Nano-emulsions for Drug Delivery and Biomedical Imaging

Lipophilic molecular rotor to assess the viscosity of oil core in nano-emulsion droplets

Characterization of nanoscale formulations is a continuous challenge. Size, morphology and surface properties are the most common characterizations. However, physicochemical properties inside the nanoparticles, like viscosity, cannot be directly measured. Herein, we propose an original approach to measuring dynamic viscosity using a lipidic molecular rotor solubilized in the core of nano-formulations. These molecules undergo conformational changes in response to viscosity variations, leading to observable changes in fluorescence intensity and lifetime, able to sense the volume properties of dispersed nano-domains. The lipophilic molecular rotor (BOPIDY derivatives) was specifically synthesized and characterized as oil viscosity sensing in large volumes. A second part of the study compares these results with rBDP-Toco in nano-emulsions. The objective is to evaluate the impact of the formulation, droplet size and composition on the viscosity of the droplet's core. The lipophilic rotor showed a universal behavior whatever the oil composition, giving a master curve. Applied to nano-formulations, it reveals the viscosity inside the nano-emulsion droplets, enabling the detection of slight variations between reference oil samples and the nano-formulated ones. This new tool opens the way to the fine characterization of complex colloids and multi-domain nano and micro systems, potentially applied to hybrid materials and biomaterials.

Radiopaque Iodosilane-Coated Lipid Hybrid Nanoparticle Contrast Agent for Dual-Modality Ultrasound and X-ray Bioimaging

Here, we report the synthesis of robust hybrid iodinated silica-lipid nanoemulsions (HSLNEs) for use as a contrast agent for ultrasound and X-ray applications. We engineered iodinated silica nanoparticles (SNPs), lipid nanoemulsions, and a series of HSLNEs by a low-energy spontaneous nanoemulsification process. The formation of a silica shell requires sonication to hydrolyze and polymerize/condensate the iodomethyltrimethoxysilane at the oil/water interface of the nanoemulsion droplets. The resulting nanoemulsions (NEs) exhibited a homogeneous spherical morphology under transmission electron microscopy. The particles had diameters ranging from 20 to 120 nm with both negative and positive surface charges in the absence and presence of cetyltrimethylammonium bromide (CTAB), respectively. Unlike CTAB-coated nanoformulations, the CTAB-free NEs showed excellent biocompatibility in murine RAW macrophages and human U87-MG cell lines in vitro. The maximum tolerated dose assessment was evaluated to verify their safety profiles in vivo. In vitro X-ray and ultrasound imaging and in vivo computed tomography were used to monitor both iodinated SNPs and HSLNEs, validating their significant contrast-enhancing properties and suggesting their potential as dual-modality clinical agents in the future.

Biodistribution of 68/67Ga-Radiolabeled Sphingolipid Nanoemulsions by PET and SPECT Imaging

Background and Purpose

Non-invasive imaging methodologies, especially nuclear imaging techniques, have undergone an extraordinary development over the last years. Interest in the development of innovative tracers has prompted the emergence of new nanomaterials with a focus on nuclear imaging and therapeutical applications. Among others, organic nanoparticles are of the highest interest due to their translational potential related to their biocompatibility and biodegradability. Our group has developed a promising new type of biocompatible nanomaterials, sphingomyelin nanoemulsions (SNs). The aim of this study is to explore the potential of SNs for nuclear imaging applications.

Methods

Ready-to-label SNs were prepared by a one-step method using lipid derivative chelators and characterized in terms of their physicochemical properties. Stability was assessed under storage and after incubation with human serum. Chelator-functionalized SNs were radiolabeled with ⁶⁷Ga and ⁶⁸Ga, and the radiochemical yield (RCY), radiochemical purity (RCP) and radiochemical stability (RCS) were determined. Finally, the biodistribution of ^67/68Ga-SNs was evaluated in vivo and ex vivo.

Results

Here, we describe a simple and mild one-step method for fast and efficient radiolabeling of SNs with ⁶⁸Ga and ⁶⁷Ga radioisotopes. In vivo experiments showed that ^67/68Ga-SNs can efficiently and indistinctly be followed up by PET and SPECT. Additionally, we proved that the biodistribution of the ^67/68Ga-SNs can be conveniently modulated by modifying the surface properties of different hydrophilic polymers, and therefore the formulation can be further adapted to the specific requirements of different biomedical applications.

Conclusion

This work supports ^67/68Ga-SNs as a novel probe for nuclear imaging with tunable biodistribution and with great potential for the future development of nanotheranostics.

Optimizing the Fluorescence Properties of Nanoemulsions for Single Particle Tracking in Live Cells

Nanoemulsions (NEs) are biocompatible lipid nanoparticles composed of an oily core stabilized by a surfactant shell. It is acknowledged that the surface decoration with poly(ethylene glycol), through the use of nonionic surfactants, confers high stealth in biological medium with reduced nonspecific interactions. Tracking individual NE by fluorescence microscopy techniques would lead to a better understanding of their behavior in cells and thus require the development of bright single particles with enhanced photostability. However, the understanding of the relationship between the physicochemical properties and chemical composition of the NEs, on the one hand, and its fluorescence properties of encapsulated dyes, on the other hand, remains limited. Herein, we synthesized three new dioxaborine barbituryl styryl (DBS) dyes that displayed high molar extinction coefficients (up to 120 000 M^-1 cm^-1) with relatively low quantum yields in solvents and impressive fluorescence enhancement when dissolved in viscous oils (up to 0.98). The reported screening of nine different oils allowed disclosing a range of efficient "oil/dye" couples and understanding the main parameters that lead to the brightest NEs. We determine vitamin E acetate/DBS-C₈ as the representative most efficient couple, combining high dye loading capabilities and low aggregation-induced quenching, leading to <50 nm ultrabright NEs (with brightness as high as 30 × 10⁶ M^-1 cm^-1) with negligible dye leakage in biological media. Beyond a comprehensive optical and physicochemical characterization of fluorescent NEs, cellular two-photon excitation imaging was performed with polymer-coated cell penetrating NEs. Thanks to their impressive brightness and photostability, NEs displaying different charge surfaces were microinjected in HeLa cells and were individually tracked in the cytosol to study their relative velocity.