Walking in orthostatic tremor modulates tremor features and is characterized by impaired gait stability

Primary orthostatic tremor (OT) is characterized by high-frequency lower-limb muscle contractions and a disabling sense of unsteadiness while standing. Patients consistently report a relief of symptoms when starting to ambulate. Here, we systematically examined and linked tremor and gait characteristics in patients with OT. Tremor and gait features were examined in nine OT patients and controls on a pressure-sensitive treadmill for one minute of walking framed by two one-minute periods of standing. Tremor characteristics were assessed by time-frequency analysis of surface EMG-recordings from four leg muscles. High-frequency tremor during standing (15.29 +/- 0.17 Hz) persisted while walking but was consistently reset to higher frequencies (16.34 +/- 0.25 Hz;p < 0.001). Tremor intensity was phase-dependently modulated, being predominantly observable during stance phases (p < 0.001). Tremor intensity scaled with the force applied during stepping (p < 0.001) and was linked to specific gait alterations, i.e., wide base walking (p = 0.019) and increased stride-to-stride fluctuations (p = 0.002). OT during walking persists but is reset to higher frequencies, indicating the involvement of supraspinal locomotor centers in the generation of OT rhythm. Tremor intensity is modulated during the gait cycle, pointing at specific pathways mediating the peripheral manifestation of OT. Finally, OT during walking is linked to gait alterations resembling a cerebellar and/or sensory ataxic gait disorder

Conformational induced behaviour of copolymer-capped magnetite nanoparticles at the air/water interface

Biocompatible and stimuli-responsive copolymer-capped Fe3O 4 nanoparticles (NPs) were studied at the air/water interface, below and above their lower critical solution temperature (LCST). The NP layers have been characterized in situ by compression-expansion isotherms, infrared reflection-absorption spectrometry, X-ray reflectivity, and by transmission electron microscopy after being transferred onto solid support. The data obtained highlight the different interfacial behaviour of the NPs below the LCST (good dispersibility in the aqueous subphase) and above the LCST (lack of dispersibility in the subphase, high affinity for hydrophobic interactions, and agglomeration at the interface). Conformational transitions of the copolymer from pancake to brush and mushroom-like structures are the key factors of the stimuli-induced behaviour of the NPs at the air/water interface. These conformational changes of the copolymer shell are due to the ability of the ethylene oxide units to form hydrogen bonds with the water molecules of the subphase or which are trapped inside the mushroom-like structure. The red shift of the C-O-C band accompanied by the blue shift of the CH2 scissor band gives comparative information about the degree of hydration of the ethylene oxide groups for the different conformations

Langmuir and Gibbs Magnetite NP Layers at the Air Water Interface

The interfacial properties of Fe3O4@MEO2MA90-co-OEGMA10 NPs, recently developed and described as promising nanotools for biomedical applications, have been investigated at the air/water interface. These Fe3O4 NPs, capped with catechol-terminated random copolymer brushes of 2-(2-methoxyethoxy) ethyl methacrylate (MEO2MA) and oligo(ethylene glycol) methacrylate (OEGMA), with molar fractions of 90% and 10%, respectively, proved to be surface active. Surface tension measurements of aqueous dispersions of the NPs showed that the adsorption of the NPs at the air/water interface is time- and concentration-dependent. These NPs do not behave as classical amphiphiles. Once adsorbed at the air/water interface, they do not exchange with NPs in bulk, but they are trapped at the interface. This means that all NPs from the bulk adsorb to the interface until reaching maximum coverage of the interface, which corresponds to values between 6 × 10−4 and 8 × 10−4 mg/cm2 and a critical equilibrium surface tension of ∼47 mN/m. Moreover, Langmuir layers of Fe3O4@MEO2MA90-co-OEGMA10 NPs have been investigated by measuring surface pressure−area compression−expansion isotherms and in situ X-ray fluorescence spectra. The compression−expansion isotherms showed a plateau region above a critical surface pressure of ∼25 mN/m and a pronounced hysteresis. By using a special one-barrier Langmuir trough equipped with two surface pressure microbalances, we have shown that the NPs are squeezed out from the interface into the aqueous subphase, and they readsorb on the other side of the barrier. The results have been supported by TEM as well as AFM experiments of transferred Langmuir−Schaefer films on solid supports. This study shows the ability of Fe3O4@MEO2MA90-co-OEGMA10 NPs to transfer from hydrophilic media (an aqueous solution) to the hydrophobic/hydrophilic interface (air/water interface) and back to the hydrophilic media. This behavior is very promising, opening studies of their ability to cross biological membranes

Modelling of membrane and comparison to the experiment

International audiencePorous media in extraction and especially pertraction are often suspected to add unnecessary diffusive resistance and considerably slow down extraction kinetics. In the practical case of the separation of rare earth compounds from water into an organic phase, the use of specific ion binding ligands in high concentrations is required. These tend to form complex liquid crystalline phases preferentially at ion-rich locations inside a pertraction membrane. We will report on the modeling of the behavior of such fluids in the case of pertraction as well as in the case of a miniaturized pertraction device. We will show that diffusive and reactive solute transport can be accurately simulated without any free parameters. Overall, this work can be generalize as enabling the measurement of solute transfer rates at the liquid-liquid interface, a key parameter in pertraction and membrane separation which is difficult to measure using classic methods of extraction

Thermal spraying developements

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