Brookfield digital viscometer

Gellan gum dispersion (0.7%, w/v) was prepared by sprinkling over boric acid/borax buffer (pH 7.4) at 80 °C while stirring. The mixture was stirred continuously until a clear dispersion was obtained. After allowing to cool, optimized FLB niosomes were incorporated into gellan gum dispersion to attain an FLB concentration of 10 mg/g. Then, the niosomal loaded in situ gel was kept for 12 h at 4 °C before evaluation to allow the removal of entrapped air bubbles within the gel during preparation. Raw FLB loaded in situ gel was prepared at the same concentration as a control for comparison. The prepared FLB niosomal in situ nasal gel formulation was evaluated for viscosity and gelation before and after the addition of simulated nasal fluid (SNF) [24 ,25 (link)]. The viscosity was evaluated using a Brookfield digital viscometer (Brookfield Engineering Laboratories, Middleborough, MA, USA). The apparent viscosity was measured at 10 rpm after 30 s before and after gelation.

The characteristics of the transdermal formulation based on IND-NPs were determined according to our previous reports [10 (link),11 (link),13 (link),14 (link),16 (link)]. Briefly, the zeta potential of IND-NPs was measured using a model 502 zeta-potential analyzer (Nihon Rufuto Co., Ltd., Tokyo, Japan). The particle-size distribution and number of IND-NPs were determined by a NANOSIGHT LM10 (QuantumDesign Japan, Tokyo, Japan), and the measurement conditions were as follows: time 60 s, viscosity of the suspension 1.27 mPa∙s, and wavelength 405 nm. The viscosity of the IND transdermal formulations was measured at 22 °C by a Brookfield digital viscometer (Brookfield Engineering Laboratories, Inc., Middleboro, MA, USA). The soluble IND and solid IND (IND-NPs) in the transdermal formulations were separated by centrifugation (1 × 10⁵ g) using an Optima^TM MAX-XP Ultracentrifuge (Beckman Coulter, Osaka, Japan), and the levels of soluble IND and IND-NPs were analyzed by the HPLC method described below.

An aqueous warm dispersion of a weighed amount of hydroxypropyl methyl cellulose (HPMC 15000) (5%, w/w) was developed with continuous stirring until plain gel was formed. This concentration of HPMC was selected based on previous work to produce hydrogels with desirable viscosity and homogeneity. The dispersion was sonicated for 15 min to remove air bubbles. RT dispersion in distilled water was added slowly to 10 mL of aqueous HPMC dispersion while stirring took place until a homogenous RT hydrogel was formed. The calculated amount of freeze-dried selected RT-NC2 formulation was incorporated into HPMC plain gel 5%, w/v by magnetic stirring and the final weight of the gel was adjusted to 10 g with distilled water. The RT concentration in the free RT and RT-NC2 hydrogels was 0.5%, w/w. The prepared free RT and RT-NC2 hydrogels were left in the fridge for further studies. The viscosity of the hydrogel was measured by a Brookfield Digital Viscometer (Model DV-II Brookfield Engineering Laboratories, Inc., Stoughton, MA, USA). The pH of the free RT and RT-NC2 hydrogels was measured using a pH meter (3500 pH meter, Jenway, UK). The RT content of the hydrogels was measured by dissolving 0.5 g in methanol and the drug concentration was measured spectrophotometrically at λ_max of 359 nm.