Integration of Extracellular Matrices into Organ‐on‐Chip Systems

The extracellular matrix (ECM) is a complex, dynamic network present within all tissues and organs that not only acts as a mechanical support and anchorage point but can also direct fundamental cell behavior, function, and characteristics. Although the importance of the ECM is well established, the integration of well‐controlled ECMs into Organ‐on‐Chip (OoC) platforms remains challenging and the methods to modulate and assess ECM properties on OoCs remain underdeveloped. In this review, current state‐of‐the‐art design and assessment of in vitro ECM environments is discussed with a focus on their integration into OoCs. Among other things, synthetic and natural hydrogels, as well as polydimethylsiloxane (PDMS) used as substrates, coatings, or cell culture membranes are reviewed in terms of their ability to mimic the native ECM and their accessibility for characterization. The intricate interplay among materials, OoC architecture, and ECM characterization is critically discussed as it significantly complicates the design of ECM‐related studies, comparability between works, and reproducibility that can be achieved across research laboratories. Improving the biomimetic nature of OoCs by integrating properly considered ECMs would contribute to their further adoption as replacements for animal models, and precisely tailored ECM properties would promote the use of OoCs in mechanobiology. The (bio)chemical, mechanical, and structural properties of the extracellular matrix (ECM) are well‐known to guide cellular behavior and function. Yet, the integration of carefully designed and well‐controlled ECMs into Organ‐on‐Chip (OoC) platforms remains challenging. In this review, current state‐of‐the‐art design and assessment of in vitro ECM environments in OoCs are critically discussed.