Online oxygen monitoring using integrated inkjet-printed sensors in a liver-on-a-chip system

Abstract

The demand for real-time monitoring of cell functions and cell conditions has dramatically increased with the emergence of organ-on-a-chip (OOC) systems. However, the incorporation of co-cultures and microfluidic channels in OOC systems increases their biological complexity and therefore makes the analysis and monitoring of analytical parameters inside the device more difficult. In this work, we present an approach to integrate multiple sensors in an extremely thin, porous and delicate membrane inside a liver-on-a-chip device. Specifically, three electrochemical dissolved oxygen (DO) sensors were inkjet-printed along the microfluidic channel allowing local online monitoring of oxygen concentrations. This approach demonstrates the existence of an oxygen gradient up to 17.5% for rat hepatocytes and 32.5% for human hepatocytes along the bottom channel. Such gradients are considered crucial for the appearance of zonation of the liver. Inkjet printing (IJP) was the selected technology as it allows drop on demand material deposition compatible with delicate substrates, as used in this study, which cannot withstand temperatures higher than 130 °C. For the deposition of uniform gold and silver conductive inks on the porous membrane, a primer layer using SU-8 dielectric material was used to seal the porosity of the membrane at defined areas, with the aim of building a uniform sensor device. As a proof-of-concept, experiments with cell cultures of primary human and rat hepatocytes were performed, and oxygen consumption rate was stimulated with carbonyl-cyanide-4-(trifluoromethoxy)phenylhydrazone (FCCP), accelerating the basal respiration of 0.23 ± 0.07 nmol s-1/106 cells up to 5.95 ± 0.67 nmol s-1/106 cells s for rat cells and the basal respiration of 0.17 ± 0.10 nmol s-1/106 cells by up to 10.62 ± 1.15 nmol s-1/106 cells for human cells, with higher oxygen consumption of the cells seeded at the outflow zone. These results demonstrate that the approach of printing sensors inside an OOC has tremendous potential because IJP is a feasible technique for the integration of different sensors for evaluating metabolic activity of cells, and overcomes one of the major challenges still remaining on how to tap the full potential of OOC systems.

Inkjet-Printing of Nanoparticle Gold and Silver Ink on Cyclic Olefin Copolymer for DNA-Sensing Applications

“…Photonic curing after thermal sintering at 130 • C yields structures that feature about 10% of the conductivity of bulk gold, which is a 60-fold higher conductivity than previously reported structures on cyclic olefin polymer [16] that were sintered in Ar plasma for 30 min. On other substrates, like polyethylene naphthalate (PEN) or SU-8 covered polytetrafluoroethylene (PTFE) conductivities of a comparable order of magnitude were achieved by thermal sintering at 150 • C [17] and 130 • C [37], respectively. However, the latter sources report the necessity of performing an electrochemical activation step prior to use.…”

Engineered Liver-On-A-Chip Platform to Mimic Liver Functions and Its Biomedical Applications: A Review

“…Another advantage of an organ-on-a-chip is that it can achieve real-time monitoring by integrating with sensors. As shown in Figure 4b, Moya et al used an inkjet-printed oxygen sensor with a liver-on-a-chip to evaluate metabolic activity in real-time [82].…”

“…(b) Schematic, cross-section, and real image of an oxygen sensor-integrated liver chip. Reproduced with permission from[82].…”

Investigation of the hepatic respiration and liver zonation on rat hepatocytes using an integrated oxygen biosensor in a microscale device

“…Based on those works, the oxygen gradient in a flow chamber was correlated with the CYP450 gradient in rat hepatocytes . In addition, few examples of devices have integrated oxygen biosensors in the liver culture chamber to couple biological and mass transport/mechanical phenomena . In this view, we have proposed a technology in which an oxygen sensor layer containing platinium (II) octaethylporphyrin (PtOEP) was embedded at the bottom of a liver‐on‐chip device .…”

“…20,21 In addition, few examples of devices have integrated oxygen biosensors in the liver culture chamber to couple biological and mass transport/mechanical phenomena. [22][23][24] In this view, we have proposed a technology in which an oxygen sensor layer containing platinium (II) octaethylporphyrin (PtOEP) was embedded at the bottom of a liver-on-chip device. 25 The originality of our sensor allowed a 2D mapping of the oxygen profile and oxygen concentration over a large area (about 1 cm 2 ).…”