Effects of ROI positioning on the measurement of engineered muscle tissue contractility with an optical tracking method

Tissue engineering is a multidisciplinary approach focused on the development of innovative bioartificial substitutes for damaged organs and tissues, as the skeletal muscle one. Since the loss of muscle functionality occurs in several compromised conditions, it results crucial to measure the contractility of muscle engineered tissue for studying muscle functionality in physiological and pathological conditions. Within this context, first we designed and developed an innovative device for the in-vitro measurement of engineered skeletal muscle contractility, with the use of an optical tracking algorithm. The base concept of our contractility measurement was based on the deflection of one of the two pins, designed with specific dimensions and a controlled compliance, that are commonly used to fix the engineered construct. In this work, we focused on the evaluation of the errors introduced on the measurement of contractile force by moving the positioning of the Region of Interest (ROI) from the centre one. To this, to mimic the contractile kinetics of muscle engineered tissue, known displacements of 5 µm and 10 µm at a frequency of 10 Hz were imposed through a linear actuator at the end of the elastic pin, and the images were acquired through the use of a high frequency camera mounted on a stereomicroscope for post-processing correlation. The results pointed out that the errors introduced by moving the ROI were always lower than 4% both for the one relative to the centre position and the one relative to the other six ROIs. Higher values of the relative errors occurred for the lowest nominal displacements, thus indicating that for higher displacement the errors were less influent in the positioning of the ROI along the elastic pin for the measurement of the muscle contractility.