High-Throughput Manufacturing of Portable Plastic Pneumatic Logic Circuits for Integrated Microfluidic Control

Abstract

Microfluidic technology has advanced biological research and medical diagnostics by enabling large-scale parallelization and integration of multiple processes within small areas. Active microfluidic circuits have components such as valves and pumps which need to function in a highly integrated manner in full analytical systems. However, there exists a limitation in size and functionality caused by the complexity and cost of external hardware control. Autonomous microfluidic systems aim to deliver the results of complex multi-step bioassays without external controls or energy input. Embedded control enables the devices to autonomously execute pre-programmed operations and also makes scalability possible Analogous to the electronic microprocessor, microfluidic control consists of components that execute combinational logic such as multiplexers and sequential logic such as counters. Synchronization between these blocks is achieved by a timing reference such as an oscillator that generates a clock at a specific frequency. This research examines the manufacturing of a pneumatic oscillator in a ring configuration using a popular family of plastics used in microfluidics, acrylics. PMMA is one such acrylic with amenable properties available in varying thicknesses and used to fabricate microfluidic devices for various applications. The first part of the research explores the different techniques used to manufacture single pneumatic membrane valves and oscillator circuits made from them. Limitations and challenges faced with two specific methods, hot embossing and CNC milling are explained. The second part of the research focusses on the third manufacturing technique, laser engraving, which successfully produced functional devices. The development of a bonding technique of the membrane material, poly-dimethyl siloxane (PDMS) with PMMA is also discussed as part of the assembly process. Test results with a portable pneumatic source, a syringe, showed the utility of the device for portable microfluidics. Circuits made with valves driven using the oscillator output as a control signal demonstrated the repeatability and scalability of the device fabrication process. Manufacturing microfluidic logic circuits in a large scale requires techniques that can reduce the turnaround time between prototype and production. This research develops such a fabrication process, from manufacturing of layers to assembly, to produce functional devices that are useful for portable microfluidic applications.