Development of Biodegradable Composite Materials for Coronary Stents

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dc.contributor.advisor Bhattacharyy, D en
dc.contributor.advisor Fakirov, S en Kimble, Lloyd en 2014-09-25T22:04:44Z en 2014 en
dc.identifier.citation 2014 en
dc.identifier.uri en
dc.description.abstract Stents based on poly(L-lactic acid), PLLA, are very prominent in the field of biodegradable stents but a disadvantage of PLLA is its relative brittleness. Cardiologists have noted the occurrence of strut fracture during deployment of balloon expandable PLLA stents. Blends of PLLA and poly(butylene-succinate), PBS , are attractive candidates for coronary artery stents because of their ductility. Hence the motivation for this research – which aimed to evaluate effects of degradation on properties of PLLA/PBS blends relevant the intended application. PLLA/PBS blends were degraded in-vitro over a 24-week period. Their tensile strengths and Young’s moduli decrease gradually with increasing degradation time whilst those of neat PLLA exhibit less significant change. Thus PLLA/PBS blends may retain sufficient strength and stiffness to be suitable for use in biodegradable stents. Further evaluation was undertaken by investigating creep. Creep behaviour of a 75/25 wt % PLLA/PBS blend (PLLA.PBS.25) was compared with that of neat PLLA. Non-degraded PLLA.PBS.25 exhibits lower initial creep resistance than PLLA but aging during creep eventually results in nearly identical creep rates in the two materials. However, during degradation PLLA.PBS.25 loses creep resistance fairly quickly whilst PLLA experiences increasing creep resistance during the first 8 weeks of degradation, due to physical ageing, before its creep resistance decreases. This prompted investigation of potential reinforcements. Micro-fibrillar composites, MFCs, were produced from PLLA and poly(glycolic acid), PGA. The PLLA/PGA MFCs produced are stiffer and stronger than PLLA but very interestingly their creep propensity is greater due to the onset of glass transition of PGA occurring near 37 °C. PLLA/PBS blends alone are not recommended for coronary artery stents based on the effects of degradation on creep resistance. MFCs are very promising for reinforcing biodegradable stents but require further investigation. Particulate reinforcements are considered to be currently feasible but this approach of reinforcing stents is hindered by the inherent compromise of relying on the stent material to be ductile but also rigid enough to support a vessel. This may be overcome by decoupling the requirements and designing accordingly. Some stent concepts based on this are discussed. en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof PhD Thesis - University of Auckland en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. en
dc.rights.uri en
dc.rights.uri en
dc.title Development of Biodegradable Composite Materials for Coronary Stents en
dc.type Thesis en The University of Auckland en Doctoral en PhD en
dc.rights.holder Copyright: The Author en
dc.rights.accessrights en
pubs.elements-id 456980 en
pubs.record-created-at-source-date 2014-09-26 en

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