Environmentally responsive systems for topical administration of copaiba oil-resin: The effect of carbomer 974P on the mechanical, rheological, drug release and skin permeation

Topical wound therapy using copaiba oil-resin (CO) can be improved by combining it with a thermoresponsive bioadhesive release system. Emulgel systems composed of the bioadhesive carbomer 974P (C974P) and the thermoresponsive poloxamer 407 (P407) can prolong the CO contact time with the skin and facilitate the drug permeation through the skin layers. The aim of this work was to develop and investigate the C974P’s effect on rheological, mechanical, bioadhesive, in vitro drug release and ex vivo skin permeation properties of this system. The system development was based on a 23 (plus two central points) factorial design and the influence of different amounts of C974P on formulations was investigated. C974P enabled the formation of viscous and stable emulgels, and could structure with P407 and CO, resulting on physicochemical stable formulations. Formulation composed of 0.5% (w/w) C974P, 20% (w/w) P407 and 8% (w/w) CO (F8) displayed improved properties. F8 exhibited extended release, enhanced bioadhesive strength, improved hardness, compressibility, elasticity, adhesiveness, cohesiveness, pseudoplasticity with yield value, thixotropy, and high viscoelasticity. It also displayed skin permeation and retention. The P407's high capacity to form micelles with CO enabled their integration into the polymeric matrix formed by C974P, resulting in viscous and stable gel.