Cryopreservation-induced changes in the mechanical properties of human saphenous vein grafts

This study investigates the effects of cryopreservation and thawing rate on the mechanical properties of human saphenous vein grafts (SVGs) used in vascular bypass procedures. Native, non-cryopreserved veins were compared with cryopreserved grafts thawed either slowly at 2-8 °C or quickly in a 37 °C water bath. Cryopreserved grafts were treated with dimethyl sulfoxide and hydroxyethyl starch, frozen using a controlled-rate protocol, and subsequently stored below -160 °C in liquid-nitrogen vapor. Inflation experiments were performed on 36 human SVG specimens (12 per group) to characterize the pressure-strain and stress-strain behavior under physiologically relevant loading conditions. All grafts exhibited the nonlinear and anisotropic mechanical response typical of vascular tissue. Cryopreservation caused a substantial reduction in wall thickness, approximately 50% compared to native veins, resulting in markedly higher stresses during pressurization. While circumferential mechanical behavior remained similar across all groups, significant changes were observed in the axial direction. Native veins showed a stiffer axial response and some samples shortened during pressurization, whereas cryopreserved grafts were axially more compliant and predominantly elongated under load. These findings suggest that cryopreservation alters the native anisotropic mechanical response of the venous wall. No statistically significant differences were identified between slowly and quickly thawed grafts in the majority of measured quantities. However, quickly thawed samples demonstrated greater variability in mechanical response, indicating lower reproducibility. The results suggest that cryopreservation has a much stronger influence on graft biomechanics than thawing rate itself. Clinically, the observed axial elongation of cryopreserved grafts indicates that graft prestretching during implantation may be beneficial to prevent undesirable deformation after exposure to arterial pressure.