Thierry F. Vandamme

Nano-emulsions and Micro-emulsions: Clarifications of the Critical Differences

ABSTRACTMuch research has been done over the past years on self-emulsifying drug delivery systems, their main interest being the simplicity of the formulation processes, the great stability of the systems and their high potential in pharmaceutical applications and industrial scaling-up. Self-emulsifying drug delivery systems are generally described in the literature indiscriminately as either nano-emulsions or micro-emulsions. Although this misconception appears to be common, these two systems are fundamentally different, based on very different physical and physicochemical concepts. Their differences result in very different stability behaviors, which can have significant consequences regarding their applications and administration as nanomedicines. This paper aims at clarifying the problem, first by reviewing all the physical and physicochemical fundamentals regarding these two systems, using a quantitative thermodynamic approach for micro-emulsions. Following these clarifications, we show how the confusion between nano-emulsions and micro-emulsions appears in the literature and how most of the micro-emulsion systems referred to are actually nano-emulsion systems. Finally, we illustrate how to clear up this misconception using simple experiments. Since this confusion is well established in the literature, such clarifications seem necessary in order to improve the understanding of research in this important field.

Nanoparticles by spray drying using innovative new technology: the Büchi nano spray dryer B-90.

Spray drying technology is widely known and used to transform liquids (solutions, emulsions, suspension, slurries, pastes or even melts) into solid powders. Its main applications are found in the food, chemical and materials industries to enhance ingredient conservation, particle properties, powder handling and storage etc. However, spray drying can also be used for specific applications in the formulation of pharmaceuticals for drug delivery (e.g. particles for pulmonary delivery). Büchi is a reference in the development of spray drying technology, notably for laboratory scale devices. This study presents the Nano Spray Dryer B-90, a revolutionary new sprayer developed by Büchi, use of which can lower the size of the produced dried particles by an order of magnitude attaining submicron sizes. In this paper, results are presented with a panel of five representative polymeric wall materials (arabic gum, whey protein, polyvinyl alcohol, modified starch, and maltodextrin) and the potentials to encapsulate nano-emulsions, or to formulate nano-crystals (e.g. from furosemide) are also shown.

Microencapsulation of Lactobacillus plantarum spp in an alginate matrix coated with whey proteins

Whey proteins were used as a coating material to improve encapsulation of Lactobacillus plantarum strains in calcium alginate beads. L. plantarum 299v, L. plantarum 800 and L. plantarum CIP A159 were used in this study. Inactivation experiments were carried out in simulated gastric fluid (SGF) and simulated intestinal fluid (SIF). Cross-sections of freeze-dried beads revealed the random distribution of bacteria throughout the alginate network. From an initial count of 10.04+/-0.01 log(10) CFU g(-1) for L. plantarum 299v, 10.12+/-0.04 for L. plantarum CIP A159 and 10.03+/-0.01 for L. plantarum 800, bacteria in coated beads and incubated in SGF (37 degrees C, 60 min) showed a better survival for L. plantarum 299v, L. plantarum CIP A159 and L. plantarum 800 (respectively 7.76+/-0.12, 6.67+/-0.08 and 5.81+/-0.25 log(10) CFU g(-1)) when compared to uncoated beads (2.19+/-0.09, 1.89+/-0.09 and 1.65+/-0.10 log(10) CFU g(-1)) (p<0.05). Only bacteria in the coated beads survived in the SIF medium (37 degrees C, 180 min) after SGF treatment. This preliminary work showed that whey proteins are a convenient, cheap and efficient material for coating alginate beads loaded with bacteria.

Iodinated blood pool contrast media for preclinical X-ray imaging applications: A review

The in vivo X-ray micro-computed tomography (micro-CT) is a very powerful and non-invasive tool used to establish high-resolution images with isotropic voxels in typical scan times ranging from minutes to tenths of minutes. This preclinical imaging technology is primarily adapted to visualize bones. X-ray imaging of soft tissues is made possible by using opaque compounds, providing contrast through tissue vascularization. Thus, using control agents with a long-lasting time in the blood, active or passive targeting of soft tissue is made possible in small animals. In this respect, the use of hydrophilic iodinated X-ray contrast media remains limited due to their rapid blood clearance, albeit at a slightly slower pace in humans as compared with rodents. The development of an iodinated contrast medium with increased vascular residence time is thus necessary. This is precisely the scope of the present paper, which will review and compare in detail the different vectors used as long-circulating iodinated contrast agents for micro-CT, i.e. liposomes, nanoemulsions, micelles, dendrimers and other polymeric particles. The discussion is focused, for each of these nanoparticulate systems, on their method of formulation and production, their stability properties, encapsulation properties, release properties, pharmacokinetics, and toxicology. The different aspects relative to the adaptation of these properties and physico-chemical characteristics for blood pool contrast agents aimed at angiographic micro-CT applications are also discussed. The aim of this review is to propose an overview into the formulation and properties of iodinated micro-CT contrast agents for preclinical applications.

Nanocarriers as pulmonary drug delivery systems to treat and to diagnose respiratory and non respiratory diseases

The purpose of this review is to discuss the impact of nanocarriers administered by pulmonary route to treat and to diagnose respiratory and non respiratory diseases. Indeed, during the past 10 years, the removal of chlorofluorocarbon propellants from industrial and household products intended for the pulmonary route has lead to the developments of new alternative products. Amongst these ones, on one hand, a lot of attention has been focused to improve the bioavailability of marketed drugs intended for respiratory diseases and to develop new concepts for pulmonary administration of drugs and, on the other hand, to use the pulmonary route to administer drugs for systemic diseases. This has led to some marketed products through the last decade. Although the introduction of nanotechnology permitted to step over numerous problems and to improve the bioavailability of drugs, there are, however, unresolved delivery problems to be still addressed. These scientific and industrial innovations and challenges are discussed along this review together with an analysis of the current situation concerning the industrial developments.

Inorganic nanoparticles based contrast agents for X-ray computed tomography.

Nanomaterials have gained considerable attention and interest in the development of new and efficient molecular probes for medical diagnosis and imaging. Heavy metal nanoparticles as such are excellent absorber of X-rays and can offer excellent improvement in medical diagnosis and X-ray imaging. Substantial progress has been made in the synthesis protocol and characterization studies of these materials but a major challenge still lies in the toxicological studies, which are rather incomplete. The worst known cases were those associated with Thorotrast (suspension of ThO(2) nanoparticles) which resulted in many deaths over years. Properly protected nanomaterials conjugated or coated with biocompatible materials can be used for the fabrication of various functional systems with multimodality, targeting properties, reduced toxicity and proper removal from the body. This review aims mainly to provide the advances in the development of inorganic nanoparticle based X-ray contrasting agents with an overview of methods of their preparation, functionalization and applications in medical diagnosis.

Probiotic Encapsulation Technology: From Microencapsulation to Release into the Gut

Probiotic encapsulation technology (PET) has the potential to protect microorgansisms and to deliver them into the gut. Because of the promising preclinical and clinical results, probiotics have been incorporated into a range of products. However, there are still many challenges to overcome with respect to the microencapsulation process and the conditions prevailing in the gut. This paper reviews the methodological approach of probiotics encapsulation including biomaterials selection, choice of appropriate technology, in vitro release studies of encapsulated probiotics, and highlights the challenges to be overcome in this area.

Use of rodents as models of human diseases

Advances in molecular biology have significantly increased the understanding of the biology of different diseases. However, these discoveries have not yet been fully translated into improved treatments for patients with diseases such as cancers. One of the factors limiting the translation of knowledge from preclinical studies to the clinic has been the limitations of in vivo diseases models. In this brief review, we will discuss the advantages and disadvantages of rodent models that have been developed to simulate human pathologies, focusing in models that employ xenografts and genetic modification. Within the framework of genetically engineered mouse (GEM) models, we will review some of the current genetic strategies for modeling diseases in the mouse and the preclinical studies that have already been undertaken. We will also discuss how recent improvements in imaging technologies may increase the information derived from using these GEMs during early assessments of potential therapeutic pathways. Furthermore, it is interesting to note that one of the values of using a mouse model is the very rapid turnover rate of the animal, going through the process of birth to death in a very short timeframe relative to that of larger mammalian species.

Iodinated α-tocopherol nano-emulsions as non-toxic contrast agents for preclinical X-ray imaging

Micro-computed tomography (micro-CT) is an emerging imaging modality, due to the low cost of the imagers as well as their efficiency in establishing high-resolution (1-100 μm) three-dimensional images of small laboratory animals and facilitating rapid, structural and functional in vivo visualization. However use of a contrast agent is absolutely necessary when imaging soft tissues. The main limitation of micro-CT is the low efficiency and toxicity of the commercially available blood pool contrast agents. This study proposes new, efficient and non-toxic contrast agents for micro-CT imaging. This formulation consists of iodinated vitamin E (α-tocopheryl 2,3,5-triiodobenzoate) as an oily phase, formulated as liquid nano-emulsion droplets (by low-energy nano-emulsification), surrounded by a hairy PEG layer to confer stealth properties. The originality and strength of these new contrast agents lie not only in their outstanding contrasting properties, biocompatibility and low toxicity, but also in the simplicity of their fabrication: one-step synthesis of highly iodinated oil (iodine constitutes 41.7% of the oil molecule weight) and its spontaneous emulsification. After i.v. administration in mice (8.5% of blood volume), the product shows stealth properties towards the immune system and thus acts as an efficient blood pool contrast agent (t(1/2) = 9.0 h), exhibiting blood clearance following mono-exponential decay. A gradual accumulation predominantly due to hepatocyte uptake is observed and measured in the liver, establishing a strong hepatic contrast, persistent for more than four months. To summarize, in the current range of available or developed contrast agents for preclinical X-ray imaging, this agent appears to be one of the most efficient.

Highly lipophilic fluorescent dyes in nano-emulsions: towards bright non-leaking nano-droplets

Dye-loaded lipid nano-droplets present an attractive alternative to inorganic nanoparticles, as they are composed of non-toxic biodegradable materials and easy to prepare. However, to achieve high fluorescence brightness, the nano-droplets have to be heavily loaded with the dyes avoiding fluorescence self-quenching and release (leakage) of the encapsulated dyes from the nano-droplets in biological media. In the present work, we have designed highly lipophilic fluorescent derivatives of 3-alkoxyflavone (F888) and Nile Red (NR668) that can be encapsulated in the lipophilic core of stable nano-emulsion droplets at exceptionally high concentrations in the oil core, i.e. up to 170 mM and 17 mM, respectively, corresponding to ~ 830 and 80 dyes per 40-nm droplet. Despite this high loading, these dyes keep high fluorescence quantum yield and thus, provide high nano-droplet brightness, probably due to their bulky structure preventing self-quenching. Moreover, simultaneous encapsulation of both dyes at high concentrations in single nano-droplets allows observation of FRET. FRET and fluorescence correlation spectroscopy (FCS) studies showed that NR668 release in the serum-containing medium is very slow, while the reference hydrophobic dye Nile Red leaks immediately. This drastic difference in the leakage profile between NR668 and Nile Red was confirmed by in vitro cellular studies as well as by in vivo angiography imaging on zebrafish model, where the NR668-loaded nano-droplets remained in the blood circulation, while the parent Nile Red leaked rapidly from the droplets distributing all over the animal body. This study suggests new molecular design strategies for obtaining bright nano-droplets without dye leakage and their use as efficient and stable optical contrast agents in vitro and in vivo.