Topical delivery of retinol emulsions co-stabilised by PEO-PCL-PEO triblock copolymers: effect of PCL block length.

This article describes enhanced skin permeation and UV/thermal stability of retinol emulsions by the co-stabilisation of Tween20 and biodegradable poly(ethylene oxide)-block-poly(ε-caprolactone)-block-poly(ethylene oxide) (PEO-PCL-PEO) triblock copolymers having different lengths of hydrophobic PCL block. A triblock copolymer with a longer PCL block has a lower hydrophile-lipophile balance (HLB) value. Commercial Retinol 50C® (BASF Co., Ludwigshafen, Germany) was used as the source of retinol. Ultrasonication of the Retinol 50C® emulsion with the triblock copolymers led to an increase in retinol solubilisation and a decrease in average particle size of the resulting retinol emulsion. These characteristics improved skin permeation of retinol through the stratum corneum of artificial skin and subsequent proliferation of viable epidermis cell. Employment of the triblock copolymer with a longer PCL block increased both UV and thermal stabilization of the retinol. These results suggest that HLB and PCL block length are important factors to enhance the topical delivery of retinol into the skin.