Crystallization tendency and polymorphic transitions in triglyceride nanoparticles

The ability of tristearin, tripalmitin, trimyristin and trilaurin to form solid lipid nanoparticles after melt-homogenization is investigated by DSC and X-ray diffraction. Upon storage at common temperatures after preparation solid nanoparticles are formed in tristearin and tripalmitin dispersions. In contrast to literature reports, colloidal dispersions of trilaurin do not form solid particles under those conditions. They should, therefore, be regarded as emulsions of supercooled melts rather than as nanosuspensions. Trimyristin nanoparticles which can be obtained in solid or liquid form have a larger incorporation capacity for the lipophilic model drug menadione in the liquid than in the solid state. The kinetics of polymorphic transitions after crystallization of triglyceride nanoparticles are slower for longer-chain than for shorter-chain triglycerides. Addition of tristearin raises the crystallization temperature of colloidally dispersed trimyristin and trilaurin facilitating solidification during production. The structure and melting behavior of the resulting mixed nanoparticles are more complex than those of nanoparticles prepared from the simple triglycerides. Depending on the mixing ratio, the time-course of polymorphic transitions after crystallization may also be altered significantly The melting enthalpy of the mixed nanoparticle dispersions is usually not significantly different from that of dispersions of the simple triglycerides.