153
Biomechanical Characterization of Human Red Blood Cells
As stated above, the force–deformation relationship is determined when the
area compressibility modulus k and the shear modulus μ are given in Equation
(8.3). Different mechanical properties lead to different force–deformation
curves. By minimizing the deviation between the modeling results and the
experimental data, the biomechanical properties of RBCs can be characterized.
8.3 Cell Manipulation with Optical Tweezers
To study the cell mechanics of human RBCs, experiments of robotic cell
manipulation with optical tweezers were conducted. Human RBCs are
stretched at different levels of trapping forces. Through force calibrations
and image processing, the relationship between the stretching forces and the
induced deformations is established, from which the mechanical properties
of RBCs can be characterized based on the cell mechanical model.
8.3.1 Optical Tweezer System
Figure 8.3 shows a schematic diagram of our optical tweezer system, which
mainly consists of a single laser trap. The 808-nm diode laser source has a
maximum power of 2.0 W. The laser beam is reflected by a dichroic mirror into a 40× objective and focused on the observation plane. To minimize
the possible optical damage to living cells, the laser beam is focused on the
attached polystyrene beads instead of RBCs. The biological sample is placed
on a two-dimensional motorized stage that is driven by two DC motors with
a positioning accuracy of 50 nm (PI M-111.1DG, Physik Instrumente Co.,
Shanghai, China). The cell manipulation process is guided by visual feedback provided by a CCD camera, from which the positions of cell and beads
are obtained as well as the cell deformation. All of the mechanical components were supported on an antivibration table.
The mixture of RBCs and beads was contained in a home-built chamber,
which was assembled with microscopic slides and coverslips conglutinated
by super glue. All slides and coverslips were cleaned using ethanol. The
coverslips were glued to the slide with super glue and sealed at the corners
with nail polish. In cell stretching experiments, the surfaces of the chamber
were bare glass. Once adhesion between cells and beads was confirmed, the
diluted mixture was injected into the chamber from an open end, which was
then sealed with a coverslip. The chamber was then reversed for about 10
minutes to let the cells settle down and adhere. Most RBCs were attached to
the sidewall surface of the chamber, and unattached cells sank to the slide
after inverting the chamber back to its original position. Then the chamber
was ready for robotic manipulation experiments. It should be noted that all
Biomechanical Characterization of Human Red Blood Cells
As stated above, the force–deformation relationship is determined when the
area compressibility modulus k and the shear modulus μ are given in Equation
(8.3). Different mechanical properties lead to different force–deformation
curves. By minimizing the deviation between the modeling results and the
experimental data, the biomechanical properties of RBCs can be characterized.
8.3 Cell Manipulation with Optical Tweezers
To study the cell mechanics of human RBCs, experiments of robotic cell
manipulation with optical tweezers were conducted. Human RBCs are
stretched at different levels of trapping forces. Through force calibrations
and image processing, the relationship between the stretching forces and the
induced deformations is established, from which the mechanical properties
of RBCs can be characterized based on the cell mechanical model.
8.3.1 Optical Tweezer System
Figure 8.3 shows a schematic diagram of our optical tweezer system, which
mainly consists of a single laser trap. The 808-nm diode laser source has a
maximum power of 2.0 W. The laser beam is reflected by a dichroic mirror into a 40× objective and focused on the observation plane. To minimize
the possible optical damage to living cells, the laser beam is focused on the
attached polystyrene beads instead of RBCs. The biological sample is placed
on a two-dimensional motorized stage that is driven by two DC motors with
a positioning accuracy of 50 nm (PI M-111.1DG, Physik Instrumente Co.,
Shanghai, China). The cell manipulation process is guided by visual feedback provided by a CCD camera, from which the positions of cell and beads
are obtained as well as the cell deformation. All of the mechanical components were supported on an antivibration table.
The mixture of RBCs and beads was contained in a home-built chamber,
which was assembled with microscopic slides and coverslips conglutinated
by super glue. All slides and coverslips were cleaned using ethanol. The
coverslips were glued to the slide with super glue and sealed at the corners
with nail polish. In cell stretching experiments, the surfaces of the chamber
were bare glass. Once adhesion between cells and beads was confirmed, the
diluted mixture was injected into the chamber from an open end, which was
then sealed with a coverslip. The chamber was then reversed for about 10
minutes to let the cells settle down and adhere. Most RBCs were attached to
the sidewall surface of the chamber, and unattached cells sank to the slide
after inverting the chamber back to its original position. Then the chamber
was ready for robotic manipulation experiments. It should be noted that all