Chitosan Composites for Biomedical Applications: An Overview - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 18

is the most efficient at gene delivery. Oligomeric derivatives (3-6 kDa) are relatively
non-toxic and have good gene delivery properties (Kean et al., 2005).
Recent clinical data indicate that modified chitosan with amino acid moieties and
substituents at the N-atom play an active role in wound healing. In general, these
induce formation of vascularized and non refractive tissues having well-oriented col-
lagen. Trimethyl-chitosan and monocarboxymethyl chitosan has been shown to be
effective as intestinal absorption enhancers due to their physiological properties.
Chitosan-thioglycolic acid conjugates have been found to be a promising candidate as
scaffold material in tissue engineering due to their physicochemical properties. Niamsa
et al. (2009) successfully prepared the nanocomposite blend films containing methoxy
poly(ethylene glycol)-b-poly(D,L-lactide) nanoparticles with different chitosan/silk
fibroin ratios. These biodegradable nanocomposite blend films may have potential for
use in drug delivery, wound dressing, and tissue engineering applications (Niamsa
et al., 2009). Goy et al. (2009) stated that water soluble chitosan derivatives, which
can be attained by chemical introduction of CH 3 in the main chain, enhancing the
chitosan applicability in a large pH range and also improve the antimicrobial activity,
opening up a broad range of possibilities (Goy et al., 2009). According to Rujiravanit
et al. (2003), crosslinked chitosan and its blend films with SF using glutaraldehyde as
crosslinking agent exhibit drug release characteristics. The drug release was high in
acidic medium because of the protonation of the amino groups on chitosan at acidic pH,
resulting in the dissociation of hydrogen bonds between chitosan and SF (Rujiravanit
et al., 2003).
Hirano et al. (1980) prepared a series of membranes from chitosan and its deriva-
tives (Hirano, 1978; Hirano et al., 1980), and the membranes showed improved dialy-
sis properties (Arai et al., 2004; Fuchs et al., 2006). They observed that permeability
properties of N -acetyl chitosan membranes were similar to those of an Amicon Diaflo
membrane UM-10 (Amicon Ltd., England). Chitosan membranes were modified with
vinyl monomers using 60-Co g-ray irradiation, and their physicochemical properties
were also studied. The modified membranes showed improved permeability and blood
compatibility (Singh and Ray, 1994, 1997). The reactive functional groups present
in chitosan (amino group at the C2 position of each deacetylated unit and hydroxyl
groups at the C6 and C3 positions) can be readily subjected to chemical derivatiza-
tion allowing the manipulation of mechanical and solubility properties enlarging its
biocompatibility.
Fibrous Protein--silk
The SF, the typical natural macromolecule spun by Bombyx mori silkworm, has been
used as textile fiber and suture. The natural silk fibers are one of the strongest and
toughest materials mainly because of the dominance of well orientated b-sheet struc-
tures of protein chains. Recently, several researchers have investigated SF as one of
promising resources of biotechnology and biomedical materials due to its unique prop-
erties including good biocompatibility, good oxygen and water vapor permeability,
biodegradability, minimal inflammatory reaction (Minoura et al., 1990; Sakabe et al.,
1989; Santin et al., 1999), good cell adhesion and growth characteristics, protease
susceptibility, and high tensile strength (Altman et al., 2003; Gotoh et al., 2002; Lv