Meeting Abstract

P1.110  Thursday, Jan. 3  Don’t Freeze Your Tissues: Biomechanical Implications For Storage of Water Swollen Tissues SZARKO, M*; BERTRAM, J.E.A.; University of Calgary mjszarko@ucalgary.ca

General assumptions regarding freezing and thawing of articular cartilage suggest that its mechanical properties remain unchanged. Biomechanical protocols have thus allowed freezing for storage convenience. This study investigates freeze-thaw induced property changes for both low frequency (0-12.5 Hz) and high frequency (30-100 Hz) loading in osteochondral dowels stored at: +4, -20, -80, and -196 degrees C. Specimens were hydrated with PBS, brought to storage temperature, then rapidly thawed (35 degrees C) before testing at 22 degrees C. Mechanical testing consisted of non-destructive, low amplitude (0.05MPa) dynamic compression, comprising equal amplitude sine waves periodic in the time record. Compressive behaviours were calculated via Fast Fourier Transformed storage and loss moduli, from which complex modulus and phase angles were determined. Preliminary results reveal freeze-thaw treatment significantly increases the sample stiffness without affecting the fluid flow properties. Previous studies dismiss collagen alteration and proteoglycan (PG) extraction due to freeze-thaw treatment. An alternative hypothesis recalls the creation and propagation of ice in biological solutions. Planar ice growth within articular cartilage effuses solutes away from the ice interface. Freezing from the exterior to the centre of the sample, may exude positively charged solutes (Na+) towards areas in cartilage that possess the greatest proportion of PGs. This may result in an increased interaction with the positive solutes upon thawing, greatly affecting the swelling potential, disturbing equilibration, and possibly resulting in a stiffness increase. Any change in the mechanical properties may cause erroneous results when analyzing previously frozen samples.