Applied mathematicians see complex problems through the lens of modeling. Keen modelers view intractable problems for laboratory scientists as exciting opportunities of exploration. Such problems are often at the interface of many branches of science and mathematics, providing opportunities for collaboration and working with students from a broad range of backgrounds.
The research group led by mathematician Dr. Julie Simons at California State University Maritime Academy is one such collaborative effort, bringing Cal Maritime students and University of California, Berkeley, scientists together to understand problems in fertility. Gillian Hooper and Alex Rosenberger, juniors in mechanical engineering, are working on developing and running large-scale simulations of sperm swimming in groups near a spherical surface that mimics the surface of the egg.
Sperm motility is a major indicating factor for fertility potential and is driven by undulating flagella. Sperm typically swim in viscous fluids that, to a human, would feel like moving through honey or molasses. Plus, elastic polymers in the fluid are like a maze of connected springs that can both entrap sperm and propel sperm in different directions. A dense matrix of such elastic polymers surrounds the egg that sperm attempt to fertilize.
The multibillion-dollar fertility industry has long recognized issues surrounding sperm motility, and most treatments are targeted toward women. A surprising amount of the basic science involved in sperm motility is still unknown. In particular, modeling of viscoelastic fluids is notoriously complicated and until recently, some models were considered intractable because of high computational costs. Yet, fertility costs and infertility problems are becoming increasingly important. With climate change, scientists are facing mounting problems that often require fertility interventions, including food chain security and sustainable agriculture as well as global declines in biodiversity and new conservation approaches.
An interesting aspect of sperm behavior is the sperm of some species swim cooperatively in groups to effectively reach the egg. Studying sperm motility for populations and near surfaces in detail is now experimentally possible through high-resolution imagery. Mathematical and computational models have the potential to measure quantities involving forces, power and efficiency that simply cannot be measured in the laboratory.
The Simons team is trying to explain the fundamental science of how sperm reach the egg by extending computational models previously developed by Dr. Simons and her collaborators at Tulane University to more biologically relevant frameworks. These include investigating the motility of sperm populations and swimming near surfaces to elucidate whether cooperative swimming behavior is advantageous from a fluid mechanics perspective and how fluid elasticity and surfaces affect swimming behavior. This is important for understanding the evolutionary aspect of sperm development across species as well as fertility issues within species. Next summer, Hooper and Rosenberger will be validating and refining their model results by performing new laboratory experiments in the lab of Dr. Polina Lishko at UC Berkeley using human and rodent sperm and high-speed digital cameras.