Pluronic F-127 gels as a vehicle for topical formulations of indomethacin and rheological behaviour of these formulations

Topical gel formulations containing a non-steroidal anti-inflammatory drug, indomethacin (IND), were prepared using 20% w/w Lutrol PF-127 as a gel-forming agent, and 16, 20 and 24% w/w Hexylene glycol (HG) or polyethylene glycol 300 (PEG) as solvents. 1% w/w Tween 80 and 1% w/w PVP 25 were added as excipients. The effects of the amounts of solvent and excipients on the physical characteristics of IND gel such as consistency, appearance, crystallization, pH and viscosity were studied. The results indicated that 1% w/w IND is able to form a structural gel. The viscosity values were calculated from the rheograms which were determined by a Haake Rotovisco sensor at a shear rate of 10,000 l/s. Viscosities corresponding to shear rates of 1000, 3000, 6000 and 9000 l/s were also calculated. Yield points were approximated from the rheograms. Although all IND gels maintained their pseudoplastic flow behaviour, their viscosities decreased markedly with increasing shear rates. Furthermore, increasing the amount of HG or PEG gave a more viscous gel except for the 24 w/w% HG gels which turned a jelly with or without either Tween or PVP. The difference in viscosities was explained by the changes in the gel compositions. 20% of PEG-1% PVP ranked first in viscosity followed by 16% PEG-1% PVP, 16% PEG-1% Tween, 24% PEG, 20% PEG-1% Tween and 16% HG-1% PVP. The results indicate that the excipients influence the physical characteristics of the gels. The optimum concentration for gels manifesting as strength of gel was 20% PEG in combination with 1% PVP which had the highest viscosity and yield value at a low shear rate.

Characterization of microcrystalline cellulose and silicified microcrystalline cellulose wet masses using a powder rheometer

A powder rheometer has been used to study the properties of wet powder masses and the results have been compared to the mixer torque rheometer (MTR). Two different microcrystalline cellulose (MCC) grades (Avicel and Emcocel) and silicified microcrystalline cellulose (SMCC, Prosolv) were used as model powders. The wet massing behaviour of one material (Prosolv) was studied by the powder rheometer using liquid addition experiments, while the rheological properties of wet granules were studied using both the powder rheometer and the MTR. In water addition measurements the torque behaved in a similar way to MTR measurements and the maximum value of ZTL (zero torque limit) was achieved at the capillary state of wet mass. The wet granules exhibited different behaviour in the powder rheometer and the MTR experiments, which indicates that these rheometers involve different shear forces or they measure different properties of the wet granules. Emcocel wet masses achieved the capillary state at lower liquid amount than Avicel and Prosolv masses, which indicates that Emcocel is not able to hold as much water in the internal structure as Avicel and Prosolv. The powder rheometer proved to be a sensitive piece of equipment, which can be used to study both dry and wet powder masses. It was able to distinguish wet granules from wet powder masses after liquid addition, whereas the MTR could not. However, before the powder rheometer can be properly utilised in wet powder mass studies, the problem of torque overload requires resolution.

Rheological characterization of microcrystalline cellulose and silicified microcrystalline cellulose wet masses using a mixer torque rheometer

The rheological properties of silicified microcrystalline cellulose (Prosolv 50) were compared with those of standard grades of microcrystalline cellulose (Emcocel 50 and Avicel PH 101). Cellulose samples were analyzed using nitrogen adsorption together with particle size, flowability, density and swelling volume studies. The rheological behaviour of the wet powder masses was studied as a function of mixing time using a mixer torque rheometer (MTR). Silicified microcrystalline cellulose exhibited improved flow characteristics and increased specific surface area compared to standard microcrystalline cellulose grades. Although the silicification process affected the swelling properties and, furthermore, the mixing kinetics of microcrystalline cellulose, the source of the microcrystalline cellulose had a stronger influence than silicification on the liquid requirement at peak torque.