Surgical Robot: Endoscopic Retractor/Stabilizer

Team Members:

Jose Pizano, David Pearson, Jonathan Keeble, Sergio Lares, Chuc Nguyen,

and special support from Mike Dragulin

Date of Report: 3-17-2003

Revised 6-8-2003

Industrial Advisor: Dr. Mike Savitt M.D.

St. Vincent’s Hospital

Progress Report For ME492

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Contents:

Executive Summary: 2

Introduction: 2

Design Brief: 3

Latest Project Planning Document: 3

Final Product Design Specification Summary: 4

External Search Summary: 6

Internal Search Summary: 8

Final Design Selection Summary: 9

Progress on Detailed design 11

Conclusion and recommendations: 14

Appendix: 14

Project Proposal

Product Design Specifications

External Search

Internal Search

Concept Evaluation Document

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Executive Summary:

The purpose of this project is to develop a combination retractor stabilizer capable of

being inserted endoscopically into a patient’s chest to assist in robotic heart surgery. This device

would help reduce the time spent in surgery by allowing the surgeon to quickly retract the heart

and stabilize portions of interest. A single design has been chosen and partially developed. The

final goal of this project is to construct a working prototype that can be tested on a live pig.

Future plans include a production level design and a new automated design.

Introduction:

The Da Vinci robot is a system that allows surgeons to perform traditionally invasive

surgeries with minimally invasive techniques. The robot’s appendages are inserted into a patient

through small holes ranging from 6 to 15mm. The surgeon controls the robot from a nearby

console that offers stereoscopic views of the inside of the patient and tactile feed back from the

robot’s appendages. The Da Vinci Robot allows surgeons to perform complicated surgeries

while minimizing damage to the patients. This endoscopic approach minimizes the length of

hospital stays and reduces patient recovery time. At St. Vincent’s hospital, the Da Vinci robot is

used to perform valve replacement surgery and coronary bypass surgery on patents with heart

disease. The average hospital stay for these patients is reduced from 10 to 3 days when the robot

is used in place of typical open-heart surgery.

One drawback to the robotic surgery is that it usually takes twice as long as conventional

surgery, which increases the risks associated with anesthesia and costs more because it requires

more time in the operating room. Reducing operating room time helps improve the odds of

patient survival and reduce hospital costs.

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Design Brief:

The purpose of this project is to design and build a retractor/ stabilizer capable of being

used endoscopically to assist the Da Vinci robot with heart surgery. A retractor allows the heart

to be moved or rotated and a stabilizer immobilizes a portion of the heart. There are endoscopic

stabilizers available for this operation, but these require the surgeon to use the robotic grippers to

bring the heart to the stabilizer. A combination of a retractor and stabilizer would save time by

performing multiple functions and help reduce the risks associated with lengthy procedures.

Latest Project Planning Document:

In the Winter term of 2003, our team developed several preliminary designs based on the

design criteria laid out by Dr. Savitt. One of these designs was selected after a long elimination

process. The chosen design has been further developed with computer modeling and FEA

analysis.

The plans for the Spring 2003 term include final development of the chosen design using

computer aided stress analysis. A prototype will be built and tested for range of motion,

strength, and ease of use in a mock-operating room situation. If the prototype appears to work

well, it may be tested on a live pig to further prove its effectiveness.

Future plans for the device will include full scale production and distribution to help aid

in cardiac surgery. This design may also be electronically automated to allow it to be integrated

into a robotic surgery system.

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Final Product Design Specification Summary

Customers:

When a production version of the device is made, other surgeons along with hospitals, nurses

and technicians will become the customers.

Product Design Specifications:

Space constraints:

The device will need to be capable of being deployed through a guide tube which is to be

inserted in a patient’s chest. The guide tubes available have an inner diameter of 6, 10, and

12mm.

Operation:

The retractor/stabilizer must be capable of gripping and rotating a human heart 180 to

270 in either direction about the heart’s connecting vessels. Once rotated the heart’s surface

must be held in place with a rotational deflection of less than 1mm. After being rotated, the

device will need to be able to immobilize a small area of the heart ranging between 1 to 3cm2 and

resist any deflections of more than one millimeter in any direction.

User Interface:

Our prototype is being designed to function as a stand-alone device, capable of being

used in conjunction with the Da Vinci robotic surgery system. It should be able to be used by

one person in the operating room with independent control of motion, tightening, and suction of

each component of the device.

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Maintenance:

If the design is to be a multiple use item, all components will need to be replaceable and

easily cleaned. A multiple use item is intended to last for 500 surgeries, however any wear on

the tool should be visually evident to help reduce the risk of bringing a worn instrument into the

operating room.

Materials:

The device should be easy to sterilize. Rigid components should be able to survive in a

steam autoclave with no damage or corrosion, flexible components should be able to be gas

sterilized or be disposable. All materials will need to be certified by the FDA for use in surgery.

Cost:

A disposable single use device should cost between $100 and $300. A device designed

for repeated use may cost between $3000 and $5000 for manufacture.

Design Engineering Specifications:

Item Metric Importance(10 high, 1

low)Grip force / resistance to movement Force will vary, deflection must always be less than 1mm in all

directions.10

Rotational range of each set of appendages

180 to 270 degrees in both directions 10

Movement of stabilizing/retracting appendages

Must conform to the surface of an adult heart and be independently controllable and deployable.

10

Width of guide tube Can be 6, 10 or 12mm wide, circular profile 8User Interface Must be effective, comfortable, non-obstructive to robot movement 9Sterilization Able to be sterilized, allows for required strengths 10Maintenance Ease of cleaning, replaceable components 6Cost $100 to $300 disposable option or $3000 to $5000 long term use

option2

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External Search Summary:

The purpose of the surgical robot project is to combine a cardiac retractor and stabilizer

into one device. Currently there is no product on the market that combines a stabilizer and

retractor into a single device. There are many devices on the market that aid in open heart

surgery but only few that aid the Da Vinci surgical robot. When the surgical robot is used to

perform heart surgery the recovery time is cut from about ten to three days. The types of devices

most commonly used for open heart surgery are a retractor and stabilizer, see figure 1 below.

However, the retractors and stabilizers are disposable and expensive.

Fig 1: Picture of a stabilizer and retractor.

Search on Materials

As a general rule all the materials that are used in heart surgery need to be biocompatible.

The same rule is applied to this project, for example; the considered materials must be easy to

sterilize, clean, and be biocompatible. Some of the considered materials for the project (i.e.

senior project) are stainless steel (303 & 304), Stylistic™, PVC (plastic), and titanium. All of

the mentioned materials have one thing in common; they are biocompatible and are used in the

medical field.

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A newer type of technology that is used in heart surgery is the Symmetry™. This device

is simple yet claimed to be effective. The Symmetry™ uses three other tools: 1) aortic, 2)

delivery system, and the 3) aortic connector. This device has the appearance of a screwdriver, see

figure 2.

Fig 2: Picture of the Delivery System

Open heart surgery in looking to be a thing of the past. Today there are several different types of

robots including: Da Vinci™, ZEUS™ Surgical System, and the AESOP™ Robotic System. Even

though these robots exist, they are still in their infancy. Also many of these robots are difficult to

use and using them is more expensive than open-heart surgery.

Although surgical robots are relatively new, they have many obvious advantages, they are

great deal more precise and do not tremble. The incisions made will continue to get smaller and

open heat surgery will be less common. Many new exciting materials are introduced every year

such as memory alloys and Silastic™, and surgical tools are getting smaller. The materials and

technology discussed in the external search were considered while coming up with ideas for

prototype designs related to our project. We looked at proven designs of retractors and

stabilizers to help determine whether our designs would work. The materials that will be used in

our final prototype will need to have the qualities discussed in this search document.

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Internal Search Summary:

The group generated several concepts for designs that could fulfill the design

specifications. The two designs considered to have the most potential are listed below.

The first idea, called the Duck Foot, consists of a single suction cup retractor and an

articulated stabilizer. The Suction cup would unfold after passing through the guide tube and

encompass the apex of the heart. Once it was in position, suction would be applied and the

device would grip. Steel ribbon reinforcement within the suctioning device would ensure that it

would not simply tear apart once the device turns to rotate the heart.

In order for this design to stabilize the heart, a separate stabilizer is used. This stabilizer is

similar to the Octopus™ device sold by MedTronics, redesigned to fold into a compact package

for deployment through a tube. Two suction cupped arms roughly two inches in length attached

together by a hinge similar to that in the center of a pair of scissors. The main control rod for

gross movement of the stabilizer attaches to this central hinge. Initially, the arms fold together

into a narrow package that fit down the tube. Once they were over their final position, tensor

wires attached to the rear of each arm pull backwards, unfolding the arms into a shape similar to

the Octopus™. Suction applied through the arms would stop that area of the heart from moving

with the heartbeat.

The second design of importance is the Undertaker. The Undertaker is a radially

symmetric mechanical gripper. The design features three fingers individually positionable with

the controls. Once a finger is in the proper position, the control can lock the finger into place. A

simple vacuum powered suction cup at the base of the end effector holds the heart in a required

location.

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The fingers have two degrees of freedom. The fingers rotate about the base, and bend at a

swivel joint halfway along the finger. The rotation is powered through simple manual rotation of

the control, while the bending action is motivated by a combination of tensors wire connecting

the joints to the controls, along with torsion springs working to extend the joints.

The Penetrada is a similar design to the Undertaker that used a wire lasso for gripping

strength. The Chalupa used a net to enfold and grip the heart. The ET hand was an asymmetrical

three fingered gripper with suction cups at the tips of the fingers. All three of these are detailed

in the Internal Search.

Final Design Selection Summary:

The final design for the prototype was decided upon using several criteria. The most important criteria were

functionality, ease of deployment, and simplicity(see table E1 for a description of the selection criteria). The full

selection process is outlined in the Final Selection Appendix.

PDS Criteria Metric Importance(5 high, 1 low)

Functionality The ability of the equipment to operate as expected during actual surgery conditions in the hospital without breaking

5

Ease of Deployment It has to deploy within 3 to 4 inches(end tube from the bottom heart apex)

5

Simplicity It has to be as simple as possible, because of space constrains

5

Reliability Lasts 500 surgeries 4Maintenance Ease of cleaning, replaceable components 4Life Span 3-5 years 4.5Cost $100 to $300 disposable option or $3000 to $5000

long term use option1

Table E1: Description of design selection criteria.

Of the several designs considered, a few were quickly eliminated. The E.T. Hand was too

complex, and an effective prototype wouldn’t be able to fit within the space constraints. The

Chalupa was incapable of deploying properly.

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The other three designs received more discussion and consideration. The Penetrada was

eventually eliminated because the design was too complex, and it would not deploy reliably. The

Duck Foot was a workable design, but the appendages were too similar to existing patented

designs.

The concept selected for the final design was the Undertaker. The design is completely

mechanical, so the group is fully aware of its capabilities and hindrances. Its individually

positionable prongs allow it to deploy in a variety of positions and deliver force where it is

needed.

Table E2 shows a concept screening matrix used to help eliminate poor designs based on

the opinions of the group members. Our industry contact Dr. Savitt also helped us to select the

best designs based on drawings and prototypes we had built.

Concept screening1-5 (5 being the highest score)

PDS Criteria Datum E.T Hand

Duck Foot

Penetrada Undertaker Chalupa Suctioner

Functionality 0 2.5 4.5 3.75 3.5 3.0 4.0

Ease of Use/deployment

0 3.5 3.66 3.25 3.5 3.0 2.0

Cost 0 3.0 3.84 3.25 3.84 3.5 3.0

Reliability 0 3.5 3.5 3.25 3.5 3.0 2.0

Complexity 0 2.5 4 3.84 4.5 3.5 2.5

Life Span 0 3 3.20 3.5 3.33 3.0 3.0

Maintenance 0 3 3.5 3.5 3.84 3.0 3.5

Total 0 21.0 26.2 24.34 26.0 22.0 20.0

Table E2: Concept design matrix.

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Progress on Detailed design

Out of the many prototypes and conceptual ideas that were developed during the spring

and fall term only the top contenders were chosen as the final selection in the development of the

final senior project. The top two contending conceptual ideas for the final selection are as

follows: Duct foot and the Undertaker(Fig 3). However, the undertaker was chosen as the

primary prototype since it better fulfilled the PDS requirements.

Fig 3: Schematic representation of the Undertaker

The materials that are to be used with the undertaker are still yet to be determined,

however, some of the materials being considered are stainless steel (303 or 304), and titanium.

Reasons for choosing the mentioned materials are described in more detail in the materials

selection.

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As part of the final selection and materials a 3-D model and FEA (Finite Element

Analysis) was conducted, see figures 5 and 6. With the aid of CAD(computer aid design) it

becomes more efficient to make any dimensional and modification changes. Using CAD and

FEA analysis not only reduces cost and time but it also speeds up the development of the actual

prototype.

The 3-D model as seen in fig. 4 is an assembly of one of the prongs of the Undertaker,

see fig. A. The material used in construction of the FEA analysis was stainless steel (303) and

titanium so that we can determine the amount of deflection under certain loading conditions.

Fig. 4: Prong assembly of the Undertaker

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FEA Analysis of Steel/ Titanium under a 2Lbs force:

Fig 5: FEA analysis of steel (303) to determine the deflection under a certain load

Fig 6: FEA analysis of titanium to determine the deflection under a certain load

Using FEA software allows the team to get an idea on how a material will behave under certain

load and from there we can then determine the areas of interest.

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Material Considerations

Some of the materials that have been considered for the actual prototype are stainless

steel (303 and 304), Sylastic™, and titanium. All the mentioned materials are to be to resist to

corrosion and easy to sterilize. A breakdown how these materials could be used is as follows:

Swivel Joints : Stainless steel 304 balls are good resistance to corrosion

Tubing: Stainless steel 303 because it offers good strength, corrosion resistance and great

mach inability.

Sylastic™: For the suction cups

Titanium : The body readily accepts titanium since it is more biocompatible than stainless

steel and the machinability of titanium is comparable to most stainless steels.

PVC(plastic): Prototype

The materials mentioned above each has its individual purpose, for example, the PVC

will be used in aid of constructing a working prototype since machining it is much easier and

faster as opposed to stainless steel or titanium.

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Conclusion and recommendations:

The winter term of 2003 was spent developing original solutions to the requirements

outlined in the PDS. One best solution, the undertaker was chosen to be developed into a final

design. The design work completed in this term included computer modeling and FEA analysis

of the stabilizing appendages.

Next term should be spent finishing the design of the undertaker and constructing a

working prototype. This prototype will be tested in a mock-surgery with the Da Vinci surgical

system. It may also be tested on a live pig to further prove its worth.

Our recommendations are to further develop the design into an integrated part of a

robotic surgery system.

Appendix:

See attached papers/

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