Use of Friction Stir Processing and Friction Stir Welding For Nitinol Medical Devices

Metallic materials may be joined utilizing a friction stir processing technique. The friction stir processing technique utilizes a shaped, rotating tool to move material from one side of the joint to be welded to the other without liquefying the base material

Visual cue training to improve walking and turning after stroke:a study protocol for a multi-centre, single blind randomised pilot trial

Visual information comprises one of the most salient sources of information used to control walking and the dependence on vision to maintain dynamic stability increases following a stroke. We hypothesize, therefore, that rehabilitation efforts incorporating visual cues may be effective in triggering recovery and adaptability of gait following stroke. This feasibility trial aims to estimate probable recruitment rate, effect size, treatment adherence and response to gait training with visual cues in contrast to conventional overground walking practice following stroke.Methods/design: A 3-arm, parallel group, multi-centre, single blind, randomised control feasibility trial will compare overground visual cue training (O-VCT), treadmill visual cue training (T-VCT), and usual care (UC). Participants (n = 60) will be randomly assigned to one of three treatments by a central randomisation centre using computer generated tables to allocate treatment groups. The research assessor will remain blind to allocation. Treatment, delivered by physiotherapists, will be twice weekly for 8 weeks at participating outpatient hospital sites for the O-VCT or UC and in a University setting for T-VCT participants.Individuals with gait impairment due to stroke, with restricted community ambulation (gait spee

Effects of Hydrogen on the Phases and Transition Temperatures of NiTi

Austenitic (B2) NiTi samples were cathodically charged with various amounts of hydrogen. Trends are tracked based on temperature, time and voltage throughout the process to establish consistent and predictive hydrogen charging procedures. The effect of hydrogen on the austenitic structure and the formation of hydrides are studied with x-ray diffraction (XRD). An increase in the austenite lattice parameter with increased hydrogen content is observed up to a hydrogen solubility limit of approximately 85 wppm. At greater hydrogen concentrations, additional XRD peaks appear, suggesting possible hydride formation. Differential scanning calorimetry (DSC) results show a decrease in both the austenitic and martensitic transition temperatures with increased atomic hydrogen content and increased hydride phase. Scanning electron microscopy (SEM) is used to reveal the hydride phase. The effect of atomic hydrogen on NiTi and the structure of the hydride phase are compared with previous hydrogen studies

Unique deformation mechanisms of an ultra-high strength NiTiHf alloy

Ultra-high strength and energy storage has been observed of a nickel-rich (54-at. %), hafnium-lean (1-at. %), balance titanium alloy. Specifically, full recovery of 4.5% strain upon release of 2.3 GPa uniaxial stress is realized during compressive loading. Furthermore, in cyclic loading, accumulation of permanent set is not observed after the first cycle. Robustness to permanent set is attributed to precipitation of a relatively high volume fraction of fine Ni4Ti3 precipitates, which is the expected result. It was also anticipated that the ability to recover large strains would arise from superelasticity via martensitic transformation. However, in-situ diffraction experimentation revealed a different result. Martensitic (or any other) phase transformation was not observed. Instead, line profile analysis of the diffraction patterns shows the formation of ~25 nm subdomains of B2 structure within the ~5 µm parent grains, accompanied by heterogeneous deformation among similarly orientated diffracting domains. The subdomains fully revert upon unload. In this presentation, the in-situ diffraction characterization of this phenomenal deformation mechanism will be reviewed and conclusions will be supported with in-situ electron microscopy and macroscopic characterization data

Informant discrepancies in assessing child dysfunction relate to dysfunction within mother-child interactions.

We examined whether mother-child discrepancies in perceived child behavior problems relate to dysfunctional interactions between mother and child and stress in the mother. Participants included 239 children (6–16 years old; 58 girls, 181 boys) referred for oppositional, aggressive, and antisocial behavior, and their mothers. Mother-child discrepancies in perceived child behavior problems were related to mother-child conflict. Moreover, maternal stress mediated this relationship. The findings suggest that discrepancies among mother and child evaluations of child functioning are not merely reflections of different perspectives or artifacts of the assessment process, but can form components of conceptual models that can be developed and tested to examine the interrelations among critical domains of child, parent, and family functioning.This work was supported, in part, by a grant from the National Institute of Mental Health (MH67540) awarded to the first author and by grants from the Leon Lowenstein Foundation, the William T. Grant Foundation (98-1872-98), and the National Institute of Mental Health (MH59029) awarded to the second author

Differential effects of parietal and cerebellar stroke in response to object location perturbation

Background: The differential contributions of the cerebellum and parietal lobe to coordination between hand transport and hand shaping to an object have not been clearly identified. Objective: To contrast impairments in reach-to-grasp coordination, in response to object location perturbation, in patients with right parietal and cerebellar lesions, in order to further elucidate the role of each area in reach-to-grasp coordination. Method: A two-factor design with one between subject factor (right parietal stroke; cerebellar stroke; controls) and one within subject factor (presence or absence of object location perturbation) examined correction processes used to maintain coordination between transport-to-grasp in the presence of perturbation. Sixteen chronic stroke participants (eight with right parietal lesions and eight with cerebellar lesions) were matched in age (mean = 61 years; standard deviation = 12) and hand dominance with 16 healthy controls. Hand and arm movements were recorded during unperturbed baseline trials (10) and unpredictable trials (60) in which the target was displaced to the left (10) or right (10) or remained fixed (40). Results: Cerebellar patients had a slowed response to perturbation with anticipatory hand opening, an increased number of aperture peaks and disruption to temporal coordination, and greater variability. Parietal participants also exhibited slowed movements, with increased number of aperture peaks, but in addition, increased the number of velocity peaks and had a longer wrist path trajectory due to difficulties planning the new transport goal and thus relying more on feedback control. Conclusion: Patients with parietal or cerebellar lesions showed some similar and some contrasting deficits. The cerebellum was more dominant in controlling temporal coupling between transport and grasp components, and the parietal area was more concerned with using sensation to relate arm and hand state to target position

Structural and Diffusional Effects of Hydrogen in TiNi

Hydrogen can be inadvertently added to Nitinol medical devices through electropolishing, caustic cleaning, or exposure to other acidic or basic solutions. Moderately high hydrogen concentrations can lead to embrittlement characterized by lowered ductility and changes in transformation behavior. The purpose of the present report is to discuss recent results on the effects of hydrogen in annealed TiNi. Samples are charged with hydrogen and analyzed with x-ray diffraction; these data indicate that even relatively small amounts of hydrogen can affect the crystal structure. Additions of up to 1000 wppm hydrogen increase the atomic volume by more than 2%, decrease peak intensity and broaden peak width. These observations are consistent with hydrogen-induced lattice strain. Peak splitting and additional diffraction peaks are observed with the absorption of 6000 wppm hydrogen, which indicates formation of a new phase. It is speculated that the new phase may be based on the B2 structure or may be stress-induced R-phase or martensite. This paper also discusses experiments and analysis on the removal of hydrogen from TiNi wire with 800 wppm through heat treatments at 400-800°C for 30-3000 seconds. Extensive experimental and analytical computations show that the activation energy of hydrogen diffusion under these conditions is approximately 125 kJ/mol

Hemiparetic Stepping to the Beat:Asymmetric Response to Metronome Phase Shift During Treadmill Gait

Background: Walking in time with a metronome is associated with improved spatiotemporal parameters in hemiparetic gait; however, the mechanism linking auditory and motor systems is poorly understood. Objective: Hemiparetic cadence control with metronome synchronization was examined to determine specific influences of metronome timing on treadmill walking. Methods: A within-participant experiment examined correction processes used to maintain heel strike synchrony with the beat by applying perturbations to the timing of a metronome. Eight chronic hemiparetic participants (mean age = 70 years; standard deviation = 12) were required to synchronize heel strikes with metronome pulses set according to each individualg's comfortable speed (mean 0.4 m/s). During five 100-pulse trials, a fixed-phase baseline was followed by 4 unpredictable metronome phase shifts (20% of the interpulse interval), which amounted to 10 phase shifts on each foot. Infrared cameras recorded the motion of bilateral heel markers at 120 Hz. Relative asynchrony between heel strike responses and metronome pulses was used to index compensation for metronome phase shifts. Results: Participants demonstrated compensation for phase shifts with convergence back to preg-phase shift asynchrony. This was significantly slower when the error occurred on the nonparetic side (requiring initial correction with the paretic limb) compared with when the error occurred on the paretic side (requiring initial nonparetic correction). Conclusions: Although phase correction of gait is slowed when the phase shift is delivered to the nonparetic side compared with the paretic side, phase correction is still present. This may underlie the utility of rhythmic auditory cueing in hemiparetic gait rehabilitation