We report a novel injection moulding technique for fabrication of complex multi-layer microfluidic structures, allowing one-step robust integration of functional components with microfluidic channels, and fabrication of elastomeric microfluidic valves. This technique simplifies multi-layer microfluidic device fabrication, while significantly increasing device functionality. We demonstrate functional component integration through robust encapsulation of porous polyester membranes, in the context of an in-vitro research platform intended to facilitate Blood Brain Barrier (BBB) research. We also demonstrate the fabrication of normally-closed, pneumatically actuated elastomer valves, integrated using the same one-step process. These valves are demonstrated in the context of variable flow resistors used to modulate flow in a pressure driven system.
Introduction
Microfluidics has flourished in recent years as an emerging technology for addressing a wide range of research applications 1-5. Perhaps most notably, microfluidics has shown significant promise in revolutionising the biomedical field 6-9 . Hybrid microfluidic devices have been reported incorporating integrated structures such as electrode arrays 10, permeable membranes 11, micro-valves 12, 13 and other functional structures, enabling complex lab-on-a-chip research platforms and point-of-care devices. Numerous microfabrication techniques have been reported for the realisation of microfluidic devices. These commonly use the material polydimethylsiloxane (PDMS) due to its favourable chemical, mechanical, and optical properties, as well as its inherent biocompatibility 4, 14, 15 .
Conclusions
We have shown a practical method for the fabrication of monolithic microfluidic devices with complex 3D structures. This method allows for the integration of devices that enable complex functionality for microfluidic systems. This method is also suited to rapid prototyping and reduces fabrication error compared to established methods, allowing for more reliable and complex microfluidic chips to be realised in a short time. This technique allows for reduction in fabrication complexity, while allowing for increase in functional complexity, and could be applied to significantly simplify the fabrication of complex valve based research platforms such as those seen in large scale integration approaches 12, 44. Future research will investigate hybrid integration of various modular components such as membranes, electrodes, piezo-actuators, heaters, pressure sensors and biosensors within lab-on-a-chip platforms, with the potential of retaining high-resolution optical access. This technique can also take advantage of the emergence of high resolution 3D printing, enabling reusable moulds for very complex systems incorporating both valve membranes and hybrid integrated elements to be realised rapidly and reliably and should thus mark a major acceleration in the application of microfluidic platforms.
