Predator-Prey Interactions between Droplets Driven by Nonreciprocal Oil Exchange

Chemotactic interactions are ubiquitous in nature and can lead to nonreciprocal and complex emergent behavior in multibody systems. Here we show how chemotactic signaling between microscale oil droplets of different chemistries in micellar surfactant solutions can result in predator-prey-like chasing interactions. The interactions and dynamic self-organization result from the net directional, micelle-mediated transport of oil between emulsion droplets of differing composition and are powered by the free energy of mixing. The nonreciprocal behavior occurs in a wide variety of oil and surfactant conditions, and we systematically elucidate chemical design rules for tuning the interactions between droplets by varying oil and surfactant chemical structure and concentration. Through integration of experiment and simulation, we also investigate the active behavior and dynamic reorganization of multi-droplet clusters. Our findings demonstrate how chemically-minimal systems can be designed with controllable, non-reciprocal chemotactic interactions to generate emergent self-organization and collective behaviors reminiscent of biological systems

Gravitational settling of active droplets

The gravitational settling of oil droplets solubilizing in an aqueous micellar solution contained in a capillary channel is investigated. The motion of these active droplets reflects a competition between gravitational and Marangoni forces, the latter due to interfacial tension gradients generated by differences in filled- micelle concentrations along the oil-water interface. This competition is studied by varying the surfactant concentration, the density difference between the droplet and the continuous phase, and the viscosity of the continuous phase. The Marangoni force enhances the settling speed of an active droplet when compared to the Hadamard-Rybczynski prediction for a (surfactant free) droplet settling in Stokes flow. The Marangoni force can also induce lateral droplet motion, suggesting that the Marangoni and gravitational forces are not always aligned. The decorrelation rate () of the droplet motion, measured as the initial slope of the velocity autocorrelation and indicative of the extent to which the Marangoni and gravitational forces are aligned during settling, is examined as a function of the droplet size: correlated motion (small values of ) is observed at both small and large droplet radii, whereas significant decorrelation can occur between these limits. This behavior of active droplets settling in a capillary channel is in marked contrast to that observed in a dish, where the decorrelation rate increases with the droplet radius before saturating at large values of droplet radius. A simple relation for the crossover radius at which the maximal value of occurs for an active settling droplet is proposed

Predator–prey interactions between droplets driven by non-reciprocal oil exchange

Chemotactic interactions are ubiquitous in nature and can lead to non-reciprocal and complex emergent behaviour in multibody systems. However, developing synthetic, inanimate embodiments of a chemomechanical framework to generate non-reciprocal interactions of tunable strength and directionality has been challenging. Here we show how chemotactic signalling between microscale oil droplets of different chemistries in micellar surfactant solutions can result in predator–prey-like non-reciprocal chasing interactions. The interactions and dynamic self-organization result from the net directional, micelle-mediated transport of oil between emulsion droplets of differing composition and are powered by the free energy of mixing. We systematically elucidated chemical design rules to tune the interactions between droplets by varying the oil and surfactant chemical structure and concentration. Through the integration of experiment and simulation, we also investigated the active behaviour and dynamic reorganization of multidroplet clusters. Our findings demonstrate how chemically minimal systems can be designed with controllable, non-reciprocal chemotactic interactions to generate emergent self-organization and collective behaviours reminiscent of biological systems. [Figure not available: see fulltext.

Predator–prey interactions between droplets driven by non-reciprocal oil exchange

Chemotactic interactions are ubiquitous in nature and can lead to non-reciprocal and complex emergent behaviour in multibody systems. However, developing synthetic, inanimate embodiments of a chemomechanical framework to generate non-reciprocal interactions of tunable strength and directionality has been challenging. Here we show how chemotactic signalling between microscale oil droplets of different chemistries in micellar surfactant solutions can result in predator–prey-like non-reciprocal chasing interactions. The interactions and dynamic self-organization result from the net directional, micelle-mediated transport of oil between emulsion droplets of differing composition and are powered by the free energy of mixing. We systematically elucidated chemical design rules to tune the interactions between droplets by varying the oil and surfactant chemical structure and concentration. Through the integration of experiment and simulation, we also investigated the active behaviour and dynamic reorganization of multidroplet clusters. Our findings demonstrate how chemically minimal systems can be designed with controllable, non-reciprocal chemotactic interactions to generate emergent self-organization and collective behaviours reminiscent of biological systems. [Figure not available: see fulltext.

Nonelective coronary artery bypass graft outcomes are adversely impacted by Coronavirus disease 2019 infection, but not altered processes of care: A National COVID Cohort Collaborative and National Surgery Quality Improvement Program analysisCentral MessagePerspective

Objective: The effects of Coronavirus disease 2019 (COVID-19) infection and altered processes of care on nonelective coronary artery bypass grafting (CABG) outcomes remain unknown. We hypothesized that patients with COVID-19 infection would have longer hospital lengths of stay and greater mortality compared with COVID-negative patients, but that these outcomes would not differ between COVID-negative and pre-COVID controls. Methods: The National COVID Cohort Collaborative 2020-2022 was queried for adult patients undergoing CABG. Patients were divided into COVID-negative, COVID-active, and COVID-convalescent groups. Pre-COVID control patients were drawn from the National Surgical Quality Improvement Program database. Adjusted analysis of the 3 COVID groups was performed via generalized linear models. Results: A total of 17,293 patients underwent nonelective CABG, including 16,252 COVID-negative, 127 COVID-active, 367 COVID-convalescent, and 2254 pre-COVID patients. Compared to pre-COVID patients, COVID-negative patients had no difference in mortality, whereas COVID-active patients experienced increased mortality. Mortality and pneumonia were higher in COVID-active patients compared to COVID-negative and COVID-convalescent patients. Adjusted analysis demonstrated that COVID-active patients had higher in-hospital mortality, 30- and 90-day mortality, and pneumonia compared to COVID-negative patients. COVID-convalescent patients had a shorter length of stay but a higher rate of renal impairment. Conclusions: Traditional care processes were altered during the COVID-19 pandemic. Our data show that nonelective CABG in patients with active COVID-19 is associated with significantly increased rates of mortality and pneumonia. The equivalent mortality in COVID-negative and pre-COVID patients suggests that pandemic-associated changes in processes of care did not impact CABG outcomes. Additional research into optimal timing of CABG after COVID infection is warranted