Durgesh Prasad Kavishvar
Doctor of Philosophy
Department of Chemical Engineering University of Toronto
Abstract
Yield stress is a characteristic stress depicting the flow behavior of many complex materials. When the applied shear stress is lower than yield stress, materials exhibit solid-like behavior, transitioning to liquid-like behavior for shear stress>yield stress. Conventional rheometers often struggle with sensitivity in measuring low yield stress, lack real-time measurement capabilities, and are prohibitively expensive. These limitations are particularly pronounced in biological materials such as blood and mucus, where variations in yield stress can signify underlying health conditions. For instance, yield stress of blood from patients with cerebrovascular and cardiovascular diseases, hypertension, sickle cell disease, among others, exceeds that of healthy blood. Similarly, yield stress of mucus from individuals battling conditions such as cystic fibrosis or asthma can be several orders of magnitude higher than that of healthy lung mucus. Also, yield stress measurements prove valuable for quality assessment in various industries such as oil & gas as well as food industry.
In this work, we investigate, through experiments, scaling analysis, and simulation, the yielding behavior of various complex materials in a Hele-Shaw microfluidic extensional flow device (MEFD). We propose the MEFD as a new microfluidic rheometer capable of measuring a low yield stress ranging from 5 mPa−5 Pa. The design of the MEFD is such that it enables a gradient in shear stress, shear stress, such that shear stress is lower near the center or stagnation point, and higher away from the stagnation point. For a yield stress fluid, we observe that, below a certain flow rate, shear stress exceeds yield stress only in the outer region, leading to stagnation or unyielding of the fluid in the inner region. Our simulation study also corroborates the experimental findings, demonstrating the existence of an unyielded region near the stagnation point of the extensional flow. We apply scaling analysis to deduce yield stress by measuring this size of the unyielded region at center. We validate the scaling relationship using Carbopol solutions of various concentrations (0.015 to 0.3%), measuring yield stress as low as ~10 mPa to ~1 Pa, and comparing these measurements with a standard rheometer.
Furthermore, we showcase the applicability of our rheometer by measuring yield stress of human blood samples ranging between 30−80 mPa for a range of hematocrits as well as yield stress of porcine gastric mucins (20%) of 0.7 Pa. We also demonstrate measurements of yield stress of clay suspensions (2 to 6%), useful in oil & gas applications. We also show a proof of concept for food industry by measuring yield stress of a lactic drink of roughly 7 mPa. Our microfluidic rheometer offers several other advantages, including real-time measurement capability (with measurement time as short as 4 s), low volume requirement (<1 ml), ease of cleaning and reuse, and cost-effectiveness. Therefore, it attracts diverse applications in clinical research, particularly in disease detection, as well as in industries such as food and oil & gas for quality assessment.
Join Zoom Meeting
https://utoronto.zoom.us/j/83112794844
Meeting ID: 831 1279 4844
Passcode: 990844
A U of T Engineering startup co-founded by Adnan Sharif (ChemE MEng student) has its roots in an experience that is all too common for many of us — he kept forgetting to water his plants.
“I was working in a plant immunity biology lab, so if I didn’t water them, I’d have no plants to do experiments with,” says Sharif.
At the time, Sharif was a U of T undergraduate student working with Professor Keiko Yoshioka in the Department of Cell & Systems Biology. He has since graduated and is now pursuing an MEng in the Department of Chemical Engineering & Applied Chemistry.
“My dad is a mechanical engineering professor at a university in Japan, and he knows a lot about manufacturing materials with porous, three-dimensional structures. So that’s how I got the idea to make my own 3D printed soil construct, which could retain water for a week or more. That way, I wouldn’t have to go into the lab and water the plants so often.”
Today that product is called SmartSoil, and it’s one of the key innovations at the heart of Lyrata, a startup that is producing edible crops for caterers and high-end restaurants across the Greater Toronto Area.
Support from the U of T Engineering community has been key to Lyrata’s success. For example, it was a U of T Engineering alumni connection that recently led to Lyrata launching an installation at Casa Loma, a historic museum and landmark in midtown Toronto.
Abstract
Algae have long been promoted as alternative hosts for sustainable biotechnology concepts owing to their capacity for light-driven circular reuse of waste streams as inputs and the production of biomass rich in valuable natural products. The emerging capacity to tailor algal cell metabolism through genetic engineering for the sustainable production of desired biochemicals holds the promise of co-product generation from algal bioprocesses to multi-valorize waste inputs. Microalgal metabolic engineering has emerged in recent years due to the intersection of reliable DNA synthesis and improved understanding of transgene expression limitations, especially in the model green microalga Chlamydomonas reinhardtii. This alga has been a powerful workhorse for demonstrating the possibilities of eukaryotic algal metabolic engineering, especially for isoprenoid targets. Other eukaryotic microalgae are also coming to light as potential hosts for synthetic biology mediated genetic engineering concepts. The model red microalga Cyanidioschyzon merolae 10D is a polyextremophilic member of the Cyanidiophyceae that grows at pH 0.5-2 and 42-50 ˚C, lacks a cell wall, and can be cultured with low risk of contamination. C. merolae exhibits favorable genetic features such as targeted transgene integration by homologous recombination into its small nuclear genome (16 Mb) and few introns. We have recently developed a new, completely synthetic, molecular toolkit for transformation of the nuclear genome of this alga. In this presentation I will highlight advances in its metabolic engineering for heterologous generation of several products in addition to its cultivation outdoors on the mid Red Sea coast in 1000 L tubular photobioreactors. I will also describe our engineering strategies to expand the capacity of C. reinhardtii and C. merolae as green cell factories, highlight new developments in bio-process designs, the value of metabolic engineering for fundamental understanding of algal metabolism, and discuss the value of regional considerations for algal biotechnology in the Middle East.
Speaker Bio
Dr. Kyle J. Lauersen is an Assistant Professor at King Abdullah University of Science and Technology (KAUST) in Thuwal, Saudi Arabia. His group is named Sustainable & Synthetic Biotechnology with their main research focussed on engineering algae to be green cell factories. Kyle did his Doctorate of Natural Sciences at Bielefeld University in Germany, and his master’s as well as undergrad at Queen’s University in Kingston, Ontario, Canada.
Abstract
System Mapping is a set of structured visualization techniques that help groups and individuals to look at the relationships and underlying assumptions of complex systems. Systems Mapping can be useful for researchers as they seek to understand the social, environmental and economic context in which their research sits – critical information when trying to bring new ideas to market or to assess the sustainability of a new technology. This interactive seminar will introduce systems mapping, share some real world examples where mapping has been used, and invite participants to generate and share simple maps related to their own research.
Speaker Bio
Professor Emily Moore is the Director of the Troost Institute for Leadership Education in Engineering (ILead) at the University of Toronto where she researches how engineers lead as they deliver new technologies to market. Emily holds a bachelor’s in engineering chemistry (Queen’s) and a doctorate in physical chemistry (Oxford) and is a licensed professional engineer. Emily launched her career at the Xerox Research Center of Canada (XRCC), then joined engineering consulting firm Hatch where she led the water business and technology development portfolio. Emily holds 21 patents and is a Fellow of the Canadian Academy of Engineering. Emily’s leadership in industry was recognized with the 2016 Kalev Pugi Award (SCI Canada) and she was named one of 100 Global Inspirational Women in Mining by Women in Mining UK. Emily serves as a board member of Chemtrade Logistics, International Petroleum Corporation, and the Canadian Mining Innovation Council.
Abstract
Microfluidics exploits fluids and their physical and chemical properties at the microscale, enabling miniaturized platforms that offer lower cost, faster pace, higher performance, and increased portability than their macroscale counterparts. This talk will briefly discuss three research themes including droplet microfluidics, microwave sensing and soft robotic wearable systems.
- Two-phase droplet microfluidics employs monodispersed water-oil emulsions as mobilized test tubes to perform high throughput analysis (HTA). Despite numerous novel technologies reported, the adoption of droplet microfluidics as an HTA tool by non-microfluidics experts has not been seen. Modular-based droplet microfluidics, enabling easy assembly of application-specific systems, presents tremendous potential to break this barrier. This talk will introduce our work towards this goal including, a suite of physical models that can serve as design tools for passive-based droplet modules such as droplet generators, mergers, sorters and heaters, and a unique active droplet microfluidics method that relies on visual feedback of droplet position to actuate a pressure source to actively control individual droplets realizing functional modules.
- Simultaneous sensing and heating of individual droplets are critical but very challenging. Microwave resonators present tremendous potential to meet this need which will be the second part of this talk. Microwave sensing finds various applications beyond droplet microfluidics. Its applications for the detection of virus such as SARS-CoV-2 and E. coli as well as metal ions will be discussed.
- Soft robotic wearable systems offer hope to improve the quality of life for those in need because of their compliance nature. Most existing systems are expensive, power intensive and tethered to external power sources, limiting user mobility. Microfluidics enables miniaturization of the system including its front end (e.g. wearable sleeves) and back end (control unit), translating to low cost, tetherless and energy-efficient operation. This talk will present wearable sleeves for treating lymphedema, arthritis, and pressure ulcers due to the ill fit of prosthetic sockets.
Speaker Bio
Dr. Ren received her PhD in Mechanical Engineering from the University of Toronto and her master’s and bachelor’s degrees in Mechanical Engineering from Harbin Institute of Technology. She is currently a Professor of Mechanical and Mechatronics Engineering at the University of Waterloo (UW) and holds a Tier I Canada Research Chair (CRC) in Microfluidic Technologies. She is directing Waterloo Microfluidics Laboratory focusing on advancing fundamental knowledge of microfluidics and developing technologies that are impactful on a wide range of applications such as life science research, protein fractionation towards drug screening, water quality sensing and assistive technology for well-being. Besides the CRC, Dr. Ren has also received several awards from the engineering and research community, including: election as a Member of Canadian Institute of Engineering in 2024, election as a Member of Canadian Academy of Engineering in 2023, recognition as one of Canada’s 100 Most Powerful Women in 2021, election as a Member of the College of New Scholars, Scientists and Artists of Royal Society of Canada in 2018, being recognized as one of 20 leading female innovators in Women of Innovation (Dr. Ren is a co-founder of four start-up companies) in 2017.
Abstract
The concept of oxy-fuel combustion involves using O2 separated from air to burn a fuel to generate a CO2 rich stream that can then be sequestered. However, if only O2 is fed into the boiler, the combustion temperature will be too high. In practice, flue gas would need to be cooled to condense out water and then a part of the CO2 rich flue gas is recycled and mixed with the O2 as the feed oxidant to the combustion system. The remaining CO2 rich gas (>90% CO2) can be compressed and sequestered or further purified and used as new uses for CO2 are developed.
There are three different combustion systems found in pulp mills:
- Kraft recovery boiler for burning black liquor
- Lime kiln for driving CO2 from CaCO3 to generate CaO
- Biomass boiler where bark and reject wood from pulping are burned
In this presentation I will talk about the early research in oxyfuel combustion in kraft recovery boilers and lime kilns and some of the process and process chemistry implications of transitioning from traditional combustion with air to oxyfuel combustion.
Speaker Bio
Nikolai De Martini is an Associate Professor of Chemical Engineering and Director of the Pulp and Paper Centre at the University of Toronto. He joined the faculty in 2017. Prof. De Martini earned a PhD in Chemical Engineering for work on nitrogen and sulfur chemistry in kraft recovery boilers at Åbo Akademi University in Turku, Finland. He currently leads the industrial consortium Effective Energy and Chemical Recovery in Pulp and Paper Mills which is supported by pulp and paper companies in Canada, the United States, Brazil, Chile, Finland and Sweden. He is also a New York Times Bestselling Author for his book, “Does Anybody Proofread”.
Abstract
Viruses are the most abundant microbial entity on the planet, impacting microbial community structure and ecosystem services. Viruses infecting bacteria and archaea have been specifically understudied in engineered environments. Using metagenomic and computational biology methods, we examined the diversity, host-interactions, and genetic systems of viruses across three North American landfills. From giant viral genomes to streamlined CRISPR-Cas systems, municipal landfills housed unique, and surprising viral ecology. Landfills, as heterogeneous contaminated sites with unique selective pressures, are key locations for diverse viruses and atypical virus-host dynamics.
Speaker Bio
Dr. Laura Hug: Associate Professor and Canada Research Chair in Environmental Microbiology. Department of Biology at the University of Waterloo.
Dr. Hug’s research examines the diversity and function of microbial communities in contaminated sites using a combination of ‘omics approaches and enrichment culturing. Current research in her group is characterizing the microbial communities colonizing municipal landfills, with foci on methane cycling, bioplastics degradation, and community interactions. Dr. Hug’s work has been featured in major news outlets including the New York Times, the Atlantic, Discover Magazine, and on Public Radio International’s “The World”. She was a featured scientist on a TFO children’s show and the BBC Radio 4 program, “Bacteria, the tiny giants” in 2023.
Abstract
Hydrogels have been widely used in a variety of biomedical and biosensing applications due to their favourable mechanical properties (mimicking those of soft tissues in vivo while facilitating high sensor flexibility), typically low non-specific protein adsorption (minimizing inflammation in vivo and reducing sensor interference), and capacity for controlling diffusion (enabling prolonged drug release in vivo and non-covalent biomolecule immobilization on biosensors). However, the elasticity of conventional pre-formed hydrogels limits their capacity to be injected or fabricated into various 2D or 3D geometries targeted for the development of functional sensor coatings and/or structured biomaterials. In situ-gelling hydrogels that can spontaneously gel following mixing of functionalized precursor polymers thus offer the potential to substantially expand the scope of feasible hydrogel applications. In this presentation, I will discuss recent work from our lab focused on designing and exploiting the properties of dynamically-crosslinked in situ-gelling materials based on poly(ethylene glycol) or zwitterionic polymer derivatives, enabling the rational design of injectable, printable, and/or processible hydrogels to address key challenges in tissue engineering and biosensing applications. In particular, I will discuss applications of our in situ-gelling synthetic hydrogels in creating injectable cell delivery vehicles for functional muscle regeneration, fabricating injectable in situ macroporous hydrogels for cell delivery, electrospinning nanofibrous hydrogel networks to create aligned/multi-cellular skin regeneration materials, 3D printing for creating microstructured cell therapeutics, and ink jet printing of surface coating-based platforms that can enhance both the specificity and selectivity of enzymatic, DNA, or aptamer-based biosensors.
Speaker Bio
Todd Hoare is the Canada Research Chair in Engineered Smart Materials and a Professor in the Department of Chemical Engineering at McMaster University as well as the Director of the NSERC CREATE Training Program for Controlled Release Leaders (ContRoL). Dr. Hoare’s work on “smart” environmentally-responsive hydrogels, in situ-gelling/printable hydrogel materials, and nanoscale drug delivery vehicles has been profiled by Popular Science, Maclean’s, and BBC for its potential in solving clinical challenges through innovative materials design. He is a Fellow of the International Union of Societies in Biomaterials Science and Engineering (IUS-BSE), was awarded an NSERC E.W.R. Steacie Memorial Fellowship (2018), has been cited as part of the 2018 Class of Influential Researchers by Industrial Engineering & Chemistry Research, and has received the 2016 Early Career Investigator Award from the Canadian Biomaterials Society and the 2009 John Charles Polanyi Prize in Chemistry in recognition of his research. He is also the co-recipient of the 2023 NSERC Brockhouse Prize for Interdisciplinary Research for his work in developing innovative drug delivery vehicles in collaboration with clinicians. Dr. Hoare is a past-president of the Canadian Biomaterials Society (2016-2017) and the Canadian Chapter of the Controlled Release Society (2013-2015), and is currently the Chair of the Macromolecular Science and Engineering Division of the Chemical Institute of Canada. He also serves as one of the Executive Editors of Chemical Engineering Journal (where he leads the applied polymer materials section) and is a member of the Editorial Advisory Board of Biomacromolecules.
Abstract
In research, we wonder, we re-examine dogma, we ask the “what if?” questions that lead to new insights and discoveries.
In business, we look for gaps, unsolved problems and intentionally develop solutions that fill a market need.
In this seminar, I will discuss both approaches in three stories. I will highlight how a series of “I wonder if?” questions led us to design a completely new way for target discovery and drug screening in cancer.
I will show how our new way to deliver therapeutics locally to the spinal cord and brain led to the invention of a new biomaterial that we have now tested clinically.
I will describe how we purposely designed a new vitreous substitute to overcome an unmet need and our path to translation.
Acknowledgements: The Shoichet Lab is grateful to have the opportunity to advance knowledge with exceptional researchers and collaborators and with the support of funding agencies: NSERC, CIHR, Medicine by Design-CFREF, Mend the Gap-NFRF, Krembil Foundation, DoD, ISRT, PRiME, among others.
Speaker Bio
Professor Molly Shoichet is University Professor, a distinction held by less than 2% of the faculty, and is Scientific Director of Precision Medicine at the University of Toronto, She is the inaugural Pamela & Paul Austin Chair in Precision and Regenerative Medicine. Dr. Shoichet served as Ontario’s first Chief Scientist in 2018 where she worked to enhance the culture of science. She has published over 800 papers, patents and abstracts and has given over 580 lectures worldwide. She currently leads a laboratory of 30 and has graduated 260 researchers. Her research is focused on drug and cell delivery strategies in the central nervous system (brain, spinal cord, retina) and 3D hydrogel culture systems to model cancer. Dr. Shoichet co-founded four spin-off companies, is actively engaged in translational research and science outreach. Dr. Shoichet is the recipient of many prestigious distinctions and the first person to be inducted into all three of Canada’s National Academies of Science of the Royal Society of Canada, Engineering and Health Sciences. In 2018, Professor Shoichet was inducted as an Officer of the Order of Canada and in 2011, she was awarded the Order of Ontario. Dr. Shoichet was the L’Oreal-UNESCO For Women in Science Laureate for North America in 2015, elected Foreign Member of the US National Academy of Engineering in 2016, won the Killam Prize in Engineering in 2017 and elected Fellow to the Royal Society (UK) in 2019. In 2020, Dr. Shoichet was awarded the NSERC Herzberg Gold Medal and won the Margolese National Brain Disorders Prize. In 2023, Dr. Shoichet was elected Fellow of the US National Academy of Inventors. Dr. Shoichet received her SB from the Massachusetts Institute of Technology (1987) and her PhD from the University of Massachusetts, Amherst in Polymer Science and Engineering (1992).
Abstract
Many chemical engineering courses are still delivered in the traditional course format of lectures with assignments and examinations as assessments. In addition, applications in the oil and gas industry are frequently used to illustrate concepts. This format and examples do not effectively engage many students. Creative ways of incorporating active-learning opportunities with relatable and/or diverse examples can improve the learning experience for undergraduate chemical engineering students. Details will be provided about an active-learning, technical elective course that uses coffee to illustrate and synthesize chemical engineering concepts; the students are literally able to taste their learning. Details will also be shared about the redesign of a fundamental course on mass transfer operations that features new examples, a case study, and in-class demonstrations.
Speaker Bio
Lauren Tribe has obtained an Honors Science degree in Biochemistry, a Bachelor of Engineering Science degree in Biochemical Engineering, and a Doctorate in Chemical Engineering from Western University and has been licensed as a Professional Engineering since 2006. She has been a faculty member at Western since 2001 and held administrative positions of Associate Chair, Undergraduate, of Chemical and Biochemical Engineering from 2015 to 2016 and Assistant Dean, First Year Studies, from 2016 to 2012. She has held special teaching roles at Western University as Experiential Learning Innovation Scholar 2020 – 2022 and Teaching Fellow 2022 – 2025. She has also received teaching awards in engineering in 2011 for the Maurice Bergougnou Teaching Award and in 2022 for the R. Mohan Mathur Award for Excellence in Teaching and then in 2023, the Edward G. Pleva Teaching Award for Teaching Excellence at Western University. Lauren is passionate about engineering and engineering education and has taught 56 courses to over 3,000 undergraduate engineering students over her career. She has developed opportunities for her students to be excited about their learning and to become engaged with experiential components in her courses. Examples include developing faculty-led study abroad courses to learn about engineering in a global context, an experiential course using coffee to synthesize chemical engineering concepts in a fun a relatable way, and incorporating examples and demonstrations to improve learning and understanding of mass transfer.