Biology Reference
In-Depth Information
allows automated control during experiments. The capacitive force
sensor (FemtoTools GmbH, http://www.femtotools.com ) is
mounted on a custom aluminum arm which is fi xed to the micro-
robot. We used the FT-S540-type robot, which has a force range
of ±180
N/V, to perform noninvasive
measurements. FemtoTools sensors from the current line are avail-
able in ± 100, ± 1,000, and ± 10,000
μ
N with a gain around 90
μ
N ranges. The sensors can be
ordered with a variety of tungsten probes glued to the tip
(Picoprobe tungsten probe tips T-4-22/T-4-35/T-4-60, GGB
industries Inc., http://www.ggb.com ). The probes stick out of the
sensor by 1-2 mm. They are thin cylinders (diameter from 22 to
60
μ
m) with conical tip that is rounded to a diameter of approxi-
mately 1-3
μ
m. The force signal is collected throughout a data
acquisition card from National Instruments ( http://www.ni.com )
that is connected to the computer either by USB (NI USB-6009)
or PCI (NI PCIe-6321).
The CFM robot used here was mounted on a custom-made
stage (optomechanical components from Thorlabs GmbH, http://
www.thorlabs.com ) on the top of an inverted microscope (Olympus
IMT-2) (Fig. 2 ). The whole setup sits on an anti-vibration table
(TMC 63-530 series, http://www.techmfg.com ) and is covered
with a custom plexiglass box to minimize disturbance coming from
acoustic vibrations and air currents. The table and setup are also
electrically grounded. The light source for the microscope was
replaced with LED rings (AmScope, http://www.amscope.com )
placed on the top of the plexiglass enclosure to avoid sources of
heat within the box. It is important to keep in mind that the capac-
itive force sensors are sensitive to light. When choosing a light
source, make sure that there will be no strong gradient in light that
could affect force measurements. In case of CFM on inverted
microscope, imaging in refl ection mode can be an issue because
the light beam is concentrated through the objective. Prefer trans-
mission with light sources far away from the sensor. While per-
forming force measurements in liquid, it is crucial to keep the
capacitor plates and electronics of the sensor dry. A high magnifi ca-
tion digital microscope (DigiMicro 2.0, dnt GmbH, http://www.
dnt.de ) was used to provide a side view of the sensor tip (Fig. 2 )
and check the liquid level. Make sure that the camera focal length
is long enough for use with the setup (a few cm).
The controlling software comes in different versions, either cus-
tom applications implemented in LabVIEW (National Instruments,
http://www.ni.com , used in ref. [ 15 ]) or a stand-alone C++ library
currently under development. The software is freely available from
the authors ( http://www.MorphoRobotX.org ).
μ
Flat samples, such as epidermal peels, can be immobilized using
laboratory tags (Tough-Tags, Diversifi ed Biotech, http://divbio.
com ). Otherwise, they can be partially embedded in
2.2 Biological
Samples
Search WWH ::




Custom Search