Polymorphism, crystallinity and hydrophilic–lipophilic balance of stearic acid and stearic acid–capric/caprylic triglyceride matrices for production of stable nanoparticles

There is an increasing interest in lipid nanoparticles because of their suitability for several administration routes. Thus, it becomes even more relevant the physicochemical characterization of lipid materials with respect to their polymorphism, lipid miscibility and stability, as well as the assessment of the effect of surfactant on the type and structure of these nanoparticles. This work focuses on the physicochemical characterization of lipid matrices composed of pure stearic acid or of mixtures of stearic acid–capric/caprylic triglycerides, for drug delivery. The lipids were analyzed by Differential Scanning Calorimetry (DSC), Wide Angle X-ray Diffraction (WAXD), Polarized Light Microscopy (PLM) and hydrophilic–lipophilic balance (HLB) in combination with selected surfactants to determine the best solid-to-liquid ratio. Based on the results obtained by DSC and WAXD, the selected qualitative and quantitative composition contributed for the production of stable nanoparticles, since the melting and the tempering processes provided important information on the thermodynamic stability of solid lipid matrices. The best HLB value obtained for stearic acid–capric/caprylic triglycerides was 13.8, achieved after combining these lipids with accepted surfactants (trioleate sorbitan and polysorbate 80 in the ratio of 10:90). The proposed combinations were shown useful to obtain a stable emulsion to be used as intermediate form for the production of lipid nanoparticles.

WAXS characterization of lipid materials to assess the crystallinity, polymorphism and lipid miscibility, of stearic acid or mixtures (70:30) of stearic acid–capric/caprylic triglycerides.Figure optionsDownload as PowerPoint slideHighlights
► For the production of long-term stable lipid nanoparticles, analysis of HLB values allows anticipating the best solid to liquid lipid ratio.
► A suitable surfactant/co-surfactant combination needs to be reached to develop more homogeneous emulsions, with no foaming or phase separation.
► The perfect interaction of hydrophilic and lipophilic emulsifiers on the o/w interface of emulsion is a demand.