Singular value decomposition-based gait characterization.

Background: Human gait varies based on personal characteristics, the existence of walking problems, or variability of gait parameters. Identifying the sources of variations is significant in detecting walking problems, designing orthotic/prosthetic products, etc. Research questions: What are the types of variations in joint angles and ground reaction forces? How do age, sex, height, weight, and walking speed affect the distribution of the modes? Methods: In this study, temporal variations in the joint angles and ground reaction forces were obtained using singular value decomposition. Then, the relationships among age, sex, height, weight, walking speed, and the coefficients obtained by singular value decomposition were investigated using Pearson's correlation coefficient matrix. Results: The first mode of joint angles and ground reaction forces represent the overall characteristics; the first six modes of joint angles and the first two modes of ground reaction forces express 99.9% of the gait parameter space. We concluded that the walking speed dramatically affects joint kinematics and ground reaction forces. In addition, the effects of age, gender, height, and weight on the joint kinematics and ground reaction forces were also found, but with less contribution. Significance: The temporal behavior of the joint angles and ground reaction forces was expressed using a few coefficients due to singular value decomposition. The effects of age, sex, weight, height, and walking speed on the modes were found. The proposed method can be applied to understand the progression of an abnormality, and design orthotic/prosthetic products etc. in future studies.

Detection of gait variations by using artificial neural networks.

Walking is an everyday activity and contains variations from person to person, from one step to another step. The variation may occur due to the uniqueness of each gait cycle, personal parameters, such as age, walking speed, etc., and the existence of a gait abnormality. Understanding the normal variation depending on personal parameters helps medical experts to identify deviations from normal gait and engineers to design compatible orthotic and prosthetic products. In the present study, we aimed to obtain normal gait variations based on age, sex, height, weight, and walking speed. For this purpose, a large dataset of walking trials was used to model normal walking. An artificial neural network-based gait characterization model is proposed to show the relation between personal parameters and gait parameters. The neural network model simulates normal walking by considering the effect of personal parameters. The predicted behavior of gait parameters by artificial neural network model has a similarity with existing literature. The differences between experimental data and the neural network model were calculated. To determine how much deviation between predictions and experiments can be considered excessive, the distributions of differences for each gait parameter were obtained. The phases of walking in which excessive differences were intensified were determined. It was revealed that the artificial neural network-based gait characterization model exhibits the behavior of the normal gait parameters depending on the personal parameters.

Magnetically Manipulable Ionic Liquid Crystals Incorporating Neutral Radicals.

Invited for this month's cover are the collaborating groups of Dr. Yoshiaki Uchida from Osaka University, Japan, Prof. Rui Tamura and Prof. Masahito Sugiyama from Kyoto University, Japan and Dr. Dmitrii G. Mazhukin from Novosibirsk State University, Russia. The cover picture depicts a contrast between localized spins and conductive ions in the newly-synthesized ionic liquid crystalline (ILC) nitroxide radicals. The ILC droplet of the new compounds is magnetically manipulable. More information can be found in the Full Paper by Yoshiaki Uchida, Rui Tamura, and co-workers.

Magnetically Manipulable Ionic Liquid Crystals Incorporating Neutral Radical Moiety.

With a view to fabricating a new remote input-output system by applying functional ionic liquid crystalline (ILC) materials, we have developed novel ILC compounds containing a nitroxide radical unit in the organic cations, which show an enantiotropic smectic A (SmA) phase. We have implemented the magnetic manipulation of a droplet of one of the ILC compounds on the basis of the intermolecular magnetic interactions between radical moieties. This ILC monoradical compound shows a 55 % larger increase in paramagnetic susceptibility at the solid-to-LC melting point in the first heating process than the non-ionic LC monoradical compounds. It is most likely owing to the nanosegregation of strongly bonded ionic and non-ionic moieties. The increased molar magnetic susceptibility is preserved not only in the SmA phase but also in the isotropic liquid and solid phases during the first cooling process.

Magnetic Mixed Micelles Composed of a Non-Ionic Surfactant and Nitroxide Radicals Containing a D-Glucosamine Unit: Preparation, Stability, and Biomedical Application.

Metal-free magnetic mixed micelles (mean diameter: < 20 nm) were prepared by mixing the biocompatible non-ionic surfactant Tween 80 and the non-toxic, hydrophobic pyrrolidine-N-oxyl radicals bearing a D-glucosamine unit in pH 7.4 phosphate-buffered saline (PBS). The time-course stability and in vitro magnetic resonance imaging (MRI) contrast ability of the mixed micelles was found to depend on the length of the alkyl chain in the nitroxide radicals. It was also confirmed that the mixed micelles exhibited no toxicity in vivo and in vitro and high stability in the presence of a large excess of ascorbic acid. The in vivo MRI experiment revealed that one of these mixed micelles showed much higher contrast enhancement in the proton longitudinal relaxation time (T1) weighted images than other magnetic mixed micelles that we have reported previously. Thus, the magnetic mixed micelles presented here are expected to serve as a promising contrast agent for theranostic nanomedicines, such as MRI-visible targeted drug delivery carriers.

Unique Superparamagnetic-like Behavior Observed in Non-π-delocalized Nitroxide Diradical Compounds Showing Discotic Liquid Crystalline Phase.

A unique superparamagnetic-like behavior and a large "positive magneto-LC effect" were observed in the solid phases and the hexagonal columnar (Colh ) liquid crystalline (LC) phase, respectively, of novel achiral non-π-delocalized nitroxide diradical compounds (R,S)-1, which showed polymorphism in the solid phases (solids I and II). The SQUID magnetization measurement revealed that (1) (R,S)-1 containing a small amount of racemic diastereomers (R*,R*)-1 possessed an unusual and large temperature-independent magnetic susceptibility (χTIM >0) component in the original nanocrystalline solid I that was responsible for the observed superparamagnetic-like behavior under low magnetic fields and did not arise from the contamination by extrinsic magnetic metal or metal ion impurities, besides ordinary temperature-dependent paramagnetic susceptibility (χpara >0) and temperature-independent diamagnetic susceptibility (χdia <0) components, (2) a large increase in molar magnetic susceptibility (χM ) (positive magneto-LC effect) that occurred at the solid I-to-liquid crystal transition upon heating was preserved as an additional χTIM increase in the resulting polymorphic nanocrystalline solid II by cooling, and (3) such unique magnetic phenomena were induced by thermal processing for (R,S)-1 or by adding a small amount of (R*,R*)-1 to (R,S)-1 as the impurity.

Preparation of Robust Metal-Free Magnetic Nanoemulsions Encapsulating Low-Molecular-Weight Nitroxide Radicals and Hydrophobic Drugs Directed Toward MRI-Visible Targeted Delivery.

With a view to developing a theranostic nanomedicine for targeted drug delivery systems visible by magnetic resonance (MR) imaging, robust metal-free magnetic nanoemulsions (mean particle size less than 20 nm) consisting of a biocompatible surfactant and hydrophobic, low molecular weight 2,2,5-trimethyl-5-(4-alkoxy)phenylpyrrolidine-N-oxyl radicals were prepared in pH 7.4 phosphate-buffered saline (PBS). The structure of the nanoemulsions was characterized by electron paramagnetic resonance spectroscopy, and dynamic light scattering and small-angle neutron-scattering measurements. The nanoemulsions showed high colloidal stability, low cytotoxicity, enough reduction resistance to excess ascorbic acid, and sufficient contrast enhancement in the proton longitudinal relaxation time (T1 ) weighted MR images in PBS in vitro (and preliminarily in vivo). Furthermore, the hydrophobic anticancer drug paclitaxel could be encapsulated inside the nanoparticles, and the resulting paclitaxel-loaded nanoemulsions were efficiently incorporated into HeLa cells to suppress cell growth.

Preparation, characterization and magnetic behavior of a spin-labelled physical hydrogel containing a chiral cyclic nitroxide radical unit fixed inside the gelator molecule.

An optically active amphiphilic nitroxide radical compound [(S,S,R)-], which contains a paramagnetic (2S,5S)-2,5-dimethyl-2,5-diphenylpyrrolidine-N-oxyl radical group fixed in the inner position together with a hydrophobic long alkyl chain and a hydrophilic (R)-alanine residue in the opposite terminal positions, was found to serve as a low-molecular-weight gelator in H2O to give rise to a spin-labelled physical hydrogel. Characterization of the hydrogel was performed by microscopic (SEM, TEM and AFM) techniques, XRD and SAXS measurements, and IR, UV and CD spectroscopies. The gel-sol transition temperature was determined by EPR spectral line-width (ΔHpp) analysis. Measurement of the temperature dependence of relative paramagnetic susceptibility (χrel) for the hydrogel and sol phases was achieved by means of the double-integration of VT-EPR spectra.

Anisotropic and inhomogeneous magnetic interactions observed in all-organic nitroxide radical liquid crystals.

An anisotropic and inhomogeneous magnetic interaction (the average spin-spin interaction constant (-)J > 0) was observed in the various liquid crystalline (LC) phases of racemic and nonracemic all-organic radical LC compounds 1a and 1b. We discussed how the LC superstructures induced the magnetic interaction to operate in the LC phases in terms of spin-spin dipole and exchange interactions by means of VT-EPR spectroscopy. The magnitude of the magnetic interaction depended on the type of LC phase, or the superstructure. Furthermore, these radical LC droplets floating on water were commonly attracted to a permanent magnet and moved freely under the influence of this magnet, whereas the crystallized particles of the same compounds never responded to the magnet. The response of the LC droplets to the magnet also varied depending on the type of LC phase, that is, the extent of the magnetic interaction.

Miscibility behavior of two-component monolayers at the air-water interface: perfluorocarboxylic acids and DMPE.

Surface pressure (pi)-molecular area (A) and surface potential (DeltaV)-A isotherms have been measured for two-component monolayers of four different perfluorocarboxylic acids [FCn; perfluorododecanoic acid (FC12), perfluorotetradecanoic acid (FC14), perfluorohexadecanoic acid (FC16), and perfluorooctadecanoic acid (FC18)] and dimyristoylphosphatidylethanolamine (DMPE) on 0.15M NaCl (pH 2) at 298.2K. The present study is focused on the miscibility and the interfacial behavior for the binary DMPE/FCn monolayers upon compression. From the isotherms, the miscibility has been elucidated in terms of the additivity rule, the interaction parameter, and the interaction energy. The interaction parameter (or energy) is compared with that for the previous dipalmitoylphosphatidylcholine (DPPC)/FCn systems [Colloids Surf. B 41 (2005) 285-298] to understand the effect of phospholipids' polar headgroup on the binary miscibility. Furthermore, the phase behavior of the DMPE/FCn systems has been morphologically examined using fluorescence microscopy (FM) and atomic force microscopy (AFM). These images reveal the different interaction modes among the four systems; DMPE can be miscible with FC12 and FC14 and immiscible with FC16 and FC18 in the monolayer state. These systematic examinations indicate that the miscibility of perfluorocarboxylic acids and phospholipids depends on combination of hydrocarbon and fluorocarbon chain lengths and on phospholipids' polar headgroups within a monolayer.

EPR studies on molecular orientation in a surface-stabilized paramagnetic liquid crystal cell.

By EPR spectroscopy, we have developed a new method for determining the molecular orientation in a surface-stabilized liquid crystal (LC) cell, which includes a paramagnetic LC, (2S,5S)-2,5-dimethyl-2-heptyloxyphenyl-5-[4-(4-octyloxybenzenecarbonyloxy)phenyl]pyrrolidine-1-oxy (1), whose spin source is fixed in the rigid core. For each phase of racemic [(+/-)] and enantiomerically enriched [(S,S)] 1 in a surface-stabilized LC cell (4 microm thickness), the observed g-value profiles depending on the angle between the applied magnetic field and the cell plane were successfully simulated by the orientation models: (i) the LC molecule in the nematic (N) phase of (+/-)-1 freely rotates around the long axis, which is always parallel to the rubbing direction; (ii) the long axis of the freely rotating LC molecule in the chiral nematic (N*) phase of (S,S)-1 is always parallel to the cell plane but rotates in the plane to form a helical superstructure; and (iii) in the crystalline phase of (S,S)-1, the molecular long axis forms a helical superstructure similar to that of the N* phase, but the molecule is fixed around the long axis so that the NO bond lies in the cell plane. Fitting the temperature profile of the g-value in the N phase of (+/-)-1 by use of the Haller equation, we determined the molecular g-values along the molecular long axis (g(parallelM)) and short axis (g(perpendicularM)), which were successfully reproduced by the use of the set of principal g-values of a similar nitroxide with consideration of the structure of the LC molecule optimized by Molecular Mechanics 3 (MM3).

Spontaneous racemization and epimerization behavior in solution of chiral nitroxides.

[reaction: see text] Enantiomerically enriched samples of chiral cyclic nitroxides with a 4-hydroxyphenyl group on the stereogenic center bearing the NO radical group undergo unprecedented spontaneous racemization and/or epimerization in aprotic solvents, which can be well accounted for by the multistep equilibrations involving planar quinoid intermediates.

Preparation and characterization of new chiral nitronyl nitroxides bearing a stereogenic center in the imidazolyl framework.

A synthetic procedure for optically active and racemic alpha-nitronyl nitroxides (alpha-NNs) having a stereogenic center at the 4-position of the imidazolyl ring is described. This procedure consists of (1) the synthesis of a dissymmetric vic-dinitro compound by Kornblum reaction, (2) the enantiomeric resolution of the racemate by a diastereomer method for obtaining the optically active sample, (3) the quick reduction of the optically active or racemic vic-dinitro compound to the bis(hydroxyamino) derivative with Al/Hg, (4) the solvent-free condensation of the bis(hydroxyamino) compound with an aldehyde to give the 1,3-dihydroxyimidazolidine, and (5) the final oxidation of the alpha-NN precursor with aqueous NaIO(4). The absolute configuration of the optically active alpha-NNs was assigned by correlating with the X-ray crystal structure of the (-)-(1S,4R)-camphanic acid ester derivative of the optically active vic-dinitro compound. The molecular conformation of the optically active alpha-NNs was found to be folded both in solution and in the solid state by CD spectroscopy and energy minimization with the Monte Carlo method. The magnetic properties of both optically active and racemic alpha-NNs in solution and in the solid state were characterized by EPR spectroscopy and magnetic susceptibility measurement, respectively.