Changes in the mechanical and biochemical properties of aortic tissue due to cold storage.

BACKGROUND Temporary cold storage is a common procedure for preserving tissues for a short time before using them in a clinical or experimental setting. The process of storing tissues at refrigeration or freezing temperatures can affect the mechanical properties of the tissue. Previous studies were limited to uniaxial tensile tests and did not have substantial explanations for what was structurally occurring in the tissue to account for the changes in mechanical properties. MATERIALS AND METHODS This study involved biaxial tensile testing of bovine thoracic aortas that had been stored at common storage temperatures (4°C, -20°C, or -80°C) for three different time points (48 h, 1 wk, or 3 wk). The slopes of the initial and stiff region of the stress-strain curves were measured. The knee point of the stress-strain curves was also determined. Collagen content before and after storage was quantified using a Sircol collagen assay kit. RESULTS The stored arteries showed decreased initial slope and increased stiff slope after 48 h of 4°C refrigeration. The -20°C and -80°C storage conditions had similar initial slopes compared with the fresh ones but an increase in the stiff slope. There was also a significant shift of the knee point to a higher strain and stress. The soluble and insoluble collagen content decreased significantly due to storage but the percentage of cross-linked collagen was unchanged. CONCLUSIONS Cold storage causes several changes in the mechanical properties due to structural and biochemical changes in the tissue. Overall, freezing protocols (either -20°C or -80°C) are suggested over refrigeration (4°C) for maintaining the initial stress-strain behavior.