Development of PDMS-based Cranial Windows for Optical Recording of Neural Activity

Cranial windows are a common tool for recording brain activity via fluorescence microscopy. Glass is the preferred material for window transparency, but it induces mechanical stress on the brain due to its rigidity and complicates further functionalization with high-temperature fabrication processes. By using PDMS as a window substrate, a transparency comparable to glass is possible, while the polymeric flexibility grants repeated mechanical access to the brain with pointy electrodes or pipettes. A solid ceramic frame is used for mechanical stabilization and the possibility of further electrical functionalization. This work focuses on developing a process for homogeneous PDMS-filling with smooth window surfaces. The findings provide insights into the challenges of this process, such as trapped air bubbles and uneven surfaces. Strategies for overcoming these obstacles were developed, resulting in a PDMS-filling process that provides sufficient optical properties, as shown through transmission measurements of the finalized cranial window samples.