title: Knitted nitinol represents a new generation of constrictive external vein graft meshes.
abstract: OBJECTIVE
  Constriction of vein grafts with braided external nitinol meshes had previously led to the successful elimination of neointimal tissue formation. We investigated whether pulse compliance, smaller kink-free bending radius, and milder medial atrophy can be achieved by knitting the meshes rather than braiding, without losing the suppressive effect on intimal hyperplasia.
  
  
  METHODS
  Pulse compliance, bending stiffness, and bending radius, as well as longitudinal-radial deformation-coupling and radial compression, were compared in braided and knitted nitinol meshes. Identical to previous studies with braided mesh grafts, a senescent nonhuman primate model (Chacma baboons; bilateral femoral interposition grafts/6 months) mimicking the clinical size mismatch between vein grafts and runoff arteries was used to examine the effect of knitted external meshes on vein grafts: nitinol mesh-constricted (group 1); nitinol mesh-constricted and fibrin sealant (FS) spray-coated for mesh attachment (group 2); untreated control veins (group 3), and FS spray-coated control veins (group 4).
  
  
  RESULTS
  Compared with braided meshes, knitted meshes had 3.8-times higher pulse compliance (3.43 ± 0.53 vs 0.94 ± 0.12%/100 mm Hg; P = .00002); 30-times lower bending stiffness (0.015 ± 0.002 vs 0.462 ± 0.077 Nmm(2); P = .0006); 9.2-times narrower kink-free bending radius (15.3 ± 0.4 vs 140.8 ± 22.4 mm; P = .0006), and 4.3-times lower radial narrowing caused by axial distension (18.0% ± 1.0% vs 77.0% ± 3.7%; P = .00001). Compared with mesh-supported grafts, neointimal tissue was 8.5-times thicker in group I (195 ± 45 μm) vs group III (23.0 ± 21.0 μm; P < .001) corresponding with a 14.3-times larger neointimal area in group I (4330 ± 957 × 103 μm(2)) vs group III (303 ± 221× 103 μm(2); P < .00004). FS had no significant influence. Medial muscle mass remained at 43.4% in knitted meshes vs the 28.1% previously observed in braided meshes.
  
  
  CONCLUSIONS
  Combining the suppression of intimal hyperplasia with a more physiologic remodeling process of the media, manifold higher kink-resistance, and lower fraying than in braided meshes makes knitted nitinol an attractive concept in external vein graft protection.
authors.affiliation: Christiaan Barnard Department of Cardiothoracic Surgery, University of Cape Town, Cape Town, South Africa. peter.zilla@uct.ac.za
authors.forename: Peter
authors.initials: P
authors.lastname: Zilla
authors.forename: Loven
authors.initials: L
authors.lastname: Moodley
authors.forename: Michael F
authors.initials: MF
authors.lastname: Wolf
authors.forename: Deon
authors.initials: D
authors.lastname: Bezuidenhout
authors.forename: Mazin S
authors.initials: MS
authors.lastname: Sirry
authors.forename: Nasser
authors.initials: N
authors.lastname: Rafiee
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Lichtenberg
authors.forename: Melanie
authors.initials: M
authors.lastname: Black
authors.forename: Thomas
authors.initials: T
authors.lastname: Franz
mesh_terms: D000497:Alloys; D000818:Animals; D001696:Biomechanical Phenomena; D003187:Compliance; D004867:Equipment Design; D005263:Femoral Artery / Q000503:physiopathology / Q000601:surgery* / Q000648:ultrastructure; D005268:Femoral Vein / Q000503:physiopathology / Q000637:transplantation* / Q000648:ultrastructure; D015718:Fibrin Tissue Adhesive; D006965:Hyperplasia; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D023421:Models, Animal; D048549:Papio ursinus; D011673:Pulsatile Flow; D013526:Surgical Mesh; D013997:Time Factors; D058017:Vascular Grafting / Q000009:adverse effects / Q000295:instrumentation*
chemical_list: D000497:Alloys; D015718:Fibrin Tissue Adhesive; C013616:nitinol