Purpose: There is an urgent need for new implantable devices to help understand and treat “brain network disorders.” For maximum research and clinical benefit, these implantable devices should allow signals to be recorded from clinically relevant volumes of brain, 100 cm2, at resolutions of 100 microns or less. Many of the devices that have been used over the past two decades are spatially and temporally too coarse. Furthermore, many are based on penetrating electrodes that can cause tissue swelling and injury. For many applications, such as epilepsy or motor control, surface electrodes provide comparable or better resolution than penetrating electrodes. Highly flexible arrays of subdural electrodes may adhere to the brain’s irregular contours and movement, promising long term signal quality and reduced injury to brain. Microfabricated devices with integrated amplification and multiplexing circuitry eliminate the “one wire per electrode” constraint that limits resolution and area, while also reducing brain edema related to the number of wires.
The Litt and Kagan groups at the University of Pennsylvania have developed flexible implantable electrodes for tissue sensing and stimulation. The flexible devices made at Penn by the Kagan group are based on actively controlled by organic (Bink, 2011, Saudari, 2010) or nanocrystal semiconductor-based electronic circuitry (Choi, 2012, Kim, 2012). This circuitry allows low-voltage signal amplification and enables the integration of multiplexing electronics. Recent progress in device manufacturing has allowed for common cleanroom fabrication and device scaling for increased bandwidth and speed of operation (Choi, 2013).
Method of Fabrication/Use: The flexible electrode arrays are fabricated on thin plastic substrates, such as the Kapton. The electrodes are defined by photolithography and evaporation of metals, allowing application specific designs to be created. The organic and nanocrystal active semiconductor layers are deposited by solution-based spin-coating or printing. Vertical interconnect access holes to connect different metal layers are formed through either additive deposition or subtractive etching through atomic layer deposited Al2O3 or coated parylene. The electrodes are connected via zero insertion force connectors to external electrical measurement equipment.
Results: The Kagan Lab has demonstrated high-performance, flexible organic and nanocrystal circuitry for multiple applications. The Kagan and Litt lab have used these platforms to sense replicated human ECoG signals on the scale of local field potentials.
Bink H, Lai Y, Saudari SR, Helfer B, Viventi J, Van der Spiegel J, Litt B, Kagan C. Flexible organic electronics for use in neural sensing. Conf Proc IEEE Eng Med Biol Soc 2011; 2011 5400-5403.
Saudari SR, Lin YJ, Lai Y, Kagan CR. Device configurations for ambipolar transport in flexible, pentacene transistors. Adv Mater Nov 24 2010; 22 (44): 5063-5068.
Choi JH, Fafarman AT, Oh SJ, Ko DK, Kim DK, Diroll BT, Muramoto S, Gillen JG, Murray CB, Kagan CR. Bandlike transport in strongly coupled and doped quantum dot solids: a route to high-performance thin-film electronics. Nano Lett May 9 2012; 12 (5): 2631-2638.
Kim DK, Lai Y, Diroll BT, Murray CB, Kagan CR. Flexible and low-voltage integrated circuits constructed from high-performance nanocrystal transistors. Nat Commun 2012; 3 1216.
Choi JH, Oh SJ, Lai Y, Kim DK, Zhao T, Fafarman AT, Diroll BT, Murray CB, Kagan CR. In Situ Repair of High-Performance, Flexible Nanocrystal Electronics for Large-Area Fabrication and Operation in Air. ACS Nano Aug 22 2013;