Meeting Abstract

25.9  Jan. 5  Freeze-Thaw Treatment Alters Articular Cartilage Dynamic Behaviour SZARKO, M.J.**; BERTRAM, J.E.A.; University of Calgary; University of Calgary mjszarko@ucalgary.ca

Recent development of new procedures aiming to combat osteoarthritis has placed an importance on articular cartilage for tissue transplant. The general assumption of freezing not altering the mechanical properties of cartilage has caused many protocols to involve freezing for storage convenience. However, evidence for this is derived from loading at relatively low loading rates. In this study we investigate mechanical property changes induced by the freeze-thaw process for both near-static (0-25 Hz) and dynamic (10-119 Hz) loading. Effects of different freezing protocols are also assessed. Osteochondral dowels (8mm dia.) from mature bovine tibiae were harvested and split into four freezing temperature groups: 4, -20, -80, and -196 degrees C. Specimens were hydrated with PBS, brought to storage temperature, then thawed (4 degrees C) before testing at 22 degrees C. Two spectra of compressive loading rates (0-200 Hz and 0-25 Hz) were applied as a sinusoid. Waveform frequencies utilized a �chirp� function, comprising equal amplitude sine waves periodic in the time record over the full frequency spectrum. Loading was non-destructive and low amplitude (0.1 MPa). Complex moduli were determined from storage and loss moduli generated from transducer and force beam comparisons and were used to characterize the material behaviour. Freezing of articular cartilage does indeed produce a difference in material behaviour, most evident at higher loading rates. Frozen samples were significantly more elastic, having lost much of the viscous material properties inherent in fresh articular cartilage. This change in material properties may cause erroneous approximations between the biomechanical behaviours of frozen and in vivo articular cartilage.