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Endoscopic Bipolar Forceps Team Leader: Matthew Gaudioso John Emoto-Tisdale Jeff Kandel Armin Moosazadeh Stephen Potter

Industry Partner: Medtronic

ME 189B – Team 5

03/16/12

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Table of Contents Executive Summary – 3 Introduction – 4 Technical Considerations – 5 Design Considerations – 9 Design Evolution and History – 9 Final Design – 11 Results of Design Efforts – 13 Modeling Efforts – 15 Prototyping Efforts – 15 Testing Efforts – 16 Analytical Efforts – 17 Status of Proposed Design – 24 Recommendations and Proposed Efforts – 26 Appendices - 28

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Executive Summary For our senior capstone project, we are working with industry partners Medtronic to develop endoscopic bipolar forceps. This is a medical device Figure 1: Competitor’s Endoscopic Bipolar Forceps used with an endoscope to grasp brain tissue and cauterize it by applying electrical current through it. Our design requirements fall into three main categories. To be endoscopic, the device must have no greater than a 2.0 mm outer diameter in order to fit through a 2.1 mm inner diameter endoscope and be 20 cm in length. To be bipolar, it must be capable of cauterization by passing current though the tissue. As forceps, it must be able to grasp tissue effectively. Our end result of this project will be a to-scale prototype with grasping and cauterizing abilities. The prototype will not be comprised of all final materials. Our design’s mechanical parts primarily consist of two shafts, inner and outer, each with parallel tips that can close to make contact. The inner shaft slides through the outer shaft to contact the overhanging tip of the outer shaft. Through this action, the device can pinch tissue in order to grasp and cauterize it. We have prototyped a proof-of-concept model that can grasp and cauterize tissue, and shows functionality of our selected design. Our device must contain to wires running through the shafts to connect from an electrical connector in the handle, compatible with the Kerwin Generator, to the forceps tips. Analysis was performed in selecting wires, in order to meet the requirement that they successfully transmit 0.22 amps of current to the forceps tips. These wires must be electrically and thermally insulated for safety of the device. After analyzing several materials, we selected Teflon PFA coating to insulate the wires. Additionally, they will be fixed into place using a silicone potting. One wire will be engraved along the inner shaft, while the other will be potted along the top of the outer shaft. Analysis has been performed and checked that the outer shaft will reach a steady state and not exceed a temperature rise of 2° C as anything higher would be considered a risk for causing brain damage. The device must incorporate a non-stick characteristic in the grasping surfaces to ensure effective cautery. That is burned and cauterized tissue must become affixed to the grasping surfaces. To satisfy these non-stick conditions, we have selected to coat the grasping surfaces of our device with PTFE Teflon, due to its exceptionally low coefficient of friction. We have modeled a handle design which will push the inner shaft through a user action. Medtronic has informed us that the most desired style of grip for surgeons is a pencil grip handle. The handle also contains a force limiting mechanical stop, which prevents fracture caused by the user applying an excess amount of force to the device. The device should be limited to applying 4.5 N of force to the tissue. Testing and Analysis has been performed on all parameters of the design, and we believe to have a high probability of success in developing this device. 3


Introduction Hydrocephalus is a disease in which there is a fluid buildup inside the skull and results in brain swelling. It is caused by poor circulation of the cerebrospinal fluid (CSF) inside the brain. CSF acts as a cushion for the brain, providing mechanical and immunological protection, while helping to regulate cerebral blood flow. Normally, CSF transports through the brain and spinal cord and absorbs into the bloodstream (the flow path can be seen in Figure 1 below), but abnormal flow can be caused by several factors. The main causes for disruption of flow are blocked flow, overproduction, or poor absorption into the bloodstream. Hydrocephalus may also be caused by infection or injury. Buildup of CSF puts pressure on the brain, causing it to push against the skull and damage brain tissue. Hydrocephalus causes many problems and may be fatal if not treated. Symptoms include an enlarged head, convulsion, and tunnel vision, while damaged brain tissue can lead to mental disability. The disease is most common in children, but can also be present in adults and the elderly. Without treatment, hydrocephalus has a mortality rate of 60%. The goal of hydrocephalus treatment is to prevent or reduce brain damage by improving the flow of CSF. This can be done using two methods. The first and most commonly used method is placing a shunt in the brain to redirect the CSF. The shunt redirects fluid through a catheter into an alternate part of the body such as the abdomen, where the fluid can be absorbed into the bloodstream. While this is a very effective method of treatment, there are problems associated with placing a shunt. The procedure requires a very invasive open surgery called a craniotomy, in which a bone flap is temporarily removed from the skull in order to operate on the brain. Performing a craniotomy has many risks associated with it such as infection, excessive bleeding, blood clots, and edemas, which is swelling due to fluid buildup. The shunt may also experience complications like blockage, kinking, tube separation, or infection. Some of these issues may require another craniotomy and reintroduce further risks. For certain forms of hydrocephalus, an alternate, less invasive procedure may be used called an endoscopic third ventriculostomy. In this procedure, a device may be entered into the brain through an endoscope, and directed into the third ventricle as shown in Figure 2. Tissue may then be removed from the third ventricle in order to remove CSF blockage and restore normal flow. Endoscopic procedures contain far less risks than performing a craniotomy, and also do not require the lifelong support of a shunt. The device used in this 4

Figure 2


procedure must be capable of cauterizing tissue and grasping it to remove it, while fitting within a neurological endoscope. Currently there are two separate devices used in this procedure: a bipolar probe used for cauterizing tissue, and a mechanical forceps used for grasping and removing the tissue. Our project aims to combine these tools to create an endoscopic bipolar forceps. The scope of our project involves creating a functional prototype with full cautery and grasping capabilities. Our prototype will meet the size requirement of an external diameter of 2.0 mm. A handle will be designed and used to control grasping through the shaft of the device. It will contain wires used to transmit a current to the forceps tips used to cauterize tissue. The wires will have a standard outlet in the handle which may be used to connect to a cautery machine using a standard cable. In addition to these features, our device will not exceed a temperature rise of more than 2ยบ C to not affect the environment of the brain and cause damage. Furthermore, the forceps tips will have a nonstick coating which will prevent tissue from burning onto them and negatively affect the performance of the device. It will also include a mechanical stop, which is a safety feature which limits the maximum force applied to the device by the user and prevent dangerous fracture. [1][2][3]

Technical Considerations To consider the project a success the final device needs to be able to meet technical specifications outlined in the updated project completion requirements documentation (PCR). The main technical challenges focused on were those deemed most critical to a working endoscopic bipolar forceps. Broadly they are the ability: 1. To operate from within an endoscope. 2. To transport a force to the grasping surfaces. 3. To be able to cauterize tissue at the grasping surfaces. 4. To prevent an excessive temperature rise at the surface of the device. 5. To prevent any current from reaching the brain except at the designed cautery points. 6. To prevent cauterized tissue from building up on the grasping surfaces. 7. To prevent the user from applying enough force to damage the device. Fitting down the endoscope is a geometrically restricting technical challenge. The outer diameter of the shaft must be no larger than 2mm. The shaft must also be at least 20 cm long in order to access the necessary areas of the brain. This requirement heavily limited the design choices available to meet each of the other technical challenges. How this requirement effected the potential options to solving other technical challenges is addressed alongside the description of challenge.

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The ability to transport to transport a force to the grasping surfaces is broken into two parts. The first is translating user action through the handle to the shaft. The second is transporting that force down the shaft and to the grasping surfaces in a useable fashion. Research has shown that in order to “1-2 N of force would be necessary to effectively grasp/spread loosely connected soft tissue� [4] This 1-2 N of force must also be below the force required (with a safety factor) for the materials chosen to yield. To apply the force to the shaft the handle needs to translate user action into a linear force along the shaft. As indicated by Medtronic two main handle designs are preferred by the surgical

Figure 3

Figure 4

public. They are referred to as pencil grip (figure 3) and scissor grip (Figure 4). The pencil grip is considered the more preferable of the two. The pencil grip is actuated by a squeeze motion, which means a force perpendicular to the shaft is applied. The challenge in making the pencil design work is translating one linear motion into a perpendicular linear motion. In the case of the scissor design the surgeon actuates the forceps by rotating the arms. The technical issue in making this design feasible is translating that rotational motion into linear motion. Both of these designs are made more complicated by the necessity to limit the force the user is allowed to apply. Due to the incredibly small size of some of the components the surgeon has the ability to damage the forceps if they apply too much force. The device that limits force needs to be able to transmit any force exactly as input by the surgeon up until the cut-off force. For any input force over the cut-off force the force limiter will need to output the cut-off force. The specific cut off force is dependent on the final chosen design itself. Failure to fracture occurs at a specific stress for each material, which is the force per area. While the minimum force as specified in the PCR doesn’t change different designs can and will have different stress concentrations that could cause failure at a small part. This complicates the design of the force limiter as very accurate testing or analysis will be needed to ensure a safe cut off force. The design choices for the transport of the forces are limited by the space required by the components used in cautery and temperature dispersion. Also important was ensuring that the force down the shaft could then still be translated back into a useable force of 2N between the grasping surfaces.

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This makes the design of how the grasping surfaces open and close critical in guaranteeing the minimum force. The ability to cauterize tissue at the grasping surfaces is characterized in the PCR by a minimum burn depth, but in terms of design the requirement is accomplished by the ability to pass the necessary current through the tissue. The interaction point between the device and the tissue is at the grasping surface and because of this the design must be able to transport current to the grasping surfaces. To transport current, two wires must run down the inside of the shaft. One delivers the current specified by the surgeon with the Kerwin Bipolar Generator. The other is the ground wire and completes the electrical circuit and prevents current flowing into any other areas of the brain. The primary technical challenge for this requirement is sizing the wires. They must be able to fit within the shaft without impacting the mechanical components and insulations components (for the temperature restrictions), handle the necessary current applied from the Kerwin Bipolar Generator, and be limited to a maximum power dissipation down their lengths. Control of the power dissipated along the wires requires a minimum wire size. The wire cross sectional size is proportional to the power dissipated and is given by the equation where is the resistivity of the material, is the length of the wire, Ac is the cross sectional area of the wire and is the applied current. As excessive power dissipation is the only technical challenge that requires a minimum wire diameter (all other major technical challenges are related to space concerns within the shaft), the diameter determined through this analysis is the minimum baseline choice. Control of the power dissipation along the length of the wires is the most critical part of preventing an excessive temperature rise at the surface of the device, where excessive temperature rise is defined as 2oC above the temperature of the brain. The wire’s power dissipation is the sole reason that the temperature in the shaft can increase. In addition to restricting the power that is dissipated into the shaft, that power must be transported to the surface without any specific point on the surface raising 2oC. This restriction is due to FDA restrictions stating anything above this point carries an increased risk of brain damage. This requires the placement of the wires to be symmetrical as well as a balance between the elements of the design that transport the force, hold the wires in place, and insulate the wires. Heat transportation through a material is given by the equation ( ) where K is thermal resistivity of the material and q is the rate of heat transport. If there is a high variance in the K for each of the chosen materials more heat will flow to the surface through the materials with the lowest resistance to heat transport. If this happens a small point on the shaft’s surface may not satisfy the requirement despite no problems being shown in the hand calculations for power dissipation above. 7


Current over 2 mA through brain tissue poses as strong risk for brain damage. To prevent current from reaching the brain at any point other than those designated for cautery, the wires need to be covered in an effective insulation material. The resistivity of most wire insulation materials is sufficient for this and can be shown in the equation where is the current traveling across the insulation material around the wire and V is the voltage difference between the wire and the ground. In order for cautery to be repeatable during a surgery, cauterized tissue cannot accumulate on the grasping surface. A material coating on the grasping surfaces at the cautery surfaces is needed to prevent the burning of tissue onto the surfaces. The material coating still needs to be able to pass current through it to the tissue. The equation above showing current through insulation material can be used to show if sufficient current can still pass through the coating. Through testing it will be shown that the chosen material will be able to resist buildup of cauterized tissue. All of our technical challenges can be summarized in Table 1 Performance Criteria Necessary Opening/closing force Max applicable force Bipolar Burn Depth and Burn Radius Successful cautery with Electrosurgical Generator Max current flow to the brain Non-stick grasping surfaces Max brain temperature rise Shaft diameter Shaft Length

Value 2N Design and Testing Dependent Yes 1 mm2 Kerwin Generator 2 mA Yes 2oC 2 mm 19.7 cm

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Design Considerations Design History To begin the design process, devices that were provided by Medtronic were benchmarked to get a starting point for the design of bipolar forceps. Medtronic provided mechanical forceps, which can be seen in Figure 5. The forceps are actuated by the opening and closing Figure 6: Medtronic Bipolar Probe of a handle. The opening and closing of the handle pushes a cable, which rotates around a pulley, and this cable pushes a pin, resulting in the opening and closing of grasping surfaces. The outer diameter of the shaft is 2 mm and can fit down the endoscope, which was provided by Medtronic, which has a 2.1 mm ID. Medtronic also provided a bipolar probe, which can be seen in Figure 6. The bipolar probe is used to cauterize tissue. The bipolar probe also has a standard connection, which allows a generator to be connected to the bipolar probe to allow the bipolar probe to be able to cauterize.

Figure 5: Medtronic Mechanical Forceps

Medtronic stressed that the best possible design would be to take a combination of the Mechanical Forceps and the Bipolar probe that they provided. If the Mechanical forceps were able to have wires in them that were threaded down the shaft, the wires then connected to the tips, and these forceps able to cauterize, then the project would be at the best case scenario. Medtronic also stressed that surgeons prefer a pencil grip handle, which can be seen in Figure 7. The first highly considered design was using the premise of adding the electrical capabilities to the Figure 7: Johnson & Johnson Codman Figure 8: Shaft of design using the combination of the mechanical forceps and bipolar probe mechanical forceps. ISOCOOL Bipolar Forceps This design would use the handle provided by the Medtronic Mechanical Forceps, which was the scissor grip and 9


not the preferred pencil grip. The pencil grip was given lower priority due to the design would still be functional without a pencil grip. The shaft of this design can be seen in Figure 8. When the handle is opened or closed, this would push the cable down the shaft, which would actuate the tips. The shaft had an H-structure, which would be made from either steel or plastic, which would hold the cable in place. Electrical wires would be threaded down the shaft and would have teflon coating and potting around the wires. The potting would be used to hold the wires in place. The problem with this design is that the H-structure would be so thin (.1 mm thick) that the design would not be manufacturable. This design would require micro-welds and the steel would be flimsy on that scale and not able to hold the cable in place. Due to the critical failure of the H-structure, the design was no longer considered. The next highly considered design was a sliding sheath mechanism, which can be seen in Figure 9. This design is actuated by sliding the sheath forward, which closes the tips, and then the sheath is slid backwards, and this open Figure 9: Sliding Sheath mechanism the tips. The part connecting the tips to the the horizontal part within the shaft would act as a spring, meaning that when this part is Hinge Pin compressed it would act to retard the motion, and thus sliding the sheath backwards would be easier for the surgeon since this part would effectively be a spring acting to open the tips. This design never proved ineffective, but was undesirable due to the inaccuracy of the closing tips. These tips do not close directly on the target, and thus the surgeon would have to overshoot his target to actually close on the target. This design has not proven to not be feasible and thus is currently a backup design, but this design does not offer anything that the final design offers, and thus there would be reason that this design would perform, while the final design would not.

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The next highly considered design can be seen in Figure 10. This design had two coaxial shafts to maximize the space allowed for two copper wires, which would be inserted into the center of the inner shaft. The way that this design is actuated is by applying a force to the inner shaft, which is connected to a pin, which results in the translation of linear motion to rotational motion about a hinge to close the grasping surfaces. When FEA was run on the design, with a 3 N grasping surface force, the pin had a high stress concentration, which resulted in stress failure. Due Figure 10: Pin-Hinge Mechanism to this critical failure, this design was no longer considered. Final Design The final design that was considered and is currently going forward to be manufactured during UCSB’s Spring Quarter of 2012 can be seen in Figure 11. Due to the challenges of rotational motion about a hinge and the size constraints on the pin, a design was created which is actuated purely by linear motion. This completely got rid of the pin and the hinge. This design is very simple and has an inner shaft and outer shaft. A force is applied to the inner shaft, by a handle, and this results in the closure of the grasping surfaces.

Figure 11: Final Design

This design has been prototyped and shown to successfully cauterize on a larger scale (10 mm outershaft). The design has been modeled in Solidworks and COMSOL. The analysis shows that the design will not mechanically fail when the required force is applied to the grasping surfaces. Also, the analysis shows that the wires will be electrically insulated from each other. Also, the analysis shows that the outer shaft will not raise 2 deg C at steady state. The current handle design utilizes a pencil grip and can be seen in Figure 12. The design works by the user depressing a pin with the pointer finger and this pushes the inner shaft forward to close the grasping surfaces. By letting go of the pin, the inner shaft is brought backwards and the grasping

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surfaces are released. This is achieved by having the vertical rack compressing a spring. A detailed description of the handle Figure 12: Handle Design design will follow. The user depressed the pin, which pushes the vertical rack downwards. The vertical rack actuates a gear, which is attached to a shaft. The shaft is attached to a mechanical stop, which will be described in detail shortly. The output of the mechanical stop rotates another shaft which is attached to a gear. This gear then rotates a horizontal rack, which pushes the inner shaft. Thus, linear vertical motion is translated into rotation and then Figure 13: Mechanical Stop translated back to linear horizontal motion. An in depth description of the mechanical stop will follow and an image of the mechanical stop can be seen in Figure 13. The purpose of the mechanical stop is to allow the user to only be able to apply a maximum force of 4 N to ensure that the outer shaft of the bipolar forceps will not fracture. The outer shaft will fracture when 9.5 N is applied to the outer shaft from the inner shaft. The shaft rotates the mechanical stop and provides the input to the mechanical stop. The shaft then rotates the first contacting surface, which can be seen in Figure 14. The second contact surface will rotate due to the friction of the contacting surfaces. The friction is proportional to the normal force between the two plates, and thus by tightening the bolts, the frictional force can be controlled. The second plate is part of the second shaft and thus the second shaft will rotate and provide the output shaft’s rotation. Figure 14: Contacting surfaces of the mechanical stop

We are also considering an alternative design which may be simpler to manufacture. This design Figure 15: Cross section which includes the outer shaft and inner shaft

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utilizes a pencil grip and uses an electromechanical stop. A cross section of the final design can be seen Figure 15. The outer shaft has a 2 mm OD, which meets the specification given by Medtronic to successfully fit down a 2.1 mm ID endoscope. An exploded view, which represents what is circled in red in Figure 15 is shown in Figure 16. In the exploded view, a copper wire has Teflon PFA coating around it. This coating ensures that the two copper wires (the other copper wire is at the top of the shaft with Silicone potting holding it in place and also has Teflon PFA coating around it) are electrically insulated fro m each other. The Silicone potting holds the wire in place. The wire at the top of outer shaft will be connected to the top tip. The other wire will be threaded through the inner shaft and be connected to the bottom tip. These two Potting tips will be closed around the tissue and result in cautery. The handle, inner and outer shaft, and the tips will be made of 316 Surgicalgrade stainless steel, which will allow the forceps to be used during surgry since the steel is surgical grade. This high-strength material will allow the forceps to not undergo mechanical failure. One con of the design is that the tip

Teflon PFA coating Copper wire

area has been decreased from 7.5 mm^2 to Figure 16: Exploded view showing the potting, Teflon coating, and 3.5 mm^2, but this will still be sufficient to copper wire cauterize, and the only downside will be that the surgeon will not be able to grasp as much tissue, but the surgeon can still switch out the design with their previous designs if necessary.

Results of Design Efforts As the design considerations were evolving, results needed to be produced to validate the performance requirements were being met. In order to meet those performance requirements, the range of success was established upon three fundamental design considerations: a functional grasping mechanism, cautery mechanism and thermal performance. The cautery mechanism and thermal performance were reliant on the actuation of the product because the arrangement of bipolar leads and insulating material were in conjunction with the grasping mechanism. Thus, the grasping mechanism was to be addressed first. This grasping mechanism would satisfy the forceps characteristics of the device and needed to show how the user would operate the device to grasp brain tissue. To facilitate the highest rate of success, multiple design choices were 13


generated for the grasping mechanism. However, there had to be a way to choose the correct design choice. Hence, a methodical process was taken into action to determine which design considerations would be chosen as the final design. A trade study chart was created to evaluate all three design choices in subcategories. These subcategories consisted of tip area, non-stick ability, heat dissipation, opening/closing range, opening/closing accuracy, tip material, insulation material, and strength. A fundamental grading system (consisting of a check for satisfactory, X for poor, circle for neutral, and – for undetermined) was utilized in the trade study chart to correlate how suitable each design choice was for the given characteristic or action. The results of the trade study chart can be seen in Table 2.

Table 2: Trade study chart to determine suitability of design choices to performance features As shown in the trade study chart, the linear actuation design (Design 1) received the highest honors in the grading system, which meant it had a better satisfaction rating for both the critical and non-critical features for the device in comparison to the other two design choices. Therefore, Design 1 was carried forward as part of the final design to satisfy the grasping mechanism feature. However, these grades could not be determined without the proper design efforts in the fields of prototyping, modeling, testing and analysis. Thus, the design considerations were implemented on all 3 design choices by means of the PTMA activities.

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Modeling Efforts The first of the PTMA activities prepared was modeling. This would help ensure the ideas of the team members were being portrayed in an illustrative fashion and would educate the entire team on how the specific design operated. The purpose of modeling was to show how the actuation of the grasping mechanism would perform. Once the models were designed, they could be utilized to perform analysis and determine whether they could withstand forces provided through the actuation by the user along with effective cautery upon running of current through the bipolar leads, and a minimal increase in temperature to satisfy the thermal requirements. As mentioned before in the trade study, there were 3 design choices to model. These designs have been previously uttered in the Design Considerations of the Engineering Report, but it is important to take note of the efforts in the modeling of these designs. Design 1 delivered a linear actuation in order to close the tips and grasp brain tissue. This was the most innovative of all our design choices because this grasping mechanism has yet to be used in industry. In addition, the tips are designed at a 30o angle in order to maximize the tip area and increase the amount of brain tissue to be grasped. The actuation of Design 1 as well as the other designs can be seen in the figures on Table 2 (and previously in Design Considerations). Design 2, which consists of the pin-hinge actuation, utilized a standard method of closing the forceps tips, where one tip would rotate about a pin to meet the stationary tip upon impact. This method has been performed before and is seen in the current market of forceps. The inspiration behind Design 2 came from the benchmarked mechanical forceps provided by Medtronic. The collapse of this design was due to stress failure on the pin, which will be addressed later in the analytical efforts. Finally, Design 3 delivered a tweezers actuation, where the user would pull back on the handle to close the tips and grasp tissue. Further modeling beyond hand sketches were not performed on this design choice because the Medtronic team insisted that this was not the ideal method to grasp tissue because it would inhibit the opening/closing accuracy of the user to the desired tissue site (due to the tips closing at a given distance behind the opening position). Therefore, this design choice would be put aside as a backup in case Design 1 faltered in any critical way. Prototype Efforts An effective way to prove the validity of models is to create prototypes, and that was the next step taken in order to illustrate the results of the design efforts. The modeling and analysis yielded the linear actuation (Design 1) as the grasping mechanism for the final design, and it was now necessary to demonstrate that the user can effectively activate the inner shaft of the device to close the tips together and grasp brain tissue. Therefore, a proof-of-concept prototype was created to show the action can indeed be performed. The proof-of-concept prototype consisted of 2 pieces of aluminum, one being a solid rod and the other a hollow cylinder. The hollow cylinder had a larger inner diameter than the solid rod’s outer diameter in order to slide the rod inside the hollow cylinder. The ends of both parts were machined to a 30o angle as noted in the design 15


previously to maximize tip area. Thus, the tips close and come together at 30o. The prototype can be seen in Figure 17.

Figure 17: Proof-of-concept prototype incorporating cautery mechanism and non-stick tips As seen in the figure, the prototype had additional materials attached to the 2 aluminum parts. That is because the prototype was created not only to validate the linear actuation and grasping of tissue, but to validate effective cautery and non-stick characteristic of the tips. Thus, two copper wires were connected to the prototype (a wire to each tip) to simulate the bipolar leads, which could be tested for successful cautery. Also, a square sheet of PTFE Teflon was attached to each tip, which could be tested for the non-stick condition during cautery procedures. Teflon was utilized for the non-stick condition because it demonstrates a very low coefficient of friction to allow the brain tissue to slide right off the tips upon release and excellent dielectric properties to make it suitable as an insulator. Upon the correct thickness of Teflon coating on the tips will also ensure enough voltage to carry through to the brain tissue for cautery. The test procedure and results of these tests can be read further in the Testing portion of the Engineering Report. Testing Efforts A crucial ingredient to engineering design work entails transferring theoretical evaluations to physical demonstration, or testing. For the scope of this project, the purpose of testing was to validate successful connection to the Kerwin Generator provided by the Medtronic team, effective cautery and establishing the non-stick characteristic of the tips. Therefore, these tasks were broken down into multiple tests and isolated from the other tasks to show success, and finally brought in together as one large test to show that they can also work hand in hand. The first test was to validate successful connection to the Kerwin Generator, and this was performed in numerous ways. First, two simple banana cables were connected to the outlets of the 16


generator. Successful connection was established by running current through the cables and onto a piece of pork. As this test proved success (pork was indeed burned), the next connection was the benchmark open-surgery bipolar forceps, which also demonstrated success. Efforts were pressed forward to the next test after observing success in the connection to the Kerwin Generator. The second test would be the demonstration of effective cautery. The tests specimens included both pork and cow brain in order to simulate the human brain. These test specimens (tested individually) were also mixed with saline solution to effectively simulate cerebral spinal fluid that wraps around and throughout the human brain. Effective cautery was measured as a success if two individual tissues were merged together when the tips are provided a current (voltage is applied to the tissues) to make them one single tissue. Once again, multiple devices were tested in connection to the Kerwin Generator. The benchmark bipolar forceps were experimented followed by the proof-of-concept prototype, both of which showed satisfactory remarks. The final test, which was to demonstrate non-stick conditions for the tips, was performed in addition to the cautery test with the proof-of-concept prototype. Once the tips grasped two separate entities of brain tissue and current was applied through the tips for effective cautery, the test involved release of the brain tissue to see whether the tissue remained on the tips or slid right off. After testing with the prototype, test results demonstrated that the tissue did slide off the tips upon release, which meant the tips had exhibited the non-stick characteristic that was desired. Therefore, all three tests were shown to be a success, whether performed with benchmark devices or the proof-of-concept prototype. The test procedure and test report can be referenced for further review in the appendix.

Analytical Efforts TASK 1: Must actuate forceps within 2mm OD shaft without mechanical failure: Because of the 2mm outer diameter constraint, initial design that utilized rotational motion about a pin to actuate the grasping surfaces required a small pin. Stress analysis was performed on the pin to determine feasibility of using the .3 mm diameter pin necessary with those designs. Both Finite Element analysis and hand calculations were performed. Hand calculations were used to determine the yield strength of the chosen pin material necessary to avoid failure, given a safety factor of 1.63, when a force of 2 Newtons is applied to the middle of the grasping surface (see figure 18 for free body diagram of grasping surface/pin system). The reaction forces on the two pins (sliding pin and hinge pin) were obtained by applying the two static principles that the net moment about any point must be zero and the net force in every direction must also be zero. The force on the hinge pin was calculated to be 9.57 Newtons, resulting in a maximum bending moment of 2.44 Newton-mm on the pin. 17


FIGURE 18 OF FBD OF GRASPING SURFACE/HINGE AND OF JUST THE HINGE

Next the distortion energy theory was used to solve for the yield strength needed to withstand the 2.44 Newton-mm bending moment with a safety factor of 1.63.

(Eq. 1)

[ [ (

) ]

â „

]

n is the safety factor (1.63) d is the pin diameter (.3 mm) Se is the yield strength (solving for this) Kf is the stress concentration factor (1.58) Ma is the alternating bending moment (2.44 N-mm)

Solving for the yield strength yields Se = 711.2 GPa. Diamond’s yield strength is on the order of 10 GPa. Therefore, according to our analytical calculations, use of the specified pin size to withstand the 2 Newton load on the grasping surfaces is not feasible for any material. However, to confirm our approximations were correct finite element analysis was used to simulate the stress profile on the grasping surface/hinge mechanism. Figure 19 below shows the stress profile

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given a load on the grasping surfaces of 2 Newtons with mechanical failure occurring at the hinge pin. FIGURE 19 OF THE FEA

As mentioned in previous sections, the failure of the pin design due to high stress at the hinge pin demanded a different actuation method in order to either enlarge the pin or eliminate it. The latter option was chose with our linear actuated design. It was then necessary to demonstrate that this new linearly actuated design did, in fact, solve the problem that the rotationally actuated design had created. Thus, a Finite Element model of the new design was made to analyze the stress profiles created by applying various loads to the grasping surfaces. Figure 20 below shows the stress profile produced by applying a 9.5 Newton load. FIGURE 20 OF THE FEA

19


After iterating the finite element analysis it was determined that the shaft would yield at the fillets circled in figure 20 when a load of 9.5 Newtons is applied, giving a safety factor of 2.25 because the mechanical stop will only allow 4.5 Newtons to be applied. This result analytically proves that our design solves the problem of actuating forceps within a 2mm OD shaft without mechanical failure. TASK 2: Must electrically insulate wires Materials used for electrical insulation often have a “dielectric strength” value documented, which is a measure of the voltage difference per unit thickness that the given material can withstand—insulate—without permitting electric current to flow through said material. So, given the dielectric strength of a material it can be determined if a specified thickness of that material can insulate a desired voltage difference. The following must be true for successful insulation: (Inequ. 1)

is the voltage difference is the dielectric strength t is the thickness of the insulation material

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For our project, both and t are design variables that we can change by choosing a different material or changing the thickness, respectively. However, cannot be changed directly—it is determined by the power generator being used (Kirwan Model 26-1500) and the equivalent resistance of the electrical circuit created by our device and the tissue being cauterized. Figure 21 shows the relationship between this equivalent resistance and the power supplied by the generator.

FIGURE OF POWER VERSUS LOAD FOR GENERATOR The following is true for power output from the generator through the circuitry: (Eq. 2)

(

)

is the power generated in watts ( ) is mean of the voltage output squared in squared volts is the equivalent electrical resistance in ohms —

We are interested in finding (Eq. 3)

√(

)

can be conservatively approximated as: This is shown in appendix page 1 to be conservative a conservative approximation—i.e. is actually guaranteed to be less than or equal to √(

In order to obtain ( model of our design.

)

,

)

.

must first be determined. Figure 22 shows the electric circuit

21


FIGURE OF ELECTRIC CIRCUIT MODEL

[5] From figure 21,

for

Solving Eq. 4 for (

) (

.

yields: )

Eq 4

(

)(

)

Now, we can return to Ineq 2 to determine the necessary material and thickness of which to insulate 80.5 volts. Through material research, we found that Teflon PFA coatings had the highest dielectric strength of wire coatings that can be applied in extremely small sizes. Thus, the dielectric strength of Teflon PFA—see appendix page 2 was used to determine the necessary coating thickness to properly insulate the given voltage difference.

(

)

This result analytically proves that, given the coating thickness of 195 microns of our design, the wires will be electrically insulated. TASK 3: Brain must not be increased more than 2°C in temperature Due to Ohmic heating of the small diameter wires, we performed heat transfer analysis both through hand calculations and Finite Element Analysis to determine the smallest diameter that the electrical wires can be to maintain an outer shaft temperature of no more than 2°C above initial brain temperature during cautery. 22


Hand calculations used the conservation of energy principle, applied to the system (see appendix page 3) at steady state (i.e. constant temperature profile): Eq 5

is heat flux measured in Watts/meter (steady-state conditions) (steady-state conditions)

Heat generated in Eq 5 is that created by ohmic heating of the wires: (

)

(

Eq 6

)

(resistivity of copper)

(combines area of both wires) Eq 7

( )

It is conservative to make the following approximation (see appendix page 1): Eq 8

( )

Heat convected from the forceps to the brain is: Eq 9

(

)

(conservative value—see appendix page XX—for heat transfer coefficient of brain fluid surrounding shaft) (

)

(circumference

of shaft)

Equating Eq X and X, d is solved as follows: Eq 10 (

(

)

)

Thus, a wire diameter of .0268 mm will result in a steady state temperature rise of 2°C on the outside of the shaft touching the brain.

23


This result analytically proves that the wire diameter used in our design (.0282 mm) will cause a temperature rise to the brain surrounding the shaft of less than 2°C. Status of Proposed Design The previously described testing, prototyping, modeling, and analysis have shown that our current design does solve all of the technical challenges presented. The remaining issue is manufacturing feasibility of our design into a working prototype. Ability to either manufacture each individual component within our design to the correct size or purchase such from a vender has already been verified—see appendix page 4 for component manufacturability table. Integration tasks, however, are what pose the greatest obstacle because all components need to be integrated and precisely aligned within a 2mm OD/ 1.4mm ID shaft. Integration challenges include:   

Transportation of .0282 mm wires down shaft with OD of 2mm and ID of 1.4mm. Secure wires in proper position within shaft with electrical potting. Electrically connecting the wires to the grasping surfaces.

 Electrically connecting the wires to the electrical connector within the handle. Transportation of wires down shaft Our projected method is to attach the wire to a rigid needle-like object that can easily be fed down the length of the shaft. The wire would then be detached from the “needle” after the end of the shaft has been reached. This process has been proven feasible through testing with shafts from David Bothman. A 1.2mm OD shaft was used to feed an attached (soldered) .05mm wire down a 2.1mm OD shaft. This test was successful and verifies the manufacturing process (see Test procedure/report 4 in spendix). Securing the wires Securing the wire that fits in the groove channel on the inner shaft does not pose a problem, as this will be performed before the inner shaft is placed within the outer shaft, which allows direct physical access to the wire placement. However, potting (securing the wire with silicon electrical potting) the other wire within the outer shaft in proper position is more involved since the inside of the shaft cannot be directly accessed. The basic steps of our projected process are as follows: 1. Attach one machined cap on either end of the shaft. a. The cap on the handle end of the shaft will have a precisely located hole to feed the wire through 2. Apply tension to wire to straighten it into correct position. 3. Heat correct volume of silicon potting material to melting temperature and pour through hole on the shaft so that it settles within the shaft. 24


4. Heat the shaft to be sure the silicon potting is fully liquous within shaft, so that it takes the shape of its container (this is the shape specified by our design) 5. Allow shaft to cool and remove end caps. Preliminary testing on a 5mm shaft, using standard epoxy as the potting, showed that the above steps are feasible to inject the potting into the shaft in the right orientation. However, due to lack of time the precision machined caps could not be designed and manufacturing—so, the hole to locate the wire was not present in our test. Therefore, while it was verified that the potting could be precisely located, the ability to accurately place the wires within the potting still needs to be verified. Full testing will be performed by 4/2/2012 to verify the feasibility of this process (see Test procedure 1 in appendix). Connecting wires to grasping surfaces Initially, connection of the wire to the grasping surfaces was intended to be performed through precision soldering by Greg Dahlen. Dahlen has experience on soldering on the same size scale with the use of a jeweler’s torch. However, we are now also considering using a mechanical fastener to secure the wire to the grasping surface connection to eliminate the fragile soldering to stainless steel. Testing still needs to be performed to determine which method is more feasible. This decision will be finalized by 4/27/2012 when the project completion requirements are due. Connecting wires to electrical connector within handle Because it has not yet been determined whether the handle will be disposable or reusable, the nature of the wire connection within the handle has been postponed. If it is decided that the handle will be disposable, then no special connection within the handle is necessary. The wires from the shaft can just be extended through the handle and connected to the Kerwin Generator outside of the handle. However, if we aim to make the handle reusable, an electrical connection between the shaft and handle will need to be implemented so that the handle can simply release from the shaft assembly. This decision will be finalized by April 2, 2012. Feasibility of all the component manufacturing and integration processes for our design has been shown. Therefore, successful achievement of all values stated within our Project Completion Requirements (PCR) appear achieveable—reference appendix page 5 for PCR.

25


Recommendations We made changes to the PCR. The maximum opening/closing force of the forceps was changed from 15 N to 4.5 N. The 15 N force was based off of research of breaking tissue, and after our design was finalized, we realized that 4.5 N would be the maximum allowed value of the mechanical stop to avoid fracture of the grasping surfaces. We got rid of the requirement of 6.5 N maximum force to release the tissue, which was our non-stick requirement. Our design can only apply 4.5 N, so this requirement will now become the maximum force to release the tissue, which makes our non-stick requirement stricter in the sense that we will need to release the tissue with a smaller force. We have added the requirement of minimum grasping force of 2 N because we will have determined that to successfully cauterize, we will need 2 N grasping force based off of research. [4] The fracture strength of the shaft has been changed from 280 MPa to 180 Mpa. The 280 Mpa fracture strength was a rough calculation based off a force that could be expected. The 180 Mpa is the strength of the material that will be used in the finalized design and be able to withstand the required force with a safety factor of 2. In the original PCR, there was a requirement that 97.5% of voltage input will be transferred to the grasping surfaces. This is a measure that the electrical wires have been insulated. The main concern is that the forceps can cauterize, which will imply that the electrical wires are insulated. Therefore, we have changed the requirement to minimum burn depth and burn radius to 1 mm. 1 mm still needs to be verified to be considered successful cautery. Maximum overshoot distance of 2 mm was a value that was created when a design where the grasping surfaces would be pulled backward to close was being considered. Since this design is no longer being considered, the PCR value is no longer in our PCR. A new PCR value has been added which is a minimum opening distance of 4 mm, which allows the forceps to close on the amount of tissue that would be necessary for successful cautery. This value still needs to be verified to show that this will result in successful cautery. We need to finalize our handle design. We currently have a handle which utilizes a gear design and has been modeled. We also have a design which is based off a CAD model given to us by Medtronic, which is actuates the forceps with a pencil grip. We also need to finalize a keyway design, which will prevent rotation of the inner shaft. By doing FEA on the model, it is clear that a keyway needs to be designed at grasping surface 26


and near the handle. This keyway will be achieved by inserting a pin through the outer shaft and having it prevent rotation of the inner shaft when contact occurs between the pin and the inner shaft. This pin will be inserted at the grasping surfaces and the handle. Manufacturing processes have been created which are based off already existing manufacturing processes. These manufacturing processes will need to be tested to prove feasibility. We will also contact manufacturers to find out who would be able to complete these manufacturing processes. Once the handle and keyway designs are finalized and we have tested the feasibility of the manufacturing processes, then we will know whether or not we will be able to manufacture a fully functional prototype. If a fully functional prototype is not able to be manufactured, then we will create a proof-of-concept prototype. We have already shown through analysis that the design is feasible if the design can be manufactured. By 4/27/12, we will finalize our project completion requirements, which implies we will know what prototype we are manufacturing. We will then begin building our prototype, which will be built at UCSB’s machine shop and also built in other machine shops, which have the manufacturing capabilities that we need. We will need to perform testing to prove that our design works. We may also need to redo analysis if our prototype does not meet the finalized project completion requirements.

27


Appendices References Project Team with assigned responsibilities, Faculty Advisers/Industry sponsors, Acknowledgements Drawing Package Test Procedures and Test Reports Analysis Component Manufacturability Table Revised PCR Insulation Specifications Project Budget and Expenses to date

References [I1]

http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002538/

[2]http://en.wikipedia.org/wiki/Cerebrospinal_fluid [3]http://en.wikipedia.org/wiki/Hydrocephalus

[4] Multifunctional Forceps for Use in Endoscopic Surgery---Initial Design, Prototype, and Testing Andrew C. Rau, Mary Frecker, Abraham Mathew, and Eric Pauli, J. Med. Devices 5, 041001 (2011), DOI:10.1115/1.4005225

http://dx.doi.org/10.1115/1.4005225 [5]http://iopscience.iop.org/0967-3334/20/4/201/pdf/pm94r1.pdf (Resistivity of human tissues)

28


Project Team with assigned responsibilities, Faculty Advisers/Industry sponsors, Acknowledgements Team Roles and Responsibilities

Team Member Matt Gaudioso John Emoto-Tisdale Jeff Kandel Armin Moosazadeh Stephen Potter

Primary Role Team Leader, Modeling Testing Analysis Testing Prototyping

Secondary Role Analysis Analysis Modeling Prototyping Modeling

Acknowledgements: Faculty Advisors: Sumita Pennathur Greg Dahlen Dave Bothman Kirk Fields Stephen Laguette

Industry Partners: Medtronic Jeff Bertrand Chris Mulholland Drawing Package

29


Test Procedures and Test Reports TEAM No. [5] – Endoscopic Bipolar Forceps

Test Report – TR9 Effective Cautery with Non-Stick Condition [Matthew Gaudioso], [Jeff Kandel], [Armin Moosazadeh], [Stephen Potter], [John EmotoTisdale]

REV. DATE [02/12/2012]

30


Table of Contents

1.0 Introduction

Page 3

2.0 Reference Documents

Page 3

3.0 Test Procedures

Page 4

4.0 Recorded Data

Page 4

5.0 Test Results

Page 4

6.0 Summary of Test Results

Page 5

7.0 Anomalies

Page 5

8.0 Conclusions and Recommendations

Page 5

Appendices

Page 6

List of Tables

Table 1

: Cautery/Non-stick Test Results

Page 4

Definitions

Cautery – Successful fusion of two separate entities of tissue into one homogenous entity. Non-stick – Cauterized tissue does not stick to the grasping surfaces.

31


1.0 Introduction

The following describes the results of Test Procedure 9, which aimed to characterize cautery and non-stick performance of both the benchmark bipolar forceps and our proof-of-concept prototype when connected to the Kerwin Bipolar Generator. The specimens used for testing were both pork and cow brain saturated in saline solution to simulate the brain environment per Medtronic’s recommendation. These results will be used to disposition our current grasping surface material choice.

1.1 Purpose

The results given in this document are for the purpose of confirming of disproving our design choice for the grasping surfaces material/coating.

1.2 Objectives

The objective is to compare the respective cautery and non-stick performances of the benchmark bipolar forceps and our proof-of-concept electrical prototype to determine if our design maintains/exceeds benchmark performance.

1.3 Importance

The results are important because without successful non-stick cautery the design is a failure. This test will indicate if a different coating or coating thickness is necessary.

1.4 Background

Because the electrical model of our design has the highest resistance at the grasping surface coatings and the tissue itself, most of the power will be dissipated across these two elements. The power that is dissipated across the tissue must be high enough to cauterize it. Therefore, the resistance of the grasping surface coating must be small enough such that sufficient power is passed through the tissue instead of the coating. 32


Because Teflon coatings are common in the cautery field for non-stick performance, it is expected that non-stick performance will be achieved in this test.

19.7 Reference Documents

Test Procedure 9 Teflon PFA properties (page 6) Cautery videos (E-Binder)

3.0 Test Procedures

Two separate entities of the specimen to be tested were be soaked in saline solution. The bipolar forceps being used were connected to the Kerwin Generator. The two tissue entities were grasped with the forceps and then the foot pedal was suppressed to supply power to the grasping surfaces. The grasping surfaces were then released and examined for sticking tissue. The tissue was examined to determine if the two separate entities were fused into one continuous entity.

4.0 Recorded Data

The following table illustrates the test results. Successful cautery was defined as fusion of two tissue entities into one entity. Successful non-stick performance was defined as having no tissue left on the grasping surface after the grasping surfaces were released.

Trial

Criteria

Benchmark Bipolar Forceps

Trial #1 Pork

Cautery Non-Stick Cautery

Pass Pass Pass

Trial #1 Cow

Proof-of-concept Model w/ TEFLON PFA Coated Grasping Surfaces Pass Pass Pass 33


Brain Trial #2 Pork

Non-Stick Cautery Non-Stick Trial #2 Cow Cautery Brain Non-Stick Trial #3 Pork Cautery Non-Stick Trial #3 Cow Cautery Brain Non-Stick Table 1: Cautery/Non-stick Test Results

Pass Pass Pass Pass Pass Pass Pass Pass Pass

Pass Pass Pass Pass Pass Pass Pass Pass Pass

5.0 Test Results

There was no performance difference between the benchmark and our proof-of-concept prototype. Because the sample Teflon coatings used on the grasping surfaces on the proof-ofconcept prototype were relatively thick (10 Âľm) compared to industry capabilities (5-10 Ă… thick) it was not expected that all trials were yield successful cautery with our model. However, all cautery was successful. Therefore, when a thinner coating is used on the final prototype, cautery will be enhanced.

6.0 Summary of Test Results

These test results verify that our current electrical design is feasible because cautery was successful. The results also verify our choice for non-stick grasping surface material. Because the coating used was PFA Teflon, our design coating (PTFE Teflon) is guaranteed to work as well because PTFE has a lower coefficient of friction than PFA (.1 compared to .2), while maintaining the same electrical conductivity.

7.0 Anomalies

34


A necessary note for the non-stick results is that tissue did stick to the machined cuts made on the outer edges of the grasping surfaces, but this was expected because of the rough edge finish. However, no tissue stuck to the actual part of the surfaces that grasp the tissue. Therefore, this was deemed successful cautery because the final prototype will have precisely machined grasping surfaces. Those surfaces will not have the roughness fault produced by crudely chopping a portion of coated sheet metal into rectangles with rough edges as was done for this test.

8.0 Conclusion and Recommendations

These test results proved that our cautery/non-stick design successfully meets all cautery and non-stick performance parameters established by our bipolar forceps benchmark, and, therefore, verifies our grasping surface material choice.

Appendices

Attached below is the properties of PFA Teflon.

35


36


TP No. [5] – PROJECT NAME

Test Procedure – TP1 Securing Wires with Potting Matt Gaudioso, John Emoto-Tisdale, Jeff Kandel, Armin Moosazadeh, Stephen Potter

REV. DATE 03/16/12

37


Table of Contents

1.0 Introduction

Page ##

2.0 Reference Documents

Page ##

3.0 Test Configuration

Page ##

4.0 Test Procedures

Page ##

Appendices

Page I

List of Figures

Figure 1

Page ##

Figure 2

Page ##

Figure 3

Page ##

List of Tables

Table 1

Page ##

Table 2

Page ##

Table 3

Page ##

Acronyms

ACRONYM 1 – Expanded Meaning ACRONYM 2 – Expanded Meaning ACRONYM 3 – Expanded Meaning 38


Definitions

Term 1 – Definition Term 2 – Definition Term 3 – Definition

39


9.0 Introduction This is a test to prove manufacturability of transporting wires through the shaft, and securing them in place.

9.1 Purpose The test will give us results on whether our wire layout is feasible.

9.2 Objectives Obtain a yes or no answer as to whether our manufacturing idea is feasible

9.3 Importance If this idea is not proven feasible, we cannot move forward with our current design

9.4 Background Potting is a method of securing by pouring a liquid silicone material to harden in desired shape around the wire

10.0

Reference Documents

None

3.0 Test Configuration

40


We will have a hollow shaft and two end caps used to contain the potting. The end caps will have holes to first feed the wires through, and secondly pour potting through. Potting will be contained in a syringe to be injected into the shaft.

3.1 Test Approach

The wire will be fed through the shaft using a smaller shaft acting as a needle. The shaft will have both ends capped and the wire will be held in tension to remain straight, heated potting will be injected and the shaft will be heated to ensure that the potting is fully liquous inside the shaft, to take the shape of this container. Once desired shape is reached, shaft will be cooled and end caps will be removed, leaving us with a fixed wire.

3.2 Equipment Needed

We will need the outer shaft and wire, a hot plate, a syringe, potting, and two machined caps.

3.3 Test Reporting Requirements

We will record a yes or no value to measure if the test was successful. We will measure the amount of potting used, the temperature it is heated to.

4.0 Test Procedures

4.1 Test 1

Table 1. Test 1 Procedures Step

Procedure

Expected Result

Pass / Fail 41


1

Feed wire through Wire in Shaft Shaft

Wire is through shaft

2

Wire fed through caps

Caps on wire

Wires are passed through the shaft

3

Caps secured on shaft

Caps on shaft

Caps securely placed on the ends of the shaft

4

Wire held in tension

Tight Wire, in place

Wire held stable, securely, and tight.

5

Potting heated to be filled

Liquid potting

Potting at desired melting temperature

6

Potting filled

Potting in shaft

Desired amount of potting within shaft

7

Shaft Heated

Potting fully liquous in shaft and formed to its shape

Shaft heated to desired temperature

8

Shaft Cooled

Potting Hardened

All potting solidified, wire inside of solid potting

9

Caps Removed

Just Shaft, wires and potting in assembly

Caps repmoved with other components intact

10

Wires modified to Neat clean wires desired length

Wires formatted as needed

42


TP No. [09] – Endoscopic Bipolar Forceps

Test Procedure – TP9 Effective Cautery with Non-Stick Condition [Matthew Gaudioso], [Jeff Kandel], [Armin Moosazadeh], [Stephen Potter], [John Tisdale]

REV. DATE [01/30/2012]

43


Table of Contents

1.0 Introduction

Page 03

2.0 Reference Documents

Page 04

3.0 Test Configuration

Page 04

4.0 Test Procedures

Page 06

Appendices

None

List of Figures

None

List of Tables

Table 1

Page 05

Table 2

Page 06

Acronyms

PTFE (Polytetrafluoroethylene): A synthetic fluoropolymer of tetrafluoroethylene that has many applications. The most well known brand of PTFE is Teflon, which is what this test utilizes.

Definitions

44


Cautery – The burning of part of a body to remove or close off a part of it, which destroys some tissue, in an attempt to mitigate damage, remove an undesired growth, or minimize other potential medical harmful possibilities such as infections.

Non-stick surface – A surface engineered to reduce the ability of other materials to stick to it.

45


11.0

Introduction

11.1

Purpose

This document will be followed in order to conduct effective cautery testing with nonstick conditions on the equivalent of brain tissue and the brain environment. The test that will be performed is a circuit test which will be used to determine if the connection to the Kerwin Generator provides current to both benchmark bipolar forceps and the proof-ofconcept prototype for successful cautery, and whether the proof-of-concept prototype possesses a non-stick condition in the tips (which is made of PTFE Teflon). Results yielded from this test procedure will be utilized in order to determine if the future functional prototype can also connect to the Kerwin Generator to conduct cautery procedures and maintain non-stick characteristic.

11.2

Objectives

The objective of the test is to gather two pieces of meat (simulated as brain tissue) and burn them together into one cohesive piece to attain successful cautery. In addition, upon release of the tissue, the tissue must slide off the tips to attain successful non-stick conditions.

11.3

Importance

The importance of the test relies on the fact that the endoscopic bipolar forceps we are designing must cauterize brain tissue effectively. The purpose of the device is to seal two entities as one in the brain through the action of burning. Thus, the action of cauterization must be tested and verified with the generator that the device will be connected to understand how the device will perform as well as achieving successful cautery. When dealing with a medical device that will be utilized on a live human brain, safety is the most significant aspect of the operation. Thus, it must be verified that successful cautery is possible with thr medical device prior to operation. Failure to comprehend this characteristic can lead to a tragic injury or even death. In addition, another importance of the test is demonstrating superior non-stick conditions with the tips. If the tissue does not slide off the tips upon release, it may tear off and also lead to severe bleeding. 46


11.4

Background

Background for understanding the test is that current will travel through the path of least resistance (a conductor rather than an insulator if both are applied within the system). Therefore, connection of the prototype to the Kerwin Generator will involve attaching the ends of the wires (bipolar leads) to banana cables, which will be plugged into the generator. In addition, it is important to understand why PTFE Teflon is a non-stick material. Due to its very low coefficient of friction and resistance to attractive or repulsive forces between molecules, PTFE Teflon is excellent for non-stick applications.

12.0

Reference Documents

PTFE Teflon: http://en.wikipedia.org/wiki/Polytetrafluoroethylene

19.7 Test

Configuration

3.1 Test Approach

Pork soaked in saline solution will be used in this test as an approximation for brain tissue and the brain environment. In order to subject the test sample to effective cautery, the test sample must be laid down on a clean, insulated mat. This will also ensure that the test specimen will be the only path that the current will travel. In addition, the pork will be cut into fine pieces so that the forceps can grasp and cauterize them. The test site will contain two of the small pieces of pork next to each other prior to grasping. The benchmark forceps or proof-of-concept prototype will be connected to the Kerwin Generator, which will be grounded to a power supply.

Once all test supplies are prepared in the test site, the user will grasp the two pieces of pork with the medical device (whether the benchmark bipolar forceps or proof-of-concept prototype). Then the user will press on the foot pedal that is a part of the Kerwin 47


Generator to supply current to the device, which will in turn burn the pieces of pork. Once the pieces of pork cease to burn (instantaneous process, lasts no longer than 1 second), the user will release the foot pedal to discontinue the supply of current and release grasping of the tissue. The pork will be examined to ensure the two pieces have combined to one and cautery was a success. If the device in use was the proof-of-concept prototype, further testing will be involved upon release of the tissue grasping. Once the user releases grasping of the tissue, the tips will be examined to ensure tissue was not stuck to the tips (or tissue was not torn and stuck to the tips) for the tips to demonstrate non-stick conditions.

If the tests come to successful conclusions, it will be known that cautery can be achieved in connection to the Kerwin Generator and PFTE-coated tips achieve non-stick conditions. To ensure accurate results, 3 trials will be run with both the benchmark device and proof-of-concept prototype.

3.2 Equipment Needed

Table 1: Test Equipment Equipment/Items Needed Kerwin Electrosurgical Generator

Power Supply

Pork soaked in saltwater

Plastic Mat

Description/Notes The Kerwin Generator provides the current across the device, which in turn provides voltage across the test sample. It has been provided to the team for use by Medtronic. The power supply provides the ground for the Kerwin Generator. It is provided to all students in the design lab and available for use. Pork will be used as the test sample to simulate brain tissue and the brain environment. It will be purchased from Isla Vista Market prior to testing. The insulated mat will be used to place the test sample on, which allows for safety of current to run from the device to the test sample. It will be brought in by one of the team member’s home. 48


Benchmark Bipolar Forceps

The benchmark bipolar forceps will be used to successfully cauterize the test sample in this procedure. It has been provided to the team for use by Medtronic. The prototype will also be used to successfully cauterize the test sample and demonstrate non-stick conditions. It has been fabricated in the UCSB Machine Shop.

Proof-of-Concept Prototype

3.3 Test Reporting Requirements

The requirements for reporting test results will be the careful observation of the test specimen, whether the two pieces have joined as one after a voltage is applied across them, and if release of grasping the tissue yielded it sliding right off the tips. If cautery was not shown to be a success, the test will be performed once again to achieve the desired results.

4.0 Test Procedures

4.1 Test 1

Table 2: Test 1 Procedures Step

Procedure

Expected Result

Pass / Fail

1

Place plastic mat on the work space (table).

Mat is placed on top of the table.

Mat should be on the table to pass.

2

Cut pork into 2 fine (~2 cm long) pieces and place on the mat next to

Pork is cut into pieces and laid on the mat.

Pork should be on the mat to pass.

49


each other. 3

Pour saltwater on the pork.

Pork is soaked in saltwater.

Pork should be soaked in saltwater to pass.

4

Plug in the Kerwin Generator to the outlet followed with the ground cable connected to the power supply ground port. The Kerwin Generator must be in the “Off” position.

Kerwin Generator is connected to the outlet and its ground plug is connected to the power supply ground port.

Kerwin Generator should connected to the wall and the power supply while turned off to pass.

5

Connect the benchmark bipolar forceps to the Kerwin Generator.

The forceps are connected to the Kerwin Generator.

A firm connection between the forceps and generator must be established to pass.

6

Turn the Kerwin Generator to the “On” position.

Kerwin Generator is active.

The Kerwin Generator should be on (the LED light is lit) to pass.

7

Grasp the pieces of pork with the bipolar forceps.

The pork is grasped by the bipolar forceps.

The two pieces of pork must be grasped together by the bipolar forceps to pass.

8

Press on the foot pedal until pieces of pork have been burned.

The pieces of The two pieces of pork should come pork will be together as one entity to pass burned together in successful cautery. the process of cautery upon pressing of the foot pedal. Cautery should only take 1 second.

50


9

Release the foot pedal and grasping of the pork.

The foot pedal is released and the pork is released from the forceps.

The foot pedal is released from active duty in addition to grasping of the pork by the forceps to pass.

10

Repeat Steps 7-9 with new pieces of pork 2 more times.

Successful cautery will be achieved on new pieces of pork.

More pieces of pork should come together as single entities to pass successful cautery.

11

Turn off the Kerwin Generator.

The Kerwin Generator is off.

The Kerwin Generator must be in the off position to pass.

12

Disconnect the benchmark bipolar forceps from the Kerwin Generator and attach the proofof-concept prototype to it. Link the wires from the prototype to banana cables, and connect the banana cables into the generator.

The benchmark forceps will be disconnected and the prototype will be connected to the Kerwin Generator.

The prototype should replace the benchmark forceps as the test device to pass.

13

Repeat Steps 7-10 now with the proof-of-concept prototype.

Successful cautery will be achieved on new pieces of pork with the prototype.

The two pieces of pork should come together as one entity to pass successful cautery.

14

Examine the tips of the prototype to ensure test specimen have

The test specimen will slide right off the tips upon release of its grasping to

No pieces of meat should stick to the tips to pass non-stick characteristic.

51


15

slid off them.

demonstrate nonstick condition.

Turn off the Kerwin Generator, disconnect all devices and clean up.

The Kerwin The generator has been turned off Generator is and everything that was used for the turned off, and all test has been put away to pass. items are gathered and cleaned up from the work space.

52


TEAM No. [5] – Endoscopic Bipolar Forceps

Test Procedure – TP4 Feeding Wires Down 2.1mm OD Shaft [Matthew Gaudioso], [Jeff Kandel], [Armin Moosazadeh], [Stephen Potter], [John Emoto-Tisdale]

REV. DATE [03/11/2012]

53


Table of Contents

1.0 Introduction

Page 3

2.0 Reference Documents

Page 3

3.0 Test Configuration

Page 3-4

4.0 Test Procedures

Page 4

List of Tables

Table 1

Page 4

54


13.0

Introduction

This test aims to verify the process of feeding the electrical wires down the 2mm OD shaft. Because the wires are so small (.0282mm), they are prone to buckle/bend and make simply feeding them down a long, small shaft (2mm OD, Length of 19.7cm) a challenge. Our process to simplify this task will be verified with this test.

13.1

Purpose

This procedure will be used to verify our process for feeding the wires down the endoscopic bipolar forceps shaft.

13.2

Objectives

The objective is to prove feasibility of our process or determine that a different process is needed to successfully feed the wires down the shaft.

13.3

Importance

This test is important because it is necessary to feed the wires down the shaft to the grasping surfaces to perform cautery. If the wires cannot be fed to the grasping surfaces, the design is not for a bipolar forceps, but simply a mechanical forceps.

13.4

Background

This process being tested is simple in nature. It is essentially an imitation of using a needle to sew.

14.0

Reference Documents

55


None applicable

3.0 Test Configuration

A soldering iron will be present to solder the wire to the smaller shaft. The larger and smaller shafts will be set up concentrically and horizontal in orientation.

3.1 Test Approach

The wire will first be soldered with tin-lead solder to the smaller shaft (1.2mm OD). Then the smaller shaft will be fed through the larger shaft (2.1mm OD) and pulled entirely through.

3.2 Equipment Needed

Soldering Iron Pb-Sn Solder .05mm diameter copper wire 1.2mm OD shaft 2.1mm OD shaft 3.3 Test Reporting Requirements

The only foreseeable anomaly would be a broken solder connection. This is not a critical failure—so long as successful wire transportation is achieved 50% of the trials it will be deemed a successful method. This is because performance of the endoscopic bipolar forceps will not be effected by how many trials it takes to feed the wires down the shaft.

4.0 Test Procedures

56


4.1 Test 1

Table 1. Test 1 Procedures Step

Procedure

Expected Result

Pass / Fail

1

Solder Wire to inside of smaller shaft.

Successful solder bond.

Wire must be successful bonded to inside of shaft.

2

Smaller shaft will be pushed through the larger shaft with the “non-wire side� being pushed through first (the wire should be trailing as a tail).

Smaller shaft will exit the opposite end with wire still attached

Wire must still be attached to smaller shaft.

3

De-solder the solder bond.

Wire will be separated from smaller shaft.

Wire must be separated from smaller shaft, but still inside the larger shaft.

57


Analysis

Appendix Page 1

58


Appendix Page 2

59


Appendix Page 3

60


Component Manufacturability Table

COMPONENT MANUFACTURABILITY TABLE COMPONENT .0282 mm diameter copper wires coated with Teflon PTFE to .0381 mm total diameter 2 mm OD, 1.7 ID stainless steel 304 shaft

Grasping Surfaces

Teflon PTFE Coating for Grasping Surfaces

Gear with pitch diameter of 1.5 mm and mating racks for the handle mechanism

PROOF OF MANUFACTURABILITY California Fine Wire Company manufactures and coats wires to this specification (see chart from calfinewire.com on page 6 of appendix) Mcmaster.com manufactures/supplies stainless steel 304 tubing all the way down to .2 mm OD with a wall thickness of .05 mm. (p/n 8988K434). Already obtained a shaft with 2mm OD from David Bothman. Grasping surfaces of correct size are commonly manufactured as on our mechanical benchmark forceps from Metronic. Anaheim Crest Coatings supplied us with sample coatings, which were used on our proof-of-concept prototype to verify cautery and non-stick performance with this coating. (See Test Result 9) Still in the process of contacting gear manufacturers to perform this task.

Appendix Page 4

61


Revised PCR Requirements Specification

Description

Value

Verification Method

Trials

1

Max. current flow to the brain from any point on the wire. (Safety Concern)

2

Max. opening/closing force allowed by mechanical stop (Safety Concern)

3

Min force applied by the grasping surfaces

2N

The forceps must apply 2 N in order manipulate tissue. The force will be tested per TP[3].

4

Diameter of forceps shaft

2 mm

The diameter dimension will be measured with calipers

3

5

Fracture strength of shaft

180 Mpa

The bending strength of the forceps will be tested per TP[4] to confirm analytical expectations.

5

6

Min. burn depth and burn radius

1 mm / 1 mm

The burn depth and burn radius will be tested per TP[5], and compared with the analytical prediction.

5

7

Min Opening Distance (distance between open tips)

4 mm

The distance between the grasping surfaces will be measured per TP[6].

3

8

Maximum brain temperature rise caused by forceps

2째C

The temperature rise caused by the use of the bipolar forceps will be estimated per TP[7]. The results will be compared with the analytical modeling.

5

9

Must Connect to Standard Electrosurgical Generator

Kerwin Generator

Connection of the bipolar forceps to the Kerwin Generator electrosurgical generator will be attempted.

3

10

Shaft Length

19.7 +/- .1 cm

The shaft length will be measured with calipers.

3

Approved

The Bipolar forceps user manual will be reviewed by Medtronic engineers. Attempts at operating the device per the user manual will be performed by surgeons as well as colleagues.

11

Bipolar forceps user manual

2 mA

Maximum current flow will be tested per TP[1]. Results will be compared with those forecasted by analytical models.

5

4.5 N

The maximum allowed force will be tested per TP[2]. Test results will be used to confirm the design performs as predicted by analytical modeling.

5

5

Appendix Page 5

62


Insulation Specifications

Appendix Page 6

63


Project Budget and Expenses to date

Budget Fall Quarter

Item

Vendor

Prototyping supplies (pvc, wire, wood, insulation) Home Depot Total Fall

Cost

Purchased by

~$40

Matt

~$40

Winter Quarter Test Sample

Cow Brain Pork Pork + Salt

Santa Cruz Market IV market IV market

Wires

Silver Wire Copper Wire

McMaster Carr McMaster Carr

Benchmark

Forceps + Connector cable ebay

~$45

Raw Material

PTFE Film Shop material

McMaster Carr UCSB ME Shop

~$40 John $7.50 Stephen/Armin

Printing Cost

Final Report

Alternative Copy Total Winter

$36 John $8 Various $11.71 Armin

$30 Jeff $10 Stephen

Matt

$20 Matt $208.21

64


UCSB Capstone Engineering Report