Stress analysis of the circumferential and burst strength test in small diameter vascular grafts of segmented polyurethanes based on amino acids of L-arginine and L-lysine

Abstract

Event Abstract Back to Event Stress analysis of the circumferential and burst strength test in small diameter vascular grafts of segmented polyurethanes based on amino acids of L-arginine and L-lysine Omar Castillo1, Cesar Pérez-Aranda1, 2, Francis Avilés1, Juan Cauich-Rodríguez1 and Diego Mantovani3 1 Centro de Investigación Científica de Yucatán, A.C., Unidad de Materiales, Mexico 2 Universidad Autónoma de Yucatán, Facultad de Ingeniería, Mexico 3 Laval University, Dept. of Min-Met-Materials Engineering & CHU de Quebec Research Center, Canada Introduction: Despite the increasing incidence of cardiovascular diseases (CVD), only few biomaterials are commercially available for small diameter vascular grafts (SDVG) (<6 mm)[1]. The dynamic mechanical environment provided by blood vessels creates a complicated sequence of events in which the walls are stretched and the inner lumen is sheared. Changes of mechanical characteristics at the interface between host artery and vascular graft (VG) leads to weakening of the artery wall, loss of endothelial cell (EC) viability, and dilatation of the surgical connection, known as anastomotic aneurysm[2]. Dacron and ePTFE are widely used for big caliber VG but they have unacceptable performance in SDVG[3],[4]. In this regard, segmented polyurethanes (SPUs) are promising candidates not only due to their excellent mechanical properties and good biocompatibility but also given that they can be tailored to specific needs[5]-[7]. Recently, our group demonstrated that the use of SPUs based on amino acid promotes the growth of EC[8]. In this study we analyze the stress distributions existent in the circumferential tensile strength (CTS) and burst strength (BS) tests of SDVG prepared with SPUs based on L-arginine (R) and L-lysine (K). For this, theory of curved beams and pressurized cylinders were applied. Materials and Methods: SPUs were synthesized by the reaction of poly (ε-caprolactone) diol with an excess of 4,4’-methylene-bis-cyclohexyl diisocyanate and then chain extended with either R or K. SDVG were obtained by wrapping a SPUs film around a mandrel, diameter = 5.5 mm. CTS and BS tests were conducted according to ISO 7198 and analysed using the elasticity solutions for curved beam and theory of thick wall cylinders under pressure[9]-[10]. Tecoflex™ was used as reference. Results and Discussions: During CTS test three stresses are generated i.e. circumferential (σϴCTS), radial (σrCTS) and shear (τϴrCTS) as shown in Figures 1a and 1b. At point a and b, τϴrCTS is significant while σϴCTS and σrCTS are negligible. In c and d, τϴrCTS is negligible while σϴCTS and σrCTS are significant, as shown in Figures 1c and 1d. Therefore, CTS test can be considered as an uniaxial pure stress state because σϴCTS is predominant over σrCTS and τϴrCTS. SPUK exhibited lower CTS. During BS test two stresses are generated i.e. tangential (σtBS) and radial (σrBS), Figures 2a and 2b. σtBS is maximum at the inner surface and σrBS is zero at the outer surface. σrBS is maximum at the inner surface and equals the applied pressure (-Pi)[10], Figure 2c. SPUR and SPUK have similar σtBS. Conclusions: SDVG from SPUK and SPUR were tested under CTS and BS and analyzed with elasticity solutions for curved beams and pressurized cylinders. We consider this stress analysis as an innovative contribution for SDVG because ISO 7198 does not include this analysis. O. Castillo-Cruz was awarded of a Government of Canada ELAP Mobility Scholarship; This work was partially funded by CONACYT project No. 220513; NSERC-Canada, CFI-Canada.