Session N03: Biophysics and Medical Physics II

Collective Dynamics in Lipid Membranes: From Fundamental Physics to Health and Disease

Lipid bilayers, the main matrix of cell membranes, are evolutionary marvels of molecular self-assemblies. They host a myriad of vital biological processes and are ubiquitous in a variety of research areas at the interface of biophysics, health care, and biotechnology. To understand the functional properties of lipid membranes and fully utilize their potential in biotechnological applications, it is imperative to investigate biophysical membrane properties on the length and time scales of key biological processes. Among those, collective membrane fluctuations and molecular reorganization remain poorly understood despite their crucial role in various cellular phenomena, including protein-membrane interactions, viral budding, and signaling events. This talk will highlight recent advances in neutron scattering studies and molecular dynamics (MD) simulations illuminating the role of collective dynamics in regulating viscoelastic membrane properties and their response to compositional changes and environmental cues. Specific focus will be placed on new findings related to the dynamic response of membranes to cholesterol content and protein binding events. These findings provide new insights into the behavior of lipid membranes on largely unexplored spatiotemporal scales, with far-reaching implications in biological function and future designs of engineered membranes and artificial cells with real-world functionalities.   

Physics of Wound Healing: Investigating Calcium-Mediated Syncytia Formation

By studying the tissue-level response to wound healing in Drosophilae, whose cells divide regularly, we gain a foothold in understanding how other mitotically competent organisms (such as ourselves) will respond to wounds. In laser ablation wounds on the epithelium, we have seen that a cavitation bubble expands over the tissue and then recedes, stimulating a first wave of calcium signaling outside of the individual cells. Simultaneously, the cavitation bubble also causes small tears in the cell borders that are temporarily resealed. In the resealing process, scramblases flip phosphotidylserine (PS) from the inner layer to the outer layer. These openings also allow calcium to flow into the cell before they are sealed, which later causes a second calcium flash where the calcium passes from cell to cell via gap junctions. Calcium signaling activates actin dynamics, which propels regions of membrane into contact with each other. Regions of plasma membrane damage post-wound have been carefully mapped by the Hutson group at Vanderbilt, and they correlate strongly to regions where syncytia form. More investigation is needed to confirm whether calcium mediates the formation of syncytia as opposed to these processes simply being parallel to each other. By imaging the cell borders and calcium flash in real time via electron microscopy, I hope to determine if calcium plays an active role in the cell fusions that assist in wound healing, with followup gene knockdown experiments in order to confirm calcium triggers the formation of syncytia around the borders of a wound.   

Effects of tracheal microstructures on insect respiratory flows

Insects have evolved respiratory systems that transport air inside complex microscale tracheal networks in a highly efficient way, as evidenced by the fact that their metabolic range is the highest in the animal kingdom. Insect respiratory flows are characterized by low Reynolds numbers (~0.1), but the Knudsen numbers in insect tracheae span the continuum, slip, and transitional regimes (~0.0001-1). In this work, we investigate the effects of the fine-scale internal tracheal morphology on intratracheal flows in insects in silico. We hypothesized that the helically winding taenidial microstructures found on the inner surface of the tracheal tubes determine the structure of the flow field near the wall and play a vital role in transport. We have closely reproduced the internal morphology of the tracheal tubes of the American cockroach, Periplaneta americana, in our computational geometry. To investigate this hypothesis, we performed a series of simulations at a Reynolds number of 0.1. We found that the presence of taenidia creates transverse helical flows close to the tracheal wall and concentrates streamwise velocity near the centerline of the channel, enhancing vertical transport.