Biomedical Engineering Reference
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TNF-α secretion in the incubation media recovered with the concentration of chitosan.
These results and reports once again suggest that chitosan may have an antiinflamma-
tory effect on LPS-stimulated inflammation and the effect of chitosan on IL-6 secretion
may be induced via the stimulus of TNF-α in RAW264.7 cells. In the experiment [147],
upon stimulation with increasing concentrations of chitosan, LPS-stimulated NO secre-
tion was also significantly recovered within the 6 h and 12 h incubation media of RAW264.7
cells. These results once again suggest that chitosan may have an antiinflammatory effect
on LPS-stimulated inflammation.
In the TNF-α-treated group, chitosan did not affect LPS-stimulated IL-6 and NO secre-
tion in RAW264.7 cells. These results again confirmed that the recovery effect of chitosan on
IL-6 and NO secretion might be induced via the stimulus of TNF-α in RAW 264.7 cells.
3.4.1.4 Antiinflammatory Activity of COSs
Chitosan has been used as a source of potential bioactive material in the past few decades.
However, in the biomedical field, COSs are more widely applicable due to their water solu-
bility and higher absorption profiles at the intestinal level, quickly getting into the blood
flow and having systemic biological effects on the organism. To explore the antiinflamma-
tory activities of COS, two COS mixtures (obtained via enzymatic activity, with MW < 3
and <5 kDa) at several concentrations were tested, by carrageenan-induced pawedema
methodology, in mice. The inflammatory response was quantified by increase in paw
size (edema), which is maximal around 5 h post-carrageenan injection, and is modulated by
inhibitors of specific molecules within the inflammatory cascade. COS showed antiinflam-
matory action, which increased with increasing MW. COS < 5 kDa even showed a higher
effect than the control, indomethacin, after 2 h, with no harmful secondary effects. The data
suggest that COS possesses antiinflammatory effect, and is dose and MW dependent.
3.4.1.5 Sustained Release Matrix of Chitosan Microspheres
Chitosan has been used for sustained release systems, preparation of mucoadhesive for-
mulations, and improvement of the dissolution rate of poorly soluble drugs, drug target-
ing, and enhancement of peptide drug absorption. So far, studies on the preparation of
chitosan microspheres have been carried out. Microspheres were prepared by using a
cross-linking agent such as glutaraldehyde combined with an emulsion technique. Other
approaches used an emulsion/solvent evaporation technique and spray drying. In general,
chitosan microspheres can be prepared as follows [148]. Chitosan (0.25% w/v) was dis-
solved in an aqueous solution of acetic acid (2% v/v) containing 1% polysorbate 80. A solu-
tion of sodium sulfate (20% w/v) was added dropwise (5 mL/min) during stirring with a
blade stirrer at 400 rpm and ultrasonication. The formation of microspheres was indicated
by turbidity and examined by transmission measurements at 500 nm. After the addition of
sodium sulfate, stirring and sonication were continued for another 1 h. The microspheres
were purified by centrifugation for 15 min at 3000 rpm. The obtained sediment was then
suspended in water. These two purification steps were repeated twice. All purified micro-
spheres were then lyophilized.
The production process of the present microspheres is based on the solubility behavior of
chitosan, which is poorly soluble in water. Addition of an acid improves the solubility as a
result of the protonation of the amino groups. The solubility is also dependent on other
anions present in the solution. In the presence of acetate, lactate, or glutamate, chitosan shows
good solubility, whereas phosphate, polyphosphates, and sulfate decrease the solubility. For
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