1
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
2
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
3
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
4
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
5
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.
6
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
7
(
)
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.
8
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
9
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
10
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
11
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
12
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
13
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
14
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.
15
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
16
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
17
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