An Opening in the Abdomen

An Opening in the Market:

Hernia Tensiometer

GROUP 2:Martha IngramMegan

JohnstonChelsea Samson

What Is a Hernia?

Laparoscopic

Open

•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

Timeline - Done

• Met with advisors• Researched

hernia surgery and device requirements• Innovation

Workbench• Literature

research on current technologies

Timeline - Current

• Finalize materials list• Determine force sensor

type and design circuit• Finalize mechanical system

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

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

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

Modified Mechanics

• Flexiforce measures compression• Convert

tensile force to compression force• System pulls

against itself

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

Circuit Design• Design

proposed by Flexiforce –Converts change in resistance to change in voltage

• Voltage will be converted to Force

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

Current Issues

Federal Constraints--having minimal

contact points with the body allows for easier acceptance through IRB

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

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.

Current Issues

System

environment

environment

Hernia-Tensiometer Interface

The system (tensiometer) needs to be self-contained, having minimal points of contact with the environment (patient)

Potential SolutionsFederal 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

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