Structural and rheological properties of chitosan semi-interpenetrated networks.

The local structure and the viscoelastic properties of semi-interpenetrated biopolymer networks based on cross-linked chitosan and poly(ethylene oxide) (PEO) were investigated by Small Angle Neutron Scattering and rheological measurements. The specific viscosity and the entanglement concentration of chitosan were first determined, respectively, by capillary viscosimetry and steady-state shear rheology experiments performed at different polymer concentrations. Mechanical spectroscopy was then used to study the gelation process of chitosan/PEO semi-interpenetrated networks. By fitting the frequency dependence of the elastic and loss moduli with extended relations of relaxation shear modulus around the sol-gel transition, it was shown that the addition of PEO chains had a significant effect on the viscoelastic properties of aqueous chitosan networks but no effect on the gelation time. The improvement of mechanical properties was in accordance with the correlation length decrease deduced from Small Angle Neutron Scattering experiments.

[Interactions between cyclodextrins and triglycerides: from emulsion stabilisation to the emergence of a new drug delivery system called "beads"]. / Interactions entre les cyclodextrines et les triglycérides : de la stabilisation des émulsions à l'obtention d'un nouveau système galénique appelé << billes >>.

Natural cyclodextrins are cyclic oligosaccharides which can be modified to obtain more water soluble or insoluble derivatives. The main interest of cyclodextrins results from their ability to form an inclusion complex with hydrophobic molecules. Inclusion constitutes a true molecular encapsulation. This property is employed in pharmaceutical industry to facilitate the formulation of poorly water soluble and/or fragile drugs. A more recent application of cyclodextrins consists in their use in the preparation of dispersed systems such as micro- and nanoparticles or even liposomes. When incorporated in dispersed systems, cyclodextrin can enhance drug solubility, drug stability and drug loading. Interestingly, cyclodextrins themselves can also be employed to form or stabilise dispersed systems (material or emulsifying agent). For example, the interactions between cyclodextrins with components of the vegetable oils (more especially with triglycerides) allow to stabilise simple or multiple emulsions but also to form particles called "beads". Very rich in oil, this novel lipid carrier presents an important potential for the encapsulation of highly lipophilic compounds and their delivery by topical and oral routes. These two applications are more particularly developed in the present paper.

In vitro and in vivo characteristics of a thermogelling and bioadhesive delivery system intended for rectal administration of quinine in children.

The aim of this work was to improve the rectal bioavailability of quinine hydrochloride by designing thermosensitive and mucoadhesive gels intended for rectal delivery. The rheological and mucoadhesive properties of poloxamer 407 solutions have been modulated by addition of hydroxypropylmethycellulose (HPMC) and propanediol-1,2. In vitro release and rectal absorption of quinine have been highlighted by a dialysis dissolution testing method and by the determination of bioavailability of the different formulations in rabbits. Increasing the proportions of HPMC and poloxamer in the formulations resulted in a prolonged release of quinine. Indeed, compared to the DT 50% of a rectal solution and a simple HPMC gel (27 and 65 min, respectively) the DT 50% of thermosensitive ternary systems was increased and ranged between 80 and 138 min, depending on the system composition. The release rate depended strongly on the elasticity of the gels after thermogelation. The absolute rectal bioavailability of quinine determined in rabbits was significantly improved with these thermosensitive and adhesive systems. It increased from 62% for the rectal solution to 98% for a ternary system 16/0.5/30 (poloxamer (16%)/HPMC (0.5%)/propanediol-1,2 (30%)). As a result of combined bioadhesion and prolonged release of quinine in vivo, higher average values of MRT and t(max) (9.1+/-0.2h and 30 min, respectively) were obtained compared to the rectal solution (6.9+/-0.9h and 15 min, respectively). Moreover, these formulations presented a very good rectal tolerance. Modulation by HPMC of the viscoelastic and mucoadhesive properties of poloxamer 407 thermogelling solutions allowed a prolonged release of quinine hydrochloride and an improvement of bioavailability in rabbit.

Formulation and characterisation of beads prepared from natural cyclodextrins and vegetable, mineral or synthetic oils.

A continuous external shaking for 2.5 days of a mixture composed of alpha-cyclodextrin (6%), soybean oil (19.6%) and water (74.4%) resulted in a calibrated lipid carrier namely bead with a high fabrication yield. The purpose of this work was to explore the possibility to substitute alpha-cyclodextrin by other natural cyclodextrins, i.e. beta- and gamma-cyclodextrin and then soybean oil by mineral (Primol) 352 and Marcol 82) or synthetic (Silicon 200) fluid 10, 50 or 100cSt) oils. Beads can be successfully prepared using Marcol 82 with alpha-cyclodextrin and Silicon 50 or 100cSt with gamma-cyclodextrin. The area inside oil/cyclodextrin/water ternary diagram corresponding to bead occurrence was superior for the Marcol 82/alpha-cyclodextrin couple compared to that observed with soybean oil/alpha-cyclodextrin couple. Only a few ratios of Silicon 50 and 100cSt/gamma-cyclodextrin/water led to beads. The combinations which did not induce bead occurrence gave either emulsions, two non-miscible liquids or a solid mixture. Whatever the materials used, beads exhibited similarities: presence of a crystalline organisation and viscoelastic properties. Manufacturing process of paraffin- and silicon-based beads need further optimisation to increase fabrication yield and later on, to take advantages from the high stability of both oils for the formulation of drugs with beads.

Assessment of oil polarity: comparison of evaluation methods.

In multiple emulsion systems, oily or aqueous transfers may occur between the dispersed droplets through the continuous phase. These transfers are controlled by both the surfactant system (micellar transport), and the partial solubility of one phase in another (molecular transport). The latter could be anticipated from the knowledge of oil polarity, if this information could easily be obtained. In this work, the relative polarity of eight oils used for various purposes has been evaluated from the comparison of their dielectric requirement for solubilization, their interfacial tension and chromatographic analysis. The results showed the complementarities of HPLC analysis and interfacial tension measurements and their superiority over the solubilization method for classifying oils as a function of their polarity.

alpha-Cyclodextrin/oil beads: an innovative self-assembling system.

The aim of this work was to characterise a new type of particulate system, named beads, prepared by a straightforward technique starting from a mixture of alpha-cyclodextrin aqueous solution and soybean oil without the use of any organic solvent or surface-active agent. Mechanisms involved in bead formation were also investigated. Optimal ratio between alpha-cyclodextrin (6%, w/w), soybean oil (19.6%, w/w) and water (74.4%, w/w) led to homogeneous bead size (1.6 mm) with a fabrication yield superior to 80% after a continuous external shaking during 2.5 days. After freeze-drying, oil and alpha-cyclodextrin contents were estimated at 80% (w/w) and 20% (w/w), respectively. X-ray diffraction studies revealed that beads presented a crystalline organisation and microscopic techniques showed that their inner structure was constituted by a matrix containing oily compartments. Beads offer interesting prospects for the microencapsulation of lipophilic and poorly stable molecules. Due to their semi-solid consistency and their ability to be freeze-dried, these beads have great potentialities for pharmaceutical (oral and topical routes) and cosmetic applications.

Modulation of the rheological and mucoadhesive properties of thermosensitive poloxamer-based hydrogels intended for the rectal administration of quinine.

The aim of this work was to formulate and characterize thermosensitive gels based on poloxamer 407, a thermosensitive polymer, and hydroxypropylmethylcellulose (HPMC), a bioadhesive polymer, intended for the rectal delivery of quinine in children. In order to avoid the macroscopic phase separation between the two polymers it was necessary to add propanediol-1,2. After the formulation of stable ternary systems, their rheological properties were studied as a function of temperature. It was thus possible to obtained the gelation temperature of the systems as well as their elastic modulus, G', at 37 degrees C. It appeared that HPMC in the presence of propanediol-1,2 had a synergistic effect on the gelation of poloxamer 407. Tests on the rabbit rectal mucous membrane, founded on a technique of traction of the adhesive/adhered joint, made it possible to characterize the bioadhesive properties of the gels by measuring the work of adhesion, W, and the maximum detachment force, F(max). Over small concentration ranges of poloxamer and HPMC, very important variations of the viscoelastic and mucoadhesives properties were observed. It was shown that the viscoelastic and the bioadhesive properties were tightly correlated. Indeed, an empirical equivalence relation was established between the shear frequency and the rate of deformation in traction and allowed to describe all our samples by a master curve. This master curve would make it possible to predict the values of W at various rates of traction by the simple non-destructive measurement of the elastic modulus, G', at an equivalent shear frequency.

Release of antiseptics from the aqueous compartments of a w/o/w multiple emulsion.

A w/o/w multiple emulsion drug carrier system has been developed for local vaginal therapy. To improve its efficacy and to extend the antimicrobial spectrum activity of benzalkonium chloride (CBZ), which is introduced in the external aqueous phase, chlorhexidine digluconate (CHD) was added to the internal aqueous phase of the multiple emulsions. The minimal bactericidal concentrations (MBC) for the association of CHD and CBZ in emulsion were determined towards Escherichia coli and Staphylococcus aureus. The main release mechanism considered for the CHD encapsulated in the inner phase was a swelling-breakdown phenomenon which followed dilution of the emulsion under hypo-osmotic conditions. In order to demonstrate this release, the bactericidal effect of multiple emulsions undiluted and diluted 1-5 and 1-10 in hypo-osmotic conditions at two CHD concentrations was evaluated. To validate and quantify this release, rheological and release kinetics studies were used. The bactericidal activity of combination CBZ-CHD in the emulsion was synergistic on the two bacterial strains and the release of encapsulated CHD in the internal phase was obtained following its dilution in hypo-osmotic conditions. Vaginal administration could be carried out following dilution at 1-5 in sterile water for multiple emulsions containing the lower concentration of CHD.

Study of mass transfer in oil-water-oil multiple emulsions by differential scanning calorimetry.

A multiple emulsion of the type O1/W/O2 is studied experimentally by means of differential scanning calorimetry (DSC). The aim of this work is to characterize and measure the time-dependent changes within the emulsion. In particular, interest is focused to quantify the concentration changes in the internal and external phases of the O1/W/O2 multiple emulsion. In order to accomplish the objective, the measurement and analysis carried out by DSC are based on the crystallization behavior of the emulsion. A volume of a few mm3 is periodically removed from the O1/W/O2 multiple emulsion. The sample is submitted to steady cooling and the crystallization thermogram is recorded. The experimental data provided by the crystallization thermogram makes it possible to quantify the crystallized mass for both phases, the internal and the external. In addition, the composition in each phase can also be deduced from the thermogram. To deduce the composition, a diagram of crystallization temperatures is elaborated, employing several mixtures of known composition. In addition to the main objective previously mentioned, the influence of formulation parameters such as surfactant concentration in the aqueous phase and the mass ratio of the internal and external phases are also analyzed. The experimental results made it possible to conclude that a mass transfer took place from the internal phase toward the external phase; this transfer is caused by the composition difference on both sides of the aqueous membrane. In this work we analyzed the mass transfer in the multiple emulsion carried out by a composition gradient through the aqueous membrane. The most likely mechanism of mass transfer through the aqueous membrane is a solution-diffusion of tetradecane enhanced by the micelles of the surfactant Tween 20. The model of mass transfer confirms that the osmotic pressure difference controls the kinetics of tetradecane transfer. It is also confirmed that an increment of surfactant concentration in the aqueous phase allows a faster kinetics of the tetradecane transfer.

A very promising new glucolipidic surfactant: Lipowheat.

Lipowheat is an entirely biodegradable 100% natural active ingredient, extracted from non-transgenic wheat. Thanks to its very interesting properties, it can integrate the composition of most cosmetic and pharmaceutical products. The aim of this work was first to realize a large range of stable simple or multiple emulsions, in order to determine and evaluate the ability of a new glucolipidic surfactant Lipowheat to form and stabilize emulsions. The rheological properties of these emulsions were tested during a 30-day storage period at three different storage conditions (cold, room temperature and at 40 degrees C). In addition to dynamic and static rheological tests, droplet size distribution of the cream was also determined. Furthermore, a stable simple emulsion was selected to realize percutaneous absorption and evaluate the properties of Lipowheat.

pH compartmented w/o/w multiple emulsion: a diffusion study.

In order to develop w/o/w emulsions characterized by two separate aqueous phases of different pH, a preliminary study was carried out to obtain a better insight into the possible diffusion processes taking place between an inner acidic aqueous phase and an external phase of higher pH (pH approximately 6). In fact, such systems could be of great interest for pharmaceutical use. For this purpose, a model emulsion was formulated. The study of pH and conductivity showed that acidic species transport take place between the two aqueous compartments. The three main release mechanisms that might be responsible for this passage across the oil phase were investigated: breakdown of oil globules, facilitated transport by surfactant micelles across the oil phase or by Fickian diffusion. It appears that this last mechanism was involved. In order to control this diffusion process, an alkaline species, octadecylamine was introduced in the oil phase. This compound could form an ion pair with the lactate ion at the interface of the external aqueous phase and the oil phase, thus, limiting the acidification of the external aqueous phase.

Hydrogels of poly(ethylene glycol): mechanical characterization and release of a model drug.

Thermosensitive polymer networks were synthesized from poly(ethylene glycol), hexamethylene diisocyanate and 1,2,6-hexanetriol in stoichiometric proportions. By varying the amount of 1,2,6-hexanetriol and the molar mass of the poly(ethylene glycol), a wide range of networks with different crosslinking densities was prepared. The networks obtained were characterized by the temperature dependence of their degree of equilibrium swelling in water and by their Young's moduli. For each network, the molecular weight between crosslinks was estimated. The structure of the hydrogels was analysed with respect to scaling laws, and it was found that the results obtained with PEG 1500 and PEG 6000 hydrogels are in agreement with theoretical predictions, whereas those obtained with PEG 400 hydrogels are in disagreement. The release properties of PEG hydrogels were studied by the determination of the diffusion coefficient for acebutolol chlorhydrate and by an analysis of the effect of temperature on these coefficients. Finally, these release properties were correlated with the swelling and structural properties of the hydrogels.

Formulation of shear rate sensitive multiple emulsions.

This work mainly concentrates on the formulation of W/O/W multiple emulsions capable of breaking and releasing their inner aqueous phase under shear rates compatible with agroalimentary, pharmaceutical and cosmetic applications. Three kinds of multiple emulsions were studied: one with a high concentration of primary emulsion, not viscosified in the external aqueous phase; multiple emulsions gelified with a synthetic polymer (Carbopol 974P((R))); and other multiple emulsions thickened with chemically modified cellulose (hydroxypropylcellulose). The results of this study show the influence of the composition of the external aqueous phase of the emulsions on their fragmentation and release as a function of the shear rate. Despite these differences of behavior with respect to the shear rate, each emulsion fits to Taylor's theoretical framework, indicating that the bursting mechanisms of the globules under shear are the same whatever the composition of the multiple emulsions.

Kinetics of swelling-breakdown of a W/O/W multiple emulsion: possible mechanisms for the lipophilic surfactant effect.

The properties and behavior of a W/O/W multiple emulsion formulation were analyzed during a swelling-breakdown process. Various experimental analyses, such as granulometry, rheology and conductimetry were performed, as well as a micropipette aspiration method. The predominant role of the lipophilic surfactant during the swelling phase confirmed. Two different mechanism can be proposed. Both imply the migration of the lipophilic surfactant from one interface to another and probably take place successively. The lipophilic surfactant could diffuse from the first to the second interface, thus rigidifying the membrane, or from the oily phase to the first interface, resulting in delayed coalescence of the aqueous droplets during swelling.

In vitro microbicidal activity of W/O/W multiple emulsion for vaginal administration.

The microbicidal activity of a W/O/W multiple emulsion destined for vaginal application, containing lactic acid in the internal aqueous phase, octadecylamine (ODA) in the oily phase and benzalkonium chloride (CBZ) in the external aqueous phase was evaluated against three microbial strains: Escherichia coli, Staphylococcus aureus and Candida albicans. The results were different depending on the procedure used. Interpretable results were obtained if only a gentle agitation was used just after the introduction of the microbial suspension to the product. This suggested that vigorous agitation lead to a variable fraction of CBZ or ODA entrapped in the micelles of ethylene and propylene oxide copolymer (COE).

Water state characterization, swelling behavior, thermal and mechanical properties of chitosan based networks.

Two kinds of chitosan-based hydrogels, a crosslinked chitosan reference gel and a chitosan-poly(ethylene oxide) semi-interpenetrating network (semi-IPN), with potential pH-sensitive swelling and drug delivery properties are characterized. Swelling studies were performed on the two kinds of hydrogels by differential scanning calorimetry (DSC) at pH 1.2 and by the gravimetric method at pH 1.2 and pH 7.2. Both methods lead to similar results. If pH-dependent swelling properties were observed with both hydrogels, they were however improved for the semi-IPN. The amount of bound water in the xerogels could be determined from DSC measurements and a thermogravimetric analysis. The results obtained by both techniques were in good agreement and indicated that the semi-IPN contained more bound water than the reference gel probably due to the presence of the hydrophilic poly(ethylene oxide) chains. Young modulus of the swollen hydrogels was determined by indentation analysis. The semi-IPN displayed improved mechanical properties compared to the reference gel.

A very stable W/O/W multiple emulsion.

The comparison of the results of microscopic, conductimetric and rheologic analyses carried out on the same triple W/O/W emulsion, immediately following its manufacture and 10 years later, indicates the remarkable stability of such system. This stability illustrates the great potential of this formula in the protection of unstable ingredients, with regard to external stress, when encapsulated with a high yield.

[Dynamic viscosity and corneal endothelial protection with Healonid, Healon GV, Provisc and Viscoat during phacoemulsification]. / Viscosite dynamique et protection endotheliale corneenne du Healonid, du Healon GV, du Provisc et du Viscoat au cours de la phacoemulsification.

PURPOSE: To demonstrate the utility of a viscoelastic substance which maintains high viscosity during phacoemulsification, we conducted a double study. METHODS: We compared in vitro the corneal endothelial protection offered by Healon, Healon GV, Provisc and Viscoat after <> phacoemulsification. Eight samples of ten to fifteen freshly enucleated pig eyes were operated; the first four groups were the controls, whereas the other four tested the different viscous solutions. In parallel, we determined the rheologic properties of the four viscoelastic substances in a physicS laboratory. To measure the percentage of corneal endothelial cell damage, we used the Janus Green spectrometric technique. RESULTS: Corneal endothelial cell damage averaged 31.67% in eyes in which no viscoelastic substance was used. Damage was 14.29% in specimens that received Healon, 12.85% with Healon GV, 2.48% in the Viscoat group and 15.43 in those that received Provisc. There is a significant difference (p <0.001) between the Viscoat group and all other samples. The values of the viscosity at different shear rates and the graph of viscosities as a function of shear rate of the four viscous solutions are given. CONCLUSION: Viscoat has a very high dynamic viscosity at high shear rate. This property and a poor cohesion provide a better corneal endothelial protection during in vitro phacoemulsification.

Low molecular weight heparin gels, based on nanoparticles, for topical delivery.

A commercial suspension of nanoparticles (Eudragit RS 30D) was used to manufacture a gel for topical application. Gels were prepared by mixing a polycationic polymer (Eudragit(®) RS 30D) and a low molecular weight heparin (LMWH), an antithrombotic agent. Gels formed spontaneously at a ratio of 1:1 as a result of electrostatic interactions between the polyanionic drug and the polycationic polymer. Different types of heparin were used: Bemiparin, Enoxaparin (Lovenox), Nadroparin (Fraxiparin) and Tinzaparin (Innohep). Several LMWH concentrations were tested. Rheological measurements were performed to investigate the gel behavior. Gel formation was confirmed by dynamic rheological measurements as the elastic modulus (G') was higher than the viscous one (G″). The amount of heparin incorporated into the gel matrix was determined. A maximum of incorporation (100%) was reached using a heparin solution of 600 IU/mL. The release kinetics of LMWH from the gel were also studied. Regardless of the LMWH used in the formulation, a biphasic release profile was observed. Accordingly, a burst effect was observed. Afterwards, the release rate became steady. The penetration of the LMWH through the dermal barrier was also investigated.

Rheological and syringeability properties of highly concentrated human polyclonal immunoglobulin solutions.

This study of highly concentrated polyvalent immunoglobulin solutions, IgG, aimed at analyzing the relationships between protein concentration and aggregation on the one hand and viscosity on the other hand. Viscosity variations as a function of IgG concentration showed two well-defined behaviours: a Newtonian behaviour for low-concentrated solutions and a shear-thinning behaviour for highly concentrated ones. The viscosity data fitted very well with the Mooney model, suggesting the absence of intermolecular interactions in the IgG solutions that behaved like a non-interacting suspension of hard particles. The polyclonal nature of IgG seems to prevent intermolecular interaction. The shape factor, determined from Mooney fitting, revealed a non-spherical shape of the polyclonal IgG molecules. The rheological properties were also correlated with the injection force (F) through hypodermic needles by syringeability tests. Here, F was mainly affected by three parameters: the solution viscosity, the injection flow rate, and the needle characteristics. In fact, syringeability tests showed that F increased with IgG concentration and flow rate and decreased with the internal diameter of the needle. A zone for optimal injection conditions was then identified taking into account the different affecting parameters and mainly a maximum force for manual injection, which was fixed at 30N.