title: Biologic response to polymer-coated stents: in vitro analysis and results in an iliac artery sheep model.
abstract: OBJECTIVE
  To evaluate biologic response to poly(hydroxymethyl-p-xylylene-co-p-xylylene) (PHPX)-coated stents in vitro and in vivo in sheep.
  
  
  METHODS
  Physical stability, hemocompatibility, and cytotoxicity of the coating were first assessed in vitro. Thirty-six self-expanding nitinol (Memotherm), 24 stainless steel balloon-mounted (Palmaz), and 12 self-expanding nitinol (ZA) stents were coated with PHPX by using chemical vapor deposition polymerization. Seventy-two coated and 72 uncoated stents were placed into iliac arteries of 36 sheep. Sheep were classified into three groups of 12 animals each. In each group, six sheep were killed after 1 month; six, after 6 months. In each sheep, two uncoated stents were placed into one limb; two coated stents of the same type, into the opposite limb. In groups 1 and 2, Palmaz and Memotherm stents were used; in group 3, Memotherm and ZA stents were used. In groups 1 and 3, arteries were healthy. In group 2, arteries were pretreated with a Fogarty maneuver. Stent patency was measured with intravascular ultrasonography (US) and histologic analysis. Cellular response to coated and uncoated stents was assessed. Measurements were compared (Wilcoxon test).
  
  
  RESULTS
  In vitro, PHPX coating was stable; hemocompatibility and cytotoxicity were similar to those of stainless steel. In vivo, patency of coated and uncoated Palmaz and ZA stents was not different (P >.05). Patency of coated and uncoated Memotherm stents did not differ in four of six follow-up subgroups, but it was significantly reduced in group 2 after 6 months (intravascular US, P =.03; histologic analysis, P =.01) and in group 3 after 1 month (histologic analysis, P =.01). Histologically, the cellular response to coated and uncoated stents was not different (P >.05).
  
  
  CONCLUSIONS
  PHPX coating had good physical stability and biocompatibility in vitro and in vivo. Performance of coated and uncoated Palmaz and ZA stents was similar. Patency of Memotherm stents was similar in four of six follow-up subgroups. Materials effects did not result in severely enhanced neointimal hyperplasia.
authors.affiliation: Departments of Diagnostic Radiology, Pathology, and Textile and Macromolecular Chemistry, University of Technology, Pauwelsstrasse 30, D-52057 Aachen, Germany.
authors.forename: Karl
authors.initials: K
authors.lastname: Schürmann
authors.forename: Joerg
authors.initials: J
authors.lastname: Lahann
authors.forename: Pascal
authors.initials: P
authors.lastname: Niggemann
authors.forename: Bernd
authors.initials: B
authors.lastname: Klosterhalfen
authors.forename: Julius
authors.initials: J
authors.lastname: Meyer
authors.forename: Arthur
authors.initials: A
authors.lastname: Kulisch
authors.forename: Doris
authors.initials: D
authors.lastname: Klee
authors.forename: Rolf W
authors.initials: RW
authors.lastname: Günther
authors.forename: Dierk
authors.initials: D
authors.lastname: Vorwerk
mesh_terms: D000818:Animals; D007083:Iliac Artery / Q000000981:diagnostic imaging / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D011108:Polymers; D011859:Radiography; D012756:Sheep; D015607:Stents
chemical_list: D011108:Polymers