Novel physically structured lipid matrices of beeswax and a homolipid from Capra hircus (goat fat): a physicochemical characterization for application in drug delivery

Abstract

Lipid based materials are fast becoming the carrier of choice for delivery of new chemical entities and active agents. It is important to know the thermal characteristics, crystal habit, texture and appearance of a new lipid matrix when determining its suitability for use in pharmaceutical formulations. In this study, physically structured lipid matrices containing various proportions (25% w/w, 50% w/w and 75% w/w) of beeswax in a novel homolipid from Capra hircus (goat fat) were prepared by fusion, and subjected to thermal treatments in a differential scanning calorimeter (DSC) to obtain the thermal characteristics. Further characterization of the lipid matrices was performed by X-ray diffraction, polarized light microscopy (PLM) and transmission electron microscopy (TEM). Kinetics of crystallization of the molten lipid matrices was studied in an isothermal heat conduction microcalorimeter (IMC). Analysis of thermal data from DSC indicated that the physically structured lipid matrices revealed varied melting peaks between those of the pure lipids. PLM observation exhibited qualitatively different textures for the different structured lipid matrices. The lipid matrix containing 50% w/w of beeswax presented an interference at 2θ = 1.2° d = 73.63 A different from those of the two pure lipids. The lipid matrix containing 75% w/w of beeswax showed a change in crystallization behavior after 34 h. Crystallization kinetic analysis indicated that the structured lipid matrix containing 50% w/w beeswax possessed the highest Avrami kinetic exponent n. Results obtained indicated that mixtures of beeswax and goat fat produced matrices composed of mixtures of crystals alongside mixed crystals with imperfections necessary for increased drug loading and retention capacities. The matrix containing 50% w/w of beeswax possessed ideal crystal properties for the formulation of colloidal and microparticulate lipid drug carrier systems of drug delivery.