# Pluronic 123 Liquid Lyotropic Crystals for Transdermal Delivery of Caffeic Acid—Insights from Structural Studies and Drug Release

## TL;DR

This study explores how the structure and temperature of Pluronic 123 gels affect the skin delivery of caffeic acid.

## Contribution

The study provides new insights into the relationship between mesophase structure, temperature, and drug permeation in transdermal delivery systems.

## Key findings

- Higher polymer concentration increases gel viscosity, but adding caffeic acid enhances microstructure fluidity.
- Temperature increases reduce viscosity and boost caffeic acid permeation rates.
- Cubic mesophase LLC 30/CA showed better skin permeation and accumulation at both tested temperatures.

## Abstract

Background: This study aims to evaluate the percutaneous permeation profiles of caffeic acid (CA) from the cubic and hexagonal liquid crystalline phases of Pluronic P123/water mixtures. Method: The resulting drug-loaded mesophases were subjected to characterisation through deuterium nuclear magnetic resonance spectroscopy and polarised optical microscopy observations. These analyses aimed to evaluate the structural changes that occurred in the mesophases loading with CA. Additionally, steady and dynamic rheology studies were conducted to further explore their mechanical properties and correlate them to the supramolecular structure. Finally, CA release experiments were carried out at two different temperatures to examine the behaviour of the structured systems in a physiological or hyperthermic state. Results: As the concentration of the polymer increases, an increase in the viscosity of the gel is noted; however, the addition of caffeic acid increases microstructure fluidity. It is observed that the temperature effect conforms to expectations. The increase in temperature causes a decrease in viscosity and, consequently, an increase in the rate of permeation of caffeic acid. Conclusions: The CA permeation profile from the prepared formulations is mostly dependent on the structural organisation and temperature. Cubic mesophase LLC 30/CA showed greater skin permeation with good accumulation in the skin at both tested temperatures.