Morphological Variations In Poly (L-Lactic Acid) (Plla) Vascular Scaffolds For The Treatment Of Coronary Heart Disease (Chd)
ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY(2016)
Abstract
Poly (L-lactic Acid) (PLLA) is a semicryst. and biocompatible polymer that is used in bioresorbable vascular
scaffolds for the treatment of Coronary Heart Disease (CHD). To treat CHD, a PLLA scaffold is deployed in the
occluded artery to restore blood circulation. Implants made of PLLA undergo hydrolysis to form L-lactic acid that
is readily metabolized by the human body, allowing them to harmlessly disappear in two years. The polymer is
subjected to tube expansion and laser cutting before it is crimped onto a balloon. When the crimped scaffold is
in position in the diseased artery, the balloon is inflated to deploy the scaffold. The resulting semicryst.
structure changes over distances of a few microns, requiring X-ray microdiffraction to shed light on the
structural changes that occur in PLLA vascular scaffolds which govern their therapeutic function. Crimping
places the outer bend (OB) of a U-crest under elongation and the inner bend (IB) under compression. X-ray
diffraction patterns indicate highly oriented PLLA crystallites where elongation was imposed (near the OB) and
crystallites tilted out of plane where compression was imposed (at the IB). Between the IB and the OB, there is
an unperturbed region with an orientation similar to the expanded tube. Deployment profoundly alters the
structure created during crimping. The tilting of crystallites at the IB during crimping allows them to gracefully
sep. into diamond shaped voids when the IB is placed under tension during deployment. Consequently, the OB
experiences relatively mild compressive stress during deployment and a highly uniform structure is obsd.
Despite PLLA's reputation as a brittle plastic, the solid state deformation does not fracture the scaffold; rather,
the deployed PLLA scaffold has a high degree of orientation, giving the scaffold the radial strength to hold the
blood vessel open.
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Key words
Scaffold,Elongation,Compression (physics),Polymer,Crystallite,Compressive strength,Deformation (engineering),Tension (physics),Biomedical engineering,Materials science
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