Effect of chain length of oil on location of dye within AOT nanometer-sized droplet microemulsions at constant water content

Study of structure of nonaqueous reverse micelles with o-nitroaniline and methyl orange as molecular probes: comparison with an aqueous reverse micelles

Instead of water reversed micelles can also be formed with polar organic solvents possessed with high dielectric constant and very low solubility in oil phase. Nonaqueous reverse micelles or microemulsions represent an interesting microreactors for various reactions, especially for reactions, where reagents can react with water. Study of localization places of molecular probes in organic polar pockets of reverse micelles is topical. The solvatochromic behavior of optical probes ortho-nitroaniline (o-NA) and methyl orange (MO) was studied in nonaqueous reverse micelles on the basis of surfactants sodium bis (2-ethylhexyl) sulfosuccinate (AOT) and polyoxyethylene (4) lauryl ether (C12E4) and polar organic solvents (acetonitrile, dimethylformamide, glacial acetic acid, etc.) insoluble in oil phase hexane. The strength of binding of o-NA and MO to AOT and C12E4 reversed micelles was assesssed via binding constant (K b ) and association degree (α) respectively. Donor, acceptor, or dipole-dipole interactions ability of the solvent to the head groups of surfactant was taken into account in order to explain results obtained with UV–visible spectroscopic method. The binding constants of o-NA with reverse AOT micelles in the presence of various solvents in the pockets of reversed micelles increase in the following row water < glacial acetic acid < acetonitrile < dimethylformamide < dimethyl sulfoxide, but this sequence is reversed when o-NA binds to C12E4 reverse micelles. The high value of the proton donor or acidity parameter in the water molecule (x d  = 0.37) determines the weak binding of o-NA to the head AOT groups (K b  = 20.8) in case of aqueous reverse micelles. The high value of the dipole parameter in the dimethylformamide molecule (x n  = 0.40) promotes its strong interaction with nonionic polyoxyethylene groups of C12E4, which results in low value of binding constant (K b  = 26.5) in case of optical probe o-NA and low value of association degree (α = 0.60) using MO as absorption probe. The results of this article will contribute to the improvement of the concept of interfacial processes, viz.: (i) some issues of supramolecular chemistry, (ii) revealing the contribution of parameters of donor, acceptor or dipole-dipole interaction in a polar organic solvent at the surfactant/nonpolar organic solvent interface, and (iii) features of the dissolution of optical probes in non-aqueous reverse micelles.

Ex vivo permeation parameters and skin deposition of melatonin-loaded microemulsion for treatment of alopecia

Background

Melatonin (MEL) is a powerful antioxidant molecule with anti-androgenic property. A microemulsion (ME) system loaded with MEL was designed for treatment of androgenic alopecia. Pseudo-ternary phase diagram was constructed, and ME formulae were developed using coconut oil, Tween 80 and PEG 400. In the present study, MEL ME was characterized and evaluated for droplet size, polydispersity index, zeta potential, morphology using TEM imaging. MEL ex vivo permeation study through rat skin followed by tape stripping for stratum corneum (SC) was performed for different ME formulae, to determine skin permeation parameters and detect SC-MEL deposition.

Results

Spherical and uniform particles of MEL-loaded microemulsion were formulated with high stability. In ex vivo permeation study, MEL ME exhibited low steady-state skin flux along with pronounced SC deposition which prevailed a controlled release manner.

Conclusion

The results suggested that MEL ME could be a promising candidate for further permeation and in vivo studies for androgenic alopecia treatment.

Development and Evaluation of Azelaic Acid-Loaded Microemulsion for Transfollicular Drug Delivery Through Guinea Pig Skin: A Mechanistic Study

Purpose: Azelaic acid is a natural keratolytic, comedolytic, and antibacterial drug that is used to treat acne. The topical application of azelaic acid is associated with problems such as irritation and low permeability. For dissolving, the problem is that microemulsion (ME) is used as a drug carrier. The aim of this study was to increase the azelaic acid affinity in the follicular pathway through ME.

Methods: Azelaic acid-loaded MEs were prepared by the water titration method. The properties of the MEs included formulation stability, particle size, drug release profile, thermal behavior of MEs, the diffusion coefficient of the MEs and skin permeability in the non-hairy ear skin and hairy abdominal skin of guinea pig were studied in situ.

Results: The MEs demonstrated a mean droplet size between 5 to 150 nm. In the higher ratios of surfactant/co-surfactant, a more extensive ME zone was found. All MEs increased the azelaic acid flux through both hairy and non-hairy skin compared with an aqueous solution of azelaic acid as a control. This effect of the ME was mainly dependent on the droplet diffusion coefficient and hydrodynamic radius. MEs with a higher diffusion coefficient demonstrated higher azelaic acid flux through hairy and non-hairy skin. Drug flux through both skins was affected by the surfactant/co-surfactant ratio in that the higher ratio increased the azelaic acid affinity into the follicular pathway.

Conclusion: Finally, the ME with the highest droplet diffusion coefficient and the lowest surfactant/co-surfactant ratio was the best ME for azelaic acid delivery into the follicular pathway.