and physical vapor deposition technique.2.The Ca P-Mg bi-layer coating possessed strong antibacterial activity to S.aureus in vitro in the first three hours.3.In vivo osteosynthesis experiments showed that Ca P-Mg bi-layer coating had good osteogenic ability.