DEXTRAN MICROSPHERES AS A POTENTIAL NASAL DRUG-DELIVERY SYSTEM FOR INSULIN - IN-VITRO AND IN-VIVO PROPERTIES

The influence of the particle size of dextran microspheres on nasal absorption and the localisation of insulin in the spheres have been investigated in rats. Using scanning electron microscopy, it was shown that the freeze-drying process used to load insulin into the microspheres had a significant impact on the integrity and surface properties of the spheres. It was confirmed via confocal laser scanning microscopy (CLSM) that the distribution of insulin in the dextran microspheres was governed by the cut-off limit of the spheres. A cut-off of 5000 Da excludes insulin from the dextran matrix, leaving insulin on the surface of the spheres. A cut-off of 30 000 Da, on the other hand, allows insulin to penetrate into the swollen spheres and be deposited inside the spheres after the lyophilisation process. Spheres with insulin on the surface were more effective in promoting insulin absorption than those with insulin distributed within the dextran matrix. There seems to be a tendency for the particle size to influence the kinetics of the insulin effect curve.