Incorporation of lipid nanoparticles into calcium alginate beads and characterization of the encapsulated particles by differential scanning calorimetry

The aim of this study was to encapsulate lipid nanoparticle dispersions into calcium alginate microbeads and to investigate the feasibility of this incorporation as well as the stability of the enclosed nanoparticles. Two methods were used to prepare the lipid-containing microbeads by external gelation, i.e. an electrostatic droplet generation technique and a spraying method using the two-fluid spray nozzle of a spray dryer. The particle sizes of the hydrogel beads were determined with laser diffraction. The first method produced particles with median sizes between 330 and 1350 μm, depending on the needle applied. Using the second method smaller particles (∼45 μm) could be prepared. Small tyloxapol-stabilized trimyristin nanoparticles (<100 nm) could easily be incorporated into the differently sized alginate beads. The small size of the lipid nanoparticles leads to a typical melting behavior characterized by the occurrence of multiple discrete melting peaks in their differential scanning calorimetry (DSC) thermograms which enabled the characterization of the lipid particles within the microbeads. Thus, any negative influence of the preparation procedure on the lipid dispersions could be detected and it was possible to verify optimization options of the incorporation procedure. Finally, handling and shelf life of the hydrogel beads were improved by a freezing process.