3-Point Bending Device to Measure Transmural Strains for Multilayer Soft Tissue Composite Jennifer Olson Sarah Rivest Brian Schmidtberg Sponsor: 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 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

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

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

Questions?