Design and Testing of a New Microinjector With Capacitive Force Sensor for Biological Microinjection

Microinjection with force sensing plays an important role in delivering foreign materials into biological entities. In this paper, a new force-sensing microinjector with compliant mechanism is presented. It provides a high sensitivity of force sensing by offering a small stiffness in the direction of microinjection. Meanwhile, it enables a sufficient load-bearing capability thanks to a large stiffness in the lateral direction. The small stiffness is realized by the combination of a positive-stiffness mechanism and a negative-stiffness mechanism, rather than a zero-stiffness mechanism. A custom-made capacitive force sensor based on tilted micropillar array is introduced to measure the microinjection force based on the microinjector’s output displacement. Moreover, a prototype has been fabricated for experimental testing. Experimental results show that the sensitivity of the proposed design has been improved by two-fold over previous work. The developed microinjector has been applied to successfully detect the microinjection force during the injection of zebrafish larvae, which renders a promising solution for regulating the microinjection force. Note to Practitioners —Force-assisted microinjection can provide force feedback, which is desirable to protect biological samples from excessive force and to judge successful penetration. Currently, most existing force sensor-based microinjectors can only puncture biological samples, rather than injecting materials, mainly due to the inability of bearing the weight of linker for the injection needle and actuator. In this work, a new microinjector with capacitive force sensor is presented for microinjection of zebrafish larvae. Based on the combination of a positive-stiffness mechanism and a negative-stiffness mechanism, a small-stiffness mechanism is introduced to design the microinjector. It simultaneously provides large axial sensitivity and large lateral loading ability. Moreover, a capacitive force sensor based on tilted micropillar array is devised to measure the microinjection force based on the overall displacement of the microinjector. For fixing zebrafhish larvae, a micro-array petri dish is fabricated by silicon wafer mould. Experimental results show that the microinjector is capable of delivering foreign materials and detecting the microinjection force, which is beneficial to the microinjection operation.