Stimuli-responsive materials in organ-on-a-chip systems: from dynamic microenvironment modelling to functional readout.

Organ-on-a-chip (OoC) systems provide an in vitro platform for modelling tissue phenotypes and functions. Compared with conventional cell culture or animal testing, they allow dynamic responses to be monitored in a setting more closely aligned with human biology. By integrating platform materials, membrane-based biointerfaces, hydrogel matrices, and readout materials, OoC systems connect structural support, tissue-tissue communication, microenvironment regulation, and real-time monitoring under controlled conditions. However, the dynamic changes that occur in living tissues are often insufficiently reproduced by commonly used materials in these components. Stimuli-responsive materials offer a way to address this gap by changing structural, transport, or readout properties in response to defined physical, chemical, or biological cues. Such responsiveness helps OoC models better reproduce evolving tissue microenvironments and improves their usefulness for biomedical testing. Unlike prior reviews that treat OoC materials or sensing components separately, this review adopts a module-based material perspective. This review summarizes recent advances, particularly those reported over the past 3 years, in the use of stimuli-responsive materials to shape microenvironmental dynamics, mediate tissue interfaces, and enable functional readout in OoC systems. By mapping these material strategies across different roles within the chip, this review connects material design with measurable biological performance and offers a material-centred perspective for future OoC design and translation.