Films of bacteria at interfaces: three stages of behaviour

Bacterial attachment to a fluid interface can lead to the formation of a film with physicochemical properties that evolve with time. We study the time evolution of interface (micro)mechanics for interfaces between oil and bacterial suspensions by following the motion of colloidal probes trapped by capillarity to determine the interface microrheology. Initially, active bacteria at and near the interface drive superdiffusive motion of the colloidal probes. Over timescales of minutes, the bacteria form a viscoelastic film which we discuss as a quasi-two-dimensional, active, glassy system. To study late stage mechanics of the film, we use pendant drop elastometry. The films, grown over tens of hours on oil drops, are expanded and compressed by changing the drop volume. For small strains, by modeling the films as 2D Hookean solids, we estimate the film elastic moduli, finding values similar to those reported in the literature for the bacteria themselves. For large strains, the films are highly hysteretic. Finally, from wrinkles formed on highly compressed drops, we estimate film bending energies. The dramatic restructuring of the interface by such robust films has broad implications, e.g. in the study of active colloids, in understanding the community dynamics of bacteria, and in applied settings including bioremediation

Elastometry of deflated capsules elastic moduli from shape and wrinkle analysis

Elastic capsules, prepared from droplets or bubbles attached to a capillary (as in a pendant drop tensiometer), can be deflated by suction through the capillary. We study this deflation and show that a combined analysis of the shape and wrinkling characteristics enables us to determine the elastic properties in situ. Shape contours are analyzed and fitted using shape equations derived from nonlinear membrane-shell theory to give the elastic modulus, Poisson ratio and stress distribution of the membrane. We include wrinkles, which generically form upon deflation, within the shape analysis. Measuring the wavelength of wrinkles and using the calculated stress distribution gives the bending stiffness of the membrane. We illustrate this method on two very different capsule materials: polymerized octadecyltrichlorosilane (OTS) capsules and hydrophobin (HFBII) coated bubbles. Our results are in agreement with the available rheological data. For hydrophobin coated bubbles the method reveals an interesting nonlinear behavior consistent with the hydrophobin molecules having\ud a rigid core surrounded by a softer shell

Cirrhosis Diagnosis and Liver Fibrosis Staging: Transient Elastometry Versus Cirrhosis Blood Test.

INTRODUCTION: Elastometry is more accurate than blood tests for cirrhosis diagnosis. However, blood tests were developed for significant fibrosis, with the exception of CirrhoMeter developed for cirrhosis. We compared the performance of Fibroscan and CirrhoMeter, and classic binary cirrhosis diagnosis versus new fibrosis staging for cirrhosis diagnosis. METHODS: The diagnostic population included 679 patients with hepatitis C and liver biopsy (Metavir staging and morphometry), Fibroscan, and CirrhoMeter. The prognostic population included 1110 patients with chronic liver disease and both tests. RESULTS: Binary diagnosis: AUROCs for cirrhosis were: Fibroscan: 0.905; CirrhoMeter: 0.857; and P=0.041. Accuracy (Youden cutoff) was: Fibroscan: 85.4%; CirrhoMeter: 79.2%; and P<0.001. Fibrosis classification provided 6 classes (F0/1, F1/2, F2±1, F3±1, F3/4, and F4). Accuracy was: Fibroscan: 88.2%; CirrhoMeter: 88.8%; and P=0.77. A simplified fibrosis classification comprised 3 categories: discrete (F1±1), moderate (F2±1), and severe (F3/4) fibrosis. Using this simplified classification, CirrhoMeter predicted survival better than Fibroscan (respectively, χ=37.9 and 19.7 by log-rank test), but both predicted it well (P<0.001 by log-rank test). Comparison: binary diagnosis versus fibrosis classification, respectively, overall accuracy: CirrhoMeter: 79.2% versus 88.8% (P<0.001); Fibroscan: 85.4% versus 88.2% (P=0.127); positive predictive value for cirrhosis by Fibroscan: Youden cutoff (11.1 kPa): 49.1% versus cutoffs of F3/4 (17.6 kPa): 67.6% and F4 classes (25.7 kPa): 82.4%. CONCLUSIONS: Fibroscan\u27s usual binary cutoffs for cirrhosis diagnosis are not sufficiently accurate. Fibrosis classification should be preferred over binary diagnosis. A cirrhosis-specific blood test markedly attenuates the accuracy deficit for cirrhosis diagnosis of usual blood tests versus transient elastometry, and may offer better prognostication

FibroScan and non-invasive indices for the diagnosis of non-alcoholic fatty liver disease

Background. Non-alcoholic fatty liver disease (NAFLD), an independent nosological entity, is characterized by fat accumulation in hepatocytes not associated with alcohol abuse, and includes a wide spectrum of disorders: from fatty liver, non-alcoholic steatohepatitis to fibrosis with possible outcome in liver cirrhosis. Given the prevalence of this disease, the deterioration of the quality of life of patients, increased mortality from complications, there is a growing interest in developing techniques for accurate and timely assessment of fibrosis. Objective: comparative characteristics of the results of transient elastometry (FibroScan) and non-invasive laboratory indices in the determination of fibrotic transformation of the liver in patients with non-alcoholic fatty liver disease. Materials and methods. The study included patients with NAFLD, who underwent diagnostics and treatment in the department of liver and pancreas of the SI “Institute of Gastroenterology of the NAMS of Ukraine”. Results. We have examined 42 patients with NAFLD, among which 18 (45 %) men and 24 (55 %) women. All patients underwent calculation of non-invasive markers of liver fibrosis: aspartate aminotransferase to platelet ratio index (APRI), fibrosis-4 index, aspartate aminotransferase/alanine aminotransferase ratio, the measurement of liver stiffness using the FibroScan apparatus. Conclusions. Our results are consistent with most studies indicating that the most effective non-invasive index is APRI. The combination of transient elastography (FibroScan) and the APRI may provide a more effective approach to the diagnosis of liver fibrosis in patients with NAFLD

Assessment of liver fibrosis and associated risk factors in HIV-infected individuals using transient elastography and serum biomarkers

Background: Liver fibrosis in human immunodeficiency virus (HIV)-infected individuals is mostly attributable to co-infection with hepatitis B or C. The impact of other risk factors, including prolonged exposure to combined antiretroviral therapy (cART) is poorly understood. Our aim was to determine the prevalence of liver fibrosis and associated risk factors in HIV-infected individuals based on non-invasive fibrosis assessment using transient elastography (TE) and serum biomarkers (Fibrotest [FT]). Methods: In 202 consecutive HIV-infected individuals (159 men; mean age 47 ± 9 years; 35 with hepatitis-C-virus [HCV] co-infection), TE and FT were performed. Repeat TE examinations were conducted 1 and 2 years after study inclusion. Results: Significant liver fibrosis was present in 16% and 29% of patients, respectively, when assessed by TE (≥ 7.1 kPa) and FT (> 0.48). A combination of TE and FT predicted significant fibrosis in 8% of all patients (31% in HIV/HCV co-infected and 3% in HIV mono-infected individuals). Chronic ALT, AST and γ-GT elevation was present in 29%, 20% and 51% of all cART-exposed patients and in 19%, 8% and 45.5% of HIV mono-infected individuals. Overall, factors independently associated with significant fibrosis as assessed by TE (OR, 95% CI) were co-infection with HCV (7.29, 1.95-27.34), chronic AST (6.58, 1.30-33.25) and γ-GT (5.17, 1.56-17.08) elevation and time on dideoxynucleoside therapy (1.01, 1.00-1.02). In 68 HIV mono-infected individuals who had repeat TE examinations, TE values did not differ significantly during a median follow-up time of 24 months (median intra-patient changes at last TE examination relative to baseline: -0.2 kPa, p = 0.20). Conclusions: Chronic elevation of liver enzymes was observed in up to 45.5% of HIV mono-infected patients on cART. However, only a small subset had significant fibrosis as predicted by TE and FT. There was no evidence for fibrosis progression during follow-up TE examinations

Population of human ventricular cell models calibrated with in vivo measurements unravels ionic mechanisms of cardiac alternans

Cardiac alternansis an important risk factor in cardiac physiology, and is related to the initiation of many pathophysiological conditions. However, the mechanisms underlying the generation of alternans remain unclear. In this study, we used a population of computational human ventricle models based onthe O’Hara model [1] to explore the effect of 11 key factors experimentally reported to be related to alternans. In vivo experimental datasets coming from patients undergoing cardiac surgery were used in the calibration of our in silico population of models. The calibrated models in the population were divided into two groups (Normal and Alternans) depending on alternans occurrence. Our results showed that there were significant differences in the following 5 ionic currents between the two groups: fast sodium current, sodium calcium exchanger current, sodium potassium pump current, sarcoplasmic reticulum (SR) calcium release flux and SR calcium reuptake flux. Further analysis indicated that fast sodium current and SR calcium uptake were the two most significant currents that contributed to voltage and calcium alternans generation, respectively

FibroScan and non-invasive indices for the diagnosis of non-alcoholic fatty liver disease

Актуальність. Неалкогольна жирова хвороба печінки (НАЖХП) є самостійною нозологічною одиницею, характеризується накопиченням жиру в гепатоцитах, не пов’язаним зі зловживанням алкоголем, і включає широкий спектр порушень — від жирової дистрофії печінки, неалкогольного стеатогепатиту до фіброзу з можливим переходом у цироз печінки. З огляду на поширеність цієї патології, погіршення якості життя хворих, збільшення смертності від ускладнень зростає інтерес до розробки методів для точної й своєчасної оцінки фіброзу. Мета: порівняльна характеристика результатів транзієнтної еластометрії (FibroScan) і неінвазивних лабораторних індексів у визначенні фіброзної трансформації печінки у хворих із неалкогольною жировою хворобою печінки. Матеріали та методи. У дослідження включені пацієнти з НАЖХП, які проходили обстеження й лікування у відділенні захворювань печінки та підшлункової залози ДУ «Інститут гастроентерології НАМН України». Обстежені 42 пацієнти з НАЖХП, серед яких 18 (45 %) чоловіків і 24 (55 %) жінки. Усім пацієнтам було виконано розрахунок неінвазивних маркерів фіброзу печінки: APRI, FIB-4, співвідношення аланінамінотрансферази/аспартатамінотрансферази, проведено вимірювання жорсткості печінки за допомогою апарату FibroScan. Результати нашої роботи узгоджуються з більшістю досліджень, згідно з якими найбільш ефективним з малоінвазивних індексів є APRI. Висновки. Поєднання транзієнтної еластометрії (FibroScan) з індексом APRI може забезпечити більш ефективний підхід до діагностики фіброзу печінки у хворих з НАЖХП. Background. Non-alcoholic fatty liver disease (NAFLD), an independent nosological entity, is characterized by fat accumulation in hepatocytes not associated with alcohol abuse, and includes a wide spectrum of disorders: from fatty liver, non-alcoholic steatohepatitis to fibrosis with possible outcome in liver cirrhosis. Given the prevalence of this disease, the deterioration of the quality of life of patients, increased mortality from complications, there is a growing interest in developing techniques for accurate and timely assessment of fibrosis. Objective: comparative characteristics of the results of transient elastometry (FibroScan) and non-invasive laboratory indices in the determination of fibrotic transformation of the liver in patients with non-alcoholic fatty liver disease. Materials and methods. The study included patients with NAFLD, who underwent diagnostics and treatment in the department of liver and pancreas of the SI “Institute of Gastroenterology of the NAMS of Ukraine”. Results. We have examined 42 patients with NAFLD, among which 18 (45 %) men and 24 (55 %) women. All patients underwent calculation of non-invasive markers of liver fibrosis: aspartate aminotransferase to platelet ratio index (APRI), fibrosis-4 index, aspartate aminotransferase/alanine aminotransferase ratio, the measurement of liver stiffness using the FibroScan apparatus. Conclusions. Our results are consistent with most studies indicating that the most effective non-invasive index is APRI. The combination of transient elastography (FibroScan) and the APRI may provide a more effective approach to the diagnosis of liver fibrosis in patients with NAFLD

On the eigenvalues and eigenvectors of nonsymmetric saddle point matrices preconditioned by block triangular matrices

Block lower triangular and block upper triangular matrices are popular preconditioners for nonsymmetric saddle point matrices. In this note we show that a block lower triangular preconditioner gives the same spectrum as a block upper triangular preconditioner and that the eigenvectors of the two preconditioned systems are related