Category: Cellular Technologies

1010-A - Delivery of controllable hydrogen sulfide concentration via PDMS microfluidics for biological applications

Monday, February 5, 2018
2:00 PM - 3:00 PM

Introduction: Hydrogen Sulfide (H2S), which is a toxic gas in high concentrations, has been found to be produced enzymatically in different organs and is thought to be an important signaling mediator. Specifically, it is well known for its vasodilatory and antioxidant effects and for its activation of the KATP­ channels [1]. However, the exact mechanism of how hydrogen sulfide works is still unclear. The limitation is associated with H2S’s nature as H2S molecules dissolved in a solution evaporate fast to the environment, a phenomenon known as volatilization [2]. Current in vitro methods do not allow stable hydrogen sulfide concentrations with time and remains a barrier to understanding its mechanism.



Methods:
H2S is delivered via diffusion from microfluidic channels through a gas permeable membrane fabricated using polydimethylsiloxane (PDMS) soft lithography. The device consists of 3 different layers, the microfluidic channels, a 100μm thick PDMS membrane and a reservoir, where the cells can be seeded with appropriate amount of media. H2S molecules diffuse through the PDMS membrane to the cell culture reservoir microfluidics (Figure 1a,b). In this system, a defined mixture of sodium hydrosulfide (NaHS), used as a H2S donor, was injected using a syringe pump (Harvard Apparatus) through the microchannels, which then diffuses through the membrane and is able to be detected in the reservoir. The detection of the H2S concentration was achieved using electrochemical sensors (Alphasense, Essex, UK).



Results:
It is shown that H2S concentration is dependent on the concentration of the solution of NaHS and the flow rate of the solution in the microchannels. In this way different concentrations of H2S can be obtained in a controllable way either stable, by keeping the flow rate constant (Figure 1c), or variable, by changing the flow rate. Previously, only transient (minutes) cytotoxic doses of H2S were able to be delivered to cells which limited progress in understanding this molecule. We show physiological H2S levels able to be maintained for hours or at levels able to be programmed via syringe pumps controlling the flow rates of H2S donor solutions which controls the absolute H2S levels in the reservoir.

Theodore Christoforidis

Graduate Student
University of Illinois At Chicago
Chicago, IL

Theodore Christoforidis is a fourth year PhD candidate at the University of Illinois at Chicago (UIC). Prior to arriving at UIC, he earned his bachelor's degree in Microsystems at National Technical University of Athens (NTUA) on Microsystems and Nanotechnology where he firstly developed microfluidic systems. He received his bachelor's degree from the school of Mechanical engineering also at NTUA. He is currently developing microfluidic systems for cell cultures to study the effect of gaseous signalling molecules, such as hydrogen sulfide and nitric oxide, providing pioneering capabilities for the field. These gases are known to be hazardous in large doses, constituting a major problem for their study. Theodore is interested in developing automated cell culture systems, incorporating microfluidic systems and gaseous signaling molecules.