Studying Cell–Surface Interactions In Vitro: A Survey of Experimental Approaches and Techniques - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 58

Fig. 15 a Impedance spectra near resonance of a cell-free (open circle) and a cell-covered (filled
circle) 5-MHz quartz resonator. The arrow indicates the change of the minimal impedance
D|Z min |, which was used to follow cell attachment and spreading upon the resonator surface.
b Time course of the minimal impedance D|Z min | during the attachment and spreading of NRK
cells upon the quartz resonator. Changes of the load parameters are given relative to a cell-free
but medium-loaded resonator. t 1/2 is the time required to induce a half-maximal change of D|Z min |.
Mean ± SEM, n = 5; T =37C
the so-called QCM-D technique, which provides measurements of the dissipation
factor D in addition to the common measurement of the resonance frequency f. The
dissipation factor quantifies the damping of the quartz oscillation and is defined as
the ratio of the dissipated energy to the energy that is elastically stored during one
period of oscillation. Simultaneous f and D measurements are performed by
periodically switching off the driving power to the quartz oscillator and subse-
quently recording the free decay of the quartz oscillation. The measured decay
time of the damped sine wave is expressed as the dissipation factor, to which it is
inversely proportional. Readings of D indicate whether the recorded shift in
resonance frequency arises from dissipative processes, as occur with any viscous
loading of the resonator surface [ 61 ]. Thus, simultaneous f and D measurements
facilitate the detailed interpretation of QCM experiments.
Fredriksson et al. [ 63 ] and Nimeri et al. [ 64 ] used this approach to characterize
the attachment and spreading of mammalian cells and the interaction of neutro-
phils with a protein-coated surface. Reiss et al. [ 65 ] used functionalized (biotin-
doped) lipid vesicles and studied their adhesion onto a resonator surface coated
with specific ligands (avidin) as a simple model system to mimic cell attachment
and spreading. The adhesion of mammalian cells and liposomes gave rise to very
similar shifts in resonance frequency, whereas the viscous energy dissipation was
at least one order of magnitude higher when cells made contact with the resonator.
As a conclusion of these studies it was obvious that the viscous properties of the
cell-surface junction and the cell body had a great impact on QCM readings.
The second operational mode for QCM experiments is termed the passive
mode. Here, the quartz resonator is not oscillating freely but a sinusoidal voltage is
applied to the surface electrodes and the crystal is thereby forced to oscillate at
frequencies determined by the frequency of the applied AC voltage. The quartz is