Biomedical Engineering Reference
In-Depth Information
Fig. 6. Apoptotic level of fibroblasts cultured on PEG-based samples. The induction of
apoptosis in L929 cells after 48 h cultivation time on smooth PEG samples was quantified
with a caspase-3/-7 assay. The samples had before been extracted in water for 24 h. The test
was performed in triplicate with substrates of three different crosslinking densities.
2.4 Fibroblast culture on micropatterned PEG hydrogel substrates
While no cell adhesion was observed on the smooth surface of the PEG-based hydrogels, we
have discovered that cells do adhere to bulk PEG hydrogels when they are topographically
patterned (Lensen et al., 2008; Schulte et al., 2009).
Figure 7
depicts some representative
images of fibroblasts adhering to the micropatterned surface of the PEG hydrogels.
In order to explain this observation we have considered that proteins may adsorb to the
physically patterned gels and/or that the cells themselves 'feel' the physical pattern and
respond on the level of cytoskeletal adaptations. In two follow-up studies we investigated
those two (biochemical and biophysical) arguments in more detail. Thus, we examined the
possibility of protein adsorption to the gels and we explored the effect of systematic
variations of geometry and stiffness of the hydrogels on the enabled cell adhesion.
The first investigation concerned the systematic variation of the deformability of the
topographic structures that the cells are assumed to perceive. Although it is unlikely that the
cells are able to really deform the micrometer-sized bars, we did envisage that the
deformability of the surface structures to depend on the groove width, on the aspect ratio of
the bars, and on the inherent mechanical properties of the gels. Thus we prepared line
patterns with different groove width (5, 10, 25 and 50 µm) and depth (5, 10 and 15 µm). Also
we prepared hydrogel formulations resulting in gels with three different stiffnesses,
denoted soft (~90 kPa), intermediate (~350 kPa) and stiff (~1 MPa).
