Influence of size, surface coating and fine chemical composition on the in vitro reactivity and in vivo biodistribution of lipid nanocapsules versus lipid nanoemulsions in cancer models.

Lipid nanocapsules (LNCs) and lipid nanoemulsions (LNEs) are biomimetic synthetic nanocarriers. Their in vitro and in vivo performance was evaluated as a function of their size (25, 50 and 100 nm) and the surface PEG chain length. Analysis methods included complement activation test, particle uptake in macrophage and HEK293(ß3) cells and biodistribution studies with tumor-grafted mice by fluorescence imaging. A particular attention was paid to keep the concentration of each nanocarrier and to the amount of fluorescent dye in comparable conditions between the in vitro and in vivo studies. Under these conditions, no significant differences were found among the three tested particle sizes and the two nanocarrier types. Longer PEG chains on the LNE surface provided better stealth properties, whereas PEG modification on the LNC formulations inhibited the production of stable nanocarriers. Passive accumulation of LNCs and LNEs in different tumor types depended on the degree of tumor vascularization. FROM THE CLINICAL EDITOR: This study of lipid nanocapsules and lipid nanoemulsions compares their vitro and in vivo performance as a function of size and surface PEG chain length, demonstrating no significant difference among the tested particle sizes. Longer PEG chains on the LNE surface provided better stealth properties, whereas PEG modification on the LNC formulations inhibited the production of stable nanocarriers.

Effect of sugars, surfactant, and tangential flow filtration on the freeze-drying of poly(lactic acid) nanoparticles.

Poly(D,L-lactic acid) nanoparticles were freeze-dried in this study. With respect to drying, effect of protective excipients and purification from excess surfactant were evaluated. The nanoparticles were prepared by the nanoprecipitation method with or without a surfactant, poloxamer 188. The particles with the surfactant were used as such or purified by tangential flow filtration. The protective excipients tested were trehalose, sucrose, lactose, glucose, poloxamer 188, and some of their combinations. The best freeze-drying results in terms of nanoparticle survival were achieved with trehalose or sucrose at concentrations 5% and 2% and, on the other hand, with a combination of lactose and glucose. Purification of the nanoparticle dispersion from the excess surfactant prior to the freeze-drying by tangential flow filtration ensured better drying outcome and enabled reduction of the amount of the protective excipients used in the process. The excess surfactant, if not removed, was assumed to interact with the protective excipients decreasing their protective mechanism towards the nanoparticles.

Quantitative determination of drug encapsulation in poly(lactic acid) nanoparticles by capillary electrophoresis.

Capillary electrophoretic (CE) methods were used for the quantitative determination of model drugs [salbutamol sulphate (SS), sodium cromoglycate (SCG) and beclomethasone dipropionate (BDP)] in poly(D,L-lactic acid) (PLA) nanoparticles, which were prepared by the nanoprecipitation method. Zeta potential and size distribution of the nanoparticles were determined by electrophoretic mobility determinations and photon correlation spectroscopy, respectively. Interactions between the drugs, the PLA nanoparticles and the fused-silica capillary were investigated by electrokinetic capillary chromatography (EKC). A quantitative CE method was developed for salbutamol sulphate and sodium cromoglycate, and the linearity and repeatability of migration times, peak areas and peak heights were determined. Microemulsion electrokinetic chromatography was used for the quantitative determination of beclomethasone dipropionate. According to this study, the applied electromigration techniques were suitable for the interaction, drug entrapment and dissolution studies of pharmaceutical nanoparticles. The results suggest that even quantitation of the drug located inside the nanoparticles was possible. Encapsulation of the more hydrophilic model drugs (SS, SCG) in the PLA nanoparticles was less efficient than in the case of BDP.

Freeze-drying of low molecular weight poly(L-lactic acid) nanoparticles: effect of cryo- and lyoprotectants.

The chemical and physical stability of polymeric nanoparticles is poor in aqueous suspensions, and the drying of these particles is often problematic. In the present study, the stability of freeze-dried low molecular weight poly(L-lactic acid) (PLA) nanoparticles was enhanced by adding glucose and/or lactose to the formulation as cryo- and lyoprotectants, respectively. Also the effect of an extra stabilizer, Tween 80, was studied. The best freeze-dried PLA nanoparticle formulations were achieved, when glucose and lactose were added in combination so that the amount of lactose was double the amount of glucose. With this combination the redispersion of high-quality nanoparticles (homogenous particle dispersion with original size and without aggregates) was achieved. The addition of Tween 80 further improved the quality of freeze-dried PLA nanoparticles by facilitating the redispersion of the lyophilized cake into optimal nanoparticles.

Layer-by-layer polyelectrolyte coating of low molecular weight poly(lactic acid) nanoparticles.

Low molecular weight (M(w)) poly(L-lactic acid) (PLA) nanoparticles were coated with polyelectrolytes (PEs) by layer-by-layer (LbL) technique using a filtration approach. Poly(allylamine hydrochloride) and poly(sodium 4-styrenesulfonate) were applied as PEs in coating. LbL coating is aimed to use in producing (nano)particulate drug delivery systems with improved biocompatibility and sustained or targeted release of drug substances. Nanoparticles of rapidly biodegradable polymers, like the low M(w) PLA, open up a possibility to control the release of the encapsulated substance by the coating, but set challenges to the coating process due to increased aggregation tendency and degradation rate of the polymer. When the core PLA nanoparticles were prepared by nanoprecipitation, surface properties of the nanoparticles were affected by solvent selection. Successful LbL coating of the PLA nanoparticles was obtained only with chloroform, but not with dichloromethane as the solvent during nanoprecipitation. Reason for this was found to be the more charged surface of the nanoparticles prepared with chloroform compared to the nanoparticles prepared with dichloromethane.

Evaluation of surface deformability of lipid nanocapsules by drop tensiometer technique, and its experimental assessment by dialysis and tangential flow filtration.

Deformability of nanoparticles might affect their behaviour at biological interfaces. Lipid nanocapsules (LNCs) are semi-solid particles resembling a hybrid of polymer nanoparticles and liposomes. Deformability of LNCs of different sizes was modelled by drop tensiometer technique. Two purification methods, dialysis and tangential flow filtration (TFF), were applied to study experimental behaviour and deformability of LNCs in order to evaluate if these properties contributed to membrane passing. Rheological parameters obtained from the drop tensiometer analysis suggested decreasing surface deformability of LNCs with increase in diameter. Dialysis results showed that up to 10% of LNCs can be lost during the process (e.g. membrane accumulation) but no clear evidence of the membrane passing was observed. Instead, LNCs with initial size and size distribution could be found in the TFF filtrate although molecular weight cut-off (MWCO) of the membrane used was smaller than the LNC diameter.

Novel, dynamic on-line analytical separation system for dissolution of drugs from poly(lactic acid) nanoparticles.

A novel method for investigating drug release in a dynamic manner from nanoparticles including, but not limited to, biodegradable poly(lactic acid) (PLA) is reported. The PLA nanoparticles were prepared by the nanoprecipitation method. Two poorly soluble drugs, beclomethasone dipropionate (BDP) and indomethacin, were encapsulated into PLA nanoparticles, and their dissolution from the nanoparticles were followed in a dynamic way. The on-line method comprised a short column (vessel) packed with the PLA nanoparticles, on-line connected to an analytical liquid chromatographic column via a multiport switching valve equipped with two loops. The system allowed monitoring of the drug release profiles in real time, and the conditions for the drug release could be precisely controlled and easily changed. The effects of solvent composition and temperature on the rate of dissolution of the drugs from the PLA nanoparticles were investigated. The system proved to be linear for the drugs tested over the concentration range 10-3000 ng (n=6, R(2)=0.999 and 0.997 for indomethacin and beclomethasone, respectively) and repeatable (RSD of peak areas <0.5%). The recoveries of the dissolution study were quantitative (120 and 103% for indomethacin and beclomethasone, respectively).

Nanodispersions of taxifolin: impact of solid-state properties on dissolution behavior.

Nanosizing is an advanced formulation approach to address the issues of poor aqueous solubility of active pharmaceutical ingredients. Here we present a procedure to prepare a nanoparticulate formulation with the objective to enhance dissolution kinetics of taxifolin dihydrate, a naturally occurring flavonoid with antioxidant, anti-inflammatory, and hepatoprotective activities. Polyvinylpirrolidone was selected as a carrier and the solid nanodispersions of varying compositions were prepared by a co-precipitation technique followed by lyophilization. The formulation technology reported herein resulted in aggregate-free, spherical particles with the mean size of about 150 nm, as observed by scanning electron microscopy and measured by photon correlation spectroscopy. Furthermore, the co-precipitation process caused taxifolin dihydrate to convert into an amorphous form as verified by X-ray powder diffraction, differential scanning calorimetry, hot stage microscopy and Raman spectroscopy. Finally, in vitro dissolution behavior of the nanodispersion of taxifolin was shown to be superior to that of either pure drug or a drug-polymer physical mixture, reaching 90% of taxifolin released after 30 min. Such enhanced drug release kinetics from the nanodispersion was attributed to both the reduced particle size and the loss of crystallinity.