A platform for stop-flow gradient generation to investigate chemotaxis

The ability of artificial microswimmers to respond to external stimuli and the mechanistical details of their origins belong to the most disputed challenges in interdisciplinary science. Therein, the creation of chemical gradients is technically challenging, because they quickly level out due to diffusion. Inspired by pivotal stopped flow experiments in chemical kinetics, we show that microfluidics gradient generation combined with a pressure feedback loop for precisely controlling the stop of the flows, can enable us to study mechanistical details of chemotaxis of artificial Janus micromotors, based on a catalytic reaction. We find that these copper Janus particles display a chemotactic motion along the concentration gradient in both, positive and negative direction and we demonstrate the mechanical reaction of the particles to unbalanced drag forces, explaining this behaviour

Hospitalization Costs of COVID-19 Cases and Their Associated Factors in Guangdong, China: A Cross-Sectional Study

Background: The ongoing COVID-19 pandemic has brought significant challenges to health system and consumed a lot of health resources. However, evidence on the hospitalization costs and their associated factors in COVID-19 cases is scarce.Objectives: To describe the total and components of hospitalization costs of COVID-19 cases, and investigate the associated factors of costs.Methods: We included 876 confirmed COVID-19 cases admitted to 33 designated hospitals from January 15th to April 27th, 2020 in Guangdong, China, and collected their demographic and clinical information. A multiple linear regression model was performed to estimate the associations of hospitalization costs with potential associated factors.Results: The median of total hospitalization costs of COVID-19 cases was $2,869.4 (IQR:$3,916.8). We found higher total costs in male (% difference: 29.7, 95% CI: 15.5, 45.6) than in female cases, in older cases than in younger ones, in severe cases (% difference: 344.8, 95% CI: 222.5, 513.6) than in mild ones, in cases with clinical aggravation than those without, in cases with clinical symptoms (% difference: 47.7, 95% CI: 26.2, 72.9) than those without, and in cases with comorbidities (% difference: 21.1%, 21.1, 95% CI: 4.4, 40.6) than those without. We also found lower non-pharmacologic therapy costs in cases treated with traditional Chinese medicine (TCM) therapy (% difference: −47.4, 95% CI: −64.5 to −22.0) than cases without.Conclusion: The hospitalization costs of COVID-19 cases in Guangdong were comparable to the national level. Factors associated with higher hospitalization costs included sex, older age, clinical severity and aggravation, clinical symptoms and comorbidities at admission. TCM therapy was found to be associated with lower costs for some non-pharmacologic therapies

A platform for stop flow gradient generation to investigate chemotaxis

The ability of artificial microswimmers to respond to external stimuli and the mechanistical details of their origins belong to the most disputed challenges in interdisciplinary science. Therein, the creation of chemical gradients is technically challenging, because they quickly level out due to diffusion. Inspired by pivotal stopped flow experiments in chemical kinetics, we show that microfluidics gradient generation combined with a pressure feedback loop for precisely controlling the stop of the flows, can enable us to study mechanistical details of chemotaxis of artificial Janus micromotors, based on a catalytic reaction. We find that these copper Janus particles display a chemotactic motion along the concentration gradient in both, positive and negative direction and we demonstrate the mechanical reaction of the particles to small forces deviations, explaining this behaviour

Entwicklung einer Plattform zur Generierung von Stop-Flow- Gradienten zur Untersuchung von Chemotaxis

Die Fähigkeit künstlicher Mikroschwimmer, auf äußere Reize zu reagieren und deren mechanistische Ursprünge, gehören zu den umstrittensten Fragen der interdisziplinären Wissenschaft. Die Erzeugung chemischer Gradienten ist dabei eine technische Herausforderung, da sie aufgrund von Diffusion schnell abflachen. Inspiriert von ‘Stop-flow’ Experimenten aus der chemischen Kinetik zeigen wir, dass die Erzeugung eines mikrofluidischen Gradienten durch Kombination mit einer Druckrückkopplungsschleife zur präzisen Kontrolle des Stoppens erfolgen kann. Das ermöglicht es uns, die mechanistischen Details der Chemotaxis von künstlichen katalytischen Janus-Mikromotoren zu untersuchen. Wir stellen fest, dass diese Kupfer-Janus-Partikel eine chemotaktische Bewegung entlang des Konzentrationsgradienten sowohl in positiver als auch in negativer Richtung zeigen, und wir demonstrieren die mechanische Reaktion der Partikel auf unausgewogene Widerstandskräfte, die dieses Verhalten erklären

A Platform for Stop-Flow Gradient Generation to Investigate Chemotaxis

The ability of artificial microswimmers to respond to external stimuli and the mechanistical details of their origins belong to the most disputed challenges in interdisciplinary science. Therein, the creation of chemical gradients is technically challenging, because they quickly level out due to diffusion. Inspired by pivotal stopped flow experiments in chemical kinetics, we show that microfluidics gradient generation combined with a pressure feedback loop for precisely controlling the stop of the flows, can enable us to study mechanistical details of chemotaxis of artificial Janus micromotors, based on a catalytic reaction. We find that these copper Janus particles display a chemotactic motion along the concentration gradient in both, positive and negative direction and we demonstrate the mechanical reaction of the particles to unbalanced drag forces, explaining this behaviour

Confined 1D Propulsion of Metallodielectric Janus Micromotors on Microelectrodes under Alternating Current Electric Fields

© 2019 American Chemical Society.There is mounting interest in synthetic microswimmers ("micromotors") as microrobots as well as a model system for the study of active matters, and spatial navigation is critical for their success. Current navigational technologies mostly rely on magnetic steering or guiding with physical boundaries, yet limitations with these strategies are plenty. Inspired by an earlier work with magnetic domains on a garnet film as predefined tracks, we present an interdigitated microelectrodes (IDE) system where, upon the application of AC electric fields, metallodielectric (e.g., SiO2-Ti) Janus particles are hydrodynamically confined and electrokinetically propelled in one dimension along the electrode center lines with tunable speeds. In addition, comoving micromotors moved in single files, while those moving in opposite directions primarily reoriented and moved past each other. At high particle densities, turbulence-like aggregates formed as many-body interactions became complicated. Furthermore, a micromotor made U-turns when approaching an electrode closure, while it gradually slowed down at the electrode opening and was collected in large piles. Labyrinth patterns made of serpentine chains of Janus particles emerged by modifying the electrode configuration. Most of these observations can be qualitatively understood by a combination of electroosmotic flows pointing inward to the electrodes, and asymmetric electrical polarization of the Janus particles under an AC electric field. Emerging from these observations is a strategy that not only powers and confines micromotors on prefabricated tracks in a contactless, on-demand manner, but is also capable of concentrating active particles at predefined locations. These features could prove useful for designing tunable tracks that steer synthetic microrobots, as well as to enable the study of single file diffusion, active turbulence, and other collective behaviors of active matters11sciescopu

Upstream rheotaxis of catalytic Janus spheres

Fluid flow is ubiquitous in many environments that form habitats for microorganisms. Therefore, it is not surprising that both biological and artificial microswimmers show responses to flows that are determined by the interplay of chemical and physical factors. In particular, to deepen the understanding of how different systems respond to flows, it is crucial to comprehend the influence played by swimming pattern. The tendency of organisms to navigate up or down the flow is termed rheotaxis. Early theoretical studies predicted a positive rheotactic response for puller-type spherical Janus micromotors. However, recent experimental studies have focused on pusher-type Janus particles, finding that they exhibit cross-stream migration in externally applied flows. To study the response to the flow of swimmers with a qualitatively different flow pattern, we introduce Cu@SiO2micromotors that swim toward their catalytic cap. On the basis of experimental observations, and supported by flow field calculations using a model for self-electrophoresis, we hypothesize that they behave effectively as a puller-type system. We investigate the effect of externally imposed flow on these spherically symmetrical Cu@SiO2active Janus colloids, and we indeed observe a steady upstream directional response. Through a simple squirmer model for a puller, we recover the major experimental observations. Additionally, the model predicts a "jumping" behavior for puller-type micromotors at high flow speeds. Performing additional experiments at high flow speeds, we capture this phenomenon, in which the particles "roll" with their swimming axes aligned to the shear plane, in addition to being dragged downstream by the fluid flow

Upstream rheotaxis of catalytic Janus spheres

Fluid flow is ubiquitous in many environments that form habitats for microorganisms. The tendency of organisms to navigate towards or away from flow is termed rheotaxis. Therefore, it is not surprising that both biological and artificial microswimmers show responses to flows that are determined by the interplay of chemical and physical factors. In particular, to deepen understanding of how different systems respond to flows, it is crucial to comprehend the influence played by swimming pattern. In recent studies, pusher-type Janus particles exhibited cross-stream migration in externally applied flows. Earlier, theoretical studies predicted a positive rheotactic response for puller-type spherical Janus micromotors. To compare to a different swimmer, we introduce Cu@SiO2 micromotors that swim towards their catalytic cap. Based on experimental observations, and supported by flow field calculations using a model for self-electrophoresis, we hypothesize that they behave effectively as a puller-type system. We investigate the effect of externally imposed flow on these spherically symmetrical Cu@SiO2 active Janus colloids, and we indeedobserve a steady upstream directional response. Through a simple squirmer model for a puller, we recover the major experimental observations. Additionally, the model predicts a unique “jumping” behaviour for puller-type micro- motors at high flow speeds. Performing additional experiments at high flow speeds, we capture this phenomenon, in which the particles “roll” with their swimming axes aligned to the shear plane, in addition to being dragged down- stream by the fluid flow