Grantee Research Project Results

2023 Progress Report: Measuring Toxicokinetics for Organ-on-Chip Devices

EPA Grant Number: R840031
Title: Measuring Toxicokinetics for Organ-on-Chip Devices
Investigators: Hutson, Michael Shane , McCawley, Lisa J. , Markov, Dmitry
Institution: Vanderbilt University
EPA Project Officer: Spatz, Kyle
Project Period: August 1, 2020 through May 6, 2025
Project Period Covered by this Report: August 1, 2022 through July 31,2023
Project Amount: $790,352
RFA: Advancing Toxicokinetics for Efficient and Robust Chemical Evaluations (2019) RFA Text |  Recipients Lists
Research Category: Chemical Safety for Sustainability

Objective:

As a way to reduce the need for animal testing, EPA and other regulatory agencies have funded investigations of organotypic culture models and organ-onchip devices. These new approach methodologies place multiple human cell types in appropriate 3D geometries under continuous microfluidic perfusion to better approximate in vivo cellular microenvironments – and thus yield more predictive responses to potential toxicants. Nonetheless, translating organ-on-chip results to predict human health effects still requires in-vitro-to-in-vivo extrapolation. Such extrapolation is always difficult, but becomes even more complicated for organ-on-chip devices because their high surface-to-volume ratios and permeable materials such as PDMS can sequester hydrophobic compounds. Using results from these devices thus requires two calculations: (1) from nominal inlet concentration to indevice cellular dose; and (2) from that dose to equivalent organismal exposure. The latter has been the subject of decades of work, but the former is just beginning to be explored. Our primary objective is to establish methods, measurements and models for the toxicokinetics of PDMS-based organ-on-chip devices.

Progress Summary:

During Year 3 of this grant, we completed experiments on a priority list of chemicals currently in use in other organ-on-a-chip toxicology studies. These include three organophosphate pesticides (paraoxon, parathion and chlorpyrifos) and one AhR agonist (indole). We have also conducted an incomplete set of experiments on a longer and more widely varying list of 40 chemicals. We have measured the degree to which each chemical-of-interest partitions from an aqueous solution into PDMS, the rate at which it does so, the rate at which it returns to solution, and the rate at which it diffuses across a thin (80-µm) PDMS membrane. 

1. We have developed calibration protocols based on UV/Vis spectroscopy and multiwavelength Partial Least Squares Regression for non-destructive measurements of the concentration of a chemical remaining in solution. We have used these protocols to assess limit-of-detection for cuvette-based and ATR-crystal-based measurements. 
2. We have conducted disk-soak and diffusion-through-membrane experiments, and developed nonlinear regression methods for simultaneously fitting these experimental results to models that return well-constrained estimates of the relevant parameters: PDMS-to-water partition coefficient, k; and diffusion constant in PDMS, D_p.
3. We have used disk-soak experiments for indole, which has high affinity for and high diffusion through PDMS, to test how PDMS interaction parameters vary among PDMS lots and how they are altered by annealing PDMS.
4. As a validation step, we have conducted experiments in which two fluorescent test chemicals are observed via confocal microscopy as they diffuse out of a cylindrical well containing a test solution and into a surrounding block of PDMS. 

Future Activities:

• We will conduct disk-soak and diffusion-through-membrane experiments for benzo(a)pyrene, a chemical with limited water solubility, in 50 to 70% water-DMSO mixtures. We will conduct similar experiments for indole in 0 to 100% DMSO and investigate whether a log-linear relationship can be used to extrapolate solution-PDMS partition coefficients measured at high DMSO fractions to lower DMSO fractions.
• We will use the experimental protocols and simultaneous regression techniques developed and tested on this first set of chemicals to complete measurements of PDMS interaction parameters and in-PDMS diffusion coefficients for 53 additional chemicals of interest. This set of chemicals covers a wide range of physico-chemical properties.
• We will the use the above results to build a Quantitative Structure-Property Relation (QSPR) model to predict sequestration into PDMS for a wider set of chemicals. 
• We will develop partial-differential-equation models of partitioning into PDMS and diffusion through PDMS to predict chemical distribution within the user-defined geometry of specific microfluidic devices at different flow rates. We will test these models against experiments that measure chemical concentration at the device outlet. Our goal is to develop a predictive model for in-device toxicokinetics.

Journal Articles:

No journal articles submitted with this report: View all 5 publications for this project

Supplemental Keywords:

adsorption, risk assessment, bioavailability, dose-response, mammalian, PAH, dioxin, innovative technology, decision making, biology, chemistry, physics, engineering, modeling, analytical, measurement methods, Tennessee, TN, organ-on-a-chip, organotypic cell culture, bioreactors, microfluidics 

Relevant Websites:

Vanderbilt-Pittsburgh Resource for Organotypic Models for Predictive Toxicology Exit

Progress and Final Reports:

Original Abstract

2021 Progress Report

2022 Progress Report

2024 Progress Report