Formation and stability of solid lipid nanoparticles fabricated using phase inversion temperature method

Abstract

Abstract Solid lipid nanoparticles (SLNs) are being investigated for their ability to encapsulate and protect lipophilic bioactive compounds in foods, supplements, and pharmaceuticals. In this study, the phase inversion temperature (PIT) method was used to fabricate SLNs using a model surfactant (Brij 30, C12E4)/oil (octadecane)/water system. Surfactant/oil/water (SOW) mixtures were maintained at a temperature above the PIT, and then rapidly cooled to a temperature below the lipid nanoparticle crystallization point. The PIT (≈40 °C) was determined by monitoring the turbidity versus temperature profile of the SOW system during heating. The lipid nanoparticle crystallization point, melting point, and physical state were determined using differential scanning calorimetry (DSC). The stability of the lipid nanoparticles after fabrication depended on the storage temperature relative to the PIT and melting/crystallization points. At temperatures appreciably below their melting point (≈26 °C), the lipid nanoparticles were completely solid and stable to aggregation. At temperatures around their melting point, the lipid nanoparticles were partially crystalline, which led to partial coalescence and gelation. At temperatures appreciably above their melting point but below their PIT, the lipid nanoparticles were completely liquid and prone to coalescence and phase separation. These results have important implications for optimizing the fabrication and storage conditions required to produce stable nanoemulsions suitable for utilization in commercial products using low-energy methods.