WO2009130515A2

WO2009130515A2 - Method and system for recording and promoting peripheral nerve regeneration

Info

Publication number: WO2009130515A2
Application number: PCT/GR2009/000024
Authority: WO
Inventors: Alexandros Beris
Original assignee: Alexandros Beris
Priority date: 2008-04-22
Filing date: 2009-04-15
Publication date: 2009-10-29
Also published as: EP2307090A2; GR1006568B; WO2009130515A3

Abstract

Method and system for recording and promoting the regeneration of peripheral nerves after injury that comprise one stimulating electrode that is implanted at the proximal segment of the nerve, at least one recording electrode that is implanted at the distal segment of the nerve, an implantable electronic unit, an implantable device releasing agents for stimulating nerve regeneration, such as a micro-pump, and a computing unit that is preferably placed extracorporeally for the communication of data and transfer of power to the electronic unit. The electrical signals that are produced by the distal segment of the injured nerves after appropriate electrical excitation of the distal segment of said injured nerve are recorded at various time instances. The analysis of the recorded electric signals is used to assess the state and progress of the regenerating neuroaxons; this assessment is used for determining various control parameters. Said control parameters are used by the electronic unit so as to control the release of stimulating agents in such a way that treatment is effective while keeping the administration of stimulating agents at safe levels.

Description

METHOD AND SYSTEM FOR RECORDING AND PROMOTING PERIPHERAL NERVE REGENERATION

BACKGROUND OF THE INVENTION

The present invention relates to the field of biomedical engineering and discloses a method and a system for recording the electric activity of regenerating peripheral nerves and promoting their regeneration process by locally releasing stimulating agents, such as neurotrophic factors. More specifically, the invention concerns an implanted electronic unit which first electrically excites an injured nerve and subsequently records the evoked electric activity of said nerve as well as a computing unit which analyzes the recorded electric signals aiming at estimating the state and progress of nerve regeneration. Based on the state and progress of nerve regeneration, the electric unit appropriately regulates the delivery of stimulating agents that are released by an implanted agent-release device, such as a micro-pump.

The nervous system permits the fast and specialized communication of distant parts of the human body. It consists of two parts: the central nervous system, which includes the brain and the spinal cord, and the peripheral nervous system. The peripheral nervous system consists of cranial and peripheral nerves which can be motor, sensory or mixed. Unlike the central nervous system, however, the peripheral nervous system is not protected by bony structures, leaving it exposed to mechanical injuries.

The basic components of the nervous system, responsible for its operation, are the nerve cells (neurons). Nerve cells communicate via chemical and electrical synapses in a process known as synaptic transmission. The fundamental process that triggers synaptic transmission is the action potential, for whose generation the property of the membrane of the neuron to be electrically excitable plays an important role.

Every nerve cell is composed of a soma, or cell body that contains the nucleus and most of the organelles of the cell, a long cellar extension (neuroaxon) with length up to Im, multiple short extensions with many branches (dendrites), and the specialized connections of the nerve cell with other cells (synapses). The neuroaxons can be motor or sensory, myelinated or unmyelinated. Motor and sensory nerves consist of unmyelinated and myelinated fibers at of ratio of 4:1. In unmyelinated fibres, a Schwann cell covers many neuroaxons, whereas in myelinated fibres every neuroaxon is covered by one Schwann cell which forms the myelin sheath around the neuroaxon. Each Schwann cell has an external well-formed continuous membrane which separates it from the endoneurium. Every 1 to 2mm along the myelin sheath, there are gaps called the nodes of Ranvier. These nodes play a significant role for the fast conduction of the electrical stimulation since the action potential signal jumps along the axon from node to node. The conduction velocity of the nerve fibres varies from 0.5m/sec in very thin unmyelinated nerve fibers up to lOOm/sec in thick myelinated fibres. The conduction velocity increases proportionally to the diameter of the myelinated fibres and proportionally to the square root of the diameter of unmyelinated nerve fibres. Every peripheral nerve consists of several neuroaxons that are connected together with connective tissue. Three types of connective tissue can be defined: the endoneurium, the perineurium and the epineurium. The endoneurium surrounds the neuroaxon. The perineurium surrounds several neuroaxons that form a nerve fascicle. The inner layers of the perineurium and the capillaries of the endoneurium are tightly connected together which results in the establishment of a blood-nerve barrier. Finally, the epineurium is a sheath of fibrocollagen tissue that binds the fascicles together and is further discriminated into the inner and outer epineurium. The inner epineurium surrounds individual fascicles, while the outer epineurium surrounds the whole nerve and is connected with the adipose tissue that covers the peripheral nerves.

The nerve damage is defined as the disorder of nerve function which results in the inability to conduct action potential. For the description of the various types of nerve damages, two classification systems have been used. The first, proposed by Seddon in 1943, makes use of the terms "neurapraxia", "axonotmesis" and "neurotmesis" to describe the severity of nerve damage. The second, proposed by Sunderland, divides the plethora of nerve damages into five degrees offering a more specific range for the classification of patients with nerve damage. The neurapraxia, the least severe damage, is characterized by functional disorder of the nerve without the presence of degeneration. The continuity of the nerve is maintained whereas the local to the damage site demyelization and/or ischemia is considered responsible for the interruption in conduction of the impulse. The spontaneous recovery of the damage may occur within hours, days or even few months. In axonotmesis, which is often observed in crush and avulsion injuries, the neuroaxons lose their physiological continuity, whereas the surrounding tissues (Schwann cells, endoneurium and perineurium) remain partially or completely intact. The term neurotmesis includes either the complete transection of the nerve or the structural and functional disruption with the formation of scar tissue, so as the regeneration of the neuroaxons to be considered impossible. It is characterized by the interruption of the continuity of the neuroaxons and of all the supporting structures, including the epineurium. The prognosis for spontaneous recovery without surgical intervention is almost inexistent.

The regenerative ability of human neuroaxons can reach up to 2 mm per day in small nerves and 5 mm per day in large nerves. The timing of recovery also depends on the distance of the lesion from the denervated muscle. Prerequisite for nerve regeneration is an intact Schwann cell basal lamina tube to guide and support axonal growth to the target organ. The regenerating axons must identify and grow into the correct Schwann cell tube which will guide them to the appropriate target organs. If the axon does not reach its target organ within the appropriate time, these supporting elements degenerate and effective regeneration cannot be achieved. Transected nerves do not spontaneously restore their function and continuity of the nerve has to be re-established first by surgical intervention. Nowadays, the direct nerve coaptation with sutures is considered as the method of choice as long as the clinical and surgical conditions are appropriate. Refinement of microsurgical techniques and the surgical microscope have made also feasible the selective alignment and coaptation of individual nerves or fascicles using epineural, perineural or fascicular coaptation techniques. On the contrary, autologous nerve grafting is preferred for large lesion gaps for which coaptation without nerve tension is not feasible. Nerve segments that are taken from another part of the body, mainly from sensory nerves, are inserted into the lesion to provide endoneurial tubes for axonal regeneration across the gap. However, this is not a perfect treatment since the final functional outcome is often limited. Variations of the nerve autograft include the use of allografts and xenografts which still remain at a research stage due to the high rejection rate.

Because of the limited availability of autografts, recent attempts have focused on the development of bioartificial nerve guidance conduits with the aim to guide axonal regrowth. Nerve conduits bridge the proximal with distal segment through a tube composed of biological or synthetic materials with or without neurotrophic factors.

The progress of regeneration of peripheral nerve injuries is evaluated by clinical examination (Tinel's test) and also by electrophysiologic testing. Electrophysiologic examination involves electromyography (EMG) and/or nerve conduction studies (NCS) (also known as electroneurography - ENG). EMG is performed with the use of surface or needle electrodes. Its usefulness lies in the determination of the electric activity of the muscles that are innervated by the injured nerve. However, EMG recorded changes evolve slowly over weeks and moths rather than days from injury as seen with NCS. Spontaneous electrical activity in muscle fibers develops 2-6 weeks after denervation and continues until the muscle fiber degenerates completely or is reinnervated by the regenerated nerve. The presence of spontaneous activity therefore indicates axonal loss that is at least 2-6 weeks old or reflects ongoing nerve injury. When clinical recovery fails to occur within the expected time, EMG is useful to identify the earliest signs of reinnervation or situations in which no further nerve recovery is expected.

NCS is a test commonly used to evaluate the function, especially the ability of electrical conduction, of the motor and sensory nerves. NCS is performed by stimulating the nerve and recording the action potential at a site along the pathway of the nerve. Usually, the recorded signal represents a compound nerve action potential due to the superposition of the actions potentials from the individual neuroaxons. Stimulation and recording are usually accomplished with surface electrodes or needle electrodes. With NCS the conduction velocity and response latency of peripheral nerves are measured. The amplitude of the response is also recorded. During an NCS, the measurement is repeated by stimulating the nerve at a second site along its path. The distance between the two stimulation points is measured and the difference in latency times is determined. The nerve conduction velocity can be calculated by dividing the distance between stimulation points by the difference in latency times. Conduction velocities are used to diagnose and monitor injuries and degenerative diseases that affect the peripheral nerves. Nerve injuries, most neuropathies, and nerve entrapment or compression result in a significant slowing of the nerve conduction velocity. In the first 10 days after injury, NCS and EMG can determine only if a nerve injury is present. Despite advances in microsurgical techniques, surgical repair of transected peripheral nerve is followed by permanent functional compromise in up to 90% of adults. The therapeutic failure often results from misdirection of regenerating axons to functionally inappropriate end organs. Electrical stimulation of the injured nerve has been found to positively influence the speed of axonal regeneration. Electrical stimulation in the form of weak negative electrical fields or pulsed electromagnetic fields has been applied percutaneously or by using electrodes implanted temporarily at the site of injury. Patent WO02/47757 (Richmond) discloses a method and a system for augmenting recovery from muscle denervation comprising an electrical stimulator that is implanted alongside an injured nerve. The electrical stimulator further comprises an electrode placed on the proximal stump (end) of the nerve for emitting electrical signals appropriate for stimulating nerve regeneration at different times during the recovery process and a second electrode for the recording of the signals. A similar system is disclosed in patent EP0619123 (Jeutter and Geisler).

Nerve regeneration requires a complex interplay between cells, extracellular matrix, and neurotrophic factors. The local presence of neurotrophic factors plays an important role in controlling survival, migration, proliferation, and differentiation of the various cell types involved in nerve regeneration. Neurotrophic factors include a varied group of proteins most of which produced by different cell types in target organs. Neurotrophic factors become upregulated and particular active in high- metabolism situations, such as trauma and inflammation. The exogenous administration of neurotrophic factors after nerve injury has been proved to mimic the beneficial effect of target organ-derived neurotrophic factors on neurons. The most important neurotrophic factor which belongs to the neurotrophin family is the nerve growth factor (NGF). It has been shown that Schwann cells release at the site of lesion several neurotrophic factors and one amongst them is the NGF. Some other neurotrophic factors which have been shown to play an important role in stimulating peripheral nerve regeneration are insulin-like growth factor 1 (IGF-I), fibroblast growth factor 1 (FGF-I), fibroblast growth factor 2 (FGF-2), brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF) and glial cell line- derived neurotrofic factor (GDNF).

Nerve injury therapies based on the delivery of relevant growth factors have received increasing attention in recent years. Exogenous delivery of growth factors necessitates the presence of substances with high biological activity (in pico- to nanomolar range) and their repeated delivery due to their short biological half-life

(few minutes to hours) of these proteins. Thus, growth factors should be administered locally to achieve an adequate therapeutic effect with little adverse reactions from their systematic administration.

One approach has been to combine neurotrophic factors with nerve conduits. Local delivery to the target nerve can be achieved by filling the lumen of a nerve conduit with a solution of a neurotrophic factor, neurotrophic growth factors in a matrix which is loaded into the lumen of a nerve conduit, attaching neurotrophic factors at the wall of a nerve conduit or seeding cells that produce neurotrophic factors inside the nerve conduit lumen. Patent WO9520359 (Hansson) discloses a system for promoting regeneration of a damaged nerve comprising a guide tube attached to the damaged nerve and nerve-growth-stimulating agents which are dispersed in a matrix enclosed by the guide tube. In patent WO0207749 (Patric) a method and a system for regenerating nerves are disclosed which comprise a biodegradable nerve conduit containing helper cells that direct the expression of a polynucleotide to encode a growth factor. Although in such delivery systems the growth factors can be locally released, one major disadvantage is that temporal control of the release for a prolonged time is not possible. As important as it is to control the proteins spatially, it is equally imperative to control the amount of protein delivered over a period of time. Regeneration, especially for long nerve gaps, requires several months to complete. If proteins and neurotrophic factors are only administered as a single dose at the time of application of the nerve conduit then some of the proteins will be taken up intracellularly, diffuse into the surrounding tissue and degrade. Then there will not be a therapeutic level of protein able to promote axonal outgrowth over the time necessary for the completion of regeneration. In addition, the rate of growth factor delivery from nerve conduits is dependent on the physicochemical properties, the kinetics and the size of the molecules delivered.

Sustaining the presence of proteins at the effective concentration can be achieved through a delivery system with temporally-controlled slow release. Given the short biological half-life of growth factors, a system with slow and controlled release ensures that the growth factors will last longer in the nerve gap. To this end, the use of injection devices, pumps and other drug-release devices can be suitable for the slow and long-term delivery of nerve growth factors to the injury site.

Mini- or micro-pumps are preferable since they can be implanted in the body near the injured nerve. Suitable pumps include mechanically-actuated type of pumps based on piezoelectric, electromagnetic and other actuation sources and nonmechanically-actuated types, such as an electro-osmotic pumps and osmotic pumps (W. Wang and S. A. Soper, 2007. Bio-MEMS: Technologies and Applications, Boca Raton, CRC Press). An osmotic mini-pump has been experimentally used for the delivery of exogenous BDNF to promote nerve regeneration in rats (J. G. Boyd and T. Gordon, A dose-dependent facilitation and inhibition of peripheral nerve regeneration by brain-derived neurotrophic factor, European Journal of Neuroscience, volume 15, issue 4, pages 613-626, 2002). The implanted pump consisted of a reservoir for storing the neurotrophic factor solution, an adjacent chamber with a semi-permeable membrane and a catheter attached on the injury site. BDNF was administered via the mini osmotic pump at a continual flow rate for all the treatment period. In patent WO2006/133554 (Syed and Jullien), an implantable system for promoting nerve regeneration is disclosed comprising a tube housing with integrated electrodes for the electrical stimulation of the injured nerve and also a pump configured to release agents to stimulate nerve regeneration. The pump is also fluidly connected to a reservoir which stores the stimulating agents and is placed outside the body. Despite their advantages in delivering the growth factors for a prolonged period of time, the above-mentioned systems do not include any means for monitoring the regeneration process and effectively adjusting the treatment regimen. Therefore, the parameters of growth factor release, such as dose, timing, combination of different types of growth factors are not controlled according to the progress of nerve regeneration. Patent US2006/0194724 (Whitehurst) discloses a method and a system comprising an implanted control unit which causes a stimulus to be applied to the damaged nerve for promoting the regeneration process. The implanted control unit is wirelessly connected to extracorporeal devices for power and data transfer purposes. The stimulus applied by the system is configured to promote nerve regeneration and includes a combination of electrical stimulation via electrodes and stimulation via the injection of one or more drugs into the nerve. These drugs include neurotrophic factors, nerve growth factors, etc. and are infused by a pump or a controlled drug release device. The application of the stimulus is performed in accordance with various control parameters which control the amount and rate of delivery of one or more drugs. The control parameters can be adjusted based on at least one sensed condition, such as neurotransmitter level, hormone level, electromyography signal level, etc. Although this method and system has the advantage that the drug release parameters can be controlled and adjusted, the patent does not describe or include any means of measuring any of the sensed conditions.

SUMMARY OF THE INVENTION

The present invention discloses a method and a system for recording the electric activity of peripheral nerves that are regenerating after injury and promoting the regeneration process by locally releasing stimulating agents. The recording is performed at various time instances of the regenerative period aiming at estimating the state and progress of nerve regeneration. The method and the system that are disclosed are characterized by that the parameters of the release of the stimulating agents are appropriately adjusted at various time instances based on the state and progress of nerve regeneration as assessed by the analysis of the recordings.

Referring to the recording of the electric activity of injured nerves over the regeneration period, a first electrode is directly attached to the proximal segment of the injured nerve and is responsible to apply an electric pulse to the nerve sufficient to evoke an action potential. The action potential propagates along the nerve and across the injury area. A second electrode, which is directly attached to the distal segment of the nerve, acquires the electric signals produced by the propagation of said action potential. An electronic unit is implanted into a region near the injured nerve and is connected to said electrodes. At various time instances, which are determined by a schedule, the electronic unit first generates said stimulating electric pulse and subsequently records said electric signals that were acquired by the second electrode. The electronic unit transmits said recorded electric signals, which are acquired every time a recording is performed, to a computing unit via wired or wireless means. The computing unit can either be implanted, for instance as a separate device near the electronic unit, or incorporated within the electric unit, or placed extracorporeally. The computing unit stores and analyzes said recordings. From the analysis of said recordings, a number of characteristics are calculated, such as the latency period, the conduction velocity, the amplitude of the electric signals, etc. The values of the characteristics and their comparison with those calculated from pervious recordings are used for assessing the state and progress of the regeneration process. Based on the assessment of the state and progress of the regeneration process, a number of parameters that regulate the release of the stimulating agents are determined which will be called hereafter as "agent-release control parameters". The agent-release control parameters are transmitted by the computing unit back to the electronic unit.

The promotion of the regeneration process is achieved by releasing stimulating agents, such as neurotrophic factors, into the injury area using an implanted agent- release device. The agent-release device is appropriately connected to the electronic unit. The present invention is characterized by that the release of the stimulating agents is controlled by the electronic unit in accordance with the agent-release control parameters that were determined at various time instances. In this way, the parameters of release of the stimulating agents, such as the dose, timing and rate of release are appropriately determined from the system based on the state and progress of the regeneration.

One advantage of the present invention is that it makes use of implanted electrodes for recording the electric signals that are produced by the distal segment of the injured nerve after appropriate electrical stimulation of the proximal segment. The gradual restoration of the electric activity of the distal segment indicates the sprouting and outgrowth of the regenerating neuroaxons towards correct pathways. Analysis of the recordings acquired from the system is advantageous over routine EMG and CNS measurements in that the recorded electric signals are acquired directly from the injured nerve. In addition, the recordings are free from interferences coming from neighboring nerves, muscles and other tissues. In this respect, the recording process can be reproducible and the results from the signal analysis are accurate and reflect the local changes that take place at the injury site as opposed to clinical EMG and CNS examinations. Furthermore, the implanted electrodes used by the present invention are suitable for recording nerve injuries that are located in deep layers and cannot be accessible by surface or needle electrodes. In another embodiment of the present invention, multiple electrodes are attached along the distal segment of the injured nerve at various recording sites. This makes feasible to assess not only whether the neuroaxons have established contact with the distal stump but also to assess the extent of axonal outgrowth. On the contrary, EMG signals mainly reflect the activity of the muscle fibers after their reinnervation has begun which usually occurs at the last stages of the regeneration process. Another advantage of the present invention is that it discloses a system and method that allow the local administration of exogenous stimulating agents by appropriately controlling an implanted agent-release device, such as a micro-pump. In this way, the stimulating agents, such as the neurotrophic factors, can be directly delivered to the injury area over the whole regeneration period which may last several months. The characteristic advantage is that the release of the stimulating agents can be regulated at various time instances throughout the period of nerve regeneration so that it can be effective. The regulation is performed according to the analysis of the electric signals acquired directly from the injury area. In this respect, the system presented herein makes use of its own recordings in order to determine an effective treatment regimen while keeping drug administration at safe levels. For instance, in cases where the regeneration process is delayed, the amount and rate of agents' release may be increased or a combination of different agents may be additionally applied. Similarly, when the axonal outgrowth progresses successfully, the release parameters may be altered. Another advantage of the system presented herein is that it can operate in an autonomous fashion. The recordings can be acquired according to schedules programmed within the electronic unit without necessitating the intervention of a specialist to configure the measuring set-up. Similarly, the agent-release parameters may be automatically adjusted by the system according to updates derived from the analysis of new recordings. In contrast, other systems comprising a drug-release device either apply a predetermined administration of drugs for the whole recovery period or require external measurements (such as EMG) to be performed in order to adjust the release parameters.

The electrodes, the electronic unit and the agent-release device of the system described by the present invention are fully implanted within the patient near the injured nerve. This minimizes the risk of infection and/or damage to the nerve and other neighboring tissues that might be caused by transcutaneous cables or by any external components of the agent-release device, such as a catheter or reservoirs that store the stimulating agents. Also, the computing unit may be placed extracorporeally as a portable or wearable device for wirelessly communicating data with the electronic unit and also transferring power to it. In this sense, the system does not disturb the patient during his daily activities and can be carried until the recovery is completed.

BRIEF DESCRIPTION OF THE DRAWINGS Fig.l illustrates an injured peripheral nerve (1) together with its proximal (2) and distal (3) segments which is surgically treated by direct coaptation with sutures (Fig. Ia), by the insertion of a nerve graft sutures (Fig. Ib), and by the placement of a nerve conduit sutures (Fig. Ic), respectively. Fig. 2 depicts a schematic diagram of the overall invention with the stimulating electrode (5) attached to the proximal segment (2) of the injured nerve (1), the recording electrode (6) attached to the distal segment of the injured nerve (1), the implanted agent-release device (7), the main functional components of the implanted electronic unit (9), and the main functional components of the computing unit (10).

Fig. 3 depicts one embodiment of the invention in which the implanted electronic unit (9) is connected to the electrode (5), the electrode (6), and the agent-release device (7). The agent-release device releases stimulating agents (8) directly to the injury area (4); said agent-release device (7) is placed within a housing (23) which said housing (23) is attached to the nerve (1), near the injury area (4), by appropriate supporting means (24).

Fig. 4 depicts three other embodiments of the invention in which a first embodiment utilizes a computing unit (10) which is placed extracorporeally and is wirelessly connected to the implanted electronic unit (9); a second embodiment in which two recording electrodes (6a and 6b) are attached along the distal segment (3) of the injured nerve (1) to record the regeneration of the nerve as it evolves along the distal segment (3); and a third embodiment in which the stimulating therapeutic (8) are released directly into the injury area (4) through a catheter (25) which is connected to the implanted agent-release device (7).

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the recording of the restoration of the electric activity of injured nerves during the regeneration period as well as the promotion of the regeneration process through the controlled release of stimulating agents.

Injury of peripheral nerves can be surgically treated by a variety of methods that depend on the severity of injury, the width of the injury area and other related factors. Fig. Ia illustrates an injured peripheral nerve (1) and its injury area (4). The proximal segment (2) and the distal segment (3) of the nerve (1) have been surgically coapted with sutures. Fig. Ib illustrates an injured peripheral nerve (1) in which a nerve graft (30) is inserted and coapted in-between the proximal stump (2) and the distal stump(3) of the nerve (1). Fig. Ic illustrates an injured peripheral nerve (1) where the proximal segment (2) and the distal segment (3) are bridged by interposing a synthetic nerve conduit (31); said nerve conduit guides the regenerating axons to the distal nerve stump (3).

The method disclosed by the present application and the system for applying it refer to the recording of the electric activity of injured peripheral nerves at various time instances of the regeneration period with the aim of promoting the regeneration process by the appropriate delivery of stimulating agents (8) to the injury area (4) which are released by a controlled agent-release device. Non restrictive embodiments of the current invention are hereby described with relation to the figures.

Recording the electric activity of the distal segment (3) of an injured peripheral nerve after appropriate electric stimulation of the proximal segment (2) can provide a quantitative means of assessing the state and progress of nerve regeneration. As depicted in Fig. 2, the electric activity of the distal segment (3) can be recorded by attaching a recording electrode (6) to the distal segment (3) and a stimulation electrode (5) at the proximal segment (2) of the nerve. An electronic unit (9), which is implanted into a region near the injured nerve, is connected to the electrodes (5) and (6). The electronic unit comprises a pulse generator (11) which generates an electric pulse with variable parameters including, but not limited to, intensity, duration, polarity, frequency, repetition rate; said electric pulse is applied by the electrode (5) to the nerve so as to electrically stimulate the nerve (1). Sufficient electrical stimulation evokes an action potential to the nerve (1) which propagates along the nerve (1). When the axons of the nerve (1) start re-growing towards the distal segment (3), electrical signals are conducted across the injury area (4). Said electric signals propagate along the distal segment (4) of the nerve and are acquired by the distal electrode (6). The electronic unit (9) comprises a signal acquisition module (12) that acquires, amplifies, filters, and pre-processes the received electric signals. The electronic unit (9) comprises also a controller (13) to supervise the operation of the various modules of the electronic unit (9). The controller (13) is also connected to a transmitter/receiver (15) which transmits said recorded electric signals via wired or wireless means to a computing unit (10). The computing unit (10) can either be incorporated within the electric unit (9) or located near the electronic unit (9), e.g. as a separate implanted device (9), or placed extracorporeally. The computing unit (10) comprises a data storage module (19) and a signal analysis module (18) for storing and analyzing, respectively, said recorded electric signals. The data storage module (19) may also store programs, log files, patient demographic data, and other contextual information. The computing unit (10) may also comprise a user interface (21) for visualization of the recorded electric signals and for providing input/output between the computing unit (10) and the users of the system, namely the physicians and health professionals. From the analysis of said recordings, the state and progress of the regeneration process is assessed. The computing unit (10) incorporates an agent-release regulator module (20) which determines a number of agent-release control parameters based on the state and progress of nerve regeneration. The computing unit (10) comprises a transmitter/receiver (17) which transmits the agent-release control parameters to the transmitter/receiver (15) of the electronic unit (9). The agent-release control parameters are thereafter forwarded by the controller (13) to an agent-release device regulator module (14). Regarding the promotion of the regeneration process, this is achieved by the release of at least one type of stimulating agents (8) into the injury area (4) by an implanted agent-release device (7); said agent-release device (7) is appropriately connected to the electronic unit (9). The characteristic of the present invention is that the electronic unit (9) controls the agent-release device (7) so as to release said stimulating agents into the injury area (4) according to the agent-release control parameters stored in the agent-release device regulator module (14). The agent- release control parameters define, but are not limited to, the dose, timing and rate of the release of stimulating agents and/or the types and combination of stimulating agents to be released.

Analysis of the recorded electric signals refers to the calculation of appropriate characteristics from the waveform of each signal. These characteristics include, but are not limited to, the latency period of the response, the amplitude of the waveform, the frequency content of the waveform and the conduction velocity. When the nerve is electrically stimulated by an electric pulse applied by the electrode (5), an action potential is evoked which is conducted along the neuroaxons of the nerve. The compound action potential (i.e. the superposition of the individual action potentials of each neuroaxon) is recorded by the electrode (6) as an electric signal waveform. The arrival time of the electric signal, as measured to the electric pulse initiation time point, is the latency period of the response. By knowing the distance between electrodes (5) and (6), the conduction velocity can be determined by dividing said distance by the latency period. The conduction velocity is significantly decreased in injured nerves, as compared to healthy nerves. As the regeneration progresses, the conduction velocity starts increasing. Similar trends are observed for the amplitude of the signal waveform. The signal analysis module (18) of the computing unit (10) calculates said signal characteristics from the current recording. The state and progress of nerve regeneration can be assessed based on the calculated characteristics themselves and also on their comparison with those characteristics calculated from previous recordings obtained from the same patient at earlier time instances. For this purpose, the data storage module (19) of the computing unit (10) stores all current and previous recordings along with their calculated characteristics. Also, patient- related and injury-related data are stored in the data storage module (19). This is performed because the conduction velocity and the other signal characteristics are affected by the patient age, diameter of the nerve, type of nerve, method of surgical treatment (e.g. direct coaptation, nerve graft placement). Therefore, for the assessment of the state and progress of nerve regeneration, the currently-calculated characteristics, their variation over the regeneration period as well as patient data are all taken into consideration.

The agent-release control parameters are updated depending on the state and progress of nerve regeneration as assessed by the analysis of new recordings. New recordings of the electric signals are acquired by the electronic unit (9) at various time instances throughout the period of the regeneration process according to a schedule. The new recordings are transferred and analyzed in the signals analysis module (18) of the computing unit (10) and the agent-release regulator (20) is responsible to update the agent-release control parameters based on the state and progress of nerve regeneration. Thereafter, said agent-release control parameters are transferred to the agent-release device regulator module (14) of the electronic unit (9) to control the agent-release device (7). In this way, the promotion of the regeneration process can be efficient since the release of the stimulating agents (8) corresponds to the actual needs of the regenerating nerve (1). For instance, if the regeneration process is delayed or impaired, the updated agent-release control parameters may describe an increase in the amount and rate of release of stimulating agents, or may describe the release of combination of different types of stimulating agents. The history of previous and current agent-release control parameters are long-term stored in the data storage module (19) of the computing unit (10).

Recordings are acquired according to a schedule which defines the rate, period and timing of electric pulse stimulation and electric signal acquisition throughout the regeneration period. The controller (13) of the electronic unit (9) is programmed with said schedule. The data storage module (19) of the computing unit (10) stores said schedule. The schedule is determined upon system application but may also be manually adjusted at any instance of the regeneration period by the users of the systems (physicians and other health professionals) through the user interface (21) of the computing unit (10). Any adjustments of the schedule are stored in the data storage module (19) and are also forwarded to the controller (13) of the electronic unit (9). The controller (13) of the electronic unit (9) controls and supervises the operation of the various module of the electronic unit (9) and is programmed with the schedule for the acquisition of recordings. The controller (13) also contains the parameters of electric pulse generation utilized by the pulse generator (11) and the parameters of electric signal acquisition utilized by the signal acquisition module (12). The parameters of electric pulse generaration include, but are not limited to, the intensity, duration, polarity, frequency and repetition rate of the electric pulses. The parameters of electric signal acquisition define, but are not limited to, the level of amplification, filtering, duration of recording and signal pre-processing. The transmitter/receiver (15) of the electronic unit (9) and the transmitter/receiver (17) of the computing unit (10) communicate with each other for the transfer of the recorded signals, the agent-release control parameters, and other data, such as schedules and control signals. The transmitter/receiver (15) and the (17) are also used for power transfer purposes. As depicted in Fig. 2, the electronic unit (9) is powered by an appropriate power source (16) incorporated in the electronic unit (9). Depending on the power needs of the electronic unit (9), the power source (16) may be a rechargeable battery, a capacitor or any other appropriate power source. The power source (16) is recharged, when needed, by a power charger (22) contained within the computing unit (10). The data communication and power transfer between the transmitter/receiver (15) and the transmitter/receiver (17) can be achieved via wired connections or wireless technologies using radio-frequency signals.

The agent-release device (7) utilized by the method and the system of the present invention may include any type of a variety of implantable controlled agent-release devices. A preferred controlled agent-release device comprises at least one reservoir filled with the stimulating agents (8), a pump to release said agents, a control circuitry, a number of outlet ports for the infusion of said agents and may additionally comprise valves, mixers, filters and other micro-fluid components necessary for its operation.

The pump of the agent-release device (7) may be a mechanically-actuated type of pump based on, but not limited to, piezoelectric, electromagnetic, pneumatic, electrostatic, bimetallic thermal, and thermopneumatic actuation sources or may be a nonmechanically-actuated type of pump, such as an electro-osmotic pump and an osmotic pump. Alternatively, the controlled agent-release device (7) may comprise other releasing mechanisms apart from a pump, such as those based on electrochemical or electrothermal dissolution of thin membranes covering micro- reservoirs.

The reservoirs that are contained within the agent-release device (7) may all be filled with one type of stimulating agents (8) or some of the reservoirs may be filled with different types of stimulating agents (8). The reservoirs contain all the required amount of the stimulating agents that is needed for promoting nerve regeneration and thus the reservoirs do not need to be refilled with additional amount of stimulating agents during the regeneration period.

The stimulating agents (8) used by the method and the system of the present invention may include, but are not limited to, neurotrophic factors, such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), insulin-like growth factor 1 (IGF-I), fibroblast growth factor 1 (FGF-I), fibroblast growth factor 2 (FGF- 2) and ciliary neurotrophic factor (CNTF), and products of Schwann cells.

Fig. 3 illustrates one preferred embodiment of the invention comprising the electronic unit (9), the electrodes (5) and (6) and the implanted drug-release device (7). The computing unit (10) is not shown in Fig. 3. The electronic unit (9) is implanted near the injury area (4) and is connected to the electrode (5), the electrode (6) and the agent-release device (7). The implanted electronic unit (9) disclosed in the present application is advantageous over extracorporeal devices because the risk of infection or damage to the nerve that would arise from transcutaneous cables connecting the implanted electrodes (5) and (6) to an extracorporeal device (7) is eliminated. As depicted in Fig. 3, the electrode (5) is attached to the proximal segment (2) of the nerve and has an annular shape with an opening; the angle of said opening is preferably larger than 90°. In other preferred embodiments, the electrodes may alternatively have an annular shape without an opening as shown in Fig. 3 for the electrode (6). In other embodiments, the electrodes may loop the nerve by alternatively having a helical shape as shown in Fig. 4 for the electrode (6b). Either electrodes [(5) or (6)] may have each of said annular or helical shapes. The advantage of using a stimulating electrode (5) attached directly to the proximal nerve segment (2), over the use of percutaneous or needle electrodes, is that the electric stimulation is selectively applied to the nerve of interest. The advantage of using a recording electrode (6) attached directly to the distant nerve segment (3), over the use of percutaneous or needle electrodes, is that the recorded electric signals are acquired only from the nerve of interest without any interference from neighboring nerves, muscles and other tissues. Therefore, the use of implantable electrodes provides repeatable and accurate measurements collected throughout the regeneration period.

Fig. 4 illustrates another preferred embodiment of the present invention in which two recording electrodes (6a and 6b) are attached along the distal segment (3) of the nerve to record its electric activity at two different sites. In this way, analysis of the recorded signals acquired by the most distant electrode (6b) can be used to assess whether the regenerating neuroaxons have reached at the farthest recording site. Assessment of the state and progress of nerve regeneration at the farthest recording site can be also facilitated by additionally comparing the characteristics calculated from the electric signals acquired by electrode 6b with those by electrode 6a. For example, the conduction velocity calculated from electrode 6b can be compared with that from the electrode 6a. Additionally, more than two recording electrodes (6) can be attached to several sites along the distal segment (3) of the nerve. In a similar way, analysis of the recorded signals acquired by each of the recording electrodes can be used to assess whether the regenerating neuroaxons have reached at a specific recording site. Assessment of the state and progress of nerve regeneration at a specific recording site can be also facilitated by additionally comparing the characteristics calculated from that specific site with those calculated from other recordings sites. Fig. 3 also depicts the agent-release device (7) which is implanted into the patient near the injury area (4). The agent-release device (7) may be incorporated within a housing (23). Said housing (23) is utilized to firmly support the agent-release device (7) at the desired location. In the embodiment shown in Fig. 3, the housing is mounted on the nerve (1) via appropriate supporting means. One appropriate supporting means may comprise two or more side projections (24) on the housing (23); said projections (24) may have appropriate holes to hold said housing (23) against the nerve (1) with the use of microsurgical sutures (25) that are stitched onto the epineurium of the nerve (1) or loop around the nerve (1). Alternatively, said housing (23) may be attached to the nerve (1) by using appropriate tissue glue. Fig. 3 illustrates one preferred embodiment in which the agent-release device (7) is implanted near the injury area (4) and the released stimulating agents (8) are directly infused into the injury area (4). In another embodiment, shown in Fig. 4, the agent- release device (7) is implanted at some distance from the injury area (4), e.g. in cases where there is not sufficient space near the injury area to accommodate the agent- release device (7). In embodiments, such as that depicted by Fig. 4, the stimulating agents (8) can be delivered to the injury area (4) through a catheter (26); one end of said catheter (26) is connected to an outlet port of the agent-release device (7), while the other end is firmly held at the site of injury. The catheter (26) can be firmly held in place by appropriate supporting means, such as microsurgical sutures (27) that are stitched onto the epineurium of the nerve (1) or loop around the nerve (1) as illustrated in Fig. 4. Alternatively, said catheter (26) may be attached to the nerve (1) by using appropriate tissue glue.

Fig. 4 depicts one preferred embodiment in which the computing unit (10) is a separate device placed extracorporeally. The advantage of using an extracorporeal device lies in that the users of the system can have access to the acquired recordings and other data, such as data concerning the assessment of nerve regeneration, data concerning the release of the stimulating agents, the programmed schedule of recordings. Also, an extracorporeal computing unit (10) allows the users to control the system through the user interface (21), for example, to manually refine the scheduled recordings. Another advantage of an extracorporeal computing unit (10) is that it can recharge, if needed, the power source (16) of the electronic unit (9). In the preferred embodiment shown in Fig. 4, the computing unit (10) communicates with the implanted electronic unit (9) through wireless radio-frequency link for data and power transfer purposes. The computing unit (10) is preferably located near the human body, e.g. as a portable or wearable device which is essential for the efficient transfer of power from the computing unit (10) to the electronic unit (9). The utilization of wireless technologies for the communication of the computing unit (10) with the electronic unit (9) is advantageous over a wired communication in that the risk of infection and injury associated with transdermal cables is eliminated. Furthermore, a wireless extracorporeal computing unit (10) is unobtrusive and does not interfere with the patient's everyday activities. Therefore, the patient can safely carry the system until the regeneration process is completed. However, other embodiments of the present invention may include a wired connection between the computing unit (10) and the electronic unit (9).

Claims

1. A method for recording peripheral nerve regeneration which is characterized by that it can also promote the regeneration process comprising the steps of: a. utilizing one electrode (5) placed on the proximal segment (2) of the injured nerve (1); b. utilizing at least one electrode (6) placed on the distal segment (3) of the injured nerve (1); c. generating an electric pulse which is applied by the electrode (5) to the proximal segment (2) of the injured nerve (1) so as to evoke an action potential to the nerve; d. recording the electric signals acquired by the electrode (6); said electric signals were produced by the propagation of said evoked action potential along the nerve (1); e. analyzing said recorded electric signals in order to assess the state and progress of nerve regeneration; f. determining a number of agent-release control parameters based on the state and progress of nerve regeneration; g. utilizing one agent-release device (7) for the release of at least one stimulating agent (8) into the injury area (4) of the nerve (1); h. controlling said agent-release device (7) so that the release of said stimulating agents (8) is regulated according to said agent-release control parameters as they were determined by the state and progress of nerve regeneration.

2. A system for recording peripheral nerve regeneration which is characterized by that it can also promote the regeneration process and applies the method of claim 1 comprising: a. an implanted electrode (5) attached to the proximal segment (2) of the injured nerve (1) for applying an electric pulse to evoke an action potential to the nerve (1); b. at least one implanted electrode (6) attached to the distal segment (3) of the injured nerve (1) for acquiring the electric signals of the nerve (1) produced by the propagation of said evoked action potential along the nerve (1); c. an implanted agent-release device (7) configured to release at least one stimulating agent (8) to the injury area (4) of the peripheral nerve; d. a housing (23) which accommodates the agent-release device (7). e. an implanted electronic unit (9) that i). is appropriately connected to the electrode (5) and generates said electric pulse, ii). is appropriately connected to the electrode (6) and records said electric signals of the nerve (1) acquired from the electrode (6), iii). transmits said recorded electric signals to a local or remote computing unit (10), said computing unit (10) stores and analyzes said recorded electric signals for assessing the state and progress of nerve regeneration; the state and progress of nerve regeneration are thereafter utilized to determine a number of agent-release control parameters; iv). receives said agent-release control parameters from the computing unit

(10) v). is appropriately connected to said agent-release device (7) vi). controls said agent-release device (7) so that so that the release of said stimulating agents (8) is regulated based on said agent-release control parameters as they were determined by the state and progress of nerve regeneration.

3. The system according to claim 2 characterized by that the electronic unit (9) comprises a. a pulse generator (11) connected to said electrode (5) for generating said electric pulse, b. a signal acquisition module (12) connected to electrodes (6) for recording said electric signals acquired from said electrodes (6), c. an agent-release device regulator (14) connected to said agent-release device (7) for regulating the release of said stimulating agents (8) according to said agent-release control parameters, d. a controller (13) which controls and supervises the components of said electronic unit (9) and accepts command signals from said computing unit (10) e. a transmitter/receiver (15) for the communication with or receive power from said computing unit (10), and f. a power source (16).

4. The system according to claim 2 characterized by that the computing unit (9) comprises a. a transmitter/receiver (17) for the communication with or transfer power to said electronic unit (9), b. a data storage module (19) for storing said recorded electric signals and other contextual information c. an agent-release regulator (20) for determining said agent-release control parameters, d. a user interface (21) for providing input/output to the users of said system, and e. a power charger (22) for providing power to recharge said electronic unit (9).

5. The system according to claim 2, 3 and 4 characterized by that the communication and transfer of power between said electronic unit (9) and said control unit (10) is wired or wireless.

6. The system according to claim 2 characterized by that said agent-release device (7) comprises at least one reservoir; said reservoirs are filled with one type of stimulating agents (8) or each of said reservoirs may be filled with a different type of said stimulating agents (8).

7. The system according to claims 2 and 6 characterized by that said agent-release device (7) is appropriately connected to a catheter (26); said stimulating agents

(8) are released by said agent-release device (7) and are delivered to the injury area (4) through said catheter (26).

8. The system according to claims 2, 3 and 4 characterized by that the state and progress of nerve regeneration is assessed by the latency period, the conduction velocity, the amplitude and the frequency content of said recorded electric signals acquired from said electrodes (6).

9. The system according to claims 2, 3, and 4 characterized by that said agent- release control parameters determine the amount, the rate, the timing and the type of said stimulating agents (8) to be released by said agent-release device

(7).

10. The system according to claims 2, 3, 4, 6, 7 and 9 characterized by that said stimulating agents (8) comprise at least one of a neurotrophic factor, a nerve growth factor (NGF), a brain-derived neurotrophic factor (BDNF), an insulin- like growth factor 1 (IGF-I), a fibroblast growth factor 1 (FGF-I), a fibroblast growth factor 2 (FGF-2), a ciliary neurotrophic factor (CNTF), and one of the products of the Schwann cells.

11. The system according to claims 2 and 6 characterized by that said housing (23) is attached to the nerve (1) via appropriate mechanical means;

12. The system according to claims 2 and 6 and 11 characterized by that said housing (23) may be attached to the nerve (1) via appropriate microsurgical sutures that are stitched onto the epineurium of the nerve (1) or loop around the nerve (1).

13. The system according to claims 2 and 6 and 11 characterized by that said housing (23) may be attached to the nerve (1) using appropriate tissue glue.

14. The system according to claims 2, 6 and 7 characterized by that said catheter (26) is attached to nerve (1) via appropriate mechanical means.

15. The system according to claims 2, 6, 7 and 14 characterized by that said catheter (26) may be attached to nerve (1) via appropriate microsurgical sutures that are stitched onto the epineurium of the nerve (1) or loop around the nerve (1).

16. The system according to claims 2, 6, 7 and 14 characterized by that said catheter (26) may be attached to nerve (1) using appropriate tissue glue.

17. The system according to claim 2 characterized by that said electrode (5) and said electrodes (6) are annular or annular with a circumferential opening; the angle of said opening is optimally larger than 90°.

18. The system according to claim 2 characterized by that said electrode (5) and said electrodes (6) are helical in shape.

19. The system according to claim 2, 3 and 4 characterized by that said computing unit (10) is either incorporated within said electronic unit (9) or comprises a separate device.

20. The system according to claim 2 and 4 and 14 characterized by that said computing unit (10) is either implanted within the patient or placed extracorporeally.