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allows their resorption by osteoclasts and remodeling into new bone tissue
(Constantz et al. 1995; Jansen et al. 1995).
4.2.3 In Vitro Biological Evaluation of the CPC Scaffolds
An important feature of a scaffold developed for tissue engineering applica-
tions is its performance as a cell carrier. We have seeded human mesenchymal
stem cells (hMSC), derived from bone marrow, on the plotted CPC scaffolds
to evaluate their cytocompatibility (Lode et al., forthcoming). The cell-seeded
scaffolds were cultivated over 19 days in cell culture medium containing
osteogenic supplements (dexamethasone, β-glycerophosphate, and ascor-
bic acid 2-phosphate), which are able to induce the differentiation of hMSC
into osteoblasts in vitro . SEM analyses revealed that the cells attached to and
spread over the surface of the plotted CPC scaffolds (Figure 4.9a,b).
After longer cultivation time, the cells proliferated and migrated, even
bridging the gaps between the CPC strands (Figure 4.9c) and finally formed
a thick cell sheet (Figure  4.9d). Proliferation and differentiation along the
osteoblastic lineage were evaluated by biochemical determination of the
enzyme activities of lactate dehydrogenase (LDH), a housekeeping enzyme
whose activity can be correlated with the number of living cells, and of alka-
line phosphatase (ALP), a typical marker of the early stage of osteoblastic dif-
ferentiation. Cytosolic LDH activity measurement revealed that the number
of viable cells increased over the cultivation period (Figure 4.9e). The rise of
the specific ALP activity with a maximum value at day 12 strongly indicates
the osteogenic differentiation of hMSC cultivated on the CPC scaffolds in the
presence of osteogenic supplements (Figure 4.9f). The data of the cell experi-
ment demonstrated the capability of the plotted CPC scaffolds to support
hMSC attachment, growth, and osteoblastic differentiation.
4.3 Polymer Reinforced Biphasic CPC-Alginate Scaffolds
Ceramic and polymer scaffolds developed for bone tissue engineering
applications have, defined by their intrinsic properties, specific advantages
and disadvantages. For instance, the low mechanical strength and inher-
ent brittleness of pure calcium phosphate scaffolds prepared without sin-
tering remain limitations of their clinical application. The development of
ceramic and polymer composite scaffolds is a promising option to generate
structures of enhanced quality with respect to their mechanical properties
(Gelinsky and Heinemann 2010). Such organic and inorganic composite scaf-
folds mimic the natural bone to some extent since bone is likewise composed
of an inorganic (hydroxyapatite) and an organic biopolymer part (mostly
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