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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

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.

Figure 1: Competitor’s Endoscopic Bipolar Forceps

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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

Figure 2

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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 2º 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

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.

Figure 3 Figure 4

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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.

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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 Value

Necessary Opening/closing force 2 N

Max applicable force Design and Testing Dependent

Bipolar Yes

Burn Depth and Burn Radius 1 mm2

Successful cautery with Electrosurgical

Generator

Kerwin Generator

Max current flow to the brain 2 mA

Non-stick grasping surfaces Yes

Max brain temperature rise 2oC

Shaft diameter 2 mm

Shaft Length 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

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.

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

mechanical forceps.

This design would

use the handle provided by the Medtronic Mechanical Forceps, which was the scissor grip and

Figure 5: Medtronic Mechanical Forceps

Figure 6: Medtronic Bipolar Probe

Figure 8: Shaft of design using the combination of the mechanical forceps and bipolar probe

Figure 7: Johnson & Johnson Codman ISOCOOL Bipolar Forceps

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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

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

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.

Figure 9: Sliding Sheath mechanism

Hinge Pin

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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

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.

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

Figure 10: Pin-Hinge Mechanism

Figure 11: Final Design

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surfaces are released. This is achieved by having the vertical rack compressing a spring.

A detailed description of the handle

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

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.

We are also considering an alternative design

which may be simpler to manufacture. This design

Figure 13: Mechanical Stop

Figure 14: Contacting surfaces of the mechanical stop

Figure 15: Cross section which includes the outer shaft and inner shaft

Figure 12: Handle Design

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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

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 Surgical-

grade 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

area has been decreased from 7.5 mm^2 to

3.5 mm^2, but this will still be sufficient to

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

Copper wire

Teflon PFA coating

Potting

Figure 16: Exploded view showing the potting, Teflon coating, and copper wire

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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

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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

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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.

18

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)

[

[ ( )

]

⁄

] 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

19

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

20

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

21

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 — can be conservatively approximated as:

(Eq. 3) √( ) 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 ( ) , must first be determined. Figure 22 shows the electric circuit

model of our design.

22

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.

23

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.

24

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.

25

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.

26

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

27

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.

28

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)

29

Project Team with assigned responsibilities, Faculty Advisers/Industry sponsors,

Acknowledgements

Team Roles and Responsibilities

Team Member Primary Role Secondary Role

Matt Gaudioso Team Leader, Modeling Analysis

John Emoto-Tisdale Testing Analysis

Jeff Kandel Analysis Modeling

Armin Moosazadeh Testing Prototyping

Stephen Potter Prototyping Modeling

Acknowledgements:

Faculty Advisors:

Sumita Pennathur

Greg Dahlen

Dave Bothman

Kirk Fields

Stephen Laguette

Industry Partners:

Medtronic

Jeff Bertrand

Chris Mulholland

Drawing Package

30

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 Emoto-

Tisdale]

REV. DATE [02/12/2012]

31

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.

32

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.

33

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

Proof-of-concept

Model w/ TEFLON

PFA Coated

Grasping Surfaces

Trial #1 Pork Cautery Pass Pass

Non-Stick Pass Pass

Trial #1 Cow Cautery Pass Pass

34

Brain Non-Stick Pass Pass

Trial #2 Pork Cautery Pass Pass

Non-Stick Pass Pass

Trial #2 Cow

Brain

Cautery Pass Pass

Non-Stick Pass Pass

Trial #3 Pork Cautery Pass Pass

Non-Stick Pass Pass

Trial #3 Cow

Brain

Cautery Pass Pass

Non-Stick Pass Pass

Table 1: Cautery/Non-stick Test Results

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-of-

concept prototype were relatively thick (10 µm) compared to industry capabilities (5-10 Å 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

35

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.

36

37

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

38

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

39

Definitions

Term 1 – Definition

Term 2 – Definition

Term 3 – Definition

40

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

41

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

42

1 Feed wire through

Shaft

Wire in 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

desired length

Neat clean wires Wires formatted as needed

43

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]

44

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

45

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.

46

11.0 Introduction

11.1 Purpose

This document will be followed in order to conduct effective cautery testing with non-

stick 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-of-

concept 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.

47

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

48

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 Description/Notes

Kerwin Electrosurgical Generator 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.

Power Supply 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 soaked in saltwater 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.

Plastic Mat 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.

49

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.

Proof-of-Concept Prototype 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.

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.

50

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

pork will be

burned together in

the process of

cautery upon

pressing of the

foot pedal.

Cautery should

only take 1

second.

The two pieces of pork should come

together as one entity to pass

successful cautery.

51

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 proof-

of-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.

52

slid off them. demonstrate non-

stick condition.

15 Turn off the

Kerwin

Generator,

disconnect all

devices and clean

up.

The Kerwin

Generator is

turned off, and all

items are gathered

and cleaned up

from the work

space.

The generator has been turned off

and everything that was used for the

test has been put away to pass.

53

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]

54

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

55

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

56

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

57

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.

58

Analysis

Appendix Page 1

59

Appendix Page 2

60

Appendix Page 3

61

Component Manufacturability Table

COMPONENT MANUFACTURABILITY TABLE

COMPONENT PROOF OF MANUFACTURABILITY

.0282 mm diameter copper wires coated

with Teflon PTFE to .0381 mm total

diameter

California Fine Wire Company manufactures and

coats wires to this specification (see chart from

calfinewire.com on page 6 of appendix)

2 mm OD, 1.7 ID stainless steel 304 shaft 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 Grasping surfaces of correct size are commonly

manufactured as on our mechanical benchmark

forceps from Metronic.

Teflon PTFE Coating for Grasping

Surfaces

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)

Gear with pitch diameter of 1.5 mm and

mating racks for the handle mechanism

Still in the process of contacting gear manufacturers

to perform this task.

Appendix Page 4

62

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 mA

Maximum current flow will be tested per TP[1]. Results will be

compared with those forecasted by analytical models. 5

2

Max. opening/closing force

allowed by mechanical stop

(Safety Concern) 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

3

Min force applied by the

grasping surfaces 2 N

The forceps must apply 2 N in order manipulate tissue. The

force will be tested per TP[3]. 5

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 2°C

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

11 Bipolar forceps user manual 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.

Appendix Page 5

63

Insulation Specifications

Appendix Page 6

64

Project Budget and Expenses to date

Item Vendor Cost Purchased by

Prototyping supplies (pvc,

wire, wood, insulation) Home Depot ~$40 Matt

Total Fall ~$40

Test Sample Cow Brain Santa Cruz Market $36 John

Pork IV market $8 Various

Pork + Salt IV market $11.71 Armin

Wires Silver Wire McMaster Carr $30 Jeff

Copper Wire McMaster Carr $10 Stephen

Benchmark Forceps + Connector cable ebay ~$45 Matt

Raw Material PTFE Film McMaster Carr ~$40 John

Shop material UCSB ME Shop $7.50 Stephen/Armin

Printing Cost Final Report Alternative Copy $20 Matt

Total Winter $208.21

Budget

Fall Quarter

Winter Quarter