Event Title : Soft and active living matter in complex environment: an approach using 3D bioprinting

Session Theme : Control and patterns, Session Chair : Shaon Chakrabarti
Speaker Name: 
Tapomoy Bhattacharjee
Start Time: 
Thursday, January 13, 2022 - 17:35
End Time: 
Thursday, January 13, 2022 - 17:55
Talks Abstract: 

While bacterial motility is well-studied on flat surfaces or in unconfined liquid media, most bacteria are found in disordered porous media, such as biological gels and tissues, soils, sediments, and subsurface formations. Understanding how porous confinement alters bacterial motility is therefore critical to modeling the progression of infections, applying beneficial bacteria for drug delivery, and bioremediation. We have recently developed a transparent porous media from jammed polyelectrolyte microgels to interrogate the migration of E. coli bacteria through the 3D pore space. Direct visualization enables us to reveal a new mode of motility exhibited by individual cells, in stark contrast to the paradigm of run-and-tumble motility, in which cells are intermittently and transiently trapped as they navigate the pore space; analysis of these dynamics enables prediction of single-cell transport over large length and time scales. Further, by utilizing a new approach to 3D bioprinting of cellular communities that utilizes the self-healing nature of this porous medium, we investigate how this behavior manifests in concentrated populations of E. coli in porous media. We find that cellular chemotaxis drives collective migration while confinement in a porous medium fundamentally alters chemotactic migration in two ways. First, cells bias their motion through a different primary mechanism in confinement than in bulk liquid. They primarily modulate the amplitude, not frequency, of body reorientation. Second, in porous media, populations can still coherently migrate over large length & time scales, but confinement strongly alters the dynamics & morphology of the population. Finally, I will describe a mechanism by which collectively migrating populations smooth out large-scale perturbations in their overall morphology via chemotaxis. We identify two distinct modes in which chemotaxis influences the morphology of the population: cells in different locations along a front migrate at different velocities due to spatial variations in (i) the local nutrient gradient and in (ii) the ability of cells to sense and respond to the local nutrient gradient. While the first mode is destabilizing, the second mode is stabilizing and dominates, ultimately driving smoothing of the overall population and enabling continued collective migration. This process is autonomous, arising without any external intervention; instead, it is a population-scale consequence of the manner in which individual cells transduce external signals. Together, these studies highlight how the jammed microgel medium provides a powerful platform to design and interrogate complex cellular communities in 3D—with implications for tissue engineering, studies of cellular interactions, and biophysical studies of active matter.

Event Day: 
Day 4 (13th Jan 2022)