Date of Award
Spring 2006
Document Type
Thesis - Restricted
Degree Name
Master of Science (MS)
Department
Biomedical Engineering
Abstract
Post mortem testing of human and animal tissue has considerable application to the study of biomechanics. Biological tissue, particularly of cadaveric origin, is difficult to obtain or may be irregularly supplied. When tissue becomes available it is common practice to freeze the tissue at temperatures between 0°C and -80°C until required for testing. More involved cryopreservation techniques have been developed and can be time-consuming and expensive, particularly those involving vascular tissue. A number of studies investigated effects of cryopreservation on mechanical properties of blood vessels. However, cryopreservation protocols were detailed and results were inconclusive. To our knowledge, the effect of low-temperature, long-term basic freezing storage on mechanical properties of blood vessels has yet to be determined. The purpose of this study was to determine the effect of commonly used frozen storage methodology on mechanical properties of arterial tissue. Porcine descending aorta specimens were used to accomplish this objective. Two long-term freezing groups (storage at -20°C and -80°C for 3 months) were compared to fresh, unfrozen arteries. Forty-six paired specimens were assigned to each test group. Specimens were longitudinally distracted under quasi-static loading to determine the effect of freezing on elastic, subcatastrophic [sic] failure, and catastrophic failure mechanics. To this end, the following parameters were computed: Young's modulus and stress, strain, and strain energy at subcatastrophic [sic] and ultimate failure. Light microscopy was used to histologically assess freezing effects on arterial wall structure. Motivation for characterizing failure mechanics of arterial specimens stems from clinical interest in blunt carotid artery injury. Blunt injuries to the human carotid artery often result in subcatastrophic [sic] failure, wherein the inner layer (intima) fails without complete vessel transection. Blunt carotid artery injury most commonly occurs during hyperextension and rotation of the head-neck complex, resulting in global or local stretch of the artery. Beyond physiologic strain levels, the intima may be susceptible to subfailure prior to catastrophic vessel failure. Mechanical properties of intimal layer failure may reveal the injury mechanism and associated risk factors necessary to clinically diagnose injury prior to onset of irreversible neurologic damage. Present results indicate that several blood vessel mechanical properties may be affected by basic frozen storage, including stress at subcastastrophic failure and ultimate failure, strain energy at subcastastrophic failure and ultimate failure, and Young's modulus. Parameters unaffected by freezing included strain at subcatastrophic failure and ultimate failure, and the ratios of subcatastrophic relative to ultimate failure stress, strain and strain energy. No major differences in the structural components of the aortic wall were observed between fresh and frozen groups. Based on these results, it can be concluded that basic frozen storage may affect some mechanical properties of blood vessels. Therefore, biomechanical testing of blood vessels should be undertaken with the vessel in the fresh state, or after more detailed cryopreservation protocols.
Recommended Citation
Stineman, Michael R., "Effects of Freezing on the Mechanical Properties of the Porcine Descending Aorta" (2006). Master's Theses (1922-2009) Access restricted to Marquette Campus. 4675.
https://epublications.marquette.edu/theses/4675