A Comparison of Three-Layer and Single-Layer Small Vascular Grafts Manufactured via the Roto-Evaporation Method

Abstract

This study used the roto-evaporation technique to engineer a 6 mm three-layer polyurethane vascular graft (TVG) that mimics the architecture of human coronary artery native vessels. Two segmented polyurethanes were synthesized using lysine (SPUUK) and ascorbic acid (SPUAA), and the resulting materials were used to create the intima and adventitia layers, respectively. In contrast, the media layer of the TVG was composed of a commercially available polyurethane, Pearlbond 703 EXP. For comparison purposes, single-layer vascular grafts (SVGs) from individual polyurethanes and a polyurethane blend (MVG) were made and tested similarly and evaluated according to the ISO 7198 standard. The TVG exhibited the highest circumferential tensile strength and longitudinal forces compared to single-layer vascular grafts of lower thicknesses made from the same polyurethanes. The TVG also showed higher suture and burst strength values than native vessels. The TVG withstood up to 2087 ± 139 mmHg and exhibited a compliance of 0.15 ± 0.1%/100 mmHg, while SPUUK SVGs showed a compliance of 5.21 ± 1.29%/100 mmHg, akin to coronary arteries but superior to the saphenous vein. An indirect cytocompatibility test using the MDA-MB-231 cell line showed 90 to 100% viability for all polyurethanes, surpassing the minimum 70% threshold needed for biomaterials deemed cytocompatibility. Despite the non-cytotoxic nature of the polyurethane extracts when grown directly on the surface, they displayed poor fibroblast adhesion, except for SPUUK. All vascular grafts showed hemolysis values under the permissible limit of 5% and longer coagulation times.

Keywords: biomedical applications; burst pressure; compliance; mechanical properties; roto-evaporation; vascular graft.

Scheme 1

Synthesis route for SPUUK and SPUAA.

Figure 1

(a) Process flowchart of “Roto-evaporation” to fabricate vascular grafts, (b) multilayer addition to obtain multilayer vascular grafts, (c) digital images measuring the diameter of different layers added and (d) three-layer vascular grafts (TVGs) demolded.

Figure 2

The fixtures for different mechanical tests of the tubular vascular grafts: (a) circumferential tensile strength; (b) longitudinal tensile strength; (c) burst strength in the custom-made equipment; and (d) suture retention strength.

Figure 3

FT-IR spectra (a) and Raman spectra (b) of SPUUK, Pearlbond 703 EXP and SPUAA.

Figure 4

Representative curves of the mechanical behavior of films, tubes, and rings under the tensile loading of SPUUK, Pearlbond 703 EXP, SPUAA, polymer blends (MVGs) and three-layer vascular graft (TVGs) for (a) films under uniaxial tensile loading, (b) tubes under longitudinal load, (c) rings under circumferential load and (d) the suture retention strength test.

Figure 5

(a) Change in external diameter (circumferential strain) as a function of internal pressure for SVG, MVG and TVG and (b) experimental and theoretical burst pressure estimated via a ring tensile test using the failure diameter and those reported for human carotid arteries and human saphenous veins.

Figure 6

(a) Compliance variation with pressure (50 to 150 mmHg) for single (SPUUK, Pearlbond 703 EXP, SPUAA, MVG) and three-layer vascular grafts (TVG). (b) Stiffness values obtained with Equation (6).

Figure 7

SEM micrographs of the cross-section of single-layer vascular grafts made from (a) SPUUK, (b) Pearlbond 703 EXP, (c) SPUAA and (d) MVG. (e) Three-layer vascular graft prepared with SPUUK, Pearlbond 703 EXP and SPUAA. (f) Cross-section of TVG after longitudinal testing, (g) circumferential testing and (h) the burst strength test. (i-Inner) The inner surface of the TVG based on SPUUK and (i-Outer) the outer surface based on SPUAA.

Figure 8

Viability of MDA-MB-231 cells upon exposure to extracts from the different polyurethanes. (a) CCK-8 and (b) crystal violet assay. (*) The values shown are the mean ± SD. A value of p-value < 0.05 was considered significant. (c) Confocal fluorescence micrographs of fibroblast L–929 cells 24 h after seeding onto selected films. Live cells (stained with calcein-AM) appear in green.

Figure 9

(a) Clotting time study on polyurethane films. A p-value < 0.05 was considered significant (*) and was found at 10, 20, 30 and 40 min between SPUUK and the other conditions. The results are normalized to the plastic control. The values shown are the mean ± SD. Experiments were repeated three times for three different donors, with n = 3 each time. (b) Hemolysis percentage of different polyurethanes.