3-Point Bending Device to Measure Transmural Strains for Multilayer Soft Tissue Composite

1. 3-Point Bending Device to Measure Transmural Strains forMultilayer Soft Tissue Composite Jennifer Olson Sarah Rivest Brian Schmidtberg Sponsor: Dr. Wei Sun

2. Overview • Background • Purpose • Objectives • Project Parts • Constraints • Budget • Conclusion

3. 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

4. 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

5. 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

6. 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

7. Project Parts • Outer/Inner Baths • Sliding Mechanism • Image Acquisition and Analysis • Temperature Regulation • LabVIEW

8. Inner Bath • Inner bath • Provides a surface for repeatable testing • Outer bath • Circulates temperature controlled water • Material: Lexan • Cheap, Transparent, Strong Outer Bath Combined

9. Sliding Mechanism CCD Camera Bending Bar • Contains bending bar, reference bar and CCD camera on movable cart • Cart controlled by motor system Reference Bar Top View of Sliding Mechanism Bar/Camera Set-up

10. Sliding Mechanism • Motor System • Moves bending bar into tissue specimen • Moves CCD camera during tissue deflection such that tissue never leaves frame of reference Sliding Mechanism Stepper Motor Stepper drive Linear Actuator PC equipped with LabVIEW and motion controller SH68-SH68 Cable

11. LabVIEW Program • LabVIEW 2010 • Control all aspects of the device • Integrate hardware • Perform necessary calculations • Display results • Graphs • Images • Quantitative data

12. 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

13. 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

14. 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

15. 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

16. Budget • Most expensive • Integrated Stepper • Camera • With recycling all parts, expected to spend only 13.7% of budget

17. 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

18. 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

19. Division of Labor • Jennifer Olson • CCD Camera • Image Acquisition System • Sarah Rivest • Environmental Control • Flexural Properties • Brian Schmidtberg • Force System • Motor System

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24. Acknowledgements • Dr. Wei Sun • Eric Sirois • Dave Kaputa • Dr. John Enderle

25. Questions?