Mechanically adaptive nanocomposites for neural interfacing
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troduction Neural prosthetic devices, which (re)connect the brain with the outside world, promise to be useful for many clinical applications.1–9 Microelectrodes that are inserted into the brain and left to reside in the neuronal cell body layers of the cortex are the key element to this technology.3 Such electrodes can record the activity of individual or small populations of neurons for a short time after implantation,8,10,11 but it has proven difficult to record neural signals over long periods.3 This remains one of the largest hurdles in translating research successes in this field into clinical implementation and standard of care.3,6,12–14 While the dominant mechanism is still being debated, it is well established that the recording ability of intracortical microelectrodes is related to the proximity of viable neurons and the characteristics of non-neural tissue between the electrode and neurons.10,15 The most widely accepted hypothesis for electrode failure is the development of an encapsulating scar at the electrode/tissue interface.3,12,13,15–17 Insertion-related damage is practically unavoidable and causes an acute tissue
response; this effect can be minimized by reducing the insertion trauma.18–20 For example, Sharp and colleagues have shown that implanting the device more slowly can reduce initial scar formation.20 Interestingly, however, several studies showed that the chronic response is independent of the acute reaction induced by surgical trauma.15,19 Such studies have revealed two important phenomena: (1) the formation of a dense encapsulating scar, which eventually encapsulates the electrodes, regardless of the materials used; and (2) the formation of a neuron-free dead zone surrounding the implants.3,15,21–23 Numerous factors are thought to contribute to scar formation, including the mechanical properties mismatch between stiff electrodes and the soft cortical tissue,24–26 and a localized neurotoxic environment created by the presence of a non-removable foreign object.22–24 The aim of this article is to summarize the different approaches to stabilize the neural electrode/brain interface by focusing on the mechanical mismatch of the implant and tissue, and, as an example, highlight recent work on mechanically adaptive nanocomposites for neural interfacing.
Jeffrey R. Capadona, Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH 44106, USA; [email protected] Dustin J. Tyler, Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH 44106, USA; [email protected] Christian A. Zorman, Department of Electrical Engineering and Computer Science, Case Western Reserve University, Cleveland, OH 44106, USA; [email protected] Stuart J. Rowan, Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland, OH 44106, USA; [email protected] Christoph Weder, Adolphe Merkle Institute, University of Fribourg, Switzerland; [email protected] DOI: 10.1557/mrs.2012.97
© 2012 Materials Research Society
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