Robotic Intracellular Manipulation and Measurement with Multi-Pole Magnetic Tweezers

Wang, Xian (1,2); Tsatskis, Yonit (3); Hopyan, Sevan (4); McNeill, Helen (3); Sun, Yu (1,2)

  1. Institute of Biomaterials and Biomedical, University of Toronto

  2. Department of Mechanical and Industrial Engineering, University of Toronto

  3. Lunenfeld-Tanenbaum Research Institute

  4. Mt. Sinai Hospital Program in Developmental and Stem Cell Biology, The Hospital for Sick Children

The capability to directly interrogate intracellular structures inside a single cell for measurement and manipulation has significant implications in the understanding of subcellular and sub-organelle activities, diagnosing diseases, and developing new therapeutic approaches. Compared to measurements of single cells, physical measurement and manipulation of sub-cellular structures and organelles remain underexplored. To spearhead an exciting new era of intracellular physical measurement and manipulation, we have developed a multi-pole magnetic tweezers system for micromanipulation involving sub-micrometer position control and picoNewton force control of a sub-micron magnetic bead inside a single cell for measurement on different locations (spatial) and different time points (temporal). The bead was three-dimensionally positioned in the cell using a generalized predictive controller that tackles the control challenge caused by the low bandwidth of visual feedback from high-resolution confocal imaging. The average positioning error was quantified to be 0.4 µm, slightly larger than Brownian motion-imposed constraint (0.31 µm, 1 µm = 〖10〗^(-6) m). The system is also capable of applying a force up to 60 pN with a resolution of 4 pN (1 pN = 〖10〗^(-12) N) for a period of time longer than 30 mins. The measurement results revealed significantly higher stiffness exists in the nucleus’ major axis than in the minor axis. This stiffness polarity is likely attributed to the aligned actin filament. We also proved that the nucleus stiffens upon the application of an intracellularly applied force, which can be attributed to the response of structural protein lamin A/C and the intracellular stress fiber actin filaments.  

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