A commonly used approach is to utilize PDMS microfluidic chips sealed on top of glass. The wide adoption of PDMS stems mainly from ease of fabricating even large batches of chips through casting. The casting process (other than the master fabrication) also does not require any dedicated equipment, and can be performed anywhere. In addition, PDMS is a biocompatible and optically transparent polymer that forms reversible watertight seals when placed on smooth surfaces due to its elasticity [4]. PDMS can be permanently bonded with glass or other PDMS layers by first activating both surfaces with plasma (most commonly oxygen plasma). The plasma treatment also turns PDMS hydrophilic, albeit only temporarily [14]. Other possibilities for PDMS-glass bonding include adhesive bonding with a polymeric adhesive (a glue) or a single molecular layer thick surface adhesive [15]. A typical architecture of microfluidic chips used in neurobiological applications consists of axon isolation microgrooves that are connected to two or more larger reservoirs that house the cell populations either directly (Figure 1B) [16] or through larger microfluidic channels [5]. The dimensions of the microgrooves need
