Planar Biaxial Device
Role: Implement automatic marker tracking in LabVIEW to allow for optical-based strain calculation of soft tissues
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I want to begin by acknowledging my faculty advisors who made this project possible: Dr. Manning and Professor Humphrey. Credit is also due to the graduate student 10 years ago who designed the first iteration of this device.
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My main role involved LabVIEW implementation. The primary change was to implement a local optical-based strain calculation as opposed to relying on motor positions, allowing for greater insight into the sample's anisotropy. Secondly, the force-finding algorithm was changed to ensure convergence.
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[Left] is an image of the cruciform bath and one of the step motors. I have masked the sample in this image out of respect for the donor.
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[Below] is an image of a synthetic scaffold we tested, where you can see the 4 marker beads.
Device Function
We are often interested in how biological tissue deforms under applied stresses. Many cardiopulmonary pathologies involve the stiffening of tissues that are meant to be elastic. This device is designed precisely for that purpose-- to mechanically characterize the tissue samples.
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The device is made from a cruciform bath filled with isotonic saline, in which the sample is submerged. Fish line hooks attach to the four sides of the sample. We most often test samples from the circulatory system, where our principal axes are the circumferential and axial directions. the hook lines attach to metal bars that slide along rails, moved by high-precision step motors. Each axis also has an in-line load cell allowing for a force reading. We use 4 black glass microbeads glued to the endothelial side of the sample and track their positional changes under deformation to calculate strain. A normal "test" involves, stepping back the motors, exerting a tensile force on the sample, collecting force data along with the pixel coordinates for the 4 marker beads.
(Right) I've included the theory behind how we extract the raw data from the device and prepare it for model fitting.
