Towards automatic batch biomanipulation

: study on robotic suspended cell injection system

Abstract

Biological cell injection has been widely applied in gene injection, in-vitro fertilization, intracytoplasmic sperm injection and drug development. The cells injected in biotechnology are classified as either adherent or suspended cells, corresponding to two distinct biomanipulation tasks. Currently, commercial devices are available for automation of adherent cell injection tasks. In contrast, development of methodologies for injection of suspended cells, has been the focus of many research groups. In this study, a cell injection system for automatic batch injection of suspended cells is developed. The suspended cells are held and fixed to a cell array by a specially designed cell holding device, which enables automatic injection of batch of suspended cells. Starting from image identifying the embryos and injector pipette, a proper batch cell injection process, including the injection trajectory of the pipette, is designed for this automatic suspended cell injection system. Based on those preparative works, two kinds of methodologies were developed to enhance the performance of cell injection. The first methodology is to regulate cell injection forces using geometry of cell deformations and micro vision feedback. The microscope vision system, which is already present in the biomanipulation system, is utilized to measure cell deformations, further to estimate the cell injection forces, based on a cell biomembrane point-load model. In outof- plane injection process, the total cell membrane deformation is estimated, based on the X −Y coordinate frame deformation of the cell, as measured with microscope, and the known angle between the injector and the X −Y plane. Further, a relationship between the injection force and the injector displacement of the cell membrane, as observed with the camera, is derived. Based on this visual force estimation scheme, an impedance injection force controller is developed to control the injection process. Although this visual-based force control method only utilizes the microscope for not adding complexity to this system, the limitation of the proposed approach is that the injector can only be imaged from above in depth direction, and hence the actual penetration distance into the cell, depending on the vertical position of the injector with respect to the insertion point on the cell, cannot be known. To solve this problem, in the second method, it is demonstrated that the motion of the injector pipette can be controlled through integration of a polyvinylidene fluoride (PVDF) film micro force sensor installed on the injection pipette to the visual control system. This force sensor is utilized to measure the real time injection force applied to the cells with a sensitivity of 0.1901mV /μN . The out-of-plane cell injection task can be decoupled into two relatively independent control processes: the position control in the X −Y horizontal plane and the impedance control in Z − axis. In X −Y plane, a computed torque based position control with visual feedback is used. The purpose is to accurately control the injector pipette to follow the desired injection trajectory in X −Y plane. Based on the measured injector position in X −Y plane and the calibrated relationship between the injection trajectory and force, the desired injection force in Z − axis at the moment can be determined according to the available cell deformation in X −Y plane. Utilizing this desired force, an impedance control algorithm is developed to control the injection force to follow the desired value and thus indirectly control the depth motion of the injector pipette in Z − axis. This research provides a systematic solution for automation of batch suspended cell injection. The proposed visual control methodologies have potential prospects not only in inserting genetic materials into embryos, but also in general biomanipulation tasks. The research outputs will eventually benefit the biotechnology industry and release people from laborious works.

Date of Award	15 Jul 2008
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Dong SUN (Supervisor)