Preparation and purification of polyisohexylcyanoacrylate nanocapsules

Stabilization challenges and formulation strategies associated with oral biologic drug delivery systems

Delivery of proteins to mucosal tissues of GI tract typically utilize formulations which protect against proteolysis and target the mucosal tissues. Using case studies from literature and the authors' own work, the in-process stability and solid state storage stability of biopharmaceuticals formulated in delivery systems designed for oral delivery to the GI tract will be reviewed. Among the range of delivery systems, biodegradable polymer systems for protection and controlled release of proteins have been the most studied; hence these systems will be covered in greater depth. These delivery systems include polymeric biodegradable microspheres or nanospheres that contain proteins or vaccines, which are designed to reduce the number of administrations/inoculations and the total protein dose required to achieve the desired biological effect. Specifically, this review will include a landscape survey of the systems that have been studied, the manufacturing processes involved, stability through the manufacturing process, key pharmaceutical formulation parameters that impact stability of the encased proteins, and storage stability of the encapsulated proteins in these delivery systems.

NMR relaxation dispersion of Miglyol molecules confined inside polymeric micro-capsules

Frequency dependent NMR relaxation studies have been carried out on Miglyol molecules confined inside core shell polymeric capsules to obtain a correlation between capsule dimension and the measurable parameters. The polymeric capsules were prepared using an interfacial polymerization technique for three different concentrations of Miglyol. It was shown that the variation of Miglyol concentration influences the capsule dimension. Their average size was estimated using the pulsed field gradient diffusometry technique. The relaxation dispersion curves were obtained at room temperature by a combined use of a fast field cycling instrument and a high-field instrument. The frequency dependence of relaxation rate shows a transition from a diffusion-limited to a surface-limited relaxation regime.

Nanoprodrugs of NSAIDs: Preparation and Characterization of Flufenamic Acid Nanoprodrugs

We demonstrated that hydrophobic derivatives of the nonsteroidal anti-inflammatory drug (NSAID)flufenamic acid (FA), can be formed into stable nanometer-sized prodrugs (nanoprodrugs) that inhibit the growth of glioma cells, suggesting their potential application as anticancer agent. We synthesized highly hydrophobic monomeric and dimeric prodrugs of FA via esterification and prepared nanoprodrugs using spontaneous emulsification mechanism. The nanoprodrugs were in the size range of 120 to 140 nm and physicochemically stable upon long-term storage as aqueous suspension, which is attributed to the strong hydrophobic interaction between prodrug molecules. Importantly, despite the highly hydrophobic nature and water insolubility, nanoprodrugs could be readily activated into the parent drug by porcine liver esterase, presenting a potential new strategy for novel NSAID prodrug design. The nanoprodrug inhibited the growth of U87-MG glioma cells with IC₅₀ of 20 μM, whereas FA showed IC₅₀ of 100 μM, suggesting that more efficient drug delivery was achieved with nanoprodrugs.

Design and production of nanoparticles formulated from nano-emulsion templates-a review

A considerable number of nanoparticle formulation methods are based on nano-emulsion templates, which in turn are generated in various ways. It must therefore be taken into account that active principles and drugs encapsulated in nanoparticles can potentially be affected by these nano-emulsion formulation processes. Such potential differences may include drug sensitivity to temperature, high-shear devices, or even contact with organic solvents. Likewise, nano-emulsion formulation processes must be chosen in function of the selected therapeutic goals of the nano-carrier suspension and its administration route. This requires the nanoparticle formulation processes (and thus the nano-emulsion formation methods) to be more adapted to the nature of the encapsulated drugs, as well as to the chosen route of administration. Offering a comprehensive review, this paper proposes a link between nano-emulsion formulation methods and nanoparticle generation, while at the same time bearing in mind the above-mentioned parameters for active molecule encapsulation. The first part will deal with the nano-emulsion template through the different formulation methods, i.e. high energy methods on the one hand, and low-energy ones (essentially spontaneous emulsification and the phase inversion temperature (PIT) method) on the other. This will be followed by a review of the different families of nanoparticles (i.e. polymeric or lipid nanospheres and nanocapsules) highlighting the links (or potential links) between these nanoparticles and the different nano-emulsion formulation methods upon which they are based.

Alkylcyanoacrylate nanocapsules prepared from mini-emulsions: a comparison with the conventional approach

Polyalkylcyanoacrylate nanocapsules are being prepared using two different types of o/w-emulsions: a conventional emulsion generated by intensive stirring with a home-made device and a mini-emulsion produced by the action of ultrasonic dispersion, using the alkylcyanoacrylate monomer as a hydrophobic agent. The emulsions and the resulting nanocapsule dispersions are compared using various methods of physical characterization. The formation of solid capsules is indicated by solid state NMR spectra and atomic force microscopy. Differences between the results of both synthetic approaches are found in terms of particle size distribution, zeta potential and tendency towards particle agglomeration. Capsules prepared by ultrasound via the mini-emulsion pathway tend to be smaller and more monodisperse. Their zeta potential is negative with larger absolute values as compared to capsules obtained from conventional emulsions, leading to stronger repulsive interactions and a higher stability against capsule agglomeration.

Characterisation of colloidal drug delivery systems from the naked eye to Cryo-FESEM

Poly(ethylcyanoacrylate) nanoparticles prepared by interfacial polymerisation on the basis of microemulsions were prepared in this study and both colloidal systems, nanoparticles and microemulsions, were analysed by visual observation and several microscopic techniques. Phase boundaries for the microemulsions of the two pseudoternary systems ethyloleate, polyoxyethylene 20 sorbitan mono-oleate/sorbitan monolaurate and water with and without butanol as a cosurfactant were determined by visual observation of the samples. Microemulsions containing liquid crystals were determined by polarisation light microscopy. Using freeze-fracture transmission electron microscopy and Cryo-field emission scanning electron microscopy the type of microemulsion (w/o droplet, bicontinuous, solution) was characterised. Nanoparticles prepared from the different types of microemulsion were additionally observed by conventional scanning electron microscopy. The size of the nanoparticles obtained from electron microscopy was in good agreement with particle sizing techniques (photon correlation spectroscopy) from earlier studies and no morphological differences could be observed in particles prepared from the different types of microemulsions. Cryo-field emission scanning electron microscopy proved to be a most valuable technique in the visualisation of the colloidal systems as samples could be observed close to their natural state.

Nanoparticles and nanocapsules created using the Ouzo effect: spontaneous emulisification as an alternative to ultrasonic and high-shear devices

The preparation of polymeric particles and capsules by means of spontaneous droplet formation and subsequent polymer precipitation or synthesis is well-known. However, spontaneous emulsification is a phenomenon that has often been erroneously interpreted. This Minireview provides new insights into the preparation of metastable liquid dispersions by homogeneous liquid-liquid nucleation, and is based primarily on a recent study by Vitale and Katz (Langmuir, 2003, 19, 4105-4110). This spontaneous emulsification, which they named the Ouzo effect, occurs upon pouring, into water, a mixture of a totally water-miscible solvent and a hydrophobic oil--and optionally some water--thus generating long-lived small droplets, which are formed even though no surfactant is present. Herein, we review and reinterpret the most relevant publications on the synthesis of a variety of dispersions (pseudolatexes, silicone emulsions, biodegradable polymeric nanocapsules, etc.), which we believe have actually been synthesized using the Ouzo effect. The Ouzo effect may also become a substitute for high-shear techniques, which, to date have only been of limited utility on industrial scales.

Nanocapsules as drug delivery systems

Dispersed polymer nanocapsules can serve as nano-sized drug carriers to achieve controlled release as well as efficient drug targeting. The dispersion stability and the primary physiological response are mainly determined by the type of the surfactant and the nature of the outer coating. Their release and degradation properties largely depend on the composition and the structure of the capsule walls. Another important criterion is the capsule size, where an optimum is generally seen for radii ranging between 100 and 500 nm. Nanocapsules can be prepared by four principally different approaches: interfacial polymerization, interfacial precipitation, interfacial deposition, and self assembly procedures. All these procedures offer their individual advantages and disadvantages when it comes to the design of optimized drug carrier systems. The most important capsule parameters such as capsule radius distribution, the capsule surface, the thickness and the permeability of the capsule membrane and its thermal or chemical decomposition, are discussed and examples are shown. In combination with efficient preparation procedures, nanocapsule dispersions allow for new and promising approaches in many kinds of pharmaceutical therapies.

Synthesis and characterization of polyurethane and poly(ether urethane) nanocapsules using a new technique of interfacial polycondensation combined to spontaneous emulsification

Polyurethane polymers and poly(ether urethane) copolymers were chosen as drug carriers for alpha-tocopherol. This active ingredient is widely used as a strong antioxidant in many medical and cosmetic applications, but is rapidly degraded, because of its light, heat and oxygen sensitivity. Polyurethane and poly(ether urethane)-based nanocapsules were synthesized by interfacial reaction between two monomers. Interfacial polycondensation combined with spontaneous emulsification is a new technique for nanoparticles formation. Nanocapsules were characterized by studying particle size (150-500 nm), pH, yield of encapsulation and morphologies. Polyurethanes (PUR) were obtained from the condensation of diisocyanate (isophorone diisocyanate: IPDI) and polyol: 1,2-ethanediol (EG), 1,4-butanediol (BD), 1,6-hexanediol (HD). Poly(ether urethane) copolymers were obtained by replacing diols by polyethylene glycol oligomers (PEG) M(w) 200, 300, 400 and 600. Molecular weights of di- and polyols have a considerable influence on nanocapsules characteristics cited above. The increase of molecular weight of polyols tends to increase the mean size of nanocapsules from (232+/-3)nm using EG to (615+/-39)nm using PEG 600, and led to the apparition of a population of agglomerate particles. We also noted that the yield of encapsulation increases with the increase of polyol length (from 85.6 to 92.2% w/w). Microscopic observations confirmed particle size analysis, but cannot predict the membrane structure owing the small size of the particles.

Pulsed field gradient NMR on polybutylcyanoacrylate nanocapsules

The applicability of pulsed field gradient nuclear magnetic resonance spectroscopy to nanocapsule systems is demonstrated on dispersed poly-n-butylcyanoacrylate nanocapsules as a model system. Spectroscopic data are presented that allow for the structural characterization of the inner cavities, the observation of Brownian motion of the capsules and the detection of rapid molecular exchange through the capsule walls. An analytical formula is proposed that yields equilibrium populations and average residence times of a given tracer molecule, thus leading to crucial information regarding the permeability of the capsule walls. Based on these analytical methods, two varieties of nanocapsules are compared that derive from two different preparation procedures. It is found that thinner capsule walls obtained under acidic conditions of the organic phase during interfacial polymerization lead to correspondingly higher exchange rates of benzene as a tracer molecule.

Association of cyclosporin to isohexylcyanoacrylate nanospheres and subsequent release in human plasma in vitro

Polyisohexylcyanoacrylate nanocapsules containing cyclosporin were prepared by mixing in a 1:2 ratio an oil/ethanol solution of monomer and drug with an aqueous phase. Drug nanoencapsulation rate was controlled by its partition coefficient between the inner (organic) and outer (aqueous) phases. Thus highest encapsulation yields (88 per cent) were achieved by reducing cyclosporin solubility in the aqueous phase, i.e. by reducing ethanol concentration under reduced pressure, achieving a 3-fold volume reduction. Due to the relative insolubility of cyclosporin in water, no drug was released from the nanocapsules during storage in this injectable vehicle. Upon a 1/5 dilution in human plasma at 37 degrees C in vitro around 40 per cent of the initially encapsulated cyclosporin diffused quickly out of the capsules and an equilibrium was reached, the drug being most likely dissolved in the fatty compartment of the plasma such as lipoproteins, etc. This release mechanism is different from plain polymeric nanoparticles. Indeed, in this case the drug was released in two phases: an initial burst (around 60 per cent) of adsorbed drug as a result of the dilution, followed by a slow release (around 20 per cent over 3 h) which is likely to result from the progressive enzymatic erosion of the polymer. The initial burst was markedly more pronounced (around 80 per cent) when nanoparticle suspensions were evaporated to 1/3 of their initial volume under reduced pressure. Finally, experiments performed at 0 degree C allowed a reduction of the fraction released immediately from both types of nanospheres, probably because of a reduced solubility in plasma. In the case of nanoparticles the second phase of slow release is also inhibited at 0 degree C, in agreement with an enzymatically controlled release mechanism.