Microelectrode arrays (MEAs) are designed to monitor and/or stimulate extracellularly neuronal activity. However, the biomechanical and structural mismatch between current MEAs and neural tissues remains a challenge for neural interfaces. This article describes a material strategy to prepare neural electrodes with improved mechanical compliance that relies on thin metal film electrodes embedded in polymeric substrates. The electrode impedance of micro-electrodes on polymer is comparable to that of MEA on glass substrates. Furthermore, MEAs on plastic can be flexed and rolled offering improved structural interface with brain and nerves in vivo.MEAs on elastomer can be stretched reversibly and provide in vitro unique platforms to simultaneously investigate the electrophysiological of neural cells and tissues to mechanical stimulation. Adding mechanical compliance to MEAs is a promising vehicle for robust and reliable neural interfaces.

Neural interfaces are implanted devices that couple the nervous system to electronic circuitry. They are intended for long term use to control assistive technologies such as muscle stimulators or prosthetics that compensate for loss of function due to injury. Here we present a novel design of interface for peripheral nerves. Recording from axons is complicated by the small size of extracellular potentials and the concentration of current flow at nodes of Ranvier. Confining axons to microchannels of ~100 µm diameter produces amplified potentials that are independent of node position. After implantation of microchannel arrays into rat sciatic nerve, axons regenerated through the channels forming 'mini-fascicles', each typically containing ~100 myelinated fibres and one or more blood vessels. Regenerated motor axons reconnected to distal muscles, as demonstrated by the recovery of an electromyogram and partial prevention of muscle atrophy. Efferent motor potentials and afferent signals evoked by muscle stretch or cutaneous stimulation were easily recorded from the mini-fascicles and were in the range of 35-170 µV. Individual motor units in distal musculature were activated from channels using stimulus currents in the microampere range. Microchannel interfaces are a potential solution for applications such as prosthetic limb control or enhancing recovery after nerve injury.

The spiral peripheral nerve interface (SPNI) has been developed to record neural activity by utilizing the body's own ability to regenerate axons after injury. The implantable device is capable of providing a chronic recording array for use with technology designed to compensate for a loss of motor function. The SPNI offers a good route to establishing an effective interface to the peripheral nervous system (PNS) as the signals are enclosed within an insulating array that amplifies the axon signals for the neural recording, and reduces the amount of current necessary for stimulation. This paper presents an updated fabrication process that addresses the problems of previous designs and allows for an easier integration to external electronics via a ball-bonding technique. The updated device has been tested electrically in vitro, to show that it is capable of providing a reliable electrical interface to the regenerated tissue.

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Mechanical guidance can be used to provide a supporting structure through which and onto which regenerating axons can grow. The dimensions of the mechanical guide need to be suitable to support regenerated axon outgrowth and vascularisation. In this paper, we present the design and fabrication process of a three-dimensional (3D) device comprising a bundle of parallel (100 microm x 100 microm) microchannels with embedded electrodes. This device can be used as a 3D electrode interface for peripheral nerve repair. The skeleton of the device is entirely made of flexible polyimide films. Gold microelectrodes and microchannels of photosensitive polyimide are patterned directly on polyimide substrates. After fabrication, the 2D electrode channel array is rolled into a 3D channel bundle that fits the anatomy of the peripheral nerve. Samples are rolled and inserted into 1.5mm inner diameter tube.