Sliding walls: a new paradigm for fluidic actuation and protocol implementation in microfluidics

Currently, fluidic control in microdevices is mainly achieved either by external pumps and valves, which are expensive and bulky, or by valves integrated in the chip. Numerous types of internal valves or actuation methods have been proposed, but they generally impose difficult compromises between performance and fabrication complexity. We propose here a new paradigm for actuation in microfluidic devices based on rigid or semi-rigid walls with transversal dimensions of hundreds of micrometres that are able to slide within a microfluidic chip and to intersect microchannels with hand-driven or translation stage-based actuation. With this new concept for reconfigurable microfluidics, the implementation of a wide range of functionalities was facilitated and allowed for no or limited dead volume, low cost and low footprint. We demonstrate here several fluidic operations, including on/off or switch valving, where channels are blocked or reconfigured depending on the sliding wall geometry. The valves sustain pressures up to 30 kPa. Pumping and reversible compartmentalisation of large microfluidic chambers were also demonstrated. This last possibility was applied to a 4D migration assay of dendritic cells in a collagen gel. Finally, sliding walls containing a hydrogel-based membrane were developed and used to concentrate, purify and transport biomolecules from one channel to another, such functionality involving complex fluidic transport patterns not possible in earlier microfluidic devices. Overall, this toolbox is compatible with soft lithography technology, allowing easy implementation within usual fabrication workflows for polydimethylsiloxane chips. This new technology opens the route to a variety of microfluidic applications, with a focus on simple, hand-driven devices for point-of-care or biological laboratories with low or limited equipment and resources. Microfluidics: Novel technology for microfluidic device operation-sliding walls A new technology, termed sliding walls, has been developed for operating microfluidic devices (which function at sub-millimetre scales), whereby rigid or semi-rigid walls, hundreds of micrometres thick, slide within a microfluidic chip. Fluid control in micro-devices is currently achieved largely by expensive, bulky external valves and pumps or by valves integrated in the chip. Such internal valves or actuation methods generally have shortcomings related to performance and complex fabrication. A team headed by Stephanie Descroix and Jean-Louis Viovy at the Institut Curie-Institut Pierre Gilles de Gennes, Paris applied its sliding wall technique and was able to execute several fluidic operations in which channels could be blocked or reconfigured through the sliding wall geometry. The authors believe that their technology has the potential for various microfluidic operations in biological laboratories with limited equipment and resources.