Liquid microchannels on structured surfaces are built up using a wettability pattern consisting of hydrophilic stripes on a hydrophobic substrate. These channels undergo a shape instability at a certain amount of adsorbed volume, from a homogeneous state with a spatially constant cross section to a state with a single bulge. This instability is quite different from the classical Rayleigh Plateau instability and represents a bifurcation between two different morphologies of constant mean curvature. The bulge state can be used to construct channel networks that could be used as fluid microchips or microreactors.
Cyclic AMP (cAMP) dependent catabolite repression effect in E. coli is among the most intensely studied regulatory processes in biology. However, the physiological function(s) of cAMP signalling and its molecular triggers remain elusive. Here we use a quantitative physiological approach to show that cAMP signalling tightly coordinates the cell’s protein expression program with its metabolic needs during exponential cell growth: The expression of carbon catabolic genes increased linearly with decreasing growth rates upon limitation of carbon influx, but decreased linearly with decreasing growth rate upon limitation of nitrogen or sulfur influx. In contrast, the expression of biosynthetic genes exhibited the opposite linear growth-rate dependence as the catabolic genes. A coarse-grained mathematical model provides a quantitative framework for understanding and predicting gene expression responses to catabolic and anabolic limitations. A scheme of integral feedback control featuring the inhibition of cAMP signalling by metabolic precursors is proposed and validated. These results reveal a key physiological role of cAMP-dependent catabolite repression: to ensure that proteomic resources are spent on distinct metabolic sectors as needed in different nutrient environments. Our finding underscores the power of quantitative physiology in unravelling the underlying functions of complex molecular signalling networks.
Periodic stripe patterns are ubiquitous in living organisms, yet the underlying developmental processes are complex and difficult to disentangle. We describe a synthetic genetic circuit that couples cell density and motility. This system enabled programmed Escherichia coli cells to form periodic stripes of high and low cell densities sequentially and autonomously. Theoretical and experimental analyses reveal that the spatial structure arises from a recurrent aggregation process at the front of the continuously expanding cell population. The number of stripes formed could be tuned by modulating the basal expression of a single gene. The results establish motility control as a simple route to establishing recurrent structures without requiring an extrinsic pacemaker.
Synchronization and wave formation in one-dimensional ciliary arrays are studied analytically and numerically. We develop a simple model for ciliary motion that is complex enough to describe well the behavior of beating cilia but simple enough to study collective effects analytically. Beating cilia are described as phase oscillators moving on circular trajectories with a variable radius. This radial degree of freedom turns out to be essential for the occurrence of hydrodynamically induced synchronization of ciliary beating between neighboring cilia. The transitions to the synchronized and phase-locked state of two cilia and the formation of metachronal waves in ciliary chains with different boundary conditions are discussed.
The morphology of wetting layers on structured or imprinted surfaces is determined by the geometry of the underlying surface domains. Droplets which cover a single domain exhibit contact angles which do not satisfy Young's equation. For surface patterns consisting of many surface domains, the wetting layer exhibits several distinct morphologies (homogeneous droplet patterns, heterogeneous droplet patterns, film states) and may undergo morphological transitions between these different states. The latter transitions exhibit spontaneous symmetry breaking. [S0031-9007(98)05366-6] PACS numbers: 68.45.Gd, 68.10.Cr Several experimental methods are available by which one can create structured or imprinted surfaces with domain sizes of a few micrometers. Three examples are (i) elastomer stamps by which one can create patterns of hydrophobic alkanethiol on metal surfaces [1], (ii) vapor deposition through grids which cover part of the surface [2], and (iii) photolithography of amphiphilic monolayers which contain photosensitive molecular groups [3].If such a structured surface is in contact with a liquid, the corresponding interface has a position-dependent free energy which reflects the underlying surface pattern. In order to be specific, let us consider a surface which consists of hydrophilic domains in a hydrophobic matrix and let us place a thin wetting layer of water [4] onto this surface. The water wants to wet the hydrophilic domains but wants to dewet the hydrophobic matrix, respectively. As a result, the surface pattern will modulate the shape of the water layer and thus will affect its morphology.In this Letter, we will theoretically study this interplay between the pattern of surface domains and the wetting layer morphology. We will first show that, for a single surface domain, one must distinguish three different droplet regimes, denoted by 1, 2, and 3, depending on the hydrophilicity and hydrophobicity of the two types of surface domains. If these domains are strongly hydrophilic and strongly hydrophobic, respectively, all droplets belong to the intermediate regime 2. The latter regime is unusual since the corresponding droplets are characterized by contact angles which do not satisfy the well-known Young equation.For a surface pattern consisting of many surface domains, we find that the wetting layer can exhibit several distinct morphologies: (i) a homogeneous droplet pattern where all droplets have the same size; (ii) a heterogeneous droplet pattern characterized by one large and many small droplets; and (iii) a film state for which the wetting layer covers both the hydrophilic and the hydrophobic surface regions. The relevant parameters which determine the corresponding phase diagram are (a) the water volume y per hydrophilic domain and ( b) the area fraction X of the hydrophilic domains; see Fig. 1. As one moves across the phase boundaries, the wetting layer undergoes transitions between these different morphologies.These morphologies represent equilibrium states of a certain amount of liquid and are obtai...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.