Open-source high-performance software packages for direct and inverse solving of horizontal capillary flow

This work introduces Fronts, a set of open-source numerical software packages for nonlinear horizontal capillary-driven flow problems in unsaturated porous media governed by the Richards equation. The software uses the Boltzmann transformation to solve such problems in semi-infinite domains. The scheme adopted by Fronts allows it to be faster and easier to use than other tools, and provide continuous functions for all involved fields. The software is capable of solving problems that appear in hydrology, but also in other particular domains of interest such as paper-based microfluidics. As the first known open-source implementation to adopt this approach, Fronts has been validated against analytical solutions as well as existing software achieving remarkable results in terms of computational costs and numerical precision, and is meant to aid the study and modeling of capillary flow. Fronts can be freely downloaded and installed, and offers a friendly environment for new users with its complete documentation and tutorial cases.Cited as: Gerlero, G. S., Berli, C. L. A., Kler, P. A. Open-source high-performance software packages for direct and inverse solving of horizontal capillary flow. Capillarity, 2023, 6(2): 31-40. https://doi.org/10.46690/capi.2023.02.0

Simulación numérica de procesos electroosmóticos y electroforéticos mediante una plataforma modular basada en el método de volúmenes finitos

Los procesos electroosmóticos y electroforéticos consisten en procesos de transporte de solutos y solvente, y de reacción entre diferentes electrolitos, mediante la aplicación controlada de campos eléctricos. La microescala se convierte en un escenario donde estos fenómenos, fuertemente interfaciales, se aprovechanrse de manera mas eficiente en la implementación de procesos y dispositivos, fundamentalmente en química analítica y bioanalítica: es así que en las últimas dos décadas, las plataformas microfluídicas para análisis (más conocidas como Lab-on-a-chip), han sido el principal escenario para el desarrollo de métodos y tecnologías relacionadas a los procesos electroosmóticos y electroforéticos. El desarrollo de modelos y simulaciones numéricas de estos procesos permite una mayor comprensión y un mejor aprovechamiento de las características de los Lab-on-a-chip, para mejorar sus diseños, aumentar su rendimiento y también poder expandir así su aplicabilidad. En este trabajo se presenta la implementación de la simulación numérica de procesos electroosmóticos y electroforéticos a través del acople de las diferentes ecuaciones que modelan el campo eléctrico, el campo de velocidades y presiones, el campo de concentraciones de solutos y electrolitos y el equilibrio ácido-base. Se consideran también de manera especial las heterogeneidades de concentraciones de cargas en las paredes que dan origen a la doble capa eléctrica, que en definitiva permite el flujo electroosmótico. La implementación se llevó a cabo mediante el método de volúmenes finitos utilizando la plataforma OpenFOAMR . La herramienta de simulación, ya presentada en un trabajo anterior, resulta novedosa, desde el punto de vista de las herramientas utilizadas para la resolución de casos complejos. Justamente a partir de estos casos se presentarán las innovaciones recientes en el código que permitieron resolver situaciones experimentales computacionalmente demandantes. Se pondrá énfasis en las nuevas características que ofrece la herramienta como las diferentes condiciones de borde implementadas para la simulación del transporte de electrolitos, y la optimización de las estrategias de acoplamiento entre campos.Publicado en: Mecánica Computacional vol. XXXV, no. 27.Facultad de Ingenierí

Incremento de la eficiencia de los análisis de flujo lateral a través de campos eléctricos

Los análisis de flujo lateral (AFL) representan un grupo de dispositivos portables y autónomos para la detección rápida y sencilla de diversos indicadores bioquímicos de agentes patógenos y enfermedades. Además de las aplicaciones en salud, el uso de los AFL se ha extiendido al control ambiental, fitosanitario y bromatológico, entre otros campos requiriendo de la tecnología límites de detección muy ambiciosos. Recientemente, se ha demostrado que los límites de detección de los AFL pueden incrementarse al menos dos órdenes de magnitud, si se combinan con la aplicación de campos eléctricos para el transporte electroforético de especies. Es sabido que el desarrollo de dispositivos de AFL implica importantes esfuerzos experimentales dada la necesidad de explorar diseños, caracterizar los materiales utilizados y controlar los parámetros cinéticos de las reacciones. Si a esto sumamos la aplicación de campos eléctricos a soluciones de electrolitos con conductividades eléctricas heterogéneas, el escenario para el diseño empírico se vuelve demasiado complejo. De esta manera, contar con herramientas que permitan reducir los costos y tiempos de experimentación resulta clave para la implementación efectiva de esta tecnología. Para ello el desarrollo de prototipos numéricos que permitan simular eficientemente nuevos diseños de AFL sometidos a campos eléctricos resulta de gran utilidad tecnológica y científica. En este trabajo se presenta la implementación de un prototipo numérico de un AFL sometido a campos eléctricos. El modelo consiste en la solución acoplada de: (i) un modelo fluidodinámico de imbibición capilar, (ii) un modelo de transporte de materia que incluye términos electromigrativos, (iii) un modelo de conductividad eléctrica y conservación de cargas, y (iv) un modelo reactivo de tipo antígeno-anticuerpo. El dominio completo se resuelve utilizando el método de elementos finitos utilizando PETSc-FEM, tanto para los fenómenos de transporte y reacción como para el modelo de flujo por imbibición capilar, que se resuelve con un enfoque tipo Darcy basado en permeabilidades heterogéneas. Se concluye que la realización de ensayos virtuales permite determinar la ventana de trabajo apropiada (en términos de parámetros operativos) para lograr mejorar el límite de detección y el rendimiento global de los dispositivos.Publicado en: Mecánica Computacional vol. XXXV, no. 28.Facultad de Ingenierí

Simulación de la dispersión transversal en dispositivos de microfluídica basados en papel

El desarrollo de plataformas microfluídicas que integran papel y otros derivados de la celulosa ha tenido un notable crecimiento en los últimos cinco años. En efecto, estos soportes son de gran disponibilidad y bajo costo, permiten el transporte de fluidos mediante capilaridad, son compatibles con los sistemas biológicos y permiten la adsorción/desorción de moléculas para implementar diversas reacciones químicas. Estas ventajas hacen que la microfluídica basada en papel se aplique a sistemas de análisis cada vez más diversos, y por lo tanto se vuelve cada vez más necesaria la optimización de las diferentes operaciones unitarias que se realizan en los dispositivos. Varias de esas operaciones, notablemente el mezclado, dilución, separación por tamaños y formación de gradientes, tienen un factor común que es el transporte advectivo-difusivo de especies químicas en la matriz porosa. En este marco, el presente trabajo aborda el modelado y la simulación numérica de la dispersión transversal de especies químicas en un medio poroso. Este estudio básico está dirigido a obtener reglas de escala para el mejor diseño de las operaciones mencionadas en microdispositivos basados en papel a través de diferentes aproximaciones para el término de flujo difusivo en la ecuación de transporte. La idea central es apartarse del modelo Fickiano clásico de difusión, regido por un coeficiente constante tanto en espacio como en tiempo, propio de la naturaleza química de la sustancia transportada y del solvente, para incluir modelos extraídos de literatura reciente. Estos modelos, son esencialmente sensibles (además de la naturaleza química ya mencionada) a las características del medio poroso (permeabilidad, porosidad y ángulo de contacto) y a las características del campo de fluidos para el solvente utilizado. Los modelos se implementarán a través de la herramienta OpenFOAM (R) y se utilizarán a los fines de evaluar diseños de generadores de gradientes microfluídicos en papel y estimar sus potenciales ventajas frente a generadores desarrollados en microcanales clásicos.Publicado en: Mecánica Computacional vol. XXXV, no. 28.Facultad de Ingenierí

Elective cancer surgery in COVID-19-free surgical pathways during the SARS-CoV-2 pandemic: An international, multicenter, comparative cohort study

PURPOSE As cancer surgery restarts after the first COVID-19 wave, health care providers urgently require data to determine where elective surgery is best performed. This study aimed to determine whether COVID-19–free surgical pathways were associated with lower postoperative pulmonary complication rates compared with hospitals with no defined pathway. PATIENTS AND METHODS This international, multicenter cohort study included patients who underwent elective surgery for 10 solid cancer types without preoperative suspicion of SARS-CoV-2. Participating hospitals included patients from local emergence of SARS-CoV-2 until April 19, 2020. At the time of surgery, hospitals were defined as having a COVID-19–free surgical pathway (complete segregation of the operating theater, critical care, and inpatient ward areas) or no defined pathway (incomplete or no segregation, areas shared with patients with COVID-19). The primary outcome was 30-day postoperative pulmonary complications (pneumonia, acute respiratory distress syndrome, unexpected ventilation). RESULTS Of 9,171 patients from 447 hospitals in 55 countries, 2,481 were operated on in COVID-19–free surgical pathways. Patients who underwent surgery within COVID-19–free surgical pathways were younger with fewer comorbidities than those in hospitals with no defined pathway but with similar proportions of major surgery. After adjustment, pulmonary complication rates were lower with COVID-19–free surgical pathways (2.2% v 4.9%; adjusted odds ratio [aOR], 0.62; 95% CI, 0.44 to 0.86). This was consistent in sensitivity analyses for low-risk patients (American Society of Anesthesiologists grade 1/2), propensity score–matched models, and patients with negative SARS-CoV-2 preoperative tests. The postoperative SARS-CoV-2 infection rate was also lower in COVID-19–free surgical pathways (2.1% v 3.6%; aOR, 0.53; 95% CI, 0.36 to 0.76). CONCLUSION Within available resources, dedicated COVID-19–free surgical pathways should be established to provide safe elective cancer surgery during current and before future SARS-CoV-2 outbreaks

Elective Cancer Surgery in COVID-19-Free Surgical Pathways During the SARS-CoV-2 Pandemic: An International, Multicenter, Comparative Cohort Study.

PURPOSE: As cancer surgery restarts after the first COVID-19 wave, health care providers urgently require data to determine where elective surgery is best performed. This study aimed to determine whether COVID-19-free surgical pathways were associated with lower postoperative pulmonary complication rates compared with hospitals with no defined pathway. PATIENTS AND METHODS: This international, multicenter cohort study included patients who underwent elective surgery for 10 solid cancer types without preoperative suspicion of SARS-CoV-2. Participating hospitals included patients from local emergence of SARS-CoV-2 until April 19, 2020. At the time of surgery, hospitals were defined as having a COVID-19-free surgical pathway (complete segregation of the operating theater, critical care, and inpatient ward areas) or no defined pathway (incomplete or no segregation, areas shared with patients with COVID-19). The primary outcome was 30-day postoperative pulmonary complications (pneumonia, acute respiratory distress syndrome, unexpected ventilation). RESULTS: Of 9,171 patients from 447 hospitals in 55 countries, 2,481 were operated on in COVID-19-free surgical pathways. Patients who underwent surgery within COVID-19-free surgical pathways were younger with fewer comorbidities than those in hospitals with no defined pathway but with similar proportions of major surgery. After adjustment, pulmonary complication rates were lower with COVID-19-free surgical pathways (2.2% v 4.9%; adjusted odds ratio [aOR], 0.62; 95% CI, 0.44 to 0.86). This was consistent in sensitivity analyses for low-risk patients (American Society of Anesthesiologists grade 1/2), propensity score-matched models, and patients with negative SARS-CoV-2 preoperative tests. The postoperative SARS-CoV-2 infection rate was also lower in COVID-19-free surgical pathways (2.1% v 3.6%; aOR, 0.53; 95% CI, 0.36 to 0.76). CONCLUSION: Within available resources, dedicated COVID-19-free surgical pathways should be established to provide safe elective cancer surgery during current and before future SARS-CoV-2 outbreaks

Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study

Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28–2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65–3·22], p\textless0·0001), American Society of Anesthesiologists grades 3–5 versus grades 1–2 (2·35 [1·57–3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01–2·39], p=0·046), emergency versus elective surgery (1·67 [1·06–2·63], p=0·026), and major versus minor surgery (1·52 [1·01–2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research

Column coupling isotachophoresis-capillary electrophoresis with mass spectrometric detection: Characterization and optimization of microfluidic interfaces

Two-dimensional electrophoretic separations are one of the most promising tools for the continuously growing needs of different bioanalytical fields such as proteomics and metabolomics. In this work we present the design and the implementation of a two-dimensional electrophoretic separation coupled to mass spectrometry. We started our work studying the sample transfer characteristics of different microfluidic interfaces compatible with capillary coupling for two-dimensional electrophoretic separations. These junctions are aimed at method decoupling and sample transfer in a modular two-dimensional electrophoretic separation system. In order to perform the characterization of the interfaces, we carried out capillary electrophoresis experiments and numerical simulations using three cationic compounds under different flow conditions. The comparison of the experimental and simulation results enables us to clearly define the desirable characteristics of interfaces in order to achieve method orthogonality with lossless sample transfer in a two-dimensional separation system. Finally, we present a glass microfluidic chip as interface for the implementation of a novel hybrid modular system for performing two-dimensional electrophoretic separations involving isotachophoresis and capillary electrophoresis. In this setup we include mass spectrometric and contactless capacitively coupled conductivity detection to monitor the separation process. We demonstrate the ability of the setup to be used as a flexible analysis tool by performing preconcentration, separation, detection and identification of four different human angiotensin peptides

Applicability of UV laser-induced solid-state fluorescence spectroscopy for characterization of solid dosage forms

High production output of solid pharmaceutical formulations requires fast methods to ensure their quality. Likewise, fast analytical procedures are required in forensic sciences, for example at customs, to substantiate an initial suspicion. We here present the design and the optimization of an instrumental setup for rapid and non-invasive characterization of tablets by laser-induced fluorescence spectroscopy (with a UV-laser (λ ex = 266 nm) as excitation source) in reflection geometry. The setup was first validated with regard to repeatability, bleaching phenomena, and sensitivity. The effect on the spectra by the physical and chemical properties of the samples, e.g. their hardness, homogeneity, chemical composition, and granule grain size of the uncompressed material, using a series of tablets, manufactured in accordance with design of experiments, was investigated. Investigation of tablets with regard to homogeneity, especially, is extremely important in pharmaceutical production processes. We demonstrate that multiplicative scatter correction is an appropriate tool for data preprocessing of fluorescence spectra. Tablets with different physical and chemical characteristics can be discriminated well from their fluorescence spectra by subjecting the results to principal component analysis