Is the von Mises criterion generally applicable to soft solids?

The purely viscoplastic paradigm has forged the understanding of yield stress materials, leading to misconceptions associated to the set of quantities that are needed to characterize yielding transition and also to the significance of the measured quantities (Thompson et al., 2018). The following assertions, usually taken for granted, are actually simplistic constitutive assumptions: (i) there exists a scalar that represents the yielding condition, (ii) there is a universal rule that maps the yield stress tensor onto that scalar, (iii) the von Mises yielding criterion holds (Thompson et al., 2018). That is, these statements are not necessarily true for a general yield stress material. In the present study we investigate the yielding of seven materials in two extensional loading conditions: traction and compression. We show that the von Mises criterion does not perform well for the yielding of these materials. A new criterion that includes the third invariant of the (deviatoric) yield stress tensor is proposed to handle the differences between traction and compression values of the stress at the yielding point. Even this criterion is not able to accommodate the yielding obtained in shear loading for these materials. In this regard, the most likely scenario is that no universal criterion exists for all kinds of yield stress materials.

Growth Kinetics and Mechanics of Hydrate Films by Interfacial Rheology.

A new approach to study and understand the kinetics and mechanical properties of hydrates by interfacial rheology is presented. This is made possible using a "double wall ring" interfacial rheology cell that has been designed to provide the necessary temperature control. Cyclopentane and water are used to form hydrates, and this model system forms these structures at ambient pressures. Different temperature and water/hydrocarbon contact protocols are explored. Of particular interest is the importance of first contacting the hydrocarbon against ice crystals in order to initiate hydrate formation. Indeed, this is found to be the case, even though the hydrates may be created at temperatures above the melting point of ice. Once hydrates completely populate the hydrocarbon/water interface, strain sweeps of the interfacial elastic and viscous moduli are conducted to interrogate the mechanical response and fragility of the hydrate films. The dependence on temperature, Tf, by the kinetics of formation and the mechanical properties is reported, and the cyclopentane hydrate dissociation temperature was found to be between 6 and 7 °C. The formation time (measured from the moment when cyclopentane first contacts ice crystals) as well as the elastic modulus and the yield strain increase as Tf increases.

Capsular Contracture In Silicone Breast Implants: Insights From Rat Models.

Breast augmentation with silicone implants is one of the most common procedures performed by plastic surgeons around the world. Capsular contracture is a frequent complication in breast augmentation and reconstructive surgery, that requires invasive intervention. The inflammatory response to implanted mammary prostheses appears to be directly associated to capsular contracture. This review discusses the evidences from rat models studies, on the role of inflammation and fibrosis in capsular contraction and its relation to silicone breast implants surface.

Increased Serum Mir-150-3p Expression Is Associated with Radiological Lung Injury Improvement in Patients with COVID-19.

Coronavirus disease 2019 (COVID-19) is caused by the SARS-CoV-2 virus, responsible for an atypical pneumonia that can progress to acute lung injury. MicroRNAs are small non-coding RNAs that control specific genes and pathways. This study evaluated the association between circulating miRNAs and lung injury associated with COVID-19. Methods: We evaluated lung injury by computed tomography at hospital admission and discharge and the serum expression of 754 miRNAs using the TaqMan OpenArray after hospital discharge in 27 patients with COVID-19. In addition, miR-150-3p was validated by qRT-PCR on serum samples collected at admission and after hospital discharge. Results: OpenArray analysis revealed that seven miRNAs were differentially expressed between groups of patients without radiological lung improvement compared to those with lung improvement at hospital discharge, with three miRNAs being upregulated (miR-548c-3p, miR-212-3p, and miR-548a-3p) and four downregulated (miR-191-5p, miR-151a-3p, miR-92a-3p, and miR-150-3p). Bioinformatics analysis revealed that five of these miRNAs had binding sites in the SARS-CoV-2 genome. Validation of miR-150-3p by qRT-PCR confirmed the OpenArray results. Conclusions: The present study shows the potential association between the serum expression of seven miRNAs and lung injury in patients with COVID-19. Furthermore, increased expression of miR-150 was associated with pulmonary improvement at hospital discharge.

Gender influences the relationship between lung function and cardiac remodeling in hypertensive subjects.

Hypertensive patients are predisposed to left ventricular (LV) remodeling and frequently exhibit decline in lung function as compared with the general population. Here, we investigated the association between spirometric and echocardiographic data in non-smoking hypertensive subjects and the role of gender in this regard. In a cross-sectional study, 107 hypertensive patients (60 women) enrolled from a university outpatient clinic were evaluated by clinical, hemodynamic, laboratory and echocardiographic analysis. Vital capacity, forced vital capacity (FVC), forced expired volume in 1 s (FEV1) and in 6 s (FEV6), FEV1/FVC ratio and FEV1/FEV6 ratio were estimated by spirometry. In women, higher LV mass index and E/Em ratio correlated with markers of restrictive lung alterations, such as reduced FVC (r=-044; P<0.001; r=-0.42; P<0.001, respectively) and FEV6 (r=-0.43; P<0.001; r=-0.39; P<0.01, respectively), while higher left atrial volume index correlated with markers of obstructive lung alterations, such as reduced FEV1/FVC (r=-055; P<0.001) and FEV1/FEV6 (r=-0.45; P<0.001) ratios. These relationships were further confirmed by stepwise regression analysis adjusted for potential confounders. In men, LV mass index correlated with FVC and FEV6, but these associations did not remain statistically significant after adjustment for confounding variables. Furthermore, inflammatory markers such as plasma C-reactive protein and matrix-metalloproteinases-2 and -9 levels did not influence the association between spirometric and cardiac parameters. In conclusion, these results indicate that LV remodeling is related to restrictive lung alterations while left atrial remodeling is associated with obstructive lung alterations in hypertensive women.

Lung age is related to carotid structural alterations in hypertensive subjects.

Hypertensive patients exhibit higher cardiovascular risk and reduced lung function compared with the general population. Whether this association stems from the coexistence of two highly prevalent diseases or from direct or indirect links of pathophysiological mechanisms is presently unclear. This study investigated the association between lung function and carotid features in non-smoking hypertensive subjects with supposed normal lung function. Hypertensive patients (n = 67) were cross-sectionally evaluated by clinical, hemodynamic, laboratory, and carotid ultrasound analysis. Forced vital capacity, forced expired volume in 1 second and in 6 seconds, and lung age were estimated by spirometry. Subjects with ventilatory abnormalities according to current guidelines were excluded. Regression analysis adjusted for age and prior smoking history showed that lung age and the percentage of predicted spirometric parameters associated with common carotid intima-media thickness, diameter, and stiffness. Further analyses, adjusted for additional potential confounders, revealed that lung age was the spirometric parameter exhibiting the most significant regression coefficients with carotid features. Conversely, plasma C-reactive protein and matrix-metalloproteinases-2/9 levels did not influence this relationship. The present findings point toward lung age as a potential marker of vascular remodeling and indicate that lung and vascular remodeling might share common pathophysiological mechanisms in hypertensive subjects.