Knitted nitinol represents a new generation of constrictive external vein graft meshes

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 mu m) vs group III (23.0 +/- 21.0 mu m; P < .001) corresponding with a 14.3-times larger neointimal area in group I (4330 +/- 957 x 103 mu m(2)) vs group III (303 +/- 221 x 103 mu m(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. Conclusion: 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. (J Vase Surg 2011;54:1439-50.)