Real-Time, Label-Free Monitoring of Tissue Stiffness in a Lung-on-a-Chip under Breathing-Mimetic Cyclic Strain

Physiological mechanical forces generated during respiration are essential for maintaining lung homeostasis and regulating disease progression. In pulmonary fibrosis, aberrant extracellular matrix (ECM) remodeling progressively increases tissue stiffness, disrupts mechanotransduction, and impairs respiratory function. Because stiffness also influences cellular responses to therapeutic agents, continuous mechanical assessment under physiologically relevant dynamic conditions is important for fibrosis research and preclinical drug evaluation. However, conventional in vitro models cannot simultaneously reproduce breathing-associated mechanical cues and monitor evolving tissue stiffness in real time.

Here, we developed a lung-on-a-chip platform integrating breathing-mimetic cyclic strain with real-time, label-free stiffness sensing. The device consists of a thin, alveolar-patterned polydimethylsiloxane (PDMS) membrane and a cell-laden collagen methacrylate (ColMA) hydrogel formed between the patterned regions to recreate a biomimetic alveolar microenvironment. Periodic pressure modulation in an underlying air channel generated controlled inhalation–exhalation-like deformation. Tissue stiffness was quantified by image-based deformation analysis, allowing continuous, non-destructive measurements without fluorescent labeling or destructive mechanical testing.

The platform tracked the transition from a compliant, healthy-like state to a stiff fibrotic-like phenotype during fibrosis induction and detected mechanical recovery following antifibrotic treatment. Image-derived stiffness values showed strong agreement with nanoindentation, while finite element analysis further validated the accuracy and robustness of the method. This platform provides a dynamic and predictive in vitro tool for studying fibrosis-associated mechanical remodeling and screening antifibrotic therapeutics.