We welcome Ms. Tori Nizzi, who has joined our research team as an undergraduate researcher. Tori is double majoring in mechanical engineering and materials science and engineering programs. She is currently assisting Morteza Ardakani in his research on zinc-based biodegradable alloys but should start her own independent work on computer simulations of biodegradable orthopedic implants in 2020.
Morteza has published his first first-author paper entitled “The effects of alloying with Cu and Mn and thermal treatments on the mechanical instability of Zn-0.05Mg alloy” in the Materials Science and Engineering A journal. The following is the abstract:
The detrimental effect of natural aging on mechanical properties of zinc alloys restricts their application as bioresorbable medical implants. In this study, aging of Zn-0.05Mg alloy and the effect of 0.5 Cu and 0.1 Mn (in weight percent) addition on the microstructure and tensile properties were studied. The alloys were cold rolled, aged and annealed; aiming to investigate the effects of precipitates and grain size on the mechanical properties and their stability. TEM analysis revealed that in ultrafine-grained binary Zn-0.05Mg alloy, the natural aging occurred due to the formation of nano-sized Mg2Zn11 precipitates. After 90 days of natural aging, the yield strength and ultimate tensile strength of Zn-0.05Mg alloy increased from 197±4 MPa and 227±5 MPa to 233±8 MPa and 305±7 MPa, respectively, while the elongation was drastically reduced from 34±3% to 3±1%. This natural aging was retarded by adding the third element at either 0.1Mn or 0.5Cu quantities, which interacted with Mg in Zn solid solution and impeded the formation of Mg2Zn11 precipitates. The addition of Cu and Mn elements increased alloy’s strength, ductility, and its mechanical stability at a room temperature. The measured tensile strength and elongation were 274±5 MPa and 41±1% for Zn-0.1Mn-0.05Mg and 312±2 MPa and 44±2% for Zn-0.5Cu-0.05Mg, respectively. Annealing the alloys at elevated temperatures caused increase in both grain size and dissolution of secondary phases, and both affected alloy deformation mechanisms.
We welcome Ms. Emily Tom, who has joined our research team as an undergraduate researcher. Emily is senior in materials science and engineering program. She will assist our team in research on zinc- and magnesium-based biodegradable alloys.
Congratulations to Roger Guillory for defending his PhD dissertation entitled “Degradable Zinc Material Characteristics and its Influence on Biocompatibility and in an In Vivo Murine Model” on August 20, 2019. Roger is also leaving us to take a postdoctoral fellow position at Northwestern University in Evanston (near Chicago). We wish him both professional and personal successes in his new place and in this new chapter of his live!
Our collaborators from Northeastern University in Shenyang published a new paper on Reverse Flotation of Hematite from Quartz with Magnetic Seeding Aggregation in the Minerals Engineering journal. In this work, fine magnetite was used as a magnetic seed to enhance the separation efficiency of fine hematite from quartz during reverse micro-flotation. Gradual increases in hematite recovery and iron grade were accomplished with increasing magnetite content, whereas the iron content in quartz reject decreased. Particle size analysis, sedimentation tests, and scanning electron microscopy analysis of hematite from the separation process confirmed aggregation of hematite with magnetite particles. The measurements of magnetic susceptibility of product and reject indicate predominant aggregation of magnetite with hematite, and only marginal with quartz. Zeta-potential analysis and colloidal force analysis confirmed attractive interactions between magnetite and hematite, and repulsive between magnetite and quartz. Therefore, fine hematite aggregation with magnetite particles reduces coating of quartz with fine hematite, benefiting the flotation purification of fine hematite from quartz in terms of both recovery and grade.
We are glad to report that the journal impact factor (IF) for Surface Innovations rose to 2.333 from 1.268 in 2018. This is the third year in a row when the journal climbs in ranking. The journal is listed under two categories:
1) Materials Science, Coatings & Films
The journal climbed from 14th to 6th position among 20 listed journals. Percentile improve from 74% in last year to 30% in 2019. It places the journal under Q2 category.
2) Physical Chemistry
The journal moved from 118th position to 78th among 148 journals. The percentile improved from 81% (Q4) to 53% (Q3).
Mr. Kyle Hrubecky has joined our research team as a PhD Candidate. He will work on just-awarded NIH R01 grant, developing new zinc alloys for medical applications. Kyle worked with us in the past as undergraduate researcher, during his junior year.
The U.S. National Institute of Health has awarded us with R01 funding. Our laboratory has been working to refine the composition and microstructure of biodegradable Zn-based binary alloys and test their behavior in the vascular environment over the last four years in an effort to develop a metal with mechanical properties and biocompatibility required for endovascular stent applications. Having contributed enormously to the scientific understanding of Zn-based systems, we are now ready to develop more complex Zn-based alloys with 2-3 alloying elements that meet benchmark values for biodegradable stents, including: 1) have superior corrosion fatigue resistance that eliminates early stage (6 to 9 months) fracturing of biodegradable stents (common problem in Mg-based and Zn-based stents prototyped in the last several years); 2) maintain in vivo corrosion rates close to the 0.02 mm/year value; 3) exhibit >200 MPa yield strength, and >25-30% elongation to failure; and 4) demonstrate biocompatibility in terms of short- and long-term inflammatory responses, re-endothelialization, and suppressed intimal hyperplasia, similar or better than 316L stainless steel (industrial standard for stent materials).
Our new paper entitled In Vitro Corrosion and in Vivo Response to Zinc Implants with Electropolished and Anodized Surfaces has been published in the ACS Applied Materials & Interfaces journal. Roger Guillory, PhD candidate, and Prof. Jeremy Goldman from Biomedical Engineering led this project. In this study, pure zinc samples were electropolished (EP) and anodized (AD) to engineer oxide films with distinctive physical and degradation characteristics, as determined by potentiodynamic polarization, electrochemical impedance spectroscopy and static immersion tests. The samples were then implanted within the aortic lumen of adult Sprague Dawley rats to determine the influence of surface engineering on biocompatibility responses to Zn implants. It was found that in vitro corrosion produced a porous corrosion layer for the EP samples and a densified layer on the AD samples. The AD material was more resistant to corrosion, while localized corrosion and pitting was seen on the EP surface. Interestingly, the increased variability from localized corrosion due to surface film character translated directly to the in vivo performance, where 100% of the AD implants but only 44% of the EP implants met the biocompatibility benchmarks. Overall, the results suggest that oxide films on degradable zinc critically affect early neointimal progression and overall success of degradable Zn materials.
We are glad to share with you the content of the Issue 3-4 of 2019 of Surface Innovations with nine papers on variety of topics related to surfaces and interfaces, including Invited Feature Article on chemistry of self-adaptive materials prepared by Prof. Ekaterina Skorb and her team. Hope you will find something interesting in this collection.