Biomedical Engineering Reference
In-Depth Information
19.4
Nano-HAcollagen composites
In addition to nano-HA preparations, in an attempt to mimic natural bone even more closely,
several researchers have fabricated nano-HA
23]
.In
particular, one laboratory has prepared a hierarchical structure resembling natural bone by allowing
self-assembly of collagen triple helices and the formation of nano-HA crystals on the surface of
these fibrils
[23]
. In this technique, nano-HA crystals grow on the surface of collagen fibrils such
that their c-axes orient along the longitudinal axes of the collagen fibrils and the mineralized fibrils
become aligned parallel to each other forming mineralized collagen fibers as in situ in bone. In
vitro studies have shown that this composite supports osteoblastic cell growth and new bone forma-
tion
[24,25]
. The nano-HA/collagen-based scaffolds have now been successfully used in many clin-
ical cases requiring various types of bone repair
[26]
with wound healing and no abnormalities
found in local and systematic examinations during long-term follow-up
[27]
.
collagen composites (nano-HA/collagen)
[21
19.5
Hydrogels and nano-HA
Other studies, although recognizing the advantages of nano-HA for bone regenerative purposes,
have made efforts to improve some of the properties of this material with respect to controlling its
biodegradability and porosity for better bioactivity. Because of the inherent ability of hydrogels to
swell in aqueous media and to permit the transport of enzymes and nutrients to and through various
supporting ceramic scaffolds, there has been increasing interest in the use of hydrogels with cera-
mics in tissue engineering
[28,29]
.
Chitosan is a promising hydrogel material for bone regeneration because it is biocompatible
and biodegradable with a degradation rate that is dependent on factors such as degree of deacetyla-
tion and crystallinity
[30]
. It can also be easily formed into beads, fibers, or more complex
structures
[31,32]
. In another recent study
[33]
,
chitin hydrogel/nano-HA composite scaffolds
were synthesized and shown to have improved porosity, swelling ability, protein adsorption, and
retention as well as biomineralization properties for use as a potential candidate for bone tissue
engineering applications. Although it appears to date that only in vitro studies and a preliminary
in vivo study in a rat calvarial defect model
[30]
have been conducted with this type of nanocom-
posite scaffolds, there have been a series of studies that have tested the combination of polymers
such as chitin with traditional-sized HA. These earlier studies which do include in vivo experi-
ments suggest that the composites support bony ingrowths into the implant as the matrix gradually
resorbs
[34
β
36]
.
green arrowhead: coronal extension of new bone, red dotted line: apical extension of the notch. Original
magnification
5. (J) Higher magnification of the defect shown in (I). Formation of NC and new periodontal
ligament (PDL) was confined to the area of the notch. Red arrowhead: coronal extension of NC, red dotted
line: apical extension of the notch, white dotted line: margin between the newly formed bone and old bone,
red asterisk: artifact. Original magnification
3
25. (For interpretation of the references to color in this
figure legend, the reader is referred to the web version of this topic.)
Figure from Ref. [
20
] with permission from publisher.
3
