MECHANICAL PROPERTIES OF CARBON HYBRID...

MECHANICAL PROPERTIES OF CARBON HYBRID BRAIDED STRUCTURE FOR

LOWER LIMB PROSTHESIS

A Project Report

Presented to

The Faculty of the Department of General Engineering

San José State University

In Partial Fulfillment

of the Requirements for the Degree

Master of Science in Engineering

by

Bhavana Shekhar Salma Riazi

Shirin Rahmanian

December 2009

© 2009

Bhavana Shekhar Salma Riazi

Shirin Rahmanian

ALL RIGHTS RESERVED

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SAN JOSÉ STATE UNIVERSITY

The Undersigned Project Committee Approves the Master’s Project Titled

MECHANICAL PROPERTIES OF CARBON HYBRID BRAIDED STRUCTURE FOR LOWER LIMB PROSTHESIS

by Bhavana Shekhar

Salma Riazi Shirin 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 FOR

LOWER LIMB PROSTHESIS

by Bhavana Shekhar Salma 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 project would not have been possible without his support. We would like to thank Mike Gidding and Chris Pimental of Breakey Prosthetics for sponsoring 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, Computer Engineering, 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 ........................................................................................................3

2.1 Introduction to Literature Review ..............................................................................3 2.2 Background ................................................................................................................3 2.3 Pre-amputation and Post-amputation Procedures ......................................................4 2.4 Components of a Below Knee Prosthesis ..................................................................7 2.5 Manufacturing Process of Prosthetic Limbs ............................................................10 2.6 Materials ..................................................................................................................12 2.6.1Historical Development of Composites for Orthopedics ...................................17 2.6.2 Properties of Spectra .........................................................................................18 2.7 Experimental Methods .............................................................................................19

3.0 Materials and Methods ..............................................................................................20 3.1 Tensile Testing .........................................................................................................20 3.2 Hardness Test ...........................................................................................................27 3.3 SEM Analysis ..........................................................................................................30 3.4 Discussion of Results ...............................................................................................35

4.0 Economic Justification...............................................................................................37 4.1 Executive Summary .................................................................................................37 4.2 Problem Statement ...................................................................................................38 4.3 Solution and Value Proposition ...............................................................................38 4.4 Market size ...............................................................................................................39 4.5 Competitors ..............................................................................................................40 4.6 Customers ................................................................................................................41 4.7 Cost ..........................................................................................................................42 4.7.1 Fixed Cost .........................................................................................................43 4.7.2 Variable Cost ....................................................................................................45 4.8 Price Point ................................................................................................................46 4.9 SWOT Assessment ..................................................................................................46 4.10 Investment Capital Requirements ..........................................................................47 4.10.1 Norden-Rayleigh Financial Profile .................................................................50 4.11 Personnel ................................................................................................................53 4.12 Business and Revenue Model ................................................................................55 4.13Strategic 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 6: Stress-Strain curve of Spectra-Carbon sample 1



Figure 9: Stress-Strain curve of Spectra-nylon sample 1



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

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

1.0 INTRODUCTION

There 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 was

used 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 1940’s 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 patient’s 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 patient’s 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 tissue’s 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 Adapter

Pylon

Endoskeletal finish

Ankle

Foot

Figure 1. Components of transtibial prosthesis Source: Below Knee (Transtibial) Prosthesis. (n.d.). Retrieved March 12, 2009, from Prosthetic Concepts 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 body

weight 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 Ankle joins the foot and prosthesis. This part is made of some joints which allow

axial 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 it’s 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 weight

acted 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 foot’s

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 Knee

Prosthesis).” 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 amputee’s 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).

Lange’s “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 Young’s 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 1 Mechanical properties of some materials used for prosthesis fabrication Source: Phillips, S. L., & Craelius, W. (2005). Material Properties of Selected Prosthetic Laminates. 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

1950’s due to extensive research done in aerospace industry. Development of fiberglass

in the 1930’s 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 &

17

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 ~ 1000C 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 2 Comparison of Mechanical Properties of different fibers Source: Lewin, M., Sello, S. B., & Preston, J. (1996). Handbook of fiber science and technology (Vol. III). New York: Marcel Dekker, Inc.

18

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 specifications Source: (2008). Quality and testing. In B. A. Strong, Fundamentals of Composites Manufacturing: Materials, Methods and Application (p. 277). SME.

19

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 (Young’s 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 Hook’s law and the constant of proportionality is called Young’s 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

20

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.

21

Figure 3. Stress-Strain curve of Carbon-Carbon sample 1.


22


Figure 6. Stress-Strain curve of Spectra-Carbon sample 1.

23



24

Figure 9. Stress-Strain curve of Spectra-nylon sample 1.



25

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 3 Tensile Properties of Carbon-Carbon composites

Table 4 Tensile Properties of Spectra-Carbon Composites

26

Table 5 Tensile 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 studied

samples, 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 Carbon’s 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

27

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 6 Hardness test results for Spectra-Nylon, Spectra-Carbon and Carbon composites

28

Figure 12. Box plot for Hardness test Data

29

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)

30

(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. These

images 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.

31

(a)

Fiber

Matrix

(b)

32

(c)

Resin breakage

(d) 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 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

33

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 resin

(a)

34

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

35

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.

36

4.0 ECONOMIC 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

37

quarter of 2012. The required capital will be funded from bank loans, family and friend’s

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 company’s 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.

38

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.

39

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.

40

Table 7 Major 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

41

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.

42

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 the

business 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.

43

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 8 Fixed Cost Break Down

44

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 9 The Variable Cost Break Down

45

4.8 Price Point

Based on the amount of effort and time required to test and analyze the material

provided by the customer, the price point will vary as shown in Table 10.

Table 10 Price Point Analysis

The price point has been calculated according to the number of sample types

received and services requested by the customer. For one and two types of samples the

service charge is a flat rate of $5000, while for three to four types of samples the rate

would be $7000. Finally for five or more samples the price point would be $9000. The

mean of the distribution for the price point was calculated and found to be $7000, which

will be used in the next section for calculating the revenue and breakeven.

4.9 SWOT Assessment

As a part of their planning process, any successful business needs assess their

strengths and weaknesses to explore potential threats and future opportunities. Table 11

provides a list of strengths, weaknesses, opportunities, and threats (SWOT) for Prosthetic

Labs.

46

Table 11 SWOT 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 and

variable 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.

47

Table 12 Expected Profit and Loss

Figure 17. Profit and Loss Chart

48

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

49

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 14 Cost Drivers

Number of cost drivers, N=6

Hence, a=Total/N=0.008

50

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 15 Probability density function and Cumulative distribution function for Norden-Rayleigh

Figure 19. Cumulative Distribution Function for Norden Rayleigh

51

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

52

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

53

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 manufacturer’s websites.

54

Another way is to sell advertising space of the company’s 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 16 Return on Investment for Prosthetics Labs

55

ROI

-100.00

-80.00

-60.00

-40.00

-20.00

0.00

20.00

40.00

Q1, 20

10

Q2, 20

10

Q3, 20

10

Q4, 20

10

Q1, 20

11

Q2, 20

11

Q3, 20

11

Q4, 20

11

Q1, 20

12

Q2,2012

Q3,2012

Q4, 20

12

Time

%R

OI

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.

56

5.0 PROJECT SCHEDULE The schedule for the entire project has been split in to two charts: one for ENGR 281 and the other for ENGR 298 Gantt Chart for ENGR 281

57

58

Gantt Chart for ENGR 281

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.

59

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