(73b) Preparation of Bioactive Insulin Microparticles for Pulmonary Delivery Using Supercritical Carbon Dioxide

Insulin is an important pharmaceutical protein, which is delivered into the body exclusively via subcutaneous injection for diabetes therapy. Pulmonary delivery, which is a noninvasive route, has been considered as an alternative to injection. For pulmonary delivery, fine particles with narrow size distribution are essential. For example, the efficient inhalation therapy needs microparticles with size ranging from 1 to 5 μm to reach the deep lung. Moreover, the surface morphology of particles affects the dispersibility and flowability of the powders. Therefore, elaborate control of particle size and morphology plays a key role in the development of insulin formulations for inhalation.

Supercritical fluid assisted atomization (SAA) is a promising process in producing micrometric particles that may find much application in medical and pharmaceutical fields. An improved SAA process, i.e. supercritical fluid assisted atomization introduced by hydrodynamic cavitation mixer (SAA-HCM), was proposed by our group, which uses supercritical carbon dioxide to assist atomization and a cavitation mixer to intensify mass transfer. This novel technique can be operated not only on organic solvents but also aqueous solutions. In this paper, insulin was micronized using SAA-HCM process from aqueous solution without use of any organic solvents. Insulin microparticles produced under different conditions including solution type, solution concentration and precipitator temperature presented distinct morphologies such as highly folded, partly deflated, corrugated or smooth hollow spherical shape. Solution concentration had a striking influence on particle size, and insulin microparticles produced from acidic solution had volume median diameters increasing from 2.3 μm to 4.3 μm when protein concentration increased from 3 g/L to 50 g/L. HPLC chromatograms showed no degradation of insulin after SAA-HCM processing and FTIR, CD and fluorescence data further confirmed the structural stability. TGA analysis revealed that insulin microparticles remained moderate moisture content compared with raw material. In vivo study showed that insulin processed by SAA-HCM retained identical bioactivity.

SAA-HCM is demonstrated to be successful in producing insulin microparticles with different surface morphologies and well controlled size distribution. Therefore, it presents great potential in developing insulin pulmonary delivery formulations, especially in inhaled dry powders.