UNIVERSITY WISCONSIN-MADISON

Bone Graft Design BME 201

TEAM MEMBERS: MATTHEW GRONDIN, KATIE PETERSON, MICHAEL MCGOVERN, JOHN JANSKY, AND LANE VAN EPERN

4/6/2015

ABSTRACT

The proposed problem is to repair a bone defect with dimensions 20 mm deep with a 14 mm diameter.

The graft must maintain the same mechanical stability as the existing bone. Ideally, the graft will

encourage the natural bone to grow into the graft and heal the defect. There are existing designs which

are excellent bone repair materials, such as the product developed by BonAlive. This type of technology

is too expensive for a $150 budget, so other materials were considered. PMMA is often used in bone

repair and dental surgeries. A bioreactor was also necessary to develop, so that the bone graft samples

could be tested after existing in an environment similar to that of the body. The samples of PMMA

would incubate in the bioreactor for a total of two weeks, with three samples tested directly after

fabrication (T0), after one week (T1), and finally after two weeks in vivo (T2). It was proposed that over

time the PMMA would weaken and generate a smaller Young’s Modulus after existing in the bioreactor.

However, it was discovered that there was little change in the Young’s moduli after two weeks in the

bioreactor. This shows that PMMA is a good selection for bone repair, as it did not weaken over time in

an environment similar to that of the body.

Table of Contents

Table of Contents 1.1 Motivation & Global Impact ................................................................................................................... 3

1.2 Background ............................................................................................................................................. 4

2.1 Circuit Designs ......................................................................................................................................... 7

2.2 Material Holder Designs and Fabrication ............................................................................................... 8

2.3 Arduino Code .......................................................................................................................................... 9

2.4 LabVIEW ................................................................................................................................................ 10

3.1 Material Holder Design Matrix ............................................................................................................. 11

3.2 Material Holder Design Matrix Evaluation ............................................................................................ 11

3.3 Bone Graft Biomaterial Design Matrix .................................................................................................. 12

3.4 Bone Graft Biomaterial Design Matrix Evaluation ................................................................................ 13

3.5 Proposed Final Design ........................................................................................................................... 14

4.1 Materials ............................................................................................................................................... 15

4.2 Methods ................................................................................................................................................ 16

4.3 Final Prototype ...................................................................................................................................... 16

4.4 Testing ................................................................................................................................................... 17

5.1 Statistical Analysis ................................................................................................................................. 18

Appendix A—Design Information ............................................................................................................... 22

Appendix B-Project Design Statement ........................................................................................................ 22

Appendix C-Circuit Schematic ..................................................................................................................... 25

Appendix D-SolidWorks .............................................................................................................................. 26

Appendix E-Code ......................................................................................................................................... 31

Appendix F-LabVIEW ................................................................................................................................... 32

Appendix G-Design Matrices Description ................................................................................................... 33

Appendix H-Calibration of Thermistor ........................................................................................................ 36

Appendix I—Protocols ................................................................................................................................ 37

Appendix J-Expense Report ........................................................................................................................ 40

Appendix K-Final Design ............................................................................................................................. 41

1.0 Introduction

1.1 Motivation & Global Impact The use of biomaterials in bone graft surgeries provides another solution to repairing bone defects.

Existing methods include the use of an autograft or allograft, which take bone from another site of the

patient or from a donor, respectively. These procedures can lead to increased time spent in the hospital

or long term discomfort in the case of an autograft [1]. A possible concern with allografts is that the

donor tissue may transmit disease to the patient. While both the autograft and allograft methods have

proven successful in the past, it is necessary to continue to search for solutions with less adverse effects

[2]. The use of a biomaterial provides several attractive qualities. The bone graft can be measured

ahead of time to fit the size of the patient’s defect, minimizing the time spent under anesthesia. The

patient would also not need to endure a second surgery site which occurs with an autograft. Most

importantly, there is minimal risk of disease contraction since the graft is not coming from another

human [2].

1.1.1 Existing Designs

There are already companies that specialize in the production of biomaterials used for bone

repair. BonAlive specializes in producing bone cement that promotes bone growth, is osteoinductive,

and even contains bacterial inhibitors [3]. The Stryker Company developed its Simplex P Bone Cement in

1971. Since then, Stryker has come out with other bone cement products--one with Tobramycin, and

another with faster-setting versions of the product. Styker’s bone cement products and delivery systems

have earned respect after many years of use [4]. The company Zimmer has also had its PALACOS Bone

Cement product in the industry for many years. The product contains antibiotic distribution to reduce

risk. The bone cement has properties of high viscosity and quick dough time, making it easy to use for

orthopedic surgeons. This product has built a reliable reputation with its high visibility (its green)

excellent fatigue strength [5].

1.1.2 Problem Statement

The goal of this project is to create a viable bone graft which will repair a bone defect with approximate

dimensions of 20 mm deep, and 14 mm in diameter. The graft must maintain the same mechanical

stability as the existing bone. There is a $150 budget to complete this project. This budget must cover

the cost of designing and fabricating a bioreactor in which to test the selected material, as well as the

purchase of bone graft materials. There are many issues that need to be addressed when selecting a

design for the both bioreactor and bone graft. Ease of fabrication, safety, and budget are just a few of

the major concerns. A more detailed list of issues considered may be viewed in the Project Design

Statement (PDS) in Appendix B.

1.2 Background Extensive research was done in order to understand all aspects of the project. Understanding the

physiological aspects of bone, as well as bone’s mechanical properties was needed to properly ascertain

the best biomaterial to use as a graft. Information about existing bioreactors was also conducted so

that the design team could create a functioning bioreactor for the bone graft to remain in during the

testing period. With this research, the team could begin developing a design.

1.2.1 Biology and Physiology of Bones

Bones are a necessity in the animal world, as they provide support for the exoskeleton. In addition,

specialized cells in and surrounding the bone provide important and complex functions for the body.

For example, osteoblasts form new tissue within the bone, while osteoclasts dispose of waste within the

marrow. Hematopoietic cells form new red blood cells [6]. Moreover, osteoclasts reabsorb mineralized

deposits in addition to the protein matrix that is integrated [7]. Osteocytes, which consist of 90% of all

bone cells, live in the mineral/protein matrix and communicate with each other. Their main task is to

signal and respond to bone strain in addition to acting as a highway for waste and nutrient travel within

bone [7].

Figure 1: Bone anatomy; different tissues and marrow that comprise bone. Biomaterials implanted in

the body must behave similarly to these components in order to maximize growth and compatibility.

Opposite to the osteoclasts, osteoblasts are the “builders” that form new mineralized deposits

integrated with a protein matrix. Bone has the important function of serving as a reservoir for calcium,

allowing the body to maintain normal blood calcium homeostasis [7]. Observing Figure 1, three main

types of bone tissues exist: cortical (compact), trabecular (cancellous), and subchondral tissue [6].

Compact tissue surrounds the bone and provides support due to its density. Cancellous tissue is less

dense than compact bone, but participates more in metabolic functions. In an adult bone, there is a

higher amount of cortical tissue than cancellous. Subchondral tissue is located on the ends of the bone,

directly underneath the cartilage layer. Surrounding the entire bone is a tissue called the periosteum

which is vital for nutrient exchange. Long bones, such as the femur, consist of three sections. Referring

to Figure 2, the sections include: the diaphysis-middle of the bone that has a higher percentage of

cortical tissue that can support loads, the epiphysis-which acts as an absorber of impacts and is located

at the ends of the bone, and the metaphysis-which lies between the diaphysis and the epiphysis. Large

amounts of bone marrow reside in this region, and support a large amount of trabecular tissue needed

for metabolic processes [7].

Figure 2: This diagram labels different parts of the bone. All mechanical and biological aspects of

each part of the bone must be considered when selecting a bone graft material, due to their differing

properties.

1.2.2Mechanical Strength of Bones

According to an article from Cambridge’s Journal of Materials Research [8] bone behaves similar to a

tough material at low strains, since it has a hierarchical structure beneficial to preventing cracks after

small propagations. The bone also appears to become tougher with micro-cracks appearing in the

plastic region of the stress strain curve. However, bone will fracture in a manner similar to brittle

materials at high strains. Mechanical stability of bone depends on several aspects, including the manner

of loading, humidity, and the type of bone being analyzed. Strength is also related to the orientation of

collagen fibers and the density and porosity of bone.

More research was done in order to better understand the qualifications the bone graft must meet.

There is no specific value for compressive bone failure, but rather a range due to the fact of bone

strength variation due to age, gender, etc. The range for compressive, longitudinal bone failure strength

varies from a low value of 70 MPa to a high value of 280 MPa [9]. The elastic modulus of bone ranges

from 15-25 GPa according to. Human bone consists of an organic matrix which makes up roughly 25% of

the bone. The other 75% that contributed to the main strength of the bone is the mineral complex

hydroxyapatite [9].

1.2.3Biomaterials in the Body

The interaction of the bone graft in the body is an important aspect that needs to be considered. The

graft material needs to be biocompatible and cause no adverse effects to the patient upon

implantation. It would be beneficial for the graft to be osteoinductive, which means that the graft is

capable of promoting bone growth. Osetoconductive bone grafts are materials which are able to

support and encourage the growth of surrounding bone into the site of the bone graft. This integration

is known as osseointegration. The key to all of these processes is that the implanted material will

disintegrate over time and be replaced by newly produced native bone [11].

1.2.4 Existing Bioreactors

Two main types of bioreactors were looked at. One was a bioreactor that created cartilage tissue,

keeping both a pressurization along with a deformable scaffold. This patent number was US

20020106625 A1, and the specific name was “Bioreactor for generating functional cartilaginous

tissue.” In summary cells were connected to a scaffolding material, hydroxyapatite (HA) allowed

connection of a joint to the bone cement scaffold. The reactor contains a sterile environment,

maintains specific nutrients, and a constant 37 degrees Celsius is maintained along with other standard

physiological conditions [12].

The second reactor was a, “Tubular Bioreactor system for Use in Bone and Cartilage Tissue Engineering”

with a patent number of US 20120122208 A1. In summary this bioreactor used a 3D scaffold, growth

chamber, keeping the temperature at 37 degrees Celsius, 5% CO2, passaged every 6-7 days. Certain

Biomacromolecules allowing survivability were also included in the media. A phosphate-buffered saline

(PBS) solution was also used to flush the “beads” out of the bioreactor [13].

1.2.5 Design Specifications-Bone Graft

The bone graft must have properties similar to that of the native bone. This entails maintaining

mechanical stability similar to bone. Bone has compressive strength in the longitudinal direction of 70-

80 MPa, which must be maintained for at least two weeks. The bone defect being repaired in this

project is 20 mm deep and 14 mm in diameter. The final design should have these dimensions. A more

detailed description of the specifications may be viewed in Appendix B [9].

1.2.5 Design Specifications-Bioreactor

The bioreactor will contain a PBS solution in which the selected biomaterial will be submerged. The

designed bioreactor will need to maintain a temperature of 37.2 degrees Celsius, the same as internal

body temperature. The design will need to sustain these environmental conditions for at least two

weeks in order to allow for testing of the bone graft material at different points in time. A more detailed

description of the specifications may be viewed in the Appendix B.

2.0 Preliminary Designs

2.1 Circuit Designs The purpose of this circuit is to enable fully automated controls that maintain a certain temperature in

the bioreactor. The main component of this circuit is the Arduino Uno microcontroller (see Appendix C,

Figure 6 for the complete circuit diagram). Serial communications and power is supplied to the Arduino

by a USB cable connected to a laptop. A 5V output from the Arduino is supplied to a voltage divider

containing the thermistor. Given Equation 1 below, the output voltage of this voltage divider can be

determined. The resistance of a thermistor (which is represented as R2 in the equation) changes with

temperature which results in a varying voltage output for this voltage divider. This voltage then goes

into the voltage follower. This component does not change the voltage and enables current not to be

drawn from the circuit (drawing current when measuring the voltage would be enough to change the

voltage, causing error). Then the voltage output is fed back into the Arduino at analog pin 0.

𝑉𝑂𝑢𝑡 = 𝑉𝑖𝑛 ∗𝑅2

𝑅1 + 𝑅2

Equation 1: Voltage Divider Equation

The analog output at analog pin 0 must be converted to voltage and the thermistor must be calibrated

to make this conversion. To calibrate, the thermistor was placed in a series of eight water baths of

temperatures ranging from 25 to 60 degrees Celsius, each bath five degrees warmer than the previous.

Each of these outputs at analog pin 0 is measured in ADC readings and must be converted to voltage by

utilizing Equation 2. Utilizing the collected data a graph was made and the line of best fit for the graph

was found to be linear (see Appendix H for additional information on the thermistor calibration).

𝑅𝑒𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑜𝑓 𝑡ℎ𝑒 𝐴𝐷𝐶

𝑆𝑦𝑠𝑡𝑒𝑚 𝑉𝑜𝑙𝑡𝑎𝑔𝑒=

𝐴𝐷𝐶 𝑅𝑒𝑎𝑑𝑖𝑛𝑔

𝐴𝑛𝑎𝑙𝑜𝑔 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 𝑀𝑒𝑎𝑠𝑢𝑟𝑒𝑑

Equation 2: Conversion from ADC values to voltage

The resulting voltage is processed by the Arduino code to determine how the other electrical

component will behave. If the voltage is higher than 4.132, the Arduino will output a HIGH voltage level.

This causes the Arduino to close the beefcake relay and turn on the LED, since these two components

are connected to the Arduino pins. If the voltage is lower than 4.132, the Arduino will output a LOW

voltage level. This causes the Arduino to open the beefcake relay and turn off the LED. A closed

beefcake relay enables voltage from a wall outlet to be supplied to the heating element, while an open

relay does not enable this voltage supply. The LED is used to indicate whether the heating element is on

or off. Voltage is also supplied from the Arduino to the beefcake relay. The rocker switch is placed in the

circuit to manually disable output to the beefcake relay by preventing 5V to be supplied by the Arduino

into the Beefcake Relay. The op amp, LED, rocker switch and Beefcake Relay are all grounded to the

Arduino’s ground.

2.2 Material Holder Designs and Fabrication The design team needed to create a holder that would contain the bone graft samples within the

bioreactor. The holder needed to fit inside a 500 mL Corningware jar. The material that the holder was

made of needed to withstand the environment that the PBS solution created, as well as a temperature

of 37.5 degrees Celsius-representative of normal physiological conditions of the human body. The

holder also had to evenly expose the bone graft material to the PBS solution, in order for there to be

consistency in testing. The bone graft test pieces should be easily removable from the bioreactor when

it is time to test the loading capabilities of the graft. Each design worked under essentially the same

concept: how can the bone graft sample be exposed to the maximum amount of PBS solution. Three

preliminary designs were considered before the final design was selected using a design matrix. The

three initial designs included: The Hole-y Design, and The Angled Holes, and The Orbit.

2.2.1 Hole-y Design

Figures 8-10 in Appendix D, displays a SolidWorks works model of the Hole-y Idea. This concept enables

the user to fully submerge the biomaterial in PBS solution. The bottom plate can be pushed through the

central hole on the sample holder, allowing the user to simply pull the apparatus out of the jar. The

holes in the sample holder allow fluid to seep into and flow around each specific sample

container. Three holes are drilled per specific sample holder, maximizing the amount of fluid that can

enter the space. There is also a top hole in which a sample can be placed and allow fluid to be in contact

with the top portion of the specimen. However, this design will be difficult to fabricate due to the many

holes which need to be drilled. Also, the extrusions on the base plate will be hard to fabricate,

increasing cost. The use of plastics would be preferred in this scenario.

2.2.2 Angled Holes Design

The Angled Holes design may be viewed in Figures 11 and 12 in Appendix D. This design allows one to

completely submerge the biomaterial in the PBS solution. The diameter of the whole design is small

enough to fit into the 65 mm opening of the jar. The six containment units in this design allows for one

to place the six biomaterial samples in permeable tubing that will be stabilized in these containment

units. The permeable membrane tubes containing the samples rest at an angle inward in the design.

This allows for the removal of the samples at an angle. This design allows for a lot of open surface area

to be permeated by the PBS solution for each of the samples. In terms of fabrication, a lathe would be

used in rounding the various circle containment levels to specific diameters. The holes at different

distances from the center would be difficult to fabricate, because they are not aligned vertically. A

plastic would be an optimal design material.

2.2.3 Orbit Design

Figures 13 and 14 in Appendix D show another biomaterial holder concept, the Orbit. The purpose of

this design was to create a low-cost material holder that exposes as much surface area of the sample as

possible. The material holder can accommodate six samples at a time. Samples are placed into a

permeable membrane, such as mesh tubes, inserted into each of the six holes, and then lowered into

the bioreactor and left to incubate. After incubation, the sample holder can be easily removed using the

handle attached at the top. The handle can also provide extra stability if fitted to the top diameter of

the jar. The majority of this design can be lathed using round stock plastic. After the base and plates are

fabricated, holes can be drilled to create the wells and a handle can be attached to the top of the

cylinder. Overall, the durability of this holder is sufficient for the needs of this experiment. Also, since

the material that will be used to build this piece will most likely be PLS or ABS plastic, material cost

should not be an issue.

2.3 Arduino Code A microcontroller, such as the Arduino, can act as an excellent way to control the heating of the

bioreactor, as well as process and output data. Therefore, the Arduino Uno was selected to regulate

and control the bioreactor system. The Arduino receives an output into analog pin 0 from the designed

circuit (see Appendix E for the complete Arduino code). The values from analog pin 0 is converted to a

voltage value by multiplying the analog output by (5/1023.0). This value is derived from Equation 3

below, and Equation 2 as shown above with the Arduino Uno having a bit size of n = 10.

𝑅𝑒𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 =1

2𝑛(𝑉𝑅𝐸𝐹+ − 𝑉𝑅𝐸𝐹−)

Equation 3: Resolution Equation

This new calculated voltage value varies as the resistance of the thermistor in the bioreactor increases or decreases which is dependent on the temperature within the bioreactor. As temperature increases, the resistance of the thermistor decreases, lowering the voltage output being read by the Arduino at analog pin 0. The temperature of the bioreactor decreases while not being actively heated, causing the resistance to increase, which results in a higher voltage output being read by the Arduino at analog pin 0. When the voltage exceeds 4.132, the Arduino would output a HIGH voltage level to pin 7 which the beefcake relay control is connected to. The HIGH voltage level closes the beefcake relay and power from the wall source activates the heating element. At the same time, the Arduino would output a HIGH signal to pin 6 which is connected to the LED. This would turn on the LED, indicating that power is being supplied into the heating element. The bioreactor would continue heating until the voltage readings goes below 4.132, causing the Arduino to output a LOW voltage level to pin 7. At this stage, the bioreactor is at an acceptable temperature, and the LOW voltage level causes the Arduino to withdraw power from the heating element, disconnecting the beefcake relay. At the same time, the Arduino would output a LOW voltage level to pin 6. This would turn off the LED, indicating that power is not being supplied into the heating element. Finally, the code prints the voltage values as they are measured. Figure 3 below provides a simple explanation of the software function.

Figure 3: Flowchart for Arduino logic

2.4 LabVIEW Laboratory Virtual Instrumentation Engineering Workbench, or LabVIEW provided the design team with

an excellent way to keep track of live data. Without this, members of the team would need to be

present at all times. A VI was created which communicates with the Arduino to receive data inputs.

With this done, a live graph of the current temperature could be viewed on the screen of the laptop

connected to the bioreactor. Another benefit of using LabVIEW is that the data collected over time may

be exported to a spreadsheet for further analysis. An image of the VI used in this design may be viewed

in Appendix F, Figure 17 as well as a detailed explanation of the VI, Appendix F Figure 18.

3.0 Preliminary Design Evaluation

Several designs were considered during the design process through a design matrix. Arduino and

LabVIEW were not put through a design matrix, as there is not many useful variations to the code that

would yield the same desired results.

3.1 Material Holder Design Matrix The use of a design matrix was essential in ranking the three designs based on predetermined

criteria. The selection of criteria was based on aspects the team found to be the most important for the

design. Each criterion was weighted accordingly, and the scores for each criterion per design concept

were selected as seen fit. Table 1 displays the design matrix used to select a design for the material

holder.

Design Criteria (Weight)

The Hole-y Idea

Angled Idea Orbit

Effectiveness (30) 15 20 25

Ease of Use (25) 10 10 20 Manufacturability

(20) 5 7 10

Durability (15) 15 10 15

Cost (10) 1 7 8 Total (100) 46 54 76

Table 1: Design Matrix for Material Holder Design

Table 1 displays the scoring of each criterion based on particular designs. The shaded cells indicate the

design that scored the highest in a category. Light blue indicates a tie in ranking with another design,

while the slightly darker blue highlights the design with the highest score in criteria. Finally, the dark

blue indicates the design that earned the highest relative rating overall. A detailed description of the

thought behind each category may be found in Appendix G.

3.2 Material Holder Design Matrix Evaluation The Orbit design was selected as the final proposed design, as it scored nearly the highest in all

criteria. The Orbit design ranked highest in the effectiveness criteria due to the amount of exposure

allowed for the bone cement sample. As seen in Figure 14, there are three different segments that

allow exposure to the PBS solution: the base layer, the first tier layer, and the second tier layer. The base

allows for bottom support of the bone cement sample, while the other two layers help to maintain an

upright position and near complete exposure of sample to PBS. The Orbit scored highest in the Ease of

Use criterion as well. The handle on the top of the shaft allows the user to easily remove the sample

holder, promoting quick access to the bone cement samples. Neither of the other two design had such a

feature. None of the designs scored relatively high for the manufacturability criteria. However, it was

decided that the Orbit design was the easiest design to fabricate based on the in-line and perpendicular

placement of the holes holding the individual samples, and the two tier design reducing the amount of

machining needed. Full points were received for the durability criteria. Since this design solely uses

plastic, the team decided the Orbit would be the highest ranked design. The Orbit design received the

highest value for cost as well. Assuming the capability of using a 3-D printer to produce the sample

holder, the Orbit design was found to reduce the overall amount of material needed, thus reducing the

manufacturing cost. The design seems to use a lot of material for the base. However, it was discussed

to use a honeycomb-like filling to further reduce the amount of material needed.

3.3 Bone Graft Biomaterial Design Matrix Three materials were researched including beta-tricalcium phosphate (beta-TCP)-a naturally occurring

substance found in skeletons and teeth of vertebrate animals, hydroxyapatite (HA)-a common filler

material to replace amputated bone or to promote bone ingrowth into prosthetic implants, and

poly(methyl methacrylate) (PMMA)-a biocompatible ingredient in bone cement used to affix implants

and to remodel lost bone. In-depth analysis of these materials can be found in Appendix G. Other

research was done to find a method of fabricating the material in the tissue engineering lab. From this

research, a fabrication protocol was determined. This protocol can be found in Appendix I.

A design matrix was also used to determine the best material to use as a viable bone graft sample. The

matrix was weighted in different categories selected by the design team. These categories were

selected since they seem to be the most important aspects to consider when choosing a bone graft

material.

Beta-Tricalcium Phosphate

(beta-TCP)

Hydroxyapitate (HA)

Poly(methyl methacrylate)

(PMMA)

Cost (10) 4 7 10

Fabrication (15) 3 10 10

Availability of Product (5)

3 5 5

Modulus of Elasticity (20)

5 20 10

Compressive Strength (15)

5 13 15

Biocompatibility (20) 18 18 15

Osteoconductivity (15)

12 15 0

Total (100) 50 88 65

Table 2: Design matrix used to determine the most effective bone graft material.

Table 2 displays the scoring of each criterion based given particular designs. The shaded cells indicate

the design that scored the highest in a category. Light blue indicates a tie in ranking with another

design, while the slightly darker blue highlights the design with the highest score in criteria. Finally, the

dark blue indicates the design that earned the highest relative rating overall. A detailed description of

the thought behind each design criteria may be found in Appendix G.

3.4 Bone Graft Biomaterial Design Matrix Evaluation Overall, each of the materials harbors their own specific advantage. Therefore the original decision was

to incorporate all of the materials into one specific composite material. PMMA was to be used as a

matrix for the composite itself and be reinforced with particles of HA and TCP in order to create a

desired product. This product would have both the desired mechanical and biological properties similar

to bone. However, it was found that the fabrication of HA necessitated the use of a high temperature

oven, which the team does not have access to. Therefore the team decided to utilize PMMA, which

scored second in the design matrix.

3.5 Proposed Final Design The proposed Final Design incorporates all of the aspects discussed in the preceding paragraphs, with

some slight modifications. The circuit pictured in Figure 7 of Appendix C contains the entire circuit

schematic, including the beefcake relay, LED and the originally designed circuit in Figure 6 of Appendix C.

The final code used for the Arduino will control the heating element based on the calculations done

from the calibration of the thermistor. The Arduino code may be viewed in Appendix E, and the

thermistor calibrations are located in Appendix H. The Orbit design was selected as the best biomaterial

holder for this design. As for the biomaterial, PMMA mixed with HA was deemed the best choice for a

bone graft material. Finally, a VI was designed in LabVIEW to continuously record and store

temperature data from the bioreactor. Figure 4 below provides a simple flowchart explaining the

interactions of the components of the final design.

Figure 4: Flowchart for Final Design

4.0 Fabrication and Development

4.1 Materials Various materials were used to not only construct, but also create and test the bone samples. These can

be split up into four different categories including Circuitry, Material Holder, Bone Graft, and

Miscellaneous Materials. Circuitry relates to everything housed in the box, allowing the bioreactor to

remain at a constant temperature of 37 Celsius. Material holder materials include those that held the

bone pieces in the PBS solution. Bone graft materials correspond to those that were designed to test

the effects of the human body. Miscellaneous materials include the housing unit.

4.1.1 Circuitry Materials

These related to everything housed in the external box. A thermistor was used to vary the current

depending on the temperature, allowing the microcontroller to keep the bioreactor at a constant

temperature. The Arduino was the selected microcontroller exchanging information from the

thermistor to turn the relay on or off. When closed the relay completed the circuit, supplying power to

the heating element. The voltage follower constructed with the operational amplifier allowed the

current to remain constant on both the input and the output. The breadboard connected all of these

components via wires. An LED was connected to the Arduino, creating a way to signal when the heating

element was on.

4.1.2 Material Holder Materials

The material holder was made out of ultra-high molecular weight poly ethylene (UHMPE). This rod was

turned down and then milled to create the material holder. In addition, a plastic rod was screwed into

the middle of the holder to allow easier access when lifting it out of solution. Details concerning the

dimensions may be found in Appendix I.

4.1.3 Bone Graft Materials

The bone graft materials used to simulate real bone was Poly(methylmathacrylate), or PMMA. PMMA

was made from MMA monomer liquid, PMMA granules, and Lauroyl Peroxide. Details about these

components may be viewed in Table 3 of Appendix J.

4.1.4 Miscellaneous Materials

Several other miscellaneous materials were used in the design of this bioreactor, including the box used

to house the circuitry. Additionally, a power cord plugged into the wall supplied energy to the heating

pad. The heating pad was connected to the power cord and was the source of heat for the bioreactor.

The 500mL Corningware jar contained the PBS solution, as well as the material holder with PMMA

samples. A rocker switch was connected to the Arduino to turn the bioreactor on. Lastly, USB cables

were connected to the Arduino and the computer, allowing for serial communication between LabVIEW

and the Arduino. Part numbers and specifications may be viewed in Appendix J.

4.2 Methods 4.2.1Biomaterial Fabrication

A biomaterial needed to be selected to serve as the bone graft. The material chosen was PMMA,

poly(methyl methacrylate), with HA, which is a filler that promotes bone growth. A protocol was

researched and written. This Protocol is included in Appendix I. However, this protocol was not used in

the final production of PMMA. The fabrication of HA requires use of a high temperature oven, which

the design team does not have access too. The team then decided that the use of PMMA itself was still

a viable material to use as a bone graft. The protocol followed to create a bone graft from PMMA is

included in Appendix I.

4.2.2 Material Holder Fabrication

In order to test the samples in the bioreactor a holder must be built to contain the material. Ultra-High

Density Polyethylene was chosen as the material, since the material would maintain all material

properties while submerged in the PBS solution. The material holder was cut from UHDPE round stock

and turned down with a lathe to the appropriate diameter. After this, wells were drilled into the holder

to provide a secure place for the biomaterial to incubate. A hole was drilled and tapped in the center of

the newly fabricated material in which the threaded rod should be screwed. This rod was previously

fabricated and purchased by the design team, however it was cut down to an appropriate length.

4.3 Final Prototype The final sample holder was considerably different from that proposed. Due to the reduced manufacturability of the sample holder, a revamped design had to be completed. The original final design had three different layers, a foundation layer that rested on the bottom of the Corningware jar, and two more thin layers located above which supported the six samples needed for testing, but still allowed for maximal contact surface with the PBS solution. It was found that the height of the samples, which were around 20 mm did not permit such formations of the three different layers. The distance from the foundation to the first thin layer, and first thin layer to the second thin layer, was too small for traditional lathing. Instead, a new approach was taken. This approach considered that allowing more clearance space for the placement of the sample would still allow complete sample saturation by the PBS solution. The design was changed from a three-layered design to a one-layer apparatus with six holes for the placement of samples, a drilled and tapped center hole for the threading of a threaded rod, and a reduced foundation to permit suspension of the sample holder. It was believed that reducing the height of the foundation, and suspending the sample holder, would allow for better heat transfer to the PBS solution due to the placement of the heating element, which was underneath the Corningware jar. Furthermore, the reduction in foundation height allowed the samples to be furthered lowered. Figures 15 and 16 of Appendix D contain the SolidWorks diagrams of the final sample holder. The top of the jar was drilled into to permit the threading of the threaded rod. Another hole was drilled, slightly smaller

than the was used for threading the rod, for the placement of the thermistor. Images of the final design may be viewed in Figures 21 and 22 of Appendix K.

4.4 Testing Testing was completed using an MTS, or Mechanical Testing System, which determines raw data

regarding stresses and strains accumulating from an applied load. Tensile and compressive forces can

be exerted on the material to find values such as Young’s modulus, ultimate strength and yield strength.

For the purposes of this project, the analyzing of compressive loads on individual samples was

performed. Compressive forces were increased until 9.8 kN was reached. This was the maximum force

applied for fear of damaging the testing device. Once the maximum compressive force was applied, the

test was halted and the data was saved for further analysis. It was hypothesized that with increased

submersion in the PBS solution would result in decreased Young’s modulus.

A total of nine samples were tested over a period a two weeks. Of these nine samples, three sample

groups were formed representing different testing times. These times included T0=day zero, T1=seven

days, and T2=14 days in the PBS solution. The specific testing protocol can be found in Appendix I. The

averages and standard deviations are displayed in Figure 5.

Figure 5: Graph of the Mean Young’s Modulus

After the testing of the three different sample groups, a Student’s T-test statistical analysis was

performed concerning the Young’s moduli of the different sample groups. The statistical analysis

determined whether there was enough statistical significance to retain or reject our hypothesis at the

5% significance level. The results of the analysis are stated in the following section.

5.0 Results

5.1 Statistical Analysis Two sample t-tests were performed to test whether the null hypothesis of the pairwise difference

between different poly(methylmethacrylate) bone cement sample groups had a mean equal to zero at a

significance level of 5%. The null hypothesis was stated as no difference between the mean Young’s

modulus for Sample Group 1 (t=0 days) and Sample Groups 2 and 3 (t=7 and 14 days, respectively). The

alternative hypothesis was that there was a decrease in the mean Young’s modulus for Sample Group 1

and Sample Groups 2 and 3. Using MATLAB, the t-test was performed using the ttest() function. The

default setting for using this function considered both tails, to account for variability in both

directions. The Young’s moduli for each sample in specific sample groups were placed into a vector with

and assigned a variable. The assigned variable was then placed in the ttest() function in MATLAB, and

the analysis was performed.

The output of the statistical analysis showed no significant change between mean Young’s modulus of

each sample group. The p-values for each comparison were as such: Sample Groups 1 and 2 (p-

value=.9) and Sample Groups 1 and 3 (p-value=.4). The p-values were much greater than the

significance level stated earlier. The PMMA bone cement did not decrease in Young’s moduli, nor did it

increase. According to [13], the transfer of forces from bone-to-implant and implant-to-bone is the

primary function of bone cement. Furthermore, in order for bone cement to function properly, it must

be compatible with the tissue it contacts and have adequate strength. Moreover, PMMA may reside in

vivo from 1 month to 27 years, according to [14], and may eventually lead to degradation and decrease

in mechanical properties of PMMA. Due to the potential long term in vivo placement of PMMA bone

cement, and the primary function of transferring forces, a noticeable decrease in the bone cement after

two weeks in vivo could potentially be detrimental to the success of its use.

Another point to note is that only the Young’s modulus was analyzed. While testing the samples, only a

maximum compressive force of 9.8kN could be applied. Due to this, a true representation of the

ultimate strength was not produced. Any analysis of this data would have been greatly misconstrued.

6.0 Discussion

During the biomaterial fabrication portion of the design project, the PMMA biomaterial might not have

been mixed properly. The unevenness of mixing might have resulted in portions of different bone

samples having higher concentrations of the PMMA granules, MMA monomer liquid, or Lauroyl

Peroxide; this could have affected the bone sample structure when settled. Moreover, any alterations

in bone sample structure could have adversely affected the ultimate strength and Young’s modulus,

which in turn affected the statistical analysis.

Many issues occurred with LabVIEW unexpectedly shutting down throughout the two week sampling

period. As a result, there was large loss of data, inhibiting the tracking of temperature with respect to

time. There was concern that the bioreactor continued to heat when the heating element was not on,

due to residual heat. This could have contributed to reduced interaction of the PBS solution with the

PMMA bone samples. Data might have been misconstrued due to these factors, resulting in improper

statistical analysis upon biomaterial testing at specific times. Furthermore, it is possible that human

physiological temperatures were not met.

Another temperature related concern involves the heating element. Since the heating element was

located underneath the jar, and the thermistor above the sample holder, the thermistor might not have

changed accordingly with increased temperature from the heating element. Thus, the heating element

might have continued to increase the temperature above normal human physiological conditions.

Related to the heating element and the thermistor was the voltage being read into the computer by the

Arduino. There is a chance that the voltage range selected to have regulated was too narrow, meaning

the difference between upper and lower cut off limits were too close for appropriate temperature

adjustments by the heating element. By increasing the voltage range, better regulation of temperature

could have been addressed.

Human physiological conditions may not have been met in another way as well. The PBS solution might

not have been 10X concentrated. Since each team produced their own 10X concentrated PBS solution

before placing the fluid into a class container, it is possible that miscalculations were performed that

increased or reduced the amounts of different salts added to produce the PBS solution. Another cause

might be that improper amounts of the different salts were weighed out, therefore increasing or

decreasing the concentrations of specifics ions within the solution. Moreover, the variability in PBS

concentration, and later dilution, did not truly represent the human physiological conditions.

Through sample testing and statistical data analysis, no significant difference was found between the

sample groups. Since our null hypothesis stated that no difference would be found between sample

groups affected by time, we retained the null hypothesis. The PMMA bone samples inhibited potential

degradation by the PBS solution.

Based on the evaluation of prototype performance, there are a few changes that might be implemented

in future work. One change could be increased time in the bioreactor. It is possible that no substantial

change occurred in the biomaterial properties simply due to the length of submersion in the PBS

solution. More tests should be performed to ensure the PMMA material properties were unaffected by

length of submersion time. It is believed that a different heating element would have produced better

heat distribution throughout the Corningware jar. The better heat distribution would have interacted

with the thermistor better, therefore generating an overall better response in adjustments made to the

temperature.

7.0 Conclusions

The ultimate goal of the project was to design a bioreactor that held bone graft samples, and use this

bioreactor to test biomaterials potentially used for bone repair. This reactor would create an

environment close to that of the human body, factoring in for temperature, pH, and other problems

associated with degradation upon implantation. Later the samples’ compressive strength would be

tested to see if there was a change in strength throughout the time spent in the reactor. The bioreactor

tested for this experiment contained electrical components allowing the solution to remain at a stable

37 degrees Celsius. The Arduino connected to a thermistor, relay, LED, and computer allowed

information to be analyzed. The material holder held the PMMA samples and was placed in the 500 mL

Corningware jar. The jar was filled with a 1X PBS solution to simulate both bodily pH and ionic

concentration. PMMA samples were hypothesized to degrade over time, yielding smaller Young’s

moduli as increased time was spent in the bioreactor. Post test results from the statistical analysis show

retention of the null hypothesis, meaning none of the group’s comparison proved significant. Bone graft

samples remained consistent, and were not affected by the standard human conditions simulating

implantation. One of the main issues was with the PMMA formulation. Cement hardened too quickly,

causing non-uniform samples. In addition, the LabView program was unable to record data due to

technical errors stemming from the computer. The sample size for the testing was also fairly low, and

would need additional trials in the experiment. Future projects would consist of lengthening the

timespan spent in the bioreactor, allowing the ability to graph a trend.

8.0 References

[1] (Allograft vs. Autograft) [Website] Available http://www.harthosp.org/tissuebank/humantissuegraftinformation/allograftvsautograft/default.aspx

[2]DCI Donor Services Tissue Bank(Allograft vs. Autograft) [Website]. Available http://tissuebank.dcids.org/who-we-serve/patient-education/allograft-vs-autograft/

[3]BonAlive Biomaterials LTD. (2015) [Website]. http://www.bonalive.com/

[4] Stryker.com, 'Orthopaedics Bone Cement: Stryker', 2015. [Online]. Available: http://www.stryker.com/en-us/products/Orthopaedics/BoneCementSubstitutes/index.htm. [Accessed: 07- May- 2015]. [5] Zimmer.com, 'PALACOS® Bone Cements', 2015. [Online]. Available: http://www.zimmer.com/medical-professionals/products/surgical-and-operating-room-solutions/palacos-bone-cements.html. [Accessed: 07- May- 2015]. [6] "Anatomy of the Bone".RetrievedMay, 2015 Available: http://www.uchospitals.edu/online-library/content=P00109

[7] Petre, B , "Osteology (Bone Anatomy)". Retrieved May , 2015 Available: http://emedicine.medscape.com/article/1948532-overview#showall

[8] W. Suchanek and M. Yoshimura, “Processing and properties of hydroxyapatite-based biomaterials for use as hard tissue replacement implants”, Journal of Materials Research Yokohama 226, Japan: Center for Materials Design, 1997. [9] Doitpoms.ac.uk, 'DoITPoMS - TLP Library Structure of bone and implant materials', 2015.

[Online]. Available: http://www.doitpoms.ac.uk/tlplib/bones/printall.php. [Accessed: 06- May-

2015].

[10] Introduction to Bone Biology: All About our Bones. (2015, January 1). Retrieved March 25, 2015, from http://www.iofbonehealth.org/introduction-bone-biology-all-about-our-bones

[11] M.M. Stevens, “Biomaterials for bone tissue engineering”, materialstoday, 11th ed. 2008, pp.18-25

[12] Hung, C.; Aouni-Ateshian, G.; Mauck, R.; Soltz, M.; Valhmu, W.; Wang, C.; Mow, V., “Bioreactor for generating functional cartilaginous tissue,” U.S. Patent: 20020106625 A1, issued date Aug. 8, 2002

[13] Fisher, P.; Yeatts, A.; Geibel, E., “Tubular Bioreactor System for Use in Bone and Cartilage Tissue Engineering” U.S. Patent: 20120122208 A1, issued date May 17, 2012

[14] Hasenwinkel, J., Lautenschlager, E., Wixson, R., & Gilbert, J. (1999). A novel high-viscosity, two-solution acrylic bone cement: Effect of chemical composition on properties. Journal of Biomedical Material Research, 47, 36-45. Retrieved March 23, 2015, from http://onlinelibrary.wiley.com/doi/10.1002/(SICI)1097-4636(199910)47:13.0.CO;2-R/epdf [15] Affalato, Saverio, Perspective in Total Hip Arthroplasty; Advances in Biomaterials and their Tribological Interactions. Woodhead Publishing ; ed, Vol. :2014 [16]Ries,, In nivo behavior of acrylic bone cement in total hiparthroplasty, Biomaterials, vol 27, no 2, p. 256-261 [17] Chicot, D., Tricoteaux, A., Lesage, J., Leriche, A., Descamps, M., & Rguiti-Constantin, E. (2013). Mechanical Properties of Porosity-Free Beta Tricalcium Phosphate (β-TCP) Ceramic by Sharp and Spherical Indentations [18] Chu, K., Oshida, Y., Kowolik, M., Barco, T., & Zunt, S. (2003). Hydroxyapatite/PMMA composites as bone cements. Bio-Medical Materials and Engineering, 87-105. [19] "DoITPoMS." - TLP Library Structure of Bone and Implant Materials. Web. 25 Mar. 2015. <http://www.doitpoms.ac.uk/tlplib/bones/bone_mechanical.php>. [20] Einhorn, T.A. (1995). Enhancement of fracture-healing. Journal of Bone and Joint Surgery - American Volume, Vol.77, No.6, pp. 940-956, ISSN 1535-1386 [21] Kenny, S.M.; Buggy, M. (2003). Bone Cements and Fillers: A Review. Journal of Materials Science: Materials in Medicine, Vol.14, No.11, pp. 923-938, ISSN 0957-4530 [22] Mirtchi, A., Lemaitre, J., & Terao, N. (n.d.). Calcium phosphate cements: Study of the β-tricalcium phosphate — monocalcium phosphate system. Biomaterials, 475-480. [23] Puska, M.; Aho, A.J.; Vallittu P. (2011). Polymer Composites for Bone Reconstruction, Advances in Composite Materials - Analysis of Natural and Man-Made Materials, Dr. Pavla Tesinova (Ed.), ISBN: 978-953-307-449-8, InTech, DOI: 10.5772/20657. Available from: http://www.intechopen.com/books/advances-in-composite-materials-analysis-of-natural-and-man-made-materials/polymer-composites-for-bone-reconstruction [24] Reddy R, Swamy M. The use of hydroxyapatite as a bone graft substitute in orthopaedic conditions. Indian J Orthop 2005;39:52-4 [25] Ritchie, R. O., Buehler, M. J., & Hansma, P. (2009). Plasticity and toughness in bone. Phys

Today, 62(6), 41-47. [26] Rodrigues, D. d., Gilbert, J., Bader, R., & Hasenwinkel, J. (2014). PMMA brush-containing two-solution bone cement: preparation, characterization, and influence of composition on cement properties. Journal Of Materials Science: Materials In Medicine, 25(1), 79-89. [27] “The Role of pH and Healthy Living”, ChemCraft Inc./The DEHL Group

[28] P. Godara, C.D. McFarland, R.E. Nordon, “Design of bioreactors for mesenchymal stem cell tissue engineering”, Chemical Technology and Biotechnology, 83rd ed, pp. 408-420, April 2008

[29] Learn.sparkfun.com, 'Analog to Digital Conversion - learn.sparkfun.com', 2015. [Online]. Available: https://learn.sparkfun.com/tutorials/analog-to-digital-conversion. [Accessed: 05- May- 2015].

[30] J. Webster, Bioinstrumentation. Hoboken, NJ: John Wiley & Sons, 2004.

[31] Learn.sparkfun.com, 'Voltage Dividers - learn.sparkfun.com', 2015. [Online]. Available: https://learn.sparkfun.com/tutorials/voltage-dividers. [Accessed: 05- May- 2015].

[32] Arduino.cc, 'Arduino - DigitalWrite', 2015. [Online]. Available: http://www.arduino.cc/en/Reference/DigitalWrite. [Accessed: 05- May- 2015].

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[34] Martin, R , Mechanical Properties Of Hydroxyapatite Formed At Physiological Temperature

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9.0 Appendix

Appendix A—Design Information Title:

Team: 304

Members: Matthew Grondin, Katherine Peterson, Michael McGovern, John Jansky, Lane Van Epern

Advisor: BME 201 Student Assistants Gustavo Zach Vargas, Samual Lines, and Matthew Jensen, as well

as BME Department Faculty Joseph Towels and Jolene Enge

Client: John Puccinelli (BME Department) and Amit Nimunkar (BME Department)

Appendix B-Project Design Statement Function: The bone graft will be repairing a bone defect, and will have the same mechanical stability as

that of the surrounding bone. The product graft must be easy to fabricate, biocompatible, sterile,

contains growth factors that promote bone regeneration, is osteoinductive, osteoconductive, and

osteogenic. A bioreactor must also be designed in order to mimic the physiological environment of

natural bone for testing purposes.

1. Client Requirements:

1. Our project has a $150 spending limit.

2. The bone graft has to fill a bone defect 20 mm in deep by 14 mm in diameter.

3. The bone graft must maintain mechanical stability similar to native bone in vivo for at least

two weeks.

4. Testing of synthetic bone graft must be completed.

5. The bioreactor must mimic the physiological environment.

Design Requirements (Bone Graft):

a. Performance Requirements: The product must maintain mechanical stability similar to original bone in

vivo for at least 2 weeks. Cortical bone has a longitudinal Young’s modulus 11-21 GPa. The maximum

longitudinal strength of the bone must have a value close to the material we choose in order for the

bone to grow back healthy and strong.

b. Safety: The materials used in the bone graft must be biocompatible and avoid materials that may

cause an allergic reaction in the patient.

c. Accuracy and Reliability: The graft should fill up the space that is missing bone without overflowing,

and be able to withstand the same longitudinal loading as the original bone, which is 70-280 MPa.

d. Life in Service: The product should maintain mechanical stability similar to original bone in vivo for at

least two weeks.

e. Shelf Life: The bone graft material has no specified shelf life, although it must be stored without

extraneous efforts taken to contain chemicals.

f. Operating Environment: This bone graft will be contained within the bioreactor for a duration of two

weeks, experiencing conditions similar to that of the human body. The bioreactor will maintain a

temperature of 37.5 degrees Celsius, which is the internal body temperature of humans.

g. Ergonomics: The graft should fill the defect without causing adverse ergonomic issues. The bone graft

should also be easy to fabricate so that it may be reproduced for further tests and later use.

h. Size: The graft will be approximately 20 mm deep and 14 mm in diameter.

i. Power Source: No power source will be used for the bone graft.

j. Weight: The bone graft weight and density must be similar to that of the missing human bone.

k. Materials: All materials should be biocompatible and have similar mechanics to the original bone.

l. Aesthetics, Appearance, and Finish: The volume of graft should not displace internal tissue resulting in

external visual effects. The graft should also look similar to natural bone, and have a finish which

enables tissue to grow over the repair.

m. Product Characteristics:

Quantity: There will be only nine bone graft samples produced. Three will be tested shortly

after production, three more after one week in the bioreactor, and the last three after two weeks in the

bioreactor.

Target Product Cost: The bone graft should cost a fraction of $150. The budget for this project

must cover all components of the design.

n. Miscellaneous:

Standard and Specification: The product requires FDA Class 3 approval for medical devices.

Patient-Related Concerns: Patient allergies should be considered when selecting a biocompatible

material. There should also be concern with the possibility of infection post procedure. The

graft design should consider the decay of the biomaterial i.e. does it cause further complications

or is the post-decay product toxic.

Competition: Several other designs are already in use for bone grafts. BonAlive is one such

company which uses a putty to fill in defects. This company also utilizes granules of different

sizes which is useful for repair of different sized bones. Research is also being done on bioactive

glass scaffolds as an alternative method.

Customer: The patient that has a defect causing a void in the bone. The graft can involve

injection, be screwed on, or by any other methods. However, the material is the main

concern. The graft should be designed for all age groups, pediatrics to geriatrics.

Physical and Operational Characteristics (Bioreactor):

a. Performance Requirements: The bioreactor should be able to withstand two weeks of constant

usage. The bioreactor will be stationary in the BME 201 lab for several weeks. The room will be at room

temperature with little extraneous disturbances. The circuitry for the bioreactor will be housed in a

plastic housing unit with holes drilled in the sides to allow wires to connect to the bioreactor and to the

power source.

b. Safety: The bioreactor should be sealed appropriately, and be safe to handle. The bioreactor will be

holding PBS solution in close proximity to electrical components. This could be potentially hazardous, so

the bioreactor should be appropriately sealed and the circuit components protected from exposure to

the PBS solution.

c. Accuracy and Reliability: The bioreactor should reliably maintain a temperature at or near

37.2 degrees celsius, the same as internal body temperature.

d. Life in Service: The bioreactor should be able to maintain an internal temperature of 37.2 degrees

celsius during biomaterial testing.

e. Shelf Life: The device must last through the end of our testing period, which is two weeks long.

f. Operating Environment: The bioreactor should be kept in a room at room temperature without excess

humidity, heat, or other environmental extremes.

g. Ergonomics: The bioreactor should be easy to use during testing. This means that the bone graft

samples should not be difficult to remove from the bioreactor. The bioreactor should also be easy to

operate, perhaps through the use of a simple on/off switch to control power.

h. Size: The bioreactor should be contained within the size of Corningware jar of maximum volume 500

mL.

i. Power Source: The bioreactor should use a standard voltage of 120V.

j. Weight: The bioreactor should be of reasonable weight, meaning it could be easily transported.

k. Materials: Materials given consist of an arduino microprocessor, 500 mL Corningware jar,

temperature sensor (thermistor), synthetic bone material options, stock PBS solution, computer and

software.

l. Aesthetics, Appearance, and Finish: The product should have easy to access controls, organized

components, and A/C power connection.

m. Product Characteristics:

Quantity: There will be only one unit.

Target Product Cost: The cost of the bioreactor should be a fraction of $150, which is the budget

for the entire design.

n. Miscellaneous:

Standard and Specification: An FDA Class 1 approval may be needed.

Patient-Related Concerns: This is not applicable for the bioreactor.

Customer: The bioreactor should be operable during the bone graft testing phase.

Appendix C-Circuit Schematic

Figure 6: Proposed circuit schematic.

Figure 7: Final design circuit schematic

Appendix D-SolidWorks Hole-y Design in SolidWorks

Figure 8: Hole-y design-sample holder container with dimensions

Figure 9: Hole-y design-sample holder lifting component with dimensions

Figure 10: Hole-y design-full sample holder assembly

Angled Holes Design in SolidWorks

Figure 11: Angled Holes design

Figure 12: Angled Holes design-dimensioned drawing

Orbit Design in SolidWorks—First Design

Figure 13: Original Orbit design dimensioned drawing

Figure 14: Original Orbit design

Figure 15: Final design of sample holder-dimensioned drawing

Figure 16: Final design of sample holder-sectioned view displaying depth of sample holding containers

Appendix E-Code Arduino Code

int aIn = A0;

// initialize aln to analog pin 0 of Arduino

int pin= 7;

// Beefcake Relay connected to digital pin 7 int led = 6;

// LED connected to digital pin 6 void setup() { // set up serial communication at 9600 bits per second (baud): Serial.begin(9600);

// sets the digital pin as output

pinMode (pin, OUTPUT);

// sets the digital pin as output pinMode (led, OUTPUT); } void loop() { // read the input on analog pin 0: int sensorValue = analogRead(aIn); float voltage = (float)(sensorValue)*(5/1023.0);

// convert sensorValue to a voltage value delay (500);

// wait for half a second if (voltage > 4.132){ // if the voltage measured is greater than 4.132, then pin and led should output HIGH

digitalWrite(pin, HIGH);

// close the Beefcake Relay (HIGH is the voltage level) digitalWrite(led, HIGH); // turn the LED on (HIGH is the voltage level) } if (voltage < 4.132){ // if the voltage measured is less than 4.132, then pin and led should output LOW

digitalWrite(pin, LOW);

// open the Beefcake Relay by making the voltage LOW digitalWrite(led, LOW);

// turn the LED off by making the voltage LOW } Serial.println(voltage);

// Print the float variable voltage

}

Appendix F-LabVIEW

Figure 17: Graphical representation of the program used to plot temperature versus time

Figure 18: Live graph of the temperature inside the bioreactor, as well as the controls used in the VI.

There are several aspects which are key to note in this VI. The “VISA Configure Serial Port.vi” provides

the VI with resources needed to connect to a hardware device, in this case the Arduino Uno. Error wires

were also used to ensure dataflow. With these error wires, if an error were to occur the program will

exit gracefully, meaning the node where the error occurred will not execute and pass error to the next

node in the VI. An eight byte count was used to read data from the device. Also, shift registers were a

necessary addition to the VI, so that the array generated will hold more than one data point. Without

this feature, the spreadsheet generated at the end of the testing process would only display one data

point; the data from the very last point in time that was tested.

Appendix G-Design Matrices Description Proposed Biomaterial Descriptions

Beta-tricalcium phosphate, or beta-TCP,is in the family of calcium phosphates (Ca-P) which exhibit

osteoconductive behaviors. Osteoconduction is an important characteristic of bioactive bone grafts,

and grafts with this characteristic allow for the spreading of osteoblasts and osteocytes on their surface.

Biomaterials are often customized in order to illicit a specific biological response (Einhorn, 1995; Hench

& Wilson, 1984). Beta-tricalcium phosphate is commonly used as a reinforcement to a polymer matrix

in order to increase the bioactivity of biomaterials. When constructing a bone graft, the ability of the

body to connect and grow into the implant needs to be considered. Specifically, the incorporation of

osteoconductive materials will allow for bonding between the graft and both bone and subcutaneous

tissue. Beta-tricalcium phosphate can be used clinically in cranio- and maxillofacial surgery for filling

non-load bearing bone defects. Samples of beta-TCP were tested with different settling times to obtain

material properties. As the initial setting time increased, the compressive strength decreased. Values

for compressive strength varied from 7.4 MPa at a setting time of 16 minutes to 51.0 MPa at a setting

time 5 minutes. [22]The modulus of elasticity for non-porous beta-TCP is 162 GPa, according to Chicot D

et al.

Hydroxyapitate, or HA, is a naturally occurring mineral-can also be synthesized-found in bone tissue. HA

is currently being used in many orthopedic and maxillofacial surgeries. Particles of HA have also been

used as a filler material to construct HA polymer composites. (Chu et al., 2004). These composites not

only combine the the easy processing ability of polymers, but also incorporate the osteoconductivity of

HA. The mechanical properties of polymers lead to a wide variety of uses in load-bearing and non-load-

bearing applications. Another important note to make is that HA polymers can be made to completely

degrade-if made with a biodegradable polymer matrix. The ability of a composite material to be

biodegradable lends itself to the ability of inducing new bone growth and gradually degrade, enabling

the load to be slowly transferred from the composite material to the newly grown bone. (Chu et al.,

2004). The rate of induced bone growth and degradation is dependent on the physical form of the

hydroxyapatite. Ceramic and crystalline forms are slow in bone growth and degradation, in contrast to

the non-ceramic and non-crystalline forms which are fast in resorption and bone formation. It was found

that the modulus of elasticity of hydroxyapatite 4.64 to 120 GPa throughout various studies portrayed

by Chu et al. The compressive strength for HA has been reported to be as high as 917 MPa. However,

the compressive strength for HA containing 50% porosity was 31 MPa [34].

Poly(methyl methacrylate), or PMMA as it is more commonly known, is a polymer and main ingredient

in the production of bone cement, which purpose is to serve as grouting or a space-filler or to affix an

implant. The primary function is stabilization of an implant and transferring mechanical loads between

implant and bone. (Hasenwinkel et al., 1999). PMMA is also used in hard tissue replacements, or HTRs.

(Chu et al., 2004). It is important to note that a polymer alone cannot be used to develop hard tissue

replacements; there is a need for minerals that influence the properties of the HTR. The material

properties of PMMA alone are undecided, as stated by Chu et al. in the article Hydorxyapatite/PMMA

composites as bone cements. Separate research projects, stated in the aforementioned article, have

found that the modulus of elasticity for PMMA to be between .22-3 GPa. The compressive strength

range for PMMA ranges from 83-124 MPa according to MatBase. By incorporating other materials such

as hydroxyapitate or beta tricalcium phosphate the properties of the bone cement and HTRs, which

includes PMMA, can change. The advantages of using PMMA include being surgically forgiving, allowing

fast fixation of implants, and permits good intrusion of the cement into the cone matrix. (Chu et al.,

2004). There exist many disadvantages as well. One of the main concerns is due to the increased

temperature that occurs during the polymerization. The drastic rise in temperature can cause thermal

necrosis of the bone and protein denaturation [14].

Biomaterial Holder Design Matrix

The criteria for effectiveness considers how well the material holder exposes the bone graft to the PBS

solution, meaning all faces of the bone graft should be equally exposed to the environment within the

bioreactor. This component is essential to generating accurate data when the material undergoes

compression testing. For this reason the criteria for effectiveness was given a weight of 30/100 points.

The next criterion is ease of use. The material holder should be easy to use so that the bone grafts can

be extracted from the bioreactor without too much hassle. The individuals should not have to take too

many cumbersome or time consuming safety precautions in order to remove the samples from the

bioreactor. However, the samples will only need to be removed twice over a two week period, making

this criterion of lesser importance than effectiveness. This led the team to give the criterion for ease of

use a weight of 25/100 points.

Manufacturability is the next criterion in the design matrix. This criterion concerns the difficulty the

design team would encounter when fabricating the material holder. This criterion takes into

consideration whether or not the design team has the necessary knowledge to machine the material

holder, as well as the length of time fabrication would take. The team decided that manufacturability is

of less importance than effectiveness and ease of use, and for this reason was given a weight of 20/100

points.

The criteria for durability was placed lower on the list of criteria, since the material holder only needs to

be functional for the length of the testing period of two weeks. After the mechanical testing of the bone

grafts is completed the material holder is no longer needed. For these reasons the durability criteria

was given a weight of 15/100 points.

Cost is the final criterion in the design matrix, ranked the lowest in terms of weight of all the criteria. A

high score in this category means that the design is cost effective. The design team has been given a

budget of $150 dollars, and preliminary cost projections show that the team should be well within

budget. The team would like to minimize the cost of the project in the interest of the client. This

criterion was given a weight of 10/100 points.

Biomaterial Design Matrix Description

The total selection process consisted of weighted criteria on a 100 point scale. The first criterion

selected was Cost, and was weighted with 10 points due to the limitations of flexibility with cost.

Fabrication was given 15 points due to the feasibility of designing the specified materials. Availability

was only given 5 points due to increased ability of shipment allowed by purchasing online. Modulus of

Elasticity and Compressive strength are important for testing the said material. However elasticity was

given 5 more points over compressive strength because it’s more important in determining the

properties of the material. Biocompatibility was given 20 points due to its importance in vivo and ability

to not be rejected by the patient. Lastly Osteoconductivity, ability to form new bone, was given 15

points because the ultimate goal is to not only support but also eventually heal the defect.

Matlab Code

% Close figures and clear out other variables that have been assigned

close all; clear all;

% Enter the geometric measures of your bone cross section

diameter = input( 'Enter the max outside bone diameter: ' ); length = input( 'Enter the span between rollers in your experimental test: ' );

% Load your data file

filePath = uigetdir; % Allows user to choose folder with data fileType = '*.xlsx'; % Specifies file type file = dir( fullfile( filePath, fileType ) ); % Creates a structure with different info types, only focusing name column within structure data = xlsread( [ filePath '\' file.name ] );

% import your data

disp = data( :, 1 ); % Measurement in millimeters force=data( :, 2 ); % Measurement in Newtons

epsilon = ( disp-length ) ./ length; % Determines strain sigma = force ./ ( pi*diameter^2/4 ); % Determines stress

plot( epsilon, sigma, 'k-' ) % Plots stress and strain xlabel( 'Strain ( mm/mm )' )

ylabel( 'Stress ( MPa )' ) title( 'Stress vs. Strain' )

ultimate_strength = max( sigma ) % Determines max data stress i.e. ultimate strength

f = input('first linear data point: '); % Input first data point of linear region g = input('last linear data point: '); % Input last data point of linear region

P = polyfit( epsilon( f:g ), sigma( f:g ), 1 ); % Finds first order polynomial of linear region E = P( 1 ) % First term is Young’s Modulus

Appendix H-Calibration of Thermistor After collecting and plotting temperature values vs ADC values, we compiled two graphs. One graph

consisted of a linear analysis (####) while the other was analyzed exponentially (####). The linear curve

fit generated an equation of 𝑦 = 3.5756𝑥 + 713.08, and the exponential curve fit generated an

equation of 𝑦 = 7325.25𝑒−0.006. The two R^2 values were .9875 and .9812, respectively. Therefore,

our method for determining the most accurate graph rested on R^2 values. Even though the values

were very close together the ultimate choice became the higher value. In conclusion Figure 1, the linear

approximation, was chosen over the exponential approximation due to a slightly higher R^2 value. If the

thermistor circuit is saturated, there will be errors in ADC values due to the inappropriate conversion of

output voltage from analog to digital. The ADC is only be able to convert the analog voltage values

between 0-5V. Any values above 5V will be saturated to 5V, thus causing error in conversion.

Figure 19: Plot of Analog-to-Digital conversion of temperature versus degrees Celsius with linear curve

fit

Figure 20: Plot of Analog-to-Digital conversion of temperature versus degrees Celsius with exponential

curve fit

Appendix I—Protocols PMMA with HA Fabrication Protocol—Proposed Design

Fabrication Protocol:

It is believed that the PMMA-based polymer with reinforcements needs to be fabricated using two

solutions. The first solution is made by mixing the desired concentrations of Benzoyl peroxide, or BPO,

and methyl methacrylate, or MMA, and then adding PMMA. The second solution is made by dissolving

the desired concentration of N,N-dimethyl-p-toluidine, or DMPT, in MMA followed by the addition of

PMMA. Once the two solutions are made, there should be the addition of the reinforcement additives.

The two solutions, with the reinforcement additives will then be placed in Ratio-Pak cartridges, sealed,

and placed on a rotating drum for 18 hours. After removal of cartridges from the mixer, the cartridges

will be stored upright at 4℃. To allow polymerization of these materials, the cartridges will be placed

into a Ratio-Pak pneumatic dispensing gun. The mixture of the materials occurs through a Ratio-Pak

static mixing nozzle. This technique will allow the BPO and DMPT-containing solutions to interact,

initiating polymerization and curing of the cement [15].

PMMA Fabrication Protocol—Final Design

Gather Materials: MMA monomer liquid (Fisher 507019486) PMMA granules (Fisher AC190691500)

Lauroyl Peroxide (Sigma 517909-100G) Preparation: This protocol is designed to make nine bone graft samples for testing at the beginning, after one week in the bioreactor, and finally after two weeks in the bioreactor. All of these steps should be performed in the fume hood while wearing gloves. Take care to avoid contact with skin and eyes, as well as avoid inhaling vapors. Protocol Followed in Lab: Obtain PMMA bone cement kit, beaker, and scoopula. Open PMMA powder packet and pour contents into the beaker. Break off top of glass vial and pour liquid into beaker. Mix contents with scoopula for about 5-10 minutes ---------------- or ----------------------- Protocol in manual: 0.5 g of Lauroyl Peroxide is mixed with 19.5 g of PMMA granules in the hood. Be sure to mix thoroughly; however take care not to spill the powder. Measure and add 10 mL of the MMA monomer to the powder that was just mixed.

Both Protocols: Continuously stir with scoopula for 5-10 minutes, or until a soft dough forms. After this step is complete there is only 10 minutes of time with which to complete the following steps. Collect all of the dough and knead for two or three minutes. Divide the dough into nine equal sections, and form the sections into cylinder shaped pieces. To do this, obtain plastic a sheet. Cut the sheet into rectangles with a height a little taller than the intended sample and width long enough to wrap around the circumference of the sample. Curl the plastic sheets into cylinders and place inside the plastic sample wells. After kneading, place an equal amount of dough in each plastic cylinder. A sample diameter of 15.875 mm is ideal. When finished, wait for the samples to harden.

Material Holder Fabrication

1. Obtain UHDPE round stock, 3ft long and 3’’ diameter. Other dimensions may be used as long as it may be lathed to the proper diameter. Specifications on the UHDPE used may be viewed in Appendix J.

2. Place the UHDPE round stock in drop saw and cut down the stock material until it is an appropriate length to lathe. The lathe used in this process Eisen IIII.

3. Obtain deburing tool and remove burs at edges.

4. Place the new piece of UHDPE round stock in lathe and lathe the diameter down to 60mm.

5. After doing this place the round stock vertically into the clamp under a mill. The mill used in this project was an Eisen. Use a 14 drill bit to cut a center hole in the round stock.

6. Use a 16 mm size drill to cut 6 evenly spaced wells around the center hole.

7. Obtain 14mm threading tool, and thread center hole.

8. Obtain threaded rod and screw into the center hole of the round stock.

9. Clean station and return supplies.

Testing Protocol

Protocol Steps:

1. First, file the bone samples so that the top and bottom surfaces are as smooth and flat as

possible. This will ensure the application of a constant, even normalized force onto the test

sample.

2. These samples will then be tested after a specified submersion time in the bioreactor PBS

solution. Total submersion times include: t = 0, 7 and 14 days.

3. Once the samples have met their designated bioreactor exposure time, the diameter and length

of each bone sample will be measured and recorded.

4. Each sample is placed in the MTS machine, which obtains the stress and strain data from the

specified test sample.

5. Now load the MTS program, TW Elite, this collects data for tests and controls compression rate.

Each sample will be placed on the center of the compression plate on the bottom clevis.

6. In the TW Elite program, scroll to and click on File→Open Test→MTS EM Compression

(Simplified)-BME201-2015 to load to file used for compression testing.

7. Lower the top clevis-with attached compression plate-using the down arrow bottom-for larger

distances- or the scrolling wheel-for shorter distances. The down arrow button and scrolling

wheel are located on the handset to the right of the MTS machine.

8. The top clevis should be lowered as close as possible to the bone sample without exerting any

compression force. Now zero the Load and Crosshead values with in the TW Elite program.

These two values are located at the bottom-left of the screen and can be cleared by right-

clicking and selecting Zero Value. After this, it is time to run the compression test.

9. As the bone sample is being loaded in compression, be sure to watch the increasing loading

value-it should not rise above 10kN. In order to prevent damage to the MTS machine, stop the

program at approximately 9.8kN. Even though the sample might not fail under these conditions,

acquire the Young’s modulus and Ultimate Compressive Strength values.

10. After stopping the program, select Yes on the dialogue box that appears. This will reduce the

applied compressive force to 0 kN.

11. Next, save the information found by the compressive test. There will be a spreadsheet on the

screen that displays information on performed tests. Right-click on the test that was just

performed and select Export Raw Data.

12. A dialogue box will appear prompting entry of additional information. Select OK to save the text

file, or scroll to the file browser icon. By selecting the file browser icon, it is possible to change

the save location. Once the save location has been specified, select OK. The dialogue box will

disappear and the screen displaying performed tests will reappear.

13. Next scroll to the Monitor tab and select it. If more tests need to be performed, repeat this

protocol. All nine samples must be tested using the aforementioned steps.

Appendix J-Expense Report

Table 3: Table of expenses and materials used in fabrication of prototype

Appendix K-Final Design

Figure 21: Image of the final design

Figure 22: Image of the final circuit design