In Situ Oxygen Gradient Generation Inside a Termite-Inspired Microfluidic Habitat

Microfluidic devices can be used to simulate complex microhabitats where the concentration gradients of oxygen, nutrients, or other chemical stimulants need to be dynamically controlled.  Though oxygen gradients can be achieved by flowing an oxygenated fluid through a microchannel and allowing the oxygen to diffuse through a polymer membrane/hydrogel to the cell culture area, this configuration does not allow the precise control either spatially or temporally [1]. 

The diverse microbial community of the termite gut is an example of a naturally occurring microhabitat that experiences steep oxygen gradients [2]. These oxygen gradients are really necessary for the formation of spatially-distinct microniches for the protists, bacteria, and archea inhabiting the gut, while the microniches allow microbial symbionts to co-exist with each other and the termite host while breaking down various carbon sources into useful products such as acetate.

In this presentation, we will detail a new method to generate, control, and model the oxygen gradients within a microfluidic habitat.  A novel microfabrication method was developed to photopattern gold electrodes on the vertical side walls of the microchannels for oxygen generation, as shown in Figure 1 [3]. Finite element simulations were conducted to model oxygen production rates under varied geometries, operating currents, and flow rates.  Additionally, in-plane hydrogel barriers were constructed between the channels containing the electrodes and the cell culture chambers, to maintain the stable oxygen gradient and also dampen any sudden changes to the system that could harm cells. With these recent advances in microfabrication and modeling techniques, the micro-scale physical and chemical features of a termite gut (and other communities) can be synthetically recreated in microfluidic devices. 

[1] Brune, A., D. Emerson, and J.A. Breznak, The Termite Gut Microflora as an Oxygen Sink: Microelectrode Determination of Oxygen and pH Gradients in Guts of Lower and Higher Termites. Appl Environ Microbiol, 1995. 61, 2681-2687.

[2] Brune, A., Termite Guts: The World's Smallest Bioreactors. Trends Biotechnol., 1998. 16, 16-21.

[3] Kadilak, A. L., Liu, Y., Shrestha, S., Bernard, J. R., Mustain, W. E., and Shor, L. M., Selective Deposition of Chemically-bonded Gold Electrodes onto PDMS Microchannel Side Walls. J. Electroanal. Chem., 2014. 727, 141-147.