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An Opening in the Abdomen
An Opening in the Market:
Hernia Tensiometer
GROUP 2:Martha IngramMegan
JohnstonChelsea Samson
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What Is a Hernia?
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Laparoscopic
Open
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•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
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Timeline - Done
• Met with advisors• Researched
hernia surgery and device requirements• Innovation
Workbench• Literature
research on current technologies
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Timeline - Current
• Finalize materials list• Determine force sensor
type and design circuit• Finalize mechanical system
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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
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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
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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
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Modified Mechanics
• Flexiforce measures compression• Convert
tensile force to compression force• System pulls
against itself
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Force Sensors• Strain Gage–Interlocking links–Strain gage mounted to a small piece of metal–Defected when tension applied to links–Requires Wheatstone circuit
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Circuit Design• Design
proposed by Flexiforce –Converts change in resistance to change in voltage
• Voltage will be converted to Force
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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
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Current Issues
Federal Constraints--having minimal
contact points with the body allows for easier acceptance through IRB
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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
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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
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System
environment
environment
Hernia-Tensiometer Interface
The system (tensiometer) needs to be self-contained, having minimal points of contact with the environment (patient)
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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
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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