Soft microfingers with flexible tactile sensor using liquid metal for in situ evaluation of cellular spheroid...

Inflatable soft microfingers integrated with liquid metal strain gauge sensors have been developed for the in situ evaluation of cellular spheroid stiffness. Cellular spheroids ranging from several hundred micrometers to a few millimeters in diameter, typical three-dimensional cellular aggregates, have been used as biological models. Cellular spheroids are evaluated using various methods, of which microscopic imaging is the most popular. This study focuses on mechanical characteristics, such as stiffness, related to the internal structure of cellular spheroids and reports an evaluation device for in situ stiffness measurement in pinching cellular spheroids. We demonstrated microfingers that pinch cellular spheroids and evaluated cellular spheroid stiffness so that different cellular spheroids (C3H10T1/2 and NIH3T3) could be compared and distinguished by their stiffness. Two microfingers (3.6 mm × 1.2 mm × 380 μm) made of polydimethylsiloxane are implemented for gentle pinching of an object. Flexible liquid-metal strain gauges were integrated into individual microfingers for stiffness evaluation while pinching an object without compromising the soft features of the microfingers. Our results demonstrate the potential of soft microfingers as an in-situ evaluation tool for cellular spheroids, which are anticipated to be an alternative biological model for various applications, such as drug screening.