Biomedical Engineering Reference
In-Depth Information
the corresponding ionic groups and/or polar groups; and (3) accessibility of these
corresponding groups [192]. The surface properties of chitosan/gelatin could control the
nucleation and growth of HAp crystals (
cf.
Figure 4.16).
The average size of nHA crystals
decreases with increasing gel content and increases with increasing calcium and phosphate
concentrations. The DD of the chitosan and the concentration of SBF have significant effects
on the microstructure and crystallinity of biomimetically deposited calcium phosphate
coatings. The crystallinity of coatings on the chitosans with higher DD is better because
chitosans with higher DD are also most hydrophilic. This can have an effect on the nucle-
ation and growth of calcium phosphate crystals [193]. It is found that osteoblasts proliferate
to a greater extent on amorphous carbonated CaP than on more crystalline CaP [194].
Therefore, one can modulate the osteoblast behavior by changing the properties of the
template.
Incorporating nano-HAp crystallines into chitosan can accelerate the biomineralization
process and influence the topography because the nano-HAp particles can act as nucle-
ation sites [195]. The biomineralization behavior of
N-
methylene phosphochitosan scaf-
folds is superior to that of the chitosan scaffold in Ca
2+
and HPO
2−
solutions or the SBF
solution due to the exiting of PO
3−
in the template [196]. For the same reason, stronger
interactions between the carboxyl group and Ca
2+
, the incorporation of gelatin into chito-
san also accelerates the formation of nano-HAp coating through repeated deposition in
PO
3−
and Ca
2+
ion solutions. The size of nanocrystals can be adjusted by changing the ratio
of chitosan and gelatin, concentrations of PO
3−
and Ca
2+
, and the reaction temperature
[192]. The surface topography can be modulated by the deposition times [197]. The nano-
HAp coating chitosan-based biomaterials is a suitable substrate for osteoblast-like cell dis-
tribution, attachment, and migration. And it also accelerates osteoblastic differentiation at
an early stage, and promotes ECM formation in comparison with chitosan [198,199]. In
addition, it can also inhibit the proliferation of cancer cells [200].
4.5 Self-Assembly Network
There are very complex and diverse self-assembled structures from building units (amino
acid, carbohydrate, and lipids) in a living system. The key point lies in the chemical struc-
ture of these units that should carry all the information to direct their self-assembly pro-
cess [201]. Self-assembly is the spontaneous formation of ordered structures and is an
important nanotechnology tool that may be utilized for spatially orienting macromole-
cules with nanoscale precision. Self-assembly is a “bottom-up” approach in which smaller
building block molecules associate with each other in a coordinated fashion to form larger,
more complex supramolecules. The organization of these building blocks into supramol-
ecules is governed by molecular recognition due to noncovalent interactions such as
hydrogen bonding, as well as electrostatic and hydrophobic interactions [3]. Commonly
used chitosan self-assembly methods include self-assembled nanoparticles and self-
assembled multilayers.
4.5.1 Self-Assembly Nanoparticles
The self-assembly nanoparticles can be employed to control the drug release behaviors
and it is also an effective method for controlling the spatial organization of cells [202].
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