Zinc (Zn) has recently been introduced as a promising new metal candidate for biodegradable vascular stent applications with a favorable degradation rate and biocompatibility. Corrosion resistant metal stents are often coated with drug-eluting polymer layers to inhibit harmful biological responses. In our new paper entitled “Effect of PLLA Coating on Corrosion and Biocompatibility of Zinc in Vascular Environment” and published in Surface Innovations, we investigated the interaction between biodegradable zinc metal with a conventional biodegradable polymer coating. Zn wire with a diameter of 0.25 mm was surface modified using 3-(trimethoxysilyl) propyl methacrylate (MPS) and then coated with a 1-12 µm film of poly (L-lactic-acid) (PLLA). The corrosion behavior of PLLA/MPS-coated Zn wires was studied in simulated body fluid using electrochemical impedance spectroscopy. An increase in the impedance from <1,000 to >15,000 ohms cm2 was recorded for Zn wire after its coating with PLLA. The PLLA/MPS-coated Zn specimens were implanted into the abdominal rat aorta to assess their biodegradation and biocompatibility as compared to uncoated Zn wires. PLLA/MPS-coated wires corroded at approximately half the rate as unmodified Zn during the first 4.5 months. A histological analysis of the biological tissue surrounding the Zn implants revealed a reduction in biocompatibility of the polymer-coated samples, as indicated by increasing cell toxicity and neointimal hyperplasia.
A new paper entitled A Simplified Analysis of the Effect of Nano-asperities on Particle-Bubble Interactions has been published in the Physicochemical Problems of Mineral Processing journal. This paper was invited by the editors and will be included in a special issue (first issue of 2018) honoring Professor Emeritus Kazimierz Malysa from Poland.
As well discussed in our paper, the interactions of gas bubbles with particles having rough and heterogeneous surfaces are much more complex than the commonly used DLVO – based models predict. The effects of surface roughness on flotation and particle – bubble interactions have been reported many times in the past, although a clear understanding of their origins has been lacking. To explain differences in interactions for spherical hydrophobic particles, a theoretical analysis of the interaction potential was carried out for a model rough particle interacting with a bubble surface in an electrolyte solution in this study. The attractive hydrophobic interaction potential was added to repulsive retarded van der Waals and repulsive electrical double layer interaction potentials. The rough microscopic particles were modeled as spheres decorated with nano-sized asperities. Parameters that reflect common flotation separation systems were selected for testing this theoretical model and computation of the energy barrier applicable to particle – flat bubble surface interactions. It was found that hydrophobic asperities with a height of only several nanometers can reduce the repulsive interaction energy by an order of magnitude. Theoretical analysis also reveals that surface coverage of microscopic particles by nano-sized asperities is important as well.
The review papers entitled Hydrophilic and Superhydrophilic Surfaces and Materials, published in Soft Matter in 2011, was marked again this year as Highly Cited Paper by Thomson Reuters in its Web of Science. This highly cited paper received enough citations second year in a raw to place it in the top 1% of the academic field of Materials Science based on a highly cited threshold for the field and publication year.
The SURFI team is involved with organization and preparation of the International Symposium “Biodegradable Materials for Medical Applications” at The Minerals, Metals, and Materials Society (TMS) 2018 Annual Meeting. This international symposium is organized by the TMS Biomaterials Committee. The inaugural edition of a similar symposium was held at the TMS 2013 Annual Meeting, with the second meeting in 2016, and both meetings were a runaway success. These two previous meetings were limited to magnesium-based materials. This time we want to bring experts from both academia and industry who have experience with biodegradable metals (Mg, Fe, and Zn) and polymers. The papers anticipated will cover all classes of absorbable implants including cardiovascular, orthopedic, wound closure, and emerging implant applications. Specific focus areas are anticipated to include material selection and development, in vitro and in vivo degradation, and biodegradable medical device design/certification.
Prof. Drelich has been invited to serve on the Editorial Board of a new scientific journal named 4Open. It is an open access wide-spectrum inter- and multi- disciplinary journal owned by EDP Sciences and addresses research in all four disciplines in science: Life Sciences – Medicine, Chemistry – Applied Chemistry, Physics – Applied Physics, and Mathematics – Applied Mathematics.
Ramie (Boehmeria nivea) fiber is one of the superior strength lignocellulosic fibers, but the least investigated particularly as a reinforcement to obtain tougher polymeric composites. This paper, just published in Materials Research and entitled Reinforcement of Polyester with Renewable Ramie Fibers, presents mechanical properties for polyester reinforced with aligned ramie fibers in volume up to 30 %. In this collaborative project with the Institute of Military Engineering in Rio de Janeiro (Brazil), it was found that adding 30 vol.% of ramie fibers increases the flexural strength of polyester about three times (212 MPa vs. 65 MPa) and tensile strength nearly two times (85 MPa vs. 47 MPa). Polyester-ramie fiber composites also displayed a significant improvement in toughness. The impact energy value (~1 kJ/m) as measured by Charpy test and Izod impact energy value (~0.55 kJ/m) increased two orders of magnitude for 30 vol% ramie fiber composite as compared to neat polyester (~ 0.015 kJ/m).
Fractographic studies revealed good wetting of the fibers by polyester. Limited fiber-matrix adhesion was reflected in preferential longitudinal propagation of cracks along the fiber/polyester interfaces, indicating also that most of the fracture area is associated with the fiber surface.
We are glad to share with you the content of the 2nd issue of 2017 of Surface Innovations, with six papers on advanced materials in dental and orthopedic applications, which were selected and assembled by Prof. Tolou Shokuhfar from the University of Illinois.
Congratulations to Shan and Avishan!
Our charming ladies just graduated this spring. Shan completed her PhD program on Zn-Li bioalloys and Avishan her MS program on coating Zn with biodegradable polymer. They will be leaving us at the end of May/beginning of June.
Good luck in new places and hope you will stay in touch with SURFI team in years to come.
Congratulations to Jeff!
He was selected as the recipient of the Richard Shorraw Award. The Richard Sharrow Award is given to a student who has demonstrated a significant academic improvement through his career at MTU-MSE Department, and has demonstrated good citizenship within the department. Jeff received this award during the Senior Banquette last night (April 13).
He has also received the AFS Detroit-Windsor Chapter’s Past Chairman Scholarship.
Two of the SURFI Team members, Jeff Brookins and Philip Staublin traveled to Washington D.C. with a group from Michigan Tech to attend Congressional Visit Day, which is organized by the national chapter of the Material Advantage program. They worked with two other Michigan Tech students to schedule meetings with Michigan congressmen to discuss research funding programs. In Washington, the students spoke to staff members from six offices and advocated for the continuation of funding to programs such as NIH and NSF. Using zinc stents as an example of benefits of NIH research, they hoped to provide officials with justification for opposing research budget cuts. The visit provided good experience and demonstrated the importance to the sciences of active involvement in public policy.