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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
exploitation.
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
presentation.
Emma Henderson and Arjan Buis, The National Centre for
Prosthetics and Orthotics, University of Strathclyde, Glasgow,
Scotland, UK. Contact e-mails: emma.m.henderson@strath.ac.uk and
arjan.buis@strath.ac.uk.
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
Nitinol?
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
¨ssur
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.
References
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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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.
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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