Title: Ultrafast Cellular Biophysics: Energetics, Dissipations, and Fundamental Limits.

Abstract: Speed is the essence of war. This is equally true for both multicellular organisms and single-cell organisms, which are constantly battling against various evolutionary pressures. Ultrafast phenomena have repeatedly evolved in both multicellular and single-cell organisms in many contexts, including predator-prey interactions. In fact, the fastest acceleration known in biology goes to the nematocysts of cnidarians, which ultimately is a single cell phenomenon. This raises numerous questions, as ultrafast phenomena present specific challenges at the single-cell level. For example, all the energy required for the ultrafast mechanisms has to be contained within a single cell's size, only to be deployed when the proper stimuli are present. Aside from that, they need to ensure they remain functional even after the deployment of their ultrafast mechanisms without any support from connective tissues, as extreme velocity and acceleration usually indicate the presence of extreme shear and extreme forces. These all pose additional evolutionary pressures on the organisms capable of ultrafast phenomena.

In this thesis, I present three major works. We first examine the physical meaning and proper definition of “ultrafast” at the cellular level. We show that aside from ultrafast acceleration and velocity, single-cell organisms also utilize ultrafast area strain rate, ultrafast volumetric strain rate, and ultrafast density changes for various functions. Through scaling analysis, we explore the fundamental limit of various ultrafast mechanisms. In the second part, we explore the phenomenon of “topological damping”, where entanglement in a soft-material causes mechanical jamming when they experience external stress. We discovered this unique material, formed by the entangled rough endoplasmic reticulum and vacuoles, in the context of a giant single-cell organism with ultrafast contractility (15g acceleration). We next proposed an entangled deformable particle model and demonstrated the programmed damping properties and energy dissipation mechanism of this entangled organelle architecture. In the third part, we worked on the “cellular hydraulics” of the invasion organelle from microsporidia, a group of parasites that cause huge health and economic burdens worldwide. We performed the first comprehensive biophysics analysis of the energy, pressure, and power requirements for the infection process of microsporidia. Furthermore, We proposed a novel hypothesis and demonstrated quantitatively how the buckling of the spore wall during germination plays a critical role in infection success. These works not only contribute to our understanding of extreme biological phenomena but also provide insights into potential failure modes at the cellular level and provide guidance in the design of soft robotics in the future.

Please contact Madelyn Bernstein for the Zoom link