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Use of SHG Imaging and Elastography to Characterize Heterogeneities in Cartilage Mechanics
Itai Cohen, Assistant Professor of Physics, Cornell University.

The elastographic determination of depth dependent properties of articular cartilage is based on the application of a known uniform stress state and observation of a non-uniform strain field. By staining cells or nuclei with fluorescent dyes, these structures can be used as fiduciary markers to map local strain fields (Schniagl et al, 1996). Such techniques have been successful in determining depth dependent moduli, electromechanical properties and the effects of disease (Chen et al, 2001) in cartilage. While these efforts have been quite successful, all studies to date have focused on equilibrium compressive properties, with no data on depth and frequency dependent shear properties. To address the limitations of existing techniques, we will construct oscillatory shear, compression and indentation apparatuses that mount on a high speed multiphoton imaging system, so that we can simultaneously measure applied stresses while imaging 3-D tissue microstructure over physiologically relevant frequencies. Dr. Cohen is an expert in fabricating micro-shear/stress apparatuses and using high speed imaging to collect the data (Cohen et al, 2006). The objective of this project is to apply high speed SHG microscopy to determine the local dynamic shear and compression properties as well as the dynamic changes in the local structure and alignment properties of collagen in cartilage. The shear apparatus will be mounted on the microscope, and using combined high speed SHG imaging during application of the calibrated displacement and shear stress will allow us to determine the local dynamic shear and compression properties of the cartilage. Physiological time scales of cartilage motion are 1 – 20 Hz and fast imaging (>30 frames per sec) is required . The ability to directly image collagen will allow us to quantify the role played by the collagen network in creating the depth dependent dynamic shear properties we measure, and lead to a more thorough understanding of dynamic biomechanical functioning of normal tissue, providing benchmarks and design input for efforts to replace or regenerate tissue.

References

Cohen I, Davidovitch B, Schofield A, Brenner M, and Weitz DA 2006. Slip, Yield and Bands in Colloidal Crystals under Oscillatory Shear. Phys. Rev. Lett. 97, 215502.

Chen AC, Bae WC, Schinagl RM, Sah RL. 2001. Depth- and strain-dependent mechanical and electromechanical properties of full-thickness bovine articular cartilage in confined compression. J Biomech. 34(1):1-12.

Schinagl RM, Gurskis D, Chen AC, Sah RL. 1997. Depth-dependent confined compression modulus of full-thickness bovine articular cartilage. J Orthop Res. 15(4):499-506.

 

 

 

 

 



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