Ionically cross-linked chitosan/tripolyphosphate microparticles for the controlled delivery of pyrimethamine

Abstract

Chitosan ionically cross-linked with tripolyphosphate at regulated temperatures (25°C, 40°C, and 50°C) and varying cross-linking times (30 min, 2 h and 4 h respectively) was used to form microparticles employed in the encapsulation of pyrimethamine, an antiprotozoal drug. The yields, equilibrium moisture contents, percentage concentration, swelling characteristics, entrapment efficiency, release properties, infrared spectroscopy, and differential scanning calorimetry of the formulated microparticles were evaluated. The yield of microparticles produced ranged from 0.3515 to 0.7749 g per 100 ml of cross linking solution. The products possessed relatively little amounts of moisture (0.22 − 3.04 % w/v). The entrapment efficiencies ranged from 25.55 to 99 % with the product formed at ambient temperature and cross linking time of 30 min possessing the highest efficiency. The swelling kinetics on the microcapsules revealed that all the products swelled in the various pH media following mainly anomalous sorption mechanism with a few diffusion controlled mechanism. The greatest swellings however occurred at the swelling medium of pH 1 while the least swelling occurred at pH 7. Spectral and differential scanning calorimetric properties of the chitosan used in the study were consistent with those of standard chitosan. The infrared spectroscopy and differential scanning calorimetry of the products confirmed that encapsulation actually occurred with the spectral characters of the products differing from those of the parent constituents (chitosan, tripolyphosphate and pyrimethamine). Based on these factors, tripolyphosphate cross-linked chitosan microparticles present a suitable matrix for the controlled release of pyrimethamine.