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8/2/2019 Team 10 Report Final-Version
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2009
Bhavana ShekharSalma Riazi
Shirin Rahmanian
ALL RIGHTS RESERVED
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SAN JOS STATE UNIVERSITY
The Undersigned Project Committee Approves the Masters Project Titled
MECHANICAL PROPERTIES OF CARBON HYBRID BRAIDED STRUCTURE FORLOWER LIMB PROSTHESIS
byBhavana Shekhar
Salma RiaziShirin Rahmanian
APPROVED FOR THE DEPARTMENT OF GENERAL ENGINEERING
Dr. Arthur Diaz, Department of Chemical & Materials Engineering Date
Dr. Richard Chung, Department of Chemical & Materials Engineering Date
Dr. Leonard Wesley, MSE Director, General Engineering Date
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ABSTRACT
MECHANICAL PROPERTIES OF CARBON HYBRID BRAIDED STRUCTURE FORLOWER LIMB PROSTHESIS
by Bhavana ShekharSalma Riazi
Shirin Rahmanian
The aim of this project was to test and evaluate different types of materials for lower limb
prosthesis in order to choose the most appropriate material in terms of performance and
cost. Breakey Prosthetics Inc. has provided the materials chosen for this project, which
include Carbon-Carbon, Spectra-Carbon, and Spectra-Nylon fiber composites. The tests
conducted on these materials consisted of Instron tensile test, hardness test, and SEM
failure analysis. The tensile and hardness results indicate that Carbon-Carbon fibers have
the highest tensile strength and hardness. The SEM results showed that Carbon-Carbon
has poor bonding to the resin, while the Spectra-nylon has the best bonding. Spectra-
Carbon had an average bonding. Economic analysis was also conducted to determine the
viability of this project and justify its completion.
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Acknowledgements
We would like to express our gratitude to Dr. Richard Chung, Professor, Chemical and
Materials Engineering, SJSU, for giving us an opportunity to work with him. This projectwould not have been possible without his support.
We would like to thank Mike Gidding and Chris Pimental of Breakey Prosthetics forsponsoring our project.
We would like to thank Dr. Arthur Diaz, Professor, Chemical and Materials Engineering,SJSU, for his guidance.
We would like to thank Dr. Leonard Wesley, Associate Professor, ComputerEngineering, and Dr. Micheal Jennings, Department Chair, Chemical and Materials
Engineering, for their advice and support.
We are thankful to Jaron Nimori, SEM lab; Neil Peters, Materials lab; and Craig,Machine shop, SJSU for their assistance.
Lastly, we are grateful to our family and friends for their support throughout the project.
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Table of Contents
1.0 Introduction ..................................................................................................................1
2.0 Literature Review ........................................................................................................32.1 Introduction to Literature Review ..............................................................................32.2 Background ................................................................................................................32.3 Pre-amputation and Post-amputation Procedures ......................................................42.4 Components of a Below Knee Prosthesis ..................................................................72.5 Manufacturing Process of Prosthetic Limbs ............................................................102.6 Materials ..................................................................................................................12
2.6.1Historical Development of Composites for Orthopedics ...................................172.6.2 Properties of Spectra .........................................................................................18
2.7 Experimental Methods .............................................................................................19
3.0 Materials and Methods ..............................................................................................203.1 Tensile Testing .........................................................................................................203.2 Hardness Test ...........................................................................................................273.3 SEM Analysis ..........................................................................................................303.4 Discussion of Results ...............................................................................................35
4.0 Economic Justification...............................................................................................37
4.1 Executive Summary .................................................................................................374.2 Problem Statement ...................................................................................................384.3 Solution and Value Proposition ...............................................................................384.4 Market size ...............................................................................................................394.5 Competitors ..............................................................................................................404.6 Customers ................................................................................................................414.7 Cost ..........................................................................................................................42
4.7.1 Fixed Cost .........................................................................................................434.7.2 Variable Cost ....................................................................................................45
4.8 Price Point ................................................................................................................464.9 SWOT Assessment ..................................................................................................464.10 Investment Capital Requirements ..........................................................................47
4.10.1 Norden-Rayleigh Financial Profile .................................................................504.11 Personnel ................................................................................................................534.12 Business and Revenue Model ................................................................................554.13Strategic Alliances and Partners .............................................................................56
4.14 Exit Strategy...........................................................................................................56
5.0 Project Schedule .........................................................................................................58
6.0 Conclusion ..................................................................................................................60
7.0 References.....................................................................................................................61
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List of Figures
Figure 1: Components of transtibial prosthesis
Figure 2: Sample specifications
Figure 3: Stress-Strain curve of Carbon-Carbon sample 1
Figure 4: Stress-Strain curve of Carbon-Carbon sample 2
Figure 5: Stress-Strain curve of Carbon-Carbon sample 3
Figure 6: Stress-Strain curve of Spectra-Carbon sample 1
Figure 7: Stress-Strain curve of Spectra-Carbon sample 2
Figure 8: Stress-Strain curve of Spectra-Carbon sample 3
Figure 9: Stress-Strain curve of Spectra-nylon sample 1
Figure 10: Stress-Strain curve of Spectra-nylon sample 2
Figure 11: Stress-Strain curve of Spectra-nylon sample 3
Figure 12: Box plot for Hardness test Data
Figure 13: SEM images of Carbon samples. (a) Crack area at 50x magnification (b) at
400x magnification (c) at 6000x magnification
Figure 14: SEM images of Spectra-Carbon samples. (a) Crack area at 6000x
magnification (b) at 2400x magnification (c) and (d) at 10000x magnification
Figure 15: SEM images of Spectra-Nylon samples at 3000x magnification (a) top surface
(b) fiber pull-out
Figure 16: Percent concentration of limb prosthesis companies in the U.S.
Figure 17: Profit and Loss chart
Figure 18: Break-even chart
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Figure 19: Cumulative Distribution Function for Norden Rayleigh
Figure 20: Probability Density Function curve for Norden-Rayleigh
Figure 21: ROI Chart
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List of Tables
Table 1: Mechanical properties of some materials used for prosthesis fabrication
Table 2: Comparison of Mechanical Properties of different fibers
Table 3: Mechanical Properties of Carbon-Carbon
Table 4: Mechanical Properties of Spectra-Carbon
Table 5: Mechanical Properties of Spectra-Nylon
Table 6: Hardness test results for Spectra-Nylon, Spectra-Carbon and Carbon composites
Table 7: Major Competitors
Table 8: Fixed Cost Break Down
Table 9: The Variable Cost Break Down
Table 10: Price Point Analysis
Table 11: SWOT analysis
Table 12: Expected Profit and Loss
Table 13: Funding Break Down
Table 14: Cost Drivers
Table 15: Probability density function and Cumulative distribution function for Norden-
Rayleigh
Table 16: Return on Investment for Prosthetics Labs
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1.0INTRODUCTIONThere are about 1.7 million people in the United States alone who have lost at least
one limb. Need to be fitted with a prosthetic limb to enable them to carry out normal
daily activities. Currently, only one type of fiber (for e.g. Carbon fiber) is used in the
fabrication of below knee prosthesis for all different kinds of patients. Athletes for
instance would require stronger sockets than would an average person. Hence different
socket materials can be chosen based on usage.
Although the first prosthetic leg was a wood stump, we have come a long way since
then. Some of the materials used for the fabrication of sockets include: Carbon fibers,
Kevlar fibers, glass fibers, and thermoplastic polymers. We have tested three different
composite materials that are used to make the socket of below-knee prosthesis. The
materials tested are braided carbon fiber, spectra-carbon, and spectra-nylon composites
which were provided by Breakey Prosthetics Inc., San Jose, CA. To characterize and
compare the mechanical properties of these materials, tensile test, hardness test, and
failure analysis were used. The samples were then cut into dog-bone shapes in the SJSU
machine shop to conduct the tests. All of the tests were conducted in SJSU Materials
Engineering laboratories. For the tensile testing, three samples of each
material were tested using the Instron Machine. The Rockwell hardness machine wasused to measure the hardness of the samples. Twenty test values for each composite
were obtained. Finally, for failure analysis, a Scanning Electron Microscope was used to
view the images of the failed samples to discover the cause of failure in each composite.
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To further justify the completion of this project, it is important to economically
evaluate it. The work done in this project can be viewed as a service provided by a small
start-up company offered to limb prosthetic companies to test their materials and also
give them consultations. Prosthetic Labs, Inc., is a Limited Liability Company (LLC)
which provides testing and consulting services specific to prosthetic limb manufacturers.
For tax purposes, Prosthetic Labs files as a sole proprietorship. Prosthetic Labs Inc. will
initially consist of about 9 employees, including technicians to the test, expert analysts,
marketing consultant, and the CEO. What sets this company apart from other material
testing companies is that this company will be the only company that offer tests and
consultation exclusive to limb prosthetic companies and meet tailored needs. The
economical analysis conducted has shown that the market size is large enough for starting
such service and considerable profit can be made in a short period with a relatively low
budget.
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2.0 LITERATURE REVIEW
2.1 Introduction to Literature Review
Prosthetics allow people with limb amputation to resume normal daily activities.
Developments in limb prosthesis have significantly improved over the last few years that
even in patients being able to participate in extreme sports. For instance, in the 2000
Paralympic Games, Sydney, a new world record was set for the 100m sprint for below-
knee amputees at 11.09 seconds (Gutfleisch, 2003). The 2008 record for fit and healthy
athletes was 9.69 seconds. This astounding result was due to the superior performance of
lower limb prosthesis along with the determination and talent of the athlete. This chapter
includes a literature review of materials used in lower limb prosthesis.
2.2 Background
The word prosthesis comes from the Greek word prostithenai which means to
add to. A prosthetic device is an artificial device which mimics the function of a missing
body part. The use of Peg legs, carved out of wood, as early as 3000-1800 B.C. has
been documented in Indian literature (Cochrane, Orsi, & P., 2001). James Potts
constructed The Anglesea leg in 1800. The socket and shank were made of wood; the
knee joint was made of steel, and it had an articulated foot. The shank was attached to a
leather thigh corset with the help of metal hinges and side bars (Bannister, 1978). Even in
the 1940s sockets for below knee prosthesis was made out of either blocks of wood or
leather (Verrall, 1940). The basic design of the prosthetic limb remained unchanged till
1950.
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Research on improving the design of the lower limb prosthesis was going on at the
University of California, Berkeley; and in 1958, they made their design public. It was
called Patellar Tendon Bearing (PTB) prosthesis. The socket was made of plastic and
lined with rubber and soft leather. The hollow wooden shank was reinforced with a
plastic laminate, and the articulated foot was replaced with a rubber solid ankle cushion
heel (SACH) foot. Leather straps were used above the patella to provide suspension.
Though it had a huge advantage of being much lighter than the older version and fit
properly to the residual limb; the drawback limited knee flexion, skin abrasions, and
dermatitis. In 1964, the PTB prosthesis was further modified such that the sides of the
socket extended beyond the femoral condyles. The liner was built-in with one or two
wedges to provide suspension. This design was called the PTS (patellar tendon
supracondylar) prosthesis (Bannister, 1978). The Botta prosthesis was an adaptation of
the PTS prosthesis. The socket was light in weight and was fabricated with polyester or
other synthetic resin strengthened with carbon fiber (Marquardt & J., 1984).
2.3 Pre-Amputation and Post Amputation Procedures
Some amputations of the lower limb, which are due to some diseases, can be
predicted. In this preamputation phase, before the surgery, the patients will attend certain
meetings to learn about how this surgery will affect their lives and how to deal with it.
They will also get emotional support by meeting with an amputee in the same situation as
they are. Providing information to individuals might also prevent some traumatic and
nontraumatic amputations. For example, an amputation care facility program held by the
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Department of Veterans Affairs, has decreased the number of non-traumatic amputations
by forty percent each year (Pasquina, Bryant, et al. 2006).
Different surgical techniques must be used for each amputee. Using a general
technique will not work for all individuals. In order to attach the remaining muscles two
different techniques are used which are called myodesis, and myoplasty. In myoplasty the
opposite muscles of the amputated limb are sewn to each other, whereas in myodesis the
muscles are attached to the periosteum of the amputated bone (Pasquina, Bryant, et al.
2006).
After the surgery is done, there are certain issues to have in mind and precautions to
take. The amputated part has to be taken care of properly, in order to be able to attach the
prosthetic to it without encountering any problems in the future. The cut limb has to
undergo a skin desensitization program which involves massaging the severed section of
the limb. This is done to heal the scar and not let it adhere to the bone underneath. Also,
edema should be prevented by using a residual limb stump. The cut end of the limb is
then introduced to increasing amounts of pressure so that it adapts to the forces that it will
undergo after the prosthetic is placed and utilized (Kelly, Spires and Restrepo, 2007).
A study done by Moore, Hall et al., has proved the advantages of immediate
postoperative techniques which has been done about 30 days after the amputation, in
comparison to a later post operative action. The advantages include a quicker
rehabilitation, lower number in mortality and healing rate. Therefore, the time from the
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amputation to the fitting of the prosthesis is critical and can affect the procedure directly
(Moore, Hall, et al. 1972).
For a prosthetic surgery to be successful and make it as comfortable as possible to
the recipient of the prosthetic limb many factors must be considered. Some of these
include proper diagnosis, to begin with, the patients weight and other physical
characteristics, and also their activity level (Kelly, Spires and Restrepo, 2007).
It should also be noted that for children extra consideration must be taken because
they are constantly growing. This is why adjustments to the prosthesis must be made
more regularly than those of adults (Pasquina, Bryant, et al. 2006). On average the life
expectancy of the prosthetic devices is approximately three to five years depending on
the patients physical activity, and the materials with which the prosthetics are made of.
Also, the location where the socket of the prosthesis and the limb are in contact with each
other is of great importance. The socket must not cause any damage, irritation, or allergic
reactions to the skin, since the skin at the severed end of the limb is very sensitive. The
most important issue which has to be considered is the amputated tissues response to the
applied load, after the prosthesis has been placed. Depending on the individual and their
body type the tissue will get more susceptible to pain after the amputation (Kelly, Spires
and Restrepo, 2007). Other than pain, some temperature changes might be observed in
the area which load is more. When the tissue undergoes an amount of load, due to
decrease in blood circulation, the temperature of the tissue will drop. After unloading the
tissue however, the temperature will rise (Mak, Zhang & Boone, 2001). The skin in the
contacting region of the prosthesis and the tissue might get abraded as a result of rubbing
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against the device. This might lead to some skin problems, such as skin thickening and
blisters (Mak, Zhang & Boone, 2001).
2.4 Components of a Below Knee Prosthesis
Socket
Socket Adapter
Tube Clamp AdapterPylon
Endoskeletal finish
Ankle
Foot
Figure 1. Components of transtibial prosthesisSource: Below Knee (Transtibial) Prosthesis. (n.d.). Retrieved March 12, 2009, from ProstheticConcepts Web site: http://www.prostheticconcepts.ca/belowknee.pdf
The components of a transtibial prosthesis are shown in Figure 1. The main components
of the prosthesis include:
1. The Socket connects the amputated limb to the prosthesis. It transfers the bodyweight to the prosthesis and may contain liners that act like padding. It protects the
amputated limb and enables the user to stand, walk, and move freely. Mostly in
transtibial amputation, patellar-tendon bearing socket (PTB) is used (Carroll, 2006,
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Kelly et al. 2007). Before this socket was introduced, some open-ended plug-fit
sockets were used which had some disadvantages such as skin irritation and chronic
choke syndromes (Kelly, Spires and Restrepo, 2007).
However, the socket fit and comfort depends on the individual and has to be chosen
by them and the help of the prosthetist. Some common sockets are: PTB, Total-
surface bearing (TSB), PTB-supracondylar, and joint and corset (Kelly, Spires and
Restrepo, 2007). All these sockets have their own pros and cons due to their
mechanism of load bearing, pressure transmission to the amputated area, and comfort.
As technology advances, recent and more applicable materials are being introduced
for this purpose. Sockets are now being manufactured with computer-aided designs
and are custom fitted for the patients. Some carbon graphite sockets that are now
being used are light weight and last longer. The linings of these sockets are also more
flexible and comfortable. By being custom made, the socket manufacturing will not
only be cheaper, it will also save time and accelerate the delivery time to patients
(Carroll, 2006).
2. The Anklejoins the foot and prosthesis. This part is made of some joints which allowaxial rotation. This part should also be capable of energy storing and absorption
(Kelly, Spires and Restrepo, 2007). The ankle is made from different material
depending on its use and the socket its connecting to. There are ankle joints made of
wood with a laminated outer shell. Some other ankle joints are made out of metal,
plastic or carbon fiber. There are different types of prosthetic ankles with different
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movement axes. A study done by Rita, Mason, et al. has shown that these ankles
show different results in shock absorption. Although it has to be taken into
consideration that stride length, age, weight and some other factors are involved as
well (Witra, Mason, et al. 1991).
It is common for this part to be available together with the socket; however, it is also
available separately for use in sports and heavy physical activity (Kelly, Spires and
Restrepo, 2007).
3. The Foot acts as a base support. Not only this part must be able to bear all the weightacted on it, it must also transfer the body weight to ground, act as a shock absorber,
and replace lost muscle function and biomechanics of the foot ( Kelly, Spires and
Restrepo, 2007). It must also provide cosmetic appearance and should fit in normal
shoes.The recent artificial feet are now being made to reproduce a healthy foots
function. They have energy absorption mechanism in multiple planes, as well as
being able to absorb vertical and torsional shocks which are acted upon them ( Kelly,
Spires and Restrepo, 2007).
4. Suspension systems are used to hold the prosthesis on the body (Below KneeProsthesis). The socket must have some suspension mechanism in order to not to fall
off. Different mechanisms are used for this purpose such as suction, harness, belt, and
gel suspension. A combination of them is also available (Moore, Hall, & Lim, 1972).
By using a gel elastomer, the gel suspension system provides cushioning to the
residual limb. It also provides an acceptable cosmesis to the amputee. Using a thin gel
can improve the sense of propioception in the patients, allowing them to function
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better in their activities (Carroll, 2006). Another common suspension system is using
sleeves. Sleeves have their own drawbacks, since the material can get punctured
easily; it has to be replaced quite often. They can also have ventilation problems as
well as getting hot in warm and humid regions (Carroll, 2006). This problem
however, has recently been solved by putting a valve on the sleeve to provide air
transfer.
The transtibial prosthesis is also comprised of some other components which are
mainly used for connecting the major parts to each other. They consist of a socket
adaptor which connects the socket to the rest of the prosthesis and aligns the
prosthesis; a tube clamp adaptor, which is used to connect the pipe to the socket; a
pylon, which is used to transfer the body weight and should be adjusted to achieve
proper height of the prosthetic; and finally an endoskeletal finish which envelopes the
whole prosthesis and hence protects the internal parts from dust, dirt, and moisture
(Osbourne, 2009).
2.5 Manufacturing Process of Prosthetic Limbs
After amputation, a medical doctor has to prescribe prosthesis to the patient. This
device cannot be bought in stores and is not mass produced. Following the prescription,
the patient must consult with the prosthetist and physical therapist in order to choose the
best prosthesis for his use. Some parts of the prosthesis are manufactured in factories, and
some other parts like the socket, can be custom made for each patient.
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The procedure starts with the prosthetist studying the amputees residual limb, taking
an impression of it and measuring some body segments of the patient. The impression
and the measurements are used to make a plaster cast of the stump, which is then used to
make the stump itself. Afterwards, a clear sheet of heated thermoplastic is placed onto the
mold and put into a vacuum chamber. When the air is taken out of the chamber the
thermoplastic sheet smoothly presses against the mold taking its shape without having
any air bubbles trapped between the sheet and the mold. The product of this process is the
test socket. The reason why it is clear is so that it will be easier for the prosthetist to
check the fit of the prosthesis.
The penultimate process involves the prosthetist to check and confirm that the test
socket that was just constructed properly fits the patient. After the patient puts it on he or
she walks while the prosthetist analyzes the gait. Adjustments are made both in response
to the appearance of the gait and the comfort of the patient. Only after this is done and
both patient and prosthetist are satisfied do they move on to the final procedure. Finally,
the permanent socket is formed usually using polypropylene, again, using vacuum
forming as the production or shaping process. Over time, if any anatomical changes occur
to the appendage changes to the prosthesis are made accordingly.
The manufacture of prosthetic limbs involves a wide variety of materials and
methods. Many are made using different types of plastics which are formed using
vacuum-forming, extruding, or injection molding. Those that are made of metallic
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components usually use titanium and aluminum parts which are die cast and then finished
by drilling, sanding, polishing, and other finalizing processes.
After the different parts and components that make up the prosthesis are
manufactured the assembly is done by the prosthetist technician using various tools such
as wrenches, screwdrivers and other such hand or power tools. The patient is fitted with
the assembled by the prosthetist. (Stacey, Blachford, & Cengage, 2002)
2.6 Materials
Metal, leather, and wood were used as prosthetic materials before mid 19th century.
Lower limb prostheses made before 1984 were rigid and were manufactured from metal,
leather, or plastic laminate with a foam toe filler (Lange, 1992). Although these devices
did not restore function lost by amputation, they maintained rollover in the toe section.
Since these devices were rigid, a lot of effort was put in to make partially rigid devices
which integrated foam toe fillers with clear and flesh-tone plastics that were flexible.
Cosmesis was an issue although the function and fit was satisfactory.
During 1984-1986, thermoplastics were used to fabricate custom prosthetic sockets.
Flexible Surlyn below-knee (BK) sockets which were supported within semi-rigid
polypropylene socket retainers were made at the University of Virginia Medical Center
(Schuch, 1991). Polyethylene was used to make flexible sockets, and polypropylene was
used for making socket retainers. The advantages of prosthetic sockets made of
thermoplastics were flexibility, light weight, quick and simple fabrication (Schuch,
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1991). The drawback of this material was that it was not durable, i.e., it would split or
tear. Also, thermoplastics shrink and this would loosen the fit.
Shrinkage of the material was found to be greatest, if it was stretched at the time of
fabrication. Hence, it must be carefully draped and vacuum-formed rapidly to optimize
the results (Rothschild, Fox, Michael, Rothschild, & Playfair, 1991).
Next, laminated silicone sockets were attached to hollow foot shells with silicone
sealant (Lange, 1992). To improve cosmesis, another layer of lamination was put above
the socket and the foot shell to join them permanently and a zipper was used at the back
of the socket (Lange, 1992).
Langes silicone partial foot prosthesis had two laminations and incorporated the
foot shell between the two. The result was that the foot shell was permanently bound to
the socket thereby producing an elastic, resistive toe lever. The hollow toe in the foot
shell was filled with room temperature vulcanized (RTV) foam to attain more natural
ankle motion (Lange, 1992). This design also had a zipper closure behind the socket.
Instead of adding pigments to the silicone, a nylon stockinette matching the skin tone of
the patient was coated on the foot shell to provide better cosmesis (Lange, 1992).
Fiber reinforced plastics are laminated composites made by applying resin to one or
more layers of fibers. The material properties of the resin and the fiber, the extent of
bonding between the two and the resulting structural architecture determines the
strength of the laminate (Phillips & Craelius, 2005). The tensile and flexural strengths of
the fiber reinforced plastics were found to be high along the fiber axis. From Table 1, it
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can be noted that the Youngs modulus of nylon fiber is slightly lesser than that of the
SPT (SPT Technology, Inc., Minneapolis) resin.
Although the nylon fibers are supposed to increase the strength since they are the
reinforcing materials, they do not do so because of their low modulus of elasticity when
compared to that of the resin (Phillips & Craelius, 2005). Hence it is important to choose
a fiber whose modulus of elasticity is greater than that of the resin else the material
properties will be completely controlled by the resin.
Table 1Mechanical properties of some materials used for prosthesis fabrication
Source: Phillips, S. L., & Craelius, W. (2005). Material Properties of Selected ProstheticLaminates.Journal of Prosthetics & Orthotics , 27-32.
While glass and carbon fibers have high strengths, the main drawback is that they
are brittle; during post-fabrication modification, instead of stretching, they break (Phillips
& Craelius, 2005).
A strut was designed by Madden using Kevlar-49, carbon, and S-2 glass fibers.
Carbon fiber was used to make the inner core, Kevlar-49 was used to fabricate the outer
layer, and S-2 glass was used in the middle layer. The S-2 glass acts as a transition layer
for the stress changes which is an intrinsic to the strut design. Carbon fibers and Kevlar-
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49 are comparatively weak under tensile and compressive loads respectively, S-2 glass
acts as a balance between the two, facilitating stress transfer between the layers. This
design has been used successfully for fabricating rigid frames for flexible socket
systems in prosthetics (Madden, 1991).
As discussed previously the initial material made of wood and metals for artificial
legs had major drawbacks, since they were limited by their weight, and had poor
durability to corrosion and moisture induced swelling (Ramakrishna et al., 2001). These
limitations resulted in restricting the user to slow and non-strenuous activities due to poor
elastic response during stance (Ramakrishna et al., 2001).
Due to these limitations, polymer composites were introduced for material of choice
for limb systems, because of their lightweight, corrosion resistance, fatigue resistance,
aesthetics, and ease of fabrication (Ramakrishna et al., 2001). Polymer composites can
be either thermosetting or thermoplastics composites that are reinforced with glass,
carbon, or Kevlar fibers (Ramakrishna et al., 2001).
Thermoplastic polymers have the advantage of having strong intermolecular bonds
that result in good biocompatibility and resistance to moisture damage (Evans, &
Gregson, 1998). Polyetheretherketone (PEEK), polyaryletherketone (PAEK),
polyethylene, and polysulfone have been widely used for orthopedic use (Evans, &
Gregson, 1998). While these materials have excellent biocompatibility and good
durability in the physiological environment, they are difficult in fabrication of long fiber-
reinforced composites, and thus difficult for prosthetics with sufficient strength for
highly loaded applications (Evans, & Gregson, 1998).
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Thermosetting polymers such as epoxy resins have not been so common in
orthopedics because of variable biocompatibility and durability characteristics (Evans, &
Gregson, 1998). However studies have shown that properly processed and selected epoxy
resins can have excellent biocompatibility, and these materials can have much better
processing characteristics than the thermoplastics, allowing the fabrication of more
sophisticated composite structures (Evans, & Gregson, 1998).
During the past 10 years the most notable reinforcing materials for orthopedic use
have been carbon fibers (Evans, & Gregson, 1998). Especially for lower limb prosthesis
carbon composite lay-ups are very popular (Strike & Hillery, 2000). These composites
are chosen or their flexibility and energy storage and release properties (Strike & Hillery,
2000). The fibers can be fabricated in different ways such as being braided, woven,
knitted, or laminated. According to a lower limb design by Strike & Hillery, the
lamination would allow them to have specific tensile strength and stiffness by changing
the resin and controlling the angles between successive layers (Strike & Hillery, 2000).
There are also other reinforcing materials that have been used for prosthetic use.
One of the most recent ones are Aramid fibers such as Kevlar, which have excellent
tensile properties (Evans, & Gregson, 1998). However, these fibers have poor
compressive strength and stiffness and thus have limitation during bending loads (Evans,
& Gregson, 1998).
Morever, according to Ramakrishna et al., the sockets currently in the market, are
made using a combination of knitted or braided carbon or glass fiber fabrics and water-
curable (water-activated) resins (Ramakrishna et al., 2001). The braided fabric
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reinforced sockets have the advantage of being stiff and strong, whereas the knitted fabric
reinforced sockets have the advantage of being flexible and more conformable to the
patient's stump (Ramakrishna et al., 2001).
2.6.1 Historical Development of Composites for Orthopedics
While composites have been used throughout history, the emergence of composite
materials as we know today is fairly recent, becoming most popular during the early
1950s due to extensive research done in aerospace industry. Development of fiberglass
in the 1930s has led to using these materials as reinforcement for polymers, and thus
improving composite technology (Erwin, 1947). As it has previously referred to, polymer
composites can be reinforced with glass, carbon, or Kevlar fibers (Ramakrishna et al.,
2001).
Major breakthrough in the composite development was the use of reinforcing fibers.
In 1961, the first carbon fiber was produced by Shindo et al. (Shindo, 1969). Carbon
fibers have the advantage of having a low density, high elastic modulus, and high tensile
strength. Also, due to their high specific strength and good fatigue resistance (when used
as a reinforcing polymer) makes them a good candidate for orthopedic use (Pigott &
Harris, 1980). The major drawbacks of carbon reinforced thermosetting composites are
their brittleness yielding low fracture toughness and poor impact resistance.
The next major emergence of reinforcing fibers in composite development was the
production of Kevlar by DuPont in 1971. Thermoset resins that are reinforced by Kevlar
fibers display high fracture toughness and good resistance to tensile loading (Pigott &
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Harris, 1980). However they have the disadvantage of being weak under compression and
they are also hard to fabricate because they are difficult to shape, cut, and saturate with
resins (Berry, 1987)
2.6.2 Properties of Spectra
Spectra fiber is a polyethylene fiber that is produced from a gel-spinning process
by Honeywell, Inc. (Honeywell). Spectra Fibers are available in three different series:
Spectra 900, Spectra 1000, and Spectra 2000. Spectra fibers have tensile strength that is
higher than aramid fibers at temperatures below ~ 1000
C and above this temperature their
tensile strength will decrease (Lewin, Sello, & Preston, 1996). Spectra fibers can
withstand twisting without losing their strength. These fibers also have very good
abrasion resistance, can creep well under static load, and have a good impact resistance,
when compared to aramids. The mechanical properties of Spectra fibers are shown in
Table 2 and are compared to other composite materials (Lewin, Sello, & Preston, 1996).
Table 2Comparison of Mechanical Properties of different fibers
Source: Lewin, M., Sello, S. B., & Preston, J. (1996).Handbook of fiber science andtechnology (Vol. III). New York: Marcel Dekker, Inc.
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2.7 Experimental Methods
Samples of braided carbon fiber, spectra-nylon, and spectra-carbon have been
provided by Breakey Prosthetics. At least three tensile (dog bone shape) samples of these
fiber composites will be made for mechanical testing. The dimension of the samples will
be as shown in Figure 2. The samples will be tested for their tensile strength, hardness
and bending. Fractured samples will be analyzed using a Scanning Electron Microscope.
The results will be compared to the values required by ISO standards to see if they meet
the minimum requirements.
Figure 2. Sample specificationsSource: (2008). Quality and testing. In B. A. Strong, Fundamentals of CompositesManufacturing: Materials, Methods and Application (p. 277). SME.
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3.0 MATERIALS &METHODS
3.1 Tensile Testing
Tensile test is a mechanical test in which a machine is used to deform a specimen
under gradually increasing tension load. Tension test can be used to plot a stress-strain
curve and several mechanical properties can be obtained from this curve. Some of the
most important mechanical properties that can be obtained from the stress-strain curve
include yield strength, modulus of elasticity (Youngs modulus), ultimate tensile strength,
ductility, and toughness.
The yield strength measure the stress level at which a material starts to plastically
deform. This means that up to yield strength, the material can return to its original length
after deformation. Beyond yield strength, the material will undergo plastic deformation,
in which the deformation is permanent. During elastic deformation (before reaching
yield strength), stress and strain are proportional to each other. This relationship is known
as Hooks law and the constant of proportionality is called Youngs modulus, or modulus
of elasticity. The modulus can be obtained by measuring the slope of linear portion of a
stress-strain curve. The greater the modulus, the more brittle the material is, meaning it
will go under less strain before yielding.
Another important mechanical property is the tensile strength (UTS), which is the
maximum strength in the stress-strain curve. UTS corresponds to the strain that a material
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can sustain under tension. If such stress is applied and maintained, the material will start
to non-uniformly deform and fracture will occur.
Ductility and toughness are another mechanical properties that can be obtained
from the stress-strain curve. Ductility is a measure of the amount of plastic deformation
at fracture. It can be expressed as percent elongation or percent of reduction in area the
fracture. Toughness is a measure of the ability of the material to sustain energy up to the
fracture point. Toughness can be measured by calculating the entire area under the stress-
strain curve.
Tensile test was conducted on the three different types of composite samples
under study, which were carbon-carbon, Spectra-carbon, and Spectra-nylon. The tensile
done test was done using the Instron machine on dog-bone shaped sample. For each
material several tensile tests were conducted and the three most consist results were
selected for each type of material for analysis. The strain rate used for all the samples
was 8.0 mm/min.
The stress-strain curves of the samples are shown in Figures 3-11. Figures 3, 4
and 5 show the stress-strain curve of three different carbon-carbon samples. Figures 6, 7
and 8 show the stress-strain curve of three different spectra-carbon samples. Similarly,
Figures 9, 10 and 11 show the stress-strain curve of three different spectra-nylon samples.
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Figure 3. Stress-Strain curve of Carbon-Carbon sample 1.
Figure 4. Stress-Strain curve of Carbon-Carbon sample 2.
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Figure 5. Stress-Strain curve of Carbon-Carbon sample 3.
Figure 6. Stress-Strain curve of Spectra-Carbon sample 1.
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Figure 7. Stress-Strain curve of Spectra-Carbon sample 2.
Figure 8. Stress-Strain curve of Spectra-Carbon sample 3.
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Figure 9. Stress-Strain curve of Spectra-nylon sample 1.
Figure 10. Stress-Strain curve of Spectra-nylon sample 2.
Figure 11. Stress-Strain curve of Spectra-nylon sample 3.
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From above curves the important mechanical properties were calculated,
including yield strength, yield strain, tensile strength (UTS), ductility, strain at failure, E
modulus, and toughness. Tables 3, 4, and 5 show the results of these measurements along
with mean and standard deviation of each property for carbon-carbon, Spectra-carbon,
and Spectra-nylon respectively.
Table 3Tensile Properties of Carbon-Carbon composites
Table 4Tensile Properties of Spectra-Carbon Composites
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Table 5Tensile Properties of Spectra-Nylon Composites
3.2 Hardness Test
Hardness is the ability of a material to resist plastic deformation. The Rockwell
hardness tester uses an indenter to press against the surface of the material under study.
There is a minor load (10 grams) which constantly presses on the indenter; a major load
will be applied to the material gradually until equilibrium has been reached. Then the
major load will be removed and some of the penetration it caused will recover. At this
point the residual penetration is measured which is the hardness. The three studiedsamples, which were Spectra-Nylon, Spectra-Carbon, and Carbon composites were tested
for their hardness. The hardness test was done using a Rockwell machine on an M scale
with minor load being 10 kgf and the major load 100 kgf.
As Table 6 shows, the hardness of spectra-nylon and spectra carbon are very
similar, being tenths different, whereas Carbons hardness is twice as much as the other
two. This result shows that carbon can withstand plastic deformation much more than the
other two samples. Therefore in case of hardness and plastic deformation, carbon would
be the most suitable for lower limb prostheses application. Evidently lower limb
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prostheses are constantly under load during the time they are being used, therefore it is
crucial that they do not fail and deform plastically. From the Box-Whisker plot, we can
see that the hardness value of 75.6 in Carbon sample is an outlier.
Table 6Hardness test results for Spectra-Nylon, Spectra-Carbon and Carbon composites
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Figure 12. Box plot for Hardness test Data
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3.3 SEM Analysis
A Scanning Electron Microscopic analysis on the tensile test samples were done
in the SEM lab at San Jose State University. The samples were placed in a low vacuum,
slightly humid environment inside the SEM. The fractured area was at the (0, 0) co-
ordinates of the mount so as to focus on the crack area. Figure 13 shows the SEM
pictures of the carbon fiber samples at different magnifications. Figure 13(c) shows that
the fiber surface at the crack is smooth which indicates that the bonding between the resin
and fibers is poor. We can conclude that the resin broke first which was followed by fiber
pullout.
Fiber pullout
(a)
(b)
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(c)
Figure 13. SEM images of Carbon-Carbon samples. (a) Crack area at 50x magnification(b) at 400x magnification (c) at 6000x magnification
Figure 14 are SEM images of Spectra-Carbon samples. Figure 14(a) indicates that
the failure mechanism was de-lamination. It can be seen in Figures 14(b) and 14(c) that
the resin is still attached to the fiber. Figure 14(d) shows the breakage of resin. Theseimages indicate that although the bonding between resin and fibers in the Spectra-Carbon
samples were poor, it was better than in Carbon fibers. Since Spectra-Carbon is a hybrid
of polyethylene (spectra) and carbon fibers, it is difficult to tell which of these fibers
caused this failure mode. An Energy Dispersive X-ray analysis could be done to
differentiate between the fibers by identifying their composition.
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(a)
Fiber
Matrix
(b)
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(c)
Resinbreakage
(d)Figure 14. SEM images of Spectra-Carbon samples. (a) Crack area at 6000xmagnification (b) at 2400x magnification (c) and (d) at 10000x magnification
Figure 15 shows SEM images related to Spectra-Nylon samples. Figure 15(a)
shows the resin crack and 15(b) shows the fiber breakage. The fiber has good adhesion
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with the resin but they are not strong enough. As such, the fiber was pulled out with resin
still attached to it.
Cracks in the
(a)
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Resin
Fiber
(b)Figure 15. SEM images of Spectra-Nylon samples at 3000x magnification (a) top surface
(b) fiber pull-out
3.4 Discussion of Results
The hardness and tensile tests were done in accordance to ASTM D 3039 standard. The
results of the tensile test show that the tensile strength of carbon samples to be in the
range of 83-89 MPa spectra-carbon - 27 to 36 MPa, and spectra-nylon to be in the range
of 28 to 30 MPa. According to the literature review, the tensile strength of Carbon
fiber/Epoxy resin composite was 76.8 MPa, while that of spectralon, which is a hybrid of
spectra and nylon, was 25MPa. The findings of this project are close to those in the
literature review. The ultimate tensile strength (UTS) of cortical bone is between 80 and
115 MPa (Mechanical Properties of Bone). The mean UTS of carbon sample is 92 MPa,
which is in the range of that of the cortical bone. From stress-strain curves of spectra-
carbon, and spectra-nylon, it can be seen that the UTS is very close to the point of
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fracture. This indicates that the samples are very brittle. The fact that Spectra containing
composites have no yielding and the Carbon-Carbon does have plastic deformation can
be due to the bonding strength of resin. That is the Carbon-Carbon sample continues to
plastically deform after yield strength because the resin is no longer bound to the carbon
fiber while the Carbon fibers by themselves have not failed completely. On the other
hand, Spectra-Carbon and Spectra-Nylon had good bonding with resins, therefore making
them brittle and failing without plastic deformation.
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4.0ECONOMIC JUSTIFICATION
4.1 Executive Summary
Limb prosthetics need to have certain mechanical properties to perform well and
meet different requirements and regulations. Prosthetic companies need to test their
material to optimize the performance and cost. Prosthetic Labs offers material testing and
consulting services to prosthetic limb manufacturers in order to evaluate their materials.
What sets Prosthetics Labs apart from other material testing companies is that the
services are exclusive to limb prosthetic companies. Hence, the customers can get
specialized and tailored tastings from experts in their field to choose the best and
cheapest material.
The prosthetic market was about 1.45 billion in 2006, with an estimated growth
rate of 3.9 %, which makes the testing market potentially lucrative. With more than 500
limb prosthetic companies in the U.S, the current market for material testing of these
companies is estimated to be $3,500,000. The goal of Prosthetics Lab is to gain 30% of
the market share amounting to $1,050,000. The main competitors in this market are
testing companies that offer services to a wide variety of industries, therefore being
exclusive to limb prosthetics, Prosthetic Labs has a major competitive advantage.
However, the major weakness is the limited number of potential customers.
The average price point of the different services is $7000, which was calculated
from number of test and the costs incurred. The company will start in year 2010 with an
estimated budget required is $415,816. The company will break even in the second
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quarter of 2012. The required capital will be funded from bank loans, family and friends
contribution, and venture capitals. These investments will be returned starting from 2013.
Prosthetics Labs will offer its service by using web cataloguing. The revenue will
be generated through customer referrals and advertisement in biomedical journals and
magazines. Also, advertisement space will be sold in the companys website to material
manufactures for prosthetics.
4.2 Problem Statement
In 2007, there were nearly 185,000 amputees in the United States. Due to the
large number of amputees, the prosthetic limb market is quite large. In order for the
prostheses to perform well and not fail, their material must be tested for its mechanical
properties and failure. Therefore Prosthetics Labs is offering its services to test these
materials for this purpose. The customers of Prosthetics Labs are companies which are
manufacturers of prosthetic limbs. These manufacturing companies also need
consultation in order to reduce their material cost. Also, FDA requires the prostheses
limbs to possess certain qualities for safety and efficacy.
4.3 Solution and Value Proposition
Prosthetic Labs is the only company which offers testing and consulting services
exclusive to prosthetic limb market. Working with only prosthetic limbs, makes
Prosthetic Labs an expert in this field. The company offers material selection and tailored
tests for the customers. Other companies offering testing are not aimed at prostheses.
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They offer a wide range of device testing in the biomedical field, which makes them not
as specialized as Prosthetic Labs in prostheses area.
Consulting services offered by this company will result in choosing the best and
cheapest material which has the required properties for its use. The prostheses
manufacturing companies often use unnecessary amount of expensive materials in order
to improve the performance of the prosthesis. Also, there are different prostheses for
various uses; prostheses for athletes must be much stronger and much more flexible than
prostheses for the elderly. Therefore a consulting service is required to understand these
differences and make changes to the material amount to save cost and improve
performance.
4.4 Market Size
According to a study by Frost & Sullivan, the U.S. market for prosthetics was
about $1.45 billion in 2006, and this value is estimated to reach $1.85 billion by 2013
(Prosthetics Market Growing, 2007). Based on Frost & Sullivan study the average annual
growth rate will be 3.9 % which equates to annual revenue of $56.5 million. This means
that the estimated revenue of $1,135,000 will be 2.38 % of the total market growth. This
is important because the growth rate of Prosthetics Labs completely depends on the
prostheses market. Hence, there is a great potential in the prosthetics industry which
creates a good opportunity for Prosthetics Lab Company.
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To calculate the market size for limb prosthesis testing services, the number of
limb prostheses manufacturing companies needs to be found. . There are about 500 limb
prosthesis companies in the U.S. Some of the companies in the United States that
manufacture limb prostheses are: Ossur, Becker Orthopedic Appliance Company, Hanger
Orthopedic Group Inc (Prosthetics and Orthotics, 2009).
The entire market size of material testing and consulting for prosthesis companies
can be estimated by multiplying the number of all potential customers by the average
service charge of $7000. Therefore, the estimated current market size is $3,500,000. The
goal of Prosthetics Lab is to attract 150 customers or more of these possible 500
companies by year 2013. This means that Prosthetics Lab will gain 30% of the prosthetic
limb testing market share which amounts to $1,050,000.
4.5 Competitors
Table 7 shows the major competitors for Prosthetic Labs including their annual
revenue, geographic location and the industries they serve. As it can be seen in Table 7,
most of these competitors serve wide variety of industries and located throughout the
country and worldwide. The companies that only serve Medical Device have much
smaller revenues. Furthermore, there are no competitors that are exclusive to prosthesis
companies, thus most of the competitors will be large corporate companies.
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Table 7Major Competitors
4.6 Customers
The customers for Prosthetics labs are the companies that manufacture limb
prosthesis. The principal manufacturing or R&D engineers of these companies will be the
targets for sale.
There are currently about 500 limb prosthesis companies located in the United
States. The population distribution of these companies is show in Figure 16. The states
with highest percentage of the potential customers are New York, Ohio, Florida,
Pennsylvania, and California, each having 6-7.5 % of the prosthetic companies. Since
Florida has one of the highest potential customer bases, and corporate income is not
taxable in Florida for a single-member LLC, Prosthetic Labs will be located in
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Florida.
Figure 16. Percent concentration of limb prosthesis companies in the U.S.
4.7 Cost
The cost for starting the company and providing the services for the years 2010-
2011 can be broken down into two different categories. These costs include fixed cost
and variable cost which will be discussed in detail in this section.
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4.7.1 Fixed Cost
Fixed cost is the cost needed to provide the service that does not change with the
amount of service. The fixed cost break down of Prosthetics Labs Inc. is shown in Table
8 for two years. The fixed cost of the company includes:
Startup Cost, which is the initial cost needed to set up the office including thebusiness license fees, lease deposit, rent, furniture, computers, printers, fax machine,
and etc.
Office rent Stationary, telephone and internet services, website, insurance Equipment rental, which includes Instron tensile test machine, SEM machine,
Rockwell hardness test machine, and three point bending test.
Salaries, which include salaries of seven permanent employees. The three of the
employees including the CEO, the senior consultant and the senior analyst have been
assumed to work for free for the first three months. They will start getting paid from
the first quarter, although with no benefits until the end of the first year. From the
other four employees, two of them are testing technicians. The first year only one
testing technician will be hired; however from the beginning of the second year
another testing technician will be added. SEM analyst is another employee who will
be working part-time for the first year, and full time in the second year. The last
employee would be the janitor, working 10 hours a week. Benefits have also been
included in the salaries for the full time employees in the cost break down.
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Since Prosthetics Labs Inc. only provides research and consulting services, there are no
manufacturing and material costs. There will also be no patent and intellectual property
costs.
Table 8Fixed Cost Break Down
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4.7.2 Variable Cost
The variable costs of Prosthetics Labs include the costs which are for hiring
contract professionals and advertising. The two contract employees are one marketing
analyst and another scientific analyst. Due to the low number of customers in the first
quarters, the scientific analyst is only needed a few hours a week. However, as the
company progresses and attracts more customers, the scientific analyst will be hired for
longer hours per week.
As oppose to the scientific analyst, the marketing analyst will be needed more in
the initial quarters. As the company grows and settles, the need for marketing as well as
advertising will decrease. Other variable costs are incurred by packaging, shipping,
equipment calibration and maintenance. The variable cost break down is shown in Table
9.
Table 9The Variable Cost Break Down
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Table 11SWOT analysis
4.10 Investment Capital Requirements
In order to calculate the budget needed to start the company and make a profit, the
total income and losses of company need to be calculated. The income is the revenue
that the company will be generating based on the number of customers. The expected
number of customers has been calculated based on quantitative forecasting.
The profit/loss then is calculated by subtracting the total cost (the sum of fixed andvariable costs) from the total income. Table 12 and Figure 17 show the expected profit
and loss (P&L) of the company for years 2010 to 2012.
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Table 12Expected Profit and Loss
Figure 17. Profit and Loss Chart
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The time at which a company starts to make a profit is called the break-even point.
Figure 18 shows the break-even graph. As can be seen from this figure, Prosthetics Lab
will be break-even from losses and start making profit of $36,450 in the second quarter
of 2012. The total capital required will be the sum of all the losses before break-even.
Therefore, the expected budget for Prosthetics will be $415,816.
Figure 18. Break-even chart
To fund the budget three different sources will be used which are bank loans,
venture capital and money borrowed from family and friends. The break down of the
funding is shown in Table 13.
Table 13
Funding Break Down
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4.10.1 Norden-Rayleigh Financial Profile
The Norden Rayleigh cost profile indicates the total budget spent until breakeven.
Table 15 shows the calculations of cumulative distribution function and probability
density for the curve.
Cumulative distribution function is given by (Wesley, 2009):
Where, t-time to breakeven
V(t) total amount spent
d- estimated budget
a-cost drivers
Cost drivers are those that cost money to a company. Assuming the cost drivers to
be as in Table 14, a will be equal to 0.55.
Table 14Cost Drivers
Number of cost drivers, N=6
Hence, a=Total/N=0.008
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The probability density function is given by (Wesley, 2009):
From Figure 19, it can be seen that maximum budget is spent at the end of three months.
Table 15Probability density function and Cumulative distribution function for Norden-Rayleigh
Figure 19. Cumulative Distribution Function for Norden Rayleigh
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Figure 20. Probability Density Function curve for Norden-Rayleigh
4.11 Personnel
As a start-up company, Prosthetics Lab will only need a few employees to start
the business. There are three founders of the company who will occupy the top positions.
All three of the founders will share the same set of technical and scientific skills. The
skills include having at least an M.S. degree in materials or biomedical engineering. They
must have the knowledge of material science, especially in composites and biomaterials
and experience in mechanical testing of material and analysis. They must also have a
good understanding of the prosthetics industry.
The first of these three positions is the CEO. The CEO will be responsible for
management of the employees and financial resources of the company. She will also be
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responsible for legal matters and hiring. The second position would be the senior analyst
whose responsibility is to analyze the data gathered from the material testing.
Subsequently the third top position is the senior consultant. She will be in charge of
consulting the costumers based on the analysis of the results and coming up with the most
effective material for the intended purpose.
There will also be three other permanent full time positions in the Prosthetic Labs.
The positions are two material testing technicians and one SEM technician. All three
positions must have 2 years or more experience relevant to the tasks. The material testing
technicians must have a high school diploma or higher. They must be trained to perform
the tests offered by the company including Instron tensile test, bending, and Rockwell
hardness test. The testing technicians will also be responsible for cutting the samples in
order to fit in the test machines. They must also be computer literate and have the
knowledge of operating specific software used for the tests. The SEM technician must
have at least a B.S degree in material science or material engineering. He must be
experienced to operate the SEM machine and have basic knowledge of failure analysis.
There will also be another permanent janitorial position which will only be ten hours a
week.
The rest of the employees are contract employees which are the marketing analyst
and contract scientific analyst. Since the company is a start-up the marketing analyst will
be extensively needed in the beginning phases. The marketing analyst must have five
years or more experience working with start-ups in the biomedical field, preferably
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prosthetics and have at least an M.B.A degree. The scientific analyst must have a Ph.D.
degree in material or biomedical engineering. The skills required for this position is to
give professional advice to the consultant and the scientific analyst. Due to low number
of customers in the starting period the contract scientific analyst will only be hired for
two to six hours a week depending on work load. As the company develops, the need for
the scientific analyst will increase and he will be hired for longer hours per week.
4.12 Business and Revenue Model
Any business needs a strategy to sell its product and also generate revenue, which
is called business and revenue model. In addition to on location order processing,
Prosthetics Lab will use web cataloguing to enable its customers to choose the required
testing services for their product. Web cataloguing has the advantage of being easier for
those customers who find it hard to commute to the office location. The customers will
also have all the information about the services and the amount of samples needed online.
The samples can be shipped to the testing location, after which they will be tested and
analyzed. The consultation services can either be offered by email, fax or in person as
desired by the customer.
The strategy that Prosthetics Lab plans to make revenue is by advertising and
customer referrals. Advertising will be done in several ways. One way is to advertise
Prosthetics Lab in journals related to materials and medical devices. Prosthetics Labs will
also be advertised on the internet, on different prosthesis manufacturers websites.
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Another way is to sell advertising space of the companys website to materials suppliers
for medical devices.
4.13 Strategic Alliances and Partners
Prosthetic Labs will be a sole operator and will have no strategic alliances or
partners.
4.14 Exit Strategy
Return on Investment is calculated by dividing the profit by the total cost of
investment. It signifies how profitable an investment is at each time period. Table 16 and
Figure 21 show the ROI for Prosthetic Labs.
Table 16Return on Investment for Prosthetics Labs
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ROI
-100.00
-80.00
-60.00
-40.00
-20.00
0.00
20.00
40.00
Q1,
201
0
Q2,
201
0
Q3,
201
0
Q4,
201
0
Q1,
201
1
Q2,
201
1
Q3,
201
1
Q4,
201
1
Q1,
201
2
Q2,20
12
Q3,20
12
Q4,
201
2
Time
%ROI
ROI
Figure 21. ROI Chart
The ROI is negative in the first nine quarters which shows that the company is not
making any profit. The rate of increase in the ROI is maximal between the first and third
quarter of 2012. It is by the second quarter of year 2012 that Prosthetics Labs will be able
to return the capital investments. Assuming a ten fold return for the venture capital,
Prosthetics Labs will repay about 35% of the profit starting from year 2013 for the next
20 years. The bank loans will be repaid based on their interest rate.
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5.0 PROJECT SCHEDULE
The schedule for the entire project has been split in to two charts: one for ENGR 281 andthe other for ENGR 298
Gantt Chart for ENGR 281
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Gantt Chart for ENGR 281
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6.0 CONCLUSION AND FUTURE DIRECTION
In this project the mechanical properties of Carbon-Carbon, Spectra-Carbon, and
Spectra-Nylon composites has been tested and assessed for the specific application of
lower limb prosthesis. According to the results the Carbon-Carbon composite sample had
the highest tensile strength of 92 11 and hardness of 93.5 5.8. The SEM results show
that the binding of carbon fibers and resin for Carbon-Carbon composites is poor
compared to the other samples. This result is consistent with the results from stress-strain
diagrams from which the brittleness of spectra-carbon is seen, indicating strong binding.
While it is assumed that Spectra-carbon can be a cost-effective alternative to
carbon composites, Carbon-Carbon composite is still the best material of choice for this
application because of superior mechanical properties. Future research could be done on
carbon fiber and resin binding in order to make stronger binding between the two.
Furthermore, in future more types of samples and tests could be used for testing and
analyzing for this purpose.
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