Preparation And Bacterial Inhibition Study Of Antimicrobial Coating On The Surface Of Biomedical Titanium Alloys

With the rapid development of biomaterial industry, biomaterial centered infections (BCI) has become a very knotty clinical problem.The main reason for BCI is the bacterial adhesion, proliferation and formation of bacterial biofilm on the biomaterials surface. Titanium alloys has become the preferred material for substitution or repairing human hard tissue including dental implants, bone trauma products, artificial joints because of its excellent biocompatibility, corrosion resistance, mechanical and processing properties, . However, metallic materials including titanium alloys are often sensitive to the adhesion of the bacteria, and more easily lead to bacterial infection. So, how to endow titanium implant materials antibacterial properties by surface modifications is a research focus in biomaterial field.The purpose of this study is to endow titanium alloys with anti-bacterial properties by loading anti-bacterial substances on titanium surface in order to reduce the adhesion, reproduction of bacteria,and prevent infection. The main research contents and conclusions of the study are as follows:(1) Vancomycin (VCM) was added to the solvent system of the biodegradable polylactic acid (PLA), and polylactic acid coating loaded vancomycin(PLA-VCM)was prepared onto titanium alloy surface by solvent casting method. Three different drug contents coatings (named as PLA-VCM5, PLA-VCM10, PLA-VCM15, respectively) were prepared by adding 5% ( mass ratio of VCM /PLA), 10% and 15% of VCM contents into the coating solution. By detecting the drug loading of each group, it was found that, VCM amount in the coating increased with the increase of VCM in the coating solution, but the increasing rate between them is not linear. In vitro drug release experiment showed that, VCM exhibited obvious two-phase release profile including burst release and sustained release period. The drug release time exceeded 15 days. The accumulative released amount added up to the minimum inhibitory concentration (MIC, 1.2 mg/l) of VCM against Staphylococcus aureus after 2 hours release.(2) Preliminary animal experiments were conducted with the extracted fluid of PLA-VCM10 Group samples. The experimental results of acute toxicity test, pyrogen test, hemolysis test and local irritation test all meet the requirement of biomaterials. (3) In vitro inhibition tests were conducted with PLA-VCM10 group samples. The results showed that the inhibition of samples on Staphylococcus aureus lasted for more than 15 days. Drug-loaded coating samples reduced the adhesion of bacteria as compared to the control with PLA coating without drug-loaded. Inhibition tests conducted with the eluent of samples showed that, the eluent can inhibit the growth and reproduction of Staphylococcus aureus.(4) Calcium phosphate coating was prepared onto the titanium alloy surface by the biomimetic method. The results of EDX, XRD and FTIR showed that the main component of the coating is Hydroxyapatite (HA). VCM amount in the coating increased with the increase of adding VCM into the coating solution, VCM contents of the coating became constant when the concentration of VCM exceeded 600 mg/L. So VCM should be co-precipitated with the Ca-P crystals onto titanium alloy plate.(5) In vitro release tests and osteoblast culture were conducted with the Ca-P-VCM samples prepared by adding VCM into the coating solution at a concentration of 600 mg/L. The results showed that VCM was sustained released from the coating samples more than 24 hours. Moreover, accumulative released concentration of VCM exceeded the minimum inhibitory concentration (MIC, 1.2mg/l) of VCM against Staphylococcus aureus from 2 hours beginning. VCM-loaded Ca-P coating samples and Ca-P coating samples both had obviously promotion on osteoblast attachment in early period (24 hours), but did not significantly affect the proliferation of osteoblast (2d to 8d).(6) In vitro inhibition tests of Ca-P-VCM samples showed that, the diameter of inhibition zone increased with the concentration of VCM in the coating solution from 100 mg/L to 600 mg/L, but the diameter of inhibition zone became constant and did hardly increase with the concentration of VCM in the coating solution from 600mg/l to 800 mg/l. The eluent of samples prepared by adding VCM (600mg/l) into the coating solution all had inhibitory effect on the growth of Staphylococcus aureus at a series of concentration of 102,103,104,105,106,107CFU. Moreover, the bacterial adhesion test shows that, the samples reduced the adhesion of bacteria compared to the control with Ca-P coating without VCM-loaded.(7) We explored the possibility of grafting antimicrobial peptide humanβ-defensin--3 (humanβ-defensin 3 hBD-3) onto titanium alloy. Preliminary studies showed that, antimicrobial peptide can be grafted onto titanium alloy, but its antibacterial activity is not significant. Further study is required in this aspect.