BACKGROUND: Recently, carbon fibers have been utilized to develop a depth-type microelectrode array for chronic neural recording. Since the diameter of carbon fibers is smaller than the conventional electrodes made of metal wires or microfabricated silicon, the carbon fiber electrodes showed an improved capability for chronic neural recording with less tissue damages. However, the carbon fiber based microelectrodes have a limitation of short insertion depth due to a low stiffness. METHODS: We proposed a carbon fiber based microelectrode array embedded with a mechanical support structure to facilitate the penetration into the deeper brain. The support is made of biodegradable silk fibroin to reduce the reactive tissue responses. The 4-channel carbon fiber based microelectrode arrays were fabricated and accessed in terms of electrochemical impedance, recording capability for 1-month implantation in rat hippocampi. The electrodes with tungsten supports were fabricated and tested as a control group. Immunohistochemical analysis was performed to identify the reactive glial responses. RESULTS: The carbon fiber based electrode arrays with silk supports showed about 2-fold impedance increase 2 weeks after implantation while the number of active electrodes decreased simultaneously. However, after 1 month, the electrode impedance decreased back to its initial value and the percentage of active electrodes also increased above 70%. Immunohistochemical staining clearly showed that the electrodes with silk supports induced less reactive glial responses than that with tungsten supports. CONCLUSION: The proposed carbon fiber based microelectrode array is expected to be used for long-term in vivo neural recording from deep brain regions with the minimized reactive tissue response.
Animals ; Brain ; Carbon ; Electric Impedance ; Electrodes ; Fibroins ; Microelectrodes* ; Rats ; Silicon ; Silk* ; Tungsten

Purpose: Glioblastoma (GBM) is an intractable disease for which various treatments have been attempted, but with little effect.This study aimed to measure the effect of photodynamic therapy (PDT) and sonodynamic therapy (SDT), which are currently being used to treat brain tumors, as well as sono-photodynamic therapy (SPDT), which is the combination of these two. Materials and Methods: Four groups of Sprague-Dawley rats were injected with C6 glioma cells in a cortical region and treated with PDT, SDT, and SPDT. Gd-MRI was monitored weekly and 18F-FDG-PET the day before and 1 week after the treatment. The acoustic power used during sonication was 5.5 W/cm2 using a 0.5-MHz single-element transducer. The 633-nm laser was illuminated at 100 J/cm2 . Oxidative stress and apoptosis markers were evaluated 3 days after treatment using immunohistochemistry (IHC): 4-HNE, 8-OhdG, and Caspase-3. Results: A decrease in tumor volume was observed in MRI imaging 12 days after the treatment in the PDT group (p<0.05), but the SDT group showed a slight increase compared to the 5-Ala group. The high expression rates of reactive oxygen species-related factors, such as 8-OhdG (p<0.001) and Caspase-3 (p<0.001), were observed in the SPDT group compared to other groups in IHC. Conclusion Our findings show that light with sensitizers can inhibit GBM growth, but not ultrasound. Although SPDT did not show the combined effect in MRI, high oxidative stress was observed in IHC. Further studies are needed to investigate the safety parameters to apply ultrasound in GBM.