technology. However, before medical applications of chitosan can be considered,
one has to consider first its safety for application on or in living systems.
Talking about medical application, the first question to address is “is chitosan
safe for internal application?” Recent data have confirmed the safety of chitosan.
Chitosan has very low toxicity; the LD 50 of chitosan in laboratory mice is 16 g/kg
body weight, which is close to that of sugar or salt. Chitosan is proven to be safe in
rats at up to 10% in the diet [8]. There was some concern after some Japanese
experiments showed that high doses of chitosan intravenously gave rise to
haemorrhage pneumonia, caused by complement activation. However, this should
be considered in the light of the law of the medieval scientist Paracelsus, who stated
that high concentration makes every compound a toxin. Recent data both in
medium-term feeding studies in laboratory animals and humans have confirmed
that body and organ weight remained normal, as well as neuro-, cardio-, respiratory,
hepato-, digestive, urinary and circulatory systems. There can be some discomfort,
such as belching. The only effect is a significantly lower plasma cholesterol level.
Various sterilization methods such as ionizing radiation, heat, steam and chemical
methods can be adopted for sterilization of chitosan in clinical applications [9].
2.2 Alginate
Alginate is a naturally arising, linear unbranched polysaccharide that is soluble
in water and extracted from brown seaweed. Its use in numerous biomedical
applications, including drug delivery systems, is basically due to its high
biodegradable, biocompatible and mucoadhesive polymers. Alginate polymers are
also haemocompatible, have not been found to accumulate in any important organs
and show indication of in vivo degradation. Sodium alginate is used in a variety of
oral and topical pharmaceutical formulations and has been used for the aqueous
microencapsulation of drugs, in contrast to more conventional solvent-based systems.
Alginate possesses two types of uronic acids, L-guluronic acid and D-mannuronic acid.
Micro- and nanoparticles of alginate are effortlessly achieved by gelation with
calcium ions. This property enables creation of a pre-gel consisting of miniature
aggregates of gel particles, which can be tracked by the addition of an aqueous
polycationic solution to make a polyelectrolyte complex coating. Poly-L-lysine
(PLL) is a cationic natural polymer that has been used with alginates to formulate
nanoparticles.
The mechanical properties and swelling of alginate beads shaped using cations
hinge upon a number of aspects like valence of ions, size of ions, etc. Bajpani et al.
[10] describe a comprehensive examination of swelling and degradation performance of alginate beads crosslinked with different metal ions (e.g. Ca
2+ , Ba
2+ and
Al
3+ ). The results can be explained on the basis of the extent of crosslinking in the
beads and the size of the cations involved in the crosslinking process.
276
A.K. Anal and A. Tuladhar
one has to consider first its safety for application on or in living systems.
Talking about medical application, the first question to address is “is chitosan
safe for internal application?” Recent data have confirmed the safety of chitosan.
Chitosan has very low toxicity; the LD 50 of chitosan in laboratory mice is 16 g/kg
body weight, which is close to that of sugar or salt. Chitosan is proven to be safe in
rats at up to 10% in the diet [8]. There was some concern after some Japanese
experiments showed that high doses of chitosan intravenously gave rise to
haemorrhage pneumonia, caused by complement activation. However, this should
be considered in the light of the law of the medieval scientist Paracelsus, who stated
that high concentration makes every compound a toxin. Recent data both in
medium-term feeding studies in laboratory animals and humans have confirmed
that body and organ weight remained normal, as well as neuro-, cardio-, respiratory,
hepato-, digestive, urinary and circulatory systems. There can be some discomfort,
such as belching. The only effect is a significantly lower plasma cholesterol level.
Various sterilization methods such as ionizing radiation, heat, steam and chemical
methods can be adopted for sterilization of chitosan in clinical applications [9].
2.2 Alginate
Alginate is a naturally arising, linear unbranched polysaccharide that is soluble
in water and extracted from brown seaweed. Its use in numerous biomedical
applications, including drug delivery systems, is basically due to its high
biodegradable, biocompatible and mucoadhesive polymers. Alginate polymers are
also haemocompatible, have not been found to accumulate in any important organs
and show indication of in vivo degradation. Sodium alginate is used in a variety of
oral and topical pharmaceutical formulations and has been used for the aqueous
microencapsulation of drugs, in contrast to more conventional solvent-based systems.
Alginate possesses two types of uronic acids, L-guluronic acid and D-mannuronic acid.
Micro- and nanoparticles of alginate are effortlessly achieved by gelation with
calcium ions. This property enables creation of a pre-gel consisting of miniature
aggregates of gel particles, which can be tracked by the addition of an aqueous
polycationic solution to make a polyelectrolyte complex coating. Poly-L-lysine
(PLL) is a cationic natural polymer that has been used with alginates to formulate
nanoparticles.
The mechanical properties and swelling of alginate beads shaped using cations
hinge upon a number of aspects like valence of ions, size of ions, etc. Bajpani et al.
[10] describe a comprehensive examination of swelling and degradation performance of alginate beads crosslinked with different metal ions (e.g. Ca
2+ , Ba
2+ and
Al
3+ ). The results can be explained on the basis of the extent of crosslinking in the
beads and the size of the cations involved in the crosslinking process.
276
A.K. Anal and A. Tuladhar