On-chip CO2 control for microfluidic cell culture.

Carbon dioxide partial pressure (P(CO(2))) was controlled on-chip by flowing pre-equilibrated aqueous solutions through control channels across the device. Elevated P(CO(2)) (e.g. 0.05 atm) was modulated in neighboring stagnant channels via equilibration through the highly gas permeable substrate, poly(dimethylsiloxane) (PDMS). Stable gradients in P(CO(2)) were demonstrated with a pair of control lines in a source-sink configuration. P(CO(2)) equilibration was found to be sufficiently rapid (minutes) and stable (days) to enable long-term microfluidic culture of mammalian cells. The aqueous solutions flowing through the device also mitigated pervaporative losses at sustained elevated temperatures (e.g. 37 C), as compared to flowing humidified gas through the control lines to control P(CO(2)). Since pervaporation (and the associated increase in osmolality) was minimized, stopped-flow cell culture became possible, wherein cell secretions can accumulate within the confined environment of the microfluidic culture system. This strategy was utilized to demonstrate long-term (> 7 days) microfluidic culture of mouse fibroblasts under stopped-flow conditions without requiring the microfluidic system to be placed inside a cell culture incubator.