Biomedical Engineering Reference
In-Depth Information
of U2OS and MG63 cells and the inhibited strengths were inversely
proportion to the particle size, i.e. smaller particles possessed a
greater ability to prevent cell proliferation. This suggests that nano-
sized HA can exhibit favorable cell proliferation to optimize biological
functionality, in which the particle dimensions are believed to play
a key role. These
findings are of a great significance for the
understanding of cytophilicity and biological activity of nano-sized
particles during biomineralization [432].
Studies confirmed that nano-sized ACP had an improved
bioactivity if compared to nano-sized HA since a better adhesion
and proliferation of osteogenic cells had been observed on the ACP
substrates [584]. However, in order to understand the influence
of crystallinity of the nano-sized calcium orthophosphates on the
osteogenic cells correctly, it was critical to use nano-sized ACP and
HA of the same size distribution [583]. Thus, ACP and HA particles
of ~20 nm size were synthesized and the effects of crystallinity were
studied. The adhesion, proliferation, and differentiation of MSC cells
were measured on both ACP and HA films and compared at the same
size scale. Surprisingly, more cells were adsorbed and proliferated on
the films of the well crystallized nano-sized HA than those on the films
of nano-sized ACP. Alkaline phosphatase activity assay and RT-PCR
assay were also used to evaluate the differentiation of MSC cells. The
results showed that the differentiation of MSC cells from osteoblasts
was promoted significantly by nano-sized HA. These experimental
phenomena clearly demonstrate that the crystallized phase of HA
provides a better substrate for MSC cells than ACP, when the factor
of size effect is removed. This new view on the relationship between
the crystallinity of calcium orthophosphates and the responses of
MSCs emphasized the importance of both size and phase control in
the application of biomedical materials [583, 584].
On the other hand, the chemical composition of the samples
appears to be important. Interestingly, but in spite on the fact that
the biological apatite of bones contains the substantial amount of
carbonates, among investigated samples of nanocrystalline apatites,
osteoclastic differentiation was found to be constrained on carbonate-
rich samples, leading to smaller numbers of osteoclast-like cells and
fewer resorption pits. Furthermore, the highest resorption rate was
found for nanodimensional HA with a low carbonate content, which
strongly stimulated the differentiation of osteoclast-like cells on its
surface [585].
in vitro
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