Biomedical Engineering Reference
In-Depth Information
polyetherimide surfaces with micro-post features of varying dimensions, which
were generated by laser treatment, demonstrated no cellular orientation with
respect to posts. FCs spread and elongate whether in contact with posts or
microsmooth materials.
89
Similarly, Dalby et al.
90
demonstrated reduced FC
adhesion on PMMA substrates with nano-posts (prepared by colloidal litho-
graphy) that were 100 nm in diameter, 160 nm in height and having a pitch of
230 nm. An increase in endocytosis was also noted on nano-pits using clathrin
staining indicating that these nano scale features are in the same size range as
those features with which the in vivo cells interact with. FCs have also been
studied on silicon surfaces possessing nano-posts with a height ranging from
50-100 nm and with a pitch of 230 nm that were fabricated by interference
lithography and deep reactive-ion etching.
91
Human FCs were found to attach
in a similar density on flat control surfaces. However, the cell morphology was
more elongated on the nano-posts, an effect noticed for up to seven days in
culture.
92
FC behavior has also been investigated on random nano-rough geometries.
It has been shown that decreased fibroblast numbers occur on NaOH treated
PLGA and PCL surfaces, as well as nitric acid (HNO
3
) treated PU.
93
Cousins
et al.
94
have also shown that nano-rough surfaces created with silica nano-
particles affect FC morphology, decrease cell adhesion and inhibit cell
spreading and thus cell proliferation for periods of up to seven weeks.
In general, stronger alignment, elongation, migration and decreased
proliferation of FCs were reported on grated surfaces compared with island,
post, pit and random topographies. The studies described here also showed that
feature depth, height and surface chemistry have a significant influence on
cellular response.
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2.5.6 Substrate Rigidity and Elasticity
In contrast with the voluminous amount of research on the role played by
surface morphology on cellular response, the rigidity and elasticity of
substrates have received relatively little attention. As would be expected, by far
the majority of this research has involved polymer-based substrates. The main
thrust of this type of research is to use matrices that attempt the mimicking of
the properties of natural tissue in terms of stiffness and elasticity. The obvious
implication is that such matrices can be employed as scaffolds in implant
technology. We outline some examples in this section.
The effects of the flexibility of a substrate on cellular behavior was reported
as early as the 1990s.
95
Polyacrylamide gels displaying differential elasticity
were fabricated on glass cover slips and characterized by measurement of
Young's modulus. Epithelial and fibroblast dells were cultured on collagen-
coated polymer films in order to examine mobility and adhesion characteristics,
etc. This experiment was designed in this fashion to allow polymer flexibility to
change without ostensibly changing any surface chemical conditions. Cells were
fixed and studied by standard fluorescence, microscopy and immunoblotting
protocols. The important result emanating from this work was that cells grown
