Microfluidic device for engineering 3D epithelial monolayers with controlled pressure
by Nimesh Ramesh, Integrative Cell and Tissue Dynamics
The remarkable feature of the epithelial sheets is to form specialized 3D structures suited to their physiological roles, such as highly branched structures in the lungs, drastic shape changes during embryonic development, or self-organizing organoids. These tissues are distinctive not just in the forms cells assume, but also in function. To achieve this, tissues and the cells in them exhibit coordinated behavior across the spatial and temporal scale. In a sense, 3D epithelia resemble an active material that adapts and changes in response to its biophysical-chemical stimuli like gene expression, morphogen gradients, and lumen pressure. A rheological study of the epithelia would provide unique insight on two fronts. First, to understand the fundamental physical rules of the biology, and second for inspiration of new engineering tools and design principles.
Our study focuses on the tissue response to physical forces, specifically pressure, tension, and curvature. We have fabricated a microfluidic setup to subject epithelial tissues to lumen pressure at different spatial and temporal scales. The epithelial monolayer is grown on a porous surface with circular low adhesion zones. On applying controlled pressure, the monolayer delaminates into a spherical cap (dome). Laplace law for spherical shells allows us to compute tension in the 3D structure with applied pressure and the radius of the dome.
This microfluidic device helps us to characterize the 3D epithelial shape along with the mapping of physical forces. Here, we demonstrate that the device can subject MDCK epithelial cells to a range of lumen pressure at different rates. Drastic reduction in pressure results in tissue collapsing into wrinkles; showing buckling tendency of the tissue under compression. We think that our device enables studying geometrical and biophysical constraints of tissues and unravel emergent phenomena in tissues.
Saccade rate is associated with number of items in working memory
by Sock Shing Low, Synthetic, Perceptive, Emotive and Cognitive Systems (SPECS)
Working memory has been shown to rely on theta oscillations for item representations, and the successful recall of items depends greatly on theta’s phase during both encoding and recall. At the same time, it has been observed that saccadic eye movements during visual exploration trigger theta phase-resets, raising the question of whether the neuronal substrates of mnemonic processing rely on motor-evoked responses. To quantify the relationship between saccadic eye movements and working memory load, we tested human participants performing an n-back Sternberg auditory task in combination with a colour-based catch detection task. We observed a task-specific interference in performance and an increase in saccade rate when both tasks were carried out simultaneously. Saccade rate also increased concurrently with working memory load in the Sternberg task’s pre-response stage, reflecting its hypothesised role in memory recall. Our results suggest an interplay between saccades and hippocampal theta during retrieval of items in working memory.