Biomedical Engineering Reference
In-Depth Information
surface area per HA volume for cell growth than m-HA, which might
result in increased cellular adherence and proliferation [49, 74,
133].
The origin of the effects of np20 may derive from the fact that
the internalized HA nanoparticles were partially dissolved during
lysosomal digesting and the obtained solutes such as Ca
2+
ions
diffused into the cytoplasm [17]. The proper Ca
2+
concentrations
favored osteoblast proliferation and differentiation [84].
Besides particle size, the crystallinity and the morphology of HA
particles also affect cell behavior. The studies have provided evidence
that the crystallinity of calcium phosphate affects the behavior of
cultured osteogenic cells [42, 91]. The osteogenic differentiation
is higher in cultures on amorphous calcium phosphate substrates
compared to crystalline HA substrates. It is demonstrated that
surface chemistry and topography of lower crystallinity is favorable
for cell attachment and differentiation [14, 24, 41].
The morphology should be another important parameter for
estimating the biological effect of calcium phosphate particles
[115, 156]. The cell experiment showed that HA with spherical
nanocrystals showed more favorable properties than rod-like HA for
osteoblasts. The explanation for the favorable effect of sphere-like
nano-HA on osteoblasts might be the well-organized surface which
seems beneicial for ilopodia protrusion.
Cytotoxicity was another important parameter to estimate the
biological effect of HA nanoparticles. The cells in np80 and m-HA
groups exhibited marked changes, including loss of contact with
neighboring cells, contraction of the cells, swollen mitochondria,
deformed nuclei, and condensed chromatin [115]. This means that
larger sizes of HA nanoparticles are toxic to cells. Saunders and
coworkers [112] pointed out that increased calcium phosphate
in the matrix might trigger apoptosis in osteoblasts during bone
resorption, and that bone cell apoptosis induced by high calcium and
phosphate exhibited a marked change in mitochondrial function.
Substrate micro- and nano-topography, independently of
substrate biochemistry, seem to have signiicant effects on cell
behavior [86]. As reported till now, substrate topography (with
micro- or nano-features) has direct effects on cell orientation,
morphology, and cytoskeleton arrangements. As a general rule, the
effects are more pronounced for smaller, nano-sized surface features,
although there is a lack of knowledge on the basic mechanisms the
cell uses to detect and respond to this nanotopography.
