Formation of Chitosan-Based Hydrogels Network - Chitosan Based Hydrogels: Functions and Applications - page 205

introduced into chitosan scaffolds, not only physical incorporation of the secondary
phases into the chitosan matrix occurs, but also chemical reactions among the chitosan
and β-TCP might take place. That is because of the high surface charge density of chitosan
and the ability of chitosan to form ionic complexes. The β-TCP powders are dispersed
homogeneously on the surfaces of the solid walls of the pores; β-TCP powders are expected
to slowly dissolve in physiological media and increase the concentrations of the Ca and P
ions [171].
The chitosan/β-TCP scaffold supports the proliferation of osteoblast cells as well as
their differentiation as indicated by high ALPase activities and deposition of mineralized
matrices by cells. Small bone-like spicules are observed as early as 14 days. The chitosan/
β-TCP scaffolds can be used as a matrix to grow osteoblast in a 3D structure for trans-
plantation into a site for bone regeneration in vivo [172,173]. Moreover, chitosan/β-TCP
composites are developed as bone substitutes and tissue-engineering scaffolds with a
releasing function for some drug or GF with osteogenic effect. Zhang and Zhang [174]
reported that the initial burst of antibiotic gentamicin-sulfate release in chitosan/β-TCP
is greatly reduced, and the release rate in the second stage after the initial burst is higher
and steadier than that of pure chitosan scaffold. However, the release rate of transforming
growth factor-β (β-TGF) in chitosan/β-TCP composites is higher than that in chitosan at
the initial stage. And the concentration of released β-TGF from the chitosan/β-TCP m ic ro -
granules for 28 days is sufficient to induce a biological effect. The initial burst release can
be beneficial to the early healing and regenerative effect, and the following continuous
release can help osteoblasts proliferate [175,176].
4.4.1.2 Chitosan/HAp Composite System
In the chitosan/HAp composite system, the chitosan network not only serves as a matrix
to the HAp particles but also provides an anchoring site for HAp particles in the structure.
There are multiple interactions between chitosan and HAp. For example, HAp may inter-
act with the plentiful amino and hydroxyl groups of chitosan by the formation of hydro-
gen bonds [177]. Ca 2+ ions, which appear on the terminal surface of HAp crystals, have a
coordination number of 7 and are strictly held in the composite through coordination with
the -NH 2 of chitosan. Wilson and Hull [178] prepared the nano-HAp-chitosan composites
via surface modification of nanophase HAp with chitosan. Chitosan exhibits strong
adsorption interactions with HAp, which enhance colloid stability for the processing of
chitosan/HAp nanocomposites and cause an increase in specific surface areas. However,
the hybrid composite seems to be dissociated possibly due to the degradation of the
chitosan [179].
The addition of nHAp to pure chitosan leads to a decrease in the degree of water absorp-
tion. However, the water retention ability of chitosan scaffolds and chitosan/HAp is
similar with only small differences. The compression modulus of hydrated scaffolds sig-
nificantly increases on the incorporation of nHAp and increases with increasing nHAp
content in the scaffold, which can be attributed to the strong interaction between chitosan
and HAp. Favorable biological responses of preosteoblast (MC 3T3-E1) on nanocomposite
scaffolds include improved cell adhesion, higher proliferation, and well spreading mor-
phology in relation to pure chitosan scaffold [180].
Oliveira et al. [181] prepared the chitosan/HAp bilayer scaffold; the bilayered scaffolds
exhibit excellent physicochemical properties, which appear to make them a suitable candi-
date to be used as a supportive structure for cell functions. Moreover, the in vitro cell cul-
ture studies demonstrate that both HAp and chitosan layers provide an adequate 3D