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Using optical tweezers for measuring the interaction forces between human bone cells and implant surfaces: System design and force calibration
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View: Figures


Image of FIG. 1.
FIG. 1.

A schematic showing the layout of the mmi CellManipulator, which was set up on a standard Nikon TE2000 inverted scientific microscope. The optical tweezers module was hooked up via a second level adoption on top of the fluorescence port on the back of the scope. The system included a high resolution digital three chip camera charge coupled device (CCD) camera for observation and a microbead position detection system (MBPS2), set up with two quadrant detector (QD) heads. The camera and position detection system were mounted on standard camera ports using a beam splitter (BS). As bright field illumination source a short arc mercury lamp (HBO100) was used.

Image of FIG. 2.
FIG. 2.

A principle sketch of the intensity distribution on the four individual segments of the quadrant photodiode detector.

Image of FIG. 3.
FIG. 3.

Example of quadrant detector (QD) signal as a function of distance for a sized bead. The straight line is a guide to the eye indicating the linear regime where the measurements were performed.

Image of FIG. 4.
FIG. 4.

Results obtained using polystyrene beads. (a) The tangent of the phase lag plotted as a function of oscillating frequency for a diameter bead at an amplitude of . (b) The tangent of the phase lag plotted against the distance from the cover slip for a bead. (c) The tangent of the phase lag as a function of oscillation amplitude for a bead. (d) The trap stiffness vs the relative laser power for beads of various sizes.

Image of FIG. 5.
FIG. 5.

The maximum trapping force induced by the tweezers on a bead. The force was obtained by moving the stage at the critical velocity and by oscillating the bead. Error bars obtained from repeated measurements are indicated for all data points but are for several points comparable to or smaller than the symbol.

Image of FIG. 6.
FIG. 6.

Force calibrations using sized osteoblasts. (a) The tangent of the phase lag plotted against the frequency. (b) The maximum trapping force that could be induced by the trap using the oscillation method.

Image of FIG. 7.
FIG. 7.

An optical image of a trapped cell together with an implant surface. In this particular case a fibroblast is trapped and its interaction with a glass slide modified with HA is under investigation.

Image of FIG. 8.
FIG. 8.

Characterization of the adhesive strength by which the osteoblasts adhered to the different implant surfaces. The cells were in contact with the surface for at least before they were forced away using the optical trap. 20 cells were used on each surface type.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Using optical tweezers for measuring the interaction forces between human bone cells and implant surfaces: System design and force calibration