| Summary: | The primary objective of this research was to investigate the possible effects of selected liquid crystal (LC) forming surfactants, namely ArlacelTM 2121, CrodafosTM CES and BrijTM system (BrijTM S721/ BrijTM S2) and selected oils, namely, Arlamol™ PS15E, Crodamol™ OP, Arlamol™ HD on formulation properties. The effects of the different excipients were monitored using the formulations thermal properties, water holding ability and ability to promote the permeation of ibuprofen (IBU and caffeine (CAF)) across silicone membranes. The melting endotherms of the ternary formulations containing 10% w/w Arlamol™ PS15E or Crodamol™ OP, 10% w/w surfactant and 80% w/w water resulted in high melting endotherm (>55˚C). However, the inclusion of 10% w/w Arlamol™ HD in equivalent ternary formulations lowered the melting endotherm to 45-50 ˚C, suggesting a destabilising effect of this oil. In addition, increasing the surfactant content of ternary formulations from 5% w/w to 10% w/w reduced the evaporation time of free water by 10-20 min. However, this change in the water holding ability was not the same for all surfactants. The results ranked the water holding ability of the surfactants as the Brij™ system > CrodafosTM CES > Arlacel™ 2121. The permeation profiles of IBU and CAF across model membranes showed significant enhancement (p <0.05) for both drugs from saturated formulations containing Crodamol™ OP with the Brij™ surfactant system. This was attributed to the uptake of Crodamol™ OP into silicone membrane (22.88%) and the good solubility of both model actives in this oil. In addition, the permeation results suggest that the Brij™ system was interacting with membranes at a greater extent compared with other surfactants. The thesis also investigated the hydration characteristics of the human nail using the Confocal Raman spectroscopy (CRS). The results showed the nail to absorb significant amounts of water (~15% w/w) into the top 5 µm of the nail plate after 10 min of hydration. The absorbed water was lost from the nail in a quick manner of 30 min which agreed with previous reports. The CRS was also used to monitor in vivo deposition of IBU from saturated propylene glycol (PG) solutions under infinite (occluded) conditions. The results were consistent with previous work, showing IBU signal inside the skin to increase consequently with PG content in the applied formulation. These results indicated that CRS can be used as a valid in vivo technique to monitor drug delivery.
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