Apparatus and Method for Rapid Detection of Acoustic Anisotropy in Cartilage

Purpose Articular cartilage is known to be mechanically anisotropic. In this paper, the acoustic anisotropy of bovine articular cartilage and the effects of freeze-thaw cycling on acoustic anisotropy were investigated. Methods We developed apparatus and methods that use a magnetic L-shaped sample holder, which allowed minimal handling of a tissue, reduced the number of measurements compared to previous studies, and produced highly reproducible results. Results SOS was greater in the direction perpendicular to the articular surface compared to the direction parallel to the articular surface (N = 17, P = 0.00001). Average SOS was 1,758 +/- 107 m/s perpendicular to the surface, and 1,617 +/- 55 m/s parallel to it. The average percentage difference in SOS between the perpendicular and parallel directions was 8.2% (95% CI 5.4% to 11%). Freeze-thaw cycling did not have a significant effect on SOS (P > 0.4). Conclusion Acoustic measurement of tissue properties is particularly attractive for work in our laboratory since it has the potential for nondestructive characterization of the properties of developing engineered cartilage. Our approach allowed us to observe acoustic anisotropy of articular cartilage rapidly and reproducibly. This property was not significantly affected by freeze-thawing of the tissue samples, making cryopreservation practical for these assays.