Abstract
Lab-on-a-chip platforms present many new opportunities to study bacterial cells and cellular
19 assemblies. Here, the authors describe a new platform that allows us to apply uniaxial stress to
20 individual bacterial cells while observing the cell and its subcellular assemblies using a high
21 resolution optical microscope. The microfluidic chip consists of arrays of miniature pressure
22 actuated valves. By placing a bacterium under one of such valves and partially closing the valve
23 by externally applied pressure, the cell can be deformed. Although large pressure actuated
24 valves used in integrated fluidic circuits have been extensively studied previously, here the
25 authors downsize those microfluidic valves and use flow channels with rectangular cross-
26 sections to maintain the bacteria in contact with cell culture medium during the experiments.
27 The closure of these valves has not been characterized before. First, these valves are modeled
28 using finite element analysis, and then compared the modeling results with the actual closing
29 profiles of the valves, which is determined from absorption measurements. The measurements
30 and modeling show with good agreement that the deflection of valves is a linear function of
31 externally applied pressure and the deflection scales proportionally to the width of the flow
32 channel. In addition to characterizing the valve, the authors show at a proof-of-principle level
33 that it can be used to deform a bacterial cell at considerable magnitude. They found the largest
34 deformations in 5 lm wide channels where the bacterial width and length increase by 1.6 and
35 1.25 times, respectively. Narrower and broader channels are less optimal for these studies. The
36 platform presents a promising approach to probe, in a quantitative and systematic way, the me-
37 chanical properties of not only bacterial cells but possibly also yeast and other single-