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.

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.