Implementing oxygen control in chip-based cell and tissue culture systems

Abstract

Oxygen is essential in the energy metabolism of cells, as well as being an important regulatory parameter influencing cell differentiation and function. Interest in precise oxygen control for in vitro cultures of tissues and cells continues to grow, especially with the emergence of the organ-on-a-chip and the desire to emulate in vivo conditions. This was recently discussed in this journal in a Critical Review by Brennan et al. (Lab Chip (2014). DOI: ). Microfluidics can be used to introduce flow to facilitate nutrient supply to and waste removal from in vitro culture systems. Well-defined oxygen gradients can also be established. However, cells can quickly alter the oxygen balance in their vicinity. In this Tutorial Review, we expand on the Brennan paper to focus on the implementation of oxygen analysis in these systems to achieve continuous monitoring. Both electrochemical and optical approaches for the integration of oxygen monitoring in microfluidic tissue and cell culture systems will be discussed. Differences in oxygen requirements from one organ to the next are a challenging problem, as oxygen delivery is limited by its uptake into medium. Hence, we discuss the factors determining oxygen concentrations in solutions and consider the possible use of artificial oxygen carriers to increase dissolved oxygen concentrations. The selection of device material for applications requiring precise oxygen control is discussed in detail, focusing on oxygen permeability. Lastly, a variety of devices is presented, showing the diversity of approaches that can be employed to control and monitor oxygen concentrations in in vitro experiments.

A microfluidic oxygen gradient demonstrates differential activation of the hypoxia-regulated transcription factors HIF-1α and HIF-2α

“…Microfluidic devices enable the exposure of cells to precisely controlled oxygen environments 22,23 but have also predominantly been used to generate single-condition, homogeneous environments 24–28 . Some devices have demonstrated generation of oxygen gradients, but these have relied on complex internal or external architecture, including many gas inputs, off-chip gas mixers, and on-chip dilution trees 29,30 .…”

A factorial design to identify process parameters affecting whole mechanically disrupted rat pancreata in a perfusion bioreactor

“…(6 mg L −1 vs. 8 mg L −1 ); the D.O. in saturated culture media at 21% partial pressure and 37°C is 7.02 mg L −1 . The selected values represent 18% (6 mg L −1 ) and 24% (8 mg L −1 ) partial oxygen pressure.…”

“…in saturated culture media at 21% partial pressure and 378C is 7.02 mg L 21 . 19 The selected values represent 18% (6 mg L 21 ) and 24% (8 mg L 21 ) partial oxygen pressure. Temperature and pH were set, respectively, at 378C and 7.4 for all bioreactor experiments.…”

Analysis of oxygen transport in microfluidic bioreactors for cell culture and organ‐on‐chip applications

“…Most liver functions are achieved by hepatocytes, which account for approximately 80% of the total volume of the liver. Oxygen concentration is nondimensionalized by C sat = 0.225 mM that is equivalent for 21% oxygen partial pressure in aqueous solutions at 37 • C. 24 In the case of the bioreactor without an oxygen-permeable membrane, only less than 20% of the microchannel length receives sufficient oxygen for the survival of the cells at Pe = 5 ( Figure 2). 30,31 The value of V max for human-induced pluripotent stem cells derived cardiomyocytes (hiPSC-CMs) is 1.97 × 10 −16 mol/s/cell.…”