Engineering a capillary bed bioreactor for dermal bioavailability and toxicity testing: caffeine permeation across novel hollow fibre membranes

INTRODUCTION: Traditionally, the estimation of dermal bioavailability and cutaneous toxicity of ingredients in cosmetics has been carried out using animal testing. Nowadays, there is a strong need for alternatives due to more strict regulations when animal testing is involved. In fact, the use of animals to test cosmetic products is banned in the UK and all other members of the EU, and commercialisation of products that have been tested on animals is illegal since March 2013. Toxicological assessment and skin penetration studies in vitro do not reproduce physiological conditions for two reasons: they do not consider the resistance to flow opposed by the blood vessels, and the position of the skin vasculature in vivo is much closer to the skin surface than that achieved in vitro. We propose a novel strategy to mimic skin vascularisation using hollow fibres fabricated with biocompatible materials. As a proof of concept we show that caffeine, a standard compound used in skin penetration studies, permeates through porous hollow fibres, similarly to the clearance that would occur in dermal capillaries.