Skin penetration of caffeine from commercial eye creams and eye creams designed and optimized based on Hansen solubility parameters

Computer-aided formulation design can streamline and speed up product development. In this study, ingredient screening and optimizing software, Formulating for Efficacy® (FFE), was used to design and optimize creams for the topical delivery of caffeine. FFE was set up to optimize lipophilic active ingredients, therefore, this study challenged the program's capabilities. The effect of two chemical penetration enhancers, including dimethyl isosorbide (DMI) and ethoxydiglycol (EDG), were studied based on their favorable Hansen Solubility Parameter physicochemical input parameters for the skin delivery of caffeine in the FFE® software application. Four oil-in-water emulsions containing 2% caffeine were formulated, one without a chemical penetration enhancer, one with five percent of DMI, one with five percent of EDG, and one with 2.5% of DMI and EDG each (DMI + EDG). Additionally, three commercial products were used as reference products. The cumulative amount of caffeine released and permeated, and the flux across Strat-M® membranes were determined using Franz diffusion cells. The eye creams had skin-compatible pH, excellent spreadability for the application area, were opaque emulsions with 14-17 μm droplet size, and were stable at 25 °C for 6 months. All four eye creams formulated released over 85% of caffeine in 24 h, outperforming the commercial products. DMI + EDG cream provided the highest permeation in vitro in 24 h, which was significantly higher than the commercial products (p < 0.05). FFE proved to be a valuable and quick tool to aid in the topical delivery of caffeine.