Biomedical Engineering Reference
In-Depth Information
protein adsorption equilibrium is reached. A solution would be to immerse the
sample in the culture medium for 24 h, at which time-point it may assumed that
protein adsorption equilibrium is reached, before seeding cells on top of it.
Furthermore, depending on the type of proteins that are adsorbed onto the surface,
the period for obtaining maximal cell adherence has been reported to differ from
30 min to 6 h, suggesting that 6 h might be the optimal seeding period in a cell
adherence test [ 143 ].
3.1.2 Example: Cell Proliferation
It can be assumed that tissue integration of a material correlates with optimal cell
proliferation. If cell lines are used, they are based in most cases on tumour cells of
specific organs, e.g. from bone or connective tissue. Thus, the question has to be
addressed why cells that are selected to readily proliferate and whose genetic
background is not identical to the original cell type should be a good model for
primary cells. Therefore, it is not surprising that contradictionary reports have been
published regarding their prognostic value for in vivo performance. For instance,
the optimum for titanium surface roughness for maximal MC3T3-E1 osteoblastic
cell proliferation (Ra: 0.0125-6.3 lm) [ 46 ] is similar to that found to be optimal
for in vivo bone response and implant fixation (Ra: 0.5-8.5 lm) [ 122 ]. However,
in another study comparing smooth titanium surfaces (Ra 0.1-0.2 lm) with rough
surfaces (Ra 3 lm), an inverse relationship between osteoblastic MG63 cell pro-
liferation and bone-implant contact (screws, in sheep vertebrae) was found [ 119 ].
The use of primary cells instead of cell lines, however, improves the prognostic
value only marginally. For instance, the team of Ravanetti investigated different
titanium surfaces and found an inverse relationship between human primary
osteoblast cell number as measured after 4 weeks and in vivo performance (bone
contact) after 2 weeks in rabbits [ 112 ]. In contrast, Brama and co-workers
described a direct correlation of primary human osteoblast proliferation with in
vivo performance when comparing titanium and titanium carbide-coated titanium
materials [ 24 ].
It is important to point out that not one but various cell types are present at
the location where the implants are placed and that if multiple cell types adhere
to the surface all of these will proliferate. The cell reaction on the surface might
differ depending on surface and cell types [ 78 ]. Furthermore, these cells will
interact with each other resulting in a modification of the proliferation rates
[ 41 , 151 ]. It can be hypothesized that in this case it is probably not important to
have the highest proliferation rate of osteoblast progenitor cells, but to have an
advantage relative to other cell types with which they have to compete. This
would imply that proliferation must always been seen in the context of other
cells and might be a reason why this parameter, as it is assessed now, is limited
in its prognostic value.
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