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Gore: Calcified Vessel Project

Final Report

Michael Rickerd Skyler Buchanan Cameron Fisher

Nolan Kirk Bryce Ribucan

Kathryn Shallcross

2015-16

Project Sponsor: W.L. Gore and Associates Faculty Advisor: Dr. Timothy Becker Sponsor Mentor: Jonathan Bruce Instructor: Dr. Sarah Oman

DISCLAIMER This report was prepared by students as part of a university course requirement. While considerable effort has been put into the project, it is not the work of licensed engineers and has not undergone the extensive verification that is common in the profession. The information, data, conclusions, and content of this report should not be relied on or utilized without thorough, independent testing and verification. University faculty members may have been associated with this project as advisors, sponsors, or course instructors, but as such they are not responsible for the accuracy of results or conclusions.

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EXECUTIVE SUMMARY The team was tasked by W.L. Gore & Associates with replicating a diseased portion of the superficial femoral artery through the use of non-biological materials. The team was tasked with meeting the following project requirements:

x Transparency x Lesion Durometer x Lesion Adhesion

Strength

x Lesion Length x Vessel Diameter x Lesion Thickness x Degree of Occlusion

x Vessel Length x Cost x ANSI/OSHA Safety

Standards

The team focused its attention on recreating the lesion through the use of gypsum stone (calcium sulfate) after numerous initial hardness testing trials were conducted. Once the gypsum stone was selected, further evaluation and manipulation of the material was necessary. The team manipulated the recommended mixing ratio from a 2:1 to a 1:1 (1ml of water to 1 gram of gypsum stone) and achieved a much less viscous final mixture. This final, cured material resulted in a hardness value that was within the acceptable range. This mixture’s properties allowed the solution to be injected into the mold, improving the quality of the manufactured lesions.

The lesion was created through the use of a 3D printed mold, printed from ABS plastic. Several iterations of the mold were designed and printed, with the final mold consisting of four main body pieces, two square clamps, and one plug. The four piece mold was chosen due to the fragile nature of the manufactured lesion and the need to decrease the amount of surface area each mold piece had in contact with the lesion. This final mold design yielded a 90% success rate for manufacturing lesions.

After a reproducible lesion process was created, the team moved onto the task of adhering the lesion to the inside of the mock vessel. Several types of adhesives were evaluated for their ability to adhere the lesion to the vessel as well as their ability to be injected. A silicone adhesive was chosen based on its consistent ability to adhere the lesion to the vessel and be injected through a syringe.

Once the adhesive was selected all aspects of the model were evaluated and the results are shown in Table i. The final model met all requirements associated with the client’s need.

Requirement Units Target Tolerance Range Average Result Requirement Met? Transparent % 100 -20 80-100 N/A Yes Lesion Durometer Shore A 85 ± 10 75-95 88.1 Yes Lesion Adhesion N/m 20 ± 15 5-71 350 Yes Lesion Length cm 15 ± 1 3-27 13 Yes Vessel Diameter mm 7 ± 1 4-12 7 Yes Lesion Thickness mm 6 ± 1 5-7 5 Yes Degree of Occlusion % 75 ± 10 50-95 85 Yes Vessel Length cm +10 per side ± 1 15-40 10 Yes Cost $ 3000 N/A <3000 N/A Yes ANSI Standards N/A Meets All N/A N/A N/A Yes OSHA Standards N/A Meets all N/A N/A N/A Yes Body Temperature (LTE) °C 37 ± 12 25-49 N/A Yes Blood Pressure (LTE) mPa 19 ± 9 10-28 N/A Yes

Table i - Summary of Engineering Requirement Values

ACKNOWLEDGEMENTS The capstone team would like to extend our deepest gratitude to those who assisted us during all stages of this project. The W.L. Gore & Associates mentor team leads, Johnathon Bruce, DJ Mongeau, Jason Alger, Scott Bryson, and Brandon Short gave us a challenging prompt with minimal guidance so that the team could develop an original, unguided project. The class teacher, Dr. Sarah Oman, gave us constructive criticism throughout the year as to progress the professionalism and functionality of the project. She also assisted the team by 3D printing several prototype lesions and lesion molds. The bulk of testing was conducted in NAU’s Manufacturing Building, 98c, which provided open space, access to a multitude of tools and several experts in manufacturing. This includes Chris Temme who was the primary contact for the Rapid Lab, which printed the team’s final 3D printed molds. Thank you to Dr. Timothy Becker, who gave biomechanical and biomaterial advice to the group and suggested several test methods to verify numerical values. Thank you to the NAU CEFNS capstone, which provided an opportunity to get such a practical and challenging project.

TABLE OF CONTENTS

DISCLAIMER .............................................................................................................................................. 2 EXECUTIVE SUMMARY ........................................................................................................................... 3 ACKNOWLEDGEMENTS .......................................................................................................................... 4 TABLE OF CONTENTS .............................................................................................................................. 5 1 INTRODUCTION .............................................................................................................................. 1

1.1 Background ............................................................................................................................... 1 1.2 Project Description ................................................................................................................... 2

2 REQUIREMENTS ............................................................................................................................. 3 2.1 Customer Requirements (CRs) ................................................................................................. 3

2.1.1 Industry Safety Standards (50) .................................................................................... 3 2.1.2 Manufacturability/Reproducible (80).......................................................................... 3 2.1.3 Visualization (50) ........................................................................................................ 3 2.1.4 Simulates Calcified Lesion (70) .................................................................................. 3

2.2 Engineering Requirements (ERs) ............................................................................................. 4 2.2.1 Vessel Transparency .................................................................................................... 4 2.2.2 Operate at Body Temperature ..................................................................................... 4 2.2.3 Lesion Durometer ....................................................................................................... 4 2.2.4 Lesion Adhesion Strength ........................................................................................... 4 2.2.5 Lesion Length ............................................................................................................. 4 2.2.6 Vessel Inner Diameter ................................................................................................. 5 2.2.7 Degree of Vessel Occlusion ........................................................................................ 5 2.2.8 Lesion Thickness ......................................................................................................... 5 2.2.9 Cost ............................................................................................................................. 5 2.2.10 Operate at Blood Pressure ....................................................................................... 5 2.2.11 Meets ANSI Standards ............................................................................................ 5 2.2.12 Meets OSHA Standards .......................................................................................... 5

2.3 Testing Procedures (TPs) .......................................................................................................... 5 2.3.1 Testing Lesion Durometer (#1) ................................................................................... 5 2.3.2 Testing Lesion Adhesion Strength (#2) ....................................................................... 6 2.3.3 Testing Lesion Length (#3) ......................................................................................... 6 2.3.4 Testing Lesion Thickness (#3) .................................................................................... 6 2.3.5 Testing Degree of Occlusion (#4) ............................................................................... 6 2.3.6 Testing Visualization (#5) ........................................................................................... 6

2.4 Design Links (DLs) .................................................................................................................. 6 2.4.1 Lesion Durometer – Design Link 1 ............................................................................. 6 2.4.2 Lesion Adhesion Strength - Design Link 2 ................................................................. 7 2.4.3 Lesion Length - Design Link 3 ................................................................................... 7 2.4.4 Lesion Thickness - Design Link 4 .............................................................................. 7 2.4.5 Degree of Occlusion - Design Link 5 ......................................................................... 7 2.4.6 Vessel Diameter - Design Link 6 ................................................................................ 8 2.4.7 Vessel Length - Design Link 7 .................................................................................... 8 2.4.8 Visualization of Deployment Device - Design link 8 ................................................. 8 2.4.9 Repeatable Manufacturing Processes - Design Link 9................................................ 8

2.5 House of Quality (HoQ) ........................................................................................................... 9 3 EXISTING DESIGNS ...................................................................................................................... 10

3.1 Design Research ..................................................................................................................... 10 3.2 Current Manufacturers ............................................................................................................ 10

3.2.1 Vascular Simulations ................................................................................................. 10 3.2.2 United Biologics Inc. ................................................................................................ 11 3.2.3 BoneSim Laboratories ............................................................................................... 12

3.3 System Components ............................................................................................................... 12 3.3.1 Silicone Vessels ......................................................................................................... 13 3.3.2 Calcified Lesions....................................................................................................... 14

4 DESIGNS CONSIDERED ............................................................................................................... 15 4.1 Buildup through Flow ............................................................................................................. 15 4.2 Diseased Pig Vein ................................................................................................................... 15 4.3 Vertical Centrifugal System .................................................................................................... 16 4.4 Petroleum based Product ........................................................................................................ 16 4.5 Smashed Fired Clay ................................................................................................................ 16 4.6 Sand ........................................................................................................................................ 18 4.7 3D Printing ............................................................................................................................. 18 4.8 Spray Can Texture .................................................................................................................. 18 4.9 Balloon in Tube ...................................................................................................................... 18 4.10 Two Concentric Tubes ....................................................................................................... 18 4.11 Synthetic Plaque ................................................................................................................. 18 4.12 Gum .................................................................................................................................... 19

5 DESIGN SELECTED ....................................................................................................................... 20 5.1 Rationale for Design Selection ............................................................................................... 20 5.2 Design Description ................................................................................................................. 22

5.2.1 Engineering Calculations .......................................................................................... 22 5.2.2 Modeled Drawings .................................................................................................... 22 5.2.3 Prototypes ................................................................................................................. 23

6 IMPLEMENTATION ....................................................................................................................... 25 6.1 Manufacturing ........................................................................................................................ 25 6.2 Design of Experiment ............................................................................................................. 28

6.2.1 Testing Results - Hardness ........................................................................................ 28 6.2.2 Testing Results – Lesion Adhesion Strength ............................................................. 30

7 TESTING .......................................................................................................................................... 31 7.1 Material Durometer Testing .................................................................................................... 31 7.2 Lesion Property Testing .......................................................................................................... 31 7.3 Mock Vessel Testing ............................................................................................................... 32 7.4 Adhesion Testing .................................................................................................................... 33 7.5 Miscellaneous Testing ............................................................................................................ 33

8 CONCLUSIONS .............................................................................................................................. 34 9 REFERENCES ................................................................................................................................. 35 10 APPENDICES .................................................................................................................................. 37

10.1 Appendix A – House of Quality ......................................................................................... 37 10.2 Appendix B – Pugh Chart .................................................................................................. 38 10.3 Appendix C - Schedule ...................................................................................................... 39 10.4 Appendix D – Prototyping and Display Costs ................................................................... 40 10.5 Appendix E – Hardness Testing Results ............................................................................ 42 10.6 Appendix F – Adhesion Strength Testing Results .............................................................. 45

1 INTRODUCTION For this project the team was tasked with creating a safety compliant and customizable

calcified vessel model for W.L. Gore & Associates. The model is used to better understand how lesions affect blood flow and how endoprostheses such as the VIABAHN function as they are deployed in calcified vessels of varying disease levels. This model is significant to W.L. Gore & Associates because they need the ability to test and study the deployment of their endoprostheses in an environment that is as similar as possible to a real life situation. Studying the deployment of their stents in a diseased model is very useful for future product development.

1.1 Background W.L. Gore & Associates is a privately held that designs, tests, and manufactures a

multitude of products. Their products are used in the medical, fabric, and industrial markets. In 1969 Bob Gore discovered a versatile new polymer referred to as expanded polytetrafluoroethylene (ePTFE). Since its discovery, Gore pioneered the use of ePTFE and has designed all of its products with ePTFE due to its properties. This practice has manifested a commitment to remaining a leader in the widespread application of fluoropolymers.

Gore’s VIABAHN Endoprosthesis medical device has quickly become their primary product in the medical field. Its primary use is to restore blood flow to arteries that have been clogged by plaque and calcium buildup. This kind of flow restriction can result in loss of limb, and blood clots. The VIABAHN is created with ePTFE, and the shape memory alloy Nitinol. These materials create a device that is durable, reinforced, biocompatible, and flexible. Prior to this project, Gore has used healthy models to test their stents and other potential endoprostheses. This includes the use of artificial vessels made of thermosetting and thermoplastic polymers, as well as real vessels from biological models. The use of endoprostheses however is to restore blood flow to diseased sections of vessels, so their current testing models do not provide as much information as would diseased models.

Figure 1.1 – Healthy and damaged blood flow [1]

The diseased model can improve the way that Gore tests their products. Damaged vessels develop blood flow restriction due to cholesterol in the blood that attaches to fat, calcium, and other substances found in blood and can begin to accumulate on the arterial wall. Over time this plaque can build up and effectively cause the artery to narrow and constrict the blood flow [1].

The calcification of an artery is referred to as atherosclerosis, and at first does not cause any health issues, but over time can have serious and life-threatening implications such as stroke or heart attack. The cause of atherosclerosis is not entirely understood, but several risk-factors that lead to this disease have been identified. There are many lifestyle choices that can affect one’s likelihood of developing atherosclerosis, the main ones being diet, exercise, stress, excessive alcohol consumption, and smoking [1], [2].

Medication can be prescribed to help control cholesterol levels, but in severe cases an invasive procedure is necessary [3]. The two procedures used to treat atherosclerosis are bypass surgery and stenting. Bypass surgery is when a surgeon removes a healthy blood vessel from the body and uses that to create a new path for blood to flow. Stenting is the process of inserting a catheter into the patient’s artery and using an x-ray device to track the catheter to the diseased area of the artery. A stent, a metal mesh that retains its shape, is then deployed in the constricted region of the artery. With the use of a small balloon on the catheter, the stent is expanded inside the artery. The catheter is removed and blood can now flow more easily through the previously constricted artery [3], [4].

1.2 Project Description W.L. Gore & Associates currently only possess healthy blood vessels to test and study the deployment of their endoprosthesis. Creating a diseased vessel, with the ability to increase/decrease the severity of the diseased occlusion, is a worthwhile endeavor when trying to study the deployment of their stents.

The following is the original project description provided by the sponsor:

“The scope of this project is to design, build, and test a replicable model of calcified lesions in the Peripheral Arterial System for deployment of peripheral vascular interventional devices under simulated use conditions, using non-biologic materials.”

2 REQUIREMENTS The following requirements were created using the project description given by W.L. Gore & Associates. Each customer requirement (CR) is a requirement set by the client, Gore, which the final product must meet. Each CR is given a goal value to be met, which is represented as an engineering requirements (ER). All CRs are weighted based on significance to the final design as well. These ERs feature specific target and tolerance values that control the measurable quantities for the final design.

2.1 Customer Requirements (CRs) Each of the following four CRs feature a weighted value based on their importance in relationship to the final design. The CRs are directly related to the original project description presented by W.L. Gore & Associates. Each CR is related to a broad topic associated with the final design, and each respective weight is shown in parentheses for all CRs. All weights are out of 200.

2.1.1 Industry Safety Standards (50) ANSI and OSHA standards needed to be met and adhered to for all aspects of the design. By following these guidelines, the model was safe and convenient to use, as no extra precautions were needed when using the device. The device needed to be able to function at temperatures and pressures commonly seen in the human body without any concern for the user’s physical safety. Absolutely no biological materials were used that pose any risk of infection or contamination to the user or the workplace. Creating the model involved minimal risk that could be controlled when the proper precautions were taken.

2.1.2 Manufacturability/Reproducible (80) The calcified vessel model needed to be easily reproducible in a lab environment with minimal manufacturing equipment. Multiple models needed to be created efficiently and economically. The manufacturing process of the vessel needed to be extensively documented and easily repeated by another independent party. The need for multiple models that are easily reproduced is considered a very high priority so this CR is given a weighted value of 80.

2.1.3 Visualization (50) The model needed to be transparent. A better analysis of peripheral vascular devices and their behavior within the body could be conducted if the user could easily see what was happening when the device was deployed. The material used to create the model needed a high transparency that did not distort the view into the vessel in any way.

2.1.4 Simulates Calcified Lesion (70) In order for the devices to be properly evaluated, the test conditions needed to simulate the human body. Vascular intervention devices commonly use materials designed to react at temperatures seen in the human body, making the temperature of the model a crucial aspect for proper deployment. The arterial compliance and calcification representation needed to behave similarly to the human body under conditions seen in the human body (i.e. temperature and blood pressure) to ensure an accurate model.

2.2 Engineering Requirements (ERs) The following ERs were created to attain measurable target values for each of the four CRs. Each ER features a target value along with an acceptable tolerance value based on academic research. Table 1 features each ER and their respective target and tolerance values below.

Table 1 - Summary of Engineering Requirement Values Requirement Units Target Tolerance Range Transparent % 100 -20 80-100 Lesion Durometer Shore A 85 ± 10 75-95 Lesion Adhesion N/m 20 ± 15 5-71 Lesion Length cm 15 ± 1 3-27 Vessel Diameter mm 7 ± 1 4-12 Lesion Thickness mm 6 ± 1 4-6 Degree of Occlusion % 75 ± 10 50-95 Vessel Length cm +10 per side ± 1 15-40 Cost $ 3000 N/A <3000 ANSI Standards N/A Meets All N/A N/A OSHA Standards N/A Meets all N/A N/A Body Temperature (LTE) °C 37 ± 12 25-49 Blood Pressure (LTE) mPa 19 ± 9 10-28

2.2.1 Vessel Transparency Vessel transparency allowed the user to see the deployment of interventional devices. The vessel had a transparency that approached 100% (completely clear).

2.2.2 Operate at Body Temperature This requirement was designated as a low technical effort (LTE). It was given this value because the materials proposed in the design functioned in the range of temperatures seen by the human body. The target value for this requirement was 98 ± 10°F [5].

2.2.3 Lesion Durometer Lesion durometer indicates the hardness of the calcified lesion using the Type A Shore hardness scale. Through calculations using the stress versus strain curve of a calcified lesion [6] the shore hardness of a calcified lesion was determined. The target hardness for the lesion was 85 ± 10 Shore A.

2.2.4 Lesion Adhesion Strength The ability of the lesion to stay fixed to the inside of the vessel was evaluated using the lesion adhesion strength. The adhesion strength target replicated the levels of adhesion seen inside of the human body, with no upper limit.

2.2.5 Lesion Length The length of the lesion was measured from end to end and was completely contained in the vessel. The lesion length target was 15 ± 1 cm [7], [8].

2.2.6 Vessel Inner Diameter Proper representation of the vessel diameter was needed to ensure that interventional devices deployed properly in the vessel. The target diameter for the vessel was .35 ± .08 inches [9].

2.2.7 Degree of Vessel Occlusion The degree of vessel occlusion must had to represent the degree at which interventional devices are used by surgeons. The target value for the percent of vessel occlusion was 75 ± 20% [10].

2.2.8 Lesion Thickness The lesion thickness designated the shape of the lesion as well as the degree of vessel occlusion. This value was thus based on percent occlusion and vessel diameter. The target range for the lesion thickness was .25 ± .08 inches [9], [10].

2.2.9 Cost The customer provided a budget that covered all project costs. The cost of prototyping, report materials, and final product manufacturing could not exceed $3,000.00 [11].

2.2.10 Operate at Blood Pressure This requirement was designated as an LTE. It was given this value because the materials proposed in the design functioned in the range of pressures seen in the human body. The target range for this requirement was 2.7 ± 1.3 psig [12].

2.2.11 Meets ANSI Standards The product had to meet applicable ANSI safety and testing standards.

2.2.12 Meets OSHA Standards The product had to meet applicable OSHA safety standards.

2.3 Testing Procedures (TPs) The following testing procedures highlight how each attribute of the design was tested to ensure that they fell into the ranges detailed in the engineering requirements (Table 1). ASTM testing standards were used where applicable, while more simplistic testing methods were used for all other tests.

2.3.1 Testing Lesion Durometer (#1)

The durometer of a material is determined on the surface of 100 samples of the lesion material. This test was completed with the use of an ASTM-D2240 Shore A durometer tester. This instrument was positioned vertically on each test sample and pushed until the flat test plate was flush against the test sample. The tester then gave a readout for the hardness of each sample. The tester was evaluated for accuracy using a set of certified test blocks to ensure the results were within an acceptable range [13].

2.3.2 Testing Lesion Adhesion Strength (#2)

The adhesion strength of the lesion to the vessel was evaluated using ASTM-D903. This procedure pulled the vessel at a 180 degree angle relative to the lesion using a tensile force. The force was measured using a force gauge attached to the vessel. The force gauge was pulled parallel to the force on the vessel. The strength of the adhesion between the vessel and the lesion was thus evaluated based on the force required to separate them [14].

2.3.3 Testing Lesion Length (#3)

To certify the model met this requirement, an analog measurement of length was conducted. This test was completed using a high-resolution ruler. To ensure that the model was not altered during measurement, only the natural length was evaluated.

2.3.4 Testing Lesion Thickness (#3)

Lesion thickness is constricted by the size of the mold and is determined by the 3D model before the mold is physically created. The manufactured lesion is evaluated using a set of calipers to ensure the dimensions are similar and no contraction/expansion occurred during manufacturing.

2.3.5 Testing Degree of Occlusion (#4)

The degree of vessel occlusion was evaluated numerically based on average cross sectional area of the occlusion, determined in the 3D model, divided by the cross sectional area of the vessel.

2.3.6 Testing Visualization (#5)

The transparency of the model was evaluated using a visual test. Once the lesion is placed inside the vessel, the transparency was evaluated. If the evaluator is able to see the lesion details through the vessel then the model meets the transparency requirement.

2.4 Design Links (DLs) The following design links explain how each of the engineering requirements were met through the construction of the proposed design model found in Section 5.2. The number associated with each design link correspond to the design link number in the house of quality.

2.4.1 Lesion Durometer – Design Link 1

The lesion durometer refers to the hardness of the calcified region of the model. The calcium that forms in a lesion is predominantly calcium phosphate (hydroxyapatite) and

is formed in a way similar to bone formation or bone repair [15]. A material was selected that accurately mimicked the hardness values of an SFA calcification. Thorough testing through a statistical analysis ensured that the hardness value of the selected material was appropriate.

2.4.2 Lesion Adhesion Strength - Design Link 2

Lesion adhesion strength is defined as the force required to disrupt the bond between the arterial vessel and the calcified occlusion within the vessel. It is dangerous in many cases for a calcified buildup to break free from a vessel and travel to a different area of the body. To create a model that accurately represented calcified lesions in the human body, the adhesion strength of the model lesion had to fall into the range of strengths seen in the human body. Through academic research it was determined that the lesion strength needed to withstand a maximum shear stress of six Pascals [16]. A bonding agent was selected that accurately mimicked the adhesion strength values of SFA calcification to the SFA. Thorough testing through a statistical analysis ensured that the adhesion strength value of the selected material is appropriate.

2.4.3 Lesion Length - Design Link 3

When a vessel calcifies, a certain length of the vessel changes in physical characteristics, which is known as the lesion length. To create a model that accurately represented calcified lesions in the human body, the length of the model lesion had to fall into the range of lengths seen in the human body. Through academic research, it was determined that the lesion would be an average of 6 inches in length [17]. To best represent the variability seen in human subjects, a range of ±5 inches was implemented [18]. The lesion length was also a direct reflection of the model length. The model length was set to a target value of 15 cm.

2.4.4 Lesion Thickness - Design Link 4

When a vessel calcifies, the calcified lesion achieves a certain thickness based on how long the lesion has been forming and the length of the lesion. To create a model that accurately represented calcified lesions in the human body, the thickness of the model lesion had to fall into the range of thicknesses seen in the human body. The lesion thickness had a target value of 6 mm. The lesion thickness was determined by the depth of the 3D printed model, which had a depth of 6 mm.

2.4.5 Degree of Occlusion - Design Link 5

In order to meet the design requirements, a varying degree of vessel occlusion had to be viable to manufacture to accurately model possible diseased arteries. In order to find the proper level of occlusion, research was conducted and it was found that a stent would be placed in the body with a level of occlusion between 55-95% of lumen reduction [19]. Lumen refers to the inner most walls of the artery, which blood travels through. It is the reduction of the lumen vessel (inner diameter) that is the focus of this test [20]. A target value of 75% occlusion was accomplished through the construction of the 3D printed

mold combined with the known specifications from the silicone tubing manufacturer.

2.4.6 Vessel Diameter - Design Link 6

The vessel diameter relates to the inner and outer diameter of an artery or vessel within the human body. Accurately mimicking the inner diameter of the femoral artery was of more importance than mimicking the outer diameter. Through academic research it was found that the average diameter for a femoral artery is 7 mm [21]. To best represent the variability seen in human subjects, a range of ± 1 mm was implemented. The diameter of the vessel was constant, as the vessel was procured through a silicone tubing manufacturer. Routine measurement of the acquired vessel ensured that it still met the design requirements.

2.4.7 Vessel Length - Design Link 7

In order to fully encompass the desired lesion length, the artificial vessel was 10 cm longer on either side of the lesion to allow for installation of the model into the testing system. Accounting for the length of the lesion, each artificial silicone vessel had a length of 35 cm.

2.4.8 Visualization of Deployment Device - Design link 8

In order to meet the transparency requirement, the material used to create the vessel was clear. The level of transparency had to approach 100%. This was important because the user had to be able to see the deployment of the device in order to better analyze performance. The silicone tubing provided had a high transparency and could be clearly and easily seen through without special equipment.

2.4.9 Repeatable Manufacturing Processes - Design Link 9

In order for this design to be practical in industry it had to be easily produced, as each calcified model was to be used just once to study the deployment of a particular device. Documentation was provided to the client which described the vessel and lesion creation guidelines, allowing for the creation of a customized lesion.

2.5 House of Quality (HoQ) The house of quality is used to highlight the customer requirements and their relationship to the prescribed engineering requirements. The target and tolerance values for engineering requirements are also noted in the house of quality. See Appendix A for the house of quality spreadsheet.

3 EXISTING DESIGNS There are a multitude of existing designs related to accurately simulating the human body. In particular, three designs from three different companies were analyzed to create an understanding of what has already been engineered and used in relationship to artificial vessels and calcifications. All three companies have made their products available to the market, and have used their products to better the lives of patients as well as practitioner experience and understanding.

3.1 Design Research To begin researching similar devices that replicate the human body and its characteristics, web-based research of existing designs was conducted. The results of this research are shown below. Research methods for these manufacturers and designs was obtained through the use of web-based search engines and the Cline Library Ebscohost database. All three manufacturers were contacted via email and telephone in order to more accurately understand the intricacies of their specific products.

3.2 Current Manufacturers Replicating the human body accurately has several advantages when the need to test medical devices arises. Visualizing the deployment of a stent will allow the engineer to understand if a device requires further design to function as intended. Deploying a stent in an actual patient is never simple, and having a system, such as United Biologics or Vascular Simulations, which replicates arterial geography allows the engineer to determine if their stent can be guided to any diseased location in the body with relative ease. The study of plaque buildup and its inherent material properties, is necessary when deploying stents into that environment. Stent structural requirements may be modified, after testing deployment in a life- like model, in order to more accurately handle the harsh environment of a diseased vessel.

3.2.1 Vascular Simulations Vascular Simulations is a New York based company that replicates the cranial, aortic, and abdominal blood vessels of patients in need of endovascular procedure. This is possible with the use of a 3D rotational angiogram, CT angiogram, or MR angiogram that scans the exact vasculature of the patient. The completed vascular replica is made of a hollow silicone structure that mimics the patient’s vessel walls, and is able to have fluids pumped through it.

Vascular Simulations utilizes pulsatory flow in their models to better replicate the in-vivo

environment that practitioners work in. When using pulsatory flow the silicone walls expand and contract with the variance in fluid pressure, mimicking actual blood vessel behavior. Simulated vasculature is shown in Figure 3.1. This system provides the interventionalist a near-exact vessel structure to use when practicing the endovascular procedure. Providing intravenous practice to the interventionalist greatly decreases risk to patient health during the procedure.

3.2.2 United Biologics Inc. A researcher and manufacturer of vascular simulations is United Biologics Inc. The company is engaged in designing silicone replications of human vasculature shown in Figure 3.2. Although most of their products are a model of the common pathologies of the human body, there have been physicians and engineers that have requested and received custom vessels to accurately replicate specific patient scenarios. In the company's words, "Our silicone vessels are designed to demonstrate, facilitate and challenge the development and training of endovascular medical devices" [23]. These devices contain a core model which can be purchased, and then a wide variety of attachments can be added. To simulate the real world, a surgery would require moving through the iliac artery to deploy the endovascular medical device. This "core" could be used in multiple tests, and the only change would be to the femoral artery line. This would add to a higher level of precision in testing and a more controllable environment for stent deployment.

Figure 3.1 – Vascular Simulations’ Model [22]

Figure 3.2 – United Biologics’ Vascular Model [23]

3.2.3 BoneSim Laboratories BoneSim Laboratories is a small Michigan based company that produces calcified lesion models [24]. They produce models that vary in lesion density, vessel wall thickness, vessel diameter, lumen position and lumen diameter as seen in Figure 3.3. The models do not have designation to which vessel they represent within the human body. BoneSim’s products can be ordered in both large quantities and single units. This company was researched through a website search engine, through email correspondence, and through telephone communication with the president of the company.

3.3 System Components When designing a system to replicate the human body, many subsystems are important. The necessary requirements pertaining to this design are:

x Arterial vessel similarity

x Calcified lesion similarity These requirements are met through the use of silicone tubing, which can either be manufactured in house through the use of a molding process or they can be bought through an artificial vessel manufacturer directly. The calcified lesion will be replicated through the use of a 3D printer, by either printing a mold in which a material is poured or by directly printing the calcified lesion.

Figure 3.3 - BoneSim’s calcified vessel models [18]

3.3.1 Silicone Vessels Silicone is an elastomeric polymer whose elasticity and surface texture accommodate for vessel-like flow. Silicone vessel walls are commonly used for their artery-like properties, as arteries within the human body are not rigid, and are able to expand and contract due to the pulsatory flow and body movement. Silicone’s high elasticity allows for optimal reproduction of this pulsatile expansion and contraction. It also accurately represents the structural characteristics of arteries in terms of radial strength and elasticity. 3.3.1.1 Vascular Simulations Vessels

Vascular Simulations utilizes silicone vessel walls in their synthetic vasculature to mimic the risks that a patient will face when endovascular procedures are conducted. Some of their products are exact replicas of the patient’s vasculature, showing that silicone is a viable option for vessel material due to its manufacturability and its mechanical properties. Some of their designs include a gel that surrounds the silicone vessels. This replicates the external pressure that vessels experience in the body, but does not restrict the expansion of the silicone during flow. 3.3.1.2 United Biologics Vessels

United Biologics uses a customizable core model with peripheral attachments to accurately reproduce the human arterial geography. Due to its vessel-like properties, silicone is used in all of their core models. These models are 3D printed and are extremely precise, manufactured to the specifications shown in Figure 3.4. The 3D printed silicone is able to meet the many specifications of United Biologics’ design requirements, and is highly customizable. This allows for many applications that require specific properties.

Figure 3.4 - Silicone Properties

3.3.1.3 BoneSim Laboratories Vessels

Although there is no manufacturer’s information given on the material of the tubing used to represent the vessel, it appears to be latex based on the amber color. Several inner diameters are offered, ranging from 3mm to 12mm, and all models are 100mm in length [25].

3.3.2 Calcified Lesions A calcified lesion is a clump of plaque found within a blood vessel, which has adhered to the vessel. The buildup is initially soft, but after a period of time, the plaque will become rigid. This is when the calcification of the arterial plaque occurs. Mimicking the calcification will be done through the use of either dental stone or hydroxyapatite. Testing will be completed to compare each materials properties to the researched properties of SFA calcifications.

3.3.2.1 BoneSim Laboratories Lesions

BoneSim uses reconstituted bovine bone and a synthetic binder that can be altered to create varying densities of the lesion [25]. The different densities are used to represent the varying levels of hardness found in calcified lesions. BoneSim offers three levels of occlusion, characterized by the lesion lumen size as well as three different lumen positions, offset from the center.

4 DESIGNS CONSIDERED Based on the products and systems studied during the existing design stage, the following brainstormed ideas were discussed and analyzed. The brainstorming methods focused on a traditional brainstorming session in which team members verbally communicated ideas to each other, with a single note taker. A method in which a ball was thrown from team member to team member, focusing on the repetition of previous ideas and the creation of new ideas was also used.

The focus of the brainstorming session revolved around accurately replicating the occlusion within the artery, as this particular aspect of the project has very few applications outside of this design. Another focus was centered on successfully implanting the created occlusion into the artificial artery.

4.1 Buildup through Flow This bio-inspired design idea revolved around the use of a liquid filled with particulates, which would slowly build up a calcification within a vessel represented by a stock piece of silicone tubing. The tube may need to be altered to accelerate the buildup of the calcification. This idea is similar to how coral reefs are created in nature. A gravity fed system would flow liquid through the artificial vessel and the process would be repeated until the desired calcification was achieved.

Pros:

x Replicates natural buildup

x Cheap

x Easy to manufacture

Cons:

x Time to manufacture

x Not consistent in calcification characteristics

x Would require modification to inside of silicone tube

4.2 Diseased Pig Vein This bio-inspired design would focus on the use of diseased pig vasculature. Portions of the pig arteries would be removed from the corpse and used in the experimental procedure. Varying levels of disease could be present, depending on the pig used.

Pros:

x Natural

x No manufacturing

Cons:

x Uses biological materials

x Not consistent in calcification characteristics

x Sloppy and unhealthy

4.3 Vertical Centrifugal System This design would use a system that rotates the vessel, a stock piece of silicone tubing, at a high rate of speed to distribute the material inside the model. The material used to replicate the lesion would be injected from the top in a liquid form. The lesion size could be changed by the amount of material injected into the vessel. This would require a small mechanical set-up to spin the vessel as material was injected.

Pros:

x Replicates round lesion

x Easy to manufacture

x Short manufacture time

Cons:

x Only simulates round lesions

x Material has to be liquefied

x Difficult to normalize

4.4 Petroleum based Product This design would use a petroleum based product to represent the calcification. The product would have properties such that it melted at a lower temperature than the silicone tubing used to replicate the vessel but remained solid at body temperature. This would allow the vessel to be reused with various degrees of occlusion. The petroleum product would be injected into the vessel using a syringe.

Pros:

x Reusable vessel

x Low cost

x Easy to manufacture

Cons:

x Would simulate lesions well

x Difficult to normalize occlusion

x Intervention device may become lodged inside vessel

4.5 Smashed Fired Clay This design would utilize broken pottery pummeled into a fine powder. This powder would then be placed into the silicone vessel using a liquid adhesive such as super glue. The vessel used in this model would be a stock piece of silicone tubing.

Pros:

x Low cost

Cons:

x Difficult to normalize occlusion

x Difficult to pulverize clay sufficiently

x Injection of adhesive would be difficult

4.6 Sand This design idea focuses on the use of sand to create the occlusion within an “off the shelf” silicone tube. Sand would be injected into the vessel through the use of a syringe, and it would be bonded to itself through the use of a chemical binder similar to a sand casting process.

Pros:

x Low cost

x Moderately easy to manufacture

Cons:

x Difficult to normalize occlusion

x Bonding agent may fail during testing

4.7 3D Printing This design would use a 3D printer to print an occlusion out of various materials, depending on the desired lesion durometer. The 3D printer could also be utilized to print a mold, in which a material is poured into the printed mold. Limitations on lesion size are based solely on the precision of the available 3D printer. The printed occlusion would be placed into a silicone tube using some sort of adhesive.

Pros:

x Extreme precision in occlusion representation

x Easy to adjust for various requirements

x Easy to reproduce occlusions

Cons:

x Material limitation

x 3D printer limitation

4.8 Spray Can Texture This design idea would use a texture, sprayed out of a pressurized can (similar to a drywall texture) to create the occlusion. The can nozzle would simply be placed inside the silicone tube, which represents the artificial vessel, and discharged. The properties of the spray and the material would ensure that it stuck to the inside of the vessel.

Pros:

x Easy to manufacture

x Low cost

x Short manufacturing time

Cons:

x Difficult to normalize occlusion

x Spray velocity may be too high for vessel

x Lots of wasted product

4.9 Balloon in Tube This design idea revolves around using a silicone tube to represent the vessel and then deploying a blown up balloon inside of the tube. This balloon would represent the occlusion within the artery. It would have the ability to be inflated to various sizes/pressures to offer a variety in occlusion characteristics.

Pros:

x Offers variety in occlusion characteristics

x Low cost

Cons:

x Simplistic approach

x Balloon sizing may be difficult

x Adhesion characteristics would be insufficient

4.10 Two Concentric Tubes This design would use two silicone tubes placed inside of each other. The outer tube, which would represent the artificial vessel, would have an inner diameter matching the outer diameter of the inside tube, which would represent the occlusion. This sizing would create the necessary adhesion strength between the vessel and occlusion.

Pros:

x Easy to manufacture

x Low cost

x Occlusion variability

Cons:

x Vessel properties are diminished

x Simplistic approach

x Poor representation of calcification

4.11 Synthetic Plaque This design would focus on the deployment of a premanufactured synthetic plaque into a silicone vessel. The synthetic plaque would have characteristics that accurately mimic the plaque found within the human body. The synthetic plaque would be injected into the vessel to achieve the desired level of occlusion.

Pros:

x Represents plaque very well

x Easy to manufacture

Cons:

x High cost

x Does not represent calcification well

x Simplistic approach

4.12 Gum This design idea uses preprocessed chewing gum to represent the occlusion within an artery. Silicone tubing would be used as artificial vessels, which is where the chewing gum would be inserted. Insertion of the chewing gum into the artificial vessel would be difficult, though its inherent characteristics may act as a glue to hold it to the inside of the vessel.

Pros:

x Easy to create occlusion

Cons:

x Simplistic approach

x Difficult to normalize occlusion

5 DESIGN SELECTED 5.1 Rationale for Design Selection Through the use of group brainstorming sessions, the team came up with twenty different ideas to construct both the vessel and the occlusion. These twenty ideas were not restricted to plausibility or overall effectiveness. Initial prototyping ideas came from these twenty ideas, as many are easy to construct and cheap to produce. After creating the twenty ideas, a Pugh Chart (Appendix B) was used to narrow the ideas down to a more usable number of effective ideas. A datum idea was chosen, and then the other nineteen ideas were compared to it, simply using pluses or minuses to compare each idea. The three ideas that compared most favorably to the datum were chosen to be analyzed and compared further.

In order to narrow the final design from the group brainstorming sessions to a single idea, a decision matrix was used. The decision matrix analyzed the three designs from section 4. Table 2 shows the decision matrix and the associated criteria and weights that were calculated based on each design.

Table 2 - Decision Matrix

Requirement Weight Buildup through flow 3-D

printing Two concentric

tubes Feasibility 7 42 56 49 Normalize 4 8 40 40

Accurate Representation of Plaque 5 40 35 15

Cost 2 16 14 14 Time to Manufacture 3 3 24 27

Repeatability 4 24 40 40 Total 25 133 209 185

The selected manufacturing method used to create the model of the artery and plaque was by 3D printing. The arterial vessel will be simulated by standard tubing and the focus of the project and manufacturing will be on the lesion. The limiting factor for 3D printing is the material and the tip size of the 3D printer. If the 3D printer cannot model the calcification's mechanical properties with a given material then a mold will have to be created. If a mold needs to be created it will be printed from an easy to manufacture plastic. The most common material to print in is thermoplastics and among these are Polylactic Acid (PLA), Acrylonitrile Butadiene Styrene (ABS) and PolyAmide (PA). PLA is typically made from a petroleum based plastic and can be easily manipulated. PLA melts at 130 °F which would make it a low cost material to manipulate. The primary issue with using plastics for the modeling of plaque is that a calcified lesion has a large variation in hardness. According to a study "The majority of calcified samples showed durometer values of 0.7±2.2GPa" [26]. This research also noted that as the occlusion increases in size, the durometer of the calcification increases. This large range of potential hardness values makes it difficult to use any single material to model all occlusions. Current production in the NAU manufacturing facility is limited to plastics;

however, a graduate student is currently working on a metal adaptation system. The most probable material to make the lesion out of is ceramics, which is not an option for direct 3D printing. Due to the plastic mechanical property limitation, an accurate mold made by a 3D printer could then be manufactured such that the material set in the mold would more accurately simulate the lesion. Again, this lesion simulating material will most likely be ceramic. Specifically, Alumina Silicate Refractory, which is typically associated with bricks for housing. However, the material is very similar to plaque from a property view point. This material could be easily molded into small plaque replicating tubes for testing. If there is a way to 3D print the lesions directly, it would be preferred; however, a mold seems more practical. No matter what specific manufacturing process is selected, the end product will be similar to Figure 5.1 and Figure 5.2. The first figure shows a smooth, or ideal lesion whose level of occlusion linearly increases until only 60% of regular blood flow would travel through this system. This level was selected because several medical journals note that the majority of patients can live with 60% blood flow without knowing and without seeing symptoms of occlusion [19]. Figure 5.2 shows an extremely rough section of plaque. This lesion is most constricted at only 30% blood flow, but also provides several rough texture areas. The average restriction in this system was limited to approximately 45% of regular blood flow

Figure 5.1 - Initial Ideal Lesion Smoothness

Figure 5.2 - Initial Extreme Lesion Roughness

5.2 Design Description The final lesion design that was manufactured and tested is detailed in this section. An

initial iteration of this design was created at the midpoint of the project. The final design below was reached after the mold design was optimized, and the dimensions of the lesion refined. The changes made to the mold design are detailed in Section 6.1, and this section shows the final design and dimensions for the lesion.

5.2.1 Engineering Calculations In accordance with the engineering requirements and Table 1, the following final design has been modeled in SolidWorks. The dimensions of the lesion represent the target values from Table 1. The lesion will be adhered to the vessel tubing using an adhesive. The length of the lesion will be 150mm. The diameter of the lesion will be 7mm to match the inside diameter of the vessel. The lesion design can be seen below in Figure 5.3.

Figure 5.3 - Final Design: Dimensions

5.2.2 Modeled Drawings The selected design is a 3D printed lesion, which includes all design requirements. The cross-section of the lesion model is shown in Figure 5.4. This model has an open top so that the deployment of the interventional device can be seen through the transparent vessel as it is activated. The lesion is opaque, therefore it cannot be a solid cylinder and still fulfill the transparency requirement. The rough surface represents a calcified lesion’s tendency to have non-uniform build up. Having a rough surface better replicates life-like qualities as well as allows a change in occlusion percentage.

150mm

6 R. 3.50

Figure 5.4 - Final Design: Lesion Cross-section

The lesion will be inserted into the mock vessel manually. Prior to insertion the lesion will have a bonding agent attached to the semi-circular side so that is accurately mimics life like adhesion. When the lesion is inserted, there will be an extra 10 cm of mock vessel on each side of the lesion to allow for connection to a testing system and for laminar flow to form. The lesion will also have a gradual increase in cross sectional area at each end to help maintain laminar flow. This can be seen in Figure 5.5.

Figure 5.5 - Final Design: Lesion Overview

5.2.3 Prototypes Two initial prototypes were created prior to 3D printing. These prototypes include a “Works-like” model, and a “Looks-like” model, which were made to cheaply and effectively work and look the same way that the final product would, respectively. To construct the Works- like prototype, small silicone tubes were used to represent the vessel and a wooden dowel was placed inside to represent the occlusion. This model can be seen in Figure 5.6. Creating this model helped the team understand the difficulties in placing the occlusion inside the small vessel. It was evident that the lesion must have smooth edges to ease the placement of it inside the vessel. Additionally, an assisting tool like small thin tongs may be necessary to place the lesion a full 10cm from the mock vessel ends.

Figure 5.6 – “Works-like” Prototype

In order to construct the Looks-like prototype, a large diameter clear tube was used. Foam insulation was inserted into the tube to represent the occlusion. A semi-cylindrical occlusion was chosen over a full cylinder occlusion to allow for visualization of the deployment device. Also, determining the degree of vessel occlusion through the use of the app ImageJ is easier with this semi-cylindrical occlusion. The Looks-like prototype foam was glued to the tubing, however the super glue dried before it could bond the two surfaces. Other glues did not hold the foam firmly in place, so this prototype showed that a very specific bonding agent must be chosen. This prototype can be seen below in Figure 5.7.

Figure 5.7 – “Looks-like” Prototype

6 IMPLEMENTATION Several steps were taken in the completion of this project. Materials were purchased

locally or online through Amazon.com using the W.L. Gore capstone fund. Once the material was selected several molds were created. In order to create each mold,

multiple 3D printers were utilized on campus. Two MakerBot replicators and a Fortus 250MC operated by Dr. Oman and the NAU machine shop were used. These printers were used to create all iterations of the mold including the final three molds for manufacturing the final product.

The vessel material was provided by the client, W.L. Gore and associates, after the vessel properties were determined through research. A large quantity of the selected tubing was provided and was a sufficient amount to be used for all prototyping, testing and production of the final models.

Once the final lesions were produced and the vessel tubing was cut into appropriate sizes, the lesions were adhered to the vessel wall. This was completed using a silicone adhesive placed inside a syringe. The syringe was supported by a caulking gun provided by the NAU machine shop.

Final testing of the model properties required a custom apparatus for adhesion testing. This apparatus was created by the team members and used the machine shop’s manual mills and scrap material.

6.1 Manufacturing The manufacturing approach for this project originally consisted of a 3D printed two- piece mold, in which a calcification replication material was placed into. This proved to be ineffective as it was impossible to remove the lesions from the mold once they were dry. To refine the removal process, the two piece mold was replaced with a four piece mold that allowed for more consistent removal success. Half of the final mold is shown in Figure 6.1. Note that both pieces denoted with an “x2” have a piece that mirrors their shape, which creates the lesion shape shown in Figure 5.5. There are also two hollow square pieces in total.

Figure 6.1 – Final mold design

Initial designs of the lesion shape went through multiple iterations. Due to the 3D printing manufacturing process, the subtle design of the lesion surfaces would translate from SolidWorks to the 3D printed model differently than expected. So aside from the general length and diameter changes that were made, the topography of the lesion surface had to be changed so that the printed molds would create a lesion that had the correct surface characteristics.

The calcification replication material (dental stone) is mixed by hand and placed into the mold by hand. The mold is sprayed with a dry lubricant which eases the removal of the delicate calcification. The mold is then overfilled with the wet dental stone, then clamped shut. The excess dental stone is squeezed out of the mold through runners designed into the mold, and the square piece in Figure 6.1 is pushed over the mold to clamp. After twenty five minutes the calcification is removed from the mold by removing the square clamp, and carefully separating each section from the mold.

The completed lesion was then adhered to the vessel using a silicone adhesive. This adhesive was placed into a 10mL syringe and then injected between the lesion and the wall of the vessel. The adhesive was highly viscous and was difficult inject by hand. This was ratified by using a caulking gun to apply pressure to the syringe.

Table 3 lists all materials used in the final manufacturing of the model. The table displays the material used, material source and material costs. A comprehensive list of all display and prototyping costs can be found in Appendix D.

Figure 6.2 – Final model

A schedule (see Appendix C) has been created which outlines the milestones, meetings,

and deliverables for the project. The semester began with research and the selection of a material to be used for the occlusion. As the materials are selected the team will work on to the construction and testing of the initial mold and make adjustments as necessary. The initial materials tested were dental stone, mortar, and hydroxyapatite. After the initial materials testing was completed, it was determined that the dental stone yielded the most consistent and useful properties in relationship to the ER’s. After the final materials are selected and tested the team will begin a statistical analysis of 100 samples. The final deliverables will then be prepared, including the UGRADS presentation as well as a presentation at a W.L. Gore facility. The team is currently on schedule to complete all tasks.

Application Item Source Use Cost

Lesion

ABS/PLA 3D Printed Mold

Fortus/MakerBot Lesion formation -

Gypsum Stone (Calcium Sulfate)

Amazon Lesion Material $37.46

Digital Scale Amazon Gypsum Stone Mixture

$14.99

100mL Graduated Cylinder

Amazon Gypsum Stone Mixture

$10.26

3mL Glass Droppers Amazon Gypsum Stone Mixture

$7.75

SS Mixing Bowls Amazon Gypsum Stone Mixture

$8.90

Vessel 7mm ID Silicone Tubing

W. L. Gore & Associates

Vessel Wall -

Adhesion

Loctite Silicone Waterproof Sealant

Amazon Adhesive $4.28

10x 10mL Oral Medication Syringe

Amazon Adhesive Delivery $6.42

10x 10 cm Needle Amazon Adhesive Delivery $9.98

Testing

40 in. Ruler Amazon Lesion and Vessel Length

$40.00

Shore A Durometer Tester

Amazon Lesion Hardness $39.95

Shore A Durometer Certification

Amazon Hardness Readings Certification

$379.99

6” Digital Caliper Amazon Lesion Length $39.97 Digital Force Gauge Amazon Adhesion Testing $190.00 Adhesion test apparatus

Machine shop scrap Adhesion Testing -

Total Cost - - - $799.93

Table 3 – Material used for final model

6.2 Design of Experiment The following variables were controlled and monitored during the manufacturing process:

x Water-to-powder ratio (A)

x Hardness of cured material (B)

x Removal success rate (C) The ratio of water to powder that was used for each batch of lesions was an important

variable in the design. Due to the nature of the design, the resulting hardness and the maneuverability of the lesion out of the mold were dependent on the mixture.

Three batches of the mixture were created and placed in the molds for testing, and where possible, fifteen molds were created for each. The variables B and C are dependent on A, so all results shown are a result of each different mixture. The test results shown in Section 6.2.1 detail how a change in A (water-to-powder ratio) created a change in B (hardness) and C (removal success rate). The goal for the average hardness value was 85 Shore A, and the lesions had to be able to be removed from the mold without brittle fracture or loss of shape.

6.2.1 Testing Results - Hardness The mixture values for A are low, match, and high. Low signifies a mixture ratio with less water than dental stone, at a 45:55 mL ratio. Match signifies the same amount of water as dental stone, at a 1:1 mL ratio. High signifies more water than dental stone, at a 55:45 mL ratio.

The goal hardness value was 85 Shore A, so results for B (hardness) of “low” or “high” denote that the resulting hardnesses were below or above the accepted range of hardnesses in Table 1 (75 – 95 Shore A) respectively. Results for C (removal success rate) are either pass or fail. For a mixture to pass, the resulting lesion had to be removable from the mold and could not have any disfiguration for at least 90% of the sets. If less than 90% of the created molds could not be removed without causing damage, the mixture failed. Table 4 below represents the results of the initial testing of the material samples.

The hardness values were acquired using a handheld Shore A durometer tester. An average hardness value was calculated based on the fifteen samples in each batch, gathered 3 days after each batch was created.

Table 4 - Design of Experiment (Material)

Variable Average Hardness Value

(Shore A) Comments

A B C

Low High Fail 97.2 Impossible to remove without fracture

Match In Range Pass 87.9 All testing successful

High Low N/A N/A Did not cure, was not removable or testable

The mixture with a 1:1 water to powder ratio was the only successful mixture. Its hardness values stayed within the range of acceptable values, and all lesions were successfully removed without damage from the mold. Hardness values for the 1:1 mixture were further tested with a sample of 100 pieces. The data for the hardnesses was recorded twice for each sample, 48 hours after they were set. The results are shown in Figure 6.1.

Figure 6.1 – Hardness for 100 Samples

The hardness results showed that the values for all samples were within the acceptable range of hardnesses, and that the desired hardness is repeatable for future manufacturing and testing. The 1:1 ratio of water to powder was thus a success. Additional statistical values from the 100 samples are shown in Table 5. The raw data for the hardness testing can be found in Appendix E.

Table 5 – Hardness Values: Average and Standard Deviation

Test 1 Test 2 Average

Average Hardness (Shore A) 87.63 88.66 88.14

Standard Deviation 2.36 2.19 2.33

0 20 40 60 80 100

Sh o

re A

H ar

d n

es s

Sample Number

Hardness Data

Test 1

Test 2

Test 1 Linear

Test 2 Linear

6.2.2 Testing Results – Lesion Adhesion Strength Adhesion strength values for the silicone adhesive were tested for 30 lesion/vessel samples, after they had cured for 24 hours. Each adhesion test destroyed the lesion/vessel sample, so only 30 tests were completed and averaged. The results are shown in Figure 6.2.

Figure 6.2 – Adhesion Strength Values for 30 Samples

The adhesion strength results showed that the values for all samples were within the acceptable range, and that the desired adhesion strength is repeatable for future manufacturing and testing. Figure 6.2 depicts the final output values for the adhesion strength testing. The raw data for the adhesion strength testing can be found in Appendix F.

100

200

300

400

500

600

700

0 5 10 15 20 25 30 35

A d

h es

io n

S tr

en gt

h (

N /m

)

Sample Number

Adhesion Strength Data

Adhesion Strength

Linear (Adhesion Strength)

7 TESTING

Through evaluation of the product, based on testing procedures, it was determined that all requirements were met. The average result of each test is shown in Table i. During the testing of each component, multiple redesigns were created to ensure the final product met all requirements. The following describes the redesigns during testing and the corresponding procedures used to evaluate each property.

7.1 Material Durometer Testing

Once gypsum stone was selected as the ideal material, it was determined that, based on the manufacturers recommended mixing ratio, the durometer was outside of the acceptable range. The manufacturer’s suggested mixing ratio (mL water: g powder) provided a durometer that was slightly higher than the acceptable range. This led to experimentation with mixing ratios other than the recommended value. After testing, it was determined that a mixing ratio of 1:1 consistently provided a durometer within the acceptable range. 100 disc samples were created using the 1:1 ratio and evaluated by two teammates for their durometer using the procedure outlined in TP#1. The durometer test method can be seen in Figure 7.1.

7.2 Lesion Property Testing

The lesion length and thickness were incorporated into the design of the mold. These properties were constrained by the mold and did not vary between lesions produced by the same mold. The degree of vessel occlusion is directly related to the lesion thickness and is constrained accordingly. The first iteration of the mold consisted of 2 pieces that pulled away from the lesion in a vertical direction. The lesion would then be slid out of the mold after it had cured. This mold proved to be ineffective. A second iteration was created that utilized holes for excess material to

Figure 7.1 - Hardness testing

escape as the mold halves were compressed together. This mold pulled from the sides of the lesion and also proved to be ineffective. Holes for ejection pins were added to attempt to press the lesion pieces out of the mold, which proved unsuccessful as the material would break apart due to its brittle nature. The second mold iteration with material stuck inside the cavity can be seen in Figure 7.2. A third iteration was created, which was a vertical pull mold. It utilized holes for excess material to run out of, which doubled as ejection pins, in the bottom portion of the mold. This proved to be semi-effective as some complete lesion pieces were able to be removed. It was determined that the mold needed to have minimal surface contact per piece with the lesion. A 4 piece mold was designed and incorporated 4 main body pieces held together with 2 clamps. An injection port on top of the mold was incorporated in order to inject the material. A plug was developed to plug this opening and create the lesion end. This mold proved to be very effective in producing consistent results. After a fit test of the final lesion and vessel was conducted, the dimensions of the mold were reduced in order to accommodate a slight material expansion. Then a set of 3 molds were produced for final manufacturing shown in Figure 7.3. The final lesions were evaluated using the procedures outlined in TP#3, TP#4, and TP#5 to validate the resulting lesion length, lesion thickness and degree of vessel occlusion respectively.

7.3 Mock Vessel Testing

During manufacturing of the lesion, it was determined that a premanufactured silicone tube was to be used to reduce manufacturing time and costs. The properties of the tube were

Figure 7.2 – Second mold iteration

Figure 7.3 – Final molds for manufacturing

determined through research and several samples were provided by the client. An analysis was conducted and a specific tube was selected. This tubing was cut into sections of the appropriate length and acted as the vessel. This constrained the vessel length, vessel diameter and vessel transparency due to the uniformity in the premanufactured tubing. The properties of the 12 final models were evaluated using the procedures outlined in TP#3.

7.4 Adhesion Testing

A silicone adhesive was chosen based on its effectiveness in adhering the lesion to the vessel. The adhesion strength was evaluated using the procedures in TP#2 for 30 samples. In order to complete testing, a custom apparatus was created to utilize a standard bench vise which can be seen in Figure 7.4. These samples consisted of lesions adhered to sections of the mock vessel. After validating the effectiveness of the adhesive, it was determined that simply placing the adhesive on the back of the lesion and then sliding the lesion into the mock vessel did not produce acceptable results. It was determined that the adhesive would have to be injected between the lesion and the vessel wall after the lesion was placed into the vessel. This was done using a 10ml syringe and a 10cm blunt needle. The silicone proved to be highly viscous and difficult to inject by hand. This was ratified by incorporating a caulking gun to provide the force and stability needed to successfully inject the adhesive. This set up can be seen in Figure 7.5.

7.5 Miscellaneous Testing

Due to the nature of the product all ASNI and OSHA standards were met. No tests were performed because of the overall design of the product and the manufacturing process. The material properties were not affected by a long term water bath or increase in temperature. This satisfied the 2 LTEs outlined in the design requirements.

Figure 7.5 – Caulking gun setup for adhesive application

Figure 7.4 – Adhesion test with custom apparatus

8 CONCLUSIONS The mission for this project encompassed designing, manufacturing, and testing of a synthetic diseased calcified vessel with the same dimensions and physical properties of the superficial femoral artery (SFA) in a human leg. The purpose of this vessel is to improve upon the current benchtop testing that W. L. Gore & Associates uses to test current and future Endoprothesis devices such as the Viabahn. The team was able to successfully produce an appropriately sized, artificial calcified lesion in the lumen of a silicone vessel that met all engineering requirements set by the client. This final product replicated the restricted blood flow that a mature lesion of 85% occlusion in the SFA would cause.

The overall success of the project has been supported with affordable manufacturing, fast production times, a large budget provided by W. L. Gore & Associates, and rapid prototyping with 3D printers. Manufacturing the molds for the lesion was an iterative process that required multiple prints, however the 3D printing (MakerBot and Fortus) that was available to the team provided fast turn-around and allowed the team to fully optimize the mold. With the completed mold design, of which the team made three, the production time for each lesion was just under 25 minutes. This allowed the team to make many lesion copies. The budget enabled a wide range of tests when prototyping for the lesion material. Thanks to this, the team was able to create a lesion with the correct hardness and a low cure time.

Improvements that can be made to the final product include integration of the lesion and the vessel into one mold, inclusion of the fatty tissues that surround and slightly permeate the calcified portion of the lesion, added porosity in the calcification, the introduction of pulsatile flow, and a vein attached to the side of the vessel that would provide a channel for a catheter to enter. Additionally, a range of values for degree of occlusion, length, and vessel diameter may further improve upon the current design. These items would create an artificial lesion that better replicates the in-vivo environment that the Endoprothesis are designed to work in, and a more accurate and usable benchtop model. Increased meeting regularity and communication between meetings, a more organized division of responsibilities, and more frequent meetings with the Gore mentorship team may have facilitated improved outcomes in these areas of improvement. Working towards the completion of the project, the team was able to apply and improve upon technical skills. 3D printing was crucial to the project, and the team members gained experience in creating 3D models in SolidWorks that would correctly translate through the printers. The team also saw in what manner the layer thicknesses and materials affected the outcome. Further, the team gained experience in the mold design process. This process is highly dependent on the material used and the final shape of the product. The iterative process that lead to the final mold design reflected the team’s growing understanding of molds and how to 3D print them. Finally, the team also learned about the certification of material property readings on testing devices. W. L. Gore & Associates highly values the validation of measured values for their products, so the team made an effort to accommodate for this, and was able to certify the measured hardness values to ±3 Shore A. The overall success of the project was achieved with the continued input from the Gore mentorship team and the team members. Future developments for the project that encompass the stated improvements will further assist W. L. Gore & Associates in testing their Endoprothesis for the diseased SFA.

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http://www.unitedbiologics.com/media/pdf/cp-aim01v01.pdf

10 APPENDICES 10.1 Appendix A – House of Quality

C ustom

er R equirem

ent W

eight Engineering Requirement

Vessel must be transparent

Operates at body Temperature

Lesion Durometer

Lesion adhesion strength

Lesion length

Vessel diameter

Lesion thickness

Degree of vessel occlusion

Vessel length

Cost

Handles blood pressure

Meets ANSI standards

Meets OSHA standards

1. M eets industry safety standards

50 5

5 2. M

anufacturability/reproducible 80

3 3

5 3. Visualization

50 5

3 3

4. S im

ulates calcified lesion 70

5 5

Transparency = 100%

37°C

85 (Type A Shore Hardness)

20 N/m

15 cm

7 mm

6 mm

75%

+10 cm per side

<$3,000.00

19 mPa

Meets 100% of Applicable Standards

Tolerance (U nits sam

e as Targets) -20

± 12 ± 10

± 15 ± 1

± 1 ± 1

± 10 ± 1

N /A

± 9 N

/A N

/A R

ange (U nits sam

e as Targets) N

/A 25-49

75-95 5-71

3-27 4-12

4-8 50-95

15-40 N

/A 10-28

N /A

Testing P rocedure (TP

#) 5

LTE 1

2 3

3 3

4 3

LTE LTE

N /A

D esign Link (D

L#) 8

LTE 1

2 3

6 4

5 7

LTE LTE

N /A

10.2 Appendix B – Pugh Chart

Table B.1 - Pugh Chart

Design Criteria

W ei

gh t

B ui

ld up

th ro

ug h

fl ow

U si

ng tr

ee s

ap t

o m

od el

c al

ci fi

ca tio

D is

ea se

d Pi

g V

ei n

Su ga

r a nd

s al

t b ui

ld up

w ith

e va

po ra

tin g

w at

C en

tr if

ug al

s ys

te m

(s im

ila r t

o co

tto n

ca nd

y m

ac hi

ne s)

Pe tr

ol eu

m b

as ed

p ro

du ct

w ith

h ig

h so

lid if

yi ng

te m

U si

ng H

um an

B od

y Pa

rt s

R ad

io ac

tiv e

ha m

st er

fe ce

s us

ed a

s ca

lc if

ic at

io n

Fi ll

th e

ve ss

el w

ith G

or e-

T ex

G el

at in

u se

d to

c re

at e

oc cl

us io

Fi re

d cl

ay a

s ca

lc if

ic at

io n

m at

er ia

Sa nd

a s

oc cl

us io

n m

at er

ia l

3D P

ri nt

in g

Sp ra

y ca

n te

xt ur

e (i

.e . d

ry w

al l s

pa ck

le )

W oo

d ch

ip s

as o

cc lu

si on

m at

er ia

R us

t, O

xi di

ze d

M et

T ub

ul ar

b al

lo on

to m

im ic

o cc

lis io

C on

ce nt

ri c

tu be

Sy nt

he tic

p la

qu e

or o

cc lu

si on

m at

er ia

G um

a s

oc cl

us io

n m

at er

ia l

Feasibility 70 + + - + - | - - + S - - + - + - + + - +

Ability to Normalize 40 - S - - - D - - + S + - + S - - + + S -

Accurate representation of body 50 + + + - + | + - - S + + + - - - - - + -

Cost 20 + - - + - A - - - S + + - + + + + + - +

Time to Manufacture 30 - + + - + | - - + + - + - + - - + + + +

Repeatability 40 + S + - - T - - - S + - + S - - + + S S

Meets industry safety standards 60 + + - + + | - - + S + + + S + - + + + S

Total Weighted Score Σ+ 5 4 3 3 3 U 1 0 4 1 5 4 5 2 3 1 6 6 3 3

Σ- 2 1 4 4 4 | 6 7 3 0 2 3 2 2 4 6 1 1 2 2

ΣS 0 2 0 0 0 M 0 0 0 6 0 0 0 3 0 0 0 0 2 2

10.3 Appendix C - Schedule

10.4 Appendix D – Prototyping and Display Costs Table D.1 –Initial Testing Materials

Application Item Source Use Cost

Misc.

Ready-Mix Tile Grout Amazon

Initial Testing and Prototyping

$12.88 BoneSim Sample Pack

BoneSim $190.50

Calcium Hydroxyapatite

Amazon $15.46

2x 3 GPH Pump Amazon $15.99 3/16 in. Standard Tubing

Amazon $7.99

Acrylic Cement Amazon $6.87 Contact Adhesive Amazon $4.47 3 mL Syringes with Needles

Amazon $3.89

20 pack of AA Batteries

Amazon $33.30

132 GPH Submersible Pump

Amazon $11.99

396 GPH Submersible Pump

Amazon $22.34

1.5’’ Rubber Tubing

Home Depot $5.95

1’’ Hard Foam Home Depot $3.95 .5’’ Silicone Tube Home Depot $1.75 Wood Dowel Home Depot $1.95

Total - - $355.27

Table D.2 –UGRADS Display Materials Application Item Source Cost

Display

158 GPH Submersible Pump

Amazon $13.99

290 GPH Submersible Pump

Amazon $19.89

8 ft. 2x6 Lumber Home Depot $4.37 4x 3/8 in. Brass Cap Home Depot $23.84 PTFE Tape Home Depot $2.97 Male Brass ½ in. Thread Adapter

Home Depot $27.44

½ in. 90 deg. Barbed Elbow

Home Depot $7.94

Threaded ½ in. PVC Tee

Home Depot $0.37

Nylon Tee Home Depot $4.20 ½ in. Rigid Tubing Amazon $61.56 Funnel and Valve Set Amazon $10.09 Stand and Clamp Amazon $35.88 1L Measuring Pitcher Amazon $9.99 2x 300 mL Beakers Amazon $18.98 UV Adhesive Amazon $17.67 2x Galvanized Steel Pegboard Pack

Amazon $69.92

2.5 yards Black Cotton Cloth

Michael’s $3.75

2x Red Food Dye Fry’s $6.00 UGRADS Poster NAU Printing Services $56.00

Total - - $338.85

10.5 Appendix E – Hardness Testing Results Hardness data 1:1 ratio (shore A)

Sample Test 1 Test 2 1 86 86 2 81.5 83 3 88 90.5 4 87.5 85.5 5 88.5 90.5 6 86.5 86 7 90.5 91.5 8 78.5 84 9 88.5 90.5

10 87.5 87.5 11 91.5 90 12 88.5 90.5 13 82 88.5 14 85 86 15 86.5 84 16 83 87 17 87 86 18 90.5 91 19 86.5 88.5 20 87.5 89.5 21 85.5 92 22 89 89 23 91 92.5 24 86.5 87.5 25 88 89.5 26 91.5 91 27 90 89.5 28 84.5 88.5 29 86.5 87.5 30 89 88.5 31 88.5 89.5 32 91 90 33 89.5 91 34 86 90.5 35 87.5 82 36 91 90.5 37 87 89.5 38 88.5 88.5 39 89.5 87.5 40 87 87.5

41 87 89.5 42 85 87.5 43 90.5 92.5 44 86 88.5 45 84.5 86 46 88 89 47 83 86 48 88 88 49 89.5 89.5 50 86.5 92 51 86.5 92.5 52 87.5 89 53 88.5 87 54 91.5 88 55 90.5 89.5 56 86 88 57 85 89.5 58 87 90 59 92.5 93.5 60 91.5 89.5 61 89 91 62 84 87 63 88 87.5 64 89 84.5 65 88 90 66 87.5 88.5 67 84 84.5 68 87.5 89 69 89.5 90 70 88 90.5 71 88 90 72 89 87.5 73 87 88 74 88.5 86.5 75 87.5 89 76 89.5 92 77 87.5 90 78 91 92.5 79 87.5 89.5 80 83 88.5 81 89 87.5 82 85.5 89.5 83 88.5 89.5

84 87.5 89.5 85 86.5 87 86 88 88 87 88 86 88 87 86.5 89 88 86 90 89 87 91 88.5 86.5 92 87 90 93 86 86 94 91 90 95 88.5 89 96 88 89 97 89.5 90.5 98 90 91.5 99 85 88

100 87 89.5 Test 1 Test 2

Average 87.63 88.655 STD 2.355441 2.189401 Total STD 2.330975 Total average 88.1425

10.6 Appendix F – Adhesion Strength Testing Results

Test Distance (mm)

Average F (N) Adhesion Area (mm)

Adhesion strength (Width) (N/m)

1 24 3.8 9.42 403.3970276 2 32 4.2 445.8598726 3 18 2.6 276.0084926 4 21 4 424.6284501 5 27 3.6 382.1656051 6 24 2.4 254.7770701 7 32 1.6 169.85138 8 28 4 424.6284501 9 22 2.8 297.2399151

10 38 3.6 382.1656051 11 26 1.8 191.0828025 12 36 4.2 445.8598726 13 21 2.4 254.7770701 14 25 3 318.4713376 15 34 5 530.7855626 16 30 2 212.3142251 17 31 1.8 191.0828025 18 31 2.8 297.2399151 19 30 5 530.7855626 20 21 3.4 360.9341826 21 33 2.6 276.0084926 22 21 2 212.3142251 23 24 3 318.4713376 24 19 3.2 339.7027601 25 23 3.6 382.1656051 26 17 3.4 360.9341826 27 25 5 530.7855626 28 25 4.6 488.3227176 29 25 2.2 233.5456476 30 37 5.4 573.2484076

Ave Adhesion Strength 350.3184713

Std. Dev 111.6417565