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High frequency ultrasound spectroscopy of cartilage

Tissue engineering (TE) of articular cartilage is a challenging task in the field of regenerative medicine, because articular cartilage defects do not heal spontaneously. Up to now, however, the pathway of the structural re-organization following an injury remains unclear. Re-organization starts from blood clot formation through fibrous tissue and hyaline like cartilage tissues to a highly organized native cartilage structure. Knowledge about mechanical as well as biological conditions that influence the tissue properties is limited.

Therefore a noninvasive tool that allows the monitoring of the progression of tissue synthesis inside the culture chamber would be invaluable to control and to optimize the tissue engineering process. High frequency Ultrasound BioMicroscopy (UBM) is a potential candidate to fulfill this task, as it i) can propagate sound waves though the culture chamber into the culture medium and the scaffold without the risk of contamination, ii) can provide sufficient penetration and spatial resolution to visualize the internal structure of the scaffold, and iii) is in principle possible to deduce quantitative elastic and structural information from sound propagation velocity and spectral analysis of the backscattered signals, respectively.

However, currently the application of ultrasound for the characterization of articular and TE cartilage is restricted to the quantitative evaluation of tissue thickness and the surface reflection. We have shown that in addition to morphological information obtained by the ultrasound image spectral analysis of the backscattered signals reveals additional ultrastructural information that is related to size, shape and distribution of chondrocytes and to the orientation of collagen fibers. In particular, spectral ultrasound parameters can be used to distinguish neocartilage from the scaffold and hyaline cartilage from fibrocartilaginous repair tissue (Gelse et al. 2010). UBM can be used to monitor and categorize the progression of cartilage degeneration (Männicke et al. 2014a, Männicke et al 2014b, Schöne et al. 2013).