Studying Cell–Surface Interactions In Vitro: A Survey of Experimental Approaches and Techniques - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 61

attachment and spreading occurs immediately (filled symbols in Fig. 16 a). D|Z min |
increases to a transient maximum within 350 min after cell inoculation and even
continues to increase to a final maximum. These results were confirmed by phase-
contrast micrographs recorded 10, 24 and 48 h after seeding of the NRK cell
suspension on both polymer surfaces (Fig. 16 b).
On the unmodified PS surface only a small fraction of the seeded cells has
spread on the surface within 10 h (Fig. 16 b1), whereas the predominant fraction
remains spherically shaped and forms clump-like aggregates floating in the culture
medium. 24 h after cell inoculation, small cell islets have formed (Fig. 16 b2)
showing individual cells with a quite untypical, elongated morphology. 48 h after
cell inoculation, no adherent cells can be observed on the unmodified PS surface
but large aggregates of cell fragments and apoptotic cells are floating in the culture
medium (Fig. 16 b3). By contrast, 10 h after cell inoculation upon the plasma-
treated surface, the biggest fraction of the surface is covered with spread cells
(Fig. 16 c1). As time progresses a confluent cell monolayer is established with a
gradual increase in the cell number per unit area (Fig. 16 c2, c3).
Compared to microscopic studies, an inherent advantage of the QCM approach
is that it directly provides quantitative and time-resolved data of cell spreading
kinetics without any need for complex and time-consuming image analysis. The
inability of cells to attach and spread upon unmodified, hydrophobic PS is in good
agreement with the literature [ 68 - 70 ] and might be related to the pre-adsorbed
protein layer which influences the behavior of cells approaching the surface. On
hydrophobic surfaces like unmodified PS, the soluble proteins are thought to
adsorb under conformational rearrangement (denatured conformation) on the
polymer surface, making the binding sites within the adsorbed proteins inacces-
sible to cell-surface receptors. Consequently, specific cell-substrate contacts
cannot be established and cell adhesion is almost completely inhibited. On the
other hand, PS surfaces after argon plasma treatment generally allow the proteins
to adsorb without unfolding, rendering the surface cytocompatible. Consequently,
the integrin binding sites within the adsorbed proteins should be accessible for the
cell-surface receptors of the arriving cells. This single example shows the general
applicability of the QCM approach to study the biocompatibility of different
biomaterials, no matter whether they are polymers, metals or ceramics.
4.4.3 Probing the Cell-Surface Junction Under Shear Stress
In the preceding paragraphs the QCM-device has been described as a sensor to
monitor the mechanical interactions between cells and surface. It can also be used
as an actuator capable of disturbing or even dissolving molecular recognition at
the solid-liquid interface, such as cell-surface contacts. In the actuator mode, the
resonator is used at an elevated lateral shear amplitude. The latter is controlled by
the driving voltage applied to the surface electrodes to excite the crystal. Heitmann
and Wegener [ 71 ] studied the impact of elevated lateral oscillation amplitudes on
the adhesion kinetics of different mammalian cells. By gradually increasing the