tx 1. Introduction Development and Initial Results from the Inclusion of Evaporation into a 2D dermal absorption model Benjamin Deacon1,2, Samadhi Silva1, Guoping Lian1,2, Marina Evans3, Tao Chen1 b.deacon@surrey.ac.uk 1. University of Surrey, GU2 7XH 2. Unilever, Bedford, 3. US EPA, NC 2. Evaporation 4. Conclusion 3. Model Results References In experimental scenarios, diffusion into the skin is affected by skin and chemical properties; however, in real life scenarios the vehicles' ability to deliver the active into the skin is impacted by the environment. As such evaporation of the vehicle will occur. Where evaporation will depend on the molecular weight, boiling point, vapour pressure and solubility of the solute and the temperature. The main aim is to develop an evaporation code which will be integrated into the Surrey model to improve the finite dose application. Main conclusions: • The model simulated evaporation time course • The model can be applied to a wide range of chemicals • Needs further validation with experimental data Future work includes: • Further application of the model • Experimental work for validation of the model We simulate evaporation of up to three ingredients under ideal and non-ideal conditions. Non-ideal evaporation allows ingredients in the vehicle to interact and this impacts evaporation. The main equations for evaporation of the active ingredients are given below, including calculation of diffusion coefficient and Fick’s law of diffusion: The results shown below have considered a two ingredients vehicle of Water: Diethanolamine at a starting dose of 10.6 ug/L. This dosage is inline with Hewitt et al, 2020. All simulations here have been performed at 32 oc for 24 hours. 𝐷!"#$%& = 𝐵𝑜𝑙𝑡𝑧𝑚𝑎𝑛𝑛𝐶𝑜𝑛𝑠𝑡𝑎𝑛𝑡∗𝑇 6𝜋𝜂𝑟 𝐶𝑜𝑛𝑐!"#$%& = 𝑃'"#$%& × 𝑀𝑜𝑙𝑒𝐹𝑟𝑎𝑐𝑡𝑖𝑜𝑛𝐴𝑐𝑡𝑖𝑣𝑒 𝑅𝑔× 𝑇 𝐽!"#$%& = 𝐷'"#$%&× 𝐶𝑜𝑛𝑐−0 ℎ 𝑑𝑦 𝑑𝑡'"#$%& = −𝐽'"#$%& × 𝐴 The choice of chemicals and the experimental conditions (skin thickness and dosage) have been informed from Hewitt et al., 2020. This poster has shown evaporation for Water: Diethanolamine (MW 105, Solubility 100 g/100ml, Vapour Pressure 0.03 Pa). This model makes the following assumptions: • Condensation has not been considered. • Wind has not been considered • There are no traces of the active present in the atmosphere at t = 0. • The simulation occurs at standard pressure. 0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004 0.0045 0.005 0.99965 0.9997 0.99975 0.9998 0.99985 0.9999 0.99995 1 Activity Mole Fraction of Water Activity of Diethanolamine Ellison CA, Tankersley KO, Obringer CM, Carr GJ, Manwaring J, Rothe H, et al. (2020) Partition coefficient and diffusion coefficient determinations of 50 compounds in human intact skin, isolated skin layers and isolated stratum corneum lipids. Toxicology in Vitro. Chen, L., G. Lian and L. Han (2008). "Use of “Bricks and Mortar” Model To Predict Transdermal Permeation: Model Development and Initial Validation." Industrial & Engineering Chemistry Research. Hewitt, N. J., S. Grégoire, R. Cubberley, H. Duplan, J. Eilstein, C. Ellison, , et al. (2020). "Measurement of the penetration of 56 cosmetic relevant chemicals into and through human skin using a standardized protocol." Journal of Applied Toxicology Chen, T., G. Lian and P. Kattou (2016). "In silico modelling of transdermal and systemic kinetics of topically applied solutes: model development and initial validation for transdermal nicotine." Pharmaceutical Research Water (mg) Diethanolamine (mg) 0.00E+00 2.00E+05 4.00E+05 6.00E+05 8.00E+05 1.00E+06 1.20E+06 1.40E+06 1.60E+06 1.80E+06 2.00E+06 -1 4 9 14 19 24 Concentration (ug/mL) Time (Hours) Concentration of Diethanolamine Concentration of Diethanolamine Max Solubility of Diethanolamine 0.00E+00 2.00E-03 4.00E-03 6.00E-03 8.00E-03 1.00E-02 1.20E-02 0 5 10 15 20 Volume (uL) Time (Hours) Volume Change of DIethanolamine 0.00E+00 2.00E+00 4.00E+00 6.00E+00 8.00E+00 1.00E+01 1.20E+01 -1 4 9 14 19 24 Amount (mg) Time (Hours) Change in Amount of Diet