Lateral indentation of a thin elastic film.

Indentation is a standard, widely used technique in mechanical assays and theoretical analysis. It unveils the fundamental modes of deformation and predicts the response of the material under more complex loads. Here we present an experimental setup for testing thin-film materials by studying the lateral indentation of a narrow opening cut into a film, triggering a cascade of buckling events. The force response F is dominated by bending and stretching effects for small displacements and slowly varies with indenter displacement F ∼ d2/5, to finally reach a wrinkled state that results in a robust nonlinear asymptotic relation, F ∼ d4. Experiments with films of various thicknesses and material properties, and numerical simulations confirm our analysis and help to define an order parameter that accounts for the different response regimes observed in experiments and simulations.

Buckling of elastomer sheets under non-uniform electro-actuation.

Dielectric elastomer sheets undergo in-plane expansion when stimulated by a transverse electric field. We study experimentally how dielectric plates subjected to a non-uniform voltage distribution undergo buckling instabilities. Two different configurations involving circular plates are investigated: plates freely floating on a bath of water, and plates clamped on a frame. We describe theoretically the out-of-plane deformation of the plates within the framework of weakly non-linear plate equations. This study constitutes a first step of a route to control the 3D activation of dielectric elastomers.

Elasticity and wrinkled morphology of Bacillus subtilis pellicles.

Wrinkled morphology is a distinctive phenotype observed in mature biofilms produced by a great number of bacteria. Here we study the formation of macroscopic structures (wrinkles and folds) observed during the maturation of Bacillus subtilis pellicles in relation to their mechanical response. We show how the mechanical buckling instability can explain their formation. By performing simple tests, we highlight the role of confining geometry and growth in determining the symmetry of wrinkles. We also experimentally demonstrate that the pellicles are soft elastic materials for small deformations induced by a tensile device. The wrinkled structures are then described by using the equations of elastic plates, which include the growth process as a simple parameter representing biomass production. This growth controls buckling instability, which triggers the formation of wrinkles. We also describe how the structure of ripples is modified when capillary effects are dominant. Finally, the experiments performed on a mutant strain indicate that the presence of an extracellular matrix is required to maintain a connective and elastic pellicle.

Pharmacokinetic Simulation and Area under the Curve Estimation of Drugs Subject to Enterohepatic Circulation.

Enterohepatic circulation (EHC) is a complex process where drugs undergo secretion and reabsorption from the intestinal lumen multiple times, resulting in pharmacokinetic profiles with multiple peaks. The impact of EHC on area under the curve (AUC) has been a topic of extensive debate, questioning the suitability of conventional AUC estimation methods. Moreover, a universal model for accurately estimating AUC in EHC scenarios is lacking. To address this gap, we conducted a simulation study evaluating five empirical models under various sampling strategies to assess their performance in AUC estimation. Our results identify the most suitable model for EHC scenarios and underscore the critical role of meal-based sampling strategies in accurate AUC estimation. Additionally, we demonstrate that while the trapezoidal method performs comparably to other models with a large number of samples, alternative models are essential when sample numbers are limited. These findings not only illuminate how EHC influences AUC but also pave the way for the application of empirical models in real-world drug studies.

Osteoprotegerin Is a Better Predictor for Cardiovascular and All-Cause Mortality than Vascular Calcifications in a Multicenter Cohort of Patients on Peritoneal Dialysis.

The purpose of this study was to compare vascular calcification (VC), serum osteoprotegerin (OPG) levels, and other biochemical markers to determine their value as available predictors of all-cause and cardiovascular (CV) mortality in patients on peritoneal dialysis (PD). A total of 197 patients were recruited from seven dialysis centers in Mexico City. VC was assessed with multi-slice computed tomography, measured using the calcification score (CaSc). OPG, albumin, calcium, hsC-reactive protein, phosphorous, osteocalcin, total alkaline phosphatase, and intact parathormone were also analyzed. Follow-up and mortality analyses were assessed using the Cox regression model. The mean age was 43.9 ± 12.9 years, 64% were males, and 53% were diabetics. The median OPG was 11.28 (IQR: 7.6−17.4 pmol/L), and 42% of cases had cardiovascular calcifications. The median VC was 424 (IQR:101−886). During follow-up (23 ± 7 months), there were 34 deaths, and 44% were cardiovascular in origin. In multivariable analysis, OPG was a significant predictor for all-cause (HR 1.08; p < 0.002) and CV mortality (HR 1.09; p < 0.013), and performed better than VC (HR 1.00; p < 0.62 for all-cause mortality and HR 1.00; p < 0.16 for CV mortality). For each mg/dL of albumin-corrected calcium, there was an increased risk for CV mortality, and each g/dL of albumin decreased the risk factor for all-cause mortality. OPG levels above 14.37 and 13.57 pmol/L showed the highest predictive value for all-cause and CV mortality in incident PD patients and performed better than VC.

Importance of the Ultrasound Probe Angle on the Rotation Fill-in Signature in Ultrasound Axial-Shear Strain Imaging.

The rotation fill-in is a signature of tumor benignity in rotation elastograms and has been used for breast tumor classification. It is a consequence of the bonding condition at the tumor-tissue interface. In vivo studies have revealed the presence of fluctuations when inclined uniaxial external compression is applied. However, the physical meaning of these fluctuations is not yet fully understood. In this article we present an experimental and numerical study of the rotation fill-in signature as a function of the probe's tilt angle. This angle introduces asymmetries in the stress field, modifying the bonding condition. We numerically consider this asymmetry by using a model of friction with a simple angular dependence, which allows us to capture the experimental trends. We argue that the formulation of a tumor model with a bonding condition dependence may have potential implications in correct tumor classification.

Mechanical morphogenesis and the development of neocortical organisation.

The development of complex neocortical organisations is thought to result from the interaction of genetic and activity-dependent processes. We propose that a third type of process - mechanical morphogenesis - may also play an important role. We review theoretical and experimental results in physics showing how even homogeneous growth can produce a variety of forms, in particular neocortical folding. The mechanical instabilities that produce these forms induce heterogeneous patterns of stress at the scale of the organ. We review the evidence showing how these stresses can influence cell proliferation, migration and apoptosis, cell differentiation and shape, migration and axonal guidance, and could thus be able to influence regional neocortical identity and connectivity.

Surface energy of strained amorphous solids.

Surface stress and surface energy are fundamental quantities which characterize the interface between two materials. Although these quantities are identical for interfaces involving only fluids, the Shuttleworth effect demonstrates that this is not the case for most interfaces involving solids, since their surface energies change with strain. Crystalline materials are known to have strain-dependent surface energies, but in amorphous materials, such as polymeric glasses and elastomers, the strain dependence is debated due to a dearth of direct measurements. Here, we utilize contact angle measurements on strained glassy and elastomeric solids to address this matter. We show conclusively that interfaces involving polymeric glasses exhibit strain-dependent surface energies, and give strong evidence for the absence of such a dependence for incompressible elastomers. The results provide fundamental insight into our understanding of the interfaces of amorphous solids and their interaction with contacting liquids.

Morpho-elasticity of inflammatory fibrosis: the case of capsular contracture.

Inflammatory fibrosis is a wound-healing reaction of the immune system in mammals against aggression. After a signalling cascade, fibroblasts and potentially myofibroblasts make a stiff collagenous tissue inside the body that modifies the original healthy tissue. We focus here on the implant-induced fibrosis that aims to encapsulate the implant with a typical fibrous tissue called the capsule. Focusing on breast capsules, we aim to understand the mechanical properties of these tissues, to test the validity of fibre models that have been established in other contexts such as arteries. For this purpose, we perform force-extension experiments and show that mechanical constitutive laws of these tissues are especially difficult to derive, because models are sensitive to fibre orientation and dispersion, independently of the variation between individuals. In addition, fibre breakdown, and possibly remodelling, occur during the extension experiments. However, the high stiffness of the capsular tissue, compared with the healthy tissue, added to the fact that an inflammatory process has no reason to cease, is at the origin of large compressive stresses in vivo, which explains the pain and unaesthetic deformity. We evaluate the stresses responsible for the pain and the buckling instability, which have no reason to stop if the inflammation persists.

Hábitos de lectura en alumnos de primer ingreso de psicología educativa de la Universidad Pedagógica Nacional (UPN), México / Reading habits in students of the first year community of educational psychology of the Universidad Pedagógica Nacional (UPN), Mexico

RESUMEN El objetivo de esta investigación fue identificar los hábitos de lectura en tres grupos de estudiantes de primer semestre de la licenciatura en Psicología Educativa de la Universidad Pedagógica Nacional Unidad Ajusco en la Ciudad de México. Este estudio tuvo un alcance descriptivo con un diseño no experimental en el que participaron 69 alumnos, de los cuales 60 fueron mujeres y 9 hombres con un promedio de edad de 20 años, cuya selección se realizó bajo un muestreo no probabilístico por la accesibilidad y la disponibilidad del docente responsable de los grupos. Para la obtención de los datos se utilizó el Cuestionario sobre Hábitos de Lectura el cual fue aplicado en el salón de clase de cada uno de los grupos programados y para el procesamiento de la información se utilizó el software Excel versión 2013. Los resultados mostraron que quienes fueron analizados en este estudio, a pesar de que leen periódicamente, no tienen el hábito; además se encontró que el libro sigue siendo la principal fuente de información tanto en el formato impreso como digital.

ABSTRACT The objective of this research was to identify reading habits in three groups of first semester students of the Bachelor in Educational Psychology of the National Pedagogical University Unit Ajusco in Mexico City. This study had a descriptive scope with a non-experimental design in which 69 students participated, of which 60 were women and 9 men with an average age of 20 years, whose selection was made under a non-probabilistic sampling for accessibility and availability of the teacher responsible for the groups. To obtain the data, the Reading Habits Questionnaire was used, which was applied in the classroom of each of the programmed groups and for the information processing the Excel 2013 version software was used. The results showed that the students analyzed in this study, although they read periodically do not have the habit, it was also found that the book is still the main source of information in both the printed and digital format.

Friction of viscoelastic elastomers with rough surfaces under torsional contact conditions.

Frictional properties of contacts between a smooth viscoelastic rubber and rigid surfaces are investigated using a torsional contact configuration where a glass lens is continuously rotated on the rubber surface. From the inversion of the displacement field measured at the surface of the rubber, spatially resolved values of the steady state frictional shear stress are determined within the nonhomogeneous pressure and velocity fields of the contact. For contacts with a smooth lens, a velocity-dependent but pressure-independent local shear stress is retrieved from the inversion. On the other hand, the local shear stress is found to depend on both velocity and applied contact pressure when a randomly rough (sand-blasted) glass lens is rubbed against the rubber surface. As a result of changes in the density of microasperity contacts, the amount of light transmitted by the transparent multicontact interface is observed to vary locally as a function of both contact pressure and sliding velocity. Under the assumption that the intensity of light transmitted by the rough interface is proportional to the proportion of area into contact, it is found that the local frictional stress can be expressed experimentally as the product of a purely velocity-dependent term, k(v), by a term representing the pressure and velocity dependence of the actual contact area, A/A(0). A comparison between k(v) and the frictional shear stress of smooth contacts suggests that nanometer scale dissipative processes occurring at the interface predominate over viscoelastic dissipation at microasperity scale.

Lung metastasectomy: long-term outcomes in an 18-year cohort from a single center.

Lung metastasectomy is an area of interest and controversy in surgical oncology. Most of the available evidence derives from small cohorts with short follow-up. The aim of this study was to evaluate the oncologic outcomes in an 18-year cohort from a single center. We retrospectively reviewed 398 patients with several malignancies who underwent lung metastasectomy between January 1990 and December 2008. Demographic, clinical, and surgical variables were evaluated. Uni- and multivariate analyses were performed to identify factors associated with overall survival (OS). Mean follow-up was 20 months. Wedge resection was performed in 297 cases and 101 required anatomic resections. In 303 patients the disease-free interval (DFI) was >6 months meanwhile 95 patients had a DFI ≤6 months. Complete resection was achieved in 351 patients (88.2%). Median OS for all patients was 81.9 months (95% CI, 36.9-126.9). On multivariate analysis, factors associated with a poor overall survival were DFI <6 months (HR, 1.74; 95% CI, 1.24-2.4; p=0.001) and incomplete resection (HR, 1.58 95% CI, 1.01-2.5; p=0.0047). Independent prognostic factors associated with better survival were DFI >6 months and complete resection. Size and number of metastases as well as re-do metastasectomy were not associated with worse survival.

Randomized phase II trial of All-trans-retinoic acid with chemotherapy based on paclitaxel and cisplatin as first-line treatment in patients with advanced non-small-cell lung cancer.

PURPOSE: This randomized phase II trial evaluated whether the combination of cisplatin and paclitaxel (PC) plus all-trans retinoic acid (ATRA) increases response rate (RR) and progression-free survival (PFS) in patients with advanced non-small-cell lung cancer (NSCLC) with an acceptable toxicity profile and its association with the expression of retinoic acid receptor beta 2 (RAR-beta2) as a response biomarker. PATIENTS AND METHODS: Patients with stages IIIB with pleural effusion and IV NSCLC were included to receive PC, and randomly assigned to receive ATRA 20 mg/m(2)/d (RA/PC) or placebo (P/PC) 1 week before treatment until two cycles were completed. RAR-beta2 expression was analyzed in tumor and adjacent lung tissue. RESULTS: One hundred seven patients were included, 55 in the P/PC group and 52 in the RA/PC group. RR for RA/PC was 55.8% (95% CI, 46.6% to 64.9%) and for P/PC, 25.4% (95% CI, 21.3 to 29.5%; P = .001). The RA/PC group had a longer median PFS (8.9 v 6.0 months; P = .008). Multivariate analysis of PFS showed significant differences for the RA/PC group (hazard ratio, 0.62; 95% CI, 0.4 to 0.95). No significant differences in toxicity grade 3/4 were found between groups, except for hypertriglyceridemia (10% v 0%) in RA/PC (P = .05). Immunohistochemistry and reverse-transcriptase polymerase chain reaction assays showed expression of RAR-beta2 in normal tissues of all tumor samples, but only 10% of samples in the tumor tissue. CONCLUSION: Adding ATRA to chemotherapy could increase RR and PFS in patients with advanced NSCLC with an acceptable toxicity profile. A phase III clinical trial is warranted to confirm these findings.

Wood-smoke exposure as a response and survival predictor in erlotinib-treated non-small cell lung cancer patients: an open label phase II study.

INTRODUCTION: Erlotinib, a tyrosine kinase inhibitor, has improved survival and quality of life in patients with non-small cell lung cancer (NSCLC) after first- or second-line chemotherapy. Asian origin, adenocarcinoma histology, female gender, lack of tobacco use, and expression of epidermal growth factor receptor are significant independent predictors of response to Erlotinib. Although tobacco use is considered a major cause of NSCLC, other risk factors such as wood-smoke exposure (WSE) are associated. Almost 3 billion people worldwide rely on solid fuels as their primary source of domestic energy for cooking and heating. METHODS: In this study, 150 consecutive unselected patients with histologically proven NSCLC with progression after prior first- or second-line chemotherapy and/or poor performance status were treated with Erlotinib 150 mg/d. Clinical and pathologic characteristics were associated with response. RESULTS: Overall response to Erlotinib was observed in 51 patients [34%; 95% confidence interval {95% CI}, 29.9-37.6]. In multivariate analysis, clinical features associated with response to Erlotinib were adenocarcinoma (35 versus 20%; p = 0.05) and WSE (83 versus 13%; p < 0.001). Factors associated with longer progression-free survival in Cox analysis included adenocarcinoma (7.9 versus 2.3 months; p = 0.009), female gender (8.4 versus 5.3 months; p = 0.04), and WSE (17.6 versus 5.3 months; p = 0.006). CONCLUSIONS: WSE is associated with better response to Erlotinib and improved progression-free survival in patients with NSCLC. Additional studies in epidermal growth factor receptor signaling pathway in WSE-associated NSCLC are warranted.