Bioactive Polymers and Nanobiomaterials Composites for Bone Tissue Engineering - Biomimetics: Advancing Nanobiomaterials and Tissue Engineering - page 107

PLGA/HAp composites still showed advantageous biological behavior
[93]. Further work has reported on the resorption process of PLGA/HAp
nanocomposites implanted into rabbit submaxilla bones [95]. The resorp-
tion of composite occurred simultaneously with the formation of new
bone tissue, and authors found that after 3 weeks following the implanta-
tion the bone-implant interface becomes rough, which indicated resorp-
tion of polymer with bone tissue ingrowth.

5.4.2 Natural Polysaccharide Nanocomposites

The natural polysaccharides have attracted a signifi cant interest in scien-
tifi c and industrial communities for biomedical applications. This is due
to their attractive properties such as good biodegradability, low toxicity,
low manufacturing cost, low disposal cost, environmental friendly pro-
duction and disposal and renewability prospect [97]. A large variety of
natural materials have been studied and proposed for biotechnological
applications. Some of these offer additional advantages for tissue engi-
neering applications such as biological signaling, cell adhesion, cell
responsive degradation, re-modeling, etc. However, the down side of
using natural polymers is that these may rapidly degrade with the pos-
sible loss of biological properties during formulation and storage, often
compromising their use as unique scaffold materials. Despite the minor
downside, the current research has been focused on the use of natural
polymers which include chitin and chitosan, starch and cellulose-based
polymer composites, for the fabrication of scaffolds for bone tissue
regeneration.

5.4.2.1 Chitin and Chitosan and Their Nanocomposites

Chitin, poly ( b -(1-4)-N-acetyl-D-glucosamine), is a natural polysaccharide
of major importance, synthesized by an enormous number of living organ-
isms (e.g., in the shells of crabs and shrimp, the cuticles of insects, and the
cell walls of fungi and yeast) [97, 98], and it is the most abundant poly-
mer after cellulose. Chitosan, is the most important (an N-deacetylated)
derivative of chitin containing varying fractions of the two residues [98]
randomly distributed b -(1-4)-linked D-glucosamine (deacetylated unit)
and N-acetyl-D-glucosamine (acetylated unit). It is obtained by (partial)
deacetylation of chitin in the solid state under alkaline conditions or by
enzymatic hydrolysis.
Chitin and CS-based nanocomposite materials enhance bone forma-
tion both in vitro and in vivo (Table 5.2) [99, 100], but its mechanical weak-
ness and instability, together with its incapacity to maintain a predefi ned
shape, limits the scope of its applicability. Therefore, researchers com-
bined CS with a variety of materials including HAp, calcium phosphate