Pitre, Nandan
(2024)
Investigation of Arterial Luminal Topography and Design of Crimped Fiber Composites.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
The lumen of arteries usually appears corrugated in histological cross-sections. These corrugations occur due to the wrinkling of the Internal Elastic Lamina (IEL) and have often been attributed to fixation artefacts. We quantify the IEL topography and test whether the corrugations are actually present in arteries under physiological conditions. This is done by imaging cross-sections of fixed arteries at different diameters and comparing them to the diameter measured in-vivo using ultrasound. It is seen that the IEL corrugations flatten out as the arterial diameter increases, and the IEL contour length is ~10% more than the circumference at ultrasound diameter. These results provide evidence that the luminal topography is not completely flat under physiological conditions.
Fibrous collagen exists in biological tissues in the form of crimped fibers. This crimped nature of fibers enables them to uncrimp before stretching and provide an increased stiffness as the tissue stretches, thus imparting ‘strain-hardening’ behavior to the tissues. Composites of soft material embedded with short stiffer crimped fibers have the potential to show similar mechanical behavior and have the advantage of being flow processible. Here we study the mechanics of crimped fiber composites by quantifying the stress transfer between a single crimped fiber and a an embedding soft matrix, and examining the mechanical response of crimped multifiber composites under tension, using 3D finite element analysis.
As the composite is stretched, fibers with large crimp amplitude and large relative modulus straighten significantly at small strains without bearing significant load. Thus, crimped fiber composites show a super-linear increase in stress upon tension. Stress-transfer mechanics of a crimped fiber are captured using a shear lag model, where the crimped fiber can be replaced by an equivalent softer straight fiber with increasing strain-dependent modulus. Multifiber composites show that higher fiber volume fraction yields higher reinforcement. Moreover, maximum reinforcement is achieved when the fibers are oriented along the direction of the stretch. Thus, the degree of strain-hardening and the degree of reinforcement of multi-crimped-fiber composites can be tuned by changing fiber parameters to achieve the desired mechanical behavior of the composite.
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Details
| Item Type: |
University of Pittsburgh ETD
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| Status: |
Unpublished |
| Creators/Authors: |
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| ETD Committee: |
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| Date: |
11 January 2024 |
| Date Type: |
Publication |
| Defense Date: |
31 October 2023 |
| Approval Date: |
11 January 2024 |
| Submission Date: |
10 November 2023 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
145 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Bioengineering |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Arteries, Vascular, grafts, internal elastic lamina, IEL, topography, morphology, crimped fibers, composites, multifiber composites, strain hardening, shear lag, Holzapfel Gasser Ogden, reinforcement |
| Date Deposited: |
11 Jan 2024 19:43 |
| Last Modified: |
11 Jan 2024 19:43 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/45511 |
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