Venkatasubramanian Ramji T, Grassl Erin D, Barocas Victor H, Lafontaine Daniel, Bischof John C
Department of Mechanical Engineering, University of Minnesota, Minneapolis, MN 55455, USA.
Ann Biomed Eng. 2006 May;34(5):823-32. doi: 10.1007/s10439-005-9044-x. Epub 2006 Apr 18.
Cryoplasty, a freezing therapy, is being used for the treatment of restenosis in peripheral arteries. In addition, cryo-preserved arteries are increasingly used in vascular grafts. While studies are being performed to establish the efficacy of such treatments, very little is known about the postcryosurgical or postcryo-preservation changes in mechanical properties of the arteries. Few studies have examined the effect of freezing in the absence of cryoprotective agents (CPAs), and the several studies done in the presence of CPAs have given mixed results. To examine this issue further, we froze pig femoral arteries in a controlled rate freezer, using an aluminum probe, both in the presence at (-80 degrees C to 1 degrees C/min) and absence (at -20 degrees C for 2 or 5 mins) of CPA and Fetal bovine serum (FBS). Following freezing, artery samples were subjected to uniaxial tensile testing. The weights of the tissue were measured before and after freezing. 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 cell viability, damage to extra cellular matrix (ECM), bulk redistribution of water, or changes in alignment caused by ice crystal growth. In the case of samples frozen in the absence of CPA or FBS, the results indicated a drastic reduction in weight of the tissue suggesting the importance of bulk water redistribution as one underlying mechanism. To further examine potential mechanisms, we subjected cryopreserved vessels to the same uniaxial tests. The extent of changes in mechanical properties and bulk water redistribution was greatly attenuated; reinforcing that water movement might play a role in the changes observed with freezing.
冷冻成形术，一种冷冻疗法，正被用于治疗外周动脉再狭窄。此外，冷冻保存的动脉越来越多地用于血管移植。虽然正在进行研究以确定此类治疗的疗效，但对于动脉冷冻手术后或冷冻保存后机械性能的变化却知之甚少。很少有研究在没有冷冻保护剂（CPA）的情况下检测冷冻的影响，而在有CPA存在的情况下进行的几项研究结果不一。为了进一步研究这个问题，我们使用铝探针在程序降温冷冻仪中冷冻猪股动脉，分别在有CPA和胎牛血清（FBS）（-80℃至1℃/分钟）以及没有CPA和FBS（-20℃ 2或5分钟）的情况下进行。冷冻后，对动脉样本进行单轴拉伸试验。在冷冻前后测量组织的重量。我们的结果表明，冷冻确实会对应力-应变特性产生影响，特别是在对应于生理条件的低应力区域。这种机械性能变化的机制可能包括平滑肌细胞活力的丧失、细胞外基质（ECM）的损伤、水的大量重新分布或冰晶生长引起的排列变化。对于在没有CPA或FBS的情况下冷冻的样本，结果表明组织重量急剧减少，这表明大量水的重新分布作为一种潜在机制的重要性。为了进一步研究潜在机制，我们对冷冻保存的血管进行了相同的单轴试验。机械性能和大量水重新分布的变化程度大大减弱；这进一步证明水的移动可能在冷冻观察到的变化中起作用。
