An Opening in the Abdomen An Opening in the Market: Hernia Tensiometer

1. An Opening in the Abdomen An Opening in the Market: Hernia Tensiometer GROUP 2: Martha Ingram Megan Johnston Chelsea Samson

2. What Is a Hernia?

3. Laparoscopic Open

6. Device Must: • Measure tension resisting closure at the suture line after: • - dissection of the injury area • - separating fascia from muscle • placing the mesh • Isolate abdominal tissue • Bring edges together • Read tension at center of hernia

9. Timeline - Done • Met with advisors • Researched hernia surgery and device requirements • Innovation Workbench • Literature research on current technologies

10. Timeline - Current • Finalize materials list • Determine force sensor type and design circuit • Finalize mechanical system

11. Timeline – Future • Order materials – Next week • First prototype made with acrylic • Test on porcine model – 4th week of Feb • Modify design – early March • Rebuild with surgical steel • Test new design – Late March • Report and Poster – April

12. Force Sensors • Flexible Stretch Sensor • Changes resistance when stretched • Both ends must be wired • Requires 30-40 cords for our estimated load • All cords must be insulated

13. Force Sensors • Flexiforce • 0-25lb (0-100N) • Conductance (1/R) linear with load • Both terminal at one end • Requires compression force • We have Starter Kit

14. Modified Mechanics • Flexiforce measures compression • Convert tensile force to compression force • System pulls against itself

15. Force Sensors • Strain Gage • Interlocking links • Strain gage mounted to a small piece of metal • Defected when tension applied to links • Requires Wheatstone circuit

16. Circuit Design • Design proposed by Flexiforce • Converts change in resistance to change in voltage • Voltage will be converted to Force

17. Calibration • Initial calibration • Known weights applied • Measure voltage output • Create calibration curve to convert to force • Simple in Labview, more difficult in self-contained circuit • Tare • Zero out capacitor to indicate zero force • Normal testing • Provide surgeons with weights to test every 5-10 uses to confirm accurate results

18. Current Issues Federal Constraints --having minimal contact points with the body allows for easier acceptance through IRB

19. Current Issues Physical Limitations ---with an 18cm hernia diameter, the device has to be small (~9cm, or 3.5 inches, long & 2-3 cm high) --small volume for both a movable arm and required circuitry

20. Current Issues Mechanical Difficulties -- Need for a small internal power supply --Device for keeping tissue stationary: handles get in the way --How do we hold the moving arm in desired position while taking desired tension reading? --Lesser experience/courses in utilizing magnets or advanced techniques in electronics adds some limitations to feasible solutions for our time period.

21. Hernia-Tensiometer Interface environment environment The system (tensiometer) needs to be self-contained, having minimal points of contact with the environment (patient) System

22. Potential Solutions Federal Considerations • Design the system so that the clamping arm may also support the console above the patient (not on the patient) • Use stainless steel and other surgical materials that can be sterilized Experience/Time Limitations • Seek advice from Mechanical Engineering & Electrical Engineering departments on creative internal power supply sources that are currently available Physical & Mechanical Limitations • Perhaps use test-tube holders or similar alternative holding devices in place of surgical clamps • Position circuit near top of the console, and arrange force sensors near the moving arms at the base of the console

23. References • http://multianvil.asu.edu/ASU%20Multianvil%20Page/TheCube.html • http://zone.ni.com/devzone/cda/tut/p/id/6534 • http://www.tekscan.com/flexible-force-sensors • http://www.imagesco.com/sensors/stretch-sensor.html