Prof. Julie Kornfield's Talk

Mar 14, 2019 - 17:00

Mar 14, 2019 - 18:00

Room 118, Chemical Engg Dept

Seminars

Prof. Julie Kornfield, Caltech

Abstract:Poly(L-lactide) (PLLA) is the structural material of the first clinically-approved bioresorbable vascular scaffold (BVS), a promising alternative to permanent metal stents for treatment of coronary heart disease. BVSs are transient implants that support the occluded artery for 6 mo and are completely resorbed in 2 yr, leaving behind a regenerated artery. Clinical trials of BVSs report restoration of arterial vasomotion and elimination of serious complications of metal stents that occur 5 to 7 yr after implantation. It is remarkable that a scaffold made from PLLA, known as a brittle polymer, does not fracture when crimped onto a balloon catheter or during deployment in the artery. We used X-ray microdiffraction to discover how PLLA acquired ductile character and found that the crimping process creates localized regions of extreme anisotropy. The degree and direction of orientation and crystallinity change on micron-scale distances. The distinct morphologies in the crimped scaffold work in tandem to enable a low-stress response during deployment, which avoids fracture of the PLLA hoops and leaves them with the strength needed to support the artery. After deployment, the highly oriented morphology created at points of stress localization during crimping confer resistance to hydrolysis precisely where it is needed for the scaffold to retain strength even after 9mo of hydrolysis. Thus, the ability to use processing to access nonequilibrium microstructures in the semicrystalline PLLA are essential to the clinically-approved BVS and open the way to thinner resorbable scaffolds in the future. Bio: Julia A. Kornfield, Professor of Chemical Engineering at the California Institute of Technology (Caltech), is an expert in polymer science, particularly how polymers influence and are influenced by flow. She has applied small angle neutron and x-ray scattering to diverse systems, including end-associative polymers for aviation safety and security (Wei et al., Science 2015), flow-induced crystallization of polymers (e.g., Science 2007) and the effects of flow on polymer self-assembly (e.g., Science 1997). Since she joined the Caltech faculty in 1990, Kornfield has received the Dillon Medal of the American Physical Society, been elected Fellow of the American Physical Society and the American Association for the Advancement of Science, and received the Bingham Medal of the Society of Rheology, among other honors. She holds 29 patents and is a co-founder of RxSight (formerly Calhoun Vision), which uses polymers developed at Caltech to customize vision by noninvasively optimizing a lens after it is implanted into a patients’ eye. Thus, her work spans from fundamental research on the molecular basis of polymer structure and properties, to commercialization of polymers that improve health and safety. This seminar is compulsory for students registered for course CL 702 or CL 704.