WO2010035036A2

WO2010035036A2 - Electrode

Info

Publication number: WO2010035036A2
Application number: PCT/GB2009/051247
Authority: WO
Inventors: Stuart Baker; James Burdess; Alun Harris; Richard Jackson; Andrew Jackson
Original assignee: University Of Newcastle Upon Tyne
Priority date: 2008-09-26
Filing date: 2009-09-24
Publication date: 2010-04-01
Also published as: WO2010035036A3; GB0817597D0

Abstract

An electrode (1) suitable for implantation in a body, for recording electrical signals from nervous tissues in the body and for electrically exciting nervous tissues in the body, is disclosed. The electrode (1) comprises a communication channel (11) for communicating signals to and /or from the body, and a support (3) for supporting the or each communication channel (11), such that the length of the communication channel (11) is greater than the distance between the its ends. The communication channel (11) may be flexible such that changes in the distance between the ends of the communication channel (11) can be accommodated. An anchor portion (9) anchors at least a portion of the electrode (11) to surrounding material when implanted in the body.

Description

ELECTRODE

FIELD OF THE INVENTION

The present invention relates to an apparatus suitable for implantation in a body, for communicating signals and /or fluid to and /or from the body. The invention relates particularly, but not exclusively, to an electrode for recording electrical signals from, nervous tissues in the body and for electrically exciting nervous tissues in the body.

BACKGROUND OF THE INVENTION

Implanted probes to sense electrical activity and/or deliver electrical stimulation to the nervous system have applications that include the scientific study of the brain, monitoring of abnormal brain activity caused by neurological disorders and as a component of neural prostheses to restore function following injury or disease. Currently many applications are limited by the poor long-term performance of existing designs of implanted probe. The prior art consists of fine wire electrodes or micro-machined silicon needles. These can give a good initial yield of neuronal recordings, but signal-to-noise ratio progressively deteriorates in the weeks and months after implantation. In addition, thresholds for activating neural tissue via electrical stimulation increase. The deterioration in performance is due in part to a foreign- body response in which reactive microglia and astrocytes cluster tightly around the electrode, forming a dense fibrous sheath. This insulates the electrode tip from the surrounding neurons, causing a degradation of recording quality and a rise in stimulus thresholds. In addition there may be neuronal death around the electrodes. Efforts to improve biocompatibility of electrode surfaces have had only limited success at reducing sustained tissue responses. Preferred embodiments of the present invention seek to overcome one or more of the above disadvantages of the prior art.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided an apparatus for insertion into a human or animal body for communicating signals and /or fluid to and /or from the body, the apparatus comprising: at least one communication channel for communicating signals and /or fluid to and /or from the body, the communication channel having a first end and a second end; and at least one support for supporting the or each communication channel such that the length of the communication channel is greater than the distance between the first and second ends; wherein the communication channel is flexible such that changes in said distance between the first and second ends of the communication channel can be accommodated.

Advantageously, the present invention provides an apparatus in which mechanical coupling between the two ends of the communication channel is reduced, thereby minimising movement of the ends of the communication channel with respect to their surrounding tissue when implanted in the body. Importantly, since the length of the communication channel is greater than the distance between the first and second ends, the ends of the communication channel are able to move both towards each other and apart from each other with minimal forces exerted on the tissue surrounding the end of the communication channel. For example, if there is relative movement of the tissues surrounding two different portions of the communication channel, those two portions may each remain substantially stationary with respect to their respective surrounding tissue, the relative movement between the tissues being accommodated by a change in the distance between the two portions of the communication channel. This in turn reduces the amplitude of micro-movements between a given portion of the communication channel, in particular, the 'open' end of the communication channel, and its surrounding tissue.

At least one said communication channel may comprise a plurality of bends or undulations.

For a communication channel of a given length and having a given separation between its ends, increasing the number of bends or undulations between the two ends of the communication channel reduces the overall amplitude of the bends or undulations. This reduces the transverse cross-sectional size of the apparatus, such that it may be inserted into the body more easily. Alternatively, increasing the number of bends or undulations at a given amplitude increases the total length of the communication channel, thereby allowing for a greater range of relative movement between the two ends of the communication channel.

At least a portion of at least one said communication channel may be substantially sinusoidal.

Advantageously, this profile allows for substantially equal amounts of elongation and contraction of the apparatus with respect to the initial distance between the ends of the communication channel. Also, a sinusoidal profile is suitable for a planar apparatus, allowing the apparatus to be fabricated using standard micro-fabrication techniques. At least a portion of at least one said communication channel may be coiled.

This arrangement allows preparation of the apparatus by, for example, winding a flexible communication channel around a support .

The first end of at least one said communication channel may be adapted for communicative connection to a further communication channel.

For example, the communication channel may be adapted for connection to the output of a source of current, voltage, light or fluid, or to the input of a detector, or a fluid receptacle .

At least one communication channel may be a fluid conduit for delivering fluid to and /or receiving fluid from the body.

The advantage of this feature is that the apparatus may be used to deliver fluids, which may include drugs, to a specific site in the body, or to extract samples of fluid.

At least one communication channel may be an optical fibre for transmitting light to and /or from the body.

The advantage of this feature is that the apparatus can be used to stimulate cells such as neurons genetically engineered to express Channelrhodopsin-2 which respond to light, and to record light emitted by neurons stained with voltage-sensitive dyes .

At least one communication channel may be an electrode for transmitting electrical signals to and /or from the body. The advantage of this feature is that the apparatus may be used to electrically excite neural tissue, or to record electrical activity of neurons (e.g. to record spikes) .

The support may comprise an electrically insulating layer for electrically insulating the electrode between its ends.

This feature avoids the necessity of providing separate supporting and insulating layers.

The communication channel and support may form a planar arrangement .

This feature simplifies the fabrication of the apparatus, since planar arrangements may be fabricated using standard microfabrication techniques.

The support may include poly-monochloro-para-xylylene.

Since poly-monochloro-para-xylylene (parylene C) is more compliant than, for example, metal, the use of parylene C in the support for the communication channel further reduces the transmission of mechanical forces along the apparatus. Parylene C is also electrically insulating and has good biocompatibility .

The apparatus may further comprise one or more anchor portions for anchoring at least a portion of the communication channel to surrounding material when implanted in the body.

Advantageously, an anchor portion will further reduce the movement of the anchor portion of the communication channel relative to its surroundings. Preferably the dimensions of the anchor portion, transverse to the longitudinal direction of the communication channel, are greater than the corresponding transverse dimensions of the apparatus adjacent to the anchor portion. Preferably, the anchor portion is located distally from a tethering or fixation point of the apparatus used to tether the apparatus to the body.

At least one anchor portion comprises a substantially spheroid or ovoid or ellipsoid portion.

Advantageously, this reduces movement of the anchor portion in all directions.

Preferably, at least one said anchor portion comprises a material having a density close to the density of the surrounding tissue.

This provides the advantage of preventing sudden accelerations of the body from causing movement of the apparatus relative to surrounding tissue because inertial forces on the anchor and tissue are closely matched. Preferably, the density of the anchor portion is close to 1 g/ml, as most body tissues have a density close to 1 g/ml.

Preferably, the anchor portion comprises polyimide.

Advantages of using polyimide for the anchor portion include its biocompatibility and its substantially neutral density in some tissues, in particular the brain.

According to a second aspect of the present invention, there is provided an electrode for insertion into a human or animal body for communicating electrical signals to and /or from the body, the electrode comprising: at least one electrical conductor for communicating electrical signals to and /or from the body, the conductor having a first end and a second end; and at least one support for supporting the or each conductor such that the distance between the ends of the conductor is less than the length of the conductor; wherein at least one said conductor comprises a plurality of bends or undulations, and the electrode is flexible, such that changes in said distance between the ends of the conductor can be accommodated.

According to a third aspect of the present invention, there is provided an apparatus for insertion into a human or animal body for communicating signals and /or fluid to and /or from the body, the apparatus comprising: at least one communication channel for communicating signals and /or fluid to and /or from the body; and at least one anchor portion for anchoring at least a portion of the communication channel to surrounding material when implanted in the body; wherein at least one dimension of at least one said anchor portion, transverse to the longitudinal direction of the communication channel, is greater than the corresponding transverse dimension of the apparatus adjacent to the anchor portion .

Advantageously, the third aspect of the invention provides an apparatus including a means for anchoring at least a portion of the communication channel with respect to the surrounding tissue when implanted in the body. In particular, this reduces movement between the anchor portion or the apparatus and a site of interest, for example, a neuron. The anchor portion may be located at the ^Λopen' end of the communication channel, which is adapted to be positioned at the site of interest when inserted or implanted in the body. Preferably, the anchor portion is located distally from a tethering or fixation point of the apparatus used to tether the apparatus to the body.

At least one anchor portion may comprise a substantially spheroid or ovoid or ellipsoid portion.

Preferably, at least one said anchor portion comprises polyimide .

At least one communication channel may be an electrode for transmitting electrical signals to and /or from the body.

According to a fourth aspect of the invention, there is provided an electrode for insertion into a human or animal body for communicating electrical signals to and /or from the body, the electrode comprising: at least one electrical conductor for communicating electrical signals to and /or from the body; and at least one anchor portion for anchoring at least a portion of the electrode to surrounding material when implanted in the body, wherein at least one dimension of at least one said anchor portion, transverse to the longitudinal direction of the electrode, is greater than the corresponding transverse dimension of the electrode adjacent to the anchor portion.

According to a fifth aspect of the invention, there is provided an assembly comprising an apparatus according to the first or third aspects; and a needle or rod to which at least one said communication channel is removably attached, for enabling insertion of said at least one communication channel into the body.

According to a sixth aspect of the invention, there is provided a method for preparing an apparatus according to the third aspect, the method comprising the steps of: providing at least one communication channel for communicating signals and /or fluid to and /or from a human or animal body; dipping a portion of said at least one communication channel into a liquid polymer to form a droplet of the liquid polymer on said portion of said at least one communication channel; allowing the liquid to form a substantially spheroid or ovoid or ellipsoid of solid polymer on said portion of said at least one communication channel.

Advantageously, the sixth aspect of the present invention provides a method for forming the anchor portion of an apparatus according to the third aspect of the present invention. This method may be used to form a three- dimensional anchor portion when the support and/or communication channel are fabricated using micro-fabrication techniques which result in planar devices. The solution may comprise polyimide.

At least one communication channel may be an electrode.

The method may further comprise the step of: passing current through the at least one electrode to expose the end of the electrode embedded in the polymer.

According to a seventh aspect of the invention, there is provided a method for implanting an apparatus according to any of the first or third aspects of the invention into a human or animal body, the method comprising the steps of: securing an apparatus according to the first or third aspects to a needle using a glue dissolvable in the body; inserting the needle and apparatus into the body; allowing the glue to dissolve; and removing the needle from the body, leaving the apparatus in the body.

The present invention is based at least in part on the realisation that a major contributor to the progressive deterioration in performance of implanted electrodes is likely to be low-level mechanical trauma occurring due to the elasticity of the brain and its suspension within cerebrospinal fluid in the subarachnoid space. A rigid electrode tethered or fixed to the surface of the brain, or to the skull, transmits mechanical forces to its recording tip during natural head movements and evidence suggests that resulting micro-movements of the tip relative to the surrounding neural tissue are a major cause of sustained glial reactivity. A novel electrode has been developed using micro- electro-mechanical systems (MEMS) techniques specifically to minimise mechanical coupling between each end of the electrode. Preliminary evidence suggests that it shows substantially improved long- term recording characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawing, in which:

Figure 1 is a side view of an electrode embodying the present invention;

Figure 2 illustrates an end portion of the electrode of Figure 1;

Figure 3 is a detailed cross sectional view of a first end of the electrode of Figure 1;

Figure 4 illustrates a bond pad at a second end of the electrode of Figure 2;

Figure 5 shows an array of wafers, each wafer comprising ten electrodes according to the present invention;

Figure 6 shows results of tests of the electrode of Figure 1 ; and

Figure 7 illustrates an application of the electrode of Figure 1 to closed-loop neurostimulation.

DETAILED DESCRIPTION OF EMBODIMENTS

Figures 1 to 4 show an electrode 1 embodying the present invention, suitable for implantation in the brain for recording spike activity from individual neurons. The electrode comprises a shaft 3, having a recording end 5 embedded in an anchor 9, and terminating at its opposite end in a bond pad 7. Three conductive tracks 11 are formed along the length of the electrode shaft 3, extending from the bond pad 7 to the recording end 5. When implanted in the brain to record neural activity, the electrode 1 is fixed in place by tethering it either to the surface of the brain or to the skull, at a point close to the bond pad 7. As will be appreciated by person skilled in the art, the electrode can be tethered in a number of possible ways, for example by covering in a dental acrylic resin, which coats everything and attaches to skull screws, or by gluing to the brain surface with a cyanoacrylate surgical glue.

The electrode shaft 3 is planar and is manufactured using conventional photolithographic methods from parylene C (poly- monochloro-para-xylylene) on a silicon oxide substrate. Three conductive tracks 11 of 80/20 tungsten/titanium are deposited on the electrode shaft 3, and are electrically insulated along their length by an overlying layer of parylene C.

Using photolithographic techniques, very small structures can be realised. The conductive tracks 11 have a depth of 1 μm and a width of 5 μm, with 5 μm spacing between the tracks 11 and 5 μm insulation along each edge, and are encased between two 10 μm deep layers of parylene C. The electrode shaft 3 has a small cross-sectional area, having dimensions transverse to the longitudinal path of the conducting tracks of only 20 μm deep and 35μm wide, and, being made of parylene C, is more compliant than conventional metal electrodes. The small cross-sectional dimensions of the electrode 1 helps to reduce the transmission of tethering forces to the recording end 5 of the electrode 1 and facilitates insertion of the electrode 1 into the body.

The recording end 5 of the electrode shaft 3 is a parylene C disc of radius 50 μm, out of which the recording ends 13 of the three conductive tracks 11 protrude, the area of the exposed sites being 20 μm x 1 μm each. The presence of three exposed recording sites 13 permits triangulation for more effective separation of action potentials from different neurons. However, it is not necessary to provide three conducting tracks 11. The present invention is applicable to a single conducting track 11 or to a plurality of conducting tracks 11 .

The electrode shaft 3 is about 5.5 mm long and has a sinusoidal profile longitudinally, comprising 10 sinusoidal cycles of lOOμm amplitude and 500 μm period. The sinusoidal profile greatly reduces the transmission of mechanical forces from the fixation point on the surface of the brain, or on the skull, to the recording tip 5. This is because relative movement between the ends of the electrode can be accommodated by flexing of the electrode shaft 3. Thus, in use, micromotion of the recording ends 13 of the electrode 1 relative to the surrounding neural tissue, due to relative movement between the recording site and the tethering or fixation point (by which the electrode is fixed to the surface of the brain, or to the skull) , is greatly reduced. The length of the electrode shaft 3 is greater than the distance between its ends, and so the electrode shaft 3 can accommodate relative movement of the ends of the electrode in all directions.

Although the present embodiment has a sinusoidal profile, other longitudinal profiles can be used, provided that the length of the electrode shaft 3 is greater than the distance between its ends. This requires only that the shaft 3 has one or more bends or undulations along its length. The bends may be smoothly curved or angular. For example, the profile of the shaft 3 may be a zig-zag shape, or may have a randomly meandering profile. A portion of the shaft 3 may be straight. Preferably, the electrode shaft 3 has a plurality of bends or undulations along its length, since this allows a greater length change to be accommodated, without unduly increasing the amplitude of the bends or undulations. Alternatively, the electrode shaft 3 need not be planar, but could comprise a flexible insulated conductor coiled around a further support such as a needle or rod.

The electrode 1 also includes a bead 9 of polyimide having a radius of approximately 50 μm to act as an anchor to hold the electrode tip 5 in place when implanted. This anchor 9 further reduces movement of the recording end 5 of the electrode 1 relative to its surroundings. Polyimide is close to neutrally buoyant in the brain, as it has a density of about 1.43g/ml, which is close to the density of the brain, which is about 1.05g/ml. Therefore, when implanted, the anchor 9 exerts low inertial forces on the surrounding tissue. The polyimide bead 9 is added post-fabrication to the parylene C disc at the recording end 5 of the electrode, as will be described below. This allows a substantially spheroid, or ovoid or ellipsoid, anchor 9 to be formed on an otherwise planar electrode. The substantially spheroid shape of the anchor 9 effectively anchors the tip 5 of the electrode 1 in all three directions. Although the anchor 9 is preferably located at the recording end 5 of the electrode as shown in Figures 1 to 4, the anchor 9 may be located at any position between the tethering point of the electrode and the recording end 5 of the electrode. The electrode 1 may include more than one anchor 9.

The electrode shaft 3 connects to a bond pad 7 (Figure 4) which is approximately a square of size 325 μm by 400 μm in the first embodiment, and houses three 75 μm by 75 μm connection squares 15 made of the same material as the conductive tracks 11 (80/20 tungsten/titanium) . Each conductive track 11 terminates in a respective connection square 15 on the bond pad 7. External connections to the bond pad 7 are made via three 30 μm diameter holes 17 over the metal connection squares 15 that go through the entire device "sandwich" (two 10 μm thick parylene layers encasing the three parallel 1 μm thick conductive tracks 11), which leaves a metal ring exposed at the midpoint of the cylinders created by the holes 17.

Arrays of electrodes, comprising the electrode shaft 3, and bond pad 7, are manufactured using conventional photolithographic methods. The arrays of electrodes are produced on 4 inch silicon wafers held by a 1 μm silicon oxide layer. Each silicon wafer, shown in Figure 5, holds 48 lcm² dies each containing 10 electrodes, giving a total of 480 devices per wafer.

A concentrated (48%) hydrofluoric acid (HF) etch is used to release the electrodes from the wafer. To release the 20 urn wide electrode shaft 3 from the 1 μm layer of silicon oxide usually requires an etch time of about 30 minutes. However, the bond pad 7 is much larger than the electrode shaft 3 and the thin silicon oxide layer presents a wetting problem for the HF, so a much longer etch time may be required. An etch time of around 72 hours (three days) is sufficient to release approximately 80% of the electrodes from the silicon wafer. At the end of the etch time, the electrodes are removed from the HF by pouring through filter paper. The electrodes are then left to dry.

The electrodes, once released from the silicon wafer, are sandwiched between pieces of soft rubber, leaving the bond pad 7 exposed and the recording end 5 of each electrode protruding beyond the sides of the rubber. This is to simultaneously provide a secure but soft area underneath the bond pad 7 for wiring and also to allow space around the recording end for the addition of the polyimide sphere via pipette.

A small amount of liquid polymer, polyimide (Dupont, PI2555) , is applied to the recording end 5 of the electrode 1 via a disposable 5 ml pipette. The polyimide is dissolved in a solvent N-Methyl 2-Pyrrolidone which evaporates off. In order to increase the viscosity of the polyimide, a small Petri dish of the polymer is left for 24 to 48 hours in order for approximately half of the solvent to evaporate off. The polymer is then viscous enough to leave a small amount on the electrode head which then forms a sphere located on the parylene disc under its own surface tension. The pipette is filled with a small amount of the polymer and a bead is formed on the end of the pipette. Under low magnification (Sx-IOx) the recording ends 5 of each electrode 1 can be distinguished and the bead is pushed onto the electrode tip 5 and then removed, leaving a small amount of polymer on the parylene disc at the recording end 5 of the electrode shaft 3. One bead of polymer from the pipette is sufficient to add a polymer sphere to many electrodes. Once the polyimide bead 9 has been added to the recording end 5 of the electrode 1, it is necessary to expose the tips 13 of the conducting tracks 11 by removing the polyimide covering them.

To do so, the recording end 5 of the electrode is immersed in saline solution, and a voltage applied between the electrode and saline is gradually increased until some evidence of conduction, such as a reduction in impedance, or the appearance of bubbles at the tip 5 is observed.

The electrodes are wired using 20 μm diameter stainless steel wire coated in approximately 5 μm of formvar insulator (Advent Research Materials, Fe633711) which can be burnt or scraped off with a scalpel to expose bare wire. Generally the ends of the wire are exposed and then one end is crimped to a gold plug. The other exposed end is then positioned over a connection square of the bond pad and held in place with a small amount of rubber. Under 3Ox magnification a small amount of silver paste (RS Components, 186-3593} diluted with the solvent butyl acetate (Fluka, 45860) on a thin wire or syringe can be used to connect the exposed end of the wire to a connection square of the bond pad. After drying for around 20 minutes, Araldite epoxy is used in a stepwise fashion to slowly insulate the bond pad by adding small layers, allowing each layer of epoxy to dry between applications for about 4 hours .

The small cross-sectional area of the electrode and sinusoidal shaft make it a highly flexible structure, which is not capable of penetrating the cortex unsupported. In order to implant the electrode into the brain, the electrode may be attached to a sharpened rod using polyethylene glycol (PEG) which dissolves in the brain allowing the rod to be withdrawn. In tests of the insertion method, approximately 60-80% of our penetrations resulted in successful implantation of the electrode. The main cause of failure of the insertion technique is the PEG dissolving or breaking too early. The electrodes are then tethered to the skull using dental acrylic resin. However, also electrodes could be tethered to surface of brain using cyano-acrylate glue.

The recording end 5 of the electrode 1 is positioned at a site of interest, for example to record spike activity from a single neuron. Movement of the recording end 5 of the electrode relative to the site of interest is minimised by the anchor 9 and by the shape of the electrode 1, which reduces the transmission of mechanical forces from the tethering point to the recording end 5 of the electrode. Thus, natural head movements which cause relative movement between the tethering point on the brain surface or skull and the site of interest, result in relative movement between the ends of the electrode, thereby reducing any relative movement between the recording end 5 of the electrode and the site of interest.

Initial tests of the electrodes described with reference to Figures 1 to 4 have been made by implanting the electrodes in the sensorimotor cortex of rabbits, an ideal model system for characterising long-term performance. Preliminary chronic recordings of neural activity made in the rabbit demonstrate that the recorded signal to noise ratio remains stable for at least for 6 months post-implant. Figure 6 shows recordings of neural activity made in the rabbit obtained using the electrode of Figures 1 to 4. During this test, the three conductive tracks 11 were shorted together by the wiring to the bond pad 7, such that triangulation could not be used to separate multiple neurons. However, comparison of the recordings made 1 week post-implant {Upper graph of Figure 6} and 6 months post-implant (Lower graph of Figure 6) show that the signal to noise ratio remains substantially stable over this period.

The electrode described above is suitable for both recording neural activity and as a neurostimulation device. In addition to use in the cortex, the electrode described above is also suitable for use in the spinal cord, which currently suffers similar problems of gliosis as seen in the cortex. For example, such electrodes could be used for delivering electrical stimulation to the spinal cord, in applications such as upper-limb FES, and for treatments following spinal cord injury. Different metals may be used for the conductive tracks according to the specific application. For example, although 80/20 tungsten/titanium alloy is well-suited to neural recording, different metals may be preferred for neural stimulation.

Electrodes according to the present invention may also be used in a closed-loop neurostimulation system. A schematic of a suitable closed-loop neurostimulation device is shown in Figure 7. The system consists of (i) recording electrodes 200 implanted in the cortex, (ii) a headstage 202 located close to the recording electrodes, (iii) an implanted processor and stimulation unit 204 located in the subclavicular space, (iv) stimulation electrodes (not shown) connected to the stimulation unit and located at the target site according to the specific application, and (v) an external power supply and calibration interface 206 connected via a short-range wireless link.

It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims .

While the present invention has been described with particular reference to electrodes for neural recording and /or stimulation, the present invention is applicable to any implanted micro-device, in particular In applications in which it is desirable to reduce relative movement between the open end of a communication channel and the surrounding tissue in which it is implanted, or to reduce the transmission of mechanical forces along the length of a communication channel. The electrode described above is one example of such a communication channel. The communication channel or channels of the present invention may alternatively be optical fibres or microfluidic channels, equipped with suitable connectors for connection to external optical fibres or fluid conduits respectively. In this way, the apparatus may be adapted for delivery and/or recording of optical signals, or for delivery and/or extraction of fluids.

In particular, the longitudinal profile of the apparatus may take a variety of different forms, as described above in relation to the specific embodiments, provided that length of the communication channel is greater than the distance between its ends. The support may be flexible, or rigid to aid implantation, and may be removably attached to the electrode shaft 3, using, for example, a dissolvable substance such as PEG, such that the support may be removed from the body following implantation of the electrode 1.

The communication channel 11 of the apparatus 1 may be attached to different types of support, depending on its configuration. For example, one or more communication channels 11 may be attached to a planar substrate as in the specific embodiments described above; alternatively, a communication channel 11 may be supported by an insulating covering, or it may be supported by a dissolvable glue on a further support such as a needle or rod; alternatively, a communication channel 11 may be resiliently self-supporting, in which case the material or walls of the communication channel itself may provide the support.

Claims

1. An apparatus for insertion into a human or animal body for communicating signals and /or fluid to and /or from the body, the apparatus comprising: at least one communication channel for communicating signals and /or fluid to and /or from the body, the communication channel having a first end and a second end; and at least one support for supporting the or each communication channel, such that the length of the communication channel is greater than the distance between the first and second ends; wherein the communication channel is flexible such that changes in said distance between the first and second ends of the communication channel can be accommodated.

2. An apparatus according to claim 1, wherein at least one said communication channel comprises a plurality of bends or undulations.

3. An apparatus according to claim 2, wherein at least a portion of at least one said communication channel is substantially sinusoidal.

4. An apparatus according to claim 2 or claim 3, wherein at least a portion of at least one said communication channel is coiled.

5. An apparatus according to any of the preceding claims, wherein the first end of at least one said communication channel is adapted for communicative connection to a further communication channel.

6. An apparatus according to any of the preceding claims, wherein at least one communication channel is a fluid conduit for delivering fluid to and /or receiving fluid from the body.

7. An apparatus according to any of the preceding claims, wherein at least one communication channel is an optical fibre for transmitting light to and /or from the body.

8. An apparatus according to any of the preceding claims, wherein at least one communication channel is an electrode for transmitting electrical signals to and /or from the body.

9. An apparatus according to claim 8, wherein the support comprises an electrically insulating layer for electrically insulating the electrode between its ends .

10. An apparatus according to any of the preceding claims, wherein the communication channel and support form a planar arrangement.

11. An apparatus according to any of the preceding claims, wherein the support includes poly-monochloro-para- xylylene .

12. An apparatus according to any of the preceding claims, further comprising one or more anchor portions for anchoring at least a portion of the communication channel to surrounding material when implanted in the body.

13. An apparatus according to claim 12, wherein at least one anchor portion comprises a substantially spheroid or ovoid or ellipsoid portion.

14. An apparatus according to claim 12 or claim 13, wherein at least one said anchor portion comprises a material having a density close to the density of the surrounding tissue.

15. An apparatus according to any of claims 12 to 14, wherein at least one said anchor portion comprises polyimide .

16. An electrode for insertion into a human or animal body for communicating electrical signals to and /or from the body, the electrode comprising: at least one electrical conductor for communicating electrical signals to and /or from the body, the conductor having a first end and a second end; and at least one support for supporting the or each conductor such that the distance between the ends of the conductor is less than the length of the conductor; wherein at least one said conductor comprises a plurality of bends or undulations, and the electrode is flexible, such that changes in said distance between the ends of the conductor can be accommodated.

17. An apparatus for insertion into a human or animal body for communicating signals and /or fluid to and /or from the body, the apparatus comprising: at least one communication channel for communicating signals and /or fluid to and /or from the body; and at least one anchor portion for anchoring at least a portion of the communication channel to surrounding material when implanted in the body; wherein at least one dimension of at least one said anchor portion, transverse to the longitudinal direction of the communication channel, is greater than the corresponding transverse dimension of the apparatus adjacent to the anchor portion.

18. An apparatus according to any of claim 17, wherein at least one anchor portion comprises a substantially spheroid or ovoid or ellipsoid portion.

19. An apparatus according to claim 17 or claim 18, wherein at least one said anchor portion comprises a material having a density close to the density of the surrounding tissue.

20. An apparatus according to any of claims 17 to 19, wherein at least one said anchor portion comprises polyimide .

21. An apparatus according to any of claims 17 to 20, wherein at least one communication channel is a fluid conduit for delivering fluid to and /or receiving fluid from the body.

22. An apparatus according to any of claims 17 to 21, wherein at least one communication channel is an optical fibre for transmitting light to and /or from the body.

23. An apparatus according to any of claims 17 to 22, wherein at least one communication channel is an electrode for transmitting electrical signals to and /or from the body.

24. An electrode for insertion into a human or animal body for communicating electrical signals to and /or from the body, the electrode comprising: at least one electrical conductor for communicating electrical signals to and /or from the body; and at least one anchor portion for anchoring at least a portion of the electrode to surrounding material when implanted in the body, wherein at least one dimension of at least one said anchor portion, transverse to the longitudinal direction of the electrode, is greater than the corresponding transverse dimension of the electrode adjacent to the anchor portion.

25. An assembly comprising: an apparatus according to any of claims 1 to 15 or 17 to 23; and a needle or rod to which at least one said communication channel is removably attached, for enabling insertion of said at least one communication channel into the body.

26. A method for preparing an apparatus according to any of claims 1 to 15 or 17 to 23, the method comprising the steps of: providing at least one communication channel for communicating signals and /or fluid to and /or from a human or animal body; dipping a portion of said at least one communication channel into a liquid polymer to form a droplet of the liquid polymer on said portion of said at least one communication channel; allowing the liquid to form a substantially spheroid or ovoid or ellipsoid of solid polymer on said portion of said at least one communication channel.

27. The method according to claim 26, wherein the polymer comprises polyimide.

28. The method of claim 26 or claim 27, wherein at least one communication channel is an electrode .

29. The method according to claim 28 , further comprising the step of: passing current through the at least one electrode to expose said portion of the electrode embedded in the polymer.

30. A method for implanting an apparatus according to any of claims 1 to 15 or 17 to 23 into a human or animal body, the method comprising the steps of: securing an apparatus according to any of claims 1 to 15 or 17 to 23 to a needle using a glue dissolvable in the body; inserting the needle and apparatus into the body; allowing the glue to dissolve; and removing the needle from the body, leaving the apparatus in the body.