Influence of Testing Parameters on In Vitro Tramadol Release from Poloxamer Thermogels using the Immersion Cell Method.

The immersion cell is an in vitro performance test of drug release from semisolids. Several studies made use of immersion cells to investigate drug release from thermosensitive Poloxamer-based gels; however, specifications on the parameter setting are not yet available. Therefore, the aim of this study was to evaluate the influence of testing parameters on tramadol (a model drug) release, release rate, and dissolution efficiency (DE) from Poloxamer gels, using immersion cells. The thermosensitive gelling formulation showed batch-to-batch uniformity of gelling behavior, drug content, and drug release. The use of a membrane in the immersion cell resulted in slower drug release as compared to the absence of a membrane. Moreover, the faster the paddle rotation, the faster the drug release was. Membrane thickness showed a strong and significant linear relationship with corresponding DE values (Pearson's correlation coefficient, r = -0.9470; p = 0.004). Factors that did not influence drug release include paddle position, i.e., distance between paddle and membrane, as well as membrane mean pore size. This study sets forth the importance of carefully controlling the following parameters including presence/absence of membrane, paddle rotation speed, and membrane thickness during the setup of release experiments from gels using immersion cells.

Nanoparticles Based on Linear and Star-Shaped Poly(Ethylene Glycol)-Poly(ε-Caprolactone) Copolymers for the Delivery of Antitubulin Drug.

PURPOSE: Biodegradable polymeric nanoparticles of different architectures based on polyethylene glycol-co-poly(ε-caprolactone) block copolymers have been loaded with noscapine (NOS) to study their effect on its anticancer activity. It was intended to use solubility of NOS in an acidic environment and ability of the nanoparticles to passively target drugs into cancer tissue to modify the NOS pharmacokinetic properties and reduce the requirement for frequent injections. METHODS: Linear and star-shaped copolymers were synthetized and used to formulate NOS loaded nanoparticles. Cytotoxicity was performed using a sulforhodamine B method on MCF-7 cells, while biocompatibility was determined on rats followed by hematological and histopathological investigations. RESULTS: Formulae with the smallest particle sizes and adequate entrapment efficiency revealed that NOS loaded nanoparticles showed higher extent of release at pH 4.5. Colloidal stability suggested that nanoparticles would be stable in blood when injected into the systemic circulation. Loaded nanoparticles had IC50 values lower than free drug. Hematological and histopathological studies showed no difference between treated and control groups. Pharmacokinetic analysis revealed that formulation P1 had a prolonged half-life and better bioavailability compared to drug solution. CONCLUSIONS: Formulation of NOS into biodegradable polymeric nanoparticles has increased its efficacy and residence on cancer cells while passively avoiding normal body tissues. Graphical Abstract ᅟ.

Could albumin affect the self-assembling properties of a block co-polymer system and drug release? An in-vitro study.

PURPOSE: This work investigated the influence of a model protein, bovine serum albumin (BSA), on the properties of a thermogelling formulation intended for administration inside body compartments where there is high albumin content, as in the case of inflamed joints; it also explored the relation between the variation of these properties and release performance of methotrexate (MTX), a drug used to treat forms of arthritis and rheumatic conditions. METHODS: The influence of BSA on the micellisation and gelation behaviour of Poloxamer 407, chosen as a model copolymer, was studied by differential scanning calorimetry (microDSC), dynamic light scattering (DLS), fluorescence spectroscopy and rheology studies. A release study of MTX loaded inside the hydrogel in presence and in absence of BSA was performed. RESULTS: DLS and microDSC data revealed that the micellisation process was not affected by the protein, as demonstrated by unaltered micellar size and thermodynamic parameters. While the presence of BSA in the copolymer system reduced gel consistency, the hydrogel release performance was only slightly affected. CONCLUSION: Our results suggested that the kinetics of MTX release mainly depended on the presence of the thermogelling copolymer, although other mechanisms related to BSA could be involved. Finally, the study assessed the feasibility of using a thermogelling hydrogel for in situ drug administration in areas with the presence of high protein concentrations.

Characterization of ternary phase diagrams by means of thermal and rheological analyses.

CONTEXT: Mixtures made of oil, water and surfactants give rise to a wide range of structure with different characteristics and phase manifestations. OBJECTIVE: Aim of this paper is to build up and understand the phase diagram of a model ternary system (Water, Polysorbate 80 and isopropyl myristate) by the use of common techniques such as thermal analysis and rheology, in comparison with visual assessment and polarized light microscopy. METHODS: Different ternary systems were prepared and analyzed by means of DSC and rheology in order to highlight the state of water (free, interphasal, bound water) and the samples structural characteristics. RESULTS: The resultant phase diagram is divided into four different zones. Bound water zone is predominant at elevated surfactant/oil ratios, while as the surfactant/oil ratio decreases, DSC reveals the presence of free water. Interphasal water prevails at intermediate water and surfactant content which corresponds with gels systems. Mechanical spectra allow to discern between cubic (true gel) and lamellar mesophases (weak gel), while flow curves allow to distinguish among microemulsions, emulsions or lamellar mesophases. DISCUSSION: A deeper characterization of a model ternary phase diagram is possible, with respect to the simple visual inspection, by the use of thermal analysis and rheology. The state of water molecules and the viscoelastic characteristics of the system allow to obtain important structural considerations. CONCLUSIONS: In conclusion, the knowledge of the state of water and of the viscoelastic characteristics of the systems allow a deeper understanding of the structural features of the ternary phase diagram.

Rheological properties of cellulosic thickeners in hydro-alcoholic media: The science behind the formulation of hand sanitizer gels.

Cellulosic-based thickeners are commonly used in the preparation of hydro-alcoholic hand sanitisers. Yet, little is known about the behaviour of these polymeric dispersions in hydro-alcoholic mixtures. Here, we studied the dispersion ability and rheology of hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methylcellulose and sodium carboxymethyl cellulose in water-ethanol mixtures. Hydroxypropyl cellulose formed transparent dispersions across the entire range of ethanol concentrations, while a critical ethanol concentration (CEC), above which dispersions became turbid, was found for all the other polymers. At and below the CEC, all the rheological parameters followed a bell-like shape profile as a function of ethanol concentration. Moreover, the molecular weight and degree of substitution of the polymers influenced the rheological properties. The CEC and rheological behaviour of the dispersions were both dependent on the ethanol/polymer and water/polymer interactions. As hand disinfectants should contain 60-95% ethanol, polymers of higher CEC, such as hydroxypropyl cellulose and hydroxypropyl methylcellulose, are recommended.

Characterization and stability of emulsion gels based on acrylamide/sodium acryloyldimethyl taurate copolymer.

Sepineo P 600, a concentrated dispersion of acrylamide/sodium acryloyldimethyl taurate copolymer in isohexadecane, has self-gelling and thickening properties and the ability to emulsify oily phases, which make it easy to use in the formulation of gels and o/w emulsion gels. In this paper, gels were prepared using a Sepineo P 600 concentration between the 0.5% and 5% (w/w), and then emulsion gel was also prepared from the 3% Sepineo gel by adding a specific amount of almond oil. All the prepared systems were analyzed and characterized by oscillation rheology and acoustic spectroscopy. The particle size of the oil droplets and the microrheological extensional moduli (G' and G'') of the systems were determined from acoustic parameters and used together with the classical oscillatory rheological tests to assess the stability of the systems. Classical oscillatory analysis revealed that the dynamic moduli were very dependent on polymer concentration; as this parameter increased, there was progressive improvement in the sample elasticity. In fact, the mechanical spectra of the 0.5% and 1% (w/w) Sepineo samples were characterized by strong frequency dependence and multiple crossover points, typical of dilute polymer solution with no organized structure. On the other hand, the 3-5% (w/w) concentration systems showed typical gel-like spectra, marked by the absence of crossover points between the dynamic moduli and by weak dependence on frequency. Nevertheless, the elastic properties of the gel-like structure even at elevated polymer concentrations were not strongly long-lasting, as demonstrated by the increase of the viscous contribution in the low frequency range during acoustic spectroscopy analysis. This fact could indicate that the gel structure is characterized by weak polymer-polymer interactions, an advantageous characteristic for topical administration, as the sample is thus easier to rub into the skin. Finally, both rheology and acoustic spectroscopy indicated that addition of the oily phase caused minimal changes to the elastic character of the gel. Thus, Sepineo P 600 gel and emulsion gel are very effective systems for use in topical and other types of applications.

Characterization of micellar systems by the use of acoustic spectroscopy.

Acoustic spectroscopy affords a new and unique way to characterize concentrated suspension and emulsion while avoiding the limitations imposed by dilution, an undesirable step, particularly with highly structured samples. This study sought to illustrate the potentialities of this technique by using it to characterize the self-assembling behaviour of Poloxamer 407 systems (3-25%, w/v), both alone or after the addition of various amounts of hydroxypropyl beta-cyclodextrin (5-20%, w/v). Particle size and the microrheological extensional moduli (G' and G'') of the systems were determined from acoustic parameters such as sound attenuation and speed. By monitoring the variation of the particle size and the rheological extensional moduli at increasing temperatures, it was possible to define and outline the Poloxamer 407 transitions and the effect of the HP beta-CD on them. Poloxamer 407 micelle formation due to progressive dehydration occurred within a temperature interval of 15 degrees C (including gelation) and was dependent on poloxamer concentration. Particularly, particle size of the aggregates changed within this interval. Mean diameters were 600 nm at the onset of micelle formation and decreased after the thermogel formation to more or less 75 nm. The presence of HP beta-CD changed the basic self-assembling mechanism of Poloxamer 407 by increasing micelle formation and particularly thermogelation temperatures. The results confirm that acoustic spectroscopy offers a powerful method for characterizing heterogeneous systems, thus indicating its potential for applications in the pharmaceutical field.

Stress relaxation test for the characterization of the viscoelasticity of pellets.

The characterization of the mechanical properties of single uncoated pellets was performed in order to verify if these parameters could be used to predict the pellets aptitude to be compressed or utilized differently. Different ratios of microcrystalline cellulose and lactose monohydrate were used for the preparation of four batches of pellets by an extrusion/spheronization process. The 0.6-0.71 mm pellet fraction was used for the tests. Crushing strength and stress relaxation tests were carried out on the single pellets. The first test provided information of both the mechanical strength and the fragmentation aptitude. The second test provided information about their deformation ability (viscous flow) and residual elasticity (stress relaxation modulus). The results obtained from these tests were then compared with those obtained from the Heckel analysis. An excellent consistency was discovered between the parameters obtained from both the stress relaxation and crushing strength tests on one side and the Heckel parameters on the other side. Tests performed on single pellets are very useful tools to predict their deformation and fragmentation aptitude under compression and can be used for early insight of the pellet aptitude to be compressed.

Effect of hydroxypropyl beta-cyclodextrin on the self-assembling and thermogelation properties of Poloxamer 407.

This paper deals with the rheological and thermal characterisation of the self-assembling behaviour of different Poloxamer 407 systems (15-30%, w/v), both alone or after the addition of various amounts of hydroxypropyl beta-cyclodextrin (5-20%, w/v). The knowledge of the interactions existing between the two kinds of molecules could allow the development of systems for parenteral administration containing also proteins or peptides drugs. A rheology (temperature sweep and frequency sweep test) study has been performed to characterise the thermogelation process while thermal analysis (nanoDSC) allowed the determination of both micellization and sol/gelation transition processes. These two techniques were also utilised to outline the variation in the critical micelle temperature (cmT) or in the sol/gel temperature (sgT,) of the systems containing also hydroxypropyl beta-cyclodextrin (HP beta-CD). Both the rheology and thermal analysis showed the presence of interesting interactions between the HP beta-CD and the Poloxamer 407, which cause a shift of both cmT and sgT. The presence of HP beta-CD modified also Poloxamer samples elastic characters and microrheological structure as demonstrated by the G'-G'' mechanical spectra. Rheological and thermal results outlined how these new systems could open the possibility to join the thermogelling behaviour offered by Poloxamer 407 with the well-known stabilization and protection ability of HP beta-CD, which could make possible the formulation of systems for the parenteral delivery of peptides and proteins.

Water-in-Oil Microemulsions for Protein Delivery: Loading Optimization and Stability.

BACKGROUND: Microemulsions are attractive delivery systems for therapeutic proteins and peptides due to their ability to enhance bioavailability. Although different proteins and peptides have been successfully delivered through such ternary systems, no information can be found about protein loading and the formulation stability when such microemulsions are prepared with pharmaceuticallyapproved oils and surfactants. The aim of this work was to optimise a ternary system consisting of water/ ethyl oleate/Span® 80-Tween® 80 and to determine its protein loading capacity and stability, using bovine serum albumin (BSA) as a model of biomolecule. METHODS: The optimization was carried out using a Central Composite Design and all the prepared formulations were characterised through dynamic light scattering, rheology, optical and polarized microscopy. Subsequently, the maximum loading capacity was determined and the stability of the final microemulsion with the highest content of protein was followed over six months. To investigate the structural features of the protein, BSA was recovered from the microemulsion and analysed through fluorescence spectroscopy. RESULTS: After incorporation of the protein in the microemulsion, a decrease of its aqueous solubility was observed. However, the formulation remained stable over six months and the native-like state of the recovered protein was demonstrated by fluorescence spectroscopy Conclusion: This study demonstrated the feasibility of preparing microemulsions with the highest content of protein and their long-term stability.

Acrylic polymers as thickening agents for tetraglycol cosolvent.

This article evaluated the thickening properties of two different Eudragits, L and RS, in tetraglycol cosolvent in order to obtain high viscosity systems characterized by controlled release properties. Tetraglycol was chosen for its ability to dissolve a wide range of water insoluble drugs, while Eudragit RS and L for their specific dissolution and permeability properties under physiological conditions. Study of the rheological properties was performed to characterize elastic and viscous properties of Eudragit/tetraglycol samples in function of frequency and temperature. For all systems, the results outlined a liquid like behavior, as observed for dilute polymer solutions. In fact the fitting of the log G'-log G'' versus frequency curves showed a good agreement with the Rouse or Zimm models. So despite the increase in viscosity, samples still behaved like liquid systems. After the addition of paracetamol the release characteristics were defined pointing out the great release control properties of both Eudragit L and RS, which showed different release kinetics depending on the pH of the environment. Semisolid Eudragits/tetraglycol systems can be considered as a new alterative for the sustained release of insoluble or poorly water-soluble drugs.

Rheological, adhesive and release characterisation of semisolid Carbopol/tetraglycol systems.

Gels dosage forms are successfully used as drug delivery systems considering their ability to control drug release and to protect medicaments from an hostile environment. This study deals with the gelation properties of Carbopol 971 e 974 polymeric systems in tetraglycol, a water-miscible cosolvent. In this paper, the attention was noted of the thickening properties of the different Carbopol in tetraglycol solvent at increasing temperatures, in order to obtain gels avoiding neutralisation and, at the same time, to make possible the dissolution in these gels of insoluble or poorly soluble water drugs. Samples were prepared by simply dispersing different Carbopols amount (0.5-4%) were added to tetraglycol and different systems were prepared at room temperature and by heating at 70 degrees C. All these systems were then characterised rheologically. Frequency sweep, creep-recovery, temperature sweep and time sweep analyses outlined that Carbopol 971 and 974 in tetraglycol gave rise after heating to gels with satisfactory rheological behaviour: the elastic modulus was greater than the viscous one and a remarkable elastic character was found to be present. Systems obtained by heating procedure were examined also from a mechanical point of view using a texture profile analysis. Besides, being Carbopols well known mucoadhesive polymers, gels adhesive properties were also studied using the ex vivo method. Texture and adhesion characterisation confirmed rheological results pointing out a certain greater elasticity and adhesiveness of Carbopol 974 systems. Then, the possible cutaneous irritation was also tested using the in vivo method (Draize test). No signs of cutaneous irritation were obtained for all the samples that were analysed. After rheological and mucoadhesive properties were set, paracetamol as a model drug was inserted in the composition of the gels and the release characteristics were defined. Dissolution tests pointed out the greater release control properties of tetraglycol/Carbopol 971 samples. These studies showed tetraglycol/Carbopol systems as a first-rate alternative to traditional water gels when low water-soluble drugs have to be added.

Effect of plasticizers on properties of pregelatinised starch acetate (Amprac 01) free films.

Film coating is a technique widely used in the pharmaceutical field to improve and modify technological and release characteristics of capsules, tablets and granules. In this paper physical and mechanical properties of free films of Amprac 01, obtained by the solvent cast method, were studied in order to investigate the film forming ability of this modified starch and the effects of the addition of different plasticizers. A morphological microscopical analysis (SEM) was performed to study surface properties of the films, while thermal analysis (DSC) was carried out to investigate the influence of different types of plasticizers on the glass transition temperature of the polymer. Then a mechanical characterization permitted to evaluate important parameters such as film crack resistance and deformation at break. Extensional creep/relaxation tests were also performed to investigate the viscoelastic characteristics. As clearly demonstrated by the T(g) values, the residual water present in the films acted as plasticizers, making possible the formation of free films characterised by good macroscopical and mechanical properties. Except glycerol, the kind and amount of the other tested plasticizers did not markedly improve the mechanical and crack resistance of the films.

Rheological, mucoadhesive and release properties of Carbopol gels in hydrophilic cosolvents.

Carbopol is one of the most common thickening agent for water phases. It is used after neutralisation and its rheological properties in the aqueous medium are well known. The aim of this work was to investigate the gelation properties of Carbopol 971 e 974 polymeric systems in water-miscible cosolvents such as glycerine and PEG 400. Since in these cosolvents, carboxypolymethylene precipitates after neutralisation with a base, then the attention was pointed out of the gelation properties of the different systems at increasing temperature, in order to obtain Carbopols gels avoiding neutralisation and, at the same time, making possible the dissolution in these gels of insoluble or poorly soluble water drugs. Rheological properties of PEG 400 and glycerine samples were compared with similar systems in water by performing oscillatory analyses and measuring the main rheological parameters, G', G" and delta. The results obtained showed that Carbopol 971 and 974 in PEG 400 gave rise after heating to gels that show a satisfactory rheological behaviour. The elastic modulus is greater than the viscous one showing a remarkable elastic character of these samples and the performed frequency sweeps show a typical spectrum of a "gel-like" structure. Being Carbopols well-known mucoadhesive polymers, gels adhesive properties were studied using the ex vivo method. Then, the possible cutaneous irritation were also tested using the in vivo method (Draize test). No signs of cutaneous irritation and good mucoadhesive properties were obtained for the PEG 400 and water gels of Carbopol 974 prepared by heating. After rheological and mucoadhesive properties were set, paracetamol as a model drug was then inserted in the composition of the gels and the release characteristics were defined. Dissolution tests pointed out the greater release control properties of PEG 400-Carbopol 971 samples. These studies showed PEG 400-Carbopol systems as a first-rate alternative to traditional water gels.

Determination of factors controlling the particle size and entrapment efficiency of noscapine in PEG/PLA nanoparticles using artificial neural networks.

In this study, di- and triblock copolymers based on polyethylene glycol and polylactide were synthesized by ring-opening polymerization and characterized by proton nuclear magnetic resonance and gel permeation chromatography. Nanoparticles containing noscapine were prepared from these biodegradable and biocompatible copolymers using the nanoprecipitation method. The prepared nanoparticles were characterized for size and drug entrapment efficiency, and their morphology and size were checked by transmission electron microscopy imaging. Artificial neural networks were constructed and tested for their ability to predict particle size and entrapment efficiency of noscapine within the formed nanoparticles using different factors utilized in the preparation step, namely polymer molecular weight, ratio of polymer to drug, and number of blocks that make up the polymer. Using these networks, it was found that the polymer molecular weight has the greatest effect on particle size. On the other hand, polymer to drug ratio was found to be the most influential factor on drug entrapment efficiency. This study demonstrated the ability of artificial neural networks to predict not only the particle size of the formed nanoparticles but also the drug entrapment efficiency. This may have a great impact on the design of polyethylene glycol and polylactide-based copolymers, and can be used to customize the required target formulations.

The use of acoustic spectroscopy in the characterisation of ternary phase diagrams.

This study shows novel and interesting applications of acoustic spectroscopy for characterisation of ternary systems such as isopropylmiristate (IPM)/polysorbate 80 (T)/water (W). Particle size and microrheological extensional moduli (i.e. G' and G″) of different systems were determined by means of acoustic parameters such as sound attenuation and speed. Electric conductivity was also measured using the same instrument. The ultrasonic profile in terms of attenuation and sound speed in the megahertz frequency range, allowed the characterisation of the different zones of the ternary diagram such as microemulsion, emulsion and gel zones, as well as the evaluation of water state and particle size. This last parameter is a very effective tool in quantifying the phase transitions of systems and understanding which system is formed in any phase diagram zone. In fact, it is possible to analyse samples without dilution and despite their degree of turbidity, allowing complete characterisation of both properties and structure.

Monitoring the aggregation behaviour of self-assembling polymers through high-resolution ultrasonic spectroscopy.

Poloxamer 407 is a well-known self-assembling polymer with a wide range of temperature- and concentration-dependent phase behaviour, such as micellization and gelation. This work was carried out to demonstrate the potential of high-resolution ultrasonic spectroscopy in evaluating aggregation-deaggregation behaviour of self-assembling polymers. In order to achieve this objective, six different concentrations of Poloxamer 407 water dispersion were prepared and analysed between 5 and 35 degrees C using ultrasonic spectroscopy. For comparison, the same samples were also analysed by the DSC technique. The results showed that polymer aggregation process can be successfully monitored using both ultrasonic parameters of sound speed and attenuation. Furthermore, good agreement with DSC data was observed in terms of characteristic transition temperatures and also in terms of micellization kinetics and related parameters.

Evaluation of dissolution kinetics of hydrophilic polymers by use of acoustic spectroscopy.

This paper seeks to demonstrate the feasibility of using a novel analytical technique, acoustic spectroscopy, to characterize the dissolution kinetics of hydrophilic polymers, in particular, three different model polysaccharides: lambda carrageenan, gellan gum, and xanthan gum. The influence of particle size and of analysis temperature (25 or 45 degrees C) was evaluated through the evolution over time of the microrheological acoustic parameters G' and G''. This new method was then compared with classical rheological analysis. To better compare acoustic spectroscopy and rheological analysis, the initial dissolution rate from the slope of the first part of the G' or viscosity versus time curves was calculated. Both analytical techniques gave the same rank order of kinetics for the powder types and fractions examined; differences in absolute values were due to the fact that the two methods measured different parameters and had different stirring efficiencies. The rheological data obtained with both methods of analysis and their modelling confirmed that acoustic spectroscopy is an effective tool for monitoring and quantifying dissolution kinetics and hence affords a powerful technique for following over time a great number of physical changes occurring in a specific system.

Rheological evaluation of silicon/carbopol hydrophilic gel systems as a vehicle for delivery of water insoluble drugs.

The present study analyzed the thickening properties of Carbopol 974 and 971 in a 50:50 mixture of water/Silsense A-21, a new cationic silicon miscible in any proportion with water. Samples were prepared by simply dispersing different Carbopol amounts (0.5-4%) at room temperature or at 70 degrees C without neutralizing. Temperature sweep and time sweep analysis did not reveal significant structural changes at increasing temperature in the samples prepared following the first procedure. On the other hand systems obtained at 70 degrees C possessed higher elastic character particularly at polymer concentration higher than 2% (w/v). Analysis of the G' and G'' vs frequency curves by using different fitting equations (linear fitting, power law) gave information about the viscoelastic properties of the systems. The fitting of the frequency spectra and the calculation of the relaxation times from the master curves outlined the structural differences within the samples prepared with the two different procedures, confirming stronger gel-like behaviour for the samples prepared by the heating procedure. High preparation temperature promoted the polymer-solvent interactions, aiding the solvation of Carbopol. Heating facilitated polymer-solvent and polymer-polymer interaction, giving rise to a better organised structure typical of gel-like systems. Furthermore this preparation method provided good stability properties as shown by the stress sweeps tests performed during the three months of storage. The interpretation of the rheological results was supported by statistical analysis. A design methodology (screening and optimisation) was also applied in order evaluate the influence on dynamic rheological moduli of several parameters (polymer type and concentration, preparation method, temperature of the tests). This last method showed the relevance of the interaction of two main factors: polymer concentration and preparation procedure. Thus, statistical analysis confirmed that temperature increased the polymer-solvent interaction and improved the viscoelastic properties of the systems, particularly when Carbopols were present in considerable amounts.