Effects of Freezing on the Mechanical Properties of Blood Vessels

The mechanical properties of blood vessels are important to their ability to function properly. The effects of freezing/cooling on the mechanical properties are a concern for several reasons including preservation of vascular grafts, appropriate storage of samples prior to mechanical testing, and the effects and mechanisms of cryoplasty (cryotherapy for treatment of restenosis). Many have studied the effects of freezing vessels in the presence of cryoprotective agents (CPAs), and the results are mixed, depending on the type of artery and particular mechanical test. The few studies on freezing without CPAs have also given mixed results. To examine this issue further, we froze pig femoral arteries to −20 C in the absence of CPA, and then subjected them to uniaxial tensile testing. Our results suggest that freezing does have an effect on stress-strain properties, particularly in the low stress region corresponding to physiological conditions. The mechanisms of this change in mechanical properties may include the loss of smooth muscle viability, damage to extracellular matrix (ECM), or changes in alignment caused by ice crystal growth. Understanding these changes is important in understanding the mechanisms of cryoplasty, as well as choosing appropriate storage methods for tissues to be used in vascular grafts.