**5. Conclusion**

In this chapter, we presented three technologies for achieving PNIs. The PNIs will be designed for patients of partially impaired neural networks. In Section 2, we show that restoration of motoneurons is possible by using reinnervation type electrodes which are constructed by implanting embryonic neurons into peripheral motor units. Several methods for restoring motoneuron functions have been proposedduring these threedecades because the muscles can generate the forces if some electric potentials are provided at the motor points. These electric potentials may be provided by artificial ones with some electrodes. Functional electrical stimulation (FES) has been applied to human patients with spinal cord injury and has shown higher potential forrestoring functional movements [27]. Usually in FES, some metal wires are used for transmitting the electrical signals as the motor commands for the muscles. However, themechanicalpropertiesofthemetalwiressuchaselasticityaredifferentfrombiologicaltissues: then, the mismatching between the wires and the tissues will appear and result in malfunc‐ tions of the FES systems. If we use reinnervation type electrodes constructed from embryonic neurons, which are almost same as the original motor neurons, the demanding problem of mechanical property mismatching with metal wire transmission lines will be solved. This is the reason why we seek to establish the technology around reinnervation type electrodes.

Sensory feedback in control of functional movements plays an important role for the robust‐ ness and the adaptation to environmental changes in the task executions. A few studies have been carried out to introduce sensory feedback for the restoration of motor functions [28]. We can improve greatly the quality of functional restoration by sensory feedback for the cases of partially impaired neural networks.In Section 3, we showed the possibility of sensory feedback via axial fibers of neurons in nueroprosthetic devices. A method for passing the feedback signals via axial fibers of neurons with surface electrodes has been tested. It is shown that three or four bits resolution for sensory feedback can be achieved with the proposed method.

In Section 4, we showed the possibility of practical usages of PNIs by taking walking simulation of rat. In the concept of restoring motor functions, controlling joint torques with sensory feedback is a key point of the technology. The reinnervation type electrodes described in Section 2 and the sensory feedback via axial fibers of neurons described in Section 3 will be included in such a new type of nueroprosthetic device.
