Near-infrared stimulation (NIS) is an emerging technique used to evoke action potentials in nervous systems. Its efficacy of evoking action potentials has been demonstrated in different nerve tissues. However, few studies have been performed using NIS to stimulate the deep brain structures, such as globus pallidus (GP) and subthalamic nucleus (STN). Male Sprague–Dawley rats were randomly divided into GP stimulation group (n=11 ) and STN stimulation group (n=6 ). After introducing optrodes stereotaxically into the GP or STN, we stimulated neural tissue for 2 min with continuous near-infrared light of 808 nm while varying the radiant exposure from 40 to 10 mW. The effects were investigated with extracellular recordings and the temperature rises at the stimulation site were also measured. NIS was found to elicit excitatory responses in eight out of 11 cases (73%) and inhibitory responses in three cases in the GP stimulation group, whereas it predominantly evoked inhibitory responses in seven out of eight cases (87.5%) and an excitatory response in one case in STN stimulation group. Only radiation above 20 mW, accompanying temperature increases of more than 2°C, elicited a statistically significant neural response (p<0.05 ). The responsiveness to NIS was linearly dependent on the power of radiation exposure.
We developed stretchable and flexible out-of-plane electrodes based on PDMS substrate using general MEMS
fabrication processes. The electrodes were designed to be used for devices that require large elongation without electrical
disconnection. Thus, the stretchable electrode was designed to have serpentine metal line suspended above the substrate
along its entire length. To fabricate the out-of-plane structure, the metal pattern of the electrode was created on a
parylene layer that was suspended above the PDMS substrate by using sacrificial photoresist layer. The metal line was
covered by a second parylene layer, thereby encapsulated and electrically insulated. In serpentine electrodes, the
parylene layer was attached with PDMS substrate through parylene posts located nearby the metal line, which restrained
lateral movements of the metal line. The stretch test, bending test, and twist test were performed using our customdesigned
test modules to characterize the stretchability and flexibility of the fabricated electrodes. With up to 32 % strain,
with various bending radii, and up to 360° twist angle, stable electrical connection was demonstrated. From these results,
the proposed out-of-plane electrodes would be useful in stretchable and flexible applications such as wearable
electronics and biomedical devices.