1,721,142 research outputs found
Acrylic Polymers as thickening agents for tetraglycol cosolvent
Full text linkThis 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
THE USE OF SOUND SPEED MEASUREMENTS IN THE EVALUATION OF POLYMERS MUCOADHESIVENESS
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Rheological, mucoadhesive and release properties of carbopol gels in hydrophilic cosolvents
No full textCarbopol 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 δ. 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
Evaluation of dissolution kinetics of hydrophilic polymers by use of acoustic spectroscopy,
No full textThis 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 °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
HIGH RESOLUTION ULTRASONIC SPECTROSCOPY IN THE ANALYSIS OF POLOXAMERS BEHAVIOUR
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Colloidal soft matter as drug delivery system
No full textGrowing interest is being dedicated to soft matter because of its potential in
delivering any type of drugs. Since hydrophilic, lipophilic, small and big molecules can
be loaded into these colloidal systems and administered through the parenteral or
nonparenteral route, soft matter systems have been used to solve many biomedical and
pharmaceutical problems. In fact, they make possible to overcome difficulties in the
formulation and delivery of poorly water-soluble drug molecules, settle some stability
issues typical of biological drug molecules, design parenteral sustained release forms
and provide functionalized soft particles that are very effective in drug targeting. This
review deals with the important role that colloids play in the drug delivery and
targeting, with particular attention to the more currently used systems such as microemulsions,
organogels, liposomes, micelles, and dendrimers. Though significant progress
has been made in drug targeting, some challenges still remain. Further efforts will
be required to better understand the characteristics of targets and to discover new ones.
In-depth knowledge of the physico-chemical structure and properties of the systems
used for targeting is fundamental for understanding the mechanism of interaction with
the biological substrate and the consequent drug release
Rheological evaluation of Silicon/Carbopol hydrophilic gel systems as a vehicle for delivery of water insolubile drugs
Full text linkThe present study analyzed the thickening properties of Carbopol 974 and 971 in a 50:50 mixture of water/SilsenseTM 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°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°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
Spray-drying as a method for microparticulate controlled release systems preparation: advantages and limits. I. Water soluble drugs
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Modulation of the release kinetics of starch-based erodible matrix tablets by the use of a-amilase
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