Study on robot-assisted microinjections on zebrafish embryos

: micro force measurement and control

Abstract

Microinjecting microliters of genetic material into zebrafish embryos is a standard procedure used for analyzing vertebrate embryonic development and the pathogenic mechanisms of human disease and drug discovery. The conventional manual microinjection is labor-intensive and lacks reproducibility. This study confirms that robot-assisted microinjection is precise and productive, and thus benefits the biological community. This thesis addresses three related topics in robot-assisted microinjection. The first is the design and implementation of a micro force sensor for cellular force measurement in the embryo injection process. The proposed piezoelectric force sensor is based on a simply supported beam structure. The mechano-electrical transduction of the piezoelectric material--polyvinylidene fluoride (PVDF) film--is derived theoretically, followed by establishment of the analytical expression of the relationship between penetration force and sensor output. The second topic addressed is force control of the robot-assisted injection system that interacts with zebrafish embryos. Using the micro force sensor, a novel adaptive forcetracking control algorithm is developed to regulate the needle injection force applied to the cell. The algorithm is designed first for time-varying ramp force tracking, in the form of adaptive impedance force control. This is a linear control algorithm, modeling the cell membrane as a spring. Some existing impedance-based interaction force control approaches require the desired force signal to be constant; however, the proposed force control algorithm allows the desired force for injection to be a time-varying ramp signal, which makes the proposed method more suitable to cell injection. Furthermore, the algorithm is improved so that it can be applied more broadly, with two control loops. The inner loop is an impedance control used to specify the interaction between the needle and the cell. The outer loop is a force-tracking nonlinear controller using feedback linearization. This improved algorithm provides a universal solution for various types of cell models. An online least-square parameter estimator is used to deal with the cell stiffness time-varying problem. With the proposed force control approach, penetration force can be regulated to follow a wide class of force trajectory during cell injection. The third topic of this thesis involves biological application; in particular, it focuses on transmitting the human skills of the trained operator to a robot-assisted microinjection system. After theoretical and experimental analysis of data collected during manual injection by the human expert, the expert force trajectory can be obtained. By learning these data, the robot-assisted microinjection system can use the adaptive force control algorithm to mimic and repeat microinjections like trained personnel. Considerable experimental tests have been performed to verify the effectiveness of the proposed approach. The proposed force measurement and control methodologies have potential not only in inserting genetic material into zebrafish embryos, but also in general biomanipulation. The research results will eventually benefit the biotechnology industry and release people from laborious work.

Date of Award	15 Jul 2010
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Dong SUN (Supervisor)