Research On Biological Properties Of A Novel Cu-Bearing Stainless Steel

It is generally known that stainless steel(SS) has low in cost, acceptable biocompatibility, combined mechanical properties, mechanical processing property and anti-corrosion property. Nowadays, stainless steel has been intensively applied in the domains of oral surgery, orthopaedics, surgical instruments, biology, and medical equipment, etc. Nevertheless, traditional medical stainless steel just plays a function of mechanical support but cannot avoid the bacterial infection after implantation. The corresponding inflammatory reaction persistent repeated attack, and is hard to be eliminated completely. Aiming at implant infection, antibacterial SS with good biocompatibility have been developed without sacrificing its existing materials performances. According to this conception, this work demonstrated that 317L-Cu stainless steel(SS), created by adding copper through a special solution and aging heat treatment process, belongs to a novel 317L-Cu antibacterial SS.In this work, a novel 317L-Cu SS was designed and fabricated. Firstly, materials characterizations were performed to evaluate the change of material and surface capability; Secondly, antibacterial capability was evaluated through the use of a combination of different biology methods; Thirdly, biocompatibility was evaluated through the combined usage of biology means; At last the antibacterial mechanism of 317L-Cu SS was explored preliminarily, and its potential application prospect in clinical medicine and daily life areas was assessed.The main content and results are as follows:(1) Synthesizes the previous achievements by our team and commercial cost, the copper addition should be controlled about 4.5wt.%. The scanning electron microscope, energy spectrum, hardness measurement, contact angle, surface free energy, metallographic observation and corrosion test were performed to characterize materials. The results showed that there were slightly change after the addition of copper, and both surfaces of two SS belonged to hydrophilic. Electrochemical test showed that the pitting potential of 317 L and 317L-Cu were 508.5 m V and 463.5 m V, respectively. Obviously, the data obtained from this part of work meet the requirement of follow-up studies.(2) The JIS Z2801:2000 standard is the most popular method at present, but this method cannot detecte the VBNC bacterials which could threaten the body after a recovery. Aiming at this shortage, this study extends the appraisal of antibacterial performance. And the plate count method, Live/Dead staining and q PCR were performed to evaluate the antibacterial capability of 317L-Cu SS at the cell viability, cell membrane and gene levels, respectively. The results showed that the antibacterial rate based on the reduction of sessile cell count reached 98.3% after 24-hour treatment, and sterilization performance were reflected over 3 days of incubation. The SEM images showed that plasmalemma invagination and inclusion leaks occurred in S. aureus cells. Besides, this chapter content provides medical material, articularly implant materials with rich science data and helpful advices for the optimization of antibacterial properties valuation.(3) In consideration of the Cu2+ highly potential toxicological effects, the hemocompatibility, cytocompatibility and zebrafish(Danio rerio) model were performed to evaluate the biocompatibility of 317L-Cu SS. The MTT assay result was accorded with the RTCA analysis, indicated that both 317 L and 317L-Cu SS had no negative effect on MC3T3-E1 proliferation, and 317L-Cu SS even facilitated MC3T3-E1 proliferation. Hemocompatibility assay indicated that this two kinds SS didn’t cause hemolysis(hemolysis ratio: 0.61 ± 0.07% and 0.72 ± 0.13%, respectively). As we known, zebrafish as an animal model has achieved attracting results in the drug screening. For the first time, we applied zebrafish as a whole animal model to the in vivo toxicity of 317 L and 317L-Cu SS. Results showed that both 317 L and 317L-Cu SS exhibited no cytotoxicity against zebrafish embryos.(4) The EPS formed on 317 L SS(control) and the 317L-Cu SS were analyzed using FTIR, and the coupon surfaces after incubation with S. aureus were analyzed using XPS. Then the damage processes in S. aureus cytomembrane and inclusion caused by 317L-Cu SS were investigated through the Live/Dead cell staining method and TEM. After that, the antibacterial mechanism of 317L-Cu SS was revealed: Both S. aureus cytomembrane and inclusion were damaged by Cu2+, which led to the escape of inclusion and the inhibition of biofilms; 317L-Cu SS didn’t seem to have a serious impact on the bacterial genome, because the integrity of genome DNA of S. aureus incubated with 317L-Cu SS was excellent. Finally, a reasonable explanation to the seemingly paradoxical facts between strong antibacterial effects and good cytocompatibility for 317L-Cu SS was provided: the different structure and composition between bacteria and cells, as well as the Cu2+ tolerance ability.In conclusion, 317L-Cu SS exhibited good corrosion resistance, biocompatibility and antibacterial function without sacrificing intrinsic performance, which make it has huge potential to be a bio- functionalization materials applied in the daily life and even clinical field.