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Development of Semicrystalline Morphology of Poly(L-lactic Acid) during Processing of a Vascular Scaffold


Ailianou, Artemis (2014) Development of Semicrystalline Morphology of Poly(L-lactic Acid) during Processing of a Vascular Scaffold. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9VT1Q26.


New and promising treatments for coronary heart disease are enabled by vascular scaffolds made of poly(L-lactic acid) (PLLA), as demonstrated by Abbott Vascular’s bioresorbable vascular scaffold. PLLA is a semicrystalline polymer whose degree of crystallinity and crystalline microstructure depend on the thermal and deformation history during processing. In turn, the semicrystalline morphology determines scaffold strength and biodegradation time. However, spatially-resolved information about the resulting material structure (crystallinity and crystal orientation) is needed to interpret in vivo observations.

The first manufacturing step of the scaffold is tube expansion in a process similar to injection blow molding. Spatial uniformity of the tube microstructure is essential for the consistent production and performance of the final scaffold. For implantation into the artery, solid-state deformation below the glass transition temperature is imposed on a laser-cut subassembly to crimp it into a small diameter. Regions of localized strain during crimping are implicated in deployment behavior.

To examine the semicrystalline microstructure development of the scaffold, we employed complementary techniques of scanning electron and polarized light microscopy, wide-angle X-ray scattering, and X-ray microdiffraction. These techniques enabled us to assess the microstructure at the micro and nano length scale. The results show that the expanded tube is very uniform in the azimuthal and axial directions and that radial variations are more pronounced. The crimping step dramatically changes the microstructure of the subassembly by imposing extreme elongation and compression. Spatial information on the degree and direction of chain orientation from X-ray microdiffraction data gives insight into the mechanism by which the PLLA dissipates the stresses during crimping, without fracture. Finally, analysis of the microstructure after deployment shows that it is inherited from the crimping step and contributes to the scaffold’s successful implantation in vivo.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:semicrystalline, PLLA, vascular, scaffold
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemical Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Kornfield, Julia A.
Thesis Committee:
  • Kornfield, Julia A. (chair)
  • Grubbs, Robert H.
  • Tirrell, David A.
  • Shapiro, Mikhail G.
Defense Date:5 May 2014
Funding AgencyGrant Number
Record Number:CaltechTHESIS:05302014-173923900
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8450
Deposited By: Artemis Ailianou
Deposited On:20 Sep 2016 18:56
Last Modified:04 Oct 2019 00:05

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