Peripheral nerve interface

A peripheral nerve interface is the bridge between the peripheral nervous system and a |machine processing which serves as a bi‐directional information transducer recording and sending signals between the human body and an electrical computer interface. Many researchers are focused on developing peripheral nerve interfaces for neuroprosthesis linking the human nervous system to robotic prosthetics in order to mimic natural sensorimotor control and function. Research in the area may be used to assist patients with spinal cord injury, brain injury, or neurodegenerative diseases to restore lost motor or sensory functionality. Successful implantation of peripheral nerve interfaces depend on a number of factors which include appropriate indication, preoperative testing, differentiated planning of the impant, and functional training. Typically microelectrode devices are implanted adjacent to, around or within the nerve trunk to establish contact with the peripheral nervous system. Different approaches may be used depending on the type of signal attainable and desired. Peripheral nerve interfaces may be divided into extraneural and intrafascular categories. Extraneural electrodes include the cuff and epineurial electrodes and intrafascular consist of both penetrating and regenerative electrodes.

Electrode interfacing

In bioengineering the term interface includes all the elements of a system between the machine processor and the human tissue. This includes the electrode, sensor, and internal wires that link the inner body tissues with the outer processor, data-acquisition circuitry, and command unit for controlling the effector Prosthesis) or artifact that is produced. One key component for an interface design is the electrode that captures bioelectrical activity or applies current into the living tissue, and the interface material transforming biological activity into electrical signals. From an engineering point of view, the neural interface is a bidirectional transducer that establishes a neuro-technical contact between a technical device and a neural structure within the body. The objective of this transducer is to record bioelectrical signals from natural sensors of the body and the artificial excitation of nerves and/or muscles. From a biological point of view, such an interface is a foreign body. Both views have to be brought together to consider the requirements and complex aspects of biocompatibility.

Functionality and limitations

Peripheral nerve interfaces are used for pain modulation, nerve stimulation, and to interface with neuroprosthetics, . Microelectrode devices that contact the peripheral nerves using electrical coupling methods are the most common and best-known type of interfacing devices. A wide variety of electrode designs have been manufactured and tested. These electrodes lie on a spectrum varying in degrees of invasiveness. Research in this area seeks to address issues centered around peripheral nerve/tissue damage, access to efferent and afferent signals, and selective recording/stimulation of nerve tissue. Ideally peripheral nerve interfaces are biocompatiable with minimal immune response, high resolution, minimally invasive, and chronically stable with low signal-to-noise ratios.

Types of interfaces

Epineurial Electrode Interface

Epineurial electrodes are fabricated as longitudinal strips holding two or more contact sites to interface with peripheral nerves. These electrodes are placed on the nerve and secured by suturing to the epineurium. The suturing process requires delicate surgery and can be torn from the nerve if excessive motion creates tension. Since the electrode is sutured to the epineurium it is unlikely to damage the nerve trunk.

Helicoidal Electrode Interface

Helicoidal electrodes are placed cirumjacent to the nerve and are made of flexible platinum ribbon in a helical design. This design allows the electrode to conform to the size and shape of the nerve in attempts to minimize mechanical trauma. The structural design causes low selectivity. Helicoidal electrodes are currently used for FES stimulation of the vagus nerve to control intractable epilepsy, sleep apnea, and to treat depressive syndromes.

Book Electrode Interface

The book electrode consists of a silicone rubber block with slots. Each slot contains three platinum foils which function as electrodes, anode electrodes and one cathode. The spinal roots of the nerve are placed into these slots and the slots are then covered with a flap made of silicone and fixed with silicon glue. This electrode is mostly used to interrupt reflex xircuits of the dorsal sacral roots and to control bladder function. Book electrodes are still considered very bulky.