Characterization of biologically active insulin-loaded alginate microparticles prepared by spray drying

Abstract

Background: Spray drying has been used as a means to encapsulate therapeutics in polymeric matrices to improve stability and alter pharmacokinetics. This research aims to characterize alginate microparticles formed by spray drying to encapsulate insulin for therapeutic delivery applications.

Methods: Particle size was characterized by laser diffraction spectroscopy, morphology by scanning electron microscopy, and protein and polymer distribution by confocal laser scanning microscopy. In addition, particle fines collected from the spray-dryer exhaust unit were characterized for size and morphology. The insulin encapsulation efficiency (EE) was determined after particle dissolution through quantification by spectrophotometric analysis. An in-vitro bioassay involving stimulation of rat L6 myoblasts was developed to confirm the bioactivity of released insulin.

Results: Mean diameter of the product was 2.1 ± 0.3 μm. Larger particles appeared spherical, with some smaller particles presenting surface topography variability and divoting. Protein EE was 38.2% ± 9.5%, with confocal microscopy showing the protein and polymer concentrated at the surface of larger particles, but more evenly distributed throughout smaller particles. A bioassay for the in-vitro quantification of insulin bioactivity was developed by calibrating the ratio of phosphorylated to total cellular protein kinase B (PKB; also known as AKT). in insulin-stimulated rat L6 myoblasts. Insulin released from the particles was 88% ± 15% bioactive, showing that spray drying had minimal impact on protein structure.

Conclusion: Spray drying was effective in producing microparticles containing bioactive insulin. Future studies will focus on the improvement of the EE and particle uniformity with the aim of developing this technology further for the encapsulation and delivery of peptide or protein-based therapeutics.

Keywords::

• Encapsulation
• drug delivery
• insulin bioassay
• spray drying
• alginate

Acknowledgments

The authors thank Matt Gordon and Jeff Mewburn for help with the confocal microscope, Charles Cooney for help with SEM operation, and Terri Semler for help with the fluorescent labeling of alginate. This study was supported by the Natural Sciences and Engineering Research Council of Canada and by the Way Memorial Trust Award of Queen’s University. Funding for infrastructure for the cell culture studies was provided by the Canadian Foundation for Innovation (CFI) Leader’s Opportunity Fund (LOF) and the Ontario Ministry of Research and Innovation (MRI) Ontario Research Fund− Research Infrastructure (ORF-RI) programs.

Declaration of interest

The authors report no conflicts of interest.