Quantitative measurement and control of oxygen levels in microfluidic poly(dimethylsiloxane) bioreactors during cell culture

Abstract

Microfluidic bioreactors fabricated from highly gas-permeable poly(dimethylsiloxane) (PDMS) materials have been observed, somewhat unexpectedly, to give rise to heterogeneous long term responses along the length of a perfused mammalian cell culture channel, reminiscent of physiologic tissue zonation that arises at least in part due to oxygen gradients. To develop a more quantitative understanding and enable better control of the physical-chemical mechanisms underlying cell biological events in such PDMS reactors, dissolved oxygen concentrations in the channel system were quantified in real time using fluorescence intensity and lifetime imaging of an oxygen sensitive dye, ruthenium tris(2,2'-dipyridyl) dichloride hexahydrate (RTDP). The data indicate that despite oxygen diffusion through PDMS, uptake of oxygen by cells inside the perfused PDMS microchannels induces an axial oxygen concentration gradient, with lower levels recorded in downstream regions. The oxygen concentration gradient generated by a balance of cellular uptake, convective transport by media flow, and permeation through PDMS in our devices ranged from 0.0003 (mg/l)/mm to 0.7 (mg/l)/mm. The existence of such steep gradients induced by cellular uptake can have important biological consequences. Results are consistent with our mathematical model and give insight into the conditions under which flux of oxygen through PDMS into the microchannels will or will not contribute significantly to oxygen delivery to cells and also provide a design tool to manipulate and control oxygen for cell culture and device engineering. The combination of computerized microfluidics, in situ oxygen sensing, and mathematical models opens new windows for microphysiologic studies utilizing oxygen gradients and low oxygen tensions.

Superior oxygen and glucose supply in perfusion cell cultures compared to static cell cultures demonstrated by simulations using the finite element method

“…17 Provin et al 20 also pointed out the importance of oxygen supply through the gas permeable wall based on their experimental results, in which high-density-cultured HepG2 cells in the perfusion culture exhibited the low oxygen consumption. Mehta et al 21 also reported that the flow rate of the media does not significantly affect the oxygen uptake by cells in the PDMS microfluidic perfusion culture chip, of which the result is consistent with our calculated results.…”

A microfluidic optical platform for real-time monitoring of pH and oxygen in microfluidic bioreactors and organ-on-chip devices

“…The fabricated bioreactor was stored in air for few days before use to achieve high oxygen diffusion through PDMS. 38 Owing to the fact that PDMS is highly gas permeable, 56 the PDMS chamber enabled the diffusion of oxygen and CO 2 to the flowing culture medium. 57 Fluidic chamber was fabricated by casting PDMS onto a laser cut PMMA mold in a hexagonal shape.…”

Environmental Control in Flow Bioreactors

“…For instance, a microbioreactor platform that allows for independent control of culture parameters in each well of an array has been reported [10]. To control the physical-chemical mechanisms related to cell activity in microfluidic devices, dissolved oxygen concentrations were monitored in real-time using fluorescence intensity and lifetime imaging of an oxygen sensitive dye by Metha et al [11]. In particular, if used at slow flow rates and high cell density, this microfluidic device creates oxygen-limited physiology (hypoxia conditions) that can be useful in several situations, such as maintaining the pluripotency of embryonic stem cells without the need of hypoxic chambers.…”