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EP-4736197-A1 - METHOD FOR THE PRODUCTION OF STRETCHABLE CONDUCTIVE DEVICES AND DEVICES THUS OBTAINED

EP4736197A1EP 4736197 A1EP4736197 A1EP 4736197A1EP-4736197-A1

Abstract

The present invention relates to a method for the production of devices consisting of an elastomeric polymeric support on which a metallic film is present, which maintains electrical conductivity properties even in the elongation and relaxation cycles of the support. The invention further relates to stretchable conductive devices thus obtained.

Inventors

  • SAINI, Matteo
  • FERRARI, SANDRO
  • SPREAFICO, Laura
  • SADEGHPOUR, Arezoo

Assignees

  • WISE S.P.A.

Dates

Publication Date
20260506
Application Date
20250410

Claims (19)

  1. 1 . Method for the production of stretchable conductive devices which comprises the following steps: a) preparing an elastomeric support on a surface of which there is a first metallic deposit with a thickness of between 10 and 200 nm obtained with a dry method; b) forming a second metallic deposit on top of said first metallic deposit by chemical or electrochemical deposition from a solution; characterized in that said deposition from a solution is carried out simultaneously to, or is followed by, an ultrasound treatment.
  2. 2. Method according to claim 1 , wherein said elastomeric support is made with a polymeric material selected among polyolefin-based elastomers, elastomeric fluoropolymers, polybutadiene (BR), styrene-butadiene rubbers (SBR), ethylenepropylene rubbers (EPR), ethylene-propylene-diene rubbers (EPDM), nitrile rubbers (NBR), acrylic rubbers (ACM), isobutylene-isoprene rubbers (HR), copolyesters, neoprene (polychloroprene), polyurethane rubbers and polysiloxanes (silicones).
  3. 3. Method according to any one of claims 1 or 2, wherein said polymeric material is polydimethylsiloxane (PDMS).
  4. 4. Method according to any one of the preceding claims, wherein step a) is carried out with a dry method selected between an evaporation technique and a cluster deposition technique.
  5. 5. Method according to claim 4, wherein said evaporation technique is selected among Chemical Vapor Deposition (CVD), thermal evaporation, electron-beam evaporation and sputtering, and said cluster deposition technique is selected among CBD (Cluster Beam Deposition), SCBD (Supersonic Cluster Beam Deposition) and SCBI (Supersonic Cluster Beam Implantation).
  6. 6. Method according to any one of the preceding claims, wherein the metal of said first deposit is platinum.
  7. 7. Method according to any one of the preceding claims, wherein step b) is carried out by chemical reduction in solution of a salt or a complex of the metal of the second deposit by means of a reducing agent.
  8. 8. Method according to claim 7 in which the metal of the second deposit is chosen from gold, platinum and iridium; tetrachloroauric acid, hexachloroplatinic acid and hexachloroiridic acid are used respectively as precursors of the metals; and the reducing agent is hydrogen peroxide in the case of gold and hydrazine in the case of platinum and iridium.
  9. 9. Method according to any one of claims 7 and 8, wherein step b) is carried out at a temperature between 5 and 80 °C, preferably between 15 and 70 °C, with a concentration of the metal ion to be reduced between 0.01 and 10 g/L, and the reducing agent is used in a molar ratio between 1 :10 and 1 :1000 with respect to the metal ion to be reduced.
  10. 10. Method according to any one of claims 7 to 9, wherein the solution of step b) further comprises one or more additives selected from surfactants, halogen ions and pH regulators.
  11. 11. Method according to any one of claims 1 to 6, wherein step b) is carried out by electrochemical reduction in solution of a salt or a complex of the metal of the second deposit.
  12. 12. Method according to claim 11 in which the metal of the second deposit is selected among gold, platinum and iridium; and tetrachloroauric acid, hexachloroplatinic acid and hexachloroiridic acid are used respectively as precursors of the metals.
  13. 13. Method according to any one of claims 7 to 12, wherein the thickness of the second metallic deposit is of between 50 and 1000 nm.
  14. 14. Method according to any one of claims 7 to 13, wherein the frequency of the ultrasound applied during or after the formation of the second metallic deposit is between 25 and 80 kHz.
  15. 15. Method according to claim 14, wherein said frequency is between 30 and 50 kHz.
  16. 16. Method according to claim 15, wherein said frequency is about 40 kHz.
  17. 17. Method according to any one of claims 7 to 16, wherein during the application of ultrasound the support is moved linearly with respect to an average position with a speed ranging from 5 mm/s to 20 mm/s, and/or rotated with a speed between 10 and 50 rpm.
  18. 18. Method according to claim 17, wherein the speed at which the support is rotated is between 20 and 30 rpm.
  19. 19. Method according to any one of the preceding claims, in which between step a) and step b) a chemical cleaning operation of the first deposit is carried out using a reducing agent selected among formic acid, hydrazine and an alcohol.

Description

METHOD FOR THE PRODUCTION OF STRETCHABLE CONDUCTIVE DEVICES AND DEVICES THUS OBTAINED *** *** *** FIELD OF THE INVENTION The present invention relates to a method for the production of devices consisting of an elastomeric polymeric support on which a metallic film is present, which maintains the electrical conductivity properties even in the elongation and relaxation cycles of the support. The invention further relates to stretchable conductive devices thus obtained. BACKGROUND ART In many fields of the art, there is a need to establish a stable electrical connection by means of conductors which, in addition to being flexible, are stretchable, i.e., capable of undergoing (reversible) elongations in the direction of electricity conduction. Conductors of this type, which can be elongated along the main direction of electrical conduction while maintaining the conductive properties thereof, are defined in the present text and in the claims as stretchable conductive devices or even simply stretchable conductors. Although the conductors of this type can be used in any situation in which a conductor is required, the intended main application thereof is in the production of electrodes implantable in the human (and animal) body, which requires that said electrodes can follow all the deformations of the part in which they are inserted, thus including elongations and returns to the initial length, without losing continuity and the main electrical features. This category includes, for example, implantable neural interfaces (described for example in WO 2009/090398 A2), deep brain stimulation devices (described for example in WO 2008/035344 A2), electrical stimulation devices of the spine for treating paralysis, and actuators in general, which are capable, for example, of stimulating or replacing muscle movement (known as “artificial muscles”). Given the importance of the latter application, in the remainder of the description reference will be made to implantable products and devices, but it is understood that the products of the invention are also applicable in all other situations in which a stretchable conductor is required. A first proposed methodology for producing conductors with these features consists in preparing metallic lines (wires or thin deposits) with a wavy pattern inside biocompatible elastomeric polymers, making one or more electrical contacts emerge at the surface of the polymer at predefined points depending on the intended application; when the polymer undergoes an elongation, the wavy shape of the metallic line allows the elongation or shortening thereof. Conductors of this type are described for example in patents US 7,085,605 B2 and US 7,265,298 B2. However, the methods of these patents are not entirely satisfactory. Firstly, they are quite laborious and therefore not suitable for the transfer to production on an industrial scale; secondly, the products obtained with these methods are resistant to traction only in the average direction of the track (i.e. , in the median direction of the undulation or corrugation). A second approach is described in patent US 9,107,592 B2, and consists in depositing (with known methods) metallic tracks on a pre-stressed elastomer; after deposition, the elastomer is allowed to return to its size “at rest” and the metallic deposit geometrically rearranges to follow the contraction thereof. In this case, however, the metallic deposit is compressed in the resting elastomer; this can first involve a variation in the mechanical properties of the surface of the elastomer on which the metallic deposit is formed, which can induce the fracturing thereof during the repeated elongation and relaxation cycles to which the product will be subjected. Furthermore, also the products obtained with these methods are resistant to traction only in the direction along which the elastomer was initially pre-tensioned, and for a maximum extension equal to such a pre-tensioning. Another approach is described in international patent application WO 2011/121017 A1 to the present Applicant. According to this method, the conductive line is created by implanting nano-sized aggregates of metals (for example, titanium) in an elastic polymer; the examples reported in the application demonstrate that, despite the deposit consisting of discrete particles, electrical continuity is guaranteed, as well as the maintenance thereof even after tens of thousands of elongation/shortening cycles of the conductor. The process described in this application also comprises the possibility of growing a continuous metallic layer, for example by electrochemical (galvanic) deposition, on top of the deposit obtained by nanoparticle implantation if this emerges at the surface of the support; in this case, the conductive layer obtained by particle implantation allows the connection to an external electrical circuit to provide the electrons necessary for electrochemical deposition. However, the method of this document is