Alginate Microparticles Produced by Spray Drying for Oral Insulin Delivery
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The aim of this study was to prepare biologically active insulin-loaded alginate microparticles by spray drying. Particles were produced from three alginate feed concentrations of 1, 1.5 and 2% w/v, with respective insulin loadings of 11.8, 7.8 and 5.8 mg/g of alginate and investigated in terms of mass yield, moisture content, particle size, morphology and encapsulation efficiency. The mass yield of the system was determined to be between 15 and 30%, with approximately 3% of the initial dry mass ending up in the exhaust filter. The moisture content of the particles was found to be between 4.9 and 11.1% and the mean size ranged between 1.2 and 1.6 μm. Particulate morphologies were observed to be mostly spherical with some ‘divots’ present on the surface. Lastly, the encapsulation efficiency determined by absorbance assay was approximately 40%. Particles produced from a 2% alginate feed were further assayed by determining the release of insulin in simulated gastrointestinal conditions and looking at the insulin and alginate distribution within spray dried particles. A steep release profile was observed in the first 120 min of the simulation in a gastric pH of 1.2 and a longer, more sustained release is observed in intestinal conditions, where an additional 20% of the total insulin in the particles is released over 600 min. Fluorescent labels revealed that insulin and alginate are concentrated towards the periphery of the particles. The residual bioactivity of insulin was assessed by an in vitro bioactivity assay, which was developed using Fast Activated Cell Based ELISA (FACE™) AKT kits specific for phosphylated AKT. The bioactivity of insulin in the particles after spray drying was determined to be 87.9 ± 15.3%.