(621g) Effects and Mechanism of Sodium Chloride and Tripolyphosphate On the Formation of Chitosan/Cellulose Sulphate Microcapsules

Polyelectrolyte complexes (PECs) are
association of complexes formed between oppositely charged polymers due to
electrostatic interactions. They have gained importance in modern
pharmaceutical technology especially for controlled drug delivery. Chitosan is
one of the few polycations that are widely used in the pharmaceutical industry
due to its high availability, low cost, biocompatibility and easy modification.
In order to improve the stability of chitosan PECs, crosslinking agents are
introduced. In practice, crosslinking agents may compete with polyanions for
binding sites on chitosan. Therefore, the selection of polyanions and
crosslinking agents, together with material addition sequences are important
factors in PEC preparing procedures. However, little research has focused on
the effect of crosslinking agents to the polyanions in the chitosan PEC
preparation. In this study, double-layer chitosan PECs were prepared and
studied using sodium cellulose sulphate (NaCS) as the corresponding polyanion.
Similar systems have been proved for the potential application as oral
colon-specific drug delivery systems. Tripolyphosphate (TPP) was used as a crosslinking
agent. The effect of TPP on the PEC formation was investigated by changing the
TPP addition sequence. Moreover, sodium chloride (NaCl) was used as an
adjusting agent in the chitosan/NaCS/TPP PEC formation processes.

The structure of the microcapsules formed under
different TPP addition times was characterized and compared. The mechanism of
the crosslinking effect of TPP in the chisotan/NaCS system was investigated and
the results showed that TPP had the binding priority in the system, which can
significantly affect the chitosan/NaCS PECs formation process. Drug release
behaviours from these PEC systems were also characterized.

The effects of NaCl on the microcapsule
formation process revealed that the microcapsules without NaCl in the
formulation had a thin and transparent layer on the surface, which can be
easily detached from the solid inner particle that was enclosed inside.
However, the microcapsule prepared with NaCl showed a solid particle structure
with a thicker wall and good wall-core interaction (Figure 1). The materials constructing
both the wall and the core of the two microcapsules were further analyzed using
FTIR, SEM, elemental analysis, UV spectroscopy and the mechanism of NaCl
effects was discussed. The effect of adding NaCl on controlled drug release was
investigated. The results studied can be applied to different PEC systems,
which may further facilitate the development of PEC microcapsules for
pharmaceutical applications.

Figure 1. Comparison of microcapsules prepared
with or without NaCl. (a) A microcapsule prepared without the addition of NaCl.
(b) A microcapsule prepared with the addition of NaCl.