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.

The possibility of constructing a resonator with a dielectric spiral inner is discussed. The modelling conducted shows that the mode related to the ceramic quarter-wave resonators also exists within a dielectric spiral, the properties of which are strongly dependent on the thickness and the number of turns of the spiral. The low filling factors associated with the resonant mode explains the high quality factors possessed by some of the spirals studied.Introduction: Loaded cavity resonators are often used at microwave frequencies in communication filters. They can be realised in a variety of ways but for applications at several hundred megahertz; for applications where a high quality factor of resonance is required a dielectric resonator is used. For some applications the use of dielectric resonators is prohibited at low frequencies ( 900 MHz) by volume constraints. For these applications quarter-wave resonators are used, and at still lower frequencies metal helical resonators are used. However, the loss owing to the inner structure dominates the loss of the overall resonators and hence the filter loss. An innovative solution to this problem is to replace the inner metal with a dielectric. This concept was proved to work for dielectric combline resonators (DCR) by Wang et al. [1].The dielectric spiral resonator is based on the same principle as that of a DCR [1], where the metal inner is replaced by a high permittivity dielectric rod. It is based on the concept that a ceramic material, with sufficiently high permittivity, can exclude the electric field from within the ceramic and hence behave rather like a metal [2].The key advantage is that conductor losses on the surface of the inner metal finger are eliminated with a corresponding increase in Q. This work investigates whether a dielectric spiral can act as a resonant structure and what effect the change has in the various dimensions of the spiral on the resonator frequency and losses. The Letter, also serves as a validation for the modelling software for this type of problem. A ceramic spiral was made and the method of fabrication is discussed. The frequency and Q of the spiral have been measured and are compared to the modelling results of the structure.

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