Surface wave excitations and backflow effect over dense polymer brushes

Polymer brushes are being increasingly used to tailor surface physicochemistry for diverse applications such as wetting, adhesion of biological objects, implantable devices and much more. Here we perform Dissipative Particle Dynamics simulations to study the behaviour of dense polymer brushes under flow in a slit-pore channel. We discover that the system displays flow inversion at the brush interface for several disconnected ranges of the imposed flow. We associate such phenomenon to collective polymer dynamics: a wave propagating on the brush surface. The relation between the wavelength, the amplitude and the propagation speed of the flow-generated wave is consistent with the solution of the Stokes equations when an imposed traveling wave is assumed as the boundary condition (the famous Taylor's swimmer)

Surface wave excitations and backflow effect over dense polymer brushes

Polymer brushes are increasingly used to tailor surface physicochemistry for various applications such as wetting, adhesion of biological objects, implantable devices, etc. We perform Dissipative Particle Dynamics simulations to study the behavior of dense polymer brushes under flow in a slit-pore channel. We discover that the system displays flow inversion at the brush interface for several disconnected ranges of the imposed flow. We associate such phenomenon to collective polymer dynamics: a wave propagating on the brush surface. The relation between the wavelength, the amplitude and the propagation speed of the flow-generated wave is consistent with the solution of the Stokes equations when an imposed traveling wave is assumed as boundary condition (the famous Taylor's swimmer).Comment: 5 pages, 6 figures, supplemental material (5 pages, 4 figures) attached below the letter and before bibliography, videos available on request to the corresponding author, submitted to SciRe

Coarsening scenarios in unstable crystal growth

Crystal surfaces may undergo thermodynamical as well kinetic, out-of-equilibrium instabilities. We consider the case of mound and pyramid formation, a common phenomenon in crystal growth and a long-standing problem in the field of pattern formation and coarsening dynamics. We are finally able to attack the problem analytically and get rigorous results. Three dynamical scenarios are possible: perpetual coarsening, interrupted coarsening, and no coarsening. In the perpetual coarsening scenario, mound size increases in time as L=t^n, where the coasening exponent is n=1/3 when faceting occurs, otherwise n=1/4.Comment: Changes in the final part. Accepted for publication in Phys. Rev. Let

Development of BOLD Response to Motion in Human Infants

: Behavioral studies suggest that motion perception is rudimentary at birth and matures steadily over the first few years. We demonstrated previously that the major cortical associative areas serving motion processing, like middle temporal complex (MT+), visual cortex area 6 (V6), and PIVC in adults, show selective responses to coherent flow in 8-week-old infants. Here, we study the BOLD response to the same motion stimuli in 5-week-old infants (four females and four males) and compare the maturation between these two ages. The results show that MT+ and PIVC areas show a similar motion response at 5 and 8 weeks, whereas response in the V6 shows a reduced BOLD response to motion at 5 weeks, and cuneus associative areas are not identifiable at this young age. In infants and in adults, primary visual cortex (V1) does not show a selectivity for coherent motion but shows very fast development between 5 and 8 weeks of age in response to the appearance of motion stimuli. Resting-state correlations demonstrate adult-like functional connectivity between the motion-selective associative areas but not between primary cortex and temporo-occipital and posterior-insular cortices. The results are consistent with a differential developmental trajectory of motion area respect to other occipital regions, probably reflecting also a different development trajectory of the central and peripheral visual field.SIGNIFICANCE STATEMENT How the cortical visual areas attain the specialization that we observed in human adults in the first few months of life is unknown. However, this knowledge is crucial to understanding the consequence of perinatal brain damage and its outcome. Here, we show that motion selective areas are already functioning well in 5-week-old infants with greater responses for detecting coherent motion over random motion, suggesting that very little experience is needed to attain motion selectivity

Manifestações Cutâneas do Lúpus Eritematoso Sistêmico: Desafios Diagnósticos e Estratégias de Manejo

Introduction: Cutaneous manifestations of systemic lupus erythematosus (SLE) represent a significant and challenging aspect of this autoimmune disease. This study aims to explore management strategies for these cutaneous manifestations, with the goal of improving understanding and treatment of this complex dermatological condition. Objective: The objective of this study is to analyze management strategies for cutaneous manifestations of SLE, highlighting diagnostic and therapeutic approaches, as well as challenges faced in clinical practice. The intention is to provide a comprehensive overview of available treatment options and identify areas in need of further investigation and development. Methodology: To achieve this objective, a systematic literature review was conducted using specific descriptors related to systemic lupus erythematosus and its cutaneous manifestations. Relevant studies were selected based on pre-defined inclusion criteria, considering their methodological quality and relevance to the topic at hand. Results: Analysis of selected studies revealed a variety of management strategies for cutaneous manifestations of SLE, including topical and systemic treatments, complementary therapies, and preventive measures. Additionally, diagnostic challenges such as overlap with other dermatological conditions, and therapeutic challenges such as the need for more effective treatment options with fewer side effects, were identified. Conclusion: Management of cutaneous manifestations of SLE requires a multidisciplinary and individualized approach, aiming to control disease activity, prevent complications, and improve patients' quality of life. Continuous research and development of new therapies are essential to advance the treatment of this challenging dermatological condition.  Introdução: As manifestações cutâneas do lúpus eritematoso sistêmico (LES) representam uma parte significativa e desafiadora dessa doença autoimune. Este estudo busca explorar as estratégias de manejo dessas manifestações cutâneas, com o objetivo de melhorar a compreensão e o tratamento dessa condição dermatológica complexa. Objetivo: O objetivo deste estudo é analisar as estratégias de manejo das manifestações cutâneas do LES, destacando abordagens diagnósticas, terapêuticas e desafios enfrentados na prática clínica. Pretende-se fornecer uma visão abrangente das opções de tratamento disponíveis e identificar áreas que necessitam de maior investigação e desenvolvimento. Metodologia Para alcançar este objetivo, foi realizada uma revisão sistemática da literatura, utilizando descritores específicos relacionados ao lúpus eritematoso sistêmico e suas manifestações cutâneas. Os estudos relevantes foram selecionados com base em critérios de inclusão definidos previamente, considerando sua qualidade metodológica e relevância para o tema em questão. Resultados: A análise dos estudos selecionados revelou uma variedade de estratégias de manejo das manifestações cutâneas do LES, incluindo tratamentos tópicos e sistêmicos, terapias complementares e medidas preventivas. Além disso, foram identificados desafios diagnósticos, como a sobreposição com outras condições dermatológicas, e terapêuticas, como a necessidade de opções de tratamento mais eficazes e com menos efeitos colaterais. Conclusão: O manejo das manifestações cutâneas do LES requer uma abordagem multidisciplinar e individualizada, visando controlar a atividade da doença, prevenir complicações e melhorar a qualidade de vida dos pacientes. A pesquisa contínua e o desenvolvimento de novas terapias são fundamentais para avançar no tratamento dessa condição dermatológica desafiadora

Etude mésoscopique du glycocalyx endothélial et de son interaction avec le sang

Polymer brushes are dense matrices of grafted macromolecules. In addition to brushes finely designed in laboratory, various examples are offered by Nature, as the endothelial glycocalyx, decorating the lumen of mammalian blood vessels. The interaction of such network with the flowing plasma and cells is still partially unknown.The present thesis, by mean of Dissipative Particle Dynamics simulations, proposes a coarse-grained model for the self-consistent analysis of a dense polymer brush under parabolic flow. Our mesoscale investigation highlights the relevance of collective effects, driven by hydrodynamics, and proposes novel interpretations regarding the rich phenomenology of the brush-flow system.Preliminary results are also provided for the interplay between a mesoscopic deformable flowing object (prototype of a red blood cell) and the grafted polymers.Une brosse de polymères est une matrice dense de macromolécules greffées à une surface donnée. Au-delà des brosses synthétiques réalisées en laboratoire, on trouve des exemples très variés dans la nature: un exemple emblématique est le glycocalyx endothélial, décorant la surface interne des vaisseaux sanguins des mammifères. L'interaction de cette structure avec le plasma et les cellules sous écoulement n'est encore que très partiellement explorée. La présente thèse propose, grâce à des simulations de "Dissipative Particle Dynamics", un modèle coarse-grained pour une analyse auto-cohérente d'une brosse polymérique dense sous écoulement parabolique. Cette étude mésoscopique met en évidence l'importance des effets collectifs entre molécules, entraînée par l'hydrodynamique, et propose des nouvelles interprétations à la phénoménologie du système brosse-écoulement. Des résultats préliminaires sont également produits pour l'interaction sous écoulement entre un objet mésoscopique déformable (prototype d'un globule rouge) et les polymères greffés

BOLD Response Selective to Flow-Motion in Very Young Infants.

In adults, motion perception is mediated by an extensive network of occipital, parietal, temporal, and insular cortical areas. Little is known about the neural substrate of visual motion in infants, although behavioural studies suggest that motion perception is rudimentary at birth and matures steadily over the first few years. Here, by measuring Blood Oxygenated Level Dependent (BOLD) responses to flow versus random-motion stimuli, we demonstrate that the major cortical areas serving motion processing in adults are operative by 7 wk of age. Resting-state correlations demonstrate adult-like functional connectivity between the motion-selective associative areas, but not between primary cortex and temporo-occipital and posterior-insular cortices. Taken together, the results suggest that the development of motion perception may be limited by slow maturation of the subcortical input and of the cortico-cortical connections. In addition they support the existence of independent input to primary (V1) and temporo-occipital (V5/MT+) cortices very early in life

Hydrodynamic instability and flow reduction in polymer brush coated channels

International audienceA polymer brush is a passive medium but, exposed to fluid flow, it displays a surprising dynamics, for which filamentous protrusions and their interactions via hydrodynamics come heavily into play