Direct measurement of cell protrusion force utilizing a robot-aided cell manipulation system with optical tweezers for cell migration control

Xue Gou, Hao Yang, Tarek M Fahmy, Yong Wang, Dong Sun

Cell migration refers to the directional cell movement in response to a chemoattractant gradient, a key process that occurs in a wide variety of biological phenomena. Cell protrusion force is generated by the actin polymerization of a cell, which drives the cell to move toward the stimulus as induced by the chemoattractant gradient. This paper presents a new methodology for the direct measurement of cell protrusion force utilizing a robot-aided optical tweezer system. The functionalized beads that are robotically trapped and placed near the cell serve as both cell migration stimulators and protrusion force probes. The force generated by the actin polymerization of the cell propels the bead to move away from the trapping center when the cell comes in contact with the bead. Such a deviation can be determined and used to calculate the trapping force, which is equal to the protrusion force at a balanced position. With the quantitative measurement of the protrusion, we find that the protrusion force of a live cell in response to a chemoattractant within the range of hundreds of piconewtons. We further probe the protrusion force distribution at the cell leading edge and find that the highest protrusion force appears at the cell migration direction. These measurements can help us characterize the mechanism of cell migration and lay a solid foundation for further proactive control of cell movement.

DOI

Indirect pushing based automated micromanipulation of biological cells using optical tweezers

Atul Thakur, Sagar Chowdhury, Petr Švec, Chenlu Wang, Wolfgang Losert, Satyandra K. Gupta

In this paper, we introduce an indirect pushing based technique for automated micromanipulation of biological cells. In indirect pushing, an optically trapped glass bead pushes a freely diffusing intermediate bead that in turn pushes a freely diffusing target cell towards a desired goal. Some cells can undergo significant changes in their behaviors as a result of direct exposure to a laser beam. Indirect pushing eliminates this problem by minimizing the exposure of the cell to the laser beam. We report an automated feedback planning algorithm that combines three motion maneuvers, namely, push, align, and backup for micromanipulation of cells. We have developed a dynamics based simulation model of indirect pushing dynamics and also identified parameters of measurement noise using physical experiments. We present an optimization-based approach for automated tuning of planner parameters to enhance its robustness. Finally, we have tested the developed planner using our optical tweezers physical setup and carried out a detailed analysis of the experimental results. The developed approach can be utilized in biological experiments for studying collective cell migration by accurately arranging the cells in arrays without exposing them to a laser beam.

DOI