A Reliable Reversible Bonding Method to Perfuse Microfluidic Devices

Microfl uidic devices made of poly(dimethylsiloxane) (PDMS) are suitable for cell culture applications, mainly due to both the advantageous volume and surface properties of the material itself. Bulk properties include optical transparency, gas permeability, and ease of fabrication, to name a few. On the other hand, silanol groups (SiOH) present on the surface can be easily activated through air/oxygen plasma treatments, and used to permanently bond to other materials, like silicon, glass or PDMS. The importance of a standard sealing method with no need of additional gluing materials is crucial for microfl uidic applications, where micrometer sized channels and chambers are involved. Despite the reliability of the plasma treatment to permanently seal microfl uidic devices, reversible-bonding methods are sometimes desirable e.g., high magnifi cation microscopy, sample retrieval, and multiple usages of valuable substrates. For this purpose, common techniques rely either on weakening the plasma treatment (partial treatment, only involving one of the surfaces of interest) or on increasing the self-sealing properties of PDMS (by adjusting the ratio of pre-polymer and curing agent). However, the adhesion strength of these methods is low, thus making them suitable only for static or quasi-static conditions. Whenever there is the requirement for continuous perfusion, other techniques are needed. Here, we describe a PDMS microfl uidic device for long term culture of cells, which can be reversibly sealed to different fl at substrates. The hydraulic tightness is guaranteed through magnetic forces, being the substrate interposed between a permanent magnet and the microfl uidic device, locally enriched with ferromagnetic material. In particular, neuronal networks were grown within the device, reversibly coupled to a fl at Microelectrode Array (MEA). Thus, the proposed approach allows to combine the advantageous features of microfl uidics and the multiple use of commercial MEA substrates. Indeed, it allows for electrophysiological investigations in highly controlled microenvironments.