Biomedical Engineering Reference
In-Depth Information
and the tissue engineering procedures for bone reconstructive purposes.
The placement and subsequent tissue integration of a bone implant or
tissue-engineered construct requires symbiosis between a biological and a
nonbiological system. Nanotechnology that is applied to create biomimetic
features can serve as a “lubricant” to enhance the reactions between both
systems. In this, it is vital to understand that nanomaterials have physico-
chemical and biological properties that can be totally different from their
“macroscopic” counterparts. Various nanomaterials are currently described
in the literature; however, not all materials possess the appropriate criteria
to be incorporated into, or placed onto, a bone implant or tissue-engineered
construct. Ongoing research on nanomaterials for bone implants is mainly
focused on three materials: nanohydroxyapatite (nHA), nanofibers, and car-
bon nanotubes (CNTs). Some of these materials are already proven materials
on a microscale level, while others are fairly new in the bone tissue engineer-
ing field.
4.1 Nanohydroxyapatite
Natural bone tissue consists of a high percentage of nanosized needle-like
calcium phosphate crystals of approximately 5-20 nm in width and 60 nm in
length, combined with a poorly crystallized nonstoichiometric apatite phase,
containing
CO
2−
, Na
+
, F
−
, and other ions, embedded in a collagen matrix.
4
Resembling the naturally occurring calcium phosphate crystals, nHA might
be a perfect material to use in bone implant materials (Figure 4.1). Microscale
HA, previously used for this purpose, has already shown to be osteocon-
ductive.
5,6
However, the use of nHA has several advantages over the con-
ventional ceramic microsized HA formulations; it enhances proliferation
and differentiation of bone-forming cells, as well as the synthesis of the
mineralized matrix. These beneficial features of nHA are a direct effect of
(a)
(b)
100 nm
RU
SEI 3.0 kV X5,000 1µm WD 12.3 mm
FIGURE 4.1
(a) Transmission electron micrograph of nHA. (b) Scanning electron micrograph of an nHA
coating.
