1. Force-Sensing Laparoscopic Grasper
Client: Charles P. Heise, MD, FAS, CRS Advisor: William H. Murphy, Ph.D
Team Leader: Adam Dahlen
Communication: Darshan Patel
BWIG: Andrew Eley
BSAC: Clara Zhang

2. Presentation Outline Problem Statement Background Design Constraints
Literature
Designs
Future Work

3. Problem Statement
The goal of this project is to design and build a prototype laparoscopic grasping tool that provides feedback, auditory or otherwise. A feedback mechanism would be activated when the force applied to a piece of tissue is great enough to damage the tissue. Secondly, the jaw mechanism should be redesigned to reduce tissue damage by eliminating pinching at the pivot point of the jaws. This type of device would be an educational tool to benefit students and instructors by maintaining a defined standard force for grasping tissue and would also ensure less damage to the patient

4. Background Must reduce force on tissue
Laproscopy: minimally invasive surgery viewed by video screen
Small incisions
Many benefits
Phasing out many open surgical procedures
Problems
Unknown force
Grasper pinching at pivot point
Causes damage to tissue
Must reduce force on tissue

5. Design Constraints
Foremost, re-design grasper to reduce pinching to a floating-point jaw mechanism
Increase awareness by providing feedback
Dimensions:
Fit to 5mm port
About 30cm long
Varying closure setting
Autoclavable

6. Pressure and Angles
(1-7) Data showing spatial distribution and magnitude of pressure exerted by a laparoscopic grasper as the angle of retraction increases.
(8)Pressure profile of the maximum pressure generated by the pincer grip of a surgeons finger and thumb.

7. Pressure and Angles

8. Jaw Pattern
Example of effect of apposing pressure on grip security. This graph shows the results for 2-mm teeth measured as peak load.
Increasing the apposing pressure increased the peak load for all types.

9. Jaw Pattern Grey=% of sample that tore.
No tearing occurred at any squeeze pressure with plane and wave pattern jaws.

10. Jaw Pattern
Effect of jaw design on grip security, measured as peak load.
Conducted independently of squeeze pressure.

11. Perforation of Human vs. Pig Bowel Tissue
No difference was found between the human and pig small bowel (10.3 ± 2.9 vs 11.0 ± 2.5 N).
The strength of the pig bowel is approximately comparable to the strength of the human bowel, and therefore, testing of graspers on pig bowel is justified.
However, due to the large interindividual variation, large safety margins should be taken into account.

12. Slip and damage properties of jaws of laparoscopic graspers
With increasing size of the jaws, the contact area with the tissue increases. With increasing contact area, the pinch force leading to tissue damage was increased from 15 to 37 N.

13. Jaw design Mechanical structure

14. Three Sensor designs Strain gage Micro chip force sensor ----design 3
Principle
Wheatstone bridge
Change in strain  change in resistance
Location
On the shaft-----design 1
On the handle-----design 2
Micro chip force sensor ----design 3

15. Design 1: Strain Gage Sensor on the Actuator
Measure the compression/ tension stress
Problems
Cylindrical shaft– no enough area to fix the strain gage
Not as sensitive as measuring bending moment

16. Design 2: Strain Gage on the Handle
Measures bending moment
Advantages over #1
Relatively larger area for fixation
Bending moment can be more precisely measured than compression or tension stress

17. Problems in Strain Gage Designs
conditioner needed  inconvenience
Sensing part cannot be made detachable
Difficult/expensive to install

18. Design 3: Sensor in handle
Measure force exerted to squeeze handle
Advantages
Parts already manufactured, just need to assemble
Detachable
Easily calibrated
Cost effective
Disadvantages
Not as accurate

19. Design Matrix Design Maintenance Sterilization Strength Cumbersomeness
Connectivity
Accuracy
Feasibility
Total
Strain Gage on the Handle 1 4 2 5 3 18
Strain Gage on the Actuator 14
Force Sensor 24

20. Future Work Build project Design details Testing and Calibration
Circuitry and Sensor
Grasping Mechanism
Design details
Dimensions
Materials
Solid Works Files
Testing and Calibration

21. References
J.A. Cartmill, A.J. Shakeshaft, W.R. Walsh, C.J Martin. High Pressures are Generated at the Tip of Laparoscopic Graspers. Aust. N.Z. J. Surg, 1999.
Damian D. Marucci, John A. Cartmill, William R. Walsh, Christopher J. Martin. Patterns of Failure at the instrument-Tissue Interface. Journal of Surgical Research, 2000.
E. A. M. Heijnsdijk, M. van der Voort, H. de Visser, J. Dankelman, D. J. Gouma. Inter- and intraindividual variabilities of perforation forces of human and pig bowel tissue. Surg Endosc, 2003.
E. A. M. Heijnsdijk, H. deVisser, J. Dankelman, D. J. Gouma. Slip and damage properties of jaws of laparoscopic graspers. Surg Endosc, 2004.