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Söhling, et al.
MSC on BG20 could be interpreted as a suppression of
adipogenic differentiation and as further evidence for
preferential OD.
Taken together, these results indicate good
cytocompatibility of BG20 for MSC. Cell adhesion
is high and gene expression analyses indicate that OD
processes are at least initiated by the material. The BG
component is composed of 53% SiO, 23% Na O, 20%
2
CaO, and 4% P O . The previous studies by our group on
2
5
the effect of BG on EPCs showed that especially calcium
ions released from BG supported cell differentiation . To
[7]
investigate a possible influence of calcium ions released
from BG20 on MSC, we performed an analogous
experiment with BG20. Calcium ions were selectively
bound by EGTA, and the amount of EGTA added was
based on the expected calcium ion release, which was
previously determined by colorimetric detection . IL-6
[37]
gene expression was chosen as the readout parameter
because it is rapidly and significantly downregulated
by BG20. This BG20 induced inhibition of IL-6 gene
expression could be almost completely abolished by
EGTA addition. This result is a clear indication that
calcium ions released by BG20 are causative for the
observed effects. It cannot be excluded that other ion
species of the BG component also exert effects on MSC
differentiation. However, this has not been analyzed
further in this study.
4.3. BG20: Immunological compatibility

Another significant aspect is the reaction of the immune
system to the implanted bone graft substitute. The initial
step of the foreign body reaction consists of the deposition
of proteins such as fibrin and the binding and activation
of monocytes. These, in turn, secrete chemotactic factors,
leading to the accumulation of further monocytes,
granulocytes, and fibroblasts . Immunoreactive
[57]
materials such as polymethyl methacrylate-based bone
cements elicit a strong foreign body reaction, leading to
encapsulation of the implanted material with a fibrous
membrane . The onset of foreign body reactions has
[58]
Figure 9. Inflammatory potential of BG20 (yellow) in whole-blood also been described for other bone graft substitutes .
[59]
stimulation assay I (n=3 subjects) in comparison to medium (blue),
medium containing LPS (orange), and PLA (gray) measured Whole-blood stimulation assay is an established method
by whole-blood stimulation assay I (n=3 subjects). Proteins in to predict the response of the innate immune system to
the supernatant were detected semi-quantitatively by mean of a various stimuli. In the previous work, our group was
Proteome Profiler Membrane assay. Median values are shown. able to demonstrate that different bone substitutes can
elicit characteristic and reproducible cytokine expression
to MSC proliferation, induction of cell migration, and profiles in the whole-blood stimulation assay in terms
inhibition of cell differentiation processes [54,55] . Thus, of an immunological signature [60] . In the present work,
the strong suppression of JNK-1 gene expression might test specimens made of PLA or BG20 were used in
contribute to the reduction of proliferation and support of the whole-blood stimulation assay. Subsequently, 105
cellular differentiation processes. different mediators were semi-quantitatively determined
IL-6-mediated activation of p38 is essential for using a protein array. Of the 105 different mediators,
adipogenic differentiation of MSC . In this way, the which include interleukins, chemokines, and complement
[56]
decreased p38 gene expression after incubation of factors, 23 were detected in the medium control, 24 in
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