Organ-on-chip (OoC) systems are microfluidic devices for maintaining live tissue under physiologically relevant (flow) conditions. Imaging of structure and flow is important for the characterization of OoC device design and visualizing tissue/fluid interaction. Here, we present 3D tissue and flow imaging in an OoC device with multi-modal optical coherence tomography (OCT) using a combination of OCT structural imaging and flow imaging with Doppler OCT, number fluctuation dynamic light scattering OCT, and particle image velocimetry OCT. We demonstrate the feasibility of combined imaging of OoC tissue culture morphology and high flow velocities. We also measure low velocities in the OoC tissue well showing good agreement with computational fluid dynamics simulations. Our results open up the way for studying the effect of flow on living tissue in OoC devices.

Organ-on-chip (OoC) systems are novel microfluidic microsystems that combine the advantages of well-characterised human cells with the benefits of engineered, physiological-like microenvironments manufactured in the system. The extracellular matrix (ECM) is the natural microenvironment of cells in the human body responsible for providing the appropriate stimuli to cells to control cell processes such as proliferation, migration, and apoptosis. OoCs can mimic the ECM, via channels and porous membranes, by providing the cells with physiological-like mechanical stimuli governed by the fluid dynamics in the system [1]. Understanding the fluid dynamics in OOC can aid in fine-tuning the stimuli sensed by the cultured cells, understanding cell behavior and cell fate. The current state of the art methods for characterizing fluid dynamics in the OoC systems are simulations, theoretical calculations, and empirical observations, therefore a quantitative characterization technique is lacking. Optical coherence tomography (OCT) has been used in previous studies to measure omnidirectional flow velocities in flow systems [2]. In this study, we measured the flow in a cuvette using a Thorlabs GANYMEDE II HR series (high axial resolution of 3 mm in air) spectral domain OCT system. We made quantitative 2D flow measurements using the phase-resolved Doppler method. This work was then extended to extract flow dynamics, in the Bi/ond inCHIPit using titania scattering nanoparticles, which would be a novel way of flow characterization in the field of OOC. The results are compared to the theoretical Hagen-Poiseuille equations and COMSOL simulations and found to be in good agreement. The results of the study were further extended to determine the shear stress experienced by the cells in the culture well of the OoC.