What do bull sperm know about emergent behaviors? - by Chih-Kuan Tung
Chih-Kuan Tung Department of Physics, North Carolina A&T State University
Host: Lisa Manning | Contact: Tyler Engstrom, firstname.lastname@example.org
In a complex system, some patterns or orders only emerge when the objects interact with the environment or each other. In a dynamical system, the description of how the environmental stress induces the new order can often be described by a bifurcation. In a many-body system, the interaction between individual objects often results in a phase transition or phase separation. These are arguably the most universal descriptions you can find in physics, covering phenomena from Higgs mechanism in high energy, superconductivity in condensed matter, to thermal convection in nonlinear dynamics. Biology provides vast number of different complex systems, yet people only just started to explore finding universality through their emergent behaviors. In this talk, I will focus on two emergent behaviors discovered by using microfluidics to model the physical environment of the mammalian female reproductive tract for sperm. By modeling the outward going fluid flow in the female tract, we showed that sperm swimming against a flow can be described by a bifurcation theory, such that the upstream orientation order only emerges when the flow rate exceeds a critical level, and the emergence follows a ½ power law, which is known for a mean field theory. By adding polymer into the sperm medium to model the viscoelasticity naturally found in the mucus, we found that sperm start to form aggregates, and the formation/dissociation of the aggregates is a dynamic process, similar to a liquid/gas phase separation. This aggregation is primarily mediated by the elasticity of the fluid. I will discuss the implications in both physics and biology.