Studying the colloidal behavior of chimeric liposomes by cryo-TEM, micro-differential scanning calorimetry and high-resolution ultrasound spectroscopy

The investigation of colloidal properties of nanosystems represents a fundamental issue for the development of nanotechnology-based medicines. The aim of this study is to combine various techniques in order to characterize more comprehensively chimeric nanovesicles composed of block or gradient block copolymers with different architectures and compositions. Several chimeric systems were prepared and the impact of the block [poly(ε-caprolactone)−poly(ethylene oxide); PEO-b-PCL] and gradient block [poly(2-methyl-2-oxazoline)-grad-poly(2-phenyl-2-oxazoline); MPOx] copolymers on the physicochemical and morphological characteristics of conventional 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) liposomes was examined. Light scattering techniques and cryo-TEM were used for the physicochemical and morphological characterization of the prepared systems. The size and the morphology were strongly related to the architecture and the composition of the polymeric compounds. Micro differential scanning calorimetry and high-resolution ultrasound spectroscopy were used for investigating the interactions between the DPPC lipids and the polymeric guest. An increase in the main transition temperature was observed for the prepared chimeric systems in comparison to DPPC liposomes. In conclusion, a detailed characterization of the colloidal behavior of chimeric liposomes can benefit from the combination of the aforementioned techniques that operate synergistically, giving information on their physicochemical and morphological characteristics as well as on their thermotropic behavior.