Session: 20-17-01: Rising Stars of Mechanical Engineering

Paper Number: 172191

Diffusiophoretic Transport of Biological Colloids Driven by Salt Gradients 

Diffusiophoresis describes a deterministic motion of colloidal particles along chemical gradients driven by non-equilibrium surface-solute interactions. The abundance of chemical gradients in nature makes this subtle transport process particularly relevant in biological and environmental contexts. Here, I will showcase two examples illustrating the importance of diffusiophoresis in biological systems.

First, I will demonstrate how diffusiophoresis can govern the formation and localization of biomolecular condensates, which have implications for cellular organization. The internal microenvironment of a living cell is heterogeneous and comprises a multitude of organelles with distinct biochemistry. Amongst them are biomolecular condensates, which are membrane-less, phase-separated compartments enriched in system-specific proteins and nucleic acids. The heterogeneity of the cell engenders the presence of multiple spatiotemporal gradients in chemistry, charge, concentration, temperature, and pressure. Such thermodynamic gradients can lead to non-equilibrium driving forces for the formation and transport of biomolecular condensates. Here, we show how ion gradients impact the transport processes of biomolecular condensates on the mesoscale and biomolecules on the microscale. Utilizing a microfluidic platform, we demonstrate that the presence of ion concentration gradients can accelerate the transport of biomolecules, including nucleic acids and proteins, via diffusiophoresis. This hydrodynamic transport process allows localized enrichment of biomolecules, thereby promoting the location-specific formation of biomolecular condensates via phase separation. The ion gradients further impart directional motility of condensates, allowing them to exhibit enhanced diffusion along the gradient. Coupled with a reentrant phase behavior, the gradient-induced enhanced motility leads to a dynamical redistribution of condensates that ultimately extends their lifetime. Together, our results demonstrate diffusiophoresis as a non-equilibrium thermodynamic force that governs the formation and transport of biomolecular condensates.

Next, I will discuss how diffusiophoresis can alter the flagellar motility of soil bacteria and how this understanding can be applied to bioremediation strategies. Bacteria are often required to navigate in confined spaces to reach desired destinations in various biological and environmental systems, allowing critical functions for, for example, host-microbe symbiosis, gut microbiome, infection, soil ecology, and soil bioremediation. While run-and-tumble chemotaxis is effective in finding targets in confined spaces, it is not the most ideal strategy due to the continuous monitoring of environmental cues and recorrection of their paths. Here, we show that salt gradients can be used to improve the run-and-tumble motility of flagellated soil bacteria, Pseudomonas putida, by biasing the cells’ motion toward the salt, thereby improving dispersion toward the target. We observe that salt gradients impact bacterial swimming behavior by straightening their run motion toward salt. We show that this behavior is due to non-uniform diffusiophoresis acting around the cell, thereby imposing an effective torque on the cell body. This leads to reducing random fluctuation, thus effectively stabilizing the cell motion and guiding them toward salt with straighter runs. We further demonstrate that by imposing salt gradients during chemotaxis toward or away from toxic organic contaminants, their dispersion toward the contaminants can be improved via diffusiophoresis, suggesting its potential utility in bioremediation.

Presenting Author: Sangwoo Shin University at Buffalo, The State University of New York

Presenting Author Biography: Sangwoo Shin is an Associate Professor of Mechanical and Aerospace Engineering at the University at Buffalo. Prior to joining UB in 2021, he earned his BS and PhD from Yonsei University in Seoul, Korea, completed postdoctoral training at Princeton University, and served as an Assistant Professor at the University of Hawaii. His research group focuses on understanding and controlling the transport and interfacial processes of complex fluids in natural and engineering systems. He received the CAREER Award from the National Science Foundation in 2023.

Authors:

Sangwoo Shin University at Buffalo, The State University of New York