CBE Seminar (Zoom): Characterizing the Evolution of Gel Scaffolds Using Passive Microrheology

Non-UCI people, please use this registration link: https://forms.gle/dT3ok64HyBwGPHZTA

Abstract: The evolution of gel scaffolds is designed as part of the end-use of these materials for many varied applications. Due to gel versatility, these materials are used in applications that range from home-care products to synthetic materials for targeted drug and cell delivery. To meet the need of this broad range of applications, we must first understand the change in material properties and scaffold structure during gelation and degradation. We will discuss the characterization of two gel systems: a hydrogenated castor oil (HCO) colloidal gel and a covalent adaptable poly (ethylene glycol) (PEG)-hydrazone polymeric hydrogel scaffold. In this work, we use multiple particle tracking microrheology (MPT) to measure dynamic material properties during phase transitions. MPT measures the thermal motion of embedded probe particles to characterize rheological properties.

HCO is a rheological modifier used in commercial products, including fabric and home-care products. Of concern in the design is whether the gradient that induces phase change can overcome any processing history, particularly due to shear stress. In this work, we characterize HCO evolution with MPT, μ2rheology (MPT in a microfluidic device) and bulk rheology. MPT measures that the scaffold structure varies when a single sample is gelled or degraded. To determine whether this is due to processing history, we develop a new microfluidic device for μ2rheology measurements. μ2rheology measurements of consecutive phase changes of HCO are taken starting with both a sheared solution of HCO and an unsheared HCO gel and measuring these scaffolds' return to the same equilibrium properties. We conclude that equilibrium structures depend on the shear history of the starting material, which can have implications in end-use products made with the colloidal gel scaffolds.

Covalent adaptable hydrogels (CAHs) are attractive biomaterials due to their ability to break and reform bonds in response to external stimuli better mimicking aspects of the native extracellular matrix and processes within our body. In this work, we characterize dynamic changes in a CAH in response to changes in pH in the incubation environment that mimic the pH of the gastrointestinal tract. The CAH we are characterizing is composed of 8-arm star PEG-hydrazine that chemically cross-links with an 8-arm star PEG-aldehyde creating a covalent adaptable hydrazone bond. In our previous work, we determined that scaffold degradation was pH dependent with vastly different rheological evolution. To exploit these dynamic properties, we measure CAH degradation using μ2rheology. This device enables changes in the incubation liquid around a sample even when the sample is a sol. We mimic the changing pH environment through a healthy and diseased GI tract in our microfluidic device. We determine that dynamic material property evolution is consistent with degradation at a single pH. However, the time scale of degradation is reduced by the history of degradation. These investigations inform the design of this material as a new vehicle for targeted delivery. This technique and CAH characterization will be used in future work to measure the ability to release molecules from the scaffold during digestion.

Bio: Kelly M. Schultz is an associate professor in the Department of Chemical and Biomolecular Engineering at Lehigh University. She obtained her B.S. in chemical engineering from Northeastern University in 2006 and a Ph.D. in chemical engineering with Professor Eric Furst from the University of Delaware in 2011 as a National Science Foundation graduate research fellow. While at Delaware, she was invited to speak at the American Chemical Society Excellence in Graduate Polymers Research Symposium and was selected as the Fraser and Shirley Russell Teaching Fellow. Following her Ph.D., she was a Howard Hughes Medical Institute postdoctoral research associate at the University of Colorado at Boulder, working in the laboratory of Professor Kristi Anseth. As a postdoc, she was invited to participate in the Distinguished Young Scholars Summer Seminar Series at the University of Washington. She began her position as assistant professor at Lehigh University in 2013, was named a P.C. Rossin Assistant Professor 2016-2018 and was promoted to associate professor in 2019. Schultz was named one of TA Instruments Distinguished Young Rheologists (2014), was awarded an NSF CAREER award (2018), the Lehigh University Libsch Early Career Research Award (2019), the P.C. Rossin College of Engineering and Applied Science Excellence in Research Scholarship & Leadership (2020), and was named the Pirkey Centennial Lecturer by the McKetta Department of Chemical Engineering at the University of Texas at Austin (2022). Schultz and her research group study emerging hydrogel materials developed for biological applications, such as wound healing and tissue regeneration. Of particular interest is the development of bulk and microrheological techniques that measure how 3D encapsulated human mesenchymal stem cells degrade and remodel synthetic hydrogel scaffolds during motility.

Host: Professor Ali Mohraz