Rheological properties of fresh and cryopreserved human arteries tested invitro

Cryopreservation is widely used to preserve blood vessels for a while but i s controversially suspected to affect the mechanical behavior of these allo grafts. The aim of this study was to determine whether differences in the t hree-dimensional mechanical behavior exist or not between fresh and cryopre served arteries. Using a previously developed experimental system, in vitro inflation tests were performed on twenty segments of human fresh and cryop reserved arteries, in static conditions. Opening angles were also measured from images of rings in zero-stress state. The initial reference state was chosen as the unloaded state and tests were performed on specimens stretche d at natural "in vivo" length. Mechanical measures calculated are "natural" (Hencky) strains (finite deformations), "true" (Cauchy) stresses in radial , circumferential, and longitudinal directions as well as strain energy per unit volume. Tangent moduli are derived from radial and circumferential st ress-strain characteristics using non-linear curve fitting. Values of incre mental and pressure-strain elastic parameters, wall stiffness, and complian ce per unit length are also calculated. Results are presented in terms of c haracteristics of stresses and strains in the three directions, axial force , tangent moduli vs strains or stresses, and energy per unit volume, for bo th types of artery, with reference to transmural pressure. Detailed numeric al results are given at mean transmural pressure or in the physiological ra nge. Significant differences are indicated by statistic Student T-tests. Re sults obtained show that significant differences exist between rheological properties of fresh and cryopreserved segments of human artery. Strains, st resses, axial force, strain energy, and wall stiffness values highlight tho se differences whereas elastic parameters, compliance, and opening angle do not. The usefulness of some parameters to compare the mechanical behavior existing between fresh and cryopreserved arteries is therefore underlined.