Biomedical Engineering Reference
In-Depth Information
Photocrosslinkable chitosan, bearing p-azidobenzoic acid and lactobi-
onic acid, when crosslinked by UV-irradiation (250W lamp, 2 cm distance,
240-380 nm prevalent 340 nm), resulted in a rubber-like l exible and
transparent hydrogel. h e hydrogel showed a strong adhesion to tissues,
signii cant induction of wound contraction and acceleration of wound clo-
sure and healing [102, 217].
Experimental wound dressings derived from chitins and chitosans are
available in the form of hydrogels, xerogels, powders, composites, i lms,
non-wovens, nanoi brils, sponges and scaf olds: the latter are easily colo-
nised by human cells in view of the restoration of tissue defects with the
advantage of avoiding retractive scar formation. Chitosan's positive surface
charge provides ef ective ability for promotion of cell attachment, prolifer-
ation and growth with retention of the normal cell morphology [218]. h e
occlusive, semi-permeable chitin i lm dressings are l exible, sot , transpar-
ent and less distressing in removal from wound. h ese are generally non-
absorbent, exhibiting a total weight gain of only 120-160 % in physiological
l uid. Dry chitin i lms transpire water vapour at a rate of about 600 g/m
2
/24
hr, (similar to commercial polyurethane-based i lm dressings), that rises to
2400 g/m
2
/24 hr when wet (higher than the water vapour transmission rate
of intact skin) [210] However, pure chitosan i lms, sponges, have a poor
tensile strength and elasticity due to their brittleness. Hence, addition of
other polymers is necessary to achieve i lms with improved strength and
elasticity.
Wound healing chitosan-based materials tested experimentally
include, chitosan-chitin nanoi bers [219], Chitosan glycolate-chitin
nanoi bers [182]
chitin nonoi brils-alginate [220], chitosan-polyethyl-
ene glycol [221, 222], chitosan-polyvinylpyrrolidone hydrogels [223],
Chitosan-polyurethane/poly(N-isopropylacrylamide) thermosensitive
membrane [224], semi-interpenetrating polymer networks of chitosan-
poloxamer [225], chitosan-polysaccharide composites with corn starch,
dextran [226] and polyelectrolyte complexes of chitosan with oppositely
charged polyelectrolytes as its own anionic derivatives (sulfated chitosan
or N-carboxybutyl chitosan). Chitin nanoi brils in addition to restructur-
ing the medium, contribute signii cantly to ef ectivity by improving the
overall susceptibility to lysozyme and release of chito oligomers.
To improve the healing process, chitosan has been combined with a
variety of modii ed materials such as growth factors [227, 228], extracel-
lular matrix components as hyaluronic acid [229], heparin [230], collagen
[231], gelatin [232, 233], taurine [234], and antibacterial agents as minocy-
cline [235], chlorhexidine [182, 229], norl oxacin [236], silver sulfadiazine
[237], preformed silver nanoparticles [238], etc.
