3-Point Bending Device to Measure Transmural Strains for Multilayer Soft Tissue Composite 4910 Final Presentation

Transcription

1 3-Point Bending Device to Measure Transmural Strains for Multilayer Soft Tissue Composite 4910 Final Presentation Team 6 Jen Olson Sarah Rivest Brian Schmidtberg Sponsor: Dr. Wei Sun

2 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 forcedeformation 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

3 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

4 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

5 Project Overview Five Systems Mounting bath Provide consistent area for testing Hold solution and tissue specimen Force Apply force to tissue Temperature Controller Maintain temperature of solution Image Acquisition Track sprayed on microdots on tissue throughout testing Program and Interface Connect all subsystems Provide an interface for the user to control the device Calculate all necessary results from data obtained

6 Overall Project

7 Overall Project LabVIEW program SH68-SH68 Cable Stepper Drive PC equipped with Motion Controller Sliding Mechanism Stepper Motor /Linear Actuator

8 Mounting Bath Provides a controlled environment for repeatable testing Outer Bath Hose barbs for temperature regulator Inner Bath w/ holes for stationary posts

9 Force Application System Contains motor system and sliding mechanism Motor system propels sliding mechanism along track to apply force to the specimen Sliding Mechanism Removable Bending Bar Piece Motor system

10 Components of the Sliding Mechanism Frame with grooves for wheels Cart equipped with ball bearings as wheels Frame Camera Attachment with adjustable knob for 5 of rotation Removable bending bar piece for easier calibration Camera Attachment (+5 ) Camera Attachment (-5 )

11 Temperature Controller Connects to the outer bath of mounting system Keeps temperature at 37 C ±1 Fischer-Scientific Temperature Regulator

12 Image Acquisition Track the deformation of the tissue during testing Mightex CMOS Camera Image Acquisition System

13 Program and Interface Project controlled via LabVIEW and Matlab Allows user to control the whole device Calculates data Integrates hardware

14 LabVIEW Flowchart Raw Image from Camera Image boundaries Camera Display Minimum Marker Size Maximum Marker Size Number of Markers Marker Position Undeformed Marker Position Marker Position Transmural Outputs MATLAB Script Spreadsheet

15 Testing Calibration Small weights of known mass are suspended from bending bar and displacement is measured from reference bar CCD camera captures displacement Used to create a load vs. displacement graph Information is used to determine instantaneous effective modulus of specimen

16 Testing Determining flexural rigidity Required marking beads placed along tissue Transmural strain Requires many markers Dr. Michael Sacks, Department of Bioengineering, University of Pittsburg

17 Division of Labor Brian Design of sliding mechanism and mounting baths Fabrication of sliding mechanism and mounting baths Motion control DreamWeaver Sarah LabVIEW program for motion control Flexural rigidity calculations and programming Transmural strain calculations and programming Jen LabVIEW program for image acquisition LabVIEW program for marker tracking

18 Budget Update Maximum budget: $1000 Amount saved: $886 Part Cost Aluminum $47 Accupuncture Needles $23.89 Lexan $13.07 Hose Barbs $5.48 Shoulder Screws $2.08 Ball Bearings $22.04 Total $114

19 Acknowledgements Dr. Wei Sun Dr. John Enderle Emily Jacobs Pete & Surge UCONN Machine Shop Eric Sirois Kewei Li & Thuy Pham Dave Kaputa Jennifer Desrosiers & Kerrie Wenzler

20 Questions?