improvement of the in vitro recordings in cortical slices by using customized flexible neuroprobes

We have explored the feasibility of improving the quality of multiple recordings from spontaneously oscillating cortical slices. With that purpose we have taken advantage of the advances performed in the development of flexible neuproprobes, either fabricated on polyimide, SU-8, PDMS or parylene (Hassler et al. 2011). With these materials the contact between the electrodes and the tissue is enhanced with respect to the neuroprobes fabricated on rigid substrates, such as silicon or pyrex. However, we had to find a compromise between the necessity to achieve a good contact between the electrode and the slice and the need to allow the flow of oxygenated solution to the slice to maintain its healthy state when using flexible neuroprobes. To overcome this limitation, we have designed, fabricated and characterized a 16-electrode flexible neuroprobe that allocates an array of holes in its sensing area. This neuroprobe has been developed using SU-8 negative photoresist as a substrate material in the clean room facilities of the IMB-CNM. In particular, the neuroprobes have been fabricated following the process described in a previous article from the authors (Guimerà et al. 2013); using silicon wafers with an aluminum sacrificial layer as a support for the fabrication process. Then, the neuroprobes were released from the wafer by an anodic dissolution of the aluminum layer (Metz et al. 2005). In order to validate the usability of the fabricated device, the neuroprobes were used to record spontaneous slow oscillations to study the wave propagation along the cortical networks while manipulating them by means of pharmacological drugs or electric fields. We conclude that the perforated devices provide substantial improvement in the adherence of the electrodes to the tissue, on the mechanical stability of the recordings, and in the healthiness of the slices.