Global overview of the management of acute cholecystitis during the COVID-19 pandemic (CHOLECOVID study)

Background: This study provides a global overview of the management of patients with acute cholecystitis during the initial phase of the COVID-19 pandemic. Methods: CHOLECOVID is an international, multicentre, observational comparative study of patients admitted to hospital with acute cholecystitis during the COVID-19 pandemic. Data on management were collected for a 2-month study interval coincident with the WHO declaration of the SARS-CoV-2 pandemic and compared with an equivalent pre-pandemic time interval. Mediation analysis examined the influence of SARS-COV-2 infection on 30-day mortality. Results: This study collected data on 9783 patients with acute cholecystitis admitted to 247 hospitals across the world. The pandemic was associated with reduced availability of surgical workforce and operating facilities globally, a significant shift to worse severity of disease, and increased use of conservative management. There was a reduction (both absolute and proportionate) in the number of patients undergoing cholecystectomy from 3095 patients (56.2 per cent) pre-pandemic to 1998 patients (46.2 per cent) during the pandemic but there was no difference in 30-day all-cause mortality after cholecystectomy comparing the pre-pandemic interval with the pandemic (13 patients (0.4 per cent) pre-pandemic to 13 patients (0.6 per cent) pandemic; P = 0.355). In mediation analysis, an admission with acute cholecystitis during the pandemic was associated with a non-significant increased risk of death (OR 1.29, 95 per cent c.i. 0.93 to 1.79, P = 0.121). Conclusion: CHOLECOVID provides a unique overview of the treatment of patients with cholecystitis across the globe during the first months of the SARS-CoV-2 pandemic. The study highlights the need for system resilience in retention of elective surgical activity. Cholecystectomy was associated with a low risk of mortality and deferral of treatment results in an increase in avoidable morbidity that represents the non-COVID cost of this pandemic

Investigation of silver catalyst for propylene epoxidation: promotion and reaction mechanism

Mark A. BarteauThe gas-phase epoxidation of propylene on silver catalysts has been examined. Drawing parallels from the successful catalysts used in ethylene epoxidation, several silver-based catalysts have been tested for propylene epoxidation. However, no catalyst proved to be selective to the desired product, propylene oxide. Cadmium, copper, cesium and rhenium were tested as promoters to silver, but no catalyst achieved more than 5% selectivity to propylene oxide under the conditions tested. When the catalysts were tested at 267 ??C with a feed consisting of a gas mixture of propylene, oxygen and nitrogen at volume ratio of 1:1:8, the unpromoted silver catalyst was the least selective. The most selective catalyst was the copper-silver catalyst, which exhibited 4.3% selectivity to propylene oxide. The main limitation to selectivity is the high degree of combustion of propylene to carbon dioxide. By running the catalysts at different reaction conditions, important conclusions were drawn regarding the the kinetics of the reaction. The conversion of propylene increased as the volume ratio of oxygen to propylene fed to the reactor increased. As the oxygen fed to the reactor was increased with respect to propylene, the conversion of propylene increased but the selectivity to propylene oxide remained nearly constant for all but the rhenium-silver catalyst. For the rhenium-silver catalyst the selectivity decreased as the oxygen to propylene ratio was increased. The reaction order with respect to oxygen for propylene oxidation was deduced from these data. For the silver, cadmium-silver and rhenium-silver catalysts, the reaction order was greater than 1. However, for the cesium-silver and copper-silver catalysts the reaction order with respect to oxygen was 0.4 and 0.5, respectively. The propylene effect of the activity of the cesium-silver and copper-silver catalysts was also studied. The conversion of propylene decreased as the propylene fed to the reactor was increased with respect to oxygen. These results indicate that oxygen, and not propylene, controls the rate for propylene oxidation. This hypothesis was confirmed by measuring the apparent activation energy for the reaction. For all the catalysts tested the apparent activation energy was 14-17 kcal/mol, in agreement with the energy of oxygen dissociation on silver. Thus, it was concluded that oxygen dissociation is the rate determining step of propylene oxidation. The decomposition of the desired product, propylene oxide, was also analyzed. Propylene oxide was introduced to an unpromoted silver catalyst that had been previously tested for propylene oxidation. Acetone, acrolein, allyl alcohol and propanal were detected on the effluent stream from the reactor. However, propanal was produced in larger amounts than any other compound regardless of the conditions at which the reaction was run. At 267 ??C, for example, the selectivity to propanal was 73 %, to acrolein 14.8 % and for acetone and allyl alcohol 7.0% and 5.2%, respectively. As the reaction temperature was decreased, propanal selectivity increased at about the same rate as acrolein selectivity decreased. The selectivities to acetone and allyl alcohol remained constant. However, further experiments reveal that all of the products from PO decomposition are primary products. By probing this reaction under different conditions, a mechanism of propylene epoxidation has been proposed. The proposed mechanism assumes an oxametallacycle as the crucial intermediate from which acetone, propylene oxide, propanal, acrolein and allyl alcohol are formed. All of these are products of competing reactions of surface oxametallacycles. Acrolein and allyl alcohol are formed through dehydrogenations of the oxametallacycle while acetone and propanal are formed through 1,2 H-shifts. PO is formed through simple ring closing of the oxametallacycle. The kinetics and mechanism investigated in this work provides important insights that will help guide the search for a selective catalyst for propylene epoxidation. However, future work needs to address the need to learn more about the relative ease with which the oxametallacycle undergoes ring closing against alternative reactions. This can be accomplished through Density Functional Theory calculations or careful desorption experiments.Chemical Engineerin

Design of Responsive and Active (Soft) Materials Using Liquid Crystals

Liquid crystals (LCs) are widely known for their use in liquid crystal displays (LCDs). Indeed, LCDs represent one of the most successful technologies developed to date using a responsive soft material: An electric field is used to induce a change in ordering of the LC and thus a change in optical appearance. Over the past decade, however, research has revealed the fundamental underpinnings of potentially far broader and more pervasive uses of LCs for the design of responsive soft material systems. These systems involve a delicate interplay of the effects of surface-induced ordering, elastic strain of LCs, and formation of topological defects and are characterized by a chemical complexity and diversity of nano-and micrometer-scale geometry that goes well beyond that previously investigated. As a reflection of this evolution, the community investigating LC-based materials now relies heavily on concepts from colloid and interface science. In this context, this review describes recent advances in colloidal and interfacial phenomena involving LCs that are enabling the design of new classes of soft matter that respond to stimuli as broad as light, airborne pollutants, bacterial toxins in water, mechanical interactions with living cells, molecular chirality, and more. Ongoing efforts hint also that the collective properties of LCs (e.g., LC-dispersed colloids) will, over the coming decade, yield exciting new classes of driven or active soft material systems in which organization (and useful properties) emerges during the dissipation of energy

Design of Responsive and Active (Soft) Materials Using Liquid Crystals

Liquid crystals (LCs) are widely known for their use in liquid crystal displays (LCDs). Indeed, LCDs represent one of the most successful technologies developed to date using a responsive soft material: An electric field is used to induce a change in ordering of the LC and thus a change in optical appearance. Over the past decade, however, research has revealed the fundamental underpinnings of potentially far broader and more pervasive uses of LCs for the design of responsive soft material systems. These systems involve a delicate interplay of the effects of surface-induced ordering, elastic strain of LCs, and formation of topological defects and are characterized by a chemical complexity and diversity of nano-and micrometer-scale geometry that goes well beyond that previously investigated. As a reflection of this evolution, the community investigating LC-based materials now relies heavily on concepts from colloid and interface science. In this context, this review describes recent advances in colloidal and interfacial phenomena involving LCs that are enabling the design of new classes of soft matter that respond to stimuli as broad as light, airborne pollutants, bacterial toxins in water, mechanical interactions with living cells, molecular chirality, and more. Ongoing efforts hint also that the collective properties of LCs (e.g., LC-dispersed colloids) will, over the coming decade, yield exciting new classes of driven or active soft material systems in which organization (and useful properties) emerges during the dissipation of energy

Synthesis of Optically Complex, Porous, and Anisometric Polymeric Microparticles by Templating from Liquid Crystalline Droplets

It is demonstrated that aqueous dispersions of micrometer-sized liquid crystal (LC) droplets provide the basis of a general and facile methodology for the templated synthesis of spherical and nonspherical polymeric micro-particles with complex internal structure and porosity. Specifically, nematic droplets of reactive (RM257)/nonreactive mesogens with distinct internal configurations are prepared using a range of approaches, the reactive mesogens are photopolymerized, and then the nonreactive mesogens are extracted to yield polymeric particles. It is found that LC droplets exhibiting bipolar, radial, axial or preradial configurations template the formation of spindle-shaped, spherical, spherocylindrical or tear-shaped polymeric microparticles, respectively. Each type of microparticle exhibits distinct optical signatures indicating the presence of an internal LC-templated, anisotropic polymer network. In addition, by using a microfluidic system to generate monodisperse LC droplets containing 10%-40% wt/wt of RM257, spindle-shaped microparticles with tailored aspect ratios ranging from 2.4 to 1.2 are formed. The mass density of spherical microparticles templated from radial LC droplets can be tuned to range from 0.2 to 0.6 g cm(-3), revealing the introduction of porosity (confirmed by electron microscopy) with a volume-average pore diameter of 39 +/- 16 nm (obtained from nitrogen sorption isotherms)

Global overview of the management of acute cholecystitis during the COVID-19 pandemic (CHOLECOVID study)

Background: This study provides a global overview of the management of patients with acute cholecystitis during the initial phase of the COVID-19 pandemic. Methods: CHOLECOVID is an international, multicentre, observational comparative study of patients admitted to hospital with acute cholecystitis during the COVID-19 pandemic. Data on management were collected for a 2-month study interval coincident with the WHO declaration of the SARS-CoV-2 pandemic and compared with an equivalent pre-pandemic time interval. Mediation analysis examined the influence of SARS-COV-2 infection on 30-day mortality. Results: This study collected data on 9783 patients with acute cholecystitis admitted to 247 hospitals across the world. The pandemic was associated with reduced availability of surgical workforce and operating facilities globally, a significant shift to worse severity of disease, and increased use of conservative management. There was a reduction (both absolute and proportionate) in the number of patients undergoing cholecystectomy from 3095 patients (56.2 per cent) pre-pandemic to 1998 patients (46.2 per cent) during the pandemic but there was no difference in 30-day all-cause mortality after cholecystectomy comparing the pre-pandemic interval with the pandemic (13 patients (0.4 per cent) pre-pandemic to 13 patients (0.6 per cent) pandemic; P = 0.355). In mediation analysis, an admission with acute cholecystitis during the pandemic was associated with a non-significant increased risk of death (OR 1.29, 95 per cent c.i. 0.93 to 1.79, P = 0.121). Conclusion: CHOLECOVID provides a unique overview of the treatment of patients with cholecystitis across the globe during the first months of the SARS-CoV-2 pandemic. The study highlights the need for system resilience in retention of elective surgical activity. Cholecystectomy was associated with a low risk of mortality and deferral of treatment results in an increase in avoidable morbidity that represents the non-COVID cost of this pandemic