Biomedical Engineering Reference
In-Depth Information
indicate that the adhesion, proliferation, and alkaline phosphatase (ALP) activity of osteoblasts
cultured on the larger 70 and 100 nm NTs are dramatically changed by the different sterilization
conditions at a low cell seeding density of 10,000 cells/well in 12-cell culture well. The different
autoclaving methods create huge differences in cell adherence on 70 and 100 nm NTs compared to
30 and 50 nm NTs. These results reveal that the nanofeatures of proteins adhered on the NTs can
be altered by different sterilization methods.
17.3.2
Influence of cell phenotype on the bioactivity of the NTs
NTs have been assayed for various biological purposes such as bone implants
[2,3,10
12,31]
,
transcutaneous part of the implants
[32]
, and vascular prostheses
[24]
. There is much evidence
from the various primary cell phenotypes including primary osteoblasts, osteoblast cell lines,
MSCs, endothelial cells (ECs), vascular smooth muscle cells (VSMCs), dermal fibroblasts, and
epidermal keratinocytes suggesting that different cell phenotypes respond differently to the NTs.
We have observed differential responses of primary rat calvarial osteoblasts to the NTs compared
to those of the osteoblast cell lines
[10,31]
. Our results to some degree corroborate the report by
Brammer et al.
[33]
. They have compared the effects of TiO
2
and C-coated NT surface chemistries
on osteoblast and osteoprogenitor cell behaviors. The TiO
2
NT surface induces an increase in osteo-
blast functionalities in terms of ALP activity. In contrast, it is the carbon chemistry that results in
increased bone mineral deposition and bone matrix protein expression of osteoprogenitor cells.
More significant evidence unambiguously demonstrating the phenotypic dependence of cell
responses to the NTs is obtained from ECs/VSMCs and dermal fibroblasts/epidermal keratinocytes.
Peng et al.
[24]
have found that the NTs significantly enhance EC proliferation but decrease
VSMC proliferation (
Figure 17.3
). Smith et al.
[32]
have reported increased dermal fibroblast and
decreased epidermal keratinocyte adhesion, proliferation, and differentiation on the NTs.
The evidence reminds us that when comparing the reports on the bioactivity of the NTs from
different sources, it should be borne in mind that the responses of cells to the NTs are phenotypic
dependent. In addition, the differential response of the different cell phenotypes to the NTs provides
a good approach for tissue specific implants that selectively benefit from the desired tissue integra-
tion while simultaneously inhibiting the unwanted response.
17.3.3
Influence of protein concentration in culture medium
on the bioactivity of the NTs
The proteins adsorbed to the implant surface play a key role in cell/implant interactions. We have
compared the influence of the serum concentration in the culture medium on the change in the pro-
tein adsorption amount and the consequent initial cell spreading on the NTs and flat Ti
[2]
.
Different serum concentrations do not influence cell adhesion on flat Ti control and 25 nm NTs
but seriously affect that on 80 nm NTs (
Figure 17.4
). The cells attach and spread well on the
80 nm NTs when cultured with 5% or 10% serum while 2% serum leads to poor cell adhesion.
This phenomenon can be explained by the cell adhesion mechanism. A requirement for normal cell
functionalities on biomaterials is stable adhesion or else cell apoptosis will occur
[34]
. Therefore,
the amount of adsorbed proteins is very important for the biological performance of biomaterials.
The amounts of proteins on the nanostructured surface increase with serum concentrations from
