title: Effects of fatigue on the chemical and mechanical degradation of model stent sub-units.
abstract: Understanding the fatigue and durability performance of implantable cardiovascular stents is critical for assessing their performance. When the stent is manufactured from an absorbable material, however, this durability assessment is complicated by the transient nature of the device. Methodologies for evaluating the fatigue performance of absorbable stents while accurately simulating the degradation are limited and little is known about the interaction between fatigue and degradation. In this study, we investigated the fatigue behavior and effect of fatigue on the degradation rate for a model absorbable cardiovascular stent. Custom v-shaped stent sub-units manufactured from poly(L-lactide), i.e., PLLA, were subjected to a simultaneous fatigue and degradation study with cycle counts representative of one year of expected in vivo use. Fatigue loading was carried out such that the polymer degraded at a rate that was aligned with a modest degree of fatigue acceleration. Control, un-loaded specimens were also degraded under static immersion conditions representative of simulated degradation without fatigue. The study identified that fatigue loading during degradation significantly increased specimen stiffness and lowered the force at break. Fatigue loading also significantly increased the degree of molecular weight decline highlighting an interaction between mechanical loading and chemical degradation. This study demonstrates that fatigue loading during degradation can affect both the mechanical properties and the chemical degradation rate. The results are important for defining appropriate in vitro degradation conditions for absorbable stent preclinical evaluation.
authors.affiliation: US Food and Drug Administration, Office of Medical Products and Tobacco, Center for Devices and Radiological Health, Office of Science and Engineering Laboratories, Division of Applied Mechanics, 10903 New Hampshire Avenue, White Oak Building 62-2229, Silver Spring, MD 20993, USA. Electronic address: Maureen.dreher@fda.hhs.gov.
authors.forename: Maureen L
authors.initials: ML
authors.lastname: Dreher
authors.affiliation: US Food and Drug Administration, Office of Medical Products and Tobacco, Center for Devices and Radiological Health, Office of Science and Engineering Laboratories, Division of Applied Mechanics, 10903 New Hampshire Avenue, White Oak Building 62-2229, Silver Spring, MD 20993, USA.
authors.forename: Srinidhi
authors.initials: S
authors.lastname: Nagaraja
authors.affiliation: University of Texas at Dallas, Department of Chemistry, 800 W Campbell Rd, Richardson, TX 75080, USA.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Batchelor
mesh_terms: D020341:Absorbable Implants; D006801:Humans; D008422:Materials Testing; D055595:Mechanical Phenomena; D011091:Polyesters / Q000737:chemistry; D011475:Prosthesis Failure; D015607:Stents
chemical_list: D011091:Polyesters; C033616:poly(lactide)
keywords: Absorbable stents; Fatigue; PLLA; Stent degradation