Nematic Torques in Scalar Active Matter: When Fluctuations Favor Polar Order and Persistence.

We study the impact of nematic alignment on scalar active matter in the disordered phase. We show that nematic torques control the emergent physics of particles interacting via pairwise forces and can either induce or prevent phase separation. The underlying mechanism is a fluctuation-induced renormalization of the mass of the polar field that generically arises from nematic torques. The correlations between the fluctuations of the polar and nematic fields indeed conspire to increase the particle persistence length, contrary to what phenomenological computations predict. This effect is generic and our theory also quantitatively accounts for how nematic torques enhance particle accumulation along confining boundaries and opposes demixing in mixtures of active and passive particles.

Large-scale simulations of biological cell sorting driven by differential adhesion follow diffusion-limited domain coalescence regime.

Cell sorting, whereby a heterogeneous cell mixture segregates and forms distinct homogeneous tissues, is one of the main collective cell behaviors at work during development. Although differences in interfacial energies are recognized to be a possible driving source for cell sorting, no clear consensus has emerged on the kinetic law of cell sorting driven by differential adhesion. Using a modified Cellular Potts Model algorithm that allows for efficient simulations while preserving the connectivity of cells, we numerically explore cell-sorting dynamics over very large scales in space and time. For a binary mixture of cells surrounded by a medium, increase of domain size follows a power-law with exponent n = 1/4 independently of the mixture ratio, revealing that the kinetics is dominated by the diffusion and coalescence of rounded domains. We compare these results with recent numerical studies on cell sorting, and discuss the importance of algorithmic differences as well as boundary conditions on the observed scaling.

Frame tension governs the thermal fluctuations of a fluid membrane: new evidence.

Two different tensions can be defined for a fluid membrane: the internal tension, γ, conjugated to the real membrane area in the Hamiltonian, and the frame tension, τ, conjugated to the projected (or frame) area. According to the standard statistical description of a membrane, the fluctuation spectrum is governed by γ. However, using rotational invariance arguments, several studies argued that the fluctuation spectrum must be governed by the frame tension τ instead. These studies disagree on the origin of the result obtained with the standard description yet: either a miscounting of configurations, quantified with the integration measure, or the use of a quadratic approximation of the Helfrich Hamiltonian. Analyzing the simplest case of a one-dimensional membrane, for which the arc length offers a natural parametrization, we give a new proof that the fluctuations are driven by τ, and show that the origin of the issue with the standard description is a miscounting of membrane configurations. The origin itself of this miscounting depends on the thermodynamic ensemble in which calculations are made.

Thermal shape fluctuations of a two-dimensional compressible droplet.

Analysis of thermal capillary waves on the surface of a liquid usually assumes incompressibility of the bulk fluid. However, for droplets or bubbles with submicronic size, or for epithelial cells whose out-of-plane elongation can be modeled by an effective 2D bulk modulus, compressibility of the internal fluid must be taken into account for the characterization of their shape fluctuations. We present a theoretical analysis of the fluctuations of a two-dimensional compressible droplet. Analytical expressions for area, perimeter and energy fluctuations are derived and compared with Cellular Potts Model (CPM) simulations. This comparison shows a very good agreement between theory and simulations, and offers a precise calibration method for CPM simulations.

Thermally Driven Order-Disorder Transition in Two-Dimensional Soft Cellular Systems.

Many systems, including biological tissues and foams, are made of highly packed units having high deformability but low compressibility. At two dimensions, these systems offer natural tesselations of a plane with fixed density, in which transitions from ordered to disordered patterns are often observed, in both directions. Using a modified cellular Potts model algorithm that allows rapid thermalization of extensive systems, we numerically explore the order-disorder transition of monodisperse, two-dimensional cellular systems driven by thermal agitation. We show that the transition follows most of the predictions of Kosterlitz-Thouless-Halperin-Nelson-Young (KTHNY) theory developed for melting of 2D solids, extending the validity of this theory to systems with many-body interactions. In particular, we show the existence of an intermediate hexatic phase, which preserves the orientational order of the regular hexagonal tiling but loses its positional order. In addition to shedding light on the structural changes observed in experimental systems, our study shows that soft cellular systems offer macroscopic systems in which the KTHNY melting scenario can be explored, in the continuation of Bragg's experiments on bubble rafts.

Micron-sized and submicron-sized aerosol deposition in a new ex vivo preclinical model.

BACKGROUND: The knowledge of where particles deposit in the respiratory tract is crucial for understanding the health effects associated with inhaled drug particles. METHOD: An ex vivo study was conducted to assess regional deposition patterns (thoracic vs. extrathoracic) of radioactive polydisperse aerosols with different size ranges [0.15 µm-0.5 µm], [0.25 µm-1 µm] and [1 µm-9 µm]. SPECT/CT analyses were performed complementary in order to assess more precisely the regional deposition of aerosols within the pulmonary tract. Experiments were set using an original respiratory tract model composed of a human plastinated head connected to an ex vivo porcine pulmonary tract. The model was ventilated by passive expansion, simulating pleural depressions. Aerosol was administered during nasal breathing. RESULTS: Planar scintigraphies allowed to calculate the deposited aerosol fractions for particles in the three size ranges from sub-micron to micron The deposited fractions obtained, for thoracic vs. extra-thoracic regions respectively, were 89 ± 4 % vs. 11 ± 4 % for [0.15 µm-0.5 µm], 78 ± 5 % vs. 22 ± 5 % for [0.25 µm-1 µm] and 35 ± 11 % vs.65 ± 11 % for [1 µm-9 µm]. CONCLUSION: Results obtained with this new ex vivo respiratory tract model are in good agreement with the in vivo data obtained in studies with baboons and humans.

Hydrodynamics of bilayer membranes with diffusing transmembrane proteins.

We consider the hydrodynamics of lipid bilayers containing transmembrane proteins of arbitrary shape. This biologically-motivated problem is relevant to the cell membrane, whose fluctuating dynamics play a key role in phenomena ranging from cell migration, intercellular transport, and cell communication. Using Onsager's variational principle, we derive the equations that govern the relaxation dynamics of the membrane shape, of the mass densities of the bilayer leaflets, and of the diffusing proteins' concentration. With our generic formalism, we obtain several results on membrane dynamics. We find that proteins that span the bilayer increase the intermonolayer friction coefficient. The renormalization, which can be significant, is in inverse proportion to the protein's mobility. Second, we find that asymmetric proteins couple to the membrane curvature and to the difference in monolayer densities. For practically all accessible membrane tensions (σ > 10(-8) N m(-1)) we show that the protein density is the slowest relaxing variable. Furthermore, its relaxation rate decreases at small wavelengths due to the coupling to curvature. We apply our formalism to the large-scale diffusion of a concentrated protein patch. We find that the diffusion profile is not self-similar, owing to the wavevector dependence of the effective diffusion coefficient.

Statistical mechanics of two-dimensional foams: Physical foundations of the model.

In a recent series of papers, a statistical model that accounts for correlations between topological and geometrical properties of a two-dimensional shuffled foam has been proposed and compared with experimental and numerical data. Here, the various assumptions on which the model is based are exposed and justified: the equiprobability hypothesis of the foam configurations is argued. The range of correlations between bubbles is discussed, and the mean-field approximation that is used in the model is detailed. The two self-consistency equations associated with this mean-field description can be interpreted as the conservation laws of number of sides and bubble curvature, respectively. Finally, the use of a "Grand-Canonical" description, in which the foam constitutes a reservoir of sides and curvature, is justified.

Impact of airborne particle size, acoustic airflow and breathing pattern on delivery of nebulized antibiotic into the maxillary sinuses using a realistic human nasal replica.

PURPOSE: Improvement of clinical outcome in patients with sinuses disorders involves targeting delivery of nebulized drug into the maxillary sinuses. We investigated the impact of nebulization conditions (with and without 100 Hz acoustic airflow), particle size (9.9 µm, 2.8 µm, 550 nm and 230 nm) and breathing pattern (nasal vs. no nasal breathing) on enhancement of aerosol delivery into the sinuses using a realistic nasal replica developed by our team. METHODS: After segmentation of the airways by means of high-resolution computed tomography scans, a well-characterized nasal replica was created using a rapid prototyping technology. A total of 168 intrasinus aerosol depositions were performed with changes of aerosol particle size and breathing patterns under different nebulization conditions using gentamicin as a marker. RESULTS: The results demonstrate that the fraction of aerosol deposited in the maxillary sinuses is enhanced by use of submicrometric aerosols, e.g. 8.155 ± 1.476 mg/L of gentamicin in the left maxillary sinus for the 2.8 µm particles vs. 2.056 ± 0.0474 for the 550 nm particles. Utilization of 100-Hz acoustic airflow nebulization also produced a 2- to 3-fold increase in drug deposition in the maxillary sinuses (e.g. 8.155 ± 1.476 vs. 3.990 ± 1.690 for the 2.8 µm particles). CONCLUSIONS: Our study clearly shows that optimum deposition was achieved using submicrometric particles and 100-Hz acoustic airflow nebulization with no nasal breathing. It is hoped that our new respiratory nasal replica will greatly facilitate the development of more effective delivery systems in the future.

Validation of anatomical models to study aerosol deposition in human nasal cavities.

PURPOSE: Intranasal deposition of aerosols is often studied using in vitro nasal cavity models. However, the relevance of these models to predict in vivo human deposition has not been validated. This study compared in vivo nasal aerosol deposition and in vitro deposition in a human plastinated head model (NC1) and its replica constructed from CT-scan (NC2). METHODS: Two nebulizers (Atomisor Sonique® and Easynose®) were used to administer a 5.6 µm aerosol of (99m)Tc-DTPA to seven healthy volunteers and to the nasal models. Aerosol deposition was quantified by γ-scintigraphy in the nasal, upper nasal cavity and maxillary sinus (MS) regions. The distribution of aerosol deposition was determined along three nasal cavity axes (x, y and z). RESULTS: There was no significant difference regarding aerosol deposition between the volunteers and NC1. Aerosol deposition was significantly lower in NC2 than in volunteers regarding nasal region (p < 0.05) but was similar for the upper nasal cavity and MS regions. Mean aerosol distribution for NC1 came within the standard deviation (SD) of in vivo distribution, whereas that of NC2 was outside the in vivo SD for x and y axes. CONCLUSIONS: In conclusion, nasal models can be used to predict aerosol deposition produced by nebulizers, but their performance depends on their design.

Early detection of pharyngocutaneous fistulae after total laryngectomy by cytokine in drainage: A pilot study (DEFILAC).

BACKGROUND: The determination of cytokines in the postoperative drainage (POD) fluid could be a method for early detection of the development of a pharyngocutaneous fistula (PCF). MATERIALS AND METHODS: We conducted a prospective two-center study involving 28 patients. PODs were collected on Day 1 (D1) and Day 2 (D2) postoperatively for determination of a cytokine panel and cytobacteriological examination. RESULTS: Eleven (39%) patients presented with PCF on average 13 ± 5.5 days after surgery. Patients with PCF had higher IL-10 (121 vs. 40.3, p = 0.04, effect size (ES) = 0.98 [0.16, 1.79]) and TNFα level (21.2 vs. 2.2, p = 0.02, ES = 0.83 [0.03, 1.63]) on D2. An IL-10 threshold of 72 pg/mL on D2 was diagnostic of the occurrence of PCF with a sensibility of 70%, specificity of 88%. CONCLUSION: The determination of cytokines in POD fluid on D2 is a reliable tool for predicting the development of a PCF after total laryngectomy.

Arboviral Risk Associated with Solid Organ and Hematopoietic Stem Cell Grafts: The Prophylactic Answers Proposed by the French High Council of Public Health in a National Context.

Diseases caused by arboviruses are on the increase worldwide. In addition to arthropod bites, most arboviruses can be transmitted via accessory routes. Products of human origin (labile blood products, solid organs, hematopoietic stem cells, tissues) present a risk of contamination for the recipient if the donation is made when the donor is viremic. Mainland France and its overseas territories are exposed to a complex array of imported and endemic arboviruses, which differ according to their respective location. This narrative review describes the risks of acquiring certain arboviral diseases from human products, mainly solid organs and hematopoietic stem cells, in the French context. The main risks considered in this study are infections by West Nile virus, dengue virus, and tick-borne encephalitis virus. The ancillary risks represented by Usutu virus infection, chikungunya, and Zika are also addressed more briefly. For each disease, the guidelines issued by the French High Council of Public Health, which is responsible for mitigating the risks associated with products of human origin and for supporting public health policy decisions, are briefly outlined. This review highlights the need for a "One Health" approach and to standardize recommendations at the international level in areas with the same viral epidemiology.

Statistical mechanics of two-dimensional shuffled foams: prediction of the correlation between geometry and topology.

We propose an analytical model for the statistical mechanics of shuffled two-dimensional foams with moderate bubble size polydispersity. It predicts without any adjustable parameters the correlations between the number of sides n of the bubbles (topology) and their areas A (geometry) observed in experiments and numerical simulations of shuffled foams. Detailed statistics show that in shuffled cellular patterns n correlates better with √A (as claimed by Desch and Feltham) than with A (as claimed by Lewis and widely assumed in the literature). At the level of the whole foam, standard deviations Δn and ΔA are in proportion. Possible applications include correlations of the detailed distributions of n and A, three-dimensional foams, and biological tissues.

Plastinated nasal model: a new concept of anatomically realistic cast.

BACKGROUND: For many years, researchers have been interested in investigating airflow and aerosol deposition in the nasal cavities. The nasal airways appear to be a complex geometrical system. Thus, in vitro experimental studies are frequently conducted with a more or less biomimetic nasal replica. AIM: This study is devoted to the development of an anatomically realistic nose model with bilateral nasal cavities, i.e. nasal anatomy, airway geometry and aerodynamic properties as close as possible to in vivo behaviour. METHODS: A specific plastination technique of cephalic extremities was developed by the Anatomy Laboratory at the Saint-Etienne University in the last 10 years. The plastinated models obtained were anatomically, geometrically and aerodynamically validated using several techniques (endoscopy, CT scans, acoustic rhinometry and rhinomanometry). RESULTS: Our plastination model exhibited a high level of anatomic quality, including a very good mucosa preservation. Aerodynamical and geometrical investigations highlighted a global behaviour of plastinated models perfectly in accordance with a nasal decongested healthy subject. CONCLUSIONS: The present plastination model provides a realistic cast of nasal airways, and may be a useful tool for nasal flow, drug delivery and aerosol deposition studies.

Quasistatic rheology of soft cellular systems using the cellular Potts model.

Soft cellular systems, such as foams or biological tissues, exhibit highly complex rheological properties, even in the quasistatic regime, that numerical modeling can help to apprehend. We present a numerical implementation of quasistatic strain within the widely used cellular Potts model (CPM). The accuracy of the method is tested by simulating the quasistatic strain of two-dimensional dry foams, both ordered and disordered. The implementation of quasistatic strain in CPM allows the investigation of sophisticated interplays between stress-strain relationship and structural changes that take place in cellular systems.

Degradation of ZnGa2O4:Cr3+ luminescent nanoparticles in lysosomal-like medium.

The ultimate goal of in vivo imaging is to provide safe tools to probe the inside of a body in order to obtain pathological information, monitor activities, and examine disease progression or regression. In this context zinc gallate doped with chromium III (ZGO) nanoparticles with persistent luminescence properties have been previously developed, and their biodistribution as well as in vitro toxicity were evaluated. However, to date, nothing is known about their potential transformations in biological media, which may hinder their biomedical applications. In order to know if these nanoparticles could degrade, the present work consists of studying their fate over time depending on both their coating and the aqueous media in which they are dispersed. ZGO nanoparticles have been dispersed in three different aqueous solutions for up to 90 days and characterized by numerous techniques. Among the evaluated dispersion media, Artificial Lysosomal Fluid (ALF) mimicking the intracellular lysosome environment elicited significant degradation of ZGO nanoparticles. The chelating agents present in ALF have proved to play a major role in the degradation of the ZGO, by stabilizing the nanoparticles and increasing the contact. An important time decrease of the luminescence properties has also been observed, which correlated with the release of ions from ZGO nanoparticles as well as their decreasing size. This information is valuable since it indicates, for the first time, the long-term degradation of persistent luminescent nanoprobes in an in vivo like model medium. Therefore, possible elimination of the imaging probes after in vivo preclinical applications could be foreseen.

How do aerial freestyler skiers land on their feet? A situated analysis of athletes' activity related to new forms of acrobatic performance.

Based on the course-of-action theory, this study performed a situated analysis of three elite aerial freestyle skiers' activity. Data were collected by observation, videotaping and self-confrontation interviews retrospectively build the athletes' activity. The analysis identified units of action, thought, and feelings and described their relationships during each leap. Comparisons of the different courses of action revealed six components of freestyle skiers' activity: (1) pick up speed in the descent, (2) manage the curve of the tremplin, (3) take-off, (4) manage the exit of the tremplin, (5) perform rotations, and (6) organize the landing. This study revealed the dynamic and situated property of acrobatic activity. As the leap unfolded, the athletes step-by-step enhanced their knowledge of what was occurring and what they would have to do to perform their best and land on their feet. Points of convergence and divergence with other acrobatic performances are discussed.

Temporal dynamics of acrobatic activity: an approach of elite athletes specious present.

The present study examined how "meaningful time "is constructed and used during acrobatic performance. To do so, six elite athletes (2 tumblers, 2 trampolinists, 2 acrobatic skiers) performed the same acrobatic move within the context of their respective sports. Their activity was described step-by-step using the data obtained from self- confrontation interviews linked to behaviour analysis based on video recordings. The descriptions, which identified the actions, feelings and thoughts of the athletes in relation to the unfolding time of their performance, were then compared. The results demonstrated that acrobatic performance can be divided into different periods that delineate meaningful time. Differences were observed in how the athletes organized activity (e.g. cognitive, physical) according to the specific sport. The results were interpreted as specific ways to use flight time. Key pointsElite acrobatic athletes' activities organize the unfolding of the performance by progressively informing the performers about the state of the evolving situation.The complexity of the activity involved for such acrobatic performances is reduced by a process of timed and situated organization.Athletes' activity consisted to display different jigs corresponding to a meaningful delineate specious present for efficient performance.

Correction to 'Stiffest elastic networks'.

[This corrects the article DOI: 10.1098/rspa.2013.0611.].

Joint action in an elite rowing pair crew after intensive team training: The reinforcement of extra-personal processes.

The present study is a follow-up case report of the study from R'Kiouak and colleagues (2016). From the initial study that analyzed how individual experts rowed together while they never had practiced together, we seized here the opportunity to investigate how both rowers synchronize after having intensively practiced joint action through a national training program in which they were invited to take part. The joint action of 2 individual expert rowers, which composed a coxless pair crew, was tracked on-the-water at the end of a team-training program. We first determined how each rower experienced the joint action at each instance of oars' strokes during a 12min race. A phenomenological analysis evidenced several categories of how rowers shared lived experiences of their joint action. From mechanical data captured through an automatic recording device, we then scrutinized the mechanical signatures that correlated with each phenomenological sample. By comparing the present case report to the initial study, results suggested that, after the training program (a) rowers shared more meaningful experience of their joint action, and (b) only the boat velocity's index contributed to explain why oars stroke were alternatively lived as effective or detrimental. The present case report thus suggests that joint action training in rowing might imply an increase in the joint sense-making activities, probably associated with a change from an inter-personal to an extra-personal meaningful mode of co-regulation of the joint action.