Noninvasive Measurement of Ear Cartilage Elasticity on the Cellular Level: A New Method to Provide Biomechanical Information for Tissue Engineering

Background: An important feature of auricular cartilage is its stiffness. To tissue engineer new cartilage, we need objective tools to provide us with the essential biomechanical information to mimic optimal conditions for chondrogenesis and extracellular matrix (ECM) development. In this study, we used an optomechanical sensor to investigate the elasticity of auricular cartilage ECM and tested whether sensitivity and measurement reproducibility of the sensor would be sufficient to accurately detect (subtle) differences in matrix compositions in healthy, diseased, or regenerated cartilage. Methods: As a surrogate model to different cartilage ECM compositions, goat ears (n = 9) were subjected to different degradation processes to remove the matrix components elastin and glycosaminoglycans. Individual ear samples were cut and divided into 3 groups. Group 1 served as control and was measured within 2 hours after animal death and at 24 and 48 hours, and groups 2 and 3 were measured after 24- and 48-h hyaluronidase or elastase digestion. Per sample, 9 consecutive measurements were taken +/- 300 mu m apart. Results: Good reproducibility was seen between consecutive measurements with an overall interclass correlation coefficient average of 0.9 (0.81-0.98). Although degradation led to variable results, overall, a significant difference was seen between treatment groups after 48 hours (control, 4.2 MPa [+/- 0.5] vs hyaluronidase, 2.0 MPa [+/- 0.3], and elastase, 3.0 MPa [+/- 0.4]; both P < 0.001). Conclusions: The optomechanical sensor system we used provided a fast and reliable method to perform measurements of cartilage ECM in a reverse tissue-engineering model. In future applications, this method seems feasible for the monitoring of changes in stiffness during the development of tissue-engineered auricular cartilage.