Polymethacrylate based microparticulates of insulin for oral delivery, part II: solid state characterization

The objectives of the present study were (A) to characterize insulin microparticles prepared by the coprecipitation process by size exclusion chromatography, differential scanning calorimetry, fourier-transform IR spectroscopy, and powder X-ray diffractometry, and (B) to study the solid state conformation of insulin before and after entrapment in the polymeric carrier. Microparticles were prepared by dissolving insulin in 0.01 N HCI and alcohol USP to get a final concentration of 32% v/v. Eudragit L100, a representative polymethyacrylate polymer, was then dissolved in this solution which was transferred to a beaker containing cold water with homogenization to obtain microparticulates. Insulin powder, microcapsules, and a physical mixture of insulin and Eudragit L100 were then analyzed by SEC-HPLC, DSC, FTIR, and XRD to observe changes in protein conformation as result of the manufacturing process. While DSC, XRD and FTIR results were of limited value due to limits of instrument sensitivity, size exclusion chromatography data indicated that higher order aggregates were not formed during microcapsule formation. It was concluded that formulating insulin into microparticles by the coprecipitation process is an attractive and stable method for protein delivery and might be suitable for oral delivery of insulin.