Researchers of Molecular Physiology Laboratory Optimize Microfluidic Chip Composition for Long-Term Organ-on-a-Chip Cultivation

Applied Biochemistry and Microbiology has published an article by researchers from the Molecular Physiology Laboratory at HSE University and the Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, dedicated to optimizing the gas permeability of polydimethylsiloxane (PDMS)—a material widely used for manufacturing microfluidic chips in organ-on-a-chip systems.

The Gas Permeability Problem in Microfluidic Systems

Polydimethylsiloxane (PDMS) has long been recognized as an ideal material for microfluidic device fabrication due to its transparency, biocompatibility, elasticity, and bioinertness. However, its high gas permeability creates a significant challenge: when using integrated micropumps, compressed air necessary for valve operation penetrates into the device channels, forming gas bubbles. These bubbles disrupt nutrient medium circulation and lead to cell death, substantially reducing experiment reliability and reproducibility.

"Gas permeability in PDMS is related to the flexibility of its molecular structure: silicon-oxygen chains create microcavities through which gas diffuses into the liquid medium," explains Ivan Khaustov, lead author of the study. "For long-term cell cultivation in organs-on-a-chip, we need to lower this gas permeability while preserving material elasticity and biocompatibility."

Systematic Investigation of Polymerization Parameters

The research team conducted a comprehensive study of how two key factors affect PDMS gas permeability: the base-to-curing-agent ratio (2.5:1, 5:1, 10:1) and polymerization temperature (25°C, 75°C, 125°C). For all parameter combinations, 34 microfluidic chips were fabricated and tested under both static conditions and with an active micropump.

Results revealed an unexpected pattern: the standard polymerization regime at 75°C with a 10:1 ratio, recommended by the manufacturer, actually led to the fastest gas bubble formation. Conversely, deviating from 75°C in either direction—both higher and lower—substantially reduced material gas permeability.

Optimal Parameters for Organ-on-Chip Systems

Based on a comprehensive analysis, the authors identified a 5:1 ratio at a polymerization temperature of 125 °C as optimal. This combination provides:

• Reduced gas permeability comparable to the 2.5:1 ratio
• Rapid polymerization—just 15 minutes instead of 24 hours at room temperature
• Economical material consumption—less curing agent than standard protocols
• Preserved elasticity of the material, critical for integrated micropump function

Cell Safety Assessment

The authors conducted cytotoxicity tests using two cell lines modeling the placenta. BeWo b30 cell line represents choriocarcinoma cells reproducing trophoblast function, while EA.hy926 cell line represents vascular endothelium. Both cell types were cultured with PDMS extracts at various component ratios.

Results revealed no significant differences in cell viability using the optimized PDMS composition compared to controls. Moreover, when both cell lines were directly cultured in microfluidic chips under optimal polymerization conditions, both populations remained 100% confluent after 7 days with no signs of stress or apoptosis. Vital dye staining (CellTracker Orange) demonstrated that cellular monolayers maintained normal morphology.

Practical Impact for Organ-on-Chip Models

These findings have direct application to developing long-term organ-on-a-chip models. Extended time before gas bubble formation enables longer experiments modeling physiological and pathological processes—from studying preeclampsia mechanisms to testing new pharmaceuticals.

"The optimized PDMS composition allows us to culture cell constructs for two weeks or longer without experimental interruption due to technical issues," noted Evgeny Knyazev, laboratory head. "This is critically important for modeling complex processes requiring extended timeframes for development."

Integration with Other Systems

The work demonstrates that materials engineering optimization in microfluidics directly transforms capabilities for biological research. Results are already being applied in developing integrated microfluidic systems, including multi-chamber setups with micropumps and sensors for simultaneous monitoring of multiple microenvironment parameters.

The research was supported by the Russian Science Foundation (grant 24-14-00382).