Nerve contact devices

Abstract

A material comprising an ionically conducting polymer (ICP) positioned between and in direct contact with two electronically conducting polymers (ECP).

Claims

1. A material comprising a tri-layer polymeric system, wherein the tri-layer polymeric system consists of an ionically conducting polymer (ICP) positioned between and in direct contact with two electronically conducting polymers (ECP), wherein the ICP is hydrophilic.

2. The material according to claim 1, wherein the direct contact is facilitated by the application of pressure.

3. The material according to claim 1, obtainable by polymerisation of monomers to form the ICP in contact with each ECP.

4. The material according to claim 1, obtainable by polymerisation of monomers to form each ECP in contact with the ICP.

5. The material according to claim 1, wherein the ICP is interlinked to each ECP via an interpenetrated network.

6. The material according to claim 4, wherein the polymerisation is conducted in defined areas only.

7. The material according to claim 1, which has a conductivity of at least 5×10.sup.−2 S/m.

8. The material according to claim 1, wherein the ICP is cross-linked.

9. The material according to claim 1, which is a spiral shape.

10. The material according to claim 1, which has been pre-stressed.

11. The material according to claim 10, which is a spiral shape, and which has been pre-stressed into a substantially straight strip, such that it can fold around a nerve fibre.

12. A membrane-electrode assembly comprising, as the membrane, the material according to claim 1.

13. A nerve contact device comprising the material according to claim 1.

14. A prosthetic device comprising, at a surface intended to contact viable nerves, the material according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic view of application of a bi-directional neural contact, according to an embodiment of the subject invention.

(2) FIG. 2 is a schematic view illustrating single junctions with catalyst inclusion, according to an embodiment of the subject invention.

(3) FIG. 3 is a schematic view illustrating examples of hydrophilic pre-stressing and recovery, according to an embodiment of the subject invention.

DESCRIPTION OF THE INVENTION

(4) While no material is exclusively restricted to one or the other mode of conduction, for practical purposes ratios of electronic:ionic conduction greater than 20:1 (for an ECP) and 1:20 (for an ICP) make it possible to construct working devices of acceptable efficiency.

(5) As used herein, the term “material” should be understood to encompass composite materials, such as those used in accordance with the invention. Therefore, a “material” is preferably a “composite material”.

(6) As used herein, the term “monomer” takes its usual definition in the art, and so refers to a molecular compound that may chemically bind to other monomers to form a polymer.

(7) As used herein, the term “hydrophilic polymer” refers to a polymer that dissolves in water when it is not cross-linked and absorbs water and swells to form a stable elastic solid when cross-linked.

(8) A hydrophilic ICP may be produced by processes similar to those described in GB2380055A, e.g. by dissolving or mixing the monomers forming the ionically conductive material (e.g. AMPSA) in/with monomers chosen to provide hydrophilic properties (e.g. vinyl pyrrolidinone (VP) and/or 2-hydroxyethyl methacrylate (HEMA) and/or acrylonitrile (AN)) and polymerising and crosslinking the resulting monomer mixture by suitable means including gamma irradiation, UV irradiation in the presence of a suitable UV initiator and crosslinking agent or by thermal polymerisation.

(9) Any ECP that is biocompatible is suitable for use in the invention. For example, an ECP could be formed from the polymerisation of electronically active amino acid(s) such as phenylalanine and/or tryptophan and/or histidine and/or tyrosine. Hydrophilic copolymers containing phenylalanine and tryptophan are most preferred. Likewise hydrophilic copolymers containing PEDOT:PSS may be suitable for use in the invention, but its biocompatibility is as yet unproven.

(10) Metallic conductors, such as those that are necessary in a nerve contact device can be combined with an ECP to improve the overall efficiency of the MEA, e.g. in one example a thin interpenetrated layer of ECP is formed on the surface of the polymeric membrane (preferably a hydrophilic ionomeric membrane) and a metallic conductor in the form of discrete wires or a mesh is then laid onto the ECP, after which a second layer of ECP is deposited over the metallic conductor, making good electrical contact and offering a measure of corrosion protection for the metal components.

(11) According to a first aspect, a material of the invention comprises an ionically conducting polymer (ICP) positioned between and in direct contact with two electronically conducting polymers (ECP).

(12) In some embodiments, the direct contact is facilitated by the application of pressure.

(13) In some embodiments, the ionically conducting polymer (ICP) is interlinked to each electronically conducting polymer (ECP) via an interpenetrated network.

(14) When the junction between the polymeric components is an interpenetrated network, the resulting MEA operates substantially without the need for external pressure or support to maintain its structure and the electrical contacts between the components and layers thereof. This may be advantageous in circumstances where it is difficult to maintain pressure on the material/device.

(15) The invention provides a method for the formation of interprenetrated networks between ionically conducting polymeric materials and electronically conducting polymers in which the junction comprises an interpenetrated region, by the polymerisation of one polymer from an initial monomer mixture in contact with the second material (either starting from the ECP or the ICP). Embodiments of the invention are lightweight, substantially non-metallic membrane electrode assemblies for use in, for example, nerve contact devices.

(16) A material of the invention preferably has a conductivity of at least 5×10.sup.−2 S/m 5×10.sup.2 S/m. It can have a density of no more than 1.8 g/cc.

(17) There are two routes to the production of electronic-ionic interfaces. The two routes arise because it is possible to take either a hydrophilic ionic material or an electronic material as the base structure (substrate). In the first instance, the electronic polymeric material is polymerised against the base material; in the second, it is the ionic material that is introduced as a monomer or pre-polymer and polymerised in situ against the substrate. Such products may appear to be identical although further analysis may show differences in performance.

(18) GB2479449, which is incorporated herein by reference in its entirely, describes how electronically active polymers can be linked to ionically active polymers.

(19) The present invention is based on the finding that bi-directional information flow is possible with the materials of the invention. In the case of a simple bi-layer of ECP and ICP, when it is placed near (or in contact with) a nerve, the material should experience sufficient ionic imbalance to allow a transient signal to be recorded by the electronics attached to the electronic component. The result is a small potential change compared with the surrounding (aqueous) structure which will slowly return to ‘neutral’ as the ion signal decays.

(20) Without wishing to be bound by theory, the tri-layer material of the invention allows for any charge imbalance to be dissipated rapidly (so that repeated signal pulse can be applied). This enables an electronic signal to be received and transmitted to nerve tissue.

(21) The species of ion that is generated in the material of the invention (ICP) depends upon the material of the junction and upon the aqueous solution used to hydrate one or more of the polymeric components. For example, if the system is hydrated in NaCl solution, then the predominant charge carriers within the ionic conductor are sodium ions; if KCl is the hydrating solution, then K.sup.+ ions will result.

(22) It is possible and in some circumstances advantageous to incorporate catalyst materials at or within one or both of the interfaces.

(23) FIG. 1 is a schematic illustrating the invention.

(24) In some embodiments, a material of the invention comprises a catalyst (typically Pt or similar as powder, fibres or thin micro-porous film). This may significantly increase the electro-chemical options for the operation of the device. In particular, it can reduce the potential necessary to initiate operation of the device as a generator of ions or electrons. This is illustrated in FIG. 2 (single junction/interface shown). The critical contact region is formed by the interpenetrating (IP) region between the two polymers (i.e. between the electronically conducting hydrophilic polymer and the ionically conducting hydrophilic polymer). It is (i) permanent, (ii) flexible, and (iii) gas, water, and solute permeable.

(25) In a preferred embodiment, the material has been pre-stressed. Preferably, the material that has been pre-stressed is hydrophilic and/or cross-linked. Preferably, the pre-stressed material can be returned to its original shape by hydrating the material in water. Such structures can return to their original shape when hydrated in water or suitable aqueous solutions. The resulting structure will be larger (in at least one dimension) because of the uptake of water during the hydration process. Although shape change (recovery) may be initiated by heating, hydration activated shape recovery is particularly appropriate to biological systems because it will proceed at normal body temperature.

(26) Many shapes and recovery procedures can be used; however, one particular form is of particular value as a nerve contact device. In this case, the junction region is made as a tight spiral; then pre-stressed in (for example) a straight strip; on hydration it ‘curls up’ and re-assumes the spiral form. In this example the device can be made to fold round the nerve fibre as illustrated in FIG. 3.