Biomedical Engineering Reference
In-Depth Information
zero but maintained a certain strength due to the contribution of support-
ing alginate.
Compressive strength of the biphasic scaffolds was therefore
enhanced compared to that of pure CPC ones with identical porosity and
geometry due to the binding effect of the alginate strands. Furthermore, the
alginate strands formed an interpenetrating network that further stabilized
the CPC strands in these biphasic scaffolds. That is why the biphasic scaffolds
were able to hold their bulk morphology after suffering as much as 30% com-
pressive strain. Compared to pure CPC scaffolds, the biphasic ones showed
improved toughness. The high compressive strength of pure alginate scaf-
folds in dry conditions can be explained by the apparent shrinkage of these
scaffolds during dehydration, resulting in a lower porosity, higher solid state
content, and stronger entanglement of the biopolymer chains. Therefore, in
a wet state the strength of pure alginate and mixed alginate-CPC scaffolds
decreased sharply due to the swelling of alginate hydrogel strands.
Cell culture experiments performed
in vitro
are able to provide informa-
tion concerning cytocompatibility being the first step of evaluating the per-
formance of a novel type of scaffold for tissue engineering and regenerative
therapies. As already demonstrated, CPC scaffolds are good candidates sup-
porting the attachment, growth, and osteogenic differentiation of hMSC.
Cytocompatibility of both the biphasic and mixed CPC-alginate composite
scaffolds in comparison to the pure CPC ones was evaluated by seeding of
hMSC on the printed structures. The cell-seeded scaffolds were cultured
over a period of 3 weeks with or without osteogenic supplements. The mor-
phology and distribution of the cells attached to the scaffolds were observed
by means of SEM: one day after seeding, hMSC were attached and well
spread on the surface of the biphasic CPC-alginate as well as mixed scaffolds
(Figure 4.13). Interestingly, in the course of further cultivation, differences
have been found: while viable and well spread cells were detected on pure
CPC and biphasic CPC-alginate scaffolds, both in the presence and in the
absence of osteogenic supplements, the number of cells cultivated on mixed
CPC-alginate scaffolds was strongly reduced but only in the presence of
osteogenic supplements, as indicated by SEM analysis and determination of
cytosolic LDH activity (as measured for the number of living cells). This phe-
nomenon might be caused by the apatite formation on the surface of mixed
CPC-alginate scaffolds that was observed to start on day 1 of culture result-
ing in an intense deposition of apatite particles as observed after 7 days of
culture (Figure 4.13d). A potential reason for the strong apatite precipitation
on the mixed CPC-alginate scaffolds was the high degree of supersaturation
due to the slow hydrolysis of CPC particles (mostly α-TCP) and both cal-
cium ion exchange from the Ca
2+
-cross-linked alginate and the elevated local
phosphate ion concentrations because of the presence of β-glycerophosphate
at the same time (Erisken et al. 2011).
Scaffolds with the capability to bind growth factors (GF) and drugs, and
release them in a controlled manner are preferable candidates for tissue
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