Quasi-Two-Dimensional Diffusion of Single Ellipsoids: Aspect Ratio and Confinement Effects

We report on video-microscopy measurements of the translational and rotational Brownian motions of isolated ellipsoidal particles in quasi-two-dimensional sample cells of increasing thickness. The long-time diffusion coefficients were measured along the long (Da) and short (Db) ellipsoid axes, respectively, and the ratio, Da /Db, was determined as a function of wall confinement and particle aspect ratio. In three dimensions (3D), this ratio (Da /Db) cannot be larger than 2, but in quasi-two dimensions, wall confinement was found to substantially alter diffusion anisotropy and substantially slow particle diffusion along the short axis compared to 3D

Mesoporous Silica Colloids: Wetting, Surface Diffusion, and Cationic Surfactant Adsorption

International audienceWe have investigated the wetting and surface diffusion of mesoporous colloidal silica particles at the water surface and the adsorption of cationic cetyltrimethylammonium (CTA+) surfactant on these particles. Porous silica colloids diffuse at the surface of water and in the volume, interacting with cationic surfactants that can adsorb inside the pores of the particles. We observed that surfactant adsorption on mesoporous silica depends dramatically not only on the particle pore size but also on specific counterion effects. We measured striking differences both on a macroscopic property of the interface, i.e., surface tension, and also at a single particle level by evaluating the translational diffusion of partially wetted particles at the fluid interface. We varied the pore size from 2 to 7 nm and explored the effects of ions possessing different hydration number and kosmotropic/chaotropic character. At concentrations lower than the critical micellar concentration, we evidence that cationic surfactants adsorb on silica as surface micelles and surfactant adsorption inside the pores occurs only if the pore diameter is larger than the size of surface micelles. With a view to understand the surprising different adsorption behavior of CTA+OH– and CTA+Br– on porous silica particles, we investigated the effect of counterions on the surfactant adsorption on porous silica colloids by tuning the pH and the counterion properties

Morphology of spine and footprint in athletes from different sports: an integrate approach to evaluate posture

Posture is a complex process determined by the interaction of several body structures. In the past years, different direct and indirect procedures have been proposed to understand how these anatomical structures could be modified by forces exerted during sport practice (Queen et al, 2007). A particular attention has been focused on the variations in athletes from different sports to highlight eventual correlations between morpho-functional modifications, postural diseases and injuries (Cain et al, 2007). The aim of this work is to study the morphological aspects of the footprint and the spine in different athletes by an integrate approach. 115 subjects were tested and divided accordingly to the specific sport activity (control, basketball, volleyball, football, gymnastics); only subjects without previous or current diseases of the bones, joints and muscles have been considered. The electronic baropodometry has been used to measure the pressure distribution exerted on each foot during static and dynamic conditions; the Surfacer has been used to record the position of chosen points on the back. Our results indicated that, in comparison with controls, athletes from different sports displayed specific and significant modifications in foot type and in the back morphology; in particular, statistical analysis showed that in basketball and gymnastics athletes, significant changing in foot type and in the back morphology were present; moreover, in volleyball athletes, significant changing were found in foot type. Therefore, our results suggest that each sport could determinate specific postural changes during sport practice. Our data could be useful to develop specific training protocols aimed to prevent alterations in spine morphology and foot type that are associated with sport practice and could determine injuries or other postural diseases. Reference

Neuro-degenerative and vascular diseases: methodology for functional recovery

Posture refers to the position of the body in space that is expressed through the interaction of all the districts and systems such as the musculoskeletal system, the central and peripheral nervous system. Alterations in imbalances and associated diseases produce a structural and physiologic reorganization of the anatomical structures to improve postural dynamics. Generally, these changes can occur due to trauma or following the onset of neurodegenerative diseases or vascular problems that, in different ways, ranging to compromising the proper functioning of one of the components involved in postural processes. Currently postural diseases are treated by passive (brace and orthosis) and active (robotic device and traditional rehabilitation) methods according with the severity of imbalance (1). The aim of this study is to evaluate the effects of an innovative exoskeleton, called Human Body Posturizer (HBP), in rehabilitation of different neurodegenerative and vascular diseases. We recruited 37 subjects divided according to the pathology: 9 subjects with Parkinson’s disease, 14 with multiple sclerosis, 10 post-stroke patients and 4 with infantile cerebral palsy. Subjects underwent 4 weeks HBP treatment, consisting of 30 minutes, with different timing and duration of treatment depending on the specific pathology. The samples were analyzed by using of Electronic Baropodometer, Stabilometric Platform and Sensorizer FreeSense. Each subject was sampled before and after treatment and differences between pre and post treatment were subjected to statistical analysis. In all groups, we found significant differences in the comparison between the measurements performed before and after treatment with HBP. These changes have allowed to pointing out the improvement in the parameters analyzed in the post-treatment tests. Thus, as demonstrated by other studies (2), the use of HBP could represent an integrative therapy for different postural diseases and it can be inserted as a supportive therapy during the rehabilitation process in neurodegenerative and vascular diseases

New methodology for a correct gait

A proper biomechanics of the foot is fundamental for the maintenance of posture and for a symmetrical distribution of plantar pressures. It ‘been shown that high plantar pressures are greater risks of damage to be covered by the same foot that the anatomical structures involved in the above processes postural(1). Thus numerous studies have investigated the effectiveness of orthotics that, by increasing the contact surface between the foot and the ground, they were going to decrease the load associated with certain anatomical districts(2). The aim of our study was to evaluate, through static and dynamic baropodometry, the effectiveness of the regular gait, a new support that has the task of stabilizing the arch of the foot in static and to allow proper movement of the same. These subjects underwent rating scales and baropodometric examination before and after using the orthotics. It was carried out both the analysis monopodalic, for the evaluation of the effectiveness of the insole in the redistribution of pressures between different zones of a same foot, both the bipodalic for the evaluation of the symmetry in the distribution of the pressures between the different feet. The results obtained, subjected to statistical analysis for significance, show that the insole, to how it was designed, is able to restore a correct distribution of the parameters both in analysis monopodalic that bipodalic and both in static and dynamic conditions. These redistributions, in addition, also remain in the tests posttreatment without footwear, showing that the particular conformation of the plantar, with supports positioned in specific districts of the arch of the foot, is able to stimulate the proprioceptors present therein and therefore to enable a reorganization at the central level . This reorganization allows the subject treated with the regular gait to maintain the morphology and the smooth running of the propeller breech during movement not only while wearing the insole, but also after it has been remove

Plantar support for a correct gait

Postural adjustments to maintain static and dynamic balance depend on the relationship between sensory input organs and the environment. The study of foot posture assists in the evaluation of overall posture. The human foot is the basis of support and propulsion for gait and it provides support and flexibility for effective weight transfer (1). Foot posture involves the integration of sensory information from the periphery to the body, especially mechanoreceptors in the sole of the foot, related to gravitational acceleration, the environment and the position of the segments of the body. Numerous studies have investigated the effectiveness of orthotics that, by increasing the contact surface between the foot and the ground, were going to decrease the load associated with certain areas of plantar surface (2). The aim of our study was to evaluate the effects of innovative insoles, named Regular Gait (RG), on plantar pressures distribution during standing position and walking in healthy subjects; therefore, we investigated whether these effects are maintained after insole removing. 30 subjects were tested; these were free of foot diseases or damage to the anatomical structures involved in the processes above posture. These subjects underwent rating scales and static and dynamic baropodometric examination before and after using RG. The results obtained, subjected to statistical analysis for significance, show that the RG, for as we have designed, is able to restore a correct distribution of the parameters both in static and dynamic conditions. We have also shown that the best results were obtained only after a month of treatment with RG and that the results obtained persist even in the tests post-treatment without insoles. The fact we charged to the special geometry with which the insole is designed: its supports, that are located in specific regions of the plantar arch, go to stimulate the mechanoreceptors found there. In this way, through the streets proprioceptive, you can obtain a reorganization of the plantar stance even at the higher nervous centers level. This allowed the subjects treated to improve their posture both while walking and during the maintenance of the upright position. As far demonstrated , the RG seems to be a tool whose potential does not end in the modification of the plantar stance, but that influences a number of processes, by acting on the kinetic chains that originate from the foot

Microparticle Brownian motion near an air-water interface governed by direction-dependent boundary conditions

Hypothesis Although the dynamics of colloids in the vicinity of a solid interface has been widely characterized in the past, experimental studies of Brownian diffusion close to an air-water interface are rare and limited to particle-interface gap distances larger than the particle size. At the still unexplored lower distances, the dynamics is expected to be extremely sensitive to boundary conditions at the air-water interface. There, ad hoc experiments would provide a quantitative validation of predictions. Experiments Using a specially designed dual wave interferometric setup, the 3D dynamics of 9 µm diameter particles at a few hundreds of nanometers from an air-water interface is here measured in thermal equilibrium. Findings Intriguingly, while the measured dynamics parallel to the interface approaches expected predictions for slip boundary conditions, the Brownian motion normal to the interface is very close to the predictions for no-slip boundary conditions. These puzzling results are rationalized considering current models of incompressible interfacial flow and deepened developing an ad hoc model which considers the contribution of tiny concentrations of surface active particles at the interface. We argue that such condition governs the particle dynamics in a large spectrum of systems ranging from biofilm formation to flotation process

Bistability breaks-off deterministic responses to intracortical stimulation during non-REM sleep

During non-rapid eye movement (NREM) sleep (stage N3), when consciousness fades, cortico-cortical interactions are impaired while neurons are still active and reactive. Why is this? We compared cortico-cortical evoked-potentials recorded during wakefulness and NREM by means of time-frequency analysis and phase-locking measures in 8 epileptic patients undergoing intra-cerebral stimulations/recordings for clinical evaluation. We observed that, while during wakefulness electrical stimulation triggers a chain of deterministic phase-locked activations in its cortical targets, during NREM the same input induces a slow wave associated with an OFF-period (suppression of power > 20 Hz), possibly reflecting a neuronal down-state. Crucially, after the OFF-period, cortical activity resumes to wakefulness-like levels, but the deterministic effects of the initial input are lost, as indicated by a sharp drop of phase-locked activity. These findings suggest that the intrinsic tendency of cortical neurons to fall into a down-state after a transient activation (i.e. bistability) prevents the emergence of stable patterns of causal interactions among cortical areas during NREM. Besides sleep, the same basic neurophysiological dynamics may play a role in pathological conditions in which thalamo-cortical information integration and consciousness are impaired in spite of preserved neuronal activity. (C) 2015 The Authors. Published by Elsevier Inc.Peer reviewe