(6j) Constitutive Modeling of Complex Biomaterials

Biofluids and biomaterials typically exhibit rich and complex behavior under deformation which arises from the dynamic adjustments to the internal microstructure. Moreover, these materials are extremely diverse ranging from low viscous fluids like blood to stretchable elastic materials like tendons to compact, solid materials able to support large stresses like bones. The complex behavior and function of each of these materials has been well engineered through evolution for millions of years. However, our understanding of how to characterize these materials and their overall relation to health is typically not well understood. I am interested in progressing this understanding through advanced, yet computationally inexpensive, modeling based off precise and physiologically motivated experiments. This can be achieved through carefully designed constitutive models which link the microstructure to macroscopically observable features. Constitutive modeling is advantageous to microscopic based computational techniques in that constitutive models can easily be coupled with more traditional continuum approaches like computational fluid dynamics (CFD) simulations and can be implemented in complex geometries with unsteady boundary conditions without increasing the computational cost significantly. Through more accurate modeling of these materials, we can improve our understanding of the structure and function of biomaterials, enhance health monitoring and surgical techniques, and begin to move toward synthetic, biocompatible replacement materials.

Teaching Interests:

Teaching and mentorship are largely what motivate me to pursue a career in academia. My primary interests are in fluid mechanics and transport. However, I would also hope to teach advanced courses involving rheology, colloid science, and/or computational methods. As an instructor, I would hope to incorporate more practical problems and projects motivated by current industrial and academic research. In addition to scholastic teaching interests, I am also excited to mentor future researchers. Through mentoring, I hope to challenge my students and motivate them to ask questions and subsequently search for answers via the scientific method.

Research Experience:

I am currently a 5^th year PhD candidate working with Dr. Antony Beris and Dr. Norman Wagner at the University of Delaware with a dissertation titled “An experimental and theoretical investigation of blood rheology”. Thus far in my research, I have helped to standardize approaches to measuring the rheology of blood and have pioneered experiments that are better representative of in vivo flow behavior. Using the experimental results, I have developed a transient constitutive model for the thixotropic behavior of blood. The model features several physiologically relevant parameters and can enable insight into the microstructure of the sample at any point in time and with any previous strain history. Additionally, the model significantly outperforms previous models that have been established for blood rheology. Currently, I have been working to include inhomogeneous effects in the model and incorporate it into CFD simulations that can be compared with microfluidic experiments that we are conducting. In parallel to this, I have been working on measuring blood across species to elucidate the interspecies hemorheological differences and move towards understanding the individualized evolutionary design of blood. Although my primary research focuses on measuring and modeling blood rheology, I have also worked on side projects to model flow of complex materials including viscoelastic simulation of polymer extrusion in 3D printing alongside Dr. Michael Mackay and an industry funded project on flow of dilute polymer solutions through a hyperbolic contraction.

Teaching Experience:

Throughout my undergraduate and graduate studies, I have pursued various teaching opportunities. As an undergraduate at Cornell University, I served as a teaching assistant for several core engineering courses including process control strategies, fluid mechanics, and heat and mass transfer. Additionally, I led an academic excellence workshop as a supplemental course for engineers taking an introductory course on computing with MATLAB. At the University of Delaware, I have also enjoyed many teaching positions. For two consecutive years, I served as a teaching assistant for the undergraduate fluid mechanics course and was selected to receive the Robert L. Pigford Teaching Assistant Award my second year. As a teaching assistant, I led office hours, wrote homework solutions, and helped assign grades. Moreover, I helped to develop a final project that brought in elements indirectly related to my thesis that tested and taught numerous fluid mechanics concepts. After completing my teaching assistant requirements, I also was selected as a Fraser and Shirley Russel Teaching Fellow for undergraduate fluid mechanics for the following year. This fellowship, starting in the Fall of 2019 enables me to be directly involved with the course by giving lectures, designing homework and exam problems, and holding office hours. Outside of the classroom, I have also served as a research mentor for six different undergraduate students and one high school student.

Future Direction:

Moving forward, I want to use the tools I’ve developed throughout my thesis to model other complex biomaterial systems. Various other biological materials, including synovial fluid, saliva, mucus, and vitreous humor or more elastic materials like skin, tendons, and ligaments, have been shown to demonstrate interesting rheological characteristics. However, the modeling of these fluids is lacking partly due to oversimplified or inaccurate models and partly because of a lack of reliable experimental data. After first characterizing the samples through physiologically motivated shear and extensional rheological experiments, I hope to extend my constitutive modeling framework to apply to this variety of fluids. Subsequently, I want to incorporate these models into continuum simulations to achieve a better understanding of how these biomaterials function. Finally, I hope to compare the simulation results to a range of experimental data involving but not limited to scattering, atomic force microscopy, tribology, microfluidics, and tensiometry whether obtained in my research group or through collaborations with other experimental research groups.

Publications:

1. JS Horner, MJ Armstrong, NJ Wagner, and AN Beris, “Investigation of blood rheology under steady and unidirectional large amplitude oscillatory shear,” Rheol., 62(2), 577-591 (2018).
2. M Armstrong, J Horner, M Clark, M Deegan, T Hill, C Keith, and L Mooradian, “Evaluating rheological models for human blood using steady state, transient, and oscillatory shear predictions,” Acta, 57(11), 705-728 (2018).
3. JS Horner, AN Beris, DS Woulfe, and NJ Wagner, “Effects of ex vivo aging and storage temperature on blood viscosity,” Hemorheol. Microcirc., 70(2), 155-172 (2018).
4. JS Horner, MJ Armstrong, NJ Wagner, and AN Beris, “Measurements of human blood viscoelasticity and thixotropy under steady and transient shear and constitutive modeling thereof,” Rheol., Under Revision.
5. M Armstrong, T Helton, S Rogers, and J Horner, “Analysis of transient human blood rheology using sequence of physical processes (SPP),” Acta, Under Revision.
6. JS Horner, NJ Wagner, and AN Beris, “A review on recent advances in modeling and simulation of blood flow,” Soft Matter (Invited), In preparation.

Successful Grants/Fellowships:

• Graduate Fellowship – NASA / Delaware Space Grant Consortium (DESGC) (Awarded: 05/2019)