Phase diagram of a lattice microemulsion model in two dimensions

In vitro and in vivo studies of micro-depots using tailored microemulsion for sustained local anaesthesia

In clinical practice, lidocaine is used as local anesthetic for the management of post-operative pain. The commercial formulation including gels, injections and ointments showed short duration of action (1 to 2 h). In this paper, the efforts have being made to develop tailored lidocaine-microemulsion (o/w), which on penetration in the skin layer cause micro-depots formation due to destabilization of the microemulsion system. To identify the microemulsion region, pseudo ternary diagrams were constructed using Capmul MCM as oil, Pluronic F68 as tri-block surfactant, polyethylene glycol 200 as co-surfactant at 1:4 and 1:6 ratios (S:Co-S). The selected 5%w/v lidocaine loaded microemulsion [Ld-ME-2(1:4)] was stable in thermodynamic test and during shelf life period (3 months). In ex vivo permeability study, the lidocaine release from Ld-ME-2(1:4) microemulsion was sustained in comparison to the marketed lidocaine ointment. The skin irritation study confirmed the safety of lidocaine loaded microemulsion. Tail flick test showed improved and sustain local anaesthetic effect in comparison to the market ointment. The improved efficacy of microemulsion system, was due to high penetration in the skin layer due to local precipitation of lidocaine from microemulsion. The findings suggest that the tailored microemulsion could be a potential strategy to prolong the local anaesthesia.

Lattice model results for lamellar phases in slits

A mixture of oil, water, and surfactant confined between parallel hydrophilic walls is studied close to phase boundaries between lamellar and uniform phases within a vector lattice model in a mean-field approximation. Relations between energy and force-distance profiles, and the structure of the confined fluid (given by density profiles) are found and discussed. For large wall separations L elastic response to compression or decompression, accompanied by shrinking or swelling of the period lambda of the lamellar phase, is found for lamellar and induced (by capillary condensation) lamellar phases. Very good agreement with recent experiments is obtained. For L<4 lambda the system responds to decompression by swelling of the central, either oil- or water-rich layer, with the layers adsorbed at the surfaces remaining unaffected. The solvation force is very weak and independent of L when the central layer is swollen, and jumps to much larger values when new layers are introduced into the slit.