Acousto-optical characterization of the viscoelastic nature of a nuchal elastin tissue scaffold

A nondestructive, acousto-optical method for characterizing the mechanical loss factor of biological tissues and tissue scaffolds is presented and applied to the characterization of an elastin tissue scaffold derived from bovine nuchal ligament. The method relies on launching guided surface acoustic waves into the tissue scaffold with a small speaker and simultaneously illuminating a small region of the scaffold distant from the speaker with a low-power HeNe laser. The phase lag between the driving acoustic wave and the shift in the backscattered laser speckle pattern is determined as a measure of the mechanical loss factor of the scaffold, tan delta. Measurements of tan delta and elastic modulus were also made by traditional dynamic mechanical loading techniques. Through the central portion of the loading cycle, the elastic modulus of the elastin scaffold was 1.2 x 10(6) +/- 1 x 10(5) N x m(-2) (parallel to fiber orientation). The estimated value of tan delta in the direction parallel to the elastin fibers was 0.03 +/- 0.017 by traditional methods and 0.029 +/- 0.03 when using the acousto-optical method. In the direction perpendicular to fiber orientation, tan delta was measured as 0.14 +/- 0.056 by the acousto-optical method. Because of a lack of mechanical integrity, it was not possible to measure tan delta in the direction perpendicular to fiber orientation by traditional methods. The acousto-optical method may prove to be useful in the mechanical characterization of developing engineered tissues.