Fine temporal control of the medium gas content and acidity and on-chip generation of series of oxygen concentrations for cell cultures

Abstract

We describe the design, operation, and applications of two microfluidic devices that generate series of concentrations of oxygen, [O(2)], by on-chip gas mixing. Both devices are made of polydimethylsiloxane (PDMS) and have two layers of channels, the flow layer and the gas layer. By using in-situ measurements of [O(2)] with an oxygen-sensitive fluorescent dye, we show that gas diffusion through PDMS leads to equilibration of [O(2)] in an aqueous solution in the flow layer with [O(2)] in a gas injected into the gas layer on a time scale of approximately 1 sec. Injection of carbon dioxide into the gas layer causes the pH in the flow layer to drop within approximately 0.5 sec. Gas-mixing channel networks of both devices generate series of 9 gas mixtures with different [O(2)] from two gases fed to the inlets, thus creating regions with 9 different [O(2)] in the flow layer. The first device generates nitrogen-oxygen mixtures with [O(2)] varying linearly between 0 and 100%. The second device generates nitrogen-air mixtures with [O(2)] varying exponentially between 0 and 20.9%. The flow layers of the devices are designed for culturing bacteria in semi-permeable microchambers, and the second device is used to measure growth curves of E. coli colonies at 9 different [O(2)] in a single experiment. The cell division rates at [O(2)] of 0, 0.2, and 0.5% are found to be significantly different, further validating the capacity of the device to set [O(2)] in the flow layer with high precision and resolution. The degree of control of [O(2)] achieved in the devices and the robustness with respect to oxygen consumption due to respiration would be difficult to match in a traditional large-scale culture. The proposed devices and technology can be used in research on bacteria and yeast under microaerobic conditions and on mammalian cells under hypoxia.

A paper-based invasion assay: Assessing chemotaxis of cancer cells in gradients of oxygen

“…Furthermore, hypoxia chambers do not generating gradients of oxygen to study chemotaxis. A well-defined gradient of oxygen can be formed in a microfluidic device containing cells, but these devices are predominantly used to study cellular viability, proliferation, and differentiation (7,8,(24)(25)(26)(27)(28). To our knowledge, in vitro studies of chemotaxis in the presence of a gradient of oxygen-particularly one generated by cellular metabolismhave yet to be performed for mammalian cells.…”

“…The concentration gradient of small molecules can be controlled temporally and spatially (at length scales of tens of microns, which is the scale of a single cell) in a microfluidic device (7,8,(24)(25)(26)(27)(28). These devices are often fabricated in optically transparent materials and make it possible to visualize cell migration in real time (19).…”

“…While a variety of microfluidic devices have been developed to control precise gradients of concentration of oxygen (7,8,(24)(25)(26)(27)(28)(29), only recently has a device been used to investigate the migration of cells in such gradients (29). Tung et al demonstrated that oxygen acts as a chemorepellant for A549 cells and these cells migrate toward lower concentrations of oxygen in the presence and absence of an overlapping concentration gradient of stromal cell-derived factor 1 (SDF-1); the gradient of SDF-1 was perpendicular to the concentration gradient of oxygen (29).…”

Recent Developments in Cell-Based Microscale Technologies and Their Potential Application in Personalised Medicine

“…The process of adaptation of cancer cells to altered microenvironments in vivo, in particular to hypoxic conditions, is still not fully understood. Microfluidics can provide a more in-depth insight into cell responses under these conditions mimicking specific microenvironments on chip (Polinkovsky et al, 2009). Microfluidic devices could therefore enable the study of combined effects of altered microenvironments and anticancer drugs on tumour cells and help to understand why anticancer drugs lose effectiveness in solid tumours over time (Minchinton & Tannock, 2006).…”

Circadian rhythms in Neurospora crassa on a polydimethylsiloxane microfluidic device for real-time gas perturbations

“…[8][9][10] Recently, microfluidic cell culture platforms that are capable of controlling oxygen perturbations or gradients on cells have been reported, [11][12][13][14] including oxygen gradients using spatially confined chemical reactions, 11 fine temporal control of gas content and acidity, 12 and higha) Author to whom correspondence should be addressed. Electronic mail: christian.hong@uc.edu 1932-1058/2013/7(4)/044129/7/$30.00 V C 2013 AIP Publishing LLC 7, 044129-1 resolution imaging of a three-dimensional cell culture.…”