Biomedical Engineering Reference
In-Depth Information
calcium orthophosphates was found to be quite different from that
of bone mineral [122].
Although the nanodimensional and nanocrystalline features of
natural calcium orthophosphates of bones and teeth had been known
earlier [2, 123-128], the history of the systematic investigations
of this field has started only in 1994. Namely, a careful search in
scientific databases using various combinations of keywords “nano”
+ “calcium phosphate,” “nano” + “apatite,” “nano” + “hydroxyapatite,”
etc., in the article title revealed 5 papers published in 1994 [129-
133]. No papers published before 1994 with the aforementioned
keywords in the title have been found.
Nanodimensional (size ~67 nm) HA was found to have a higher
surface roughness of 17 nm if compared to 10 nm for the submicron-
sized (~180 nm) HA, while the contact angles (a quantitative measure
of the wetting of a solid by a liquid) were significantly lower for
nano-sized HA (6.1) if compared to the submicron-sized HA (11.51).
Additionally, the diameter of individual pores in nanodimensional
HA compacts is several times smaller (pore diameter ~6.6 Å) than
that in the submicron grain-sized HA compacts (pore diameter
within 19.8-31.0 Å) [134]. A surface roughness is known to enhance
the osteoblast functions while a porous structure improves the
osteoinduction compared with smooth surfaces and nonporpous
structure, respectively [113]. Furthermore, nanophase HA appeared
to have ~11% more proteins of fetal bovine serum adsorbed per 1
cm
2
than submicron-sized HA [135]. Interfacial interactions between
calcined HA nano-sized crystals and various substrates were studied
and a bonding strength appeared to be influenced not only by the
nature of functional groups on the substrate but also by matching of
surface roughness between the nano-sized crystals and the substrate
[136]. More to the point, incorporating of nanodimensional particles
of HA into polyacrylonitrile fibers were found to result in their
crystallinity degree rising by about 5% [137].
In general, nanostructured biomaterials [138] offer much
improved performances than their larger particle sized counterparts
due to their huge surface-to-volume ratio and unusual chemical
synergistic effects. Such nanostructured systems constitute a bridge
between single molecules and bulk material systems [139]. For
instance, powders of nanocrystalline apatites [140-146] and β-TCP
[147] were found to exhibit an improved sinterability and enhanced
densification due to a greater surface area. This is explained by the
Search WWH ::
Custom Search