3-Point Bending Device to Measure Transmural Strains for Multilayer Soft Tissue Composite
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Transcript of 3-Point Bending Device to Measure Transmural Strains for Multilayer Soft Tissue Composite
3-Point Bending Device to Measure Transmural Strains forMultilayer Soft Tissue Composite
Jennifer OlsonSarah RivestBrian SchmidtbergSponsor: Dr. Wei Sun
Overview•Background•Purpose•Objectives•Project Parts•Constraints•Budget•Conclusion
Background• The client, Dr. Wei Sun, researches the mechanical
properties of tissues with a focus on heart valves
• He currently uses biaxial testing to determine the stress strain relationship of soft tissues
• This testing is insufficient because it assumes the material is homogenous and most tissues are heterogeneous
• Flexure testing is a more effective method of evaluating the force-deformation relationship of different layers of soft tissues.
• Flexure testing is especially critical to Dr. Sun’s research of heart valves because it has been hypothesized that repetitive flexural stresses contribute to the fatigue-induced failure of heart valves
Purpose of the Project• Design and construct a three-point bending device capable of
flexural testing of soft tissues• Capable of calculating the flexure rigidity, bending stiffness,
transmural strain, transverse shear stiffness• Capable of tracking the tissue deformation through use of a CCD
camera and tissue markers
• Principle Goals:• Measure the stress-strain response in the low-strain region by
evaluating the instantaneous effective modulus• Identify the location of the neutral axis• Provide a suitable environment for testing
• Human body temperature and pH • Will produce repeatable results
Objectives•Controlled testing environment that
mimics in vivo conditions•Force application system•Neutral Axis Determination•Determination of flexural properties
▫Flexure rigidity, bending stiffness, and transverse shear stiffness
•Measure transmural strains
Previous Work Done by Others• Products
• ADMET Universal Testing Systems, Instron, and Tinius Olsen all produce 3-point bend fixture for their tensile testing devices
• These are focused on the testing of plastics, metals, alloys, and ceramics
• Do not meet all the project specifications• Patents
• No relevant patents were found• Soft-tissue bending devices found in the Bioengineering
Lab at the University of CA in San Diego, Tissue Mechanics Lab at the University of Miami, and at the University of Pittsburgh
• This project was previously attempted by a senior design group at the University of Connecticut in 2009
Project Parts•Outer/Inner Baths
•Sliding Mechanism
•Image Acquisition and Analysis
•Temperature Regulation
•LabVIEW
• Inner bath▫Provides a
surface for repeatable testing
• Outer bath▫Circulates
temperature controlled water
• Material: Lexan▫Cheap,
Transparent, Strong
Inner Bath
Outer Bath
Combined
Sliding Mechanism•Contains
bending bar, reference bar and CCD camera on movable cart
•Cart controlled by motor system
Bar/Camera Set-up
Top View of Sliding Mechanism
Bending Bar
Reference Bar
CCD Camera
Sliding Mechanism• Motor System
▫ Moves bending bar into tissue specimen
▫ Moves CCD camera during tissue deflection such that tissue never leaves frame of reference
PC equipped with LabVIEW and motion controller
Stepper drive
SH68-SH68 Cable
Stepper Motor
Linear Actuator
Sliding Mechanism
LabVIEW Program• Control all aspects of the
device▫ Integrate hardware▫ Perform necessary
calculations▫ Display results
Graphs Images Quantitative data
Instantaneous effective modulus
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• LabVIEW 2010
Image Acquisition System• High resolution CCD camera
will be used to track the positions of the desired components in real time
• Positions on the tissue will be defined by sprayed on microdots
• Camera images will be acquired in LabVIEW
• CCD camera will move as the tissue is deformed
• Results will be calculated in LabVIEW using camera images to determine displacement of the tissue and positions of bending bar and reference bar
Controlled Environment▫ Simulate in vivo testing of
tissues Inner bath uses phosphate
buffered saline (PBS) solution
Provides a pH of 7.4
▫ Temperature controller used to constantly regulate temperature of outside bath 37°C ± 1°C Inner bath is protected from
current flow from the constantly regulated outer bath fluid
Project Constraints•Engineering - Errors from calculation,
image acquisition, and environmental changes will be minimized.
•Environmental –The temperature and pH of the test environment will be controlled
Safety Issues• Biological Hazards
▫The device will be routinely cleaned because the tissues used may expose the device to harmful bacteria.
▫Surface materials will be smooth and capable of being sterilized after each use to avoid bacterial growth.
• Equipment Hazards▫Wires will be insulated to avoid
electrocution/electrical fires▫Electrical components will be kept out of
contact with the bath solution
Budget•Most expensive
▫Integrated Stepper
▫Camera•With recycling
all parts, expected to spend only 13.7% of budget
Item / Part Projected Cost Purchased? Supplier
CCD Camera (Mightex)
-Computer Megapixel Lens -VM100 Extension Tube Kit
$749.00
$122 $53
Yes
Yes Yes
Sentech America, Inc
Tissue Bath - Bath Materials - Flow Pump - Bath Solution
$60 $40 $75
No Yes Yes
Hardware Store AquaLife Sigma-Aldrich
Surgical Steel Bending Bar(s) $2 x 10 No OnlineMetals /
UCHC Motor Parts
- Danaher Motion 2 Phase 1.8” Stepping Motor - 2-Axis Motion Controller PCI Card - 2-Axis Integrated Stepper Drive Power Unit (115 V) - 68 pin VHDCI to 68 pin VHDCI Cable - MID Connector Kit
$30 x 2
$765
$1800
$135
$44
Yes
Yes
Yes
Yes
Yes
National Instrument
Linear Actuator
-Model DL 15-25-SV $480 Yes Del-Tron Precision
Tissue Fixation Setup -Lexan for bath setups
$45 No US Plastic Corp
Steel Frame
1 ft x 1ft x 2 ft square tubes 0.5 in x 1 ft x 2ft sheet (Cart) .036 in x 1 ft x 2 ft (Rails)
$3.10 x 4
$5.30 $9.94
No No No
Metal Depot
Plastic Cart Wheels $30 No Home Depot Miscellaneous Parts $100 No Total Amount Needed: $282.64
Progress Through First Semester•Project design•Identified necessary components that can
be utilized from the Biomechanics Lab ▫CCD Camera▫Linear Actuator ▫Stepper Drive▫Stepper Motor▫Flow Regulator
•CCD camera installed and tested•LabVIEW Outline
Work to Be Completed•Program the components of the project in
LabVIEW•Consolidate VI’s•Machine device•Connect components of entire device•Debug device•Test multiple samples•Write user’s manual/test method
Division of Labor•Jennifer Olson
▫CCD Camera▫Image Acquisition System
•Sarah Rivest▫Environmental Control▫Flexural Properties
•Brian Schmidtberg▫Force System▫Motor System
Timeline
Timeline
Timeline
Timeline
Acknowledgements•Dr. Wei Sun•Eric Sirois•Dave Kaputa•Dr. John Enderle
Questions?