SHAPE-ADAPTIVE MEDICAL IMPLANT

Abstract

The invention relates to a shape-adaptive medical implant having at least one actuator, by means of which the implant can be changed from a first implant geometry to a second implant geometry, the implant having a different geometric shape in the second implant geometry from that in the first implant geometry, wherein the actuator has a swellable chemical substance which swells when supplied with liquid, and wherein the implant has at least one liquid transport means, which is designed to supply liquid present outside the implant to the swellable chemical substance. The invention also relates to the use of an electrical signal source.

Claims

1. A shape-adaptive medical implant comprising: at least one actuator for changing the implant from a first implant geometry to a second implant geometry, the implant having a different geometric shape in the second implant geometry than in the first implant geometry, the at least one actuator having a swellable chemical substance which swells as a consequence of supply of liquid, and the implant having at least one liquid-transport means configured to supply liquid present outside the implant to the swellable chemical substance; and one of, a plurality of, or all of the following features a), b), c), d): a) the implant has an electrical signal-delivery arrangement suppliable with electrical signals, wherein the electrical signal-delivery arrangement comprises an arrangement of electrical conductors and/or electrodes which is configured to supply the swellable chemical substance of the actuator with an electric and/or electromagnetic field, the swellable chemical substance being configured to convert from a swollen state into a nonswollen state as a consequence of its supply with the electric and/or electromagnetic field by the electrical signal-delivery arrangement, b) the implant has a liquid-tight sealing means composed of a liquid-soluble chemical substance which seals the liquid-transport means in a liquid-tight manner, c) the implant or actuator has a lateral limiting means for limiting the lateral expansion of the implant and/or of the actuator as a consequence of the swelling of the swellable chemical substance is limited, and d) the actuator or the swellable chemical substance contains an ionic medicament for delivery of active ingredient after implantation of the implant in the body.

2. The implant as claimed in claim 1 wherein the swellable chemical substance is, or at least predominantly comprises, a polyelectrolytic hydrogel.

3. The implant as claimed in claim 1 wherein the at least one liquid-transport means has a membrane-type structure and/or has a form of micropores of an outer skin of the actuator.

4. The implant as claimed in claim 1 wherein the liquid-soluble chemical substance of the liquid-tight sealing means is, or at least predominantly comprises, polyvinylpyrrolidone.

5. The implant as claimed in claim 1 wherein the at least one actuator has a fiber reinforcement which is integrated into an outer skin or is attached thereto.

6. The implant as claimed in claim 5 wherein the fiber reinforcement is in a form of a unidirectional fiber reinforcement.

7. The implant as claimed in claim 5 wherein the electrical signal-delivery arrangement is formed at least in part by electrically conductive fibers of the fiber reinforcement.

8. The implant as claimed in claim 5 wherein at least some fibers of the fiber reinforcement have a linked structure.

9. The implant as claimed in claim 1 wherein the implant is in a form of a cochlear implant and further comprises an electrode support on which stimulation electrodes for the stimulation of the cochlea are arranged.

10. A method to explant an implant according to claim 1 from a state implanted in a body, comprising using an electrical signal source to supply the electrical signal-delivery arrangement with electrical signals sufficient in order to explant the implant from the state implanted in the body.

11. The implant as claimed in claim 6 wherein the unidirectional fiber reinforcement has a fiber direction in a transverse direction of the actuator.

Description

[0031] The invention will be more particularly elucidated below on the basis of exemplary embodiments with use of drawings, where:

[0032] FIG. 1shows a first embodiment of the invention and

[0033] FIG. 2shows a second embodiment of the invention.

[0034] The figures use the same reference signs for elements which correspond to one another.

[0035] FIG. 1 shows, in illustration a), a shape-adaptive medical implant in the form of a cochlear implant in lateral sectional view. Illustrations b) to d) show, in accordance with the sectional plane A-A, the implant in various stages of swelling of the swellable chemical substance.

[0036] The implant 10 has a base body 1, which can be formed from silicone for example, and additionally contacts 2, electrical connecting lines 4, an actuator 3, filled with a swellable chemical substance 30 which is arranged within a flexible shell 31 of the actuator 3. The contacts 2 can form the electrodes, for example cochlea stimulation electrodes. Porous channels in the outer structure of the base body 1 are present as liquid-transport means 5. The contacts 2 and the connecting lines 4 can, for example, be formed from an inert material, for example from platinum.

[0037] Illustration a) shows a cross-section through the implant 10 in the prepared state, i.e., the implant has not yet been implanted into a body. The actuator 3 filled with the swellable chemical substance 30 is closed off from the environment by a silicone sheath formed by the base body 1. The porous channels 5 are closed off by means of a water-soluble polymer 6 which is dispersed therein and which serves as liquid-tight sealing means. As shown by illustration b), the water-soluble polymer 6 dissolves upon contact with an aqueous solution and leaves the porous channels 5, thus a fine porous structure. The porous structure serves as a permeable connection which allows supply of water from the outside into the actuator 3, but at the same time prevents escape of the hydrogel 30 from the actuator 3. As a result of the inflow of water, the hydrogel 30 and thus the entire actuator 3 swells, as depicted by reference sign 7 in illustration d). This generates self-bending of the implant and consequently an adaptive matching of the contours of the implant with a cavity in a body in which the implant was inserted.

[0038] For the use of the invention in an electrode support for cochlear implant systems, the electrode support would have to be reconstructed. The hitherto design of a partially conical silicone cylinder with platinum contacts and platinum wires embedded therein would have to be additionally extended by the swelling hydrogel actuator 3 and the selective permeable membrane. To this end, a silicone rubber with a polyelectrolytic hydrogel 30 introduced therein could be applied on the electrode structures and partially vulcanized. Thereupon, a mixture of a water-soluble powder and a silicone rubber would be applied and completely crosslinked in the next step. Owing to its demonstrated biocompatibility and swellability, a polyacrylamide supplemented with ionic groups would be suitable as polyelectrolytic hydrogel. The polyacrylamide can, for example, be supplemented with ionic groups in the form of acrylic acid groups. For the porous membrane, polyvinylpyrrolidone would be used for example.

[0039] After the implantation of the electrode support, the polyvinylpyrrolidone would dissolve in the chlorinated fluid of the inner ear (perilymph) and leave a defined pore structure 5. Ideally, the inlying hydrogel 30 would, owing to its crosslinked macroscopic structure, not be able to penetrate the pores, but water would be able to flow from the fluid of the inner ear into the hydrogel 30. With increasing water uptake by the hydrogel 30, the electrode support would snuggle up to the target structures and thus reduce the contact between the targeted nerve cells and the electrode contacts.

[0040] To reduce the swelling of the hydrogel 30 in the event of a necessary explanation, it would be possible with an integrated electrical signal-delivery arrangement 9, optionally with the electrode contacts 2, to apply an electric field over the length of the electrode support. Accordingly, when using a swellable chemical substance in the form of an ionic polyacrylamide, the collapse of the hydrogel can be realized within a day with a field strength of from about 0.41 V/cm to 1.66 V/cm.

[0041] In this connection, it is not necessary for the swellable chemical substance to be completely reversibly returnable to the nonswollen state; in many applications, a partial reduction in swelling is sufficient enough.

[0042] FIG. 2 shows one embodiment of the invention in which the implant 10 additionally has lateral limiting means 8, for example in the form of unidirectional reinforcement fibers close to the surface. Illustration a) shows, just as in FIG. 1, a longitudinal section through the implant 10. Illustrations b) and c) show the same states as illustrations b) and c) of FIG. 1.

[0043] In the embodiment as per FIG. 2, the implant does not have a separate electrical signal-delivery arrangement 9. Here, the electrical signal-delivery arrangement is formed by electrically conductive fibers in the form of the reinforcement fibers 8.

[0044] Illustration d) shows the start of the swelling process of the swellable chemical substance, similar to illustration d) of FIG. 1. Via illustration e), it is clarified that the reinforcement fibers 8, which are arranged close to the surface in the base body 1 at its outer surface, limit the lateral swelling of the implant and distinctly reduce it compared with the first embodiment.

[0045] The reinforcement fibers 8 can be in the form of carbon fibers, for example having a diameter in the order of magnitude of 7 micrometers. This makes it possible to readily realize bending radii in the mid-two-digit micrometer range.

[0046] The reinforcement fibers 8 close to the surface do not substantially suppress the desired stretching in the axial direction. Accordingly, what are introduced in the base body are, for example, unidirectional fibers (warp) without cross thread (weft), which can absorb forces in the lateral direction, but not in the axial direction.

[0047] In both embodiments, a second part of the electrical signal-delivery arrangement can be formed by the contacts 2, optionally in conjunction with the connecting lines 4.

[0048] In the case of an implant having a diameter of, for example, 0.8 mm, the necessary field strength for reducing the swelling of the hydrogel can already be achieved with a voltage of 0.066 volts.