Nondestructive method to evaluate the collagen content of fibrin-based tissue engineered structures via ultrasound

In the field of tissue engineering, there is a growing need for quantitative methods to analyze in situ and in real time the tissue development in three-dimensional scaffolds. To evaluate the performance of cell-gel constructs in terms of extracellular matrix synthesis, we are still restricted to time-consuming histological and biochemical assays that are not able, as a destructive method, to monitor the tissue formation online. Ultrasound is a well-known noninvasive and nondestructive imaging method. Therefore, the potential of ultrasound for the quantitative in vitro evaluation of tissue development in fibrin-based tissue-engineered structures was evaluated in this study. As simplified parameter, the gray-scale values of ultrasound scans of cell-embedded fibrin gels were correlated with the hydroxyproline content and the histological and immunohistological images of the same gels at different culturing time points. The gray-scale value of the ultrasound demonstrated a good correlation with the hydroxyproline content (Pearson correlation coefficient of 0.98) as marker of collagen formation and with the histological findings. In conclusion, the described simple ultrasound method is a good tool to evaluate the collagen formation of fibrin-based tissue-engineered constructs and facilitates the broad use to monitor tissue development and remodeling in bioreactor systems.