Abstract
Bidirectional neural interfaces for multi-channel, high-density recording and electrical stimulation of neural activity in the central nervous system are fundamental tools for neuroscience and medical applications. Especially for clinical use, these electrical interfaces must be stable over several years, which is still a major challenge due to the foreign body response of neural tissue. A feasible solution to reduce this inflammatory response is to enable a free-floating implantation of high-density, silicon-based neural probes to avoid mechanical coupling between the skull and the cortex during brain micromotion. This paper presents our latest development of a reproducible microfabrication process, which allows a monolithic integration of a highly-flexible, polyimide-based cable with a silicon-stiffened neural probe at a high resolution of 1 µm. For a precise and complete insertion of the free-floating probes into the cortex, a new silicon-based, vacuum-actuated insertion tool is presented, which can be attached to commercially available electrode drives. To reduce the electrode impedance and enable safe and stable microstimulation an additional coating with the electrical conductive polymer PEDOT:PSS is used. The long-term stability of the presented free-floating neural probes is demonstrated in vitro and in vivo. The promising results suggest the feasibility of these neural probes for chronic applications.
Highlights
Understanding the complex functionality of the brain is the major objective in neuroscience
For medical applications, e.g., neuroprosthetics, the neural interfaces must be stable for several years
Due to the foreign body response of the neural tissue to the implanted probes, a glial scar is formed around the probe, which electrically insulates the microelectrodes [1]
Summary
Understanding the complex functionality of the brain is the major objective in neuroscience. To allow investigation of the natural behavior of the neurons, in vivo experiments are commonly performed with awake laboratory animals For these experiments, neural interfaces are implanted chronically to have the system in a stable homeostatic condition over the course of the experiment or over prolonged periods of time without short term processes of the immune defense. The essential approach of these developments is the reduction of the probe stiffness using soft biocompatible polymer materials like parylene-C, polyimide, and SU-8 [6] Using these flexible materials the mechanical coupling between the implanted probe and the skull can be reduced significantly, which leads to a reduced inflammatory response of the neural tissue during brain micrMoimcroomatcihoinnes [2701,88, ]9., x FOR PEER REVIEW. FurthermoPrEeD, OaTn:PeSwS, wsihliicchosnh-obwassesudp,evriaorcupruompe-raticetsureagtaerddiinngseelretcitorondetoimopl eidsapncreesaendntcehdar,gwe ihnijecchtioanllows easy handling ocfapthaceitfylo[1a7t,i1n8g]. pFurortbheersmdourer,inagntehwessiulicrogne-rbyaspedr,ovcaecduuurme-.aTcthuaetelodnings-etretriomn stotaobl iislitpyreosfenttheed,polyimide electrical iwsntahsbuicilhliatyatiloolofnwthsiesepadoselyymihmaoindndeslitenrlgeactoterfidctahileninfvlsouiatltariotnio.gnIpnirsovdbeievmsoodnursretircnaogtertddhieinnsgvusirtgrooer.fyInnpevruiovcroeadrleuacrocer.tdiTvinhigetyslooanfrgne-etuesrrhmaol wn using chronicallyacitmiviptylaanreteshdopwrnoubseinsginchrroanticcaolrlyteixm.planted probes in rat cortex
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