Chemical Distribution Kinetics of Five Polycyclic Aromatic Hydrocarbons in a Microphysiological System

As next-generation risk assessment accelerates the shift towards non-animal models, it also necessitates the development of tools that quantify the chemical in vitro distribution to derive an effective concentration. Although several predictive models have already been developed, none have thus far specifically focused on microphysiological systems. Unlike static well plates, microphysiological systems use (micro-) fluidic flow, consist of largely hydrophobic plastic surfaces, and often rely on protein-rich hydrogel matrices for cell scaffolding. However, these properties can alter the nominal concentration in microfluidic systems, thereby affecting the freely available chemical fraction that can reach the cells. Our objective was to measure the mass distribution in the Organoplate 2-lane^® in the absence of cells to develop an in silico mass balance model using five polycyclic aromatic hydrocarbons under three conditions: bare (no serum), 2% serum media, and bare medium with Matrigel. Our mass distribution analysis showed significant chemical losses in all conditions over 16 h of exposure due to evaporation and plastic sorption, likely accelerated by media movement and the device characteristics. Next, we modelled the in vitro mass balance kinetics of the five polycyclic aromatic hydrocarbons using both raw and loss-corrected measurement data to derive and compare the rate constants and free/bound fractions. As expected, already 2% serum was the main contributor to chemical binding, leaving no free fraction, while the presence of Matrigel delayed the overall distribution kinetics. Based on these results, we emphasise the need to study in vitro distribution, particularly in microphysiological systems, as the nominal concentration of chemicals may not align with the free fraction that reaches the cells.