Polyphosphazene microspheres for insulin delivery

Polyphosphazene based microspheres for insulin delivery were prepared following three different procedures: (A) suspension-solvent evaporation; (B) double emulsion-solvent evaporation; (C) suspension/double emulsion-solvent evaporation. Methods A and C allowed for higher protein loading than procedure B. Scanning electron microscopy showed that all preparation procedures achieve microparticles with spherical shape, porous surface and internal honeycomb structure. In all cases insulin was released 'in vitro' by a bi-modal behaviour: fast release during the first 2 hours followed by a slow release. However, both the physical properties and the 'in vitro' release profiles were found to depend upon the preparation conditions. Subcutaneous administration to diabetic mice of microspheres obtained with methods A and C rapidly reduced the glucose levels of about 80% but most of activity was lost in 100 hours. Both preparations B induced a remarkable decrease in glucose levels and the activity was maintained throughout 1000 h. Finally all preparations stimulated anti-insulin antibody production that constantly increased over a period of 8 weeks.