Nondestructive rheological measurement of aqueous dispersions of solid lipid nanoparticles: effects of lipid types and concentrations on dispersion consistency

Abstract

Purpose: To investigate dispersion consistency of solid lipid nanoparticles as functions of lipid types and concentrations. Methods: Viscoelastic measurement at an application of low stress was employed to characterize the internal microstructure developed within the dispersions. Pure triglycerides with different length of fatty acid chains, trimyristin (C14), tripalmitin (C16), and tristearin (C18) were studied with respect to the partial triglyceride with C22 chain length (Compritol 888 ATO), and cetyl palmitate wax (C16). Results and discussion: Increasing fatty acid chain length of triglycerides induced more particle shape anisometry; therefore, elastic behavior of triglyceride dispersion increased in sequence of trimyristin < tripalmitin < tristearin. Because of an imperfect crystalline structure, Compritol 888 ATO particles yielded the dispersion with a less elastic behavior. Despite having an equal fatty acid chain length (C16), cetyl palmitate wax provided the dispersion with lower network strength than tripalmitin as a result of the lower ordered crystal packing of fatty acid chains in the wax particle. Increasing lipid concentration improved the dispersion consistency owing to the more pronounced interaction between lipid particles. Data obtained from particle size analysis did not help explain the resulting microstructures in relation to the types and concentrations of lipid. Conclusions: A nondestructive rheological experiment is a powerful tool in revealing the microscopic structures of SLNs, which provides the information on viscous and elastic behaviors, corresponding to the internal structure of the dispersions. Consequently, viscoelastic data might assist pharmaceutical industry in selecting type of lipid appropriate for developing SLN formulations with the desired consistency.