Microencapsulation of indomethacin by gelatin-acacia complex coacervation in the presence of surfactants.

Gelatin-acacia microcapsules containing indomethacin were prepared by a complex coacervation method. To improve the wetting of hydrophobic core material different surfactants, cationic benzalkonium chloride, anionic sodium lauryl sulphate (SLS) or non-ionic polysorbate 20, were used. The effects of surfactants on microencapsulation were investigated at concentrations below, at and above their critical micelle concentration (CMC) using three different stirring speeds (200, 310 and 420 rpm). A considerable fraction of the core was leached out during the dehydration of microcapsules with isopropanol when the capsules were prepared without surfactant, and especially with SLS. SLS was noted to be an unsuitable surfactant for this process of microencapsulation, and this was considered to be due to ionic complexes, solubilization of gelatin and too-effective spreading of small coacervate droplets. Benzalkonium chloride enhanced encapsulation at concentrations below and at CMC, but above CMC the encapsulation was slightly decreased due to too-effective spreading of coacervate. Polysorbate 20 enhanced encapsulation with all the concentrations allowing for the formation of intact-walled microcapsules. All the microcapsules reduced in size with increasing stirring speed. The two lowest concentrations of benzalkonium chloride and all the concentrations of polysorbate 20 increased microcapsule size due to a greater amount of the colloids being available in formation of thicker walled microcapsules. The dissolution of unencapsulated indomethacin was very slow, but the drug was released quickly from all the microcapsules whether or not any type of surfactant was used. A hydrophilic wall of gelatin-acacia microcapsules in itself ensured quick wetting of hydrophobic indomethacin.