Tissue conforming interface body

Abstract

A device including an interface body. The interface body includes a flexible electrode array. The flexible electrode array includes one or more encapsulation layers, one or more electrodes disposed towards a distal end of the flexible electrode array and one or more electrode contact pads, each one of the electrode contact pads contacting one of the electrodes. The interface body also includes a softening polymer layer in direct contact with a surface of at least a portion of at least one of the encapsulation layers. A Young's modulus of the softening polymer layer is decreased by at least 50 percent when wet and at an elevated temperature of at least 35 °C as compared to the Young's modulus of the softening polymer layer when dry and at room temperature.

Description

TISSUE CONFORMING INTERFACE BODYCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 570,143 filed March 26, 2024, by Stuart F. Cogan, et al. entitled “TISSUE CONFORMING INTERFACE BODY”, commonly assigned with this application and incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] This application is directed, in general, to devices, and more specifically, electronic devices that include a flexible electrode array able to conform to curved target surfaces such as present in biological tissues.BACKGROUND

[0003] In the past it has been demonstrated that softening polymers, including shape-memory- polymers (SMP), are able to serve as a substrate body for flexible electronic devices. It can be difficult to achieve the degree of softening necessary to modulate the chronic tissue response (e.g., scar formation such as glial scar formation) and also achieve the electrical encapsulation needed to minimize leakage currents and prevent devices from seeping excess power through the substrate into areas of tissue that are not at electrode sites.SUMMARY

[0004] The present disclosure provides in one embodiment, a device that includes an interface body. The interface body includes a flexible electrode array. The flexible electrode array includes one or more encapsulation layers, one or more electrodes disposed towards a distal end of the flexible electrode array and one or more electrode contact pads, each one of the electrode contact pads contacting one of the electrodes. The interface body also includes a softening polymer layer in direct contact with a surface of at least a portion of at least one of the encapsulation layers. A Young’s modulus of the softening polymer layer is decreased by at least 50 percent when wet and at an elevated temperature of at least 35 °C as compared to the Young’s modulus of the softening polymer layer when dry and at room temperature.

[0005] In some embodiments, the one or more electrode contact pads are connected to conductive interconnects to electrically connect the electrodes to a connector of the interface body. In somesuch embodiments, the connector is a wire bonded connector. In some such embodiments, the conductive interconnects contact electrical contact pads of the connector. In some such embodiments, the conductive interconnects are composed of metals including: gold, platinum, titanium, tantalum, nickel, chromium, tungsten or alloys thereof. In some such embodiments, the conductive interconnects are adhered to at least one of the encapsulation layers by a transfer-by- polymerization process, such as disclosed in US Patent no. 11 ,013,835, which is incorporated by reference in its entirety herein.

[0006] In some embodiments, the one or more encapsulation layers include one or more polyimide layers, one or more amorphous silicon carbide layers, one or more silicon nitride layers, one or more liquid crystal polymer layers or combinations thereof.

[0007] In some embodiments, the flexible electrode array includes a cross-sectional structure with asymmetric intrinsic or induced residual stresses with respect to a neutral axis of the flexible electrode array. In some such embodiments, one or more the one or more encapsulation layers or a conductive interconnect layer include the asymmetric intrinsic or induced residual stresses with respect to the neutral axis of the flexible electrode array.

[0008] In some embodiment, the interface body includes two or more of the softening polymer layers.

[0009] In some embodiments, when the softening polymer layer is wet and at the elevated temperature, asymmetric intrinsic or induced residual stresses of the flexible electrode array cause the interface body to contour to a curved target body surface.

[0010] In some embodiments, the softening polymer layer is attached to the encapsulation layers by a mechanical interlock, an adhesive bond or combination thereof.

[0011] In some embodiments, when dry and at room temperature, the softening polymer layer has a Young’s modulus that is greater than a Young’s modulus of the flexible electrode array.

[0012] In some embodiments, the Young’s modulus of the softening polymer layer is decreased by at least 90 percent when wet and at the elevated temperature. In some embodiments, the Young’s modulus of the softening polymer layer is decreased by at least 99 percent when wet and at the elevated temperature.

[0013] In some embodiments, the softening polymer layer has a polymer backbone obtained by polymerization of thiol, acrylate, alkene or epoxy monomers. In some such embodiments a chain of covalently bonded monomers that form the polymer backbone is free of ester groups.

[0014] In some embodiments, the softening polymer layer includes between about 5% and 50% of the thiol monomers, the electrodes include gold, and at least one of the encapsulation layers is a silicon carbide layer and at least another one of the encapsulation layers is a polyimide layer.

[0015] In some embodiments, the softening polymer layer includes between about 5% and 50% of the thiol monomers, the electrodes include gold, the electrode contact pads includes titanium nitride, ruthenium oxide or iridium oxide, and at least one of the encapsulation layers is a silicon carbide layer and at least another one of the encapsulation layers is a polyimide layer.BRIEF DESCRIPTION OF FIGURES

[0016] For a more complete understanding of the present disclosure, reference is now made to the following detailed description taken in conjunction with the accompanying FIGURES, in which:

[0017] FIG. la presents perspective view of a portion of an example embodiment of a device of the disclosure;

[0018] FIG. lb presents a cross-sectional view of the device shown in FIG. la, along view line A— A’;

[0019] FIG. 2 presents a cross-sectional view of a portion of another example embodiment of the device of the disclosure, analogous to the view shown in FIG. lb;

[0020] FIG. 3 presents a cross-sectional view of a portion of another example embodiment of the device of the disclosure, showing an electrode site of the device;

[0021] FIG. 4a shows a plan view of another example embodiment of the device of the disclosure showing the interface body with a two-dimensional electrode array;

[0022] FIG. 4b presents a cross-sectional view of a portion of another example embodiment of the device of the disclosure showing the interface body with plurality of electrodes arranged as an electrode array;

[0023] FIG. 4c shows a cross-sectional view of a portion of the embodiment of the device analogous to that shown in FIG. 4b with the interface body conforming to a non-planar target surface;

[0024] FIGs. 5a presents a cross-sectional view of a portion of another example embodiment of the device where a flexible electrode array is located along a neutral axis of the interface body;

[0025] FIGs. 5b presents a cross-sectional view of a portion of another example embodiment of the device where a flexible electrode array is displaced from a neutral axis of the interface body;

[0026] FIGs. 6a presents a cross-sectional view of the portion of the example embodiment showed FIG. 5b and whereupon softening of the SP layers, the tissue interface body acquires a curled shape due to the flexible electrode array having a compressive intrinsic residual stress;

[0027] FIGs. 6b presents a cross-sectional view of the portion of the example embodiment showed FIG. 5b and whereupon softening of the SP layers, the interface body acquires a curled shape due to the polyimide layer having a tensile intrinsic residual stress;

[0028] FIG. 7 presents a cross-sectional view of a portion of another example embodiment of the device with the flexible electrode array including two polyimide layers and two amorphous silicon carbide layers;

[0029] FIG. 8 presents a cross-sectional view of a portion of another example embodiment of the device with the flexible electrode array including two polyimide layers and two amorphous silicon carbide layers, the two amorphous silicon carbide layers having different widths;

[0030] FIG. 9a presents a cross-sectional view of a portion of another example embodiment of the device with the flexible electrode array including two polyimide layers and two amorphous silicon carbide layers enclosed by the polyimide layers;

[0031] FIG. 9b presents an isometric view of a portion of a device embodiment analogous to that shown in FIG. 9a;

[0032] FIG. 9c presents a plan view of a portion of a device embodiment analogous to that shown in FIG. 9a;

[0033] FIG. 10a presents a plan view of a portion of the device illustrating example intrinsic compressive or tensile residual stress lines in the flexible electrode array;

[0034] FIG. 10b presents a cross-sectional view of a portion of the device analogous to that shown in FIG. 10a with intrinsic compressive residual stress in the flexible electrode array;

[0035] FIG. 10c present a perspective view of a portion of the device analogous to that shown in FIG. 10a with intrinsic tensile residual stress in the flexible electrode array;

[0036] FIG. 1 la presents a plan view of a portion of a device embodiment analogous to that shown in FIG. 10a with exterior openings depicted in the flexible electrode array;

[0037] FIG. 1 lb presents a plan view of a portion of a device embodiment analogous to that shown in FIG. 10a with interior openings depicted in the flexible electrode array;

[0038] FIG. 12a presents a plan view of a portion of a device embodiment analogous to that shown in FIG. 10a with exterior and interior openings depicted in the flexible electrode array;

[0039] FIG. 12b presents a cross-sectional view of a portion of a device analogous to that shown in FIG. 10a with an interior opening depicted in the flexible electrode array;

[0040] FIG. 12c presents an isometric view of a portion of a device embodiment analogous to that shown in FIG. 12a; and

[0041] FIGs. 13a- 13e presents cross-sectional schematic views of a portion of example embodiments of an interface body of the device at different stages of assembly and interfacing with a target biological tissue.DETAILED DESCRIPTION

[0042] One embodiment of the disclosure is a device (e.g., a medical electronic device in some embodiments).

[0043] FIG. la presents a perspective view of a portion of an example embodiment of a device 100 of the disclosure, FIG. lb presents a cross-sectional view of the device shown in FIG. la, along view line A — A’, FIG. 2 presents a cross-sectional view of a portion of another example embodiment of the device of the disclosure, analogous to the view shown in FIG. lb and FIG. 3 presents a cross-sectional view of a portion of another example embodiment of the device of the disclosure, showing an electrode 120 of the device,

[0044] With continuing reference to FIGs. la-13e throughout, the device 100 includes an interface body 105 (e.g., a tissue interface body in some embodiments). The interface body 105 can include a flexible electrode array 1 10. The flexible electrode array includes one or more encapsulation layers 115, one or more electrodes 120 disposed towards a distal end 142 of the flexible electrode array, and one or more electrode contact pads 125, each one of the electrode contact pads contacting one of the electrodes.

[0045] As further illustrated, embodiments the interface body 105 can further include a softening polymer (SP) layer 130 which can be in direct contact with a surface 132 of at least a portion of at least one of the encapsulation layers 115. In some embodiments, a Young’s modulus of the SP layer is decreased by at least 50 percent when wet and at an elevated temperature of at least 35 °C as compared to the Young’s modulus of the softening polymer layer when dry and at room temperature.

[0046] The term flexible electrode array as used herein refers to at least portion of the interface body having the ability to adopt a non-planar shape that follows contours of a curved target body surface (e.g., as further disclosed herein, a curved or other non-planar surface of biological tissueor non-biological artificial tissue or tissue-implantable device body surfaces, in various embodiments) so that the one or more electrodes 120 of the flexible electrode array 110 arc within 10, 50, 100, 250, 500, 750, 1000, 1500, 2000, 3000, 4000, 5000, 6000 microns of the body surface.

[0047] The term electrodes as used herein refers to a layer of electrically conductive materials including metals (e.g., Ta, Ti, Pt, Ir,) or metal compounds (e.g., iridium oxide, titanium nitride, ruthenium oxide), electrically conducting polymers (e.g., poly(ethylenedioxythiophene)), graphene, or carbon nanotubes.

[0048] The term electrode contact pad as used herein refers to one or more layers of electrically conductive materials, (e.g., gold, platinum, titanium, tantalum, nickel, chromium, tungsten or alloys thereof) to provide a high electrical conductivity or enhance adhesion.

[0049] The term softening polymer (SP) as used herein refers to one or more polymer layers such as a hydrogel or SMP layer that softens (e.g., Young’s modulus decrease by 50 percent in magnitude) from room temperature (about 20°C, to 35 °C or higher (e.g., 37 to 40 °C in some embodiments).

[0050] The term wet, as used herein, means that the SP layer or layers has been exposed to and absorbed liquid water (such as present in body fluids or secretions or artificial body fluids) so as to have a water content of at least 0.1, 0.2, 0.3, 0.4 0.5 gm of water per gram of wet SP layer or layers.

[0051] The term dry, as used herein, means that the SP layer has not been exposed to liquid water and has a water content of less than 0.1, 0.2, 0.3, 0.4 0.5 gm of water per gram of wet SP layer or layers.

[0052] As further disclosed herein in some device embodiments, the one or more electrode contact pads 125 are connected to conductive interconnects 127 to electrically connect the electrodes 120 to a connector 415 of the interface body. E.g., in some embodiments, the connector is a wire bonded connector. E.g., in some embodiments, the connector ban be a wire bonded connector. E.g., in some embodiments, the conductive interconnects 127 contact electrical contact pads 417 of the connector. E.g., in some embodiments, the conductive interconnects 127 can be composed of metals including: gold, platinum, titanium, tantalum, nickel, chromium, tungsten or alloys thereof. E.g., the conductive interconnects 127 can be adhered to at least one of the encapsulation layers by the transfer-by-polymerization process.

[0053] In some embodiments, the one or more encapsulation layers 115 can include one or more polyimidc layers, one or more amorphous silicon carbide layers (a-Si-C) one or more silicon nitride layers, one or more liquid crystal polymer layers or combinations thereof (e.g., layers 310, 310a FIG. 3). The term polyimide layer as used herein refers to any polymer containing an imide group in the polymer backbone and can include thermoset, thermoplastic, aliphatic, aromatics, and semiaromatics polymers as familiar to one skilled in the pertinent art. Non-limiting examples include the PI2600 series of polyimide precursors, available from HD Microsystems, that on cure form polyimide films with an elastic modulus of about 7 GPa. The term amorphous silicon carbide refers to a silicon carbide structure that is substantially devoid of crystal structures such as indicated by an x-ray diffraction scan that would not show discrete sharp peaks of scattered radiation corresponding to crystalline or crystallite forms of silicon carbide. For example, substantially the entire (e.g., at least about 99% percent) x-ray diffraction spectrum of an a-SiC structure of the disclosure may have no x-ray diffraction peaks with a full width at half maximum of less than about 5 degrees in diffraction angle.

[0054] Non-limiting further examples of electrode, electrode contact pad, interconnect, SP layer and a-SiC layer compositions are disclosed in US patent No. 10,485,109, 11,045,646, 11,261,345, or 11,224,371 all of which incorporated by reference herein in their entirety.

[0055] As further disclosed herein, embodiments of the encapsulation layers 115 can include a cross-sectional structure with asymmetric intrinsic or induced residual stresses with respect to a neutral axis of the flexible electrode array (e.g., neutral axis 510, FIGs 5a-5b). E.g., in some such embodiments one or more the one or more encapsulation layers or a conductive interconnect layer (e.g., encapsulation layers 115, 115a, conductive interconnect layer 127, FIG. 7) can include the asymmetric intrinsic or induced residual stresses with respect to the neutral axis of the flexible electrode array 110. Intrinsic residual stress can occur within an individual layer of the encapsulation layers 115 (e.g., a-SiC and / or conductive interconnect layers). Such intrinsic residual stress is often associated with the process of fabrication of a layer. The magnitude of the intrinsic residual stress and whether the stress is compressive or tensile may be controlled by the selection of process variables during fabrication. As used herein, intrinsic residual stresses differ from induced residual stresses. An induced residual stress occurs in a layer when that layer is acted upon by another layer having intrinsic residual stress. It is sufficient for both intrinsic and induced residual stress layers to be disposed in any location within the flexible electrode array. One or alllayers in a flexible electrode array may possess both intrinsic and induced residual stresses. In some embodiments, the encapsulation layer can include a handle layer (c.g., a polyimidc or similar material layer) to facilitate device fabrication by serving as base structure upon which other layers can be assembled on or the SP layers can be connected to. Such handle layers may have low or no intrinsic residual stresses.

[0056] Embodiment of the interface body 105 can include two or more of the SP layers (e.g., SP layer 130, 130b, FIG 2). For some embodiments, when one or more SP layers 130 are wet and at the elevated temperature, asymmetric intrinsic residual stresses in the flexible electrode array 110 allow the flexible electrode array to contour to a curved body surface 405 (FIG. 4c). E.g., the flexible electrode array 110 can contour to a curved surface 405 of a tissue body 410 such as the pial surface 405 of a brain tissue body 410.

[0057] As further disclosed herein, embodiments of the SP layer 130 can be attached to the flexible electrode array 110 by a mechanical interlock, an adhesive bond or combination thereof. In some embodiments when dry and at room temperature, the one or more softening polymer layers have a Young’s modulus that is greater than a Young’s modulus of the flexible electrode array. For some embodiments of the SP layer, the Young’s modulus of the SP layer is decreased by at least 90 or in some embodiment, 99 percent, when wet and at the elevated temperature. Some embodiments of the SP layer has a polymer backbone obtained by polymerization of thiol, acrylate, alkene or epoxy monomers. In some such embodiments, a chain of covalently bonded monomers that form the polymer backbone is free of ester groups, to thereby increase the hydrolytically stability of the softening polymer or softening polymer layers.

[0058] Embodiments of the device 100 and its methods of manufacture produce a flexible electrode array 110 capable of being conformed to a tissue surface. The array 110 may have one or more electrodes 120 suitable for recording or electrically stimulating neural tissue. In some embodiments the electrodes may be adapted to sense and measure chemical constituents of the physiological environment, including, for example, pH, oxygen, neurotransmitters, glucose, and other biological molecules. The flexible electrode array 110 can include one or more polyimide layers, electrically conductive interconnects 127, target surface facing electrodes, and electrical contact pads 125. In some embodiments, the interface body 105, can include a SP layer 130. The SP layer can include at least a SP segment that provides rigidity for surgical placement and then softens in the body to allow the electrode array to conform to the target surface. Without limitation,the target surface may include the surface of the brain, an internal region of the brain including penetrating into brain tissues such as the cerebral cortex, the spinal cord, spinal nerves, dorsal root ganglia, the retina, the perilymph and endolymph filled ducts of the cochlea, sensory nerves, cranial nerves, nerves and ganglia of the peripheral nervous system, and the innervation of major organs such as the heart, liver, stomach, colon, and spleen..

[0059] The device embodiments disclosed herein have the ability to achieve both electrical stability and softening conformability in the same device. The device embodiments are preferably assembled in a layer-by-layer process employing, for some layers lithography. Lithography, and photolithography, in particular, is advantageous for allowing precise control of the geometry of individual layers in the device. Individual layers may also be formed by thin-film processing techniques such as vacuum deposition, spin-coating, and plasma etching. Such thin-film processing techniques are well known in the art and may include sputtering, evaporation, plasma enhanced chemical vapor deposition, and reactive ion etching, A feature of the thin-film processing is the ability to create and control the magnitude of stresses in individual layers of the coating. Such stresses may be advantageously used to provide a tissue conforming function of the device.

[0060] Embodiments of the flexible electrode array can be thin-film structures, and can include a first layer of polyimide, a metal layer patterned into electrical interconnects and a second polyimide layer disposed over the metal and first polyimide layers. The second polyimide layer can be patterned to expose the metal layer to create tissue-facing electrode sites and electrical contacts. At least one electrical contact and at least one electrode site are connected via one or more metal traces formed by patterning the metal layer. In some embodiments a range of thickness the polyimide layers can be 1 to 500 pm and the metal layer can be 0.05 to 5 pm.

[0061] Some embodiments of the flexible electrode array can include one or more layers of a-SiC. Some such embodiments may include: a polyimide layer (0.5 to 500 pm), a-SiC layer (0.05 to 5 pm), metal layer metal (0.05 to 5 pm), a-SiC layer (0.05 to 5 pm), polyimide layer (1-500 pm).

[0062] The layer or layers of a-SiC can be useful for providing stability of the flexible electrode array over long periods of time in a fluid environment, e.g., of a biological body. In some embodiments, the a-SiC may be deposited such that the a-SiC layer possesses a compressive or tensile residual stress. The residual stress state of the individual a-SiC layers can be controlled to provide an overall stress in the flexible electrode array. This overall residual stress can be further influenced by creating and controlling the residual stress in the metal layer such that the overallresidual stress is determined by the sum of the individual residual stresses from the metal and a- SiC layers and the respective locations of the individual layers within the cross-sectional geometry of the flexible electrode array 110. By appropriate selection of the residual stress states of the individual layers and the cross-sectional geometry of the electrode array, the electrode array may be fabricated to adopt a three-dimensional shape that is advantageous for placing the tissue-facing electrode sites in close apposition to the target surface. This close apposition has the advantage of increasing the spatial selectivity of neural recording and / or stimulation, and may also reduce the electrical thresholds required for electrical stimulation of neural tissue. Reduced electrical thresholds result in reduced power consumption for the delivery of therapeutic stimulation and consequently have the advantage of decreasing the discharge rate of a battery or batteries of the device that provide power to the implanted interface body. The batteries may be implanted or may be external to the body that the interface body is implanted in.

[0063] The surgical placement of three-dimensional structures can be difficult to achieve, particularly if the electrodes of the flexible electrode array must be placed within a confined body structure such as the scala tympani of the cochlea, slid under tissue structures such as the cranium at the margins of a craniotomy, within a blood vessel, or within or on other electrically excitable tissue structures. Whereas the flexibility of the flexible electrode array is advantageous for conforming to the external geometry of target tissue, the flexibility of the flexible electrode array makes insertion of the array into a tissue structure, such as the parenchyma of the brain or the scala tympani of the cochlea, difficult without external mechanical aides such as a stylet. These difficulties can be overcome as disclosed herein by creating a novel structure that comprises at least one flexible electrode array integrated with at least one SP layer. One embodiment of the invention is a SP layer integrated with one or more flexible electrode arrays. The SP layer can provide the rigidity necessary for placement of the flexible electrode array within or adjacent to a target surface. Subsequently, the SP layer softens due to contact with the body environment of wetness and / or elevated temperature, e.g., one or both of exposure to the higher than ambient body temperature and ingress of water into the SP layer. The desirable property of softening on insertion into or on the target body may be obtained by formulating the SP to have a glass transition temperature that decreases from above body temperature prior to implantation, for example, that is greater than about 35, 36, 37°C, to a lower than body temperature, that is less than about 37, 38, 39°C, after implantation. The glass transition temperatures may not be sharply defined. Thus, thechange in glass transition temperature should result in a decrease in stiffness of the SP after insertion into the body, regardless of the specific glass transition temperatures involved. In some embodiments, the rigidity of the SP layer prior to implantation holds the flexible electrode array in a geometric configuration suitable for surgical placement or implantation. After implantation, the SP layer softens and the flexible electrode array conforms to the target surface. In some embodiments the flexible electrode array is designed such that the residual stresses within one or more layers of the array cause the array to conform closely to the target surface, thereby providing the advantages of improved spatial recording and stimulation selectivity and reduced electrical stimulation thresholds.

[0064] The combinations of flexible electrode array and SP layers as disclosed herein, provides a means of electrically interfacing to a wide range of neural tissues to address many unmet therapeutic needs. Further, such a combination provides a large design space that allows the fabrication of many useful devices.

[0065] Embodiments of the flexible electrode array can be a flexible multilayered structure including one or more polyimide layers, one or more metal layers, optionally one or more a-SiC layers, and optionally a low impedance electrode to facilitate either or both of recording and stimulation of a target body. Some embodiments of the polyimide layer (PI) can have a thickness in the range 0.5 to 100 pm. Some embodiments, of the amorphous silicon carbide layer or layers, e.g., deposited by plasma enhanced chemical vapor deposition (PECVD), can have a thickness in the range 0.05 to 5 pm.

[0066] Some embodiments of the SP layer can include softening polymers which includes thiol- based chemistries including thiol-enes, thiol-acrylates, thiol-epoxies monomers and ester-free polymer networks including crosslinked networks of such multi-functional monomers. Embodiments of the electrode can include electrode coatings, e.g., to provide a low impedance interface to a target body, such as neural tissue. The electrode coating can include an iridium oxide, titanium nitride, ruthenium oxide, an intrinsically conducting polymer such as poly (ethylenedioxy thiophene), platinum, iridium, a platinum-iridium alloy, graphene, or carbon nanotube coating.

[0067] Some embodiments of the electrode include a coating that provides a low impedance interface to a target tissue. Non-limiting examples of the electrode coating, include iridium oxide, titanium nitride, ruthenium oxide, an intrinsically conducting polymer such aspoly(ethylenedioxythiophene), platinum, iridium, a platinum -iridium alloy, graphene, or carbon nanotubcs.

[0068] The flexible electrode array can include a single or multiple layers of metal or metals that serve as electrical interconnects between electrode and electrode contact pads. Typically, the electrodes are positioned towards the distal end of the electrode array (e.g., FIG. la, distal end 142) and the electrical contact pads positioned towards the proximal end (e.g., FIG. la, proximal end 140) of the flexible electrode array. Embodiments of the metal layer include a metal having high electrical conductivity such as gold, platinum or tantalum. In some embodiments, the metal layer includes metal layers to enhance adhesion such as titanium, chromium, or a titanium-tungsten alloy. An example metal layer can include a titanium layer (e.g., 0.05 pm thick), a gold layer (e.g., 0.2 pm thick) and a titanium layer (e.g., 0.05 pm thick).

[0069] In an example embodiment, the cross-section of the flexible electrode array 110 can include a polyimide layer 115. The interface body 105, can include a SP layer 130, the SP layer is bonded along substantially one major surface 132 of the array (FIG. 1 a- lb). In a related embodiment, a SP layer is bonded along substantially two major surfaces 132, 132a of the array 110 (FIG. 2).

[0070] Examples of cross-sectional thickness are 5 to 75 pm for the SP layer or layers, 5 to 20 pm for the flexible electrode array, and, comprising the flexible electrode array, 4 pm for polyimide layer or layers, 1 pm for the a-SiC layer or layers, and 0.3 pm for the metal layer. The overall thickness of the interface body may be 10 to 95 pm. Thinner or thicker interface bodies are also within the scope of the invention.

[0071] FIG. la shows a portion of an interface body 105 example embodiment with SP embodiment 130, flexible electrode array 110 example embodiment 110, electrodes 120 in a polyimide layer 115 connected to the SP layer 130. FIG. lb shows a cross-section of the interface body at cross-section A-A’ in FIG. la.

[0072] FIG. 2 shows a portion of an interface body 105 example, with a flexible electrode array 110 example embodiment contained between two SP layers 130, 130b to yield a SP / flexible electrode array / SP three-layer structure. In some such embodiments, the SP layers can be patterned and etched to form sites for electrodes 120 and electrical contact pads 125. An example of the cross-section of an electrode site created through SP patterning and etching, and after applying a low impedance electrode coating to form an electrode 120 is shown in Fig. 3.

[0073] Embodiments of the interface body 105 can be arranged to form a surface electrode array or as a tissue or ductal penetrating electrode array.

[0074] FIGs. 4a-4c show a surface electrode array embodiment (e.g., a two dimensional array of electrodes 120) that can be advantageous when electrically stimulating or recording electrical signals from a target surface 405 such as a pial surface of a brain tissue body 410, such as in electrocorticography. Such interface body embodiments 105 can be adapted to conform to other target tissue surfaces, including the epidural or subdural surface of the spinal cord or the surface of the bladder. As illustrated in FIG. 4a the flexible electrode array 110 can be connected to a connector 415 of the interface body 105.

[0075] The SP layer or layers can provide stiffness that aids in surgical handling and allows the placement of the electrode array under the bony margins of a craniotomy. Once placed on the surface of the brain, the SP layers soften and the flexible electrode array relaxes against the surface of the brain causing the electrode sites to be in apposition to the brain tissue. Such embodiments are particularly useful when placing subdural electrode arrays on the pial surface of the brain. The electrodes of the flexible electrode array can be connected via metal layer traces (not shown) to an electrical connector (e.g., connector 415, FIG. 4a) having electrical connector pads. One skilled in the pertinent arts would be familiar with the procedure to make electrical connections between the electrodes of the electrode array and instruments for conducting electrical stimulation and recording, including attaching an electrical connector to the electrical connector pads by soldering or by adhesive bonding with an electrically conductive epoxy. Alternatively, as familiar to one skilled in the pertinent arts, the electrodes of the electrode array can be terminated inside an implanted electronics module such as an implanted-pulse-generator. The implanted electronics module can include wireless powering and communication devices.

[0076] In some embodiments of the interface body, the flexible electrode array can penetrate into a target tissue. Example target tissues include brain, spinal cord, peripheral nerve, or other organ or other tissue structures for which it is desired to record or stimulate electrical activity. The SP layer or layers provides the stiffness and rigidity to insert the electrode array into the target tissue. After insertion, the SP layers softens, and the electrode array becomes flexible. In some embodiments, the flexibility of the electrode array can adapt to contour to the target surface of the tissue. The flexibility can be adjusted by selecting an appropriate thicknesses for the individual layers (e.g., polyimide, a-SiC, SP layers) of the interface body. In some embodiment, reducing thethickness of one or more such layers can increase the flexibility of the electrode array. In some such embodiments, it is possible to insert a highly flexible electrode array into tissue without the need for a needle or stylet or other mechanical means to support the array during insertion. In some embodiments, increasing the flexibility of the electrode array can advantageously reduce the foreign body response of tissue to the implanted electrode array, e.g., thereby improving the neural recording and stimulation properties of the electrode array.

[0077] Some embodiments of the flexible electrode array can be fabricated to have a geometric shape that conforms to the target surface. As disclosed herein, non-planar conforming shapes of an electrode array may be obtained by designing the cross-sectional structure of the array to be asymmetric with respect to the geometric center of the array. The individual layers making up the electrode array can possess some intrinsic residual stress that originates during the deposition or fabrication of the layers. This residual stress may be compressive or tensile and the magnitude of the stress can be controlled by appropriate selection of deposition condition.

[0078] The occurrence of such intrinsic residual stresses involved in thin-film fabrication is often considered to be problematic and efforts are often made to reduce such stresses by choice of deposition conditions. In contrast, in some embodiments of the present invention, these residual stresses are used advantageously to engineer the shape of the electrode arrays to conform to the target surface of tissue being targeted for electrical recording or stimulation. The residual stresses may be used in various ways to obtain a desired non-planar surface geometry.

[0079] E.g., in some embodiments such as shown in FIG. 5b, the flexible electrode array 110 (and electrodes, contact pads and a-SiC layers thereon when present) can be located asymmetrically such that these layers are not located around the neutral axis 510 of a cross-section of an interface body. That is, the flexible electrode array 110 has a non-zero offset distance 515 from the neutral axis 510. When the flexible electrode array is displaced from the neutral axis, the interface body, including the flexible electrode array, will naturally acquire a curled shape. The direction of the curl depends on whether the flexible electrode array has a tensile intrinsic residual stress or a compressive intrinsic residual stress and these intrinsic residual stresses and geometry may be used to control the shape of the interface body.

[0080] E.g. in some embodiments such as shown in FIG. 6a once the SP layers 130, 130a soften (due to elevated temperate and wetting) the flexible electrode array with a compressive intrinsic residual stress may curl outwards. E.g. in some embodiments such as shown in FIG. 6b once theSP layers 130, 130b soften the polyimide layer with a tensile intrinsic residual stress may curl inwards.

[0081] In some embodiments, the polyimide layer or layers of the flexible electrode array may be connected to the SP layer or layers to form the interface body. Prior to softening (e.g., due to implantation), the embodiments of the flexible electrode array can be restrained to be substantially planar and consequently the electrodes of the array are aligned with each other is a same plane. When the electrode array is implanted, the SP portion of the interface body softens and the shape of the interface body acquires the shape of the flexible electrode array, when the electrode array is unconstrained. The shape of the electrode array may be predetermined through designs to advantageously cause the electrodes of the array to be placed close to or in contact with a target surface (e.g., a neural tissue surface) from which recordings are desired (e.g., neural recordings from neural tissue) or that is to be stimulated by an electrical signal (e.g., neural stimulation of neural tissue). Design features can include the use of thin-film deposition processing to establish a desirable residual stress states in one or more layers in the flexible electrode array, selecting an appropriate offset distance of the flexible electrode array from the neutral axis of the interface body, or combinations thereof.

[0082] In some embodiments, the electrodes or contact pads of the flexible electrode array can be arranged to be located at the neutral axis of the array and the shape of the array can be controlled by varying the thickness of one or more layers in the array. E.g., one or more of the polyimide or a-SiC layer or layers can be fabricated such that the thicknesses 710, 715, 720, 725 of individual layers within the electrode array 110 are asymmetric with respect to the neutral axis 510 of the array as shown in FIG. 7. In some embodiments, the a-SiC layers 310, 310a can have different thicknesses 720, 725 and the polyimide layers 115, 115a have same thicknesses 710, 715. In some embodiments the a-SiC layers 310, 310a have same thicknesses 720, 725 and the polyimide layers 115, 115a have different thicknesses 710, 715. For example, both a-SiC layers 310, 310a could have a thickness 720, 725 of 1 micron and one polyimide layer (one of layers 115, 115a) can have a thickness of 2 microns and the other polyimide layer (the other of layers 115a, 115) can have a thickness of 6 microns. In some embodiments the polyimide layers and the SiC layers all have a different thickness from each other.

[0083] In some embodiments, of the present invention, individual layers of the flexible electrode array can be fabricated with different intrinsic residual stress. In some embodiments, e.g., the arraycan be fabricated with two a-SiC layers. The a-SiC layers, which can have the same thickness, can be deposited through control of a-SiC deposition conditions so as to have different residual stresses. E.g., both SiC layers may have residual compressive stress but at different stress levels, alternatively both SiC layers may have residual tensile stress but at different stress levels. In some embodiments one a-SiC layer can have residual tensile stress and a second a-SiC layer can have a residual compressive stress. One skilled in the pertinent arts would be familiar with methods for controlling the type of residual stress, either compression or tension, and the magnitude of the residual stress state. Non-limiting examples include the selection of deposition temperature and, when a-SiC is deposited by plasma enhanced chemical vapor deposition (PECVD), selection of plasma power and frequency, deposition pressure, and plasma gas composition.

[0084] In some embodiments, individual layers of the flexible electrode array can be patterned differently to provide an asymmetric structure capable of assuming a desire target tissue conforming geometry. E.g., as shown in FIG. 8, the array 110 can have two layers of a-SiC, one a-SiC layer 310 patterned to have a different width 810 than a width 815 of the other a-SiC layer 310a. The difference in widths 810, 815 can result in an asymmetric stress state within the electrode array which results in a non-planar surface geometry. E.g., a particular geometry can be achieved by the choice of a-SiC layer 310, 310a widths 810, 815 to conform to the surface of a target tissue. E.g., as shown in Fig. 8, a-SiC layer 310a has a smaller width 815 as compared to the width 810 of a-SiC layer 310. The widths and lengths of individual layers may be selected to induce a curvature around a longitudinal axis of the electrode array as shown in FIG. 8 or to induce curvature around a transverse axis of the electrode array.

[0085] In some embodiments, a pattern that provides geometric asymmetry may be used for one or more layers of the flexible electrode array to control the shape of the array. E.g., as shown in FIG. 9a- 9c one edge 910 of the a-SiC layer 310a in the array can be patterned to form a wavy edge. The wavy edge can introduce asymmetry that can be used to control the overall shape of the polyimide array. It should be appreciated that the asymmetry may be incorporated into encapsulating dielectric layers in the array, such as a-SiC, or in metal layers (e.g., layer 915) of the array. Amorphous silicon carbide, a-SiC, can be an advantageous encapsulating dielectric because it is stable in the biological tissue and has high resistance to corrosion.

[0086] Other dielectrics such as silicon oxide, silicon nitride, and siliconoxynitride, well-known in the art, can be used in a similar fashion. For clarity, the array shown in Fig. 9 is shown withoutan SP layer or layer, but SP layer or layers would be bonded to the other layers (e.g., polyimide or a-SiC layers) to provides stiffness to facilitate manipulation of the interface body, as disclosed elsewhere herein, e.g., to facilitate tissue penetration. As disclosed elsewhere herein, after insertion into or on a target body, the SP softens and the electrode array can adopt a tissue conforming shape.

[0087] Based on the present disclosure, a combination of one or more of layer thickness, layer position with respect to the neutral axis of the electrode array, geometric pattern, and intrinsic residual stress of one or more layers of the electrode array, can be implemented to form a wide variety of shapes conforming to a target tissue surface and thereby place electrodes of the array at a desired close distance to the target body. An optimum distance of electrodes site from a target surface will depend on the desired spatial selectivity of stimulation, recording, or both, and in some embodiments, avoid stimulation-induced tissue body damage. Other factors related to reducing power requirements for stimulation or the desire to employ multi-electrode stimulation in bipolar, tripolar or multipolar configurations also influence the choice of electrode-to-tissue target distance.

[0088] As disclosed herein through the control of the shape and thickness of the layers of the flexible electrode array, the location of electrode sites within the cross-section of the electrode array, and the presence or thickness of the SP layer or layers, advantageously allows a variety a desired distance between electrode and target bodies to be achieved. Such desired distances may be small (e.g., less than 1 mm and in some embodiments less than 5 microns), where the electrodes are in contact or near contact with a target body surface, or, when advantageous, the electrodes can be several millimeters from the target body.

[0089] In some embodiments, the intrinsic stress states of the layers of the flexible electrode array can cause the array (e.g., upon softening of the SP layer or layers) to adopt a three-dimensional structure having, e.g., multiple radii of curvature in different directions. Such embodiments can be advantageous for adapting embodiments of the interface body to contact tissue with complex surface geometry, such as the gyri on the surface of the brain, the surface of the modiolus contacting the scala tympani of the cochlea, or an external or internal surface of the heart.

[0090] In some embodiments, multiple radii of curvature may be obtained by creating intrinsic residual stresses that vary with the direction within the plane of the array. For instance, as illustrated in FIG. lOa-lOc, compressive or tensile residual stress lines 1005, 1010 respectively, may advantageously cause the electrode array (upon softening of the SP layer or layers, not shown in FIG. 10a- 10c) to adopt a transverse compressive shape (e.g., FIG. 10b) or an longitudinal tensileshape (e.g., FIG. 10c). In some embodiments, one or more layers of the electrode array can be fabricated with a transverse and / or compressive residual stress, e.g., in a tissue facing surface of the electrode array containing the electrodes. In some embodiments, the electrode array can develop a transverse curvature upon implantation in a target body and softening of SP layer or layers (not shown), in which the electrode sites are located on a convex surface of the array, such as illustrated in FIG. 10b. In some embodiments, where the array includes one or more layers with a longitudinal tensile residual stress, upon implantation in a target body and softening of SP layer or layers (not shown), the array can adopt a curled structure such that the electrode sites are located on a concave surface with respect to the longitudinal direction of the array, such as illustrated in FIG. 10c.

[0091] Based on the present disclosure, one skilled in the pertinent art would understand how various different residual stress states in the transverse and longitudinal directions of the electrode array could be created by controlling the intrinsic stress within one or more of the individual layers of the array. Alternatively, or in combination, as disclosed elsewhere herein, various different residual stress states may be created by asymmetrically positioning the individual layers in the array at a position that is not symmetric with respect to the neutral axis of the cross-section of the flexible electrode array. In a related embodiment, the flexible electrode array is placed in a position that is not symmetric with respect to the neutral axis of the cross-section of the interface body.

[0092] In some embodiments, causing the flexible electrode array to have different radii of curvature in different directions within the array may lead to the formation of creases or wrinkles in the array when the SP layer or layers softens on implantation into or on a target body. In some such embodiments, the formation of such creases or wrinkles may be minimized or avoided by creating one or more openings (e.g., through-holes, vias, cavities slits, notches or channels) that can be included in the SP layer or layers to mitigate such crease or wrinkle forming displacements when the array adopts a non-planar shape. E.g., as illustrated in Fig. I la, one or more exterior surface openings 1105 can be patterned into the SP layer 130. E.g., as illustrated in Fig. 1 lb, one or more interior openings 1110 can be patterned into the SP layer 130.

[0093] In some embodiments, the adhesion of SP layer or layers to other layers of the electrode array (e.g., polyimide or a-SiC layers) can be increased, e.g., to help prevent or reduce creases or wrinkles. E.g., as illustrated in FIGs. 12a-12c one or more openings 1205 (e.g., through-holes, vias, cavities, Y-shaped through-holes) can be patterned into one or more of the polyimide or a-SiC layers 115, 115a, 310, 310a and portions of the SP layer 130 can be formed in such openings. For instance, an uncurcd or partially cured SP formulation can be applied as a liquid or gel to the polyimide layer 115a such that the SP formulation enters the opening 1205. The uncured or partially cured SP formulation is then subject to further curing such as polymerization by thermal or photo-initiation, to form the SP layer 130. The SP layer 130 within the opening 1205 can form a robust mechanical interlock attachment between the flexible electrode array and the SP layer. Curing or polymerization of the SP in contact with polyimide or a-SiC layers of the array can also create chemical attachments between the polyimide, e.g., by one or both of primary bonds (e.g., covalent bonds) or secondary bonds (e.g., van der Waals bonds). In some embodiments, such chemical bonding may be improved with the pre-treatment of the layers of the array with an adhesion promoter or by roughening the surface of the SP layer facing layers of the array by, for example, abrasive treatment or plasma treatment. Mechanical interlocking of the flexible electrode array to SP layers can be facilitated by pressure bonding, optionally with heat, e.g., to force the SP formulation into the openings 1205. As illustrated in FIGs. 12a and 12c embodiments of the electrode array can further include any of the openings (e.g., opening 1105) formed in the SP layer 130 of the electrode array such as disclosed in the context of FIGs 1 la- 1 lb.

[0094] FIGs. 13a- 13e present cross-sectional schematic views of a portion of example embodiments of an interface body 105 of the device at different stages of assembly and interfacing with a biological tissue 1305 (e.g., a peripheral nerve). A distal end 142 of an interface body 105 can be fabricated to acquire a target body-wrapping structure when implanted. The electrode sites on the distal end of the electrode array are placed in contact or in close proximity to a target surface 1310 of the body 1305 (e.g., epineural surface of the nerve). One sequence of steps suitable for fabricating the cuff-forming interface body and the manner of operation of the interface body is as follows:

[0095]

[0093] As illustrated in FIG. 13a, the electrode array 110, which can include any suitable combination of the layers disclosed herein, can be fabricated by thin-film processing as a planar structure on a suitable planar handle substrate 1315 (e.g., a silicon wafer substrate). As disclosed elsewhere herein, layers of the flexible electrode array can have one or more asymmetric residual stress states to facilitate the electrode array adopting a non-planar shape to contour to the target surface. As illustrated in FIG. 13b, when the electrode array is removed from the planar substrate 1315 the distal end acquires a non-planar (e.g., nerve-wrapping geometry) due to the relaxation ofthese asymmetric stress states. As illustrated in FIG. 13c, to facilitate implantation of the electrode array in a non-planar (e.g., circumncural) geometry, the electrode array can be attached to a stiffening SP layer 130. The stiffening SP layer is sufficiently rigid to form a planar interface body 105 to facilitate interface body implantation or handling. As disclosed elsewhere herein, the SP layer has the property of softening. That is, once hydrated or heated, or some combination of hydration and heating, the rigidity of the SP layer is reduced. As illustrated in FIG. 13d on or into the target body 1305, the distal portion of the electrode array can be placed at a desirable target surface 1310 location of the body. As illustrated in FIG. 13e, as the SP layer 130 softens, the stiffness of the SP decreases sufficiently that the interface body’s shape becomes dominated by the asymmetric residual stress, causing the distal portion of the interface body to contour to the target surface (e.g., curl around the nerve).

[0096] In some embodiments, the interface body can be a cochlear implanted body and the flexible electrode array can be a cochlear electrode array where at least a portion of the electrode array is designed to have a stiffness and curvature that facilitates implantation in the cochlear, e.g., within a scala tympani of the cochlear. The residual stress state of the electrode array can be designed to contour to match the surface geometry defined of a cochlear modiolus where the modiolus defines a boundary of the scala tympani. After implantation, the softening SP layer or layers lose rigidity, and the electrode array adopts a shape that conforms closely to the surface of the modiolus facing the scala tympani. In some embodiments the electrode array can be designed to advance further into the scala tympani, e.g., as a cochlear lead embodiment. In some such embodiments, the electrode sites can be placed close to the spiral ganglia and afferent neural processes that are the target of electrical stimulation to facilitate the restoration of hearing.

[0097] In some embodiments, the interface body can be a spinal cord stimulation body and the flexible electrode array can be a spinal cord stimulation array, where at least a portion of the interface body is designed to have stiffness and curvature that facilitates implantation on the spinal cord, and to resist the aggressive mechanical forces that can be present in spinal leads to thereby mitigate lead failure and / or lead migration. Such embodiments can possess the requisite toughness, tear strength and conformability to provide spinal cord stimulation with the electrodes of the flexible electrode array portion of the interface body implanted in the epidural spinal space or subdurally on the spinal cord.

[0098] Still other embodiments of the interface body can be adapted such that the electrode array serves as a probe of the gastrointestinal system to help diagnose and treat conditions such as gastroesophageal reflux disease (GERD), gastroparesis and neurological conditions affecting the colon, stomach and bowels that include dysregulated motility. Yet other embodiments of the interface body can be adapted such that the electrode array serves as a lead for cardiac pacing and achieving finer neurological control of systems innervating the heart and surrounding tissues.

[0099] Some embodiments of the electrode arrays can be adapted for neural stimulation and recording for sensory prostheses, including cochlear implants, subdural cortical or intracortical vision prostheses, and retinal arrays; electrocorticography arrays for monitoring and stimulation in epilepsy; epidural and subdural spinal cord stimulators for pain management; vagus nerve stimulation electrode arrays and leads; peripheral nerve stimulation electrode arrays and leads; cardiac pacing and cardiac rhythm management arrays and leads.

[0100] Those skilled in the art to which this application relates will appreciate that, based on the present disclosure, other and further combinations, additions, deletions, substitutions and modifications may be made to the described embodiments.

Claims

WHAT IS CLAIMED IS:

1. A device, comprising: an interface body, including: a flexible electrode array, the flexible electrode array including: one or more encapsulation layers, one or more electrodes disposed towards a distal end of the flexible electrode array, and one or more electrode contact pads, each one of the electrode contact pads contacting one of the electrodes; and a softening polymer layer in direct contact with a surface of at least a portion of at least one of the encapsulation layers, wherein a Young’s modulus of the softening polymer layer is decreased by at least 50 percent when wet and at an elevated temperature of at least 35 °C as compared to the Young’s modulus of the softening polymer layer when dry and at room temperature.

2. The device of claim 1, wherein the one or more electrode contact pads are connected to conductive interconnects to electrically connect the electrodes to a connector of the interface body.

3. The device of claim 2, wherein the connector is a wire bonded connector.

4. The device of claim 2, wherein the conductive interconnects contact electrical contact pads of the connector.

5. The device of claim 2, wherein the conductive interconnects are composed of metals including: gold, platinum, titanium, tantalum, nickel, chromium, tungsten or alloys thereof.

6. The device of claim 2, wherein the conductive interconnects are adhered to at least one of the encapsulation layers by a transfer-by-polymerization process.

7. The device of claim 1, wherein the one or more encapsulation layers include one or more polyimide layers, one or more amorphous silicon carbide layers, one or more silicon nitride layers, one or more liquid crystal polymer layers or combinations thereof.

8. The device of claim 1, wherein the flexible electrode array includes a cross-sectional structure with asymmetric intrinsic or induced residual stresses with respect to a neutral axis of the flexible electrode array.

9. The device of claim 8, wherein one or more the one or more encapsulation layers or a conductive interconnect layer include the asymmetric intrinsic or induced residual stresses with respect to the neutral axis of the flexible electrode array.

10. The device of claim 1, the interface body includes two or more of the softening polymer layers.

11. The device of claim 1 , wherein, when the softening polymer layer is wet and at the elevated temperature, asymmetric intrinsic or induced residual stresses of the flexible electrode array cause the interface body to contour to a curved target body surface.

12. The device of claim 1, wherein the softening polymer layer is attached to the encapsulation layers by a mechanical interlock, an adhesive bond or combination thereof.

13. The device of claim 1, wherein, when dry and at room temperature, the softening polymer layer has a Young’s modulus that is greater than a Young’s modulus of the flexible electrode array.

14. The device of claim 1, wherein the Young’s modulus of the softening polymer layer is decreased by at least 90 percent when wet and at the elevated temperature.

15. The device of claim 1, wherein the Young’s modulus of the softening polymer layer is decreased by at least 99 percent when wet and at the elevated temperature.

16. The device of claim 1, wherein the softening polymer layer has a polymer backbone obtained by polymerization of thiol, acrylate, alkene or epoxy monomers.

17. The device of claim 16, wherein a chain of covalently bonded monomers that form the polymer backbone is free of ester groups.

18. The device of claim 16, wherein the softening polymer layer includes between about 5% and 50% of the thiol monomers, the electrodes include gold, and at least one of the encapsulation layers is a silicon carbide layer and at least another one of the encapsulation layers is a polyimide layer.

19. The device of claim 16, wherein the softening polymer layer includes between about 5% and 50% of the thiol monomers, the electrodes include gold, and at least one of the encapsulation layers is a silicon carbide layer and at least another one of the encapsulation layers is a polyimide layer.

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