Bingchun Zhang

Research on super-hydrophobic surface of biodegradable magnesium alloys used for vascular stents

Micro-nanometer scale structure of nubby clusters overlay was constructed on the surface of an AZ31 magnesium alloy by a wet chemical method. The super-hydrophobicity was achieved with a water contact angle of 142° and a sliding angle of about 5°. The microstructure and composition of the super-hydrophobic surface were characterized by SEM and FTIR. Potentiodynamic polarization and electrochemical impedance spectroscopy were used to evaluate the corrosion behavior, and the hemocompatibility of the super-hydrophobic surface was investigated by means of hemolytic and platelet adhesion tests. Results showed that the super-hydrophobic treatment could improve the corrosion resistance of magnesium alloys in PBS and inhibit blood platelet adhesion on the surface, which implied excellent hemocompatibility with controlled degradation.

Study on compression behavior of porous magnesium used as bone tissue engineering scaffolds

In this work, porous magnesium (Mg) with a three-dimensional open-cellular structure, potentially employed as bone tissue engineering scaffolds, was fabricated by the mechanical perforation method. The influences of porosity, pore size and pore arrangement on compressive behavior and the anisotropy of new porous Mg were analyzed theoretically using orthogonal arrays and the finite element method (FEM). The results showed that the parameters of porosity, pore size and pore arrangement had different effects on the compressive properties. The compressive strength could be improved by optimizing these parameters. The anisotropy of porous Mg was also verified in this study. The theoretical results showed good agreement with the experimental ones before the strain reaches 0.038.

In vivo degradation and tissue compatibility of ZK60 magnesium alloy with micro-arc oxidation coating in a transcortical model

Magnesium alloys were studied extensively as a class of biodegradable metallic materials for medical applications. In the present study, ZK60 magnesium alloy was considered as a candidate and the micro-arc oxidation (MAO) treatment was adopted in order to reduce the degradation rate of the alloy. The in vivo degradation behaviors and biological compatibilities of ZK60 alloys with and without MAO treatment were studied with a transcortical model in rabbits. The implant and the surrounding bone tissues were characterized by CT, SEM and histological methods at 2, 4 and 12 weeks after the implantation. The results demonstrated that both the bare and MAO-coated ZK60 alloys completely degraded within 12 weeks in this animal model. The MAO coating decreased the degradation rate of ZK60 alloy and enhanced the response of the surrounding tissues within the first 2 weeks. After then, an acceleration of the degradation of the MAO-coated ZK60 alloy was observed. It was found that the alloy could be degraded before the complete degradation of the MAO coating, leading to the local peeling off of the coating. An in vivo degradation mechanism of the MAO-coated ZK60 alloy was proposed based on the experimental results. The severe localized degradation caused by the peeling off of the MAO coating was the main reason for the acceleration of the degradation of the MAO-coated ZK60 alloy.

Enhanced Efficacy of Sirolimus-Eluting Bioabsorbable Magnesium Alloy Stents in the Prevention of Restenosis

Purpose To determine the efficacy of sirolimus-eluting bioabsorbable magnesium alloy stents (SEBMAS) in restenosis prevention. Methods A balloon-expandable bioabsorbable magnesium alloy stent (BMAS) was created and coated with biodegradable poly(lactic acid-co-trimethylene carbonate) that contained the antiproliferative drug sirolimus (140±40 μg/cm2). Both the uncoated BMAS and the coated SEBMAS were deployed 2 cm apart in balloon-injured infrarenal abdominal aortas of 20 New Zealand white rabbits. The stented aortic segments were removed at 30, 60, 90, and 120 days (5 rabbits per interval) after implantation. The average stent strut sectional area of each group was measured to evaluate the degree of magnesium corrosion and to forecast the biodegradation time profile of the magnesium stent. Histology and histopathology of the sectioned stented aortic segments were performed to evaluate neointima formation, endothelialization, and inflammation. Results The SEBMAS degraded gradually after being implanted into the rabbit aorta, and total biocorrosion occurred after ∼120 days. In all groups, the lumen area was significantly greater, but the neointimal area was significantly smaller in SEBMAS segments compared with the uncoated BMAS segments (p<0.05) at all time points. There was no significant difference in the injury or inflammation scores between the groups. Endothelialization was delayed at 30 days in the SEBMAS segments vs. the uncoated BMAS segments. Conclusion SEBMAS further reduces intimal hyperplasia and improves the lumen area when compared to uncoated BMAS; however, it delays vascular healing and endothelialization.

Correlation for gas–liquid equilibrium prediction in Fischer–Tropsch synthesis

A correlation for the prediction of the solubilities of gaseous solutes in heavy waxes in Fischer–Tropsch synthesis was developed on the basis of cubic equation of state. The correlation can be used for the systems with a wide range of solutes, including CO, H2, CO2, CH4, C2H4 and C2H6, and heavy wax solvents from C20 to C61, and requires critical temperature and critical pressure together with molecular weight instead of the acentric factor of the corresponding pure compound as input information. By using a single binary interaction factor, it is sufficient for this correlation to represent a binary system over a wide range of temperatures and pressures. For 406 experimental data points of 29 binary systems from literature, the correlation can provide good approximations with an overall average absolute deviation less than 6%, which can meet the demands of the engineering design of Fischer–Tropsch process.

In vitro and in vivo evaluation of MgF2 coated AZ31 magnesium alloy porous scaffolds for bone regeneration

Porous magnesium scaffolds are attracting increasing attention because of their degradability and good mechanical property. In this work, a porous and degradable AZ31 magnesium alloy scaffold was fabricated using laser perforation technique. To enhance the corrosion resistance and cytocompatibility of the AZ31 scaffolds, a fluoride treatment was used to acquire the MgF2 coating. Enhanced corrosion resistance was confirmed by immersion and electrochemical tests. Due to the protection provided by the MgF2 coating, the magnesium release and pH increase resulting from the degradation of the FAZ31 scaffolds were controllable. Moreover, in vitro studies revealed that the MgF2 coated AZ31 (FAZ31) scaffolds enhanced the proliferation and attachment of rat bone marrow stromal cells (rBMSCs) compared with the AZ31 scaffolds. In addition, our present data indicated that the extract of the FAZ31 scaffold could enhance the osteogenic differentiation of rBMSCs. To compare the in vivo bone regenerative capacity of the AZ31 and FAZ31 scaffolds, a rabbit femoral condyle defect model was used. Micro-computed tomography (micro-CT) and histological examination were performed to evaluate the degradation of the scaffolds and bone volume changes. In addition to the enhanced the corrosion resistance, the FAZ31 scaffolds were more biocompatible and induced significantly more new bone formation in vivo. Conversely, bone resorption was observed from the AZ31 scaffolds. These promising results suggest potential clinical applications of the fluoride pretreated AZ31 scaffold for bone tissue repair and regeneration.

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 Hanks 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-6Mo 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 beta-tricalcium phosphate (beta-TCP) was fabricated on pure magnesium via the chemical deposition in a simulated Hanks 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 investigated. Scanning electron microscopy (SEM) images showed that the coating had three layers and X-ray diffraction (XRD) patterns showed that the coating mainly contained Ca-3(PO4)(2) and (Ca,Mg)(3)(PO4)(2). Electrochemical test showed that the corrosion current density (I-corr) 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.

Research on the corrosion resistance and formation of double-layer calcium phosphate coating on AZ31 obtained at varied temperatures

In this study, the effect of varied processing temperatures on the corrosion resistance and formation of dual-layer calcium phosphate coating on AZ31 was investigated. The microstructure, phase and morphology were characterized by a scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffractometer (XRD), respectively. The in vitro degradation behavior of coated AZ31 samples were evaluated by electrochemical and immersion tests in simulated body fluid. The results showed that the varied processing temperatures responded to different microstructure, phase and morphology; and a dual-layer coating was formed during the deposition process at 70°C. Meanwhile the higher processing temperature induced a faster coating formation rate and greater surface coverage. The in vitro degradation tests in simulated body fluid indicated that the corrosion rates of AZ31 alloy were effectively decreased with increasing processing temperature, which was attributed to the denser protective coating. The formation mechanism of dual-layer coating influenced by deposition temperature was proposed.

A novel ureteral stent material with antibacterial and reducing encrustation properties

Ureteral stents have been used to relieve ureterostenosis. Complications such as infection and encrustation occur in the long time of stent implantation, which is a clinical problem needs to be resolved. Indwelling ureteral stents have shown to develop microbial biofilm that may lead to recurrent infection and encrustation. This study was aiming to reduce those complications by using a novel material, Cu-bearing antibacterial stainless steel. The antibacterial performance, encrustation property, and biocompatibility were examined by SEM, image analysis, MTT and would healing. The in vitro immersion test showed that 316LCu-bearing stainless steel (316LCu-SS) not only inhibited proliferation of bacteria and formation of biofilm, but also had less encrustation deposition. Its antibacterial effectiveness against Escherichia coli reached to 92.7% in the artificial urine for 24h and 90.3% in the human urine for 6h. The encrustation surface coverage percentage was 30.2% by 12weeks, which was nearly one half of NiTi alloy. The in vitro tests showed that 316LCu-SS had no toxicity, and promoted the migration of urethral epithelial cells.