title: In-situ investigation of stress conditions during expansion of bare metal stents and PLLA-coated stents using the XRD sin(2)ψ-technique.
abstract: Drug eluting stents (DES) consist of platform, coating and drug. The platform often is a balloon-expandable bare metal stent made of the CoCr alloy L-605 or stainless steel 316 L. The function of the coating, typically a permanent polymer, is to hold and release the drug, which should improve therapeutic outcome. Before implantation, DES are compressed (crimped) to allow implantation in the human body. During implantation, DES are expanded by balloon inflation. Crimping, as well as expansion, causes high stresses and high strains locally in the DES struts, as well as in the polymer coating. These stresses and strains are important design criteria of DES. Usually, they are calculated numerically by finite element analysis (FEA), but experimental results for validation are hardly available. In this work, the X-ray diffraction (XRD) sin(2)ψ-technique is applied to in-situ determination of stress conditions of bare metal L-605 stents, and Poly-(L-lactide) (PLLA) coated stents. This provides a realistic characterization of the near-surface stress state and a validation option of the numerical FEA. XRD-results from terminal stent struts of the bare metal stent show an increasing compressive load stress in tangential direction with increasing stent expansion. These findings correlate with numerical FEA results. The PLLA-coating also bears increasing compressive load stress during expansion.
authors.affiliation: University of Rostock, Faculty of Mechanical Engineering and Marine Technology, Chair of Materials Science, 18051 Rostock, Germany. Electronic address: wolfgang.kowalski@uni-rostock.de.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Kowalski
authors.affiliation: Cortronik GmbH, 18119 Rostock-Warnemünde, Germany. Electronic address: markus.dammer@biotronik.com.
authors.forename: Markus
authors.initials: M
authors.lastname: Dammer
authors.affiliation: Cortronik GmbH, 18119 Rostock-Warnemünde, Germany. Electronic address: frank.bakczewitz@biotronik.com.
authors.forename: Frank
authors.initials: F
authors.lastname: Bakczewitz
authors.affiliation: University of Rostock, University Medicine, Institute for Biomechanical Engineering, 18119 Rostock-Warnemünde, Germany. Electronic address: klaus-peter.schmitz@uni-rostock.de.
authors.forename: Klaus-Peter
authors.initials: KP
authors.lastname: Schmitz
authors.affiliation: University of Rostock, University Medicine, Institute for Biomechanical Engineering, 18119 Rostock-Warnemünde, Germany. Electronic address: niels.grabow@uni-rostock.de.
authors.forename: Niels
authors.initials: N
authors.lastname: Grabow
authors.affiliation: University of Rostock, Faculty of Mechanical Engineering and Marine Technology, Chair of Materials Science, 18051 Rostock, Germany. Electronic address: olaf.kessler@uni-rostock.de.
authors.forename: Olaf
authors.initials: O
authors.lastname: Kessler
mesh_terms: D002857:Chromium / Q000737:chemistry*; D020099:Coated Materials, Biocompatible / Q000737:chemistry*; D003035:Cobalt / Q000737:chemistry*; D054855:Drug-Eluting Stents; D020342:Finite Element Analysis; D008422:Materials Testing; D011091:Polyesters / Q000737:chemistry*; D013314:Stress, Mechanical; D013499:Surface Properties; D014961:X-Ray Diffraction
chemical_list: D020099:Coated Materials, Biocompatible; D011091:Polyesters; D002857:Chromium; D003035:Cobalt; C033616:poly(lactide)
keywords: CoCr-alloy; Expansion; L-605; Load stresses; PLLA-coated stent; Residual stresses; Semicrystalline polymer; Stent; X-ray diffraction