Design of an Atraumatic Laparoscopic Grasper

Christine Emery May 6, 2016

Advisor: Prof. Carr Everbach

Abstract: In this E90, I propose a novellaparoscopic grasper design that is intended to reduce the risk of inadvertent tissue damage during surgery. The small, V-shaped jaws of traditionallaparoscopic graspers apply high and uneven pressures to tissue and cause slippage when grasping, inducing tissue perforation and cell death. Potential adverse effects of grasper usage include bleeding, scar tissue, adhesion, and fistula formation. My design utilizes parallel, rather than V-shaped, jaws to maximize contact area and prevent slippage between the jaws and tissue. I have developed a working grasper prototype using aluminum and 3D-printed parts. While this prototype is effective in achieving the parallel jaw motion and manipulating tissue, design changes must be made to determine the design's efficacy in minimizing tissue damage.

Table of Contents

1. Introduction ........................................................................................................................................ 3

2. Background .......................................................................................................................................... 3

3. Theory .................................................................................................................................................... 5

4. Design ..................................................................................................................................................... 5

4.1. Brainstorming designs ........................................................................................................... 5

4.2. Parallel Grasper Design .......................................................................................................... 6

5. Prototype .............................................................................................................................................. 8

6. Results ................................................................................................................................................ 10

7. Discussion ......................................................................................................................................... 10

8. Conclusion ......................................................................................................................................... 12

9. References ......................................................................................................................................... 13

10. Appendices ........................................................................................................................................ 14

10.1. Appendix A: Design drawings ........................................................................................ 14

10.2. Appendix B: Mechanical Testing .................................................................................. 16

1. Introduction

While surgery can be a life-saving act, many procedures result in unfavorable

adverse effects. One contributing factor to these adverse effects is the inadequacy of

certain surgical tools. A surgeon's instruments may be effective in performing the

general task, but may be ineffective in performing tasks safely. I have explored this

idea through the laparoscopic grasper, a tool used to hold and manipulate tissue in

laparoscopic procedures. In this project, I propose a new grasper design that can

potentially minimize the risk of inadvertent tissue damage.

2. Background

Laparoscopy is a minimally invasive surgical technique performed for

abdominal or pelvic procedures. In laparoscopic surgery, a surgeon inflates a

patient's abdomen with carbon dioxide, makes three to four small incisions along

the abdomen, and uses special tools and the aid of a camera to perform the

procedure (Figure 1). Compared to open procedures, laparoscopy significantly

reduces patient pain and recovery time by eliminating the large incisions. Common

laparoscopic procedures include hernia repairs, gastric bypass, bowel resection, and

organ removal.

With open surgery, tactile feedback allows surgeons to control the force they

apply to tissue. The surgeon's hand can easily manipulate the tissue by grasping,

stretching, and palpating the tissue. Open surgery also allows for optimal hand-eye

coordination. With laparoscopic surgery, however, surgeons are deprived of direct

view and contact with the operating field. Tissue is manipulated with grasping

instruments, rather than a hand, resulting in limited movement possibilities and

decreased sensation. A surgeon must "feel" the forces applied to the tissue through

the instrument handles, which provide an inaccurate representation of the true

force applied to tissue (Sjoerdsma eta!., 1997). Due to the limited viewing field and

significantly reduced tactile feedback, surgeons must put more trust in their

instruments to perform correctly.

Many laparoscopic procedures require the usage of laparoscopic graspers to

hold and manipulate tissues within the abdominal or pelvic cavities. A typical

laparoscopic grasper is Smm or 10mm in diameter and ~35cm long. The jaws of the

grasper are typically lined with sharp ridges to provide grip on the tissue. While

this design is intended to help maneuver tissue delicately, the small grasper jaws

generate high local pressures on the tissue, resulting in potential damage and

perforation (E. aM. Heijnsdijk, Dankelman, & Gouma, 2002). By interrupting the

blood supply and crushing intracellular structures, graspers can have the following

serious effects on tissue: pathological scar tissue formation, bleeding, adhesion,

fistula formation, and tissue apoptosis and necrosis, which are two forms of cellular

death (De et al., 2007). Each of these side effects may require patients to undergo

unnecessary pain and, in some cases, additional surgeries.

The design of a safer laparoscopic grasper is a critical step in improving the

safety and efficacy of laparoscopic procedures. In this E90 project, I have designed a

laparoscopic grasper that may reduce the risk of inadvertent tissue damage. This

project involved designing and modeling a grasper on SolidWorks, developing a

prototype through aluminum and 3D-printed parts, and performing grasping

experiments to determine the efficacy of the design.

Figure 1. Surgical setup for laparoscopic procedures.

3. Theory

During dissection, surgeons exert pinch and pull forces on the tissue through

the graspers. When the pull force is higher than the pinch force, tissue may slip out

of the graspers, and the ridged jaws may perforate the tissue. When both pull and

pinch forces are high, tissue damage is likely to occur (E. A.M. Heijnsdijk, de Visser,

Dankelman, & Gouma, 2004). Based on a theoretical model of grasper manipulation

by Heijnsdijk et al. (2004), a working range for the grasper can be determined by

identifying the forces at which neither slip or damage occur (Figure 2). A wider

working range ensures safer graspers. My goal was to achieve a wide working range

with my grasper design.

pinch i Ioree (N)

pu• IO<ce (N)

Figure 2. Theoretical model of the pull and pinch forces affecting the working range of the grasper (E. A.M. Heijnsdijk et al., 2004).

4. Design

4.1. Brainstorming designs

Before redesigning the grasper, I considered the problems that exist with the

traditional grasper design. The most severe issue with the grasper is that surgeons

cannot feel the forces they apply to tissue, resulting in potential serious tissue

damage. I considered four approaches to solve this problem.

The first approach is to develop a grasper with a force transducer that

digitally outputs the jaw forces in real time. The surgeon could read and interpret

the digital outputs during surgery to better sense how much force to apply to the

tissue. This approach may be limiting because the stress tolerances are not known

for all tissues, and surgeons would be required to guess what appropriate force

levels would be. Surgeons may also have difficulty discerning the differences

between tissues when viewing the internal cavity through a camera projection.

The second approach is to design a system in which the grasper handle

provides improved tactile feedback to the surgeon. This system could be either a

mechanical or electrical one, and would allow the surgeon to better feel how much

force is applied to the tissue.

A third approach is to design a grasper with suction elements to grab the

tissue. The intention with suction power is to apply less force to the tissue, since the

tissue would not be compressed. However, no data yet exists on the effects of

suction on internal tissue.

The fourth approach is to redesign the grasper jaws so that they minimize

tissue damage, despite the surgeon's inability to feel the tissue through the grasper

handles. This approach would need to ensure that a new jaw design had less risk of

slip and damage to the tissue. I chose to pursue this approach for the E90 project.

4.2. Parallel Grasper Design

Before beginning the design process, I outlined four functional requirements

that my design must meet to determine its success. The grasper prototype must:

1. Grab and move tissue easily without visible tissue damage

2. Minimize excessive tissue compression

3. Minimize excessive slippage

4. Match the dimensions of graspers currently on the marketplace

I began the design process by identifying the weaknesses in the current jaw

designs. While the jaw shapes and sizes vary drastically for different types of

graspers, the jaws are consistently small and apply high, localized pressures to the

tissue. The jaw teeth, too, vary drastically between graspers, but are typically sharp

enough to cause tissue perforation. The V-shape of the grasper also prevents an

even distribution of pressure to be applied to the tissue (Figure 3). Tissue situated

in the deep part of the "V" experiences much higher levels of force, and in some

cases, can get caught in the grasper. Additionally, the V-shaped jaws tend to push

tissue out of the jaws as they close, requiring repeated grasping attempts and

providing a higher risk of tissue damage.

I propose an alternate grasper design that incorporates jaws that open and

close in a parallel manner (Figure 4). With parallel jaws, pressure will be applied

evenly to the tissue, regardless of the tissue size. The parallel configuration also

ensures a wide opening between the jaws across their whole length. There is no

possibility for tissue to get caught between the jaws, and there is a reduced risk of

tissue pushing out of the grasp as the jaws close.

In addition to the parallel jaw configuration, this grasper design incorporates

wider jaws and duller teeth to prevent tissue damage and perforation. As

discovered by Heijnsdijk et al. (2004), the least tissue damage occurs when the

grasper jaws have a large contact area and a slight teeth profile. Therefore, with an

increased jaw width and rounder teeth, this grasper would maintain its ability to

prevent slip and damage while achieving successful manipulation of the tissue.

With these design elements in mind, I drafted a 3D model of my grasper

design on SolidWorks. The specific design I implemented is based on a similar

project from a Mechanical Engineering laboratory at MIT (Teo et al., 2011). The

jaws are separated by a four-bar linkage, which is attached to a rod that connects to

the grasper handles. The four-bar linkage ensures that the jaws open and close in a

parallel manner.

Figure 3. Standard V-shaped jaws of a laparoscopic grasper.

Figure 4. Solidworks model of the parallel grasper design.

5. Prototype

I developed a prototype of the parallel grasper design using aluminum and

3D-printed parts (Figures S-6). While surgical tools must be constructed from

surgical-grade stainless steel for safety and sterilization procedures, my design is

purely a prototype that is not intended for animal use. Aluminum is therefore an

acceptable material for this prototype. The dimensions for this prototype can be

found in the Appendix A of this report.

The grasper is powered by a gear system located within the handle (Figure

7). By moving the lower handle back and forth, the gears are set into motion and the

grasper jaws open and close. The jaws are connected to a rod that slides through

the grasper shaft. This rod is connected to a rack that interfaces with the gear

system. The rack must move 12mm to bring the jaws from the fully closed to fully

open position. Knowing this, I designed a gear system such that the lower handle

moves twice the distance of the rack to actuate the gears, which provides the user

with better control over the jaw movement. To achieve this 1:2 ratio between the

rack and the handle, I connected the rack to a 12-tooth spur gear with a 24 pitch

diameter, and connected that gear to a 24-tooth spur gear of the same pitch. This

larger gear connected to another rack that attached to the lower handle.

Figure 5. Parallel grasper prototype.

---__ .

Figure 6. Parallel jaws in the fully open (top) and fully closed (bottom) positions.

Figure 7. Gear system located within grasper handle.

6. Results

To determine the efficacy of this design, I performed a simple grasping

experiment on synthetic tissue samples of different thicknesses. In the experiment,

I grasped the tissue between the jaws, moved the tissue around, and pulled back on

the grasper to determine whether slippage would occur. The grasper was effective

in gripping and moving both tissue samples (Figure 8). However, the grasper was

ineffective in maintaining its grip as the grasper was pulled away from the tissue.

Each time this step was performed, the jaws immediately slipped off the tissue.

Despite the slippage, no macroscopically visible tissue damage occurred in either

sample.

Figure 8. Grasping experiment with thin (left) and thick (right) tissue samples.

7. Discussion

The parallel grasper prototype met two out of the four functional

requirements set at the beginning of this project. The grasper could grab and move

tissue without visible tissue damage and met the dimensions of a traditional

grasper. However, due to the slippage when the pull force was applied, the

prototype could not be tested for its efficacy in minimizing tissue compression and

slippage. Ideally, a mechanical testing procedure would be necessary to determine

the working range of the grasper; a sample mechanical testing procedure is outlined

in Appendix B. Several changes must be made to the prototype before it is ready for

mechanical testing.

The biggest area for improvement lies within the grasper's ability to

maintain its grip as pull force is applied. This task could be achieved either by

increasing the friction between the jaws and tissue or increasing the pinch force of

the grasper. An increase of the frictional force could involve changing the shape,

size, and number of teeth on the grasper jaws. The teeth also may need to be

slightly sharper to achieve a better grip. Additionally, a silicone coating may be

added to the jaw surface to add another frictional element to the system. In addition

to providing a tacky surface, the silicone would minimize tissue perforation should

the grasper slip off the tissue.

An increase in the pinch force could be achieved by altering the geometry of

the system. The four-bar linkage connecting the two jaws allows the highest levels

of force to be applied when the grasper is at its fully open position. When the

linkages approach their parallel position, they provide less pull on the jaws, and the

jaws cannot apply as strong of a pinch force to the tissue. To maximize the pinch

force, the grasper may need to be redesigned such that the four-bar linkage does not

approach a parallel position as the jaws become parallel.

Another opportunity for improvement regards the handle and gear system.

The rack and spur gears contain very course, plastic teeth. The gears and racks do

not mesh very fluidly and tend to "wiggle" in their place. One can move the grasper

handle -lmm without any actuation of the gear system. The slack in this should not

exist in a surgical tool that requires such precise movements. By replacing the gear

system with finer gears and racks, the user would have better control over the

grasper.

The prototype material may also need to be changed to improve the grasper

efficacy. The grasper may behave differently if the jaws and shaft were constructed

from surgical steel, rather than aluminum. Similarly, the grasper handle would need

to be constructed from a sturdier plastic for a hospital-grade device. The

ergonomics of the handle would also need to be improved for ease of use.

8. Conclusion

While this prototype could not be evaluated for its efficacy in minimizing

tissue damage, the prototype demonstrates that a parallel grasper design is

achievable and, with a few changes, could potentially improve a surgeon's ability to

safely manipulate tissue during surgery. This idea of creating a safer laparoscopic

grasper can be extended to numerous other surgical tools. With improvements to

surgical technology, surgery can hopefully become an easier and safer process for

both patients and surgeons.

9. References

De, S., Rosen,)., Dagan, a., Hannaford, B., Swanson, P., & Sinanan, M. (2007).

Assessment of Tissue Damage due to Mechanical Stresses. The International

journal of Robotics Research, 26(11-12), 1159-1171.

http:/ jdoi.org/10.1177 /0278364907082847

Heijnsdijk, E. aM., Dankelman, )., & Gouma, D.). (2002). Effectiveness of grasping

and duration of clamping using laparoscopic graspers. Surgical Endoscopy,

16(9), 1329-31. http:/ jdoi.org/10.1007 js00464-001-9179-2

Heijnsdijk, E. A M., de Visser, H., Dankelman, )., & Gouma, D. ). (2 004). Slip and

damage properties of jaws oflaparoscopic graspers. Surgical Endoscopy And

Other Interventional Techniques, 18(6), 974-979.

http:/ jdoi.org/10.1007 js00464-003-9153-2

Sjoerdsma, W., Herder,). L., Harward, M. )., jansen, a., Bannenberg, ). ). G., &

Grim bergen, C. a. (1997). Force transmission oflaparoscopic grasping

instruments. Minimally Invasive Therapy &Allied Technologies, 6(4), 274-278.

http:/ jdoi.org/10.3109 /13645709709153075

Teo, G. S. L., Flander, M.S., Sepp, T. R., Corral, M., Diaz, ). D., Slocum, A., & Vakili, K.

(2011). Design and Testing of A Pressure Sensing Laparoscopic Grasper. In

Design of Medical Devices Conference (pp.1-8).

10. Appendices

10.1. Appendix A: Design drawings

Note: all dimensions are measured in millimeters.

B

A

2

(~------j-+-:,,+-~---'-1-:~!j-----'--1 -----13 f-

\I

2

DIMENSIONSARE IN INCfiES TOLERANCES fRACnONAL! ANGULAR: MACH! BEND ! T'WO PLACE DECIMAL !

THREE PlACE DECIMAl !

B

0.83

TITLE: A

SIZE DWG. NO REV

A Jaw_l-26 SCALE: 2: 1 WEIGHT SHEET 1 OF 1

B

A

B

A

2 13.68

i;?i0.50

F0.50

~--------------------------- 40 -------------------------------1

39---------lf

0.50

2

2

DIMENSIONS ARE IN INCHES TOLERANCES

ANGULAR: MA.CHt BEND! l'NQPLACE DEC!MAl !

THREEPLACE DECIMAl !

TITLE:

SIZE DWG. NO. REV

Ainks_updated SCALE: 5:1 WEIGHT:

1

1

SHEET 1 OF 1

0 19.98 *s= ,~-------,;: 11!=='1 == ~ ~ -il.9~

14.98 I ' ~¢,,

PIOPIIn.UYANDCONFIDfNTIAL

THE INfOR,..AT!Oi'l CONIAINEO IN THIS DRAWINGISIHESOU:I'ROPERTYOf ~INSERTCO"'J>ANYNAMEHERE>. At{'( REP~OOUCTION IN PART Oil AS A WHOLE Wfi'HOUllHEWRiiTENI'ERMISSIONOF <lNSEii'TCOMI'ANY NAMEHERE> IS I'IIDHIBITEO.

2

15.43 j

UNLESS OTHERWISE SPECIAEO·

DIMENSIONS ARE IN INCHES TOLE RANCES FRACOONAI.! ANGULAR: MACH ! BEND !

TWO PLACE DECIMAL ! THREE PLACE DECIMAL !

INTE~ f-9:8 GEOMETall:: Q.A.

TITLE:

SIZE DWG. NO. REV

P8ar_updated SCALE: 2:1 WEIGHT: SHEET 1 OF 1

B

A

B

A

10.2. Appendix B: Mechanical Testing

A mechanical testing experiment is necessary to determine the efficacy of this grasper in minimizing tissue damage. The general testing procedure would resemble a peel-test. Two silicone tissue phantoms would be held in the upper and lower grips of a universal testing machine, and the grasper would approximate the

two samples (Figure 9). The crossheads of the UTM would slowly move away from each other, causing the silicone samples to be in tension. The force at which the

samples slip out from the grasper jaws would be recorded. I would perform two peel-test experiments to evaluate the efficacy of the

grasper. The first experiment would involve identifying the jaw widths necessary to prevent slippage and damage. With wider jaw spacing, the grasper would have a looser hold on the tissue, allowing the specimen to be more susceptible to slippage, and subsequently tearing. With smaller jaw spacing, the grasper would have a tight hold on the tissue and could apply unnecessarily high forces. My goal is to identify the minimum jaw width needed to prevent slippage and the maximum jaw width needed to prevent damage. In this case, slippage is defined as the slipping of tissue out of the jaws within 5 seconds of the testing procedure, and damage is defined as

macroscopically visible tears or imprints in the sample. Any jaw width between the minimum and maximum widths could be considered a safe working range for the grasper. I would evaluate the safe range of jaw widths for my grasper, and compare this range to that of a commonly used grasper. The grasper with the wider range would be ultimately considered a safer grasper.

The second experiment would involve performing the peel-test to determine whether the samples slip as the force exceeds 5 N, which is considered the approximate maximum "pull force" exerted by surgeons. If the samples do not slip when the pull force exceeds 5 N, the grasper would be considered unsafe.

Figure 9. Mechanical test setup.