Freeze-Fracture Electron Microscopy on Nano- and Micro-Delivery Vehicles for Biological Active Compounds

Abstract

The potency of nano- and micro-vehicles, loaded with therapeutics or/and diagnostics (theranostics) is strongly depending upon their morphology adopted at their site of action. Freeze-fracture transmission electron microscopy (ff-TEM) as a cryo-fixation method is a powerful technique to monitor the morphology of nano- as well as micro-particles in biological relevant environments. At the resolution limit of 2nm we are able to characterize nano-particles such as quantum dots (coupled to drug-loaded immunoliposomes), gold nano-particles, superparamagnetic iron oxide nano-particles loaded in polymeric immunomicelles, micelles (spherical-, disc-, and worm-type micelles), single-wall carbon nano-tubes embedded in hydrated gels, and small unilamellar liposome (targeted and non-targeted). Furthermore, ff-TEM includes the production of beam-damage-resistant replica from much larger, micrometer-size objects such as multilamellar liposome, niosomes, cationic liposome/DNA complexes, integrin-targeted lipopolyplexes, polymer-, lipid- or surfactant-stabilized gas bubbles, cochleate cylinder, and depofoam particles. Ff-TEM enables us not only to monitor self-assembling of lipid-, polymer-, as well as protein/peptide-based carriers encapsulating drug-, gene-, vaccine, antimicrobial- and imaging molecules but is the method of choice as well to study their fate related to their pay load, application milieu, and during cell interaction. Furthermore, we investigated structural modifications within mono- and bilayers such as domain-formation but also transformations to non-bilayer structures such as hexagonal and cubic phases. Currently we are focused on cochleate cylinder as macrocarrier for antibiotics combating bacterial multidrug resistance.