ME-424



ME-424

Remote-Operated Guiding Device

Group 8:

Matthew Grande

Steven Isaacs

Cesar Rondon

Christopher McCalmont

I pledge my Honor that I have abided by the Stevens Honor System

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Table of Contents

1. Business Statement

i. Mission Statement…………………………………………………………3

ii. Goals………………………………………………………………………4

iii. Market Information………………………………………………………..5

2. Introduction/Background………………………………………………………….6

3. Medical Background………………………………………………………………8

4. Patents/Current Technologies……..……………………………………………..13

5. Design Process…………………………………………………………………...21

i. Previous Concepts………………………………………………………..22

ii. Testing…………………………………………………………………...26

iii. Final Design……………………………………………………………...30

6. Controlling Mechanism

i. Previous Concepts………………………………………………………..33

ii. Final Design…………………………………………………………… 35

7. Material Selection………………………………………………………………..37

8. Calculations………………………………………………………………………41

9. Goals Met….……………………………………………………………………..45

10. Senior Design Day……………………………………………………………….46

11. Conclusion……………………………………………………………………….48

12. Appendices

a. Gantt Chart………………………………………………………………50

b. Materials Information……………………………………………………51

c. Additional Patent Information…………………………………………...53

d. References………………………………………………………………..56

e. Acknowledgements………………………………………………………58.

1.1 Mission Statement

Our mission is to promote the use of minimally invasive surgery for the diagnosing and treatment of heart and related vascular conditions. To accomplish this, we will introduce our product into the medical device market. We have created a device that is sufficiently different from any others that may be found in the market, but yet was designed through research of its predecessors. This device was designed with the hope of giving both the doctor and patient more options. We hope that our device will help decrease the patient’s recovery time, and reduce any associated costs, so that it may become more widely implemented. The design of the device also has extensive considerations for safety, which essentially is, the only thing that will guarantee the success of our project.

1.2 Goals

From the beginning of the Fall of 2004 semester, we developed a set of goals that we wanted to have accomplished by this point and time for this project. These goals can be divided into goals that were meant to be accomplished by the conclusion of last semester, and goals that were meant to be accomplished by the conclusion of this semester, and they are as follows:

Fall Semester:

• The production of a scaled up prototype

• The completion of extensive patent research

• Perform some preliminary testing with the prototype to be developed

Spring Semester:

• The production of a final prototype

• The production of a prototype for the controlling mechanism

• Filing for a United States patent

• Definition of device specifications such as basic design concepts, materials used, size, and capabilities

1.3 Market Information

Our device falls into the medical device market. This is a well established market, but one of few competitors as large amounts of funding are required for survival within the market. Some of the larger names that one may stumble across when reading financial information regarding the market are Johnson and Johnson, Boston Scientific, Guidant, General Electric, Tyco, Medtronic, 3M and Becton Dickinson. Out of all of these, Johnson and Johnson currently stands as the leader both in manufacturing output as well as in international sales, and the results of a recent acquisition of Guidant should give them even more of an advantage.

The market has shown signs of rapid growth in the last couple of years; a growth trend that has been witnessed both domestically and internationally. Domestically, the latest market report shows that year 2005 should produce record numbers for the FDA’s Medical Technology Review Programme, a section of the Federal Food and Drug Administration that deals with the reviewing and approval of new devices entering the market. Internationally, China has shown a growing demand for such devices, and many companies are beginning to focus a larger percentage of their importing towards the eastern-Asia country.

A small senior design group from a college could never compete with any of these corporations, but the development of a patentable device could provide revenues by means of licensing or other form of legal distribution of product information.

2. Introduction and Background

Heart disease is the number one cause of death in America. It comprises about thirty percent of all annual deaths, and every year, both the percentage and the actual number tend to increase. Another type of conditions that pertains to the circulatory system are vascular conditions (mainly stroke and aneurysms), and these make up about seven percent of all annual deaths, making it the third leading cause of death in America. While some of these conditions have some sort of hereditary value, a lot can be done to prevent them.

In many cases, a proper diet accompanied by proper exercise is recommended, but in most cases, there is no way to prevent them, only to treat them. Currently, the most popular method of treatment is through what is commonly known as “open” surgery (any surgery in which a physician makes a large incision and manually removes, replaces, or bypasses the site of the problem). Advances in technology, however, have begun to decrease the number of “open” invasive surgeries and replacing them with “minimally invasive” surgeries (surgeries in which only a small incision is made and the site of the condition is approached with a medical device, most commonly a catheter).

The main problem with “open” procedures is that they take a great deal of energy away from the patient and thus long periods of recovery usually follow the procedure. Another problem with them, is that in a lot of cases, the patient will become very weakened by them (either because of their duration, loss of blood, or depending on the type of surgery, the type of incision required). This brings up another alarming number to the previous topic on annual causes of death: every year, twelve thousand deaths occur due to unnecessary procedures. Why unnecessary? Simple, there should be sufficient technology available to eliminate “open” procedures except for when they are the only possible way to treat a patient.

Most of the catheters that are currently available in the industry work fine for procedures that need to be performed in the torso of a patient. However, more technologies are necessary to be able to perform procedures away from the torso (mainly the abdomen) and over the extremities, head and chest. Current technologies and “minimally invasive” procedures will be discussed in greater detail later on in this report.

3. Medical Background

A larg percentage of annual deaths, both in the United States and worldwide, occur due to vascular related diseases. The three main causes behind these deaths are cardiovascular diseases, cerebrovascular diseases and aneurysms.

Heart diseases, most commonly heart attacks, are accountable for 31% of deaths in the United States every year. In actual numbers, that percentage equals about 730,000 deaths every year. It is by far the main killer today with cancer coming in second with 23% of all deaths. This is an alarming number of lives lost every year due to heart attacks and other forms of heart diseases, a number that can and must be reduced.

Stroke and other forms of cerebrovascular diseases make up 6.8% of the number of deaths every year. This number, in the United States alone, equals about 164,000 deaths every year, making it the third leading cause of deaths. This is the statistical number for the year 2001. In the year 1997, this was also the third leading cause of deaths, but the number was actually around 155,000 deaths that year. This means that we can project that in the year 2005 the number will actually be around 173,000 deaths, and that four years after that it will be around 183,000.

If this is not alarming enough, then consider the fact that Abdominal Aortic Aneurysms (AAA) are the 13th leading cause of death in the United States with about 15,000 deaths a year. Adding to the figures, nearly two million people in the United States have been diagnosed with AAA, with 50,000 new cases every year. This means that 30% of the people diagnosed with AAA every year, will not survive the condition. This is another figure that can be reduced.

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Figure 3.1

For background the necessary terminology will be established to describe cardiovascular and cerebrovascular diseases, and aneurysms. After that, discussion shall be offered about the current screening and operating procedures are, and then offer GIRMZ grain of sand towards helping solve the problem.

An aneurysm is a bulge that forms in the wall of a blood vessel, usually as the result of the accumulation of fatty deposits on the vessel wall. If the aneurysm forms in the aorta (the body’s main blood vessel) that extends through the abdomen, it is called an Abdominal Aortic Aneurysm.

Cerebrovascular diseases include, as mentioned before, Strokes; and also Cerebral Ischemia, Cerebral Infarction, Hypertensive Cerebrovascular Disease, and Saccular (Berry) Aneurysms. A stroke is simply defined as a neuralgic deficit with sudden onset due to vascular disease. Cerebral ischemia is a decrease in cerebral blood flow with resultant decrease in cerebral oxygenation. A Cerebral Infarction is usually the result of a vascular occlusion, which is most commonly due to atherosclerosis or emboli (both caused by thrombotic occlusions) from cardiac lesions. Following vascular occlusion, whether or not an infarct occurs (as well as its size and shape) is determined by which vessel is occluded and by the pattern or the extent of its anastomotic connections with surrounding vessels. Occlusion of the internal carotid artery or of a vertebral artery may not cause an infarction if there is adequate collateral circulation provided by the Circle of Willis or middle of the artery. On the other hand, occlusion of a cerebral artery (particularly of the more distal branches) usually results in an infarction, since these vessels have few or no collaterals. There are three different kinds of infarctions: acute, chronic and hemorrhagic. Hypertensive Cerebrovascular Disease or Hemorrhages usually result from the rupture of micro aneurysms that form where cerebral arterioles split. Finally, Saccular or Berry Aneurysms present themselves in large numbers, usually at the branches of the cerebral artery.

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Figure 3.2

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Figure 3.3

Heart diseases can be separated into many subcategories, but the main three are Heart Attack, High Blood Pressure, and High Blood Cholesterol. All three of these refer to an abnormality in the heart, or its functioning. It is important to distinguish heart diseases from heart failure and other forms of cardiovascular diseases. These usually result in heart failure, which means that the heart cannot, for a number of possibilities, supply the necessary blood to satisfy the circulatory demands of the body.

Ultimately, the most important part of the vascular system is that blood can flow unimpeded to the extremities of the body. If the passage of blood flow is obstructed, it can result in many problems throughout the body.

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Figure 3.4

4. Current Technologies and Patents

There are four main competitors in this market: Abbot Vascular, Guidant, Johnson & Johnson, and Boston Scientific. After researching those competitors it was Guidant was chosen to be the focal point. At the outset of this project, Guidant was the leader in terms of market share for minimally invasive vascular surgery devices. Recently it has been publicized that Guidant was acquired by Johnson & Johnson. Their products form the current basis of the industry. The basic target technique considered was the current practice of using many differently shaped, pre-formed catheters, one at a time through a single delivery sheath. A logical next step of removing the need for choices of just one catheter with additional features and abilities was approached. A manipulable tube that could be maneuvered to achieve the same mechanical results as all of the pre-formed insertion shapes would cut material cost, surgery time and recovery time.

There are several existing surgical techniques. The classical technique is open surgery. To perform surgery in order to remove or repair an aneurysm required opening the skin and surrounding muscular structure to gain the required access. Once a large incision has been made into the abdomen the surgeon will manually remove or repair the aneurysm. Problems with this procedure include increased need for anesthesia, longer operating time and increased recovery time. In fact recovery time usually includes several days under intensive care before the patient is healthy enough to be in standard recovery care. This type of procedure cannot be performed on some patients due to complications such as additional heart diseases and diabetes. A more attractive alternative for most patients is usually a technique with less recovery time, such as stent grafting or open heart surgery.

For heart disease surgery, there are two main kinds of surgery, open heart surgery and bypass surgery. Open heart surgery requires the breaking of the patient’s breast plate and then a manual surgery performed on the heart. This gives doctors the chance to do heart transplants or insert bypasses in a bypass surgery. In this surgery, a stent is inserted to bypass the flow across a clogged artery inside the heart. A procedure similar to the previously discussed stent procedures, but at the same time different since this time the stent is used as a “new” artery as opposed to a inner coating for the actual artery. These procedures require the use of a heart/lung machine to keep the patient alive during surgery.

Stent grafting is the placement of elastic, expandable tube or metal-lattice that acts as a barrier, a support or an inner replacement layer for the artery. It is delivered the aneurysm sight and then expanded and fixed at the site so as to alleviate the pressure applied to the weakened tissue, preventing continued expansion of the aneurysm which could eventually cause arterial leaking or rupturing. The images below depict the artery before and after the procedure.

[pic][pic]

Figure 4.1

The picture on the left shows an aneurysm in the abdominal aorta. The one on the right shows the same artery after the placement of the stent graft. The stent graft is the darker black tube. It extends from the healthy portion of the arterial wall to the also healthy arterial bifurcation. It helps to prevent blood collecting within the aneurysm.

For the treatment of cerebrovascular diseases, five procedures are commonly used today: Carotid endarterectomy, Stent-supported angioplasty, Intravenous thrombolysis, Intra-arterial thrombolysis, and Platinum Micro-Coils. A carotid endarterectomy is an open procedure in which an incision is made into the carotid artery (the artery that carries most of the blood supply to the brain). Any plaque buildups are then manually removed and the artery is then sealed back up. A depiction of the procedure is presented below.

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Figure 4.2

Stent-supported angioplasty is a procedure that uses a stent similar to the stent graft used for AAA’s. Intravenous thrombolysis and Intra-arterial thrombolysis are two procedures in which a micro catheter is inserted into the vein or artery to deliver a clog dissolving medication that will curtail the stroke.

The foundation of minimally invasive surgery is the ability to reach remote areas of the cardiovascular system to correct ailments before they become a full bore problem by the delivery of stents, anticoagulants, balloon catheters, plaque removal tools (atherectomy), time-release medicines and angiography (cameras). These tools present the front line offense against major open surgery and are generally referred to as intervention.

The systems as they exist use preformed tips inserted through a guide wire. The tips have two purposes; guiding the wire through the branching in the vascular system and holding the guide wire in place while the selected intervention is performed. Below is an image of a carotid stent placement which employs an embolic protection system or plaque catcher downstream from where the procedure is being performed. Stent placement differs from stent grafting in that the stent uses only its springiness and a web like shape to hold it in the desired position. It is similar to angioplasty with the exception that it is a long term treatment. Additional reasons to place stents include log term drug delivery systems based on similar technology to the well known nicotine patch.

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Figure 4.3 Image of placement of carotid stent Courtesy Guidant Technologies®

The platinum micro-coil procedure is the most advanced of all of these and it involves the insertion of a rolled up platinum coil, which is inserted into the artery by means of a guide similar to the one we are proposing. The coil is brought up to the aneurysm or blood clot and inserted into it. Once in there, the coil is released and allowed to expand inside the aneurysm. The purpose of this is for the coil to fill up the inside of the aneurysm and block it, preventing the flow of blood around it. A graphic depiction of the procedure is provided below.

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Figure 4.4

The catheters must be made in many different shapes and lengths to achieve the required variety of procedures. In order to reach a certain position a specific catheter is placed within the delivery sheath and controlled by the doctor. During an intervention, a doctor may have to use several different tips to reach the affected area. (Figure 4.6)

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Figure 4.5 Figure 4.6

The catheter is inserted to the end of the guide wire and then will be rotated and extended to provide a path for the guide wire to follow. The manipulation is limited to extension, retraction and rotation of the tip. It is important to note that the preformed catheter must me delivered in a distorted shape and that it will form to its desired shape as it is extended from the guide wire. This presents additional complications as the surgeon will need to retract it if he can feel that the device is not seating properly further extending the surgery time. Below is an image of a preformed tip depicting how it could be moved within the vascular system.

During the first semester, the group researched many patents that possibly would provide aid in development stages. An extensive patent search was conducted to understand the current state of technology and to confirm for the patentability of our device. We found one similar product, but there were some very different features. Patent #6,793,667, filed in June of 2002 by Hebert and Levine of California is for a manipulable delivery catheter for occlusive devices. The main difference between the two devices is that the Hebert-Levine design must be configured beforehand to either bend or twist, where as, the device designed herein will have the ability to bend and twist at the same time. It is felt that this increases the chances of successfully patenting said device. An additional differentiator of the intended device is that it is proposed to work in both the heart and brain, whereas the Hebert-Levine device is not specifically designed for the brain.

Patent #4,884,579, which was used in the previous patent, is for a catheter guide wire. Engelson filed it in April of 1988. Assuming that the guide wire is sufficient for the Hebert and Levine design, this catheter would be a good starting point for deciding what material to use. Later on in the patent research we found a catheter that we feel would be a better fit for our design, Engelson also patented that catheter design.

Patent #6,824,553 was very important in helping us pick which other types of materials to use. It describes a high performance braided catheter that is resistant to kinks. It was patented in August of 2000 by Samson, Chee, Nguyan, Snyder, and Engelson. The non-kinking portion of the patent was especially interesting to us because that is a major problem we will face. A second problem we will face, mentioned earlier in the report, is the damaging of the vessel walls and surrounding tissue. This catheter is specifically designed for soft tissue, as in the brain.

Patent #6,802,849, is for a delivery system for a stent. It helped to better understand how the intended device should work. The patent is recent, filed in October of 2004 by Blaeser, Lorentzen, and Willard. This group’s main focus was on how the stent would be released from the guide wire. This showed us that even currently, there are not many people looking for new ways of designing guiding devices; they are just attempting to improve upon the current ones.

A patent that may assist in the future of the intended product is Patent #6,810,281 for a medical mapping system. This system generates a display of the body structure. It involves a sensor that can be traced within the body. It could be attached to the tip giving the surgeon an image of the person’s circulatory system and where the location of tip. This would help the surgeon control the device better. This patent was made in December of 2001 by Brock and Rogers.

Late in the semester Patent # 6,793,667 (Manipulated delivery catheter for occlusive devices (II)) was uncovered. The previously mentioned patents aided in the initial material selections, determining different methods for manipulating the device, and providing ideas for future additions and compatibilities for the device. The patent was filed June 27, 2002, by Stephen Hebert (Berkeley, CA) and Marc-Alan Levine (San Francisco, CA). It took over two years to finally be approved (September 21, 2004). Some of the detailed drawings contained within this patent are attached to this report in Appendix C. After reviewing this patent, it became clear that the patents that had been reviewed earlier pointed the right direction. A few of them were actually used by Hebert and Levine in their patent. These patents can be seen as C.

The similarities between the group’s device and this patented device begin with the functioning of the device. Both devices have the same objective; provide a manipulated tip to aid in the delivery of surgical devices. The manipulation is produced in both devices with the use of guide wires attached to an inner lumen at different points throughout the length.

The patented device still requires multiple attachments as shown in this statement from the patent, “facilitate the rapid exchange of catheter devices by the user”. The fact that our device is specifically designed to be able to perform surgeries within the brain, while the patented device is not designed for brain surgery is a major improvement that our device offers.

5. Design Process

The main principle behind the functioning of the device is to use wires which are run through a catheter tube and connected at the tip. The resulting basic design principle of our device resembles that of a tripod. When tension is applied to any three of the wires, the other two will bow in the direction of the force and cause the tip to turn in that direction. The illustration below describes the basic motion of the tip.

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Figure 5.1

A needs-metrics matrix was constructed to determine what the device needed to accomplish and what factors were most important. Figure 5.2 shows the needs-metrics matrix however there is additional information in the appendices.

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Figure 5.2

5.1. Previous Concepts

Initially, two base designs were proposed as well as three different tip designs. The main differentiators between the six possible combinations of base and tip designs at that stage in the concept design process were the number of and the positioning of the guide wires (Figure 5.3).

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Figure 5.3

The basic idea behind the six possible configurations shown above was of a hollow catheter that would have a device (operating tool, drug delivery tool, stent, etc.) travel through the center of it. A crude prototype was built using the combination of three wires from the base to three different points at the tip, and some basic motion testing was performed. The prototype proved successful in turning the way it was designed to, but one characteristic of its motion raised a couple points of concern. It was quickly noticed, that the two wires that were not in tension during any particular application of tension, were bowing out more than expected. This could prove to be troublesome further on along the design process since excessive bowing is undesirable for patient safety issues. In order to eliminate this problem, a platform was designed to hold the wires together before the tip.

The idea of using a platform led to the idea of using a different wire configuration. A new design was created using a set of wires that would go to the first platform, and a secondary set that would go directly to the tip of the device. In this way, the platform would serve two purposes: it would act as a holding ring to eliminate the bowing effect, and it would aid in the motion of the tip since it would be connected to its own set of wires. A concept selection table was developed to determine what would be the most suitable wire configuration using two platforms (the center platform and the tip).

The results are shown below in figure 5.4.

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|Design Criteria |Importance (1-5) |Design Concepts (1-5) |

| | |A |B |C |D |E |

|Simplicity of controlling tip angle |3 |5 |4 |3 |2 |1 |

|Tip stability |5 |1 |2 |3 |4 |5 |

|Cost to purchase |2 |5 |4 |3 |2 |1 |

|Cost to manufacture |3 |5 |4 |3 |2 |1 |

|Degrees of freedom |5 |1 |2 |3 |4 |5 |

|Desired degrees of freedom |5 |1 |5 |4 |3 |2 |

|Catheter maneuverability (flexibility) |5 |5 |4 |3 |2 |1 |

|Catheter maneuverability (rigidity) |3 |1 |2 |3 |4 |5 |

|Simplicity of assembly |4 |5 |4 |3 |2 |1 |

|Durability |2 |1 |2 |3 |4 |5 |

|Un-weighted total |= |30 |33 |31 |29 |27 |

|Weighted total |= |105 |123 |116 |109 |102 |

Figure 5.4

Figure 5.4 shows that concept design B is the best of the 5 designs. The new base would have to allow for 6 wires to pass through the catheter tube. Three wires would be connected to the first platform, while the other three would be connected to the tip. It is also important to note that for this model, it was decided that the guide wires should be embedded in the body of the device, rather than running through thin tubes placed on the outside as was the case in the earlier designs. The new design is shown in figure 5.5

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Figure 5.5 Figure 5.6

Another feature of the newer design was the addition of a spring at the tip that would aid in maintaining tip rigidity, and return the tip to its original position when the wires are released. This design can be seen in Figure 5.6.

After developing this design, the functionality of the product was re-evaluated and it was concluded that the device would not need to be hollow. If the tip was designed to join at a point, as opposed to a ring, the device would be steered with more accuracy and better motion could be achieved. Eliminating a hole through the center of the tube could also help in reducing the outer diameter of the device, thus allowing it to pass through some of the smaller veins, as was desired originally. One other aspect that became apparent at that point, was that an existing catheter tube could be used with the new tip design and this could prove beneficial in the long run by reducing the FDA required testing time. Figure 5.7 shows the final design at the end of last semester. [pic]

Figure 5.7

2. Testing

After the last design was developed, a new scaled up prototype was constructed so that some testing could be performed to determine the success of the design. The main results that we wanted to obtain from testing on a prototype were the amount of force required to obtain a ninety degree bend at the tip, and the behavior of different length configurations for the tip. The prototype was first mounted on a wall as shown below.

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Figure 5.8

In order to test the device, two pairs of wires were also fixed to the wall, and different sets of loads were applied to the remaining free pair. The deflections corresponding to the different load applications were marked on a piece of paper and then measured.

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Figure 5.9

The loads that were used were ½ ounce, 1 and two ounces. Consequently, different tip configurations were tested under each of the above loads. The tips configurations that were tested were the following:

• Configuration 1: L1=0.5” and L2=0.5”

• Configuration 2: L1=1” and L2=1”

• Configuration 3: L1=1.5” and L2=1.5”.

These configurations are explained in figure 5.10

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The results for the deflection vs. the loads of ½ ounce, 1 ounce, and 2 ounces applied to three different configurations of the tip are represented in chart 5.1. The forces were converted to pounds.

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Chart 5.1

The results from the test to determine the load to produce a ±90º bend are as follows:

1) L1=0.5” and L2=0.5”

Load = 5 ounces = 0.3125 lbf

2) L1=1.0” and L2=1.0”

Load = 2.5 ounces = 0.15625 lbf

3) L1=1.5” and L2=1.5”

Load = 1.5 ounces = 0.09375 lbf

It was noticed that the longer the configuration of the wires, the greater the bowing effect. This meant that perhaps the most desirable configuration would be the one with the shortest possible tip, even though more force needed to be applied to obtain the desired bending. In a later chapter, a new solution to this problem is presented within the final design section.

5.3 Final Device Design

Certain problems with this device were noticed during fabrication of the final prototype. It was very difficult to devise a simple controlling mechanism which would work in all of 6 independent controlling wires. The newly obtained materials did not allow for running the 6 wires through the catheter tubing. After thorough deliberation and further experimentation, it was realized that the device would operate acceptably with a reduced amount of wires. Therefore the design was revised to eliminate any complications using 6 wires would produce especially tube and controller design. During the deliberation that concerned the control of the device a set of tubes with multiple internal lumens were obtained from Extrumed Inc. Also receipt of a the new Nitionol fibers influenced the s change due to its super-elastic nature. As an alternative to utilizing three wires joined at the ring platform one wire is tasked with positioning the platform. The three wires that make up the tripod are still run through the ring platform attaching at the tip and when operated still produce more than enough bending to achieve our goal. The platform still performs its job of reducing the amount of wire flaring when the tip is actuated. It also shows the added benefit of being able to twist the tip giving it a dog-legged appearance that could be helpful during surgery when the device is used to maintain a static position for additional procedures. An image of the new device and its new cross section are shown in figure 5.11 and 5.12.

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Figure 5.11

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Figure 5.12 Figure 5.13

The desired design for the tubing had a different cross-section than what was readily available from ExtruMed, Inc. and it would have had to be custom built. So the available materials were utilized to their best ability. An addition was made at the end of the tubing closest to the tip. The device was altered by the placement of a small piece of tubing inside the large lumen with glue. The purpose was to force the actuating wire running through that lumen closer to outside of the tube and limit contact with the platform actuator. The platform actuator was left to run freely through the same lumen and was found to produce little or no binding in this format. A comparison of the cross sections is shown above in figures 5.12 and 5.13.

1. Previous Concepts for the Controlling Mechanism

Besides having to develop a successful design for the actual device, there was a need to develop a design for a controlling mechanism that would allow to successfully maneuver the device with ease and precision. Much like the design process for the actual device, the design of the mechanism also went through several stages and different designs. Originally, the main concept was to create something simple, which would allow a doctor to use the device quickly, but safely. Two different designs were thought of which possessed a ratchet style device to hold any wire of set of wires in tension in place. The first of the two designs was equipped with a ticker dial that would tense the wires with every tick as the dial was turned. The design is depicted in the figure below.

[pic] Figure 6.1

The controlling mechanism would be equipped with one of these for each of the wires and all of the dials would be contained within one box. The main concern with this type of design is that the motion is limited by the clicks of the dial. Basically, any one wire could only be locked down at a predetermined angle that would correspond to a specific click of the dial. It was then established that a

The other design that was developed earlier in the stage of the design process was one of a clicking syringe. Much like the clicking dial, the syringe would lock down at predetermined clicks, but the tension would be controlled by pulling or pushing a plunger, instead of by turning a dial. The syringe controller is depicted below.

[pic] Figure 6.2

After these two designs were discarded for the concern for the lack of accuracy with the clamping down of wires, a new design was developed that would eliminate this problem. This new design was small, lightweight, adaptable and mountable design had visible internal parts, for diagnostic purposes. It had six levers that to be connected to the six wires and consisted of levers that could be locked down at any position, instead of only at predetermined ones. This system would allow its multiple levers to be locked and unlocked in up to 36 different combinations to meet the surgeon’s various needs throughout a procedure. This new design, however, would require some careful machining, but the obvious advantages over its predecessors outweighed any required machining. Figure 6.3 shows a Solidworks drawing of this controlling mechanism. It is important to note that this was not the mechanism that was selected for the final design. It was replaced by one that was much simpler to control.

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Figure 6.3

6.2 Final Mechanism Design

Due to the continuing need for an actuator a third design phase was implemented. This method employs a ball and socket. The ball and socket allow for a very intuitive link with the device. It also allows the wires to be moved in opposing directions. This is a most useful feature as it causes the tip to be more movable and therefore more reactive to inputs. The tip wires are guarded by a set of struts that provide the wires with protection as well as preventing unwanted buckling. These struts are connected at one end to a platform attached to the ball joint. The other ends are connected to a jacket device that holds the base of the catheter tubing in place. This is how the design minimizes the undesired buckling effects. The device was then suspended from a lead-screw type of device that allows changing the length of the tip by turning the tip length adjuster knob in either a clockwise or counter-clockwise direction depending on whether shortening or lengthening of the tip is desired. The length of the tip is left to the user’s discretion depending on the radius of curvature required. Required radius of curvature can be dictated by several features of the arteries. These contributory features are the entrance and exit diameter and consequential bifurcation angle and general curvature and layout of the targeted vessels. There are still some issues with the controller that need to be addressed including the platform actuation and the twisting effect of the joystick mechanism.

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Figure 6.4

7. Materials

When considering material selection several factors had to be taken into account. Required flexibility is weighed and compared with the required rigidity for the application. In this case the flexibility is prized above rigidity due to the nature of the human circulatory system. In the basic concept a set of wires will be within a sheathing material. The sheathing will need to meet certain medical requirements for biocompatibility, friction, reactivity and permeability. It is of high importance to have a mechanism that acts in a predictable and reliable fashion. Having established that the minimum set of requirements concerning stress (see calculations) for the material are very slight most of the materials will meet or exceed our requirements in that department. The initial material is spring steel. Consideration is given to the concept that the device will need enough stiffness to not deflect too easily, so that it will be able to return to its original shape relatively easily. The reliability requirement is such that material will have infinite life given acceptable use. Consideration was only cursorily given to thermal effects due to the body’s temperature not exceeding 110 degrees Fahrenheit.

In the beginning of the design phase, it was necessary to select readily available materials in order to test the working concept. Of the many choices available the selections boiled down to spring steel for the fibers and PEEK and polyurethane for the tubing. The PEEK was selected due to its material properties and its typical use within the medical field. It was revisited when it was discovered that the acquired PEEK came in several different grades and was damaged during testing. The spring steel initially used was sourced from guitar strings. The small diameter and appreciable flexibility provided a solution that carried us through nearly two thirds of the design and testing process.

The constant development of the device encouraged a parallel search for suitable materials. The materials used in the first prototype satisfactorily served the purpose of concept testing and early development. The properties do not meet the requirements of actual medical applications. The metal wires need to have higher flexibility, for maneuvering purposes as well as better reactivity properties. The tubing also needs to be more flexible and of a more specific design in order to meet the new requirements for the maneuvering of the apparatus. Previously discussed medical requirements of the tubing include biocompatibility, low friction coefficients, chemical resistance, and permeability.

These requirements led to a search of medical-use tubes currently in the market. Most of the tubing found was fluoride-based tubing (such as PEEK, PFA, FEP and PTFE) which is commonly used for their high strength and low friction coefficients. Another type of tubing that was common was polyurethane, which is very flexible and usually requires reinforcement to be pushed through as a catheter.

In terms of fibers the search produced many commonly used steel alloys, a spring titanium alloy, Nitinol, and a platinum alloy (all currently used in medical applications). The platinum alloy was discarded for its exorbitant cost. The table below shows some of the found materials with their mechanical properties.

The ultimate goal of the material research is to open up new possibilities in the design of the device. Nitinol, for example, could eliminate the need for mechanical manipulation by presenting the possibility of electrical manipulation. Nitinol has two capabilities depending on production technique. One is that it is a shape memory alloy. That means that under the correct circumstances it could be made to assume a shape it previously held. This would allow the elimination of distributed forces running through the device, and subsequently from the device onto the tissue walls, by localizing the exertion of forces near the tip. The main consideration of this possibility is whether any precision in the controlling of the device would be affected. Nitinol’s other well known property is that it is what is known as a super-elastic material. See figure 7.1. Being a nickel-titanium material it has excellent tensile properties to match its extreme elasticity. The first property has been used extensively in the field of applied robotics. The second has generated a great deal of interest in the medical field.

[pic]

Figure 7.1

After performing much research, we found a company named ExtruMed, Inc. which specializes in extruded tubing for medical applications. Nearly any thermoplastic material can be used in this process. ExtruMed has materials available to them and can make an extrusion mold that will provide the specifically desired form for the tubing. Figure 7.2 is an example of what is available from ExtruMed.

[pic] [pic]

Figure 7.2 Figure 7.3

There are many other new and exciting opportunities for the medical industry being brought about by the new materials and process techniques being uncovered. One item that may give rise to better material properties in the future is multi-layered tubing. This material would also fit well in the realm of attachments. See Figure 7.3 above.

8. Calculations

Bifurcation Angle

When determining the requirements for how far the device should bend, it became necessary to calculate the possible branching angles within the vascular system. The maximum angles in the blood vessels that device needs to bend can be predicted by relating bifurcation angle to branch diameter. Figure 8.1 illustrates the results of this. [pic]Figure 8.1

The principle behind this equation is that vessels follow the course of least energy required to move blood through the system. From the results, it can be noticed that the maximum angle that a vessel may bend is ±90º. The tip of the device will therefore have to be able to bend a maximum of ±90º if it is to pass through much of the circulatory system. The force therefore has to be predicted to bend the various configurations of the tip through ±90º.

[pic]

Figure 8.2

The desired effect is for the tip to deform in a predictable manner when tension is applied to one of the wires and displacing the tip. How does the tip get its initial curve? The force required is derived from a moment applied at the tip, as shown in Figure 8.3 by forces as shown in Figure 8.4. One of the main principles behind this device is Euler’s critical buckling theory. Since the device is designed to have such a slender tip, it is primarily prone to bending. The use of extremely elastic materials allows for the required durability.

[pic] [pic]

Figure 8.3 Figure 8.4

.

Torque is applied by pulling against the tip with the force and moment calculation

below Tension required to bend the horizontal beam 80 degrees from horizontal by a vertical point force P=3.3538x10-3 calculated applied force if applied perpendicular to the base.

[pic][pic]

Calculated when considered applied at 6 degrees from horizontal.

Some formulas and sample constants used for these calculations

[pic][pic] [pic] [pic]

[pic][pic][pic] [pic]” [pic][pic][pic]psi [pic]”

Friction Calculation:

[pic][pic]

[pic][pic]

[pic][pic]

Moment

Calculated at the tip bent at an angle of [pic][pic]and an applied force angle of 6 degrees

[pic][pic][pic][pic]

[pic][pic]in-lbs

[pic][pic][pic](Modulus of Elastic Shape)

[pic][pic]

[pic][pic]

Note: the moment is applied an inch from the tip and is applied against 2 wires.

[pic]T = 2MC = 0.33945in-lbs ÷ 1in ≊ 0.34lbs

Stress

[pic][pic]"[pic][pic](Radius of curvature)

[pic][pic]psi

If the Radius of Curvature is 1/2 the stress will double, etc.

Scale changes are driven by the moment of inertia. It is accounted for in both the Modulus of elastic shape, and in the moment equation. Although the modulus of elastic shape (p) changes directly with diameter, moment does not change. The Moment at this scale does not change greatly as (p) is so small. It is also important to mention that the tension force required to produce bending effects is greater than that required to maintain them.

Configuration Example:

[pic][pic]“And[pic][pic]"

[pic]"

[pic]“ and [pic][pic]"

[pic][pic]

9. Goals Met

The team enjoyed great success as far as achieving goals was concerned. The conclusion of the fall semester marked a very important period since the team managed to produce a scaled-up prototype to perform some testing and determine the expected behavior of the device. By that point, team achieved another goal by having completed an extensive patent research. Discouraging news came, however, when the research produced a patent that had just been approved in the later months of 2004 for a very similar device to the one that was being designed for. Nevertheless, the design up to that point was a bit different, and the team was confident and eager to continue working with that design.

The spring semester was no different from the fall semester in terms of successful completion of goals. By the end of the semester, the team had developed a final working prototype that was presented on senior design day. Another accomplishment the team was proud of, was the development of the controlling mechanism, which was also presented on senior design day. Both of these new prototypes, were made using specific materials that were recommended to be used if the device were ever to be mass produced. Both devices have been discussed in the final device portion of the report, and materials have been discussed in the materials portion. The one goal that was not met, by the end of the project was the filing for a United States Patent, however, it is something that the team is considering as a possibility for the near future.

10. Senior Design Day

Senior design day took place on Wednesday, April 27th. All of the senior design groups, from all of the engineering disciplines at Stevens brought out their projects to dazzle everyone that came to walk around, and we were in no way different. The newest design of the device had been built by this point using the materials specified in the materials section and in the week that preceded the event, the final controlling mechanism was also constructed.

The next step in the preparation for this event was in preparing a display that would attract people to our project table, and keep them interested enough to wait for anyone of the four team members to give them a demonstration of the final prototype for this project. A large, three-fold poster was put together, and brochures were handed out, so that when people would leave they would remember all the key information pertaining to the device (save any involved technical information).

Throughout the course of the day, we had some customers who would just stop by, on their way from table to table for a brief description and demonstration of the device working. All of these people gave us an impression of approval; they were all usually rather skeptical during the verbal description of the device, but once they saw it moving about they all commended us on a job well done. The key people, however, were those who spent extended periods of time at our station watching the device work and asking questions that were not answered in the pamphlets, as well as questions of our work in general for the entire project, our future goals with the device, future personal plans, etc.

This gave us a great feeling of reward, because we had accomplished what we had originally set out to do, create a device that was unique enough. How did we know we had done so? By the response all the different people gave us on that day.

There were two people that we met on that day who we would have hoped to have met sooner, perhaps while still in the design stages of the device, since they were from the biomedical department here at Stevens. Their comments were very helpful, as they helped to explain some things about the industry in general that we were still somewhat unfamiliar with, and to notify us about possible future careers in the biomedical and pharmaceutical areas. They also encouraged us to continue researching and considering a possible application for a patent, as they felt that our device was indeed, unique enough. They did suggest, however, that in order to make a patent application successful, we would need to target out device for one condition in particular, instead of having multiple uses for it, as we have been doing thus far. This is something that we will have to discuss in the near future, should a patent application be filed. We thank them for all of their encouragement, and wish we could have met them sooner.

11. Conclusion

Many conclusions can be drawn when looking back at the project in its entirety, was the project successful? What kind of learning experience did it provide? Was there anything that could have or should have been different? Some of these have already been discussed, but they will be reiterated to show them in a final conclusive manner.

Beginning by looking back at the design process, we feel that our approach was correct. The process began by working from what was currently available in the market and creating a new design from it. This original design was then evolved systematically as different needs and issues were being addressed. Moreover, constant updates to and from our faculty advisor, Professor Zhu helped to maintain the design process on the right track.

The design of the controlling mechanism was not derived from current technologies, and it did not systematically evolve as did the actual device. As one can see from this report, the controlling mechanism concept change drastically with each design, and these changes were the cause of issues regarding functionality, manufacturability, and simplicity. In the end, however, our most successful design all around, was the one that was prototyped and presented on senior engineering day.

In terms of material research, many ideas floated around for quite a long time, and it was not until recently that most of the questions were answered. This was one stage of the design process that could have been carried out a little differently. All material needs should have been addressed from day one, and most of the material research performed at once, instead of on a progressive basis. In this way, we could have had our material selection completed by the beginning of this semester instead of halfway through it. Nevertheless, the materials used in this device are the most suitable out of any that we came across during our research. It is important to note that

As far as patent and current technologies are concerned, the group was successful in finding information in a timely basis. All of the medical background medical information was obtained within the first month of the project. Patent information was completed shortly after, and updated with any changes as to the latest approved patents.

In terms of oral presentations of progress, we feel that we consistently improved along the way. Our presentation format was certainly better, and always consisting of more and more relevant information, and our presentation skills we feel improved from one presentation to the next. We would like to thank Professors Berkoff, Cole, Esche, Nazalewicz and Pochiraju and Mr. Tohru Suwa for their attentive listening during these presentations and for providing us with good critique and advice, always.

In terms of general progress, we feel that we could have been a bit better schedule at times. The main problem came from us having busy schedules outside of our academic schedules, and from having different academic schedules. Nevertheless, all the work that we set out to complete has been successful by this point.

Overall, the project was an excellent learning experience. We learned a great deal about production, from the establishment of project and product needs, through the design stages, cost analysis, through the production stage (while in the machine shop), and finally to the marketing stage (through senior design day). We have, by now, a good understanding that working in groups can be arduous at times, but that good group cooperation is what gets the work finished in the end.

Appendices

a. Gantt Chart

[pic]

Material Information

|treatment |Φ OutsideDiameter: inch(mm) |Tensile strength |

|[pic] | | |

| |from |Up to |PSI(kgf/mm2) |

|Full annealed wire |0.0012(0.030) |0.0090 (0.230) |99,561 to 149,342 |

| | | |(70 to 105) |

|Hardened wire |0.0006(0.016) |0.0260 (0.660) |227,568 to 398,244 |

| | | |(160 to 280) |

|High-tension wire |0.0005 (0.013) |0.0051(0.130) |426,690 to 568,920 |

| | | |(300 to 400) |

Figure 1

Plastic Tubing:

We have decided to use peek tubing. As with the metal wires, the material properties suit our desired purpose and they are manufactured small enough for our design (Figures 2 and 3).

[pic]

Figure 2

[pic]

Figure 3

|Material |Yield Strength (psi) |Flexural Modulus (ksi) |Expansion |

|Biocompatible Polyurethane |1730 |16.8 |9.71098E-06 |

|Silicone Polyurethane (40) |1070 |5.73 |5.35514E-06 |

|Silicone Polyurethane (20) |928 |5.9 |6.35776E-06 |

|Spring Titanium Alloy |200,000 |5,350,000 |0.02675 |

|Nickelvac 304 Steel |29,700 |29,000 |0.000976431 |

|Biodur316LS Steel |137,000 |28,000 |0.00020438 |

|Carpenter Custom465 Steel |217,000 |28,800 |0.000132719 |

|Nitinol Shape Memory Alloy |812,000 |10,900 |1.34236E-05 |

|PEEK Medical Tubing |14,065 |508 |3.60825E-05 |

|PTFE Medical Sheath |4,000 |220 |0.000055 |

|FEP Medical Tubing |5,000 |50 |0.00001 |

|PFA Medical Tubing |4,500 |76 |1.67778E-05 |

Figure 4

c. Additional Patent Information

[pic]

[pic]

[pic]

d. References

The Cardiovascular System, B. Cummings



10-20-04

The Cerebro-vascular System Major Arteries (Image)



9/28/04

Collagen Biomechanics in Cerebral Arteries and Bifurcations Assessed by Polarizing Microscopy, A. Rowe, H. Finley, P. Canham,

Journal of Vascular Research, 2003; 40: 406-415

10/21/04

Peripheral Interventions: New Advances in Endovascular Technology, Julio C. Palmaz

Texas Heart Institute Journal 1997; 24:156-9



10-21-04

Guidant Vascular Intervention Product Catalog (Images)



9/28/04

Patent information and numbers



9/28/04; 10/04/04; 10/28/04; 12/06/04



9/25/2004



9/25/2004



9/28/2004

isch.html

9/28/2004



9/28/2004

9/27/2004

cdrh/devadvice/3132.html

11/30/2004

cdrh/devadvice/3122.html

11/30/2004

accessdata.scripts/cdrh/cfcods/cfcfr/cfrsearch.cfm?cfrpart=814&showfr=1 12/3/2004

mascom-ms.de/peek-tubing.htm

11/02/04

htm_files/fh_tubing.htm

11/02/04

peek_tensil_prop.asp

11/01/04



10/28/04



10/26/04

“Statics and Mechanics of Materials: An Integrated Approach 2nd Ed.”

William F. Riley, Leroy D. Sturges, Don H. Morris

John Wiley & Sons 2002 NY

Fundamentals of Machine Component Design Updated 3rd Ed.

Robert C. Juvinall, Kurt M. Marshek

John Wiley & Sons 2000 NJ

Flexible Bars

R. Frisch-Fay.

Butterworths, Washington 1962

Standard Handbook for Mechanical Engineers 7th Ed.

Theodore Baumeister, Lionel S. Marks, Eds.

Mcgraw-Hill 1967 NY

$FKE/USA.pdf

5/06/2005

5/06/2005

e. Acknowledgements

To George Wohlrab and Joe Vaspol from the machine shop:

For your time and dedication, for your ideas, help and support. For always telling us that our project was in fact, good.

To Camilla Minervini at the Mechanical Engineering Office:

For always being there and always willing to lend a hand. The ways in which you have helped us during our time here at Stevens are countless (and in more courses than just this one).

To Keith Yzquierdo:

For helping us out in the machine shop, and keeping us in line (which helped to not drive George mad). Thanks bud.

To Extrumed, Inc.:

For providing us with much helpful information and free samples of tubing. It came in very handing for this one device that we had to build, you know…that device.

And last (but most certainly not least), to Professor Zhu:

Without all your help and guidance none of this could have turned out the way it did.

-----------------------

Figure 5.10

Figure 5.10

Where:

L1= Length of first leg

L2=Length of second leg

W=Width of base (0.157”)

d=diameter of wire (0.008”)

W

d

L2

L1

The new Force:

Outer diameter = 0.073”

Large lumen diameter = 0.033”

Small lumen diameter = 0.017”

The liner is shown at right. Note that 2 wires will pass through the larger Lumen.

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