Biomedical Engineering Reference
In-Depth Information
Table 1 Total DNA and GAG contents of cartilage-carrier constructs and cartilage without
carriers according to cultivation time (n = 4-5)
Time [d]
With carrier
Without carrier
DNA [lg]
GAG [lg]
DNA [lg]
GAG [lg]
7
9.05 ± 1.39
207.7 ± 55.4
11.70 ± 0.44
523.2 ± 17.7
14
10.61 ± 0.44
399.9 ± 22.9
13.02 ± 0.45
994.6 ± 61.7
21
9.52 ± 1.53
362.3 ± 182.4
13.50 ± 0.47
1568.5 ± 84.5
28
10.80 ± 2.32
236.8 ± 91.1
15.62 ± 0.26
2005.4 ± 124.4
35
11.58 ± 1.62
415.9 ± 107.1
14.50 ± 0.54
2339.5 ± 134.8
strength of fibroblasts predominantly with increasing surface energy and, in the
second instance, with increasing roughness on metallic and polymeric substrates.
Dos Santos et al. [ 24 ] observed that, by culturing osteoblasts on hydroxyapatite,
surface topography influenced cell differentiation more than changing surface
chemistry. In particular, it could be shown that roughness on the micro- and
nanometer scale influences cell morphology, cytoskeletal organisation, prolifera-
tion or differentiation of various cell types [ 24 ]. Again, the reason for cell
behaviour on different surfaces was unclear. Ponche et al. [ 18 ] described that,
considering the relevant scale, the arithmetic roughness parameter R a correlated
with the wettability of titanium surfaces, which may influence selective adsorption
and arrangement of proteins. However, other effects on cell behavior on modified
surfaces structures can also be found in the literature. For example, Papenburg
et al. [ 29 ] stated that surface topography seems to have a predominant effect versus
wettability on the morphology of pre-myoplasts cultured on various materials.
To eliminate the effects of biomaterial composition, surface structures were
modified by various methods such as photolithography and chemical treatment
[ 57 , 58 ], glancing angle deposition [ 22 ], laser blasting or deep reactive ion etching
[ 59 ]. With these techniques, highly organized surface structures of different geo-
metrically forms such as pillars, cubes or grooves in the nano- and micrometer
scale range can be produced [ 18 , 25 ]. However, these methods are sophisticated
and consequently the carriers are very different from carriers which can be used as
implants in the clinical routine. To work according to clinical applications and to
ensure exactly the same chemistry of the biomaterial, in the following study the
above-mentioned commercially available hydroxyapatite carrier was used for the
investigation of different surface topographies. Because of the low mechanical
stability of the carriers—a low hardness of 14.0 ± 5.5 MPa and Young's modulus
of 1.7 ± 0.4 GPa were determined by nanoindentation measurements—conven-
tional grinding/polishing failed to create smooth and homogeneous surfaces. Soft
materials like plain paper and ink jet polymer sheet foils were therefore used as
grinding tools to modify the surface topography in the direction of smooth (using
plain paper) or structured (using rough polymer sheets), when compared to the
rough and inhomogeneous untreated carrier (Fig. 7 ). These methods did not
influence the nano-scale roughness, grain size and porous structure, but the
macroscopic surface topographies of the hydroxyapatite.
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