gms | German Medical Science

Objective: Show the feasibility of using penetrating flexible multi-shank and multi-site microelectrode arrays (MEAs) for retinal applications.

Materials and methods: To reduce the insertion trauma of silicon (Si)-based penetrating probes used previously for electrical recording and stimulation of the retina (Rincón Montes et al., 2019), the design and fabrication of the penetrating MEAs were optimized to the retina and carried out using softer and flexible polymers such as polyimide and parylene-C. Insertion tests of the flexible penetrating probes were first conducted on polydimethylsiloxane (PDMS) phantom retinas and further tested in vitro with light-adapted wildtype and degenerated rd10 mice retinas. Furthermore, intraretinal recordings of spontaneous activity and responses to light stimulation were examined using the penetrating flexible devices.

Results: Flexible and penetrating MEAs with a thickness between 6-10 µm were fabricated and used for retinal applications. The flexible probes were successfully inserted in phantom retinas and in explanted retinal tissue. Additionally, spontaneous activity of retinal ganglion cells was captured at different insertion depths inside the retina. Finally, spiking and low frequency responses to light stimulation were captured when recording from wildtype retinas, while typical pathologic rhythmic activity was recorded from rd10 retinas.

Discussion: The mechanical mismatch between the retina and the intraretinal probes is reduced using flexible polymer substrates instead of stiff materials like Si. Moreover, the optimized design of the penetrating devices makes it possible to insert flexible intraretinal MEAs without the use of an external aid, allowing in this way to capture the electrical activity of the retina. Thus, intraretinal devices with a reduced insertion trauma and footprint open the door to future in vivo intraretinal implants aiming a bidirectional communication with the tissue, where electrical stimulation and recording is performed simultaneously.

Acknowledgment: The silicon probes used as reference were designed and fabricated by Stefan Lück and Wilfried Mokwa at the Institute of Materials in Electrical Engineering 1 (IWE-1) of RWTH Aachen University. The polymer-based probes were fabricated at the Helmholtz Nano Facility (HNF) of Forschungszentrum Jülich. This study was supported by the DFG grants OF-22/11-3 and MU-3036/3-3.