Pressure predictions for lab-on-chip operations using a microfluidic network solver and Fluigent PX 

Introduction to pressure prediction 

Microfluidic flow protocols have evolved to allow multiple fluidic tasks to be integrated into a single device, making it increasingly important to ensure reliable flow control via excellent flow rate and operating pressure prediction. More precisely, predicting the pressures required to reach the desired flow rates with a given configuration and hydrodynamic resistance has become essential. To this end, “microfluidic design automation”¹ tools have been developed. By defining resistive networks, it is possible to predict the flow rate within the microfluidic network (MFN). 

We report the use of our pressure-based flow controller Fluigent PX for the development of a microfluidic platform managing fluids with a microfluidic network solver. The software is called mfnSolver. The platform allows for accurate prediction of pressure settings with excellent response time for operations at steady state. It also enables knowledge about on-chip pressure drop and flow characteristics to be gained. The microfluidic automated operations are demonstrated by making laminar co-flow of up to four components, and variable-composition droplets in several regimes (dripping, transition, jetting) from up to three components. 

Microfluidic chip: 

• Chip: flow-focusing unit (FFU) of the Leibniz-IPHT PDG2 Droplet Generator Chip (PDG2). The PDG2 chip has 4 inlets (P1, P2, P3, P5) and 1 outlet (P4)¹. 
• Channel width: 165 µm before the flow focusing region, 200 µm at the observation chamber, and 150 µm otherwise – Channel height: 100 µm. 
• Surface treatment (for droplet generation): PlusOne Repel-Silane ES (solution of Dimethyldichlorosilane (2% w/v) in Octamethylcyclotetrasiloxane). 

Buffer and Reagents: 

• Dye solutions: 2 mmol/L Bromophenol blue solution (Sigma-Aldrich) for which 13 mg of the sodium salt dye was dissolved in 10 mL sodium phosphate buffer – 4.9 mmol/L Orange G solution containing 22 mg disodium salt dye in a 10 mL buffer 

• Surfactant for droplet generation: Fluigent dSurf (2% surfactant in Novec™ 7500) 

mfnSolver: 

The microfluidic network solver developed by Böke et al. gives the pressure and flow rate at all defined nodes and edges of the chip¹. It can solve a complete microfluidic system in less than 200ms. The user only has to define the flow rates along arbitrary edges of the network for the solver to compute the differential pressure required to reach them. In addition, the mfnSolver can help users to design and optimize microfluidic components, predict network performance, and automate the operation of devices based on pressure-driven fluid management. 

Conclusion 

In this application note, we have reported that the microfluidic network solver mfnSolver is a tool for reliable and easy lab-on-chip operations, thanks to its fast and accurate operating pressure predictions at steady state and its support in obtaining information about on-chip pressure drop and flow characteristics.  

With the growing complexity of microfluidic setups, the automation of fluid management is becoming a non-negligeable advantage. Fluigent PX helped in the development of this flow automation project as a solution to provide flows with excellent accuracy and response time. 

References 

1. Böke, J. S., Kraus, D. & Henkel, T. Microfluidic Network Simulations Enable On-Demand Prediction of Control Parameters for Operating Lab-on-a-Chip-Devices. Processes 9, 1320 (2021).