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Its its amazing to have this movement, just gets me more excited about now, about the future
says Iraq war veteran Sergeant Juan Arredondo. One of the first recipients of the bionic hand
with movements controlled by the brain (i-LIMB), he compares the innovation to the bionics in the
films Star Wars and Terminator, what with its ability to deal with moving and stationary objects
with comparable ease. These smart prosthetics have become a divine intervention for numerous
victims of amputation, and plastics has enabled these devices in becoming a feasible option for the
common man. Sundeep Nadkarni discovers that for giving a new lease of life to people who have
lost hope without a limb, the word is not only prosthetics but also plastics. Read on
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April 2009 Modern Plastics & Polymers 43
in an excerpt from his book
Wings of Fire, the ace scientist
and past President of India
Dr APJ Abdul Kalam, quotes
the following incident as one of the
four milestones of his illustrious
career. In his own words, One day anorthopaedic surgeon from the Nizam
Institute of Medical Sciences visited my
laboratory. He lifted the material and
found it so light that he took me to his
hospital and showed me his patients.
There were these little girls and boys
with heavy metallic calipers weighing
over 3 kg each, dragging their feet
around. He asked me to remove the
pain of his patients. In three weeks,
we made these floor reaction orthosis
300 gm calipers and took them to theorthopaedic centre. The children did
not believe their eyes. From dragging
around a 3 kg load on their legs, they
could now move around! Their parents
had tears in their eyes. That was my
fourth bliss!
Plastics redefine prostheticsThis dream of not needing to carry
the burden of 3 kg metal prosthetics was
realised with the use of plastics. Polymeric
applications have redefined flexibilities
in prosthetic movements. Material
manufacturers are on an innovation spree,
due to the supreme heights reached
by the prosthetics industry in enabling
unimaginable limb replacements.
A number of companies and
research laboratories have successfully
employed degradable & non-
degradable structure-controlled,
dendritic macromolecules to
function as a scaffold to support
in-growth of human tissue culture
cells like osteocytes, chondrocytes, or
hepatocytes. This holds promise for
the eventual development of artificial
human organs without the need for
harvesting cadaver or living donor
organs, mentions Miguel Linares,
director - Medical Engineering and
Design, Linares Medical Devices.
The company is developing a large
number of plastic-metal, plastic-
ceramic, and plastic-mineral alloy
compounds to improve upon the
materials currently used for medical
applications. Our proprietary materials
are being blended to optimise their
functional lifespan, with an emphasis
on durability. The high fidelity imitationof nature is a perfect example of the
superiority of plastics over metals for
orthopaedic applications, Linares adds.
The company specialises in the
development of polymers for the
prosthetic & orthopaedic market,
and presently has over 50 patents
emphasising the use of plastics in
these applications.
Plastics and polymers are widely
used in the fabrication of prosthetics
or artificial limbs and orthotic
supports. The technique of moulding
a lightweight, load-bearing artificial
limb comprises the steps providing
a number of carbon-fibre sheets.
The prosthetic limb socket can be
designed by taking a negative cast
and then moulding a positive cast of a
patients residual limb, known as stump.
Thermoplastics are moulded over the
positive cast to form a socket, which is
worn over the stump. Another method
of fabricating a socket is the lamination
process in which a blend of resins,
accelerators and catalysts have wide
applications.
The socket fabrication is a
significant aspect because the entire
fitment of the artificial limb depends
on how the socket has been fabricated.
For giving the artificial limb a cosmetic
appearance, it is necessary to provide
it with a covering of polyurethane
foam that is shaped to give a natural
appearance similar to a real limb.
Polyethylene foam is also widely
used as it is suitable for skin contact,
does not absorb perspiration, does
not support the growth of micro-
organisms, is tough with a soft-feel,odourless and has increased resilience.
The combination of being lightweight
and having excellent shock dissipation
makes it a good padding material for
body protection between the rigid
plastics and the skin. These are easy-
to-fabricate, economical and improve
the performance of the prosthetic &
Miguel Linaresdirector - Medical Engineering and Design, Linares Medical Devices
Blending plastics with ceramics or metals at
the molecular level allows the best properties
of both substances to be retained. Novel
plastics have been developed resulting in
materials with lightweight and elasticity,
combined with strength and durability.
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orthotic devices, states Dr V J S Vohra,
co-founder and director, Nevedac
Prosthetic Centre. Dr Vohra is also
the honorary prosthetic advisor to
Governments of Punjab, Haryana,
Chandigarh, and Himachal Pradesh.
Biocompatible and mechanicalproperties
Plastics score more than any
conventional materials in terms
of performance, economics and
compatibility. The favourable
characteristics of plastics in healthcare
include flexibility, ductility, toughness
and lightweightedness. These materials
are inert, non-toxic and biocompatible,
and hence can come in contact with
blood, tissue, etc. Transparency of
the materials is vital to monitor flow
through the tube visually as well as
electronically. Flexibility in design,
forming & jointing, ease-of-sterilisation,
and low costs are other features
that work in favour of polymers in
prosthetic devices.
A range of screws and pins made
from re-absorbable polymers has
been recently launched to replace
metal screws and pins in orthopaedic
& trauma applications in order to
avoid the traditional requirement for
explantation. A device based on the
development of a monobloc polymer
material is under development. Actinglike a shock absorber, this material has
a flexible central part and rigid, upper
& lower outer parts. The product a
prosthesis for inter-vertebral discs is
manufactured from biocompatible
polymers and has greater compression
and torsional-tensile strength.
Currently, using the results of a similar
technology, intra-ocular lenses are also
being produced, states D L Pandya,
CEO, Medical Plastics Data Service.
Material selection is driven by
performance potential and ease of
processing. With a broad range of
medical-grade resins available, there are
greater possibilities for medical OEMs to
choose from. OEMs must apply the right
material to a device design to enhance
human interaction while reducing the
development cycle and minimising
scrap or production interruptions.
Test data helps confirm the
attributes necessary to deliver the
appropriate level of design flexibility,
strength, clarity, and chemical
resistance, which are key attributes
for devices with maximum integrity.
Comparing data makes materialselection simpler. Material properties
are also matched to application
performance, secondary operations,
and regulatory guidelines. In the
case of a product redesign that leads
to material conversion, companies
should seek out materials compatible
with their existing sterilisation and
validation processes to contain costs
and expedite processing, feels Mark
J Costa, executive vice president
- Polymers Business Group, EastmanChemical Company.
Down to the boneOne of the chief advantages
associated with the use of plastic-
based orthopaedic prosthetics and
implantable hardware is the possibility
to precisely match the strength,
hardness, and elasticity of plastics with
that of the bone. This is dramatically
different from the case where metal
is in direct contact with the bone. The
ability of plastics to mimic the native
bone is important for the long-term
health of the native bone that is in
direct contact with the prosthesis or
implanted hardware.
Normal bone is a living tissue,
which is capable of remodelling
and rebuilding itself continuously
in response to the conditions it
Dr V J S Vohraco-founder and director, Nevedac Prosthetic Centre
Manufacturers of basic resins produce different
polymers to meet the needs of prosthetic
patients. Manufacturing basic resins requires the
plastic to be heated to a molten state twice, once
to make the resin and a second time to blend in
the additives that affect its final characteristics.
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is experiencing. Just like muscles
become stronger when subjected
to weightlifting, bones, too, become
denser, larger, and stronger in response
to the stress of increased loads. The
opposite occurs when bones are
not stressed, ie, they become lessdense, thinner, and weaker when
not experiencing loads. The same
effect occurs in the long thighbone
following a hip replacement. There is
a loss of 10-45 per cent of bone mass
in the bone surrounding the implant
during the first few years after total
hip replacement. This is because the
titanium implant cemented in the
centre of the femur is much harder
and stronger than the surrounding
bone. As the titanium rod is hardand strong, the surrounding bone no
longer has to work hard to support the
patients weight, and thus is unloaded.
The removal of stress from the bone
by an implant is known as stress
shielding, and leads to bone thinning
& weakness, and eventually the bone
surrounding the titanium implant
breaks down, says Linares.
Replacing natureBy matching the strength and
hardness of the implant with that of
the natural bone, the loads should
be evenly distributed between the
implant and host-bone. Plastic-
based orthopaedic hardware has an
advantage the host-bone and the
implant can be adjusted so it matches
that of the bone. Linares Medical
Devices has developed a method of
transitioning so that the articulating
surface can be made softer and more
elastic to mimic cartilage, while the
bone segment can be made with the
same hardness as the natural bone.
This helps in creating a longer lasting
and better performing product and
improving patients satisfaction.
Currently, there are only a select
few plastics that have been approved
by the FDA for permanent human
implantation. Because of the limited
choices for FDA-approved plastics,
the Linares Medical Devices team has
developed an entirely new class of
materials. These materials are blends,
or alloys, of FDA-approved plastics &
metals, or FDA-approved plastics and
ceramics. Individually, all these materials
have been approved and successfullyimplanted in humans for many years,
and hence its biocompatibility issues
have been addressed. What is new
and completely revolutionary, is
the Linares Medical Devices
proprietary method of combining
these substances in a way that
greatly enhances their biomechanical
usefulness, feels Linares.
According to him, blending
plastics with ceramics or metals at
the molecular level allows the best
properties of both substances to
be retained, while the undesirable
properties are minimised. Linares has
developed novel plastics resulting
in materials with lightweight and
elasticity, combined with strength and
durability normally found in metals
and ceramics. One major advantage
inherent to the use of plastic-based
hardware for orthopaedic surgery
applications is that it is radiolucent.
It does not interfere with radiological
imaging technologies like CT, X-rays,
or MRIs, which is extremely important
to better follow-up and evaluate the
patients after surgery, he adds.
Brawn with brainsSince decades now, scientists have
been working towards developing a
technique for interpreting brain activity
to motor output. In other words, this
D L PandyaCEO, Medical Plastics Data Service
Polymers, when combined with nano-
materials offer a range of polymer
compounds, composites & semi-finished partswith amazing functional properties, including
electrical & thermal conductivity, mechanical
properties and opto-electronic properties.
April 2009 Modern Plastics & Polymers 45
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enables in deciphering the electric
patterns of the brain and converting
them into coherent thoughts. The
majority of motor functions in our
body are driven by electrical currents
originating in the brain motor cortex
and conducted through the spinalcord and peripheral nerves to the
muscles, where the electrical impulse
is converted into motion by the
contraction & retraction of
specific muscles.
For example, when the arm is bent
at the elbow joint, the bicep muscles
contract and the triceps relax. This
seemingly simple movement is the
result of the cumulative activity of
numerous brain cells in the area of the
cortex in charge of arm movement. The
neurons, following a cognitive decision
to bend the arm, generate an electric
impulse through the peripheral nerves,
causing the correct muscles to contract
or relax. Microprocessor technology
with a computer interface allows the
prosthetist and the patient to fine-tune
the adjustments to achieve maximum
performance of the artificial arm. The
i-LIMB Hand, a recent development, is
controlled by a unique, highly intuitivecontrol system that uses a traditional
two-input myoelectric (muscle signal)
to open and close the hands life-like
fingers. The modular construction of
i-LIMB means that each individually
powered finger can be quickly
removed by simply removing one
screw. This means that a prosthetist
can easily swap out fingers that require
servicing and patients can return to
their everyday lives after a short clinic
visit, states Dr Vohra.
Essentially until now, people using
the prosthetics have controlled one
motor at a time and had to think
carefully about what motor they
wanted to control and how to move it
instead of just thinking about moving
it and being able to do it. However, a
new technique called targeted muscle
reinnervation, involves taking the
nerves that remain after an arm is
amputated and connecting them toanother muscle in the body, often in
the chest. Electrodes are placed over
the chest muscles, acting as antennae.
When the person wants to move the
arm, the brain sends signals that first
contract the chest muscles, which send
an electrical signal to the prosthetic
arm, instructing it to move. This process
requires no more conscious effort
than it would for a person who has a
natural arm. The Touch Bionics i-LIMB
was developed using leading-edgemechanical engineering techniques
and is manufactured using high-
strength plastics. The result was a
next-generation prosthetic device
that is lightweight, robust and highly
appealing to both patients and
healthcare professionals.
Myoelectric controls utilise the
electrical signal generated by the
muscles in the remaining portion of the
patients limb. This signal is picked up by
electrodes that sit on the surface of the
skin. Existing users of basic myoelectric
prosthetic hands are able to quickly
adapt to the system and can master the
new functionality of the device within
minutes. For new patients, i-LIMB Hand
offers a prosthetic solution that has
never before been available, claims
Dr Vohra.
The nano effect in prostheticsThe use of both synthetic as well
as natural materials in medical and
pharmaceutical applications has been
successful due to the availability of a
wide variety of user-specific materials
at affordable prices. However, the
integration of nanotechnology into this
application has resulted in possibilities
beyond the conventional.
Polymers the wonder material
of the century when combined
with nano-materials offer a range
Mark J CostaEVP - Polymers Business Group, Eastman Chemical Company
Material properties are also matched to
application performance, secondary operations,
and regulatory guidelines. Companies should
seek out materials compatible with their
existing sterilisation & validation processes to
contain costs and expedite processing.
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of nanotechnology-based polymer
compounds, composites and semi-
finished parts with amazing functional
properties including electrical
conductivity, thermal conductivity,
mechanical properties and opto-
electronic properties for variousunique application opportunities in the
medical device sector. The electrically
conducting compounds made from
carbon nanotubes or fibres have tiny
nano-structures about 80,000 times
smaller in diameter than a human
hair. These materials smart Nano
conductors in a polymer matrix can
be intelligently used as smart-sensors
or commonly known as electrodes
for bio-potential detection. Most
common applications are for brainwave detection, cardio measurements,
and muscle movement detection in a
human body, states Pandya.
What prothetists seek?Thermoplastics over the past several
years have increased in popularity in
both orthotic as well as prosthetic
applications. Clarity, flexibility, rigidity,
faster processing times, localised
adjustment by the use of heat, inert
material and surface quality are just
a few of the benefits associated with
thermoplastics. Thermoplastics, like
any other type of technology, are
subject to lack of understanding
and failures do occur. This process
quite often discourages the user and
brands the material or process as an
unacceptable method of fabrication.
Through education and detailed study,
thermoplastics & resins have become
one of the most valuable technologies
available to prosthetists and orthotists.
Handling the plastic sheets is critical
for the success of the finished device. The
manufacturers of basic resins produce
different types of polymers to meet the
needs of prosthetic and orthotic patients.
Manufacturing the basic resin requires
the plastic to be heated to a molten
state twice, once to make the resin and
a second time to blend in the additives
that affect its final characteristics. The
rigidity, strength and resistance to fatigue
allow polypropylene to be typically used
in lower extremity prosthetic applications
like above-knee sockets and below-knee
sockets. The typical shrinkage of these
devices is around 1.5-2 per cent. Co-
polymers have less rigidity and can beprocessed at slightly lower temperatures.
These qualities allow copolymers to be
spot modified more easily. Co-polymers
are more commonly used in orthotics,
but are now also gaining acceptance for
above-knee and below-knee sockets,
explains Dr Vohra.
Linear low-density polyethylene finds
applications in all areas of traditional
polyethylene usages. It has better tensile
& puncture resistance, impact and tear
properties making linear low-density
polyethylene a good choice for above-
knee and below-knee socket liners,
thereby improving prosthetic fitment to
a great extent, which further increases
the comfort level for the patients using
the prosthetic and orthotic devices. The
stress relieving process occurs during
the extrusion process, and there are
several methods of accomplishing stress
relieving. Stress relieving has no effect
on the quality of the part produced in
the orthotic & prosthetic (O&P) industry
for several reasons. First, the stress
relieving process occurs under the
minimum forming temperature. In the
O&P industry, the plastic is heated above
this temperature, which allows the plastic
to flow freely and relieve its internal
stresses. Stress may be reintroduced intothe plastic during the forming process.
Second, it is not apparent that there are
any chemical additives added to the
plastic to change the molecular structure
so as to relieve stress. It is possible that
some of the commercial methods for
stress relieving could be adapted to
relieve stress in formed parts, which
would allow for a more reliable finished
part, mentions Dr Vohra.
Realising dreams for a bettertomorrow
Arms have become a particular
focus in the prosthetics industry, as
science has long had success with
prosthetic legs. Recent developments
on this front include more flexible
and sensitive skin & arm designs,
and wireless devices implanted in
prosthetic arms to allow more natural
movement. In recent experiments,
researchers have also used sensors
implanted in the brain to enable
monkeys control a mechanical arm, and
a paralysed man to move a cursor on a
computer screen.
Some of these methods, if
perfected and approved by regulatory
agencies, may eventually become
more viable for amputees. Polymers
are bound to drive these initiatives
forward, particularly in making this
sophisticated equipment economically
feasible for the common man. While
the reinnervation technique does not
require regulatory approval because
it is done using surgery and existing
devices, it has limitations, which even
its creators acknowledge - including
the fact that it is not feasible for every
patient and is expensive. However,
there is a possibility of these negatives
getting completely eradicated with the
advent of advanced technologies in the
world of medical plastics.
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