Nanoprecipitation versus emulsion-based techniques for the encapsulation of proteins into biodegradable nanoparticles and process-related stability issues

The goal of this study was to investigate the entrapment of 3 different model proteins (tetanus toxoid, lysozyme, and insulin) into poly(D,L-lactic acid) and poly(D,L-lactic-co-glycolic acid) nanoparticles and to address process-related stability issues. For that purpose, a modified nanoprecipitation method as well as 2 emulsion-based encapsulation techniques (ie, a solid-in oil-in water (s/o/w) and a double emulsion (w1/o/w2) method) were used. The main modification of nanoprecipitation involved the use of a wide range of miscible organic solvents such as dimethylsulfoxide and ethanol instead of the common acetone and water. The results obtained showed that tetanus toxoid and lysozyme were efficiently incorporated by the double emulsion procedure when ethyl acetate was used as solvent (>80% entrapment efficiency), whereas it was necessary to use methylene chloride to achieve high insulin entrapment efficiencies. The use of the s/o/w method or the formation of a more hydrophobic protein-surfactant ion pair did not improve protein loading. The nanoprecipitation method led to a homogenous population of small nanoparticles (with size ranging from ≈130 to 560 nm) and in some cases also improved experimental drug loadings, especially for lysozyme (entrapment efficiency >90%). With respect to drug content determination, a simple and quick matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) method provided results very close to those obtained by reverse phase-high-performance liquid chromatography. With respect to protein stability, the duration and intensity of sonication were not a concern for tetanus toxoid, which retained more than 95% of its antigenicity after treatment for 1 minute. Only a high methylene chloride:water ratio was shown to slightly decrease toxoid antigenicity. Finally, no more than 3.3% of A21 desamido insulin and only traces of covalent insulin dimer were detected in nanoparticles. In conclusion, both the double emulsion and nanoprecipitation methods allowed efficient protein encapsulation. MALDI-TOF MS allowed accurate drug content determination. The manufacturing processes evaluated did not damage the primary structure of insuli

Biomaterials Used in Injectable Implants (Liquid Embolics) for Percutaneous Filling of Vascular Spaces

The biomaterials currently used in injectable implants (liquid embolics) for minimally invasive image-guided treatment of vascular lesions undergo, once injected in situ, a phase transition based on a variety of physicochemical principles. The mechanisms leading to the formation of a solid implant include polymerization, precipitation and cross-linking through ionic or thermal process. The biomaterial characteristics have to meet the requirements of a variety of treatment conditions. The viscosity of the liquid is adapted to the access instrument, which can range from 0.2 mm to 3 mm in diameter and from a few centimeters up to 200 cm in length. Once such liquid embolics reach the vascular space, they are designed to become occlusive by inducing thrombosis or directly blocking the lesion when hardening of the embolics occurs. The safe delivery of such implants critically depends on their visibility and their hardening mechanism. Once delivered, the safety and effectiveness issues are related to implant functions such as biocompatibility, biodegradability or biomechanical properties. We review here the available and the experimental products with respect to the nature of the polymer, the mechanism of gel cast formation and the key characteristics that govern the choice of effective injectable implant

Preparation of surfactant-free nanoparticles of methacrylic acid copolymers used for film coating

The aim of the present study was to prepare surfactant-free pseudolatexes of various methacrylic acid copolymers. These aqueous colloidal dispersions of polymeric materials for oral administration are intended for film coating of solid dosage forms or for direct manufacturing of manoparticles. Nanoparticulate dispersions were produced by an emulsification-diffusion method involving the use of partially water-miscible solvents and the mutual saturation of the aqueous and organic phases prior to the emulsification in order to reduce the initial thermodynamic instability of the emulsion. Because of the self-emulsifying properties of the methacrylic acid copolymers, it was possible to prepare aqueous dispersions of colloidal size containing up to 30% wt/vol of Eudragit RL, RS, and E using 2-butanone or methyl acetate as partially water-miscible solvents, but without any surfactant. However, in the case of the cationic Eudragit E, protonation of the tertiary amine groups by acidification of the aqueous phase was necessary to improve the emulsion stability in the absence of surfactant and subsequently to prevent droplet coalescence during evaporation. In addition, a pseudolatex of Eudragit E was used to validate the coating properties of the formulation for solid dosage forms. Film-coated tablets of quinidine sulfate showed a transparent glossy continuous film that was firmly attached to the tablet. The dissolution profile of quinidine sulfate from the tablets coated with the Eudragit E pseudolatex was comparable to that of tablets coated with an acetonic solution of Eudragit E. Furthermore, both types of coating ensured similar taste masking. The emulsification-evaporation method used was shown to be appropriate for the preparation of surfactant-free colloidal dispersions of the 3 types of preformed methacrylic acid copolymers; the dispersions can subsequently be used for film coating of solid dosage form

Co-encapsulation of dexamethasone 21-acetate and SPIONs into biodegradable polymeric microparticles designed for intra-articular delivery

Objective: Intra-articular drug delivery systems still suffer from too short-lasting effects. Magnetic particles retained in the joint using an external magnetic field might prolong the local release of an anti-inflammatory drug. For the purpose, superparamagnetic iron oxide nanoparticles (SPIONs) and dexamethasone 21-acetate (DXM) were co-encapsulated into biodegradable microparticles. Methods: Poly(D,L-lactide-co-glycolide) microparticles embedding both SPIONs and DXM were prepared by a double emulsion technique. The formulation was optimized in two steps, a screening design and a full factorial design, aiming at 10-mm particle diameter and high DXM encapsulation efficacy. Results: The most significant parameters were the polymer concentration, the stirring speed during solvent extraction and the extractive volume. Increasing the polymer concentration from 200 to 300 mgml-1, both the microparticle mean diameter and the DXM encapsulation efficacy increased up to 12 mm and 90%, respectively. The microparticles could be retained with an external magnet of 0.8T placed at 3 mm. Faster DXM release was obtained for smaller microparticles. Conclusion: The experimental set-up offered the tools for tailoring a formulation with magnetic retention properties and DXM release patterns corresponding to the required specifications for intra-articular administration

Caractères physicochimiques des principes actifs : leurs conséquences sur la faisabilité et la stabilité des formes galéniques

Selon son origine ou le lot considéré, un principe actif, pourtant bien défini chimiquement, peut se comporter de façon très différente. Les opérations galéniques qu'il subit (broyage, compression, granulation, séchage) peuvent également entrainer des modifications des propriétés secondaires (dérivées) du principe actif que sont la comprimabilité, la mouillabilité, la solubilité, la vitesse de dissolution, la biodisponibilité et même l'activité pharmacologique. Des changements de propriétés peuvent aussi survenir en fonction des conditions de conservation des formes pharmaceutiques (humidité relative, température). Dans les corps solides, ces différences de propriétés, qu'elles existent initialement ou soient engendrées par un quelconque traitement, sont directement liées aux caractéristiques primaires des cristaux, c'est-à-dire à leur structure cristalline, à la fois interne (polymorphisme, pseudopolymorphisme, état amorphe) et externe (habitus, faciès cristallin), à la densité des défauts cristallins (dislocations) ainsi qu'à la présence d'impuretés. Le «dopage» de cristaux à l'aide de substances étrangères peut d'ailleurs faire partie des moyens susceptibles d'améliorer les propriétés d'intérêt technologique ou biopharmaceutique. La présente revue explique ces concepts à travers des exemples classiques ou plus récemment publiés dans la littérature.Depending on its origin or the particular batch, a given drug, although chemically well defined, may exhibit quite different behaviour. Process conditions (grinding, tabletting, granulation, drying) may also affect secondary (derived) properties of the drug, such as compactibility, wettability, solubility, dissolution rate, bioavailability and even pharmacological activity. Property changes may also be due to the storage conditions of the dosage form. In solids, these differences, which may exist initially or be generated by some treatment, arise directly from the primary characteristics of the crystals, i.e. the crystalline structure, both internal (polymorphism, pseudopolymorphism, amorphous state) and external (habitus, facies), crystal defects (dislocations) or the presence of impurities. In this respect, crystal « doping » by foreign substances may be envisaged as a means to improve drug properties of technological or biopharmaceutical interest. This review article explains these concepts using classical or more recently published examples from the literature.</p

Modifications cristallines et transformations polymorphes au cours des opérations galéniques

Plus de la moitié des composés pharmaceutiques sont sujets au phénomène de polymorphisme ou de pseudo-polymorphisme, c'est-à-dire qu'ils existent sous plus d'une structure cristalline (polymorphes vrais, hydrates, solvates) ou comme produit plus ou moins amorphe. À ce titre, il présentent, à l'état solide, des caractéristiques physico-chimiques (point de fusion, point de transition, plasticité, solubilité, hygroscopicité, réactivité chimique) différentes, qui à leur tour peuvent avoir des incidences sur les propriétés pharmaco-techniques et biopharmaceutiques des principres actifs ou des excipients (comprimabilité, vitesse de dissolution, biodisponibilité, activité pharmacologique, stabilité). Considérant une substance chimiquement bien définie, on peut se trouver en présence de tel ou tel état cristallin ou forme polymorphe en fonction de la source d'approvisionnement ou simplement du lot en question. Mais il se peut aussi que l'on observe des changements de propriétés pharmaco-techniques ou biopharmaceutiques dus à des phénomènes de transformations polymorphes, selon le traitement mécanique, thermique ou les conditions environnementales (intervention d'un solvant, désolvatation) qu'a subi le produit ou la forme médicamenteuse. Le présent article passe en revue les aspects fondamentaux liés à ces phénomènes et présente des exemples de la littérature, classiques ou récents, de transformations observées lors d'un broyage ou d'une trituration, d'une compression, de la mise en suspension d'un principe actif, d'une granulation, de tests de dissolution ou de libération, d'essais de stabilité, d'une nébulisation, d'une lyophilisation ou encore de la préparation d'adsorbats ou de complexes

Development of a nanoprecipitation method intended for the entrapment of hydrophilic drugs into nanoparticles

This study investigates formulation and process modifications to improve the versatility of the nanoprecipitation technique, particularly with respect to the encapsulation of hydrophilic drugs (e.g. proteins). More specifically, the principal objective was to explore the influence of such modifications on nanoparticle size. Selected parameters of the nanoprecipitation method, such as the solvent and the non-solvent nature, the solvent/non-solvent volume ratio and the polymer concentration, were varied so as to obtain polymeric nano-carriers. The feasibility of such a modified method was assessed and resulting unloaded nanoparticles were characterized with respect to their size and shape. It was shown that the mean particle size was closely dependent on the type of non-solvent selected. When alcohols were used, the final mean size increased in the sequence: methanol < ethanol < propanol. Surfactants added to the dispersing medium were usually unnecessary for final suspension stabilization. Changing the solvent/non-solvent volume ratio was also not a determinant factor for nanoparticle formation and their final characteristics, provided that the final mixture itself did not become a solvent for the polymer. A too high polymer concentration in the solvent, however, prevented nanoparticle formation. Both poly(lactic acid) (PLA) and poly(d,l-lactic-co-glycolic acid) (PLGA) could be used by accurately choosing the polymer solvent and in this respect, some non-toxic solvents with different dielectric constants were selected. The nanoparticles obtained ranged from about 85–560 nm in size. The nanoparticle recovery step however needs further improvements, since bridges between particles which cause flocculation could be observed. Finally, the presented results demonstrate that the nanoprecipitation technique is more versatile and flexible than previously thought and that a wide range of parameters can be modified

Méthodes de préparation des microparticules biodégradables chargées en principes actifs hydrosolubles

Cet article de revue rassemble les travaux relatifs à la préparation de microcapsules et de microsphères à base de polymères biodégradables lipophiles, contenant des principes actifs hydrosolubles. Les procédés de fabrication utilisés sont répartis en six classes: l'évaporation ou l'extraction du solvant, la séparation de phases, la nébulisation, la fluidisation et la fusion. Les avantages et limites propres à chaque procédé sont évalués en termes de faisabilité, reproductibilité, rendement, coût et toxicité. Les auteurs tentent également d'établir les liens existant entre les propriétés physico-chimiques du couple principe actif/polymère utilisé, la technique de microencapsulation adoptée et les performances des microparticules obtenues (microcapsules, microsphères). Finalement, cette étude permet de mieux comprendre pourquoi seuls trois procédés sont utilisés à l'heure actuelle pour la production industrielle de microparticules biodégradables.The present review article describes the work done on microencapsulation of water-soluble drugs using biodegradable lipophilic polymers. The manufacturing processes applied are classified into six categories : solvent evaporation or extraction, phase separation, spray drying, fluidized-bed and hot-melt methods. The processes are critically discussed. The advantages and limitations of each technique are evaluated in term of feasibility, reproducibility, yield, cost and toxicity. The authors try to explain the interactions between the physicochemical properties of drugs and polymers used, the microencapsulation technology applied and the performances of microparticles produced (microcapsules, microspheres). Finally, this work offers a better understanding on the reasons why only three of these techniques are presently used at the industrial scale for manufacturing biodegradable microparticles

Biopharmaceutical comparison of oral multiple-unit and single-unit sustained-release dosage forms

The authors review the literature dealing with the comparison of oral multiple-unit and single-unit sustained- release formulations. Some elements of gastro-intestinal physiology and the fate of dosage forms in vivo are presented. The gastro-intestinal transit time and the variability of both formulation principles are then considered in order to explain possible differences. The spreading of multiple-unit dosage forms throughout the gastro-intestinal tract is also examined. Finally, the interest of pharmacokinetic parameters for the comparison of oral sustained-release delivery system is discussed.Les auteurs passent en revue les travaux portant sur la comparaison des formes à libération prolongée divisées et monolithiques destinées à la voie orale. Quelques éclaircissements concernant la physiologie gastro-intestinale ainsi que le devenir des formes médicamenteuses in vivo sont apportés en préambule. Les éventuelles différences de comportement en termes de temps de transit et de reproductibilité sont discutées en fonction des deux principes de formulation. La dispersion des formes multiples au sein du tractus digestif est également abordée. Un dernier point traite des paramètres pharmacocinétiques et de leur intérêt dans la comparaison des formes orales à libération prolongée