Out-of-plane breathing lung model enhances physiological relevance of in vitro breathing simulation

04 August 2026

Lungs continuously expand and retract in a cyclic motion in order to allow air to be drawn in and expelled out, exposing lung tissues to a mechanical strain.  By activating mechanotransduction molecular processes in lung cells, that mainly take part through nuclear translocation of transcriptional co-activator YAP and subsequent activation of target downstream gene programs, the breathing motions of lung tissue reinforce cell–cell junctions, elevate surfactant proteins level, and modulate inflammatory signaling.

These changes directly shape how alveolar tissue responds to external stimuli such as viruses – tight-junctions reduce viral entry, antimicrobial peptides disrupt microbial membranes and recruit immune cells, surfactant proteins promote clearance of viral particles, and interferon-stimulated genes block viral RNA synthesis.  

Static air–liquid-interface and side-to-side stretching plastic membrane in vitro models lack these mechanotransduction cues, which may lead to underestimation of the host responses. While animal models capture whole-organism responses, these are likely to diverge from whole-organism responses in humans, owing to myriad species-specific differences, such as in receptor expression, clearance mechanisms, immune signaling, and gene expression.

To produce physiologically relevant breathing-like expansion and retraction in vitro, Yunji Lee, Gwangmyeong Kim and colleagues from the Pohang University of Science and Technology designed two innovative engineering approaches: synthesis of soap-film-inspired ultrathin, hydrogel membrane and construction of a negative-pressure bioreactor for out-of-plane cyclic strain.

The ultrathin stretchable membrane was obtained by withdrawing a frame from the GelMA-acrylamide precursor solution and UV-crosslinking into a hybrid 30% GelMA-5% AAm co-polymer network to obtain an optimal balance of thickness, elasticity, permeability and stability.

A three-layered human alveolar tissue, comprising an endothelial layer, a fibroblast-containing ECM layer, and an epithelial layer, was bioprinted directly onto the membrane and integrated with the bioreactor under air-liquid interface culture. Cyclical retractation and advancement of syringe piston connected to the bioreactor chamber was adjusted to match the physiological range of alveolar expansion and respiratory rate in resting adults.

Comparison under static and breathing conditions of YAP nuclear localization in the epithelial layer using immunofluorescence and expression of downstream YAP target genes using qPCR, indicated that the breathing motion decreased expression of proinflammatory cytokines, upregulated expression of cellular adhesion-related genes, and increased production of surfactant proteins.  

To investigate how this construct affects infection kinetics and drug responses, the team further built an in vitro model of influenza A infection - a major cause of mortality, particularly in vulnerable populations. qPCR analysis upon treatment with the antiviral drug oseltamivir carboxylate confirmed significant reductions in viral genome and proinflammatory cytokines expression with consistently higher levels observed in breathing tissues compared with static controls. 

By supplying the missing mechanical signals, this innovative dynamic breathing human lung model unlocks the ability to investigate the effects of mechanotransduction on human lung physiology, measure responses to respiratory toxicants, study lung disease progression and assess therapeutic efficacy of drugs.

What Puts It on the Frontier

·         Engineering of an ultrathin, hydrogel membrane that allows to reproduce physiologically relevant breathing-like expansion and retraction motion in vitro, marking a departure from static and lateral stretching models

·         Engineering of a negative-pressure bioreactor for an air-liquid interface culture under out-of-plane cyclic strain 

·         Demonstration of translation of mechanical cues into mechanotransduction molecular processes in the three-layer human bioprinted tissue integrated with the bioreactor

Impact Snapshot

·         Enhanced physiological relevance of human lung in vitro models

·         The ability to investigate in vitro the mechanotransduction molecular and cellular processes triggered by controlled mechanical cues

·         Human-relevant assessment of viral infection kinetics, respiratory toxicant clearance and drug responses under breathing conditions

Reference

Lee Y, Kim GM, Kim W, Soetanto F, Ryu G, Chung T, Kim YS, Lee J, Lee H, Jung S. 2026 Jul 30. Ultrathin hydrogel membranes inspired by soap films enable physiologically relevant breathing lung models. Advanced Materials.:e74372. doi:10.1002/adma.74372.

For weekly news, trends and insights on human‑based in vitro approaches, explore your access options.

Explore Access