PhD Candidate University of Toronto Toronto, ON, Canada
Chronic lung diseases (CLDs) such as COPD and asthma represent a global health challenge responsible for millions of deaths each year. During respiration, lungs are exposed to airborne pathogens, environmental toxicants, and pollutants that cause respiratory diseases or exacerbate underlying illnesses. New drugs for CLDs are urgently needed, but the development of new therapeutics for CLDs is hindered due to high failure rates. A major problem is that existing experimental models for testing drug delivery and pharmacological activity do not properly represent the real human tissues. In respiratory research, experimental models must overcome two main challenges: (i) accurately modeling the microenvironment of lung tissues, and (ii)modeling the delivery and exposure of airborne substances to the tissue.
A common in vitro formats for airway epithelial cells(AECs) is culturing on Transwell membrane inserts and creating an air–liquid interface (ALI) above the AECs to induce apicobasal polarization. Successful ALI culture results in expressions of tight junctions, motile cilia, and viscous mucus, which are all indicative of the morphology of airway epithelium. However, mucociliary differentiation by ALI requires approximately three weeks of culture and maintenance; such long-term culture increases the potential for contamination, dehydration, and lower cell viability. In addition, Transwell membrane inserts are 2D polymeric substrates that are not easily amenable to airflow and are biologically inert, lacking the proper 3D extracellular matrix components of native airway tissues.
Microfluidic lung-on-a-chip systems are increasingly attractive tools for studying lung physiology and function because of their ability to accurately recapitulate spatiotemporal features of the airway tissue microenvironment including cellular organization, tissue architecture, and mechanical cues such as cyclic stretching and airflow. However, most lung-on-a-chip devices to date rely on integrated design elements like membranes for airway cell culture and focus mainly on enabling on-chip monitoring and analysis while neglecting the need for off-chip analysis.
Here, an extractable floating liquid-gel-based organ-on-a-chip for airway tissue modeling referred to as “E-FLOAT” is described that is arrayable, scalable, and uniquely amenable to withstand physiologic airflow by microanchors. E-FLOAT can be combined with an airflow system that permits controlled injection of particulates for air pollution studies. Results show that airflow is critical to efficiently achieving physiologic mimicry of airway epithelium composition, tight junction expression, mucus production, and cilia formation on AECs. It is also shown that E-FLOAT allows standard on-chip analysis while permitting complete sample extraction and off-chip analysis via immunocytochemistry, microscopy, and histological sectioning and staining, thereby expanding the number and types of biological assays that can be used and questions that can be tackled. Taken together, the development of E-FLOAT offers significant potential to study lung cell biology in new ways that can advance our understanding of particle–cell–matrix interactions and the effects of air pollution on lung disease.
