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As global populations age, conditions such as stroke and diabetes require individuals to use rehabilitation technology for many years to come due to chronic musculoskeletal, sensory, and other physical impairments. One in four males currently aged 45 will experience a stroke within 40years and will often require access to prolonged rehabilitation. In addition, worldwide, one individual loses a limb every 30s due to the complications of diabetes. As a result, innovative ideas are required to devise more effective prosthetic and orthotic devices to enhance quality of life. While Nitinol has already found much favor within the biomedical industry, one area, which has not yet exploited its unique properties, is in the field of physical rehabilitation, ranging from prosthetic and orthotic devices to assistive technology such as wheelchairs. Improved intervention capabilities based on materials such as Nitinol have the potential to vastly improve patients’ quality of life and in the case of orthoses, may even reduce the severity of the condition over time. It is hoped that this study will spark discussion and interest for the materials community in a field which has yet to be fully exploited. Keywordsbiomaterials–material selection–modeling processes
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Nitinol for Prosthetic and Orthotic Applications
Emma Henderson and Arjan Buis
(Submitted April 21, 2010; in revised form January 27, 2011)
As global populations age, conditions such as stroke and diabetes require individuals to use rehabilitation
technology for many years to come due to chronic musculoskeletal, sensory, and other physical impair-
ments. One in four males currently aged 45 will experience a stroke within 40 years and will often require
access to prolonged rehabilitation. In addition, worldwide, one individual loses a limb every 30 s due to the
complications of diabetes. As a result, innovative ideas are required to devise more effective prosthetic and
orthotic devices to enhance quality of life. While Nitinol has already found much favor within the bio-
medical industry, one area, which has not yet exploited its unique properties, is in the field of physical
rehabilitation, ranging from prosthetic and orthotic devices to assistive technology such as wheelchairs.
Improved intervention capabilities based on materials such as Nitinol have the potential to vastly improve
patientsÕquality of life and in the case of orthoses, may even reduce the severity of the condition over time.
It is hoped that this study will spark discussion and interest for the materials community in a field which
has yet to be fully exploited.
Keywords biomaterials, material selection, modeling processes
1. Introduction
Nitinol has been widely utilized within the medical devices
industry in a variety of areas, from self expanding stents to
orthodontic archwires. The demonstrated biocompatibility of
the alloy, combined with its unique properties makes it an
obvious choice for many modern biomedical applications.
However, the area of prosthetics, orthotics, and rehabilitation
has remained largely untouched by the exploitation of this
material. A review of the literature has uncovered only a
handful of papers, 29 in total that discuss the utilization of a
material that has been successfully integrated into so many
other biomedical areas. The majority of papers identified
discuss the utilization of Nitinol actuators for upper limb, and in
particular hand and finger prostheses. Few focus on lower limbs
prosthetic and orthotic devices. This study is presented from a
multidisciplinary angle, combining experience from both an
engineering and prosthetics and orthotics point of view to
discuss the further exploitation of Nitinol within the biomedical
industry. A proof of concept project currently running at the
University of Strathclyde shall be cited as one example of such
2. The Field of Prosthetics and Orthotics
Global trends indicate that amputation levels are likely to
grow in years to come. This is not set to be matched by an
increase in the numbers of professionals trained and equipped
to deal with the challenges of prosthetic replacement. Without
new technological approaches, prosthetic restoration will
remain a custom, largely handcrafted technology that is in
relatively short supply. Increases in the numbers of dysvascular
amputees in general, the rate of amputation due to complica-
tions of diabetes in particular, and even the impact of landmines
in parts of the world, all are contributing to a gap between
social need for prostheses and our ability to supply.
Prostheses are interventions designed to replace a part of the
body that is absent, usually due to amputation or congenital
deformity. The focus of this discussion will be on limb
prosthesis, for replacement of upper and/or lower limbs, lost
due to illness, trauma, or congenital deformity. Orthoses are
specialized mechanical devices, designed to support (static) or
correct (dynamic) musculoskeletal deformities and/or abnor-
malities of the human body. The overall aim of orthotic
interventions is to restore function to a part of the body that is
not able to function properly.
A modern prosthesis is an engineering assembly with
components typically fashioned from a variety of materials and,
in some cases, with highly sophisticated embedded control
systems. Examples include micro-processor controlled stance
and swing phase management of prosthetic knee joints, and the
control and actuation of prosthetic hands. Prosthetic devices
can be separated into interface and structural components. It is
understood that the nature of the interface at the prosthetic
socket, between the prosthesis and the tissues of the amputeeÕs
residual limb, particularly in lower limb prostheses, is also a
critical factor for the overall success of the prosthesis.
Historically, prosthetic devices are static structures with
limited adaptability to the ever changing environment and
dynamic conditions. Current developments are mainly in the
field of componentry, for example, prosthetic feet with a high
This article is an invited paper selected from presentations at Shape
Memory and Superelastic Technologies 2010, held May 16-20, 2010,
in Pacific Grove, California, and has been expanded from the original
Emma Henderson and Arjan Buis, The National Centre for
Prosthetics and Orthotics, University of Strathclyde, Glasgow,
Scotland, UK. Contact e-mails: and
JMEPEG ÓASM International
DOI: 10.1007/s11665-011-9869-4 1059-9495/$19.00
Journal of Materials Engineering and Performance
energy return during gait and the utilization of carbon
composite-based structures. Reasonable progress has been
made in relation to actuation of joints. However, a distinction
between positional actuation, for example, the angle of an
elbow or the ground clearance of a prosthetic foot, and power
actuation used to deliver a torque for the purposes of active
assistive knee movement to enable sit-to-stand motion or stair
ascent are areas which remain underdeveloped. It may be
recognized that the requirements for achieving passive move-
ment utilizing Nitinol are less arduous than those for realizing
movement in conjunction with a usable force. This is the case
for prosthetics and orthotics alike. State of the art, motorized,
actuators are predominantly used in prostheses rather than
orthotic interventions. Examples for prosthetics include the
i-LIMB prosthetic hand from Touch Bionics (Ref 1) and the
Powerknee from O
¨ssur (Ref 2) (Fig. 1). Although motorized
actuators have proven their place within prosthetics they are
still seen as rather complex, noisy, and relatively heavy and as
such further development is required.
Contextual parallels between the engineering and the
historical aspects for prosthetics and orthotics can be drawn.
Although, there is a distinct difference between the purposes of
the interventions, both are engineering assemblies with com-
ponents fashioned from a diversity of materials to achieve the
desired behavioral characteristics. Additionally, both devices
can be separated in to an interface, where man meets machine,
and a structural component. It is understood that the nature of
the interface is a critical factor for the overall success of the
interventions; however, we will focus on the structural
components. From a historical perspective, strong similarities
are identifiable, especially the need for actuation or immobi-
lization (locking) of joints to assist in normal daily activities.
The only distinctive differences between orthoses and the
prostheses are the exercising and corrective capabilities
required in orthoses that are not required for prosthetic devices.
We ask the question, can those capabilities be generated by
both super elasticity and or shape memory properties of
3. Exploiting Nitinol
Several authors have investigated the use of Nitinol within
hand prosthesis and actuator devices, most recently OÕToole
et al. (Ref 3) in 2007 who investigate the use of shape memory
alloy wire bundles for the actuation of finger joints. The work
first quantifies the dynamic performance requirements of the
human hand, and goes on to test several bundles of shape
memory alloy wires for force and speed of actuation. The
article concludes that a bundle of 15, 150 lm diameter wires
will produce adequate force required for basic gripping actions.
Further study is directed at cooling the wire via an adaptive
control strategy and appropriate heat sinking in order to cool
the wire at similar rates to the heating, and the mechanical
framework for the device.
There have also been a small number of papers that
investigate alternative uses of the shape memory and super-
elastic properties in prosthetics and orthotics. Viscuso et al.
(Ref 4) utilize the superelasticity of Nitinol in an upper limb
orthosis for stroke patients. The device does not fully constrain
movement at the elbow. The wire was heat-treated and then two
straight wires of 2 mm diameter were used on each side of the
brace to provide a stable corrective force. The application of
constant load rather than deformation was made possible by the
utilization of Nitinol. In the small, 2 patient studies were
reported, very favorable results were found.
Pittaccio et al. (Ref 5) also investigate utilizing Nitinol for
stroke patients, concentrating on a shape memory activated
exerciser for the ankle in the early stages of poststroke care.
This device, when activated, applied dorsiflexion to the ankle
using electrical resistance before allowing the material to cool
by natural convection. The main challenge identified in this
study deals with lengthy cooling times.
Tarkesh and Elahinia (Ref 6) investigate the use of actuators
in ankle foot orthoses, focusing on those with drop foot. They
specifically discuss the requirements for controlling the com-
plex non-linear relationship between stress, martensite fraction,
and transformation temperature to adequately control the design
of shape memory alloy actuators, and advise the use of PID/
Sliding mode control for active ankle foot orthoses.
Finally, Xu et al. (Ref 7) compare using the superelastic
capabilities of Nitinol for bending overload protection in an
osseo-integrated trans-femoral prosthetic attachment system,
comparing Nitinol and steel components in a short finite
element study.
While these articles have explored avenues into the
utilization of Nitinol within the rehabilitation field, there are
still many areas ripe for exploration.
4. What is the National centre doing?
An ambitious multidisciplinary project is underway at the
University of Strathclyde to investigate the utilization of the
shape memory material properties of Nitinol to produce an
assistive device to complement current commercially available
knee joints and aid sit to stand motion and stair ascent for trans-
femoral amputees.
The two way shape memory properties of the material are
being investigated as a means to provide an additional force to
partially overcome the difficulty of the sit to stand motion. The
project, currently in its initial stages and funded by the UK
Ministry of DefenceÕs Science, Innovation and Technology
Department, aims to produce a concept design to help people
with trans-femoral amputations, including servicemen injured
by landmines or gunshot.
Fig. 1 (a) The i-LIMB prosthetic hand for Touch Bionics and (b)
The Powerknee from O
Journal of Materials Engineering and Performance
5. Conclusions
This discussion has shown that the prosthetics, orthotics, and
rehabilitation industry is ripe for twenty-first century technolog-
ical advancement. The very nature of prosthetic and orthotic
devices suggest that materials such as Nitinol hold much promise
to be employed, exploiting both their shape memory and
superelastic capabilities within the correct context. Work has
started to try and take advantage of these opportunities; however
there are still many opportunities to be realized within this field.
1. Touch Bionics, Livingston, UK
2. O
¨ssur hf, Reykjavick, Iceland
3. K.T. OÕToole, M.M. McGrath, and D.W. Hatchett, Transient Character-
isation and Analysis of Shape Memory Alloy Wire Bundles for the
Actuation of Finger Joints in Prosthesis Design, Mechanika, 2007, 6,
p 65–68
4. S. Viscuso, S. Pittaccio, M. Caimmi, G. Gasperini, S. Pironvano, E.
Villa, S. Besseghini, and F. Molteni, Pseudoelastic Nitinol-Based Device
for Relaxation of Spastic Elbow in Stroke Patients, J. Mater. Eng.
Perform., 2009, 18(5–6), p 805–813
5. S. Pittaccio, S. Viscuso, M. Rossini, L. Magoni, S. Pirovano, E. Villa, S.
Besseghini, and F. Molteni, SHADE: A Shape-Memory-Activated
Device Promoting Ankle Dorsiflexion, J. Mater. Eng. Perform., 2009,
18(5–6), p 824–830
6. E. Tarkesh and M. Elahinia, Nonlinear Control Techniques for a SMA
Active Ankle Foot Orthosis, ASME International Mechanical Engineer-
ing Congress and Exposition, 2007, Vol. 10 Part. A (November 11-15,
2007), pp. 397–403
7. W. Xu, F. Shao, and S. Hughes, A Shape Memory Alloy Overload
Protection Device for Osseointegrated Trans-Femoral Implant Prosthetic
Limb Attachment System, Smart Materials II, 2002, 4934(16–18),
p 234–241
Journal of Materials Engineering and Performance
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Spasticity is an important factor limiting independency and activity of daily living for post-stroke patients. Our aim was to develop a cost effective, customized, lightweight active orthosis, which is convenient for daily home use. The study describes the steps of the development by using cutting edge technologies, as 3D printing for the frame of the device and nitinol smart memory alloy as the active part of the orthosis. Polyamide and thermoplastic polyurethane materials were characterized in terms of mechanical behaviour in different ambient conditions. To access the feasibility of the orthosis 6 voluntary post-stroke patients were asked to test the functionality with manual function test, daily living functionality tests and Likert scale. Movement analysis was used to evaluate the range of movement in the orthosis. The results showed significantly higher functionality by using the orthosis on manual function test, most of the daily functional tests, also the overall personal impressions accessed by Likert scale were positive. The new anti-spastic orthosis is a smart, active, lightweight, personalized device, which seems to be effective help for post-stroke patients to overcome spasticity. According to the initial data it is suitable for home use, therefore offers a convenient solution for advanced rehabilitation.
... Nickel titanium SMAs, popularly known as nitinol, have wide applications in various industries such as min actuators, micromechanical systems, automation and control, aerospace robotics, heating and ventilation, and biomedicine owing to their desirable properties such as high corrosion and wear resistance, mechanical simplicity and compactness, and maximal recoverable strain [1,[3][4][5]. However, nitinol SMAs are popular for biomedical applications because of their higher shape-memory strain, good biocompatibility, and the prevention of chemicallyinduced illnesses [3,[6][7][8][9]. With the application of heat, they regain their shape and size. ...
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Shape-memory alloys such as nitinol are gaining popularity as advanced materials in the aerospace, medical, and automobile sectors. However, nitinol is a difficult-to-cut material because of its versatile specific properties such as the shape-memory effect, superelasticity, high specific strength, high wear and corrosion resistance, and severe strain hardening. Anunconventional machining process like wire-electrical-discharge-machining (WEDM) can be effectively and efficiently used for the machining of such alloys,although the WEDM-induced surface integrity of nitinol hassignificant impact on material performance. Therefore, this work investigated the surface integrity of WEDM-processed nitinol samples using digital microscopy imaging, scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) analysis. Three-dimensional analysis of the surfaces was carried out in two different patterns (along the periphery and the vertical plane of the machined surface) andrevealed that surface roughness was maximalat the point where the surface was largely exposed to the WEDM dielectric fluid. To attain the desired surface roughness, appropriate discharge energy is required that,in turn, requires the appropriate parameter settings of the WEDM process. Different SEM image analyses showed a reduction in microcracks and pores,and in globule-density size at optimized parameters. EDX analysis revealed the absence of wire material on the machined surface.
... Several combinations of SMAs were developed, including NiTi alloys discovered by Buehler et al. [2]. NiTi alloys are commonly referred to as nitinol in honor of its discovery at the Naval Ordnance Laboratory (NOL) [3] and are ideal materials for biomedical applications due to their pseudoelasticity and biocompatibility [3][4][5]. In addition, the NiTi alloy has applications in sensors, air conditioning vents, actuators, and structural elements [6,7]. ...
Machining of shape memory alloys (SMAs) without losing the shape memory effect could immensely extend their applications. Herein, the wire electric discharge machining process was used to machine NiTi—a shape memory alloy. The experimental methodology was designed using a Box-Behnken design approach of the response surface methodology. The effects of input variables including pulse on time, pulse off time, and current were investigated on the material removal rate, surface roughness, and microhardness. ANOVA tests were performed to check the robustness of the generated empirical models. Optimization of the process parameters was performed using a newly formulated, highly efficient heat transfer search algorithm. Validation tests were conducted and extended for analyzing the retention of the shape memory effect of the machined surface by differential scanning calorimetry. In addition, 2D and 3D Pareto curves were generated that indicated the trade-offs between the selected output variables during the simultaneous output variables using the multi-objective heat transfer search algorithm. The optimization route yielded encouraging results. Single objective optimization yielded a maximum material removal rate of 1.49 mm³/s, maximum microhardness 462.52 HVN, and minimum surface roughness 0.11 µm. The Pareto curves showed conflicting effects during the wire electric discharge machining of the shape memory alloy and presented a set of optimal non-dominant solutions. The shape memory alloy machined using the optimized process parameters even indicated a shape memory effect similar to that of the starting base material.
... One of the shape memory alloys which possesses superelasticity and biocompatibility is nickel-titanium alloy. Nickel-titanium alloys are also commonly referred to as nitinol in honour of its discovery at the Naval Ordnance Laboratory (NOL) and are a preferred material specifically for biomedical applications due to their high corrosion and wear resistance, pseudoelasticity and biocompatibility [1][2][3]. Shape-memory alloys (SMAs) when heated above the transition temperature recover their previous deformed shape. ...
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Nitinol, a shape-memory alloy (SMA), is gaining popularity for use in various applications. Machining of these SMAs poses a challenge during conventional machining. Henceforth, in the current study, the wire-electric discharge process has been attempted to machine nickel-titanium (Ni55.8Ti) super-elastic SMA. Furthermore, to render the process viable for industry, a systematic approach comprising response surface methodology (RSM) and a heat-transfer search (HTS) algorithm has been strategized for optimization of process parameters. Pulse-on time, pulse-off time and current were considered as input process parameters, whereas material removal rate (MRR), surface roughness, and micro-hardness were considered as output responses. Residual plots were generated to check the robustness of analysis of variance (ANOVA) results and generated mathematical models. A multi-objective HTS algorithm was executed for generating 2-D and 3-D Pareto optimal points indicating the non-dominant feasible solutions. The proposed combined approach proved to be highly effective in predicting and optimizing the wire electrical discharge machining (WEDM) process parameters. Validation trials were carried out and the error between measured and predicted values was negligible. To ensure the existence of a shape-memory effect even after machining, a differential scanning calorimetry (DSC) test was carried out. The optimized parameters were found to machine the alloy appropriately with the intact shape memory effect.
... The element composition of medical Ni-Ti alloys generally suggests a minimal difference between nickel and titanium contents and the presence of only trace impurities. Ni-Ti alloy has been used in biomedicine given its good shape-memory property, superelasticity, and excellent corrosion resistance [1][2][3]. It is also an ideal material for vascular stents considering its excellent in-body deformation and high strength. ...
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Nickel–titanium (Ni-Ti) alloy has been selected as stent material given its good biocompatibility. In this study, experimental research on this material was conducted using magnetic field-assisted electrical discharge machining (EDM). The surface topography of the machined workpiece was analyzed with a scanning electron microscope (SEM). Hydrophobicity was measured by using an optical contact angle measuring instrument. The roughness values of different positions on the surface were measured using a TR200 roughness instrument. Results showed that the composite structure of solidification bulge–crater–pore–particle can be prepared on the surface of the Ni-Ti alloy through magnetic mixed EDM using suitable processing parameters. Moreover, the contact angle of the surface reaches 138.2°.
... However, the study [32] reports that at temperatures equal to the human body the formation of a passive layer on NiTi is not as much protective than the passive layer on Ti6Al4V. Additionally, there are some limitations too in the widespread use of such alloy because even if some studies have revealed that NiTi alloy is biocompatible [31,33,34], the possible release of Ni ions represents a serious apprehension [13,15] because Ni is highly allergenic element, and it can induce intense inflammatory reactions. ...
... The most relevant experiences address biomedical problems, such as the mobilization of paralyzed hands, fingers (e.g., [7][8][9]) and other segments [10], the support of gait (e.g., [11][12][13][14][15]) and limb repositioning [16]. The corpus of published literature highlights the promising aspects of SMA technology [17] and also describes the limitations connected with those materials. Considering the designs based on the shape memory effect, most papers mention the compactness and the possibility to develop flexible technologies as valuable aspects of SMA actuation, while the trade-off between torque or force output and actuation speed appears to be the main issue in rehabilitation applications. ...
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Shape memory alloys (SMAs) are a very promising class of metallic materials that display interesting nonlinear properties, such as pseudoelasticity (PE), shape memory effect (SME) and damping capacity, due to high mechanical hysteresis and internal friction. Our group has applied SMA in the field of neuromuscular rehabilitation, designing some new devices based on the mentioned SMA properties: in particular, a new type of orthosis for spastic limb repositioning, which allows residual voluntary movement of the impaired limb and has no predetermined final target position, but follows and supports muscular elongation in a dynamic and compliant way. Considering patients in the sub-acute phase after a neurological lesion, and possibly bedridden, the paper presents a mobiliser for the ankle joint, which is designed exploiting the SME to provide passive exercise to the paretic lower limb. Two different SMA-based applications in the field of neuroscience are then presented, a guide and a limb mobiliser specially designed to be compatible with diagnostic instrumentations that impose rigid constraints in terms of electromagnetic compatibility and noise distortion. Finally, the paper discusses possible uses of these materials in the treatment of movement disorders, such as dystonia or hyperkinesia, where their dynamic characteristics can be advantageous.
The present experimental work was carried out on wire electrical discharge machine (WEDM) over NiTi shape memory alloy for biomedical applications. Improving of machineability of intricate profiles in biomaterial applications is a challenging task. The experiments were performed on WEDM by using a brass wire of 0.25 mm diameter, as tool electrode. A range of 4 to 8 ampere of current, range of 60-120 µs of pulse on time, range of 15-45 µs of pulse off time, range of 11-15 cm2/gm of wire tension and range of 4-8 m/min wire feed were selected as input parameters. The influence of these parameters was observed on surface roughness and kerf width during fabrication of rectangular slots. The discharge craters, voids, microcracks and white layer have been observed in machined surface by scanning electron microscopy (SEM). It was observed that at higher values of discharge energy, the recast layer thickness increases. The higher recast layer found is 15.88 at Ip = 8, Ton = 120, Toff = 30, WT = 11, Wf = 4. The performance of responses was analysed by the response surface methodology and artificial neural network modelling. The obtained values of 0.993 and 0.995 from ANN model shows strong correlation between selected parameters. The obtained desirability is 0.957 that presents the developed model and is quite significant for both responses.
Full-text available
Nitinol is widely used shape memory alloy (SMA) in manufacturing medical devices, actuators, mechanical couplings, etc. However, mechanical cutting of Nitinol is exceedingly difficult to machine. Machining induced surface integrity of SMA has significant impacts on device performance. In this study, Nitinol was machined by wire electric discharge machining (Wire-EDM) in both CH-oil and deionized water (DI-water). Surface characteristic evolution was examined from main cut (MC), first trim cut (TC), to finish trim cut (FC) and compared with the traditional mechanical cutting.
Full-text available
Most current lower arm/hand prosthesis designs incorporate relatively bulky, heavy de motors that produce substantial noise when performing actuation which renders them uncomfortable for the end-user. The engineering challenge is to produce more effective powered upper limb prosthetic solutions. Identification, characterisation and testing of actuation methods with better force to weight ratios are essential pre-requisites for this. The main aim of this work is to carry out a comprehensive study to establish conclusively the feasibility of employing Shape Memory Alloys (SMA's) in the actuation of prosthetic finger designs. A comprehensive review of existing literature has been undertaken in order to establish the maximum grip forces at each phalanx of the human hand under different loading conditions. An experiment was developed in conjunction with this review to estimate the time response of the hand during a gripping/releasing action. These results, in combination with physical dimensions, will be used to drive the design of a prosthetic limb. A test rig has been developed which can facilitate complete transient and steady-state characterisation of a range of SMA wire diameters and bundle configurations. A number of different configurations were tested, each configuration having a different combination of 150 μm and 300 μm diameter nitinol wires. A data acquisition system was used to capture and retain data pertaining to the full characterisation of the bundles and in particular the strain and force capabilities of the various arrangements. A direct comparison is made between the actuator capabilities and the requirements of a working limb for basic gripping actions. This work will contribute to the development of an improved powered prosthetic solution.
Conference Paper
Acute post-stroke rehabilitation protocols include passive mobilisation as a means to prevent contractures. Frequent and continual exercise can be impractical, due to clinical task scheduling and logistics. A device (SHADE) that provides repetitive passive motion to a flaccid ankle by using shape memory alloy actuators could be of great help in addressing this problem. To comply with the large displacements and forces required by the work-out range of motion, a suitable actuator was designed as a cartridge of approximately 150mmx20mmx15mm, containing 2.5m of 0.25mm-diameter NiTi wire. During tests, this actuator was activated by Joule’s effect employing a 7s current input at 0.7A. This provided 10N through 76mm displacement. Cooling and reset by natural convection took 30s. A prototype of SHADE was assembled with two thermoplastic shells hinged together at the ankle and strapped on the frontal aspect of the shin and on the foot. Two actuators were fixed on the upper shell while an inextensible thread connected each NiTi wire to the foot shell. A dedicated software switched on and off a 30Vdc-generator providing sufficient power to get shape recovery in 7s. Martensite detwinning, caused by foot weight, occurred in 30s. The passive ankle motion (PROM) generated by SHADE was evaluated optoelectronically on three flaccid patients (58±5y/o); acceptability was assessed by a questionnaire presented to further three flaccid patients (44±11.5y/o) who used SHADE for 1 week, 30min a day. SHADE was well accepted by all patients, produced good PROM and caused no pain. Actuator displacement self-adapted to account for patients’ changing ankle rigidity. The rate of dorsiflexion was comparable with self-imposed movement in patient with residual active control, while the slow plantarflexion speed (driven by wire cooling) ensured muscle stretching for around 70% of the cycle. The results prove that suitable limb mobilisation can be produced by SMA actuators.
Conference Paper
This paper is aimed toward the development and evaluation of a novel active ankle foot orthosis (AAFO) based on shape memory alloy (SMA) actuators. This device intends to fill the gap in the existing research aimed at helping patients with drop foot muscle deficiencies as well as rehabilitation activities. To check the feasibility of this idea, a brief study is done on the dynamic behavior of ankle joint and then an SMA manipulator with a similar biological concept is used for experiment. Nonlinear behavior of SMA wires requires nonlinear control techniques such as Sliding Mode Controller (SMC) for tracking the desired ankle angle. Simulation results of three different techniques are compared (PID, SMC and SMC-PID) and finally the experimental result of a SMC-PID switching control is provided. This results shows that a switching control between simple PID and Sliding Mode Control can be a good alternative to follow the desired trajectory in slow walking cycles.
The osseointegrated trans-femoral implant system provides a direct anchoring technique to attach prosthetic limb. This technique was first introduced PI Brenmark in Sweden. The UK had the first clinical trial in 1997 and currently has 6 active limb wearers. The success of this procedure has the potential for improved gait function and mobility, increased employability and significant long-term improvements in the quality of life for above knee amputees. However, the significant load involved in the trans-femoral implant system has caused permanent deformation and/or fractures of the implant abutment in several occasions. To protect the implant system, the implant abutment in particularly, an overloading protection device was introduced. The device uses mechanical mechanism to release torsion overload on the abutment. However, the bending overload protection remains unsolved. To solve the problem, a new overload protection device was developed. This device uses SMA component for bending overload protection. In this paper, the results of non-linear finite element modelling of the SMA and steel (AISI 1040) components were presented. Experiments were also carried out using steel components to assess the design which is based on the non-linear property of the materials.
A compliant brace (EDGES) promoting spastic elbow relaxation was designed to investigate the potentialities of pseudoelastic NiTi in orthotics. By exploiting its peculiar characteristics, EDGES could improve elbow posture without constraining movements and thus avoiding any pain to the patient. A commercial Ni50.7-Ti49.3 alloy heat treated at 400°C 1h+WQ was selected for this application. A prototype of EDGES was assembled with two thermoplastic shells connected by polycentric hinges. Four 2-mm-diameter NiTi bars were encastred in the upper-arm shell and let slide along tubular fixtures on the forearm. Specially designed bending tests demonstrated suitable moment-angle characteristics. Two post-stroke subjects (aged 62 and 64, mild elbow flexors spasticity) wore EDGES for 1 week, at least 10h a day. No additional treatment was applied during this period or the following week. A great improvement (20°±5°) of the resting position was observed in both patients as early as 3h after starting the treatment. Acceptability was very good. A slight decrease in spasticity was also observed in both subjects. All the effects disappeared 1week after discontinuation. EDGES appears to be a good alternative to traditional orthoses in terms of acceptability and effectiveness in improving posture, especially whenever short-term splinting is planned.
SHADE: A Shape-Memory-Activated Device Promoting Ankle Dorsiflexion
  • S Pittaccio
  • S Viscuso
  • M Rossini
  • L Magoni
  • S Pirovano
  • E Villa
  • S Besseghini
  • F Molteni
S. Pittaccio, S. Viscuso, M. Rossini, L. Magoni, S. Pirovano, E. Villa, S. Besseghini, and F. Molteni, SHADE: A Shape-Memory-Activated Device Promoting Ankle Dorsiflexion, J. Mater. Eng. Perform., 2009, 18(5-6), p 824-830