Microfluidic 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 microfluidic applications, where micrometer sized channels and chambers are involved. Despite the reliability of the plasma treatment to permanently seal microfluidic devices, reversible-bonding methods are sometimes desirable--e.g., high magnification 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 microfluidic device for long-term culture of cells, which can be reversibly sealed to different flat substrates. The hydraulic tightness is guaranteed through magnetic forces, being the substrate interposed between a permanent magnet and the microfluidic device, locally enriched with ferromagnetic material. In particular, neuronal networks were grown within the device, reversibly coupled to a flat Microelectrode Array (MEA). Thus, the proposed approach allows to combine the advantageous features of microfluidics and the multiple use of commercial MEA substrates. Indeed, it allows for electro-physiological investigations in highly controlled microenvironments.
Occhetta, Paola, Emilia Biffi, Marco Rasponi
Microfluidic and Compartmentalized Platforms for Neurobiological Research