Analytical Report (1)

AN ASSESSMENT OF
NEUROPROSTHETIC
TECHNOLOGIES

AN ASSESSMENT OF
NEUROPROSTHETIC
TECHNOLOGIES
CALIFORNIA POLYTECHNIC STATE UNIVERSITY
CHANDLER JONES, STUDENT, MECHANICAL ENGINEERING
KADE SCHMITZ, STUDENT, MATERIALS ENGINEERING
ANNE SHIELDS, STUDENT, INDUSTRIAL ENGINEERING
MATT WHITMAN, STUDENT, BIOMEDICAL ENGINEERING

ABSTRACT
Neuroprosthetics are revolutionary biomedical devices that branch off of
conventional prostheses. These devices are more than just artificial limbs; they
are systems designed to generate, restore, and modulate a range of neurally
mediated functions. Neuroprosthetics are a complex and highly technical topic to
study, which can be extremely difficult for non-specialists to understand. The goal
of this document is to present a general, in-depth description of neuroprosthetics
that broadens the scope of knowledge and understanding for all readers. This
report explores the innovative technology behind the translation from neural
transmittal, to electrode detection, and finally to mechanical action. It discusses
the mechanics and inner workings of the prosthetic device and how it interacts
with the user and their brain. This report also investigates the different materials
utilized in neuroprosthetic fabrication and evaluates the functionality of each
material for best overall performance. Comparisons are made about the additive
manufacturing techniques for creating neuroprosthetics, such as 3D printing and
injection molding. Finally, the ethical implications of such a device are examined
and questioned. With this information, readers will retain a complete and overall
understanding of neuroprosthetics and their functionality. This document strives to
provide fascinating research that will excite and motivate further learning as the
technologies behind neuroprosthetics continues to evolve.
Keywords: Neuroprosthetics, neural transmittal, electrode detection, prosthetic
mechanics, materials, additive manufacturing

An Assessment of Neuroprosthetic Technologies
TABLE OF CONTENTS
1.0 INTRODUCTION ........................................................................... 1
2.0 ELECTRODE DETECTION SYSTEMS...................................................... 2
2.1 Electromyography (EMG)........................................................... 2
2.1.1 MYOMO
Device
................................................................................................
2
................................................................................................
................................................................................................
................................................................................................
................................................................................................
................................................................................................
................................................................................................
................................................................................................
2.2 Epimysial Electrodes ................................................................ 3
2.3 Electroencephalography (EEG)..................................................... 4
2.4 Extraneural Electrodes.............................................................. 5
2.5 Magnetoencephalography (MEG)................................................... 6
3.0 MECHANICS OF NEUROPROSTHEICS .................................................... 8
3.1 Commercial Standard ............................................................... 8
3.1.1 Commercial Drawbacks ...................................................... 8
3.2 Innovative Movement................................................................ 9
3.2.1 Achieving Adequate Freedom............................................... 9
3.2.2 Simplifying the Thumb ......................................................10
3.2.3 Wrist
Actuation
............................................................................................
10.........................................................................................
3.3 Connecting Man to Machine .......................................................11

3.3.1 Haptic Feedback..............................................................11
3.4 Joint Problems ......................................................................12
4.0 MATERIALS OF NEUROPROSTHETICS ..................................................14
4.1 Polymers .............................................................................14
4.1.1 Acrylic and
Epoxy
............................................................................................
14 ........................................................................................
4.1.2 Polyethylene and Polypropylene ...........................................14
4.1.3 Silicone ........................................................................14
4.1.4 Polyimide ......................................................................15
4.2 Metals ................................................................................15
4.2.1 Aluminum .....................................................................15
4.2.2 Graphene ......................................................................16
4.2.3 Steel............................................................................16
4.2.4
Titanium
............................................................................................
17.........................................................................................
4.2.5 Platinum .......................................................................17
4.2.6 Gold ............................................................................17
4.3 Composites ..........................................................................17
4.3.1 Carbon Fiber ..................................................................17
4.3.2 Plant-Based
Composites
............................................................................................
18.........................................................................................
5.0 MANUFACTURING AND PRODUCTION .................................................19
5.1 Prosthesis ............................................................................19
5.1.1 3D Printing ....................................................................20

5.1.2 Injection
Moulding
............................................................................................
22.........................................................................................
5.1.3 Hybrid Models .................................................................23
5.2 Socket ................................................................................24
5.2.1 Selective Laser Sintering ....................................................24
5.2.2 Additional Components ......................................................24
5.2.3 Socket Alternative............................................................25
6.0 ETHICS....................................................................................27
7.0 CONCLUSION.............................................................................28
8.0 REFERENCES .............................................................................29
LIST OF FIGURES
Figure A. “The Nervous System” ........................................................... 1
Figure B. “MYOPRO© Device” .............................................................. 3
Figure C. “Muscle Tissue” ................................................................... 3
Figure D. “Block Diagram of the Process of the EEG System”.......................... 4
Figure E. “Cuff Electrode Diagram” ....................................................... 5
Figure F. “Flat Interface Nerve Electrode Diagram” .................................... 6
Figure G. “Measured Cortical Activity”.................................................... 7
Figure H. “Manus Hand Movement”.......................................................10
Figure I. “Degrees of Freedom in Wrist” .................................................11
Figure J. “Armband for Detecting Simultaneous Vibrotactile Feedback” ...........12
Figure K. “Prosthesis Socket Modification” ..............................................13
Figure L. “Graphene Electrodes” .........................................................16
Figure M. “Composite Additive Manufacturing Prosthetic Finger”....................18

Figure N. “CAD Model of Prosthetic Leg” ................................................20
Figure O. “3D Printed Prosthetic Hand”..................................................21
Figure P. “Process of Injection Moulding” ...............................................22
Figure Q. “Hybrid Prosthetic Hand Model” ..............................................23
Figure R. “Prosthetic Socket with Helical Cooling Chamber” .........................25
Figure S. “Direct Skeletal Osseointegration” ............................................25
Figure T. “Osseointegration Diagram”....................................................26

1.0 Introduction 1
Prosthetic devices, in some form or another, go back for thousands of years.
Prostheses such as a peg leg or a hook have enabled users to regain a degree of
freedom in a previously unusable limb. In today’s scientific realm, an extension of
the typical prosthetic device exists. This device is the neuroprosthetic, which is a
complex and intricate system designed to generate, restore, and modulate a range
of neurally mediated functions. The neuroprosthetic relies on communication
between the brain and machine, harnessing the power of both the Central Nervous
System and Peripheral Nervous System. The Central Nervous System releases
neurons that send information to all parts of the body. The Peripheral Nervous
System receives these signals and relays the sensations, movements, thoughts,
memories, and feelings into sensory feeling and motor action. Neuroprosthetics
aim to relay the neuron transmissions from the Central Nervous System to the
mechanical prosthesis in order to regain the sensations, movements, and feelings
lost in the amputated limb.
Figure A. “The Nervous System”
Source. “The Nervous System.” National Center for
Biotechnology Information, (2016). Web. 21 May
2016.
1.0 INTRODUCTION

2.0 Electrode Detection Systems 2
Electrode detection systems are used to control the movement and functions of
neuroprosthetics. Several types of electrode detection systems can be used
depending on the desired function and output. The three main types of electrode
detection systems currently in use are surface electrodes, epimysial electrodes,
and extraneural electrodes.
2.1 ELECTROMYOGRAPHY
Electromyography (EMG) is an electrode detection system in which the electrode is
attached to the surface of the skin. EMG can be used either for detection of
electrical signals from the peripheral nervous system or in non-specific activation
of muscle fibers or nerves. This type of electrode can be used in rehabilitation for
patients that have chronic pain or musculoskeletal problems using Transcutaneous
Electrical Nerve Stimulation (TENS) (Navarro 231). Paraplegics can get health
benefits from using TENS to help improve blood flow. Used in conjunction with
neuroprosthetics, EMG can be used as a detection system to tell a computer how
to react.
2.1.1 MYOMO Device
The MYOMO© device uses EMG to detect nerve signals at the affected limb and
aids in contraction (Bleakley 2). This neuroprosthetic is used in therapeutic
scenarios where patients still have their limb, but lack the ability to fully use it.
The MYOMO© device is also used in patients that have suffered from strokes and
brachial plexus.
A study conducted at the University of Pittsburgh looked at the effects of the
MYOMO© device on stroke patient therapy. Patients with limited movement in a
limb due to a stroke used the MYOMO© device to reach for several objects.
Patients went through sixteen therapy sessions and their improvements were
tracked over the course of the study. The study found that all the patients had
improvements in their movement and range of motion in their affected limb.
2.0 ELECTRODE DETECTION SYSTEMS

Figure B: “MYOPRO© Device”
Source. Author.
2.2 EPIMYSIAL ELECTRODES
Epimysial electrodes are surgically implanted onto the epimysium of a targeted
muscle. The electrode is fixed to the epimysium using sutures or small anchors.
The epimysium is a sheath of fibrous elastic tissue surrounding a muscle, which is
modeled below in Figure C. Since the electrode is attached directly to the muscle
fibers it allows for accurate EMG measurements or stimulation of surrounding
muscular fibers. In practice, epimysial electrodes are useful in motor prosthesis
control or in coordinated muscle contractions such as grasping, standing, or
walking. To contract large groups of muscles epimysial electrodes require a large
power consumption, which when not monitored correctly can cause discomfort and
can damage muscles after long periods of use with incorrect current.
Figure C: “Muscle Tissue”
Source. Adopted from “Epimysium.” National Center for
Biotechnology Information, (2016). Web. 21 May 2016.
2.3 ELECTROENCEPHALOGRAPHY
Electroencephalography (EEG) electrodes are surface electrodes that are attached
to the scalp to over the Cerebral Cortex to measure nerve impulses using Brain
Computer Interfacing (BCI). Using the measurements the activity in the brain can
be associated with actions like opening and closing a hand. Once the computer is
trained on certain activities it can translate the brain activity to actions carried
out by a prosthesis. D below shows the process of translating brain activity to
physical action by means of a neuroprosthetic.

Figure D: “Block Diagram of the Process of the EEG System”
Source. Adopted from Belic, Jovana J. "Decoding of Human Hand Actions to Handle
Missing Limbs in Neuroprosthetics." Frontiers in Computational Neuroscience, (2015).
Web. 17 May 2016.
Research conducted at the College of London searched for a correlation in brain
activity to finger and hand movements. The study used test subjects with a
tracking glove on a healthy limb to measure the activity in the hand. While the
device was on the subjects’ brains were scanned to measure brain activity.
Subjects were instructed to do 17 simple tasks that were all variations of reaching
and grasping for objects. The results found that hand control requires only 4 or 5
dimensions to explain up to 90% of daily movements. By looking at the data found
from each of the 17 tasks, researchers were able to program the computer to
predict which action wanted to be completed. This allowed patients hooked up to
an EEG device to control a neuroprosthetic using only the thoughts of moving the
limb.
2.4 EXTRANEURAL ELECTRODES
Extraneural electrodes are placed directly onto a nerve and sutured to epineurium
(outermost layer of dense irregular connective tissue surrounding peripheral
nerve). This type of electrode requires surgery direct access to the peripheral
nervous system is required. They are unlikely to damage nerves, but the electrode
can be broken under excessive tension or motion. By attaching straight to the
nerve the electrode can selectively activate specific nerve fascicles (small bundle
of nerve fibers) allowing for activation of specific groups of nerves using
Functional Electrical Stimulation (FES). Microsurgical techniques to attach multiple
electrodes allow for bipolar or selective nerve activation.
Cuff electrodes are extraneural electrodes that completely encircle the nerve
(Navarro 238). Designed from a flexible material and able to self adjust to allow
for constant motion and prevent damage. This prevents stretching or compression

of the nerve. Since the electrode encircles the nerve the electrode cannot
selectively activate specific nerve fascicles.
Figure E: “Cuff Electrode Diagram”
Source. Adopted from “Three Ways to Plug in
to the Nervous System.” New Scientist, (2015).
Web. 20 May 2016.
Flat Interface Nerve Electrodes (FINE) is a type of electrode that is attached
directly to the nervous system (Navarro 239). This electrode uses mild to moderate
pressure to flatten a nerve, increasing the surface area of the nerve. The more the
fascicles are flattened the easier it is to selectively activate specific nerves
(Navarro 240).
Figure F: “Flat Interface Nerve Electrode
Diagram”
Source. Adopted from “Three Ways to Plug in
to the Nervous System.” New Scientist, (2015).
Web. 20 May 2016.

2.5 MAGNETOENCEPHALOGRAPHY
Magnetoencephalography (MEG) is a relatively new technique that investigates
human brain activity. This gives a live measurement of brain activity through the
use of highly sensitive sensors that are connected directly to a test subject’s head.
MEG detects which sections of the brain are active, which is then displayed on a
screen. However MEG does not have an actual scan of the brain tissue so it is often
used in conjunction with Magnetic Resonance Imaging (MRI). This allows doctors to
accurately see which areas of the brain are activated when certain actions are
completed. Currently MEG technology is restricted clinical environments, since the
sensors need to be super cooled. However MEG could be a future detection system
for neuroprosthetics as the technology continues to improve. Figure G below
illustrates how MEG measures and displays brain activity.
Figure G: “Measured Cortical
Activity”
Source. Adopted from Fukuma, Ryohei,
et al. “Real-Time Control of a
Neuroprosthetic Hand by
Magnetoencephalographic Signals from
Paralyzed Patients.” Scientific Reports,
(2016): 21781. Web. 16 May 2016.
A study conducted in Japan looked at nine test subjects to see if a prosthetic arm
could be controlled using MEG. MEG uses highly sensitive electrodes that are
attached to a patient's head to detect brain activity. The test subjects were asked
to close their paralyzed hand while their brain activity was measured by MEG. The
goal was to see if a sufficient amount of information could be acquired from MEG
to control a prosthetic arm. By measuring Slow Movement Fields (SMF),

researchers were able to successfully translate the brain activity to control the
patient’s prosthetic arm. The study concluded that a sufficient amount of
information can be taken from MEG measurements to control an invasive or non-
invasive prosthetic arm.

3.0 Mechanics of Neuroprosthetics 8
3.0 MECHANICS OF NEUROPROSTHETICS
The key focus of neuroprosthetics is to harness and connect the brain’s signals to
control a mechanical device. These complex devices aim to mimic the
functionality of a lifelike limb with an artificial prosthesis. Unfortunately,
neuroprosthetic devices even today are nowhere near the capabilities of a healthy
human hand. However, this technology is rapidly improving. Technology developed
in the last 40 years has created moving hands with the ability to grasp objects.
Computers and other technology have aided the process even further in recent
years, creating comparable prosthesis to the human hand. Interfacing man and
machine is finally becoming possible. Using a combination of electronic sensors
and computers, new prosthetic hands are beginning to understand the user’s
intentions. Almost more important is that they are also reacting to them in a
timely fashion. With new technologies being discovered seemingly daily, it seems
that a fully operational hand is within reach.
3.1 COMMERCIAL STANDARD
The three most advanced commercially available hands are the OttoBock©, Touch
Bionics© and RSLSteeper© prosthetic hands (Riet 7). These neuroprosthetic hands
are on the cutting edge of what an amputee can buy. They have a range of
motions which can each be controlled by the user through either myoelectric or
electroencephalographic control. Myoelectric control allows the user to control
the prosthesis with their mind using either an invasive or surface electrode array.
3.1.1 Commercial Drawbacks
While each of these hands has multiple varied functions, the user must choose a
single function on the display, and using his or her mind can control only an on/off
(contract/loosen) function. These prostheses are also impractical due to their
price. The three hands listed above are each between $40,000 and $75,000 dollars
for a single device (Riet 15). While this price takes into account the extensive
research to create each one, in order to create a viable product for a wider
audience, the price needs to be reduced. This current state of these devices prices
many people out from ever owning a prosthesis capable of anything resembling a
human hand. The mechanics of today’s prostheses are also limited by the
coinciding relationship between strength of grip and weight. The goal
mechanically is to create a hand that can both hold things as well as we can, as
well as not cause your arm to ache from holding itself up all day. Today’s
prostheses accomplish neither, being both heavier
than the average human hand, by over 50% an adult male and less able to carry
weight, at 50% the strength of an average adult. (Riet 6). The next generation of
neuroprosthetics will make improvements upon these design characteristics and
use methods found in the following sections
3.2 INNOVATIVE MOVEMENT

The most common method to power a prosthetic hand is to use an under-actuated
design. This allows one actuator to mimic multiple joints of a finger. By combining
the ring and pinky finger to one actuator, you can reduce the number of actuators
needed to 3, plus the movement of the thumb. Researchers have found through
studying the anatomy of the hand that there are over 20 individual degrees of
freedom you can use to contort your hand, each adding to the powerful dexterity
we have. To try to match this unparalleled design with just 3 actuators is
impossible. Current commercial designs do not adequately meet the needs of the
user by simplifying the actuation that far.
3.2.1 Achieving Adequate Freedom
Adding degrees of freedom to modern hands will enable progress towards an
adequate prosthetic hand in the future. With 11 individual degrees of freedom, a
design based out of Buenos Aires allowed a prosthetic hand to behave very
similarly to a human hand (Controzzi 2). Intrinsic to upcoming, next-generation
hands, is a very well defined, dexterous thumb, allowing the most important
factor of a grasping device, the opposition force. The Argentinian hand thus
designed itself to have 3 individual degrees of freedom on solely the thumb, one
less than a natural hand (Controzzi 3). This supreme method allows the user to not
only perform common grips such as the can-hold, precision grips like the key-hold,
or the handle grasp; but additionally, other more minute tasks that are required
throughout day-to-day life.
Figure H: “Manus Hand Movement”
Source. Adopted from Pons, J., et al. “The Manus-hand dexterous robotics upper limb prosthesis:
Mechanical and manipulation aspects.” Autonomous Robots: 16.2 (2004): 143-163. Web. 20 May
2016.
3.2.2 Simplifying the Thumb
In other areas of the field, different methods for thumb actuation are being
developed. Researchers with the MANUS-hand developed a new thumb utilizing a
Geneva wheel to power itself. The Geneva wheel allows one actuator to control 2
planes of motion, rotation and grasping (Pons et al. 143). This method is promising
as it is a fantastic way to increase degrees of freedom while minimizing weight.
3.2.3 Wrist Actuation

The MANUS hand added wrist actuation, adding 2-3 degrees of freedom, flexion
and rotation, to an otherwise stationary location. This innovation, which has been
developed in a number of next-generation hands, has promise however has lacked
proper implementation so far. In a study of active vs. passive wrists, researchers
have found that today’s active wrists have an inverse relationship between torque
and size (Bajaj 25). By making a wrist with comparable torque to a natural hand,
the prosthesis required a large area of the forearm for actuation. This mandatory
large region reduces the number of people who are able to use the wrist, as
someone who is amputated halfway down the forearm would not have the space to
spare. The researchers also found that by reducing the size to increase the
availability to the user, the wrist would not have the strength near a natural hand
and was therefore not worth implementing. Figure I demonstrates the degrees of
freedom a normal function wrist possesses, and what future neuroprosthetics will
try to imitate.
Figure I: “Degrees of Freedom in Wrist”
Source. Adopted from Bajaj, N.M. "State of the art in
prosthetic wrists: Commercial and Research devices."
2015 IEEE International Conference on Rehabilitation
Robotics (2015): 331-338. Web. 20 May 2016.
3.3 CONNECTING MAN TO MACHINE
One of the hardest challenges faced in the prosthetics industry today is creating a
feedback loop to the user. With a natural hand, one is able to feel the heat of a
stove without looking, however current prosthetic hands do not allow this. Another
example is the ability to feel a bottle slipping from your grasp, currently not
possible to do with a mechanical hand.
3.3.1 Haptic Feedback
In order to create a better relationship with machine, researchers at Massey
University in New Zealand have invented a method of haptic feedback using

vibrotactile alerts. Just as we have been trained to know that a single buzz in our
pocket means a text, and multiple means a phone call, a vibrotactile feedback
system can train the user to feel by decoding vibrations. A promising study showed
that up to four different senses could be deduced accurately in a single armband
using spatial variation (Riet 24). This armband is pictured below in Figure J.
Results showed that as the number of channels increased, accuracy deducing
between them decreased, however, a longer training period could enable subjects
to learn the system better. Other methods of haptic feedback yet to be fully
implemented in systems are pressure and proprioception (Riet 22). These
additional methods could yield a prosthesis that is able to accurately relay senses
from the hand to the brain and improve the feedback loop to the user.
Figure J: “Armband for Detecting Simultaneous Vibrotactile
Feedback”
Source. Adopted from Riet, D., et al. "Simultaneous
vibrotactile feedback for multisensory upper limb prosthetics."
Robotics and Mechatronics Conference, 6 (2013): 64-69. Web.
25 May 2016.
3.4 JOINT PROBLEMS
Recent surveys of amputees have shown that up to 20% have abandoned prosthesis
use completely due to comfort or functionality issues (Biddis 2). Advancements in
engineering have led to improvements with the functionality of the prosthesis but
developments in comfort have been lacking. Researchers have recently began
developing a method to decrease stress on the remaining arm by inventing an arm
that alternates the compression and working time of the arm in sync with users’
needs. Much like the black boots that come with a broken leg, this device has a
vacuum pump built in to ease pressure. While unused, the pressure can be
decreased to aid with comfort, however, as soon as it senses a workload, will seal
the arm and create a stable environment to work in. Advances in comfort like this
will help to decrease the number of users that discontinue prosthesis use. Figure K
illustrates this pressure sensing modification to the prosthetic socket.

Figure K: “Prosthesis Socket Modification”
Source. Adopted from Yuanjun, S., et al. “A novel socket design for upper-
limb prosthesis.” International Journal Of Applied Electromagnetics &
Mechanics, 45.4 (2014): 881-886. Web. 25 May 2016.

4.0 Materials of Neuroprosthetics 13
4.0 MATERIALS OF NEUROPROSTHETICS
Neuroprosthetics can be made using a variety of different materials. The usage of
different materials can result in a neuroprosthetic device that is more functional,
economical, and comfortable for the patient. Each different material presents its
own advantages and disadvantages that influence the effectiveness of the
prosthetic device. The variety of materials available for prosthetic devices enable
the devices to become lighter, stronger, and more durable, allowing the user to
have a more functional limb. These advances in materials and usage for
neuroprosthetics are helping to create a more lifelike prosthesis for users.
4.1 POLYMERS
Polymers are chains of linked organic or synthetic units that repeat the same
structure. They are useful in neuroprosthetics because they are easy to
manufacture and present a wide range of characteristics. Polymers are responsible
for the recent rapid advancement of the neuroprosthetic field.
4.1.1 Acrylic and Epoxy
Polymers are very heavily used in prostheses because of their weight, strength,
mouldability, and cost advantages. Different manufacturing methods require
different materials to be used. 3D printers use a wide variety of polymers to
create an intricate piece. Some printers use an epoxy or acrylic resin that hardens
when a UV laser passes through it. These materials are preferred for the socket of
the prosthesis because when heated, they can be easily moulded into the desired
shape. This resin can also be combined with different materials to give it different
properties.
4.1.2 Polyethylene and Polypropylene
Polypropylene and Polyethylene are both thermoplastics that are widely used in
prostheses. When heated, thermoplastics can be formed to their desired shape.
This is advantageous for creation of the socket because a near exact fit to the
residual limb can be created to ensure maximum comfort for the amputee.
4.1.3 Silicone
Silicone is what is used to create padding and reduce friction inside the socket.
Friction in the socket can cause redness, blistering, and calluses. Some friction
between the socket and limb is good because it is the main force that holds the
prosthesis on the limb. Problems occur when there is too much or too little
friction. Too much frictional force and the device becomes uncomfortable or too
tight. Too little friction and the device slips causing blisters. Materials, like
silicone, that have a high coefficient of friction require less force to be applied to
create the frictional force (Zhang 213). Up to 95% of prosthetic users report having
some level of discomfort due to friction (Bhatia 30). Silicone is also used as an
insulator to sheath electrodes that are implanted in the brain.

4.1.4 Polyimide
Polyimide is a semiconductor that is used in neural implants. It is flexible, durable,
and biocompatible, making it a great material to put in the brain. An experiment
by Birthe Rubehn and Thomas Stiegliz, professors at the University of Freidberg in
Germany, showed how polyimide would react when put in the body. They kept an
experimental sample in a phosphate buffered saline solution at body temperature,
98.6°F. After 17 months in the solution, the researchers preformed a stress versus
strain test on the sample and found that it performed just as well as a sample that
had not been in the experimental environment. This experiment verified that
polyimide would be a good material to use in implants.
4.2 METALS
Metals are a class of elements that are characterized by their opacity, ductility,
conductivity, and luster. Because of these unique qualities and their ability to be
combined to form alloys that give them different qualities they serve many
functions in neuroprosthetics, specifically structural support.
4.2.1 Aluminum
Aluminum is used in most widely used metal in prosthetic devices. It is mostly used
to replicate the main bone structure of a limb, such as the tibia and fibula in the
leg or humerus, ulna, and radius in the arm. Aluminum provides the best balance
between strength, weight, and cost. Because the amputee must support the some,
if not all, of the weight of the prosthesis using remaining musculature it is
imperative to keep the weight as low as possible. Aluminum is also easy to
manufacture and recycle which lowers the cost and improves the overall lifecycle
of the materials.
4.2.2 Graphene
Graphene is a very new material that has not yet completely found its way into
neuroprosthetics. At only a single atom thick, graphene is the lightest and
strongest material in the world. Made out of carbon, graphene is both conductive
and malleable making it extremely useful in neuroprosthetics. If researchers can
find a way to mass produce graphene it will no doubt have huge implications in
almost every electronics field.

Figure L: “Graphene Electrodes”
Source. Adopted from Patil, Anoop, and Nitish Thakor.
“Implantable Neurotechnologies: A Review of Micro- and
Nanoelectrodes for Neural Recording.” Medical & Biological
Engineering & Computing, 54.1 (2016): 23-44. Web. 24 May 2016.
4.2.3 Steel
Steel is also used as the main structure of the prosthesis when more strength is
required, however it is more often used as small components that are under lots of
stress. Steel pieces are often used in knee joints, ankles, and elbows to hold
together the larger aluminum pieces.
4.2.4 Titanium
In a perfect world prosthesis could be made of titanium. It is has the best strength
to weight ratio when compared to steel and aluminum. It is nontoxic,
nonmagnetic, and does not corrode. The only drawback to titanium is that it is
extremely expensive. Making prosthesis out of titanium would make it too
expensive for many people to buy which is the opposite of what companies are
trying to do with prostheses.
4.2.5 Platinum
Platinum is the main material used when putting something in the body. Platinum
is extremely stable and does not corrode when put in a warm, moist environment
like the body. Usually when a foreign substance is put in the body, the immune
system will respond with infection and scarring and the body will reject the
implant.

4.2.6 Gold
Gold is also used in electrodes that detect neurological signals from the brain.
Gold is one of the most conductive materials so it is used to transport electric
signals from the nerves to the prosthetic device. Gold is also one of the most
expensive materials so it is generally only used as a last resort option when
platinum is not transmitting the neurological signals.
4.3 COMPOSITES
Composites are composed of multiple materials, both organic and inorganic. The
multifaceted makeups of these materials enable them to showcase a variety of
properties that are not present otherwise.
4.3.1 Carbon Fiber
Carbon fiber is used in prosthetic devices because of its extreme lightweight, high
strength qualities. Carbon fiber gets its strength from strands of carbon that are
woventogether. When this weave is coated in liquid polypropylene or
polyethylene resin and dried, the result is an extremely stiff, lightweight
composite material. Carbon fiber composites have added elastic strength to
polymers to create a more natural walking motion for leg prosthetics (Scholz
1800). Carbon fiber composites can also be used in the fingers of a prosthetic
hand. The lighter the components of prostheses are, the more fluid and quick the
movements can be (Leddy 4799).
Figure M: “Composite Additive Manufacturing
Prosthetic Finger”
Source. Adopted from Leddy, M. T, J. T. Belter,
K. D. Gemmell and A. M. Dollar. “Lightweight
Custom Composite Prosthetic Components

Using an Additive Manufacturing-Based Molding
Technique.” 2015 37th Annual International
Conference of the IEEE Engineering in Medicine
and Biology Society (2015): 4797-4802. Web. 20
May 2016
4.3.2 Plant-Based Composites
Recently, researchers have been looking into using plant-based composite
materials to make sockets that are cheaper, stronger, and more durable. A study
done by a team of researchers in England compared current prosthetic sockets to
those made of plant fibers from bamboo, banana, corn, cotton, and flax. Fibers
from these plants were mixed with an environmentally friendly mix of
polyurethane and polycarbonate to create a strong composite material. They
found that the bamboo and banana composites could both serve as replacements
for acrylic. Another advantage to this method is that the plant-polymer composite
is self-curing, meaning it will harden into shape on its own (Campbell 187). If all
sockets were to be made out of these composite materials it could easily drive the
cost of a prosthesis down and make them available to more people.

5.0 Manufacturing and Production 18
5.0 MANUFACTURING AND PRODUCTION
The advancement of research on neuroprosthetics has lead to developments on
how the devices are manufactured and produced. Similar to other biomedical
devices and products, the manufacturing processes of neuroprosthetics must
ensure that the parts produced are biocompatible with the patient, cost effective
for the patient and the manufacturer, and time-efficient for the patient and
manufacturer. With these factors in mind, numerous scientists and engineers have
created prototype prosthetic parts experimenting with different manufacturing
techniques.
A specific branch of manufacturing most frequently studied and tested for
neuroprosthetics is additive manufacturing. The general definition for additive
manufacturing is “a system for layered manufacture of parts by the process of
selective solidification of photopolymers” (Mawale 94). Additive manufacturing
encompasses a number of more specific manufacturing processes such as injection
moulding, 3D printing, and selective laser sintering, among others. Since its advent
in 1968, additive manufacturing has dominated the biomedical industry, enabling
the manufacturing of complex biomedical models such as implants or prostheses
(Mawale 95). Because of its ability to produce geometrically complex, low cost,
and time efficient parts, additive manufacturing technology and its sub-
technologies for neuroprosthetics will be the focus of this report.
5.1 PROSTHESIS
The prosthesis, the artificial body part or limb of the neuroprosthetic, is the
largest production piece of a neuroprosthetic. Several case studies and reports
have researched and experimented with different manufacturing technologies,
trying to optimize overall production.
In the early stages of manufacturing, a model for the prosthesis is generated
virtually. Medical image processing based on computed tomography (CT) or
magnetic resonance imaging (MRI) is utilized to know the geometry of the
patient’s prosthesis (Maji 480). The CT and MRI technologies are critical in
determining the exact size and fit for the prosthesis, and ensuring it will be
compatible and symmetrical with the patient’s other limbs and extremities (Leddy
4797). Once these images have been developed, a prosthesis can be designed using
computer-aided design (CAD) programs. CAD software is instrumental to the early
stages of manufacturing because it provides a blueprint for the physical prosthesis.
The CAD model and drawing is engineered to reflect the specific dimensions of the
prosthesis and will dictate the size, shape, and material for the manufacturer.
CAD files can also be easily modified and scaled quite easily, which is particular
useful for fitting a prosthesis (King 59). The prosthesis piece, once manufactured,
will also be tested against the CAD model to ensure the piece is within the
allowable tolerances.

Figure N: “CAD Model of Prosthetic Leg”
Source. Adopted from Leddy, Michael, et al. “Lightweight custom
composite prosthetic components using an additive manufacturing based
molding technique.” Proceedings of the Annual International Conference
of the IEEE Engineering in Medicine and Biology Society (2015): 4797-4802.
Web. 13 May 2016.
When the prosthesis model is deemed suitable for production, a number of
decisions by the manufacturing team must be made. The most important decision
is which manufacturing technique, or how many techniques, will be utilized to
create the prosthesis. As mentioned previously, additive manufacturing is the
primary manufacturing methodology used to create prosthesis. The vast majority
of research on neuroprosthetic production has focused on 3D printing and injection
moulding as the main two additive manufacturing techniques (King 59).
5.1.1 3D Printing
3D printing is a manufacturing technique in which successive layers of material are
formed under computer control to create an object. This technique can produce
objects of almost any shape or geometry, making it a good candidate for
prosthesis production. Whencreating a prosthesis part, 3D printers receive the
instructions from an electronic source, which is usually a CAD file of the prosthesis
model. 3D printing can be used to construct almost CAD model using
thermoplastics such as ABS, PLA, and PET (King 59). The 3D printing method is
simple: “the printer requires the user only to input the thermoplastic filament and
the file to be printed. As long as there is enough filament for the print, the printer
will operate on its own for the duration of the print” (King 60). The method of 3D
printing creates a physical replica of the CAD model, ensuring compatibility with
the specific patient.

Figure O: “3D Printed Prosthetic Hand”
Source. Adopted from Bureau, Scott. “3D Printed Prosthetics
for Those in Need.” Rochester Institute of Technology News,
(2014). Web. May 17 2016.
The advantages and disadvantages of 3D printing must be considered when
deciding on a manufacturing process for neuroprosthetics. 3D printing boasts low-
costs in comparison with other manufacturing methods. For example, 1 kg of PLA
filament, which can produce approximately 5 prosthetic hands, costs only $30
(King 61). In addition to its cost effectiveness, 3D printing also offers easy
customization of fit, due to its dependency on CAD files. The disadvantages of 3D
printing include the prolonged production time and the inconsistent
reproducibility. Completion of a single hand would take between 32 and 54 hours,
which is a not a viable manufacturing time for mass production. 3D printers are
also not yet a stable technology, and “often malfunction or create irreparable,
warped objects” (Leddy 4798). Although it has it downfalls, 3D printing is a strong
option for manufacturing neuroprosthetics, and will become even more promising
with further research and innovations.
5.1.2 Injection Moulding
Injection moulding is a widely popular additive manufacturing method utilized in a
number of industries. This type of additive manufacturing involves pouring layers
of molten material into a mould cavity. In injection moulding, the mould
determines the design and shape of the finished product. Molds are usually made
of steel in high volume production settings, because it is wear resistant and
suitable for producing millions of parts. Injection moulding can host a variety of
materials including metals, glasses, and, most commonly, thermoplastic polymers
(King 62). The mould is formed by using traditional machining techniques, such as
computer numerical controlled (CNC) machining, in which computers control the
movement and operation of mills, lathes, and other cutting machines (Maji 485).
CAD models, or other similar files, can aid in the design of the mould and the fit

with the patient. The size and shape of the finished product is determined by the
design of the mould cavity.
Figure P: “Process of Injection Moulding”
Source. Adopted From Maji, Palash Kumar, et al. “Additive
manufacturing in prosthesis development – a case study.” Rapid
Prototyping Journal, 20.6 (2014): 480-489. Web. 13 May 2016.
Injection moulding also has advantages and disadvantages with regards to the
production of neuroprosthetics. An advantage to injection moulding is that the
time to produce a prosthesis is standardized because this technique has been used
in frequently utilized industry (Leddy 4798). Molten material is forced into the
mould and parts take no longer than 30 seconds to cool (King 62). Another
advantage of injection moulding is that a variety of materials can be used with this
process. This would allow the patient to express a preference in one material over
another for their artificial limb. Injection moulding also has “consistent
repeatability rating”; the process itself is meant for producing thousands of parts
(King 60). However, injection moulding has very high capital costs. A mould itself
can cost anywhere from $500 to $5000, depending on the complexity of the mould
cavity design (Leddy 4789). The machinery and equipment required to perform
injection moulding is even more expensive, which eventually trickles down to the
bottom line cost for the patient. Injection moulding, with its high costs, remains a
good candidate for neuroprosthetic manufacturing because of its reliability and
success in the industry.
5.1.3 Hybrid Models
Due to a variety of manufacturing options for neuroprosthetics, there is not one
optimal process or technique. However a number of hybrid models have been
proposed as the best solution to manufacturing a prosthesis. One model, proposed
a the 5th IEEE Global Humanitarian Technology Conference, suggested combining
3D printing and injection moulding to create a single prosthetic hand. The findings
found that, of the three major components of a prosthesis, the palm is the main
driving factor in ensuring a proper fit and should be 3D printed for maximum
customizability (King 62). The fingers and gauntlet are recommended to be
injection moulded, as a set of standardized sizes can easily cover the range of

wrist dimensions and handbreadths. This method would lead to a “70% reduction in
manufacturing time and a 68% reduction in costs” (King 62).
Figure Q: “Hybrid Prosthetic Hand Model”
Source. Adopted from King, Michael, et al. "Optimization
of prosthetic hand manufacturing." Global Humanitarian
Technology Conference, (2015): 59-65. Web. 10 May
2016.
5.2 SOCKET
A second production piece of a neuroprosthetic is the prosthetic socket. The
socket is an important element of a neuroprosthetic because it “provides the
interface between the prosthesis and residual limb and is necessary for successful
rehabilitation” (Faustini 304). The socket must also deliver comfort, efficient
movement control, and appropriate load transmission for the patient. Attaining
these objectives is extremely challenging, with 55% of lower limb amputees
reporting dissatisfaction with socket comfort, residual limb pain, or skin
breakdown (Faustini 304). Prosthetic sockets and liners can also insulate the
residual limb, causing excessive sweating and concomitant skin maceration, which
“significantly reduces the quality of life of an amputee patient” (Webber 1294).
The prosthetic socket is an essential piece of any neuroprosthetic, and therefore,
its manufacturing and production techniques should be closely examined.
5.2.1. Selective Laser Sintering
Like its prosthesis counterparts, sockets are widely manufactured by means of
additive manufacturing technologies. Selective laser sintering (SLS) is a specific
additive manufacturing technology that fabricates any closed solid model in
sequential cross-sectional layers and has shown to have certain advantages in
socket production. Firstly, SLS can directly create sockets from electronic shape
information, like CAD files, which eliminates the need for moulds and finishing
procedures (Faustini 305). Secondly, SLS has the ability to create complex
geometries with minimal costs in the manufacturing environment. From a design
perspective, this “significantly expands the options for developing and exploring
alternate socket designs, including geometric variants of traditional socket shapes,
and for incorporating compliant features in selected locations to relieve high

contact pressure at the limb–socket interface” (Faustini 305). Thirdly, the
integration of additional prosthetic components and features directly into the
socket is straightforward, due to the additive nature of SLS.
5.2.2 Additional Components
Integration of additional prosthetic socket components can aid tremendously in
amputee patient rehabilitation. A study published in the Journal of Biomechanics
analyzed a prototype prosthetic socket that was modified by incorporating a
helical cooling channel within the socket wall, using additive manufacturing
techniques (Webber 1294). The cooling chamber aims to increase patient comfort
by reducing the excessive sweating prostheses can cause. Figure R below
illustrates the model of the proposed socket.
Figure R: “Prosthetic Socket with Helical Cooling Chamber”
Source: Adopted from Webber, Christina, et al. “Design of a novel
prosthetic socket.” Journal of Biomechanics, 48.7 (2015): 1294-
1299. Web. 15 May 2016.
5.2.3 Socket Alternative
Osseointegration is a mounting method for prosthesis where a patient is givenan
implant that is anchored inside the bone of a stump limb. The process for
mounting requires surgery, but offers a more permanent option to the traditional
socket mounted prosthesis (Hagberg 2). Patients with osseointegrated prosthesis
can experience improvements in comfort, range of motion, and mobility due to
the prosthesis being directly attached to their body (Hagberg 5). Motorized
neuroprosthetics are often used in conjunction with osseointegrated prosthesis to
mimic the actual movements of the limb. Currently the operation is available for
transhumeral, transradial, finger, transfemoral, and transtibial amputations.

Figure S: “Direct Skeletal Osseointegration”
Source. Adopted from Hillock, Ronald. "Direct
Osseointegration." Direct Skeletal Osseointegration,
(2016). Web. 29 May 2016.
The procedure for osseointegration starts with locating the desired bone to which
the prosthesis will be anchored. The skin on the stump is broken and the inside of
the bone is hollowed out and debris is cleared using a bone punch. After the bone
is emptied it is reamed to widenthe inside of the bone to fit the prosthesis. The
fixture is made of platinum, which promotes bone growth, and the inside of the
bone is lined with Platelet Rich Plasma (PRP) to accelerate bone growth around
the fixture (Meta Surgical). The fixture is inserted into the bone and driven into
place against the distal end of bone using a driver. Once the fixture in the desired
position it is locked into place by bone screws. The screws are drilled
perpendicular to each other to prevent movement inside the bone. After the
surgery is complete, a silicon cone protects the wound and the abutment screw is
attached to the end of the abutment. The abutment screw is where the prosthesis
can be attached and detached.
Figure T: “Osseointegration Diagram”
Source. Adopted from Grunewald, Scott J. "Amputees May
Soon Be Implanting 3D Printed Prosthetics Directly Onto
Their Bodies." 3DPrint.com, (2016). Web. 29 May 2016.

6.0 Ethics 26
6.0 ETHICS
As with any medical innovation, the ethics behind the motive and purpose of
device or procedure must be addressed. Neuroprosthetic devices go beyond the
healing of a patient; they provide a newfound sense of identity and a re-
acclimation to normality. They can enable amputees to gain or regain varying
degrees of control of thought and behavior. These direct and indirect interventions
in the brain raise “general ethical questions about weighing the potential benefit
of altering neural circuits against the potential harm from neurophysiological and
psychological sequelae” (Glannon). The main ethical concerns surrounding
neuroprosthetics focus on whether or not these devices can alter neural and
mental functions outside of a person's conscious to a level in which it is uncertain
if the person or device controls his or her behavior. Questions are also raised about
whether the person in whom a neuroprosthetic device is implanted retains a
robust sense of autonomy or free will in voluntarily initiating and executing action
plans. However, thorough analysis and discussion amongst industry leaders has
found that these questions, in turn, should not hinder the research behind these
devices. Rather, they should inform the development of technologies aimed at
achieving a better understanding of the complete functionality of neuroprosthetics
(Glannon). These technologies will restore a greater degree of behavior control for
people with motor and mental limitations, maximizing benefit and minimizing
harm in improving the quality of their lives.

7.0 Conclusion 27
7.0 CONCLUSION
The multidisciplinary aspect of neuroprosthetics is both a blessing and a curse for
patients. While different areas of research can be conducted at the same time,
the gap between neurobiology and mechanics is wide. Only adding to the
conundrum is the brain, an organ we do not fully understand yet. In order to
create a fully versatile, dexterous bionic hand, there needs to be a seamless
connection between brain and machine.
In order to create a proper circuit, researchers have developed intricate systems
of communication. Through either electromyography or electroencephalography,
scientists have invented the potential for amputees to control prostheses with
their mind using electric signals. While this technology is still being perfected, the
progress that has been made in the last 10 years is phenomenal.
Mechanically, the prosthetics field has also progressed. Prosthetics have
transformed from hooks and stationary hands not more than 20 years ago, to fully
operational prosthetics with 15+ degrees of freedom. This was a huge chasm that
is on the verge of being crossed. Researchers have packed actuators, DC motors,
and fully-fledged joints into the palm of a hand. Prosthetics today are only gaining
power and dexterity. They are shedding weight and offering a higher level of
comfort than any of yesterday’s prosthetics.
The key to both the mechanical and electrical progress in prosthetics is in no small
part due to the advancements in materials and manufacturing. The development
of high tech polymers and composites has led to the creation of more lifelike and
functional prosthetics. Advancements in manufacturing techniques, such as 3D
printing, have enabled neuroprosthetics to be produced efficiently and at a lower
cost to the consumer.
Without each of these individual fields working cohesively, the development of
next-generation prosthetics would not be possible. As research continues,
emerging technologies will continue the headway being made. It is with
confidence that we can report that a prosthetic with similar abilities as a healthy
human hand will be available within our generation.

8.0 References 28
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