Study on β-TCP Coated Porous Mg as a Bone Tissue Engineering Scaffold Material

Three-dimensional honeycomb-structured magnesium （Mg） scaffolds with interconnected pores of accurately controlled pore size and porosity were fabricated by laser perforation technique. Biodegradable and bioactiveβ- tricalcium phosphate （β-TCP） coatings were prepared on and the biodegradation mechanism was simply evaluated the porous Mg to further improve its biocompatibility, in vitro. It was found that the mechanical properties of this type of porous Mg significantly depended on its porosity. Elastic modulus and compressive strength similar to human bones could be obtained for the porous Mg with porosity of 42.6%-51%. It was observed that the human osteosarcoma cells （UMR106） were well adhered and proliferated on the surface of the β- TCP coated porous Mg, which indicates that theβ-TCP coated porous Mg is promising to be a bone tissue engineering scaffold material.

Fluoride Conversion Coating on Biodegradable AZ31B Magnesium Alloy

A fluoride conversion coating was successfully prepared on AZ31B magnesium alloy by chemical reaction in hydrofluoric acid. Morphologies, composition, bonding strength, corrosion properties, in vitro cytotoxicity and antibacterial properties of the coating were investigated, respectively. The scanning electron microscopy observations revealed a dense coating with some irregular pores. The thin-film X-ray diffraction analysis indicated that the coating was mainly composed of MgO and MgF2. The electrochemical impedance spectroscopy results showed that the fluoride conversion coating significantly improved the corrosion resistance of AZ31B. The hydroxyapatite formed on the surface of the fluoride coated AZ31 B after being immersed in the simulated blood plasma indicated the good bioactivity of the material. The in vitro cytotoxicity test showed that the fluoride coated AZ31B alloy was not toxic to BMMSCs （human bone marrow-derived mesenchymal stem cells）. It was also found that the fluoride coated AZ31 B alloy had antibacterial capability.

In vitro Study on a New High Nitrogen Nickel-free Austenitic Stainless Steel for Coronary Stents

Most commercialized coronary stents are made of 316L stainless steels due to its good combination of properties, and currently some new stents are made of cobalt-based alloy owing to its higher mechanical properties. However, the presence of high quantity of nickel and/or cobalt elements in these materials, which are known to trigger the toxic and allergic responses, has caused many concerns. Nickel-free austenitic stainless steels have been developed in order to solve these problems. In this paper, based on the development of a new Fe- Cr-Mn-Mo-N type high nitrogen nickel-free austenitic stainless steel, properties such as mechanical property, corrosion resistance in Hankls solution, and in vitro blood compatibility including the kinetic clotting time and the platelets adhesion, were investigated in comparison to the above two conventional materials, a 316L stainless steel and a Co-28Cr-6Mo alloy. The results showed that the new high nitrogen steel possessed better combination of mechanical properties, corrosion resistance and blood compatibility than those of 316L steel and the Co-28Cr-OMo alloy, and can be a promising alternative material for manufacture of coronary stents.

Fabrication and Characterization of Ca-Mg-P Containing Coating on Pure Magnesium

A biodegradable Ca-P coating mainly consisting of β-tricalcium phosphate （β-TCP） was fabricated on pure magnesium via the chemical deposition in a simulated Hank’s solution. The method significantly accelerated the coating formation on magnesium. Moreover, the morphology, phase/chemical composition, the coating formation mechanism as well as degradation behavior in phosphate buffered saline （PBS） solution were in- vestigated. Scanning electron microscopy （SEM） images showed that the coating had three layers and X-ray diffraction （XRD） patterns showed that the coating mainly contained Ca3（PO4）2 and （Ca,Mg）3（PO4）2. Elec- trochemical test showed that the corrosion current density （Icorr） of the coated Mg was decreased by about one order of magnitude as compared to that of pure magnesium. The immersion test indicated that the coating could obviously reduce the degradation rate.

Study on corrosion resistance of pure magnesium with CaSiO_3 contained coating in NaCl solution

A composite coating was fabricated on pure magnesium by hydrothermal treatment in order to reduce its degradation in body environment. The coating was character- ized by scanning electron microscopy （SEM） and X-ray diffraction （XRD）. The XRD pattern showed that the main composition of the coating was a mixture of CaSiO3, MgSiO3 and Mg（OH）2. Electrochemical test showed that the corrosion current den- sity （icor~） of the coated magnesium was decreased by about two orders of magnitude compared with that of the bare magnesium, and the EIS measurement also showed that the corrosion resistant performance of the coated magnesium was significantly enhanced. Meanwhile, weight loss test showed that the weight loss of the coated magnesium was lower than that of the bare magnesium. Hence, the present study indicated that the composite coating could greatly slow down the degradation of pure magnesium.

Highly efficient visible-light photocatalytic degradation and antibacterial activity by GaN:ZnO solid solution nanoparticles

The development of high-efficiency photocatalysts is the primary goal in the field of photocatalytic antibacterial research.In this work,the Ga N:Zn O solid solution nanoparticles(NPs)photocatalyst with strong visible absorption and large specific surface area was synthesized via the sol-gel and nitridation reaction process.Also,we systematically investigated the removal efficiency of the organic pollutant and antibacterial activity on E.coli and S.aureus.Notably,methylene blue solution could be completely degraded after 100 min of visible light illumination using 2 mg/m L Ga N:Zn O catalyst.Moreover,~94%of the E.coli were inactivated within 120 min,whereas 100%antibacterial activity against S.aureus was achieved after 90 min of visible light illumination mediated by Ga N:Zn O NPs.We further explore the potential mechanism of visible light photocatalytic antibacterial activity enhanced by Ga N:Zn O NPs photocatalyst.The current work not only provides a new and efficient photocatalytic antibacterial nanomaterial but also demonstrates its promising applications in environmental and biological fields.

High nitrogen stainless steel drug-eluting stent-Assessment of pharmacokinetics and preclinical safety in vivo

Pharmacokinetic analyses were performed using 20 pigs for 120-days implantation,while one sirolimus-eluting stent was implanted into one of their coronary artery.At different time points,the residual sirolimus on the stent,delivered locally(to artery wall),regionally(to adjacent and downstream muscle)and systemically(to plasma and visceral organs),was detected throughout 120 days.Preclinical safety evaluation was performed using 32 pigs for 180-days implantation to study the safety of metal platform material and the effectiveness of sirolimus eluting coating on the HNS stent.The neointima area,restenosis rate and inflammatory grade for HNS and control group stents were detected and analyzed.Approximately 80%sirolimus was eluted from the sirolimuseluting stents after 30-days implantation in vivo.Additionally,there was sustained sirolimus in the artery wall,cardiac muscle and heart throughout 120-days implantation,and sirolimus accumulated to the peak at 90-days implantation.It was inferred that the sirolimus eluting stent in this study was covered by neointima before 90-days implantation,indicating that the sirolimus eluting coating on the HNS stent was safe and effective.Very little sirolimus was distributed in visceral organs after 14-days implantation.HNS sirolimus-eluting stent exhibited lower restenosis rate and lower inflammatory grade than control group,which verified that the sirolimus-eluting coating design in this study was reasonable and practical.In addition,there were no significant difference in restenosis rate and inflammatory score between HNS bare-metal stent and drug-eluting stents,illustrating that HNS has good bio-compatibility and is suitable to use as coronary artery stent material.

In vitro study on infectious ureteral encrustation resistance of Cu-bearing stainless steel

Cu-bearing stainless steel has been found to have obvious inhibition performance against encrustation in vitro. This study was aiming to further investigate the inhibitory effect of a Cu-bearing stainless steel（316 L-Cu SS） on the infectious encrustation based on its antimicrobial activity. The encrustation in presence of bacteria, antibacterial performance, urease production and Ca and Mg precipitation were examined by scanning electron microscopy, antibacterial assay, enzyme-linked immunosorbent assay and inductively coupled plasma-mass spectrometry, respectively. It was found that 316 L-Cu SS could inhibit the formation of bacterial biofilm due to the release of Cu^（2＋） ions and then decrease the urease amount splitting by bacteria, which produced a neutral environment with pH around 7. However, more encrustations coupled with bacterial biofilms on the surface of comparison stainless steel（316 L SS） with an alkaline environment were recorded. It can thus be seen that the 316 L-Cu SS highlights prominent superiority against encrustation in the presence of microorganisms.

In Vivo Study on Degradation Behavior and Histologic Response of Pure Magnesium in Muscles

When an orthopedics device is implanted into bone injury site, it will contact the soft tissue （skeletal muscle, fascia, ligament etc.） except for bone. Magnesium based biodegradable metals are becoming an important research object in orthopedics due to their bioactivity to promote bone healing. In this study, pure Mg rods with and without chemical conversion coating were implanted into the muscle tissue of rabbits. Implants and their surrounding tissues were taken out for weight loss measurement, cross- sectional scanning electron microscopy observation, elemental distribution analysis and histological examination. The results showed that the chemical conversion coating would increase the in vivo cor- rosion resistance of pure Mg and decrease the accumulation of calcium （Ca） and phosphorus （P） elements around the implants. For the bare magnesium implant, both Ca and P contents in the surrounding tissues increased at the initial stage of implantation and then decreased at 12 weeks implantation, while for the magnesium with chemical conversion coating, Ca and P contents in the surrounding tissues de- creased with the implantation time, but were not significant. The histological results demonstrated that there was no calcification in the muscle tissue with implantation of magnesium for up to 12 weeks. The chemical conversion coating not only increased the in vivo corrosion resistance of pure Mg, but also avoided the depositions of Ca and P in the surrounding tissues, meaning that pure magnesium should be biosafe when contacting with muscle tissues,

A novel polymer critical re-melting treatment for improving corrosion resistance of magnesium alloy stent

Polymer coating was widely used as a protective coating on Mg alloy stent due to its excellent deformability. However, the polymer coating with lots of macro-and micro-holes after solvent evaporation during forming process would make corrosion medium permeate easier and decrease the corrosion resistance of Mg alloy stent. In this study, a novel critical re-melting method was adopted to improve the polymer coating densification, which was evaluated by the surface morphology of coating. The corrosion resistance of Mg alloy stent after critical re-melting treatment was examined by the electrochemical and immersion tests. The results indicated that the corrosion resistance of Mg alloy stent with polymer coating was improved significantly by polymer critical re-melting treatment.

Assessment of structure integrity, corrosion behavior and microstructure change of AZ31B stent in porcine coronary arteries

Magnesium alloy coronary stent becomes a hot research topic due to its biodegradable character for avoiding late thrombosis and late restenosis.However,fracture of Mg alloy stent was a common issue after implantation.In this study,18 drug-eluting biodegradable AZ31 B stents were implanted into porcine coronary arteries to assess its structural integrity,corrosion behavior and microstructure change in vivo.The coronary artery tissue responses to AZ31 B stent implantation were detected by quantitative coronary angiography and optical coherence tomography at the set time periods.In addition,further analyses were focused on the stent structure integrity,corrosion behaviors and the microstructure change of Mg alloy stents after implantation.A large number of fractures on stent struts were observed by high-resolution transmission X-ray tomography clearly.Moreover,degradation products,twins and grain refinement that appeared in Mg alloy stent matrix after implantation were also observed during the study.Inferred from this study,it is shown that the loss of AZ31 B stent structural integrity may be the result of stress concentration,degradation and microstructure change.