title: The biodurability of covering materials for metallic stents in a bile flow phantom.
abstract: BACKGROUND
  Covered biliary metal stents have been introduced for the purpose of overcoming tumor ingrowth and treatment of benign biliary stricture. The aim of this study was to evaluate the biodurability of three commercially available biliary metal stent covering materials [e-PTFE (expanded polytetrafluoroethylene), silicone, and polyurethane] in a bile flow phantom.
  
  
  METHODS
  By operation of a peristaltic pump, human bile was circulated continuously in an experimental perfusion system containing covered metal stents. Each stent was removed, respectively, 1, 2, 4, and 6 months after bile exposure. We performed a gross inspection of the covered stents. The covering membrane was detached from the stent and observed by scanning electron microscopy (SEM). Finally, we measured tensile and tear strength of the membranes.
  
  
  RESULTS
  Bile-staining of the membrane showed gradual progression after bile exposure; however, progress was the fastest in e-PTFE. SEM examination showed that the polyurethane surface was smooth, and the silicone surface was relatively smooth. However, e-PTFE had a rough and uneven surface. After bile exposure, there were no significant changes in polyurethane and silicone; however, biofilms and microcracks were observed in e-PTFE. In contrast to a gradual decrease of tensile/tear strength of polyurethane and silicone, those of e-PTFE showed a rapid reduction despite of the strongest baseline tensile and tear strength.
  
  
  CONCLUSIONS
  e-PTFE tended to form biofilms more frequently than polyurethane and silicone during bile exposure. e-PTFE seemed to be less durable than silicone and polyurethane, however, as clinically applicable material because of strong absolute tensile/tear strengths.
authors.affiliation: Division of Gastroenterology, Department of Internal Medicine, Inha University School of Medicine, 7-206, 3-Ga, Sinheung-Dong, Jung-Gu, Incheon 400-711, South Korea.
authors.forename: Byoung Wook
authors.initials: BW
authors.lastname: Bang
authors.forename: Seok
authors.initials: S
authors.lastname: Jeong
authors.forename: Don Haeng
authors.initials: DH
authors.lastname: Lee
authors.forename: Jung Il
authors.initials: JI
authors.lastname: Lee
authors.forename: Se Chul
authors.initials: SC
authors.lastname: Lee
authors.forename: Sung-Gwon
authors.initials: SG
authors.lastname: Kang
mesh_terms: D018441:Biofilms / Q000254:growth & development; D002779:Cholestasis / Q000601:surgery*; D020099:Coated Materials, Biocompatible; D008422:Materials Testing; D008670:Metals; D008855:Microscopy, Electron, Scanning; D008954:Models, Biological; D008961:Models, Structural; D011138:Polytetrafluoroethylene; D011140:Polyurethanes; D012828:Silicones; D015607:Stents; D013718:Tensile Strength
chemical_list: D020099:Coated Materials, Biocompatible; D008670:Metals; D011140:Polyurethanes; D012828:Silicones; D011138:Polytetrafluoroethylene
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