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|Title: ||Force characterization and motion planning in automated cell manipulation by optical tweezers|
|Other Titles: ||Guang nie zai sheng wu xi bao zi dong hua cao zuo zhong de li xue biao ding he yun dong gui hua|
|Authors: ||Wu, Yanhua ( 吳燕華)|
|Department: ||Department of Manufacturing Engineering and Engineering Management|
|Degree: ||Doctor of Philosophy|
|Issue Date: ||2011|
|Publisher: ||City University of Hong Kong|
|Subjects: ||Optical tweezers.|
Cytology -- Technique.
|Notes: ||CityU Call Number: TK8360.O69 W8 2011|
ix, 95 leaves : ill. 30 cm.
Thesis (Ph.D.)--City University of Hong Kong, 2011.
Includes bibliographical references (leaves 84-94)
|Abstract: ||Optical tweezers, which are based on the transfer of photon momentum, can trap
and move microscale and nanoscale particles without physical contact. Rapid and
precise transportation of live cells can benefit cell microsurgery, rare cell isolation,
tissue engineering and cell-to-cell interactions. Increasing demands for both accuracy
and efficiency in biological cell manipulation highlight the need for automation with
robotics technology. Understanding the forces exerted on live cells is essential to
biomechanical characterization and cell manipulation. However, traditional numerical
force measurement assumes live cells to be ideal objects, ignoring their complicated
inner structures and rough membranes. Furthermore, little reported research has
specifically considered the synergy of dynamic analysis in motion planning during
automated transportation. The problem of planning cell motion with optimized motion
parameters, using cell dynamics analysis, is still very challenging.
This thesis aims to characterize the mechanical forces applied to live cells in optical
traps, and use the mechanical parameters thus obtained to plan cell motion during
automated transportation. The research principally consists of the following three
First, the forces applied to live cells are calibrated by a novel static
viscous-drag-force method. Unlike existing approaches, the proposed method does
not assume the live cells to share the same optical and/or drag parameters as those of
polystyrene/silica beads. By binding a micro polystyrene sphere to the live cell and
moving the mixture with optical tweezers, the drag force on the cell can be obtained
by subtracting the drag force on the sphere from the total drag force on the mixture,
under the condition of an extremely low Reynolds number. The trapping force on the
cell is then obtained from the drag force when the cell is in the force equilibrium state.
Second, motion planning strategy, which is designed using dynamics analysis of the optically trapped cell, is used to determine the ideal movement velocity of the cell.
Due to property changes in the aqueous medium and laser during cell transportation,
the calibrated dynamic parameters may vary, and thus, the cell movement velocity
designed using these parameters should be adjusted online. A proportional-integral (PI)
scheme is used to adjust the cell movement velocity online, to ensure that the cell
moves at an ideal speed and does not escape from the laser focus. Dynamics analysis
results are used to design the PI scheme.
Third, an optimal path for cell movement is planned, using a modified A-star
algorithm, which introduces an additional cost to penalize waypoints where the
direction of movement changes. The algorithm balances smoothness and movement
cost. Finally, experiments on moving yeast cells are conducted to demonstrate the
effectiveness of the proposed approach.
The main contribution of this study lies in the development of a new experimental
method to characterize the mechanical forces exerted on live cells, and the application
of the dynamic analysis results to motion planning for automated cell transportation.|
|Online Catalog Link: ||http://lib.cityu.edu.hk/record=b4086943|
|Appears in Collections:||MEEM - Doctor of Philosophy |
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