Sharif University of Technology

An international research team is attracting the attention of experts in the field with computational results on the behavior of ring polymers under shear forces: They showed that for the simplest case of connected ring pairs, the type of linkage -- chemically bonded vs. mechanically linked -- has profound effects on the dynamic properties under continuous shear. In these cases novel rheological patterns emerge. An international research team is attracting the attention of experts in the field with computational results on the behavior of ring polymers under shear forces: Reyhaneh Farimani, University of Vienna, and her colleagues showed that for the simplest case of connected ring pairs, the type of linkage -- chemically bonded vs. mechanically linked -- has profound effects on the dynamic properties under continuous shear. In these cases novel rheological patterns emerge. In addition to being recently published in the journal Physical Review Letters, the study received an "Editors' Suggestion" for its particular novelty. The shearing of fluids -- meaning the sliding of fluid layers over each other under shear forces -- is an important concept in nature and in rheology, the science that studies the flow behavior of matter, including liquids and soft solids. Shear forces are lateral forces applied parallel to a material, inducing deformation or slippage between its layers. Fluid shear experiments allow the characterization of important rheological properties such as viscosity (resistance to deformation or flow) and thixotropy (decrease in viscosity under the influence of shear) which are important in applications ranging from industrial processes to medicine. Studies on the shear behavior of viscoelastic fluids, created by introducing polymers into Newtonian fluids, have already been conducted in recent years. However, a novel approach in the current research involves the consideration of polymer topology -- the spatial arrangement and structure of molecules -- by using ring polymers. Ring polymers are macromolecules composed of repeating units, forming closed loops without free ends. A Matter of Linking First author Reyhaneh Farimani explains: "For our computer simulation experiments under shear, we considered two similar types of connected ring pairs: One in which the linkage is chemical, called bonded rings (BRs), and one in which the linkage is mechanical via a Hopf link, called polycatenanes (PCs)." Special emphasis was placed on taking into account hydrodynamic interactions through appropriate simulation techniques, which proved to be crucial since the emerging patterns are governed by a delicate interplay between fluctuating hydrodynamics and topology. The results were surprising: On the one hand, the response of the two components, BRs and PCs, was very different from each other -- and on the other hand, it was clearly different from that of various other polymer types, such as linear, star or branched. In particular, the dominant dynamic pattern in other polymers under shear ("vorticity tumbling") is either suppressed (BRs) or virtually absent (PCs) in these topologically modified polymers. Unexpected Types of Tumbling "What we discovered," says Christos Likos, co-author of the study, "are completely unexpected dynamic patterns in both ring polymer types, which we call gradient-tumbling and slip-tumbling." Due to an interplay between hydrodynamics and ring topology, the BR molecules tumble around the gradient direction, which is perpendicular to the vorticity and flow axes. BRs are found to be in a continuous gradient-tumbling motion under shear. On the contrary, PCs become thin, orient themselves close to the flow axis and maintain a fixed, stretched and non-tumbling conformation under shear. Instead, due to their peculiar form of mechanical linkage, PCs exhibit intermittent dynamics, with occasional exchange of the two rings as they slip through each other, a pattern the authors of the paper call slip-tumbling. These unexpected modes of motion, which bear unique signatures of the topologies of the polymer compounds, underscore the importance of the interplay between hydrodynamics and polymer architecture: In fact, the researchers found in their simulations that when the backflow effects are artificially eliminated, the differences between BRs and PCs disappear. These dynamical modes also have a noticeable effect on the mechanical properties of the solution, since BRs release internal stresses by tumbling, whereas PCs store stresses permanently, resulting in a much higher viscosity in the latter case. This leads to the hypothesis that the different tumbling motions and structures of PCs and BRs could influence the shear viscosity -- a fluid's resistance to flow under shear reflecting its internal friction and ability to deform -- of highly concentrated solutions or polymer melts of these molecules. Further experimental and theoretical studies are needed to test this hypothesis. The current study was conducted by a scientific cooperation between the University of Vienna, the Sharif University of Technology in Iran and the International School of Advanced Studies (SISSA) in Italy.

R&D VP to Drive Product Innovation During Company's Transformative Growth Phase ALISO VIEJO, Calif., Nov. 21, 2022 /PRNewswire/ -- Vertos Medical Inc., a leader in the development of innovative, minimally invasive treatments for lumbar spinal stenosis (LSS), today announced the appointment of Mehrzad Khakpour, PhD as Vice President of Research and Development. Dr. Khakpour will be responsible for directing all aspects of research and development for the company. Continue Reading Mehrzad Khakpour, Vice President of Research and Development, Vertos Medical Inc. Dr. Khakpour brings a wealth of both technological innovation and product development experience to his role at Vertos, in addition to extensive medical device experience from inception to IPO. He was most recently at Sonendo Inc., a medical technology company focused on saving teeth from tooth decay with industry-first dental innovation, where he was responsible for the development and management of the product portfolio and roadmap for the past 14 years. He holds a BS in mechanical engineering from Sharif University of Technology, an MS in mechanical engineering from the University of Minnesota, and a PhD in mechanical engineering from the University of California, Riverside. Additionally, he will soon complete the Chief Product Officer Program at Kellogg Executive Education, Northwestern University. "Mehrzad joins the Vertos team at a pivotal time of growth and transformation as we continue to evolve the mild® Procedure and also look to expand treatment options for patients suffering from back pain," said Eric Wichems, President and CEO of Vertos Medical. "Mehrzad's extensive experience building and managing results-oriented, innovative, and agile R&D teams makes him a great asset to our organization." "I'm excited to join the Vertos team during this time of significant growth," said Mehrzad. "The Company's relentless pursuit to improve patients' quality of life requires a commitment to continual innovation that I am excited to be a part of moving forward. I am eager to develop a robust product pipeline that will provide additional therapies to treat patients suffering from low back pain." About Vertos Medical Inc. Vertos Medical is an interventional pain company committed to developing innovative, minimally invasive treatments for lumbar spinal stenosis (LSS). mild®, its proprietary technology, is an image-guided outpatient procedure that removes a major root cause of lumbar spinal stenosis (LSS) through an incision smaller than the size of baby aspirin and doesn't require implants, general anesthesia, or stitches. The mild® Procedure has been clinically demonstrated to have safety outcomes similar to injections with durability out to 5 years, and patients typically return to activities of daily living within 24 hours with no restrictions. mild® is nationally covered by Medicare and has been performed on over 55,000 patients. Vertos Medical headquarters is located in Aliso Viejo, CA. To learn more and view clinical data, visit . SOURCE Vertos Medical Inc.