1,720,963 research outputs found
Transient viscoelastic tests in the study of the densification behaviour of pharmaceutical solids
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Hydroxypropyl ß-cyclodextrin effect on the self-assembling and thermogelation properties of poloxamer 407
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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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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
Application of the experimental design on the rheological characterisation of Carbopol-Silsense A-21 systems
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Characterization of micellar systems by the use of acoustic spectroscopy
Full text linkAcoustic 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 β-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 β-CD on them. Poloxamer 407 micelle formation due to progressive dehydration occurred within a temperature interval of 15°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 β-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
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
Rheological, adhesive and release characterisation of semisolid Carbopol/Tetraglycol systems
Full text linkGels 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 °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
The effect of punch tilting in evaluating powder densification in a rotary tablet machine
No full textThe effect of punch tilting on the mechanism of punch penetration in the
die of a rotary tablet machine during the compression cycle was evaluated by installing
four displacement transducers on one station of a rotary machine. Two transducers were
symmetrically positioned beside the upper punch in the upper turret, and the other two
transducers were similarly placed beside the lower punch in the lower turret. Microcrystalline
cellulose and dicalcium phosphate dihydrate were compressed at 5, 10, 15
and 20 kN using two different machine speeds, in order to quantify the effect of punch
tilting in the evaluation of punch penetration. These compression data served to
construct the powder bed reduction curves, from which it was possible to establish that
punch tilting is directly proportional to the compression force used. Tilting is maximal at
the beginning of the dwell time, disappears at half dwell time, and reaches a new
maximum at the end of the dwell time. In latter case, tilting occurred in the direction
opposite that of the first maximum. The impact of tilting in powder densification
behaviour, evaluated through the construction of Heckel plots, depends on the compression
force used in the analysis. Heckel plots are as distorted as the compression force is
elevated. Consequently, the calculated Heckel parameters differ from the real values.
Unless a very low compression force is used, a proper Heckel analysis can be performed
in a rotary machine only if it is fitted with a device that includes the effect of punch tilting
in the evaluation of punch penetration
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