Patent Publication Number: US-2023158294-A1

Title: Thin film electrodes for brain computer interface and methods of microfabricating

Description:
PRIORITY CLAIM 
     The present application is a non-provisional application of, and claims the benefit and priority under 35 U.S.C. 119(e) of U.S. Provisional Application No. 62/991,524, filed Mar. 18, 2020, entitled “THIN FILM ELECTRODES FOR BRAIN COMPUTER INTERFACE AND METHODS OF MICROFABRICATING”. The entire contents of the aforementioned application is incorporated herein by reference in its entirety for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure relates to implantable neuromodulation devices and methods of fabrication, and in particular to a monolithic thin-film lead assembly and methods of microfabricating a monolithic thin-film lead assembly. 
     BACKGROUND 
     Normal neural activity is an intricate balance of electrical and chemical signals, which can be disrupted by a variety of insults (genetic, chemical or physical trauma) to the nervous system, causing cognitive, motor and sensory impairments. Similar to the way a cardiac pacemaker or defibrillator corrects heartbeat abnormalities, neuromodulation therapies help to reestablish normal neural balance. In particular instances, neuromodulation therapies utilize medical device technologies to enhance or suppress activity of the nervous system for the treatment of disease. These technologies include implantable as well as non-implantable neuromodulation devices and systems that deliver electrical, chemical or other agents to reversibly modify brain and nerve cell activity. The most common neuromodulation therapy is spinal cord stimulation to treat chronic neuropathic pain. In addition to chronic pain relief, some examples of neuromodulation therapies include deep brain stimulation for essential tremor, Parkinson&#39;s disease, dystonia, epilepsy and psychiatric disorders such as depression, obsessive compulsive disorder and Tourette syndrome; sacral nerve stimulation for pelvic disorders and incontinence; vagus nerve stimulation for rheumatoid arthritis; gastric and colonic stimulation for gastrointestinal disorders such as dysmotility or obesity; vagus nerve stimulation for epilepsy, obesity or depression; carotid artery stimulation for hypertension, and spinal cord stimulation for ischemic disorders such as angina and peripheral vascular disease. 
     Neuromodulation devices and systems tend to have a similar form factor, derived from their predecessors, e.g. the pacemaker or defibrillator. Such neuromodulation devices and systems typically consist of an implant comprising a neurostimulator having electronics connected to a lead assembly that delivers electrical pulses to electrodes interfaced with nerves or nerve bundles via an electrode assembly. The lead assembly is typically formed of a conductive material and takes the form of an insulated wire connected to the electrodes via a first connector on one end (e.g., a distal end) and the electronics of the neurostimulator via a second connector on another end (e.g., a proximal end). In some instances (e.g., deep implants), the lead assembly comprises additional conductors and connectors such as extension wires or a cable connected via connectors between the electrodes and the electronics of the neurostimulator. 
     Conventional electrodes, conductors, and connectors are separate components typically connected to one another using various coupling means for maintaining electrical conductivity between the connected components. For example, the extension conductors of the lead assembly may be secured to a neurostimulator using a connector having set screws or spring-lock mechanisms, the extension conductors may be secured to the lead conductors using another connector having set screws or spring-lock mechanisms or using techniques such as welding or bonding (e.g., using solder or an adhesive), and the lead conductors may be connected to the electrodes using techniques such as welding or bonding. However, in the absence of hardware migration, the main reason for malfunction of the electrical neuromodulation system is disconnections and fractures of system components. These problems can occur in all types of conventional electrodes, conductors, and connectors. For example, in deep brain stimulation, most fractures occur due to migration of the extension connector between the electrode and the extension conductor. Conventionally, the incidence of fracture between components has been decreased by using improved surgical techniques such as implant and placement of the extension connector as proximal as possible to the stimulating or recording electrode. In view of these factors, it may be desirable to develop neuromodulation devices and systems that are capable of having design flexibility, and desirable mechanical properties to mitigate disconnections and fractures of system components. 
     BRIEF SUMMARY 
     In various embodiments, a monolithic thin-film cable assembly is provided that includes a proximal end; a distal end; and a supporting structure that extends from the proximal end to the distal end. The supporting structure is comprised of one or more layers of dielectric material that have a thickness from 10 μm to 150 μm. The monolithic thin-film cable assembly further includes a plurality of conductive traces formed on a portion of the supporting structure. The conductive traces have a thickness from 0.5 μm to 100 μm. The monolithic thin-film cable may have a spiral shape comprising two or more turns and a pitch between each of the turns from 10 μm to 1 cm. 
     In some embodiments, the plurality of conductive traces extend from the proximal end to the distal end. Optionally, a length of the supporting structure is from 5 cm to 150 cm. Optionally, a width of the supporting structure is from 25 μm to 5 mm. In some embodiments, the dielectric material is polyimide, liquid crystal polymer, parylene, polyether ether ketone, or a combination thereof. Optionally, a length of the plurality of conductive traces is from 5 cm to 150 cm. Optionally, a width of the plurality of conductive traces is from 2.0 μm to 500 μm. 
     In some embodiments, the plurality of conductive traces are comprised of one or more layers of conductive material, and the conductive material is copper (Cu), gold (Au), silver (Ag), gold/chromium (Au/Cr), platinum (Pt), platinum/iridium (Pt/Ir), titanium (Ti), gold/titanium (Au/Ti), or any alloy thereof. In some embodiments, a coefficient of thermal expansion for the plurality of conductive traces is approximately equal to a coefficient of thermal expansion for the supporting structure. 
     In various embodiments, a monolithic thin-film lead assembly is provided that includes a cable comprising a proximal end, a distal end, a supporting structure that extends from the proximal end to the distal end, and a plurality of conductive traces formed on a portion of the supporting structure. The supporting structure is comprised of one or more layers of dielectric material. The monolithic thin-film lead assembly further includes an electrode assembly formed on the supporting structure at the distal end of the cable. The electrode assembly comprises one or more electrodes in electrical connection with one or more conductive traces of the plurality of conductive traces. 
     In some embodiments, a thickness of the supporting structure is from 10 μm to 150 μm. In some embodiments, the plurality of conductive traces have a thickness from 0.5 μm to 100 μm. In some embodiments, a length of the supporting structure is from 5 cm to 150 cm. In some embodiments, the dielectric material is polyimide, liquid crystal polymer, parylene, polyether ether ketone, or a combination thereof. In some embodiments, a length of the plurality of conductive traces is from 5 cm to 150 cm. 
     In some embodiments, the plurality of conductive traces are comprised of one or more layers of conductive material, and the conductive material is copper (Cu), gold (Au), silver (Ag), gold/chromium (Au/Cr), platinum (Pt), platinum/iridium (Pt/Ir), titanium (Ti), gold/titanium (Au/Ti), or any alloy thereof. In some embodiments, a coefficient of thermal expansion for the plurality of conductive traces is approximately equal to a coefficient of thermal expansion for the supporting structure. 
     In some embodiments, the monolithic thin-film lead assembly further includes a connector formed on the supporting structure at the proximal end of the cable and in electrical connection with the one or more conductive traces of the plurality of conductive traces. In some embodiments, the connector comprises one or more bond or contact pads. In some embodiments, a portion of the cable is helical. Optionally, the helical portion of the cable comprises a pitch from 100 μm to 2 mm. Optionally, the helical portion of the cable comprises a pitch from 200 μm to 400 μm. Optionally, the helical portion of the cable comprises a pitch from 600 μm to 1600 μm. Optionally, the helical portion of the cable comprises a helix angle from 10° to 85°. Optionally, the helical portion of the cable comprises a helix angle from 40° to 65°. Optionally, the helical portion of the cable is wound in a clockwise direction or an anti-clockwise direction. 
     In some embodiments, the monolithic thin-film lead assembly further includes a housing encasing the portion of the supporting structure having the plurality of conductive traces. In some embodiments, the monolithic thin-film lead assembly further includes a housing encasing the helical portion of the cable. In some embodiments, the housing is comprised of a medical grade polymer material. Optionally, the medical grade polymer material is silicone, a polymer dispersion, parylene, or a polyurethane. 
     In various embodiments, a neuromodulation system is provided including a neurostimulator comprising an electronics module; and a cable comprising a supporting structure and a plurality of conductive traces formed on a portion of the supporting structure. The supporting structure is comprised of one or more layers of dielectric material. The neuromodulation system further includes an electrode assembly formed on the supporting structure. The electrode assembly comprises one or more electrodes in electrical connection with one or more conductive traces of the plurality of conductive traces; and a connector formed on the supporting structure and in electrical connection with the one or more conductive traces of the plurality of conductive traces. The connector electrically connects the one or more conductive traces of the plurality of conductive traces to the electronics module. 
     In some embodiments, a portion of the cable is helical. Optionally, the helical portion of the cable comprises a pitch from 100 μm to 2 mm. Optionally, the helical portion of the cable comprises a helix angle from 10° to 85°. 
     In some embodiments, the neuromodulation system further includes a housing encasing the portion of the supporting structure having the plurality of conductive traces. In some embodiments, the neuromodulation system further includes a housing encasing the helical portion of the cable. In some embodiments, the housing is comprised of a medical grade polymer material. Optionally, the medical grade polymer material is silicone, a polymer dispersion, parylene, or a polyurethane. 
     In various embodiments, a monolithic thin-film lead assembly is provided including a cable comprising: a first helical portion at a proximal end of the cable, the first helical portion having a pitch from 200 μm to 400 μm, a second helical portion at a distal end of the cable, the second helical portion having a pitch from 200 μm to 400 μm, a third helical portion that extends between the first helical portion and the second helical portion, the middle portion being a third helical portion with a pitch from 600 μm to 1600 μm, a supporting structure that extends from the proximal end to the distal end, and a plurality of conductive traces formed on a portion of the supporting structure; and an electrode assembly formed on the supporting structure at the distal end of the cable, where the electrode assembly comprises one or more electrodes in electrical connection with one or more conductive traces of the plurality of conductive traces. 
     In some embodiments, the monolithic thin-film lead assembly further includes a first portion of an housing formed coplanar with the first helical portion. In some embodiments, the first portion of the housing is comprised of a thermoplastic or thermosetting polymer. In some embodiments, the monolithic thin-film lead assembly further includes a second portion of an housing formed coplanar with the second helical portion. In some embodiments, the second portion of the housing is comprised of a thermoplastic or thermosetting polymer. In some embodiments, the monolithic thin-film lead assembly further includes a third portion of the housing completely encasing the third helical portion. In some embodiments, the third portion of the housing is comprised of silicone. 
     In some embodiments, the monolithic thin-film lead assembly further includes a multiplexer chip formed on the supporting structure at the proximal end or the distal end, the multiplexer chip in electrical connection with the one or more electrodes via the one or more conductive traces of the plurality of conductive traces. 
     In some embodiments, a thickness of the supporting structure is from 10 μm to 150 μm. In some embodiments, the plurality of conductive traces have a thickness from 0.5 μm to 100 μm. In some embodiments, a length of the supporting structure is from 5 cm to 150 cm. In some embodiments, the supporting structure is comprised of one or more layers of dielectric material that is polyimide, liquid crystal polymer, parylene, polyether ether ketone, or a combination thereof. In some embodiments, a length of the plurality of conductive traces is from 5 cm to 150 cm. 
     In some embodiments, the plurality of conductive traces are comprised of one or more layers of conductive material, and the conductive material is copper (Cu), gold (Au), silver (Ag), gold/chromium (Au/Cr), platinum (Pt), platinum/iridium (Pt/Ir), titanium (Ti), gold/titanium (Au/Ti), or any alloy thereof. 
     In various embodiments, a monolithic thin-film lead assembly comprises a cable comprising: a helical portion that extends between a proximal end and a distal end of the cable, the helical portion having a pitch from 600 μm to 1600 μm, a supporting structure that extends from the proximal end to the distal end of the cable, and a plurality of conductive traces formed on a portion of the supporting structure; and an electrode assembly formed on the supporting structure at the distal end of the cable. The electrode assembly comprises one or more electrodes in electrical connection with one or more conductive traces of the plurality of conductive traces. 
     In some embodiments, the monolithic thin-film lead assembly further includes a housing completely encasing the first helical portion, where the housing is comprised of silicone. In some embodiments, the electrode assembly further comprises one or more sensors in electrical connection with one or more conductive traces of the plurality of conductive traces. In some embodiments, the electrode assembly is a cuff electrode assembly. In some embodiments, the supporting structure at the distal end of the cable having the electrode assembly formed thereon is thermoformed into a cuff structure. 
     In some embodiments, the monolithic thin-film lead assembly further includes a connector formed on the supporting structure at the proximal end of the cable and in electrical connection with the one or more conductive traces of the plurality of conductive traces. In some embodiments, the connector comprises one or more bond or contact pads. In some embodiments, the monolithic thin-film lead assembly further includes a multiplexer chip formed on the supporting structure at the proximal end or the distal end, the multiplexer chip in electrical connection with the one or more electrodes via the one or more conductive traces of the plurality of conductive traces. In some embodiments, a thickness of the supporting structure is from 10 μm to 150 μm. In some embodiments, the plurality of conductive traces have a thickness from 0.5 μm to 100 μm. In some embodiments, a length of the supporting structure is from 5 cm to 150 cm. In some embodiments, the supporting structure is comprised of one or more layers of dielectric material that is polyimide, liquid crystal polymer, parylene, polyether ether ketone, or a combination thereof. In some embodiments, a length of the plurality of conductive traces is from 5 cm to 150 cm. 
     In some embodiments, the plurality of conductive traces are comprised of one or more layers of conductive material, and the conductive material is copper (Cu), gold (Au), silver (Ag), gold/chromium (Au/Cr), platinum (Pt), platinum/iridium (Pt/Ir), titanium (Ti), gold/titanium (Au/Ti), or any alloy thereof. 
     In various embodiments, a method of manufacturing a monolithic thin-film lead assembly is provided that includes: forming a first polymer layer on a wafer or panel of substrate; forming a plurality of conductive traces on a first portion of the first polymer layer, where the forming the plurality of conductive traces comprises depositing a conductive material in a spiral pattern with two or more turns on the first portion of the first polymer layer; forming a wiring layer on a second portion of the first polymer layer, where the forming the wiring layer comprises depositing the conductive material in electrical contact with the plurality of conductive traces; depositing a second polymer layer on the wiring layer and the second portion of the first polymer layer; forming at least one electrode on the second polymer layer such that the at least one electrode is in electrical contact with at least a portion of a top surface of the wiring layer; and cutting the monolithic thin-film lead assembly from the first polymer layer, where the monolithic thin-film lead assembly comprises the plurality of conductive traces in the spiral pattern on the first polymer layer and the at least one electrode on the second polymer layer electrically connected to the plurality of conductive traces. 
     In some embodiments, the first polymer layer comprises one or more layers of dielectric material. In some embodiments, the dielectric material is polyimide, liquid crystal polymer, parylene, polyether ether ketone, or a combination thereof. In some embodiments, the second polymer layer comprises one or more layers of dielectric material. In some embodiments, the dielectric material is polyimide, liquid crystal polymer, parylene, polyether ether ketone, or a combination thereof. 
     In some embodiments, the method of manufacturing a monolithic thin-film lead assembly further includes forming contact vias in the second polymer layer to the wiring layer, where the forming the at least one electrode comprises: depositing a conductive material in the contact via and on a top surface of the second polymer layer, and patterning the conductive material to form: (i) a first electrode over a first region of the second polymer layer such that the first electrode is in contact with a first portion of the top surface of the wiring layer, and (ii) a second electrode over a second region of the second polymer layer such that the second electrode is in contact with a second portion of the top surface of the wiring layer. 
     In some embodiments, the first region and the second region of the second polymer layer are separated from one another by a third region of the second polymer layer that does include at least a portion of the wiring layer but does not include an electrode. In some embodiments, the method of manufacturing a monolithic thin-film lead assembly further includes depositing the second polymer layer on the plurality of conductive traces and the first portion of the polymer layer. In some embodiments, the method of manufacturing a monolithic thin-film lead assembly further includes detaching the monolithic thin-film lead assembly from the wafer or panel of substrate. 
     In various embodiments, a method of manufacturing a monolithic thin-film lead assembly is provided that includes: obtaining an initial structure comprising: (i) a cable comprising: a proximal end, a distal end, a supporting structure that extends from the proximal end to the distal end, and a plurality of conductive traces formed on a portion of the supporting structure; and (ii) an electrode assembly formed on the supporting structure at the distal end of the cable, where the electrode assembly comprises one or more electrodes in electrical connection with one or more conductive traces of the plurality of conductive traces; winding the portion of the supporting structure in a helical pattern on a mandrel; and heating the initial structure with the portion of the supporting structure wound in the helical pattern on the mandrel to form the monolithic thin-film lead assembly. 
     In some embodiments, the winding is controlled such that the helical pattern has a helix angle from 10° to 85° and a pitch from 100 μm to 2 mm. In some embodiments, the supporting structure is comprised of one or more layers of dielectric material, and a length of the supporting structure is from 5 cm to 150 cm. In some embodiments, the dielectric material is polyimide, liquid crystal polymer, parylene, polyether ether ketone, or a combination thereof. In some embodiments, a length of the plurality of conductive traces is from 5 cm to 150 cm. 
     In some embodiments, the plurality of conductive traces are comprised of one or more layers of conductive material, and the conductive material is copper (Cu), gold (Au), silver (Ag), gold/chromium (Au/Cr), platinum (Pt), platinum/iridium (Pt/Ir), titanium (Ti), gold/titanium (Au/Ti), or any alloy thereof. 
     In some embodiments, the obtaining the initial structure comprises: forming the supporting structure on a wafer or panel of substrate; forming the plurality of conductive traces on a first portion of the supporting structure; forming a wiring layer on a second portion of the supporting structure; depositing a polymer layer on the wiring layer and the second portion of the supporting structure; forming at least one electrode on the polymer layer such that the at least one electrode is in electrical contact with at least a portion of a top surface of the wiring layer; removing the wafer or panel of substrate from the supporting structure; and cutting the initial structure from the first polymer layer. 
     In various embodiments, a method of manufacturing a monolithic thin-film lead assembly is provided that includes: obtaining an initial structure comprising: (i) a cable comprising: a proximal end, a distal end, a supporting structure that extends from the proximal end to the distal end, and a plurality of conductive traces formed on a portion of the supporting structure; and (ii) an electrode assembly formed on the supporting structure at the distal end of the cable, where the electrode assembly comprises one or more electrodes in electrical connection with one or more conductive traces of the plurality of conductive traces; winding the portion of the supporting structure in a helical pattern on a mandrel; inserting the mandrel with the portion of the supporting structure into a polymer tube to form an intermediate structure; heating the intermediate structure with the portion of the supporting structure wound in the helical pattern on the mandrel to form the monolithic thin-film lead assembly; and removing the mandrel from the monolithic thin-film lead assembly. The polymer tube may completely encase the portion of the supporting structure wound in the helical pattern. 
     In some embodiments, the polymer tube is comprised of silicone, a polymer dispersion, parylene, or a polyurethane. In some embodiments, an inner diameter of the polymer tube is less than an outer diameter of the portion of the supporting structure wound in the helical pattern. In some embodiments, the method of manufacturing a monolithic thin-film lead assembly further includes soaking the polymer tube in a solution to swell the polymer tube prior to the insertion of the mandrel with the portion of the supporting structure wound in the helical pattern into the polymer tube. In some embodiments, the solution comprises heptane. In some embodiments, the heating process results in at least a portion of the portion of the supporting structure wound in the helical pattern embedding into a wall of the polymer tube since the inner diameter of the polymer tube is less than the outer diameter of the portion of the supporting structure wound in the helical pattern. 
     In some embodiments, the method of manufacturing a monolithic thin-film lead assembly further includes treating the monolithic thin-film lead assembly with oxygen plasma. In some embodiments, the method of manufacturing a monolithic thin-film lead assembly further includes sealing ends of the polymer tube in the monolithic thin-film lead assembly. 
     In various embodiments, a method of manufacturing a monolithic thin-film lead assembly is provided that includes: obtaining an initial structure comprising: (i) a cable comprising: a proximal end, a distal end, a supporting structure that extends from the proximal end to the distal end, and a plurality of conductive traces formed on a portion of the supporting structure; and (ii) an electrode assembly formed on the supporting structure at the distal end of the cable, where the electrode assembly comprises one or more electrodes in electrical connection with one or more conductive traces of the plurality of conductive traces; winding the portion of the supporting structure in a helical pattern on a mandrel; heating the initial structure with the portion of the supporting structure wound in the helical pattern on the mandrel to form a first intermediate structure; removing the mandrel from the intermediate structure; inserting the mandrel into a polymer tube; winding the portion of the supporting structure in the helical pattern on the polymer tube and the mandrel to form a second intermediate structure; inserting the second intermediate structure into a heat shrink tube; heating the second intermediate structure with the heat shrink tube to form the monolithic thin-film lead assembly; and removing the heat shrink tube and the mandrel from the monolithic thin-film lead assembly. The heating embeds the supporting structure wound in the helical pattern into the polymer tube. 
     In some embodiments, the polymer tube is comprised of silicone, a polymer dispersion, parylene, or a polyurethane. In some embodiments, the polymer tube is comprised of polyurethane. 
     In various embodiments, a neuromodulation system is provided that includes: a neurostimulator comprising an electronics module; a cable comprising: a first helical portion at a proximal end of the cable, the first helical portion having a pitch from 200 μm to 400 μm, a second helical portion at a distal end of the cable, the second helical portion having a pitch from 200 μm to 400 μm, a third helical portion that extends between the first helical portion and the second helical portion, the middle portion being a third helical portion with a pitch from 600 μm to 1600 μm, a supporting structure that extends from the proximal end to the distal end, and a plurality of conductive traces formed on a portion of the supporting structure; an electrode assembly formed on the supporting structure at the distal end of the cable, where the electrode assembly comprises one or more electrodes in electrical connection with one or more conductive traces of the plurality of conductive traces; and a connector formed on the supporting structure at the proximal end and in electrical connection with the one or more conductive traces of the plurality of conductive traces. The connector electrically connects the one or more conductive traces of the plurality of conductive traces to the electronics module. 
     In various embodiments, a method of manufacturing a monolithic thin-film lead assembly is provided that includes: obtaining an initial structure comprising: (i) a cable comprising: a proximal end, a distal end, a supporting structure that extends from the proximal end to the distal end, and a plurality of conductive traces formed on a portion of the supporting structure; and (ii) an electrode assembly formed on the supporting structure at the distal end of the cable, where the electrode assembly comprises one or more electrodes in electrical connection with one or more conductive traces of the plurality of conductive traces; winding the portion of the supporting structure in a helical pattern on a mandrel; inserting the mandrel with the portion of the supporting structure into a heat shrink tube to form an intermediate structure; heating the first intermediate structure with the portion of the supporting structure wound in the helical pattern on the mandrel to form a second intermediate structure; removing the mandrel from the second intermediate structure such that the second intermediate structure is left with a lumen; injecting the lumen of the second intermediate structure with a polymer to form a third intermediate structure; heating the third intermediate structure with the heat shrink tube to form the monolithic thin-film lead assembly; and removing the heat shrink tube from the monolithic thin-film lead assembly. The heating embeds the supporting structure wound in the helical pattern into the polymer. 
     In some embodiments, the heat shrink tube is comprised of a fluoropolymer. In some embodiments, the polymer is comprised of silicone, a polyurethane, a copolymer thereof, or a blend thereof. In some embodiments, the polymer has a Shore durometer measured on a Shore 00 Scale of less than 50. In some embodiments, the plurality of conductive traces and the supporting structure wound in the helical pattern are coplanar with the polymer in the monolithic thin-film lead assembly. 
     In various embodiments, a method of manufacturing a monolithic thin-film lead assembly is provided including: obtaining an initial structure comprising: (i) a cable comprising: a proximal end, a distal end, a supporting structure that extends from the proximal end to the distal end, and a plurality of conductive traces formed on a portion of the supporting structure; and (ii) an electrode assembly formed on the supporting structure at the distal end of the cable, where the electrode assembly comprises one or more electrodes in electrical connection with one or more conductive traces of the plurality of conductive traces; winding the portion of the supporting structure in a helical pattern on a mandrel; cutting a slit into a polymer tube such that a lumen of the polymer tube is exposed along an entire length of the polymer tube; inserting the mandrel with the portion of the supporting structure into the lumen of the polymer tube through the slit to form a first intermediate structure; removing the mandrel from the first intermediate structure such that the first intermediate structure is left with the lumen; sealing ends of the polymer tube in the first intermediate structure to form a second intermediate structure; and heating the second intermediate structure to form the monolithic thin-film lead assembly. The polymer tube encases the portion of the supporting structure wound in the helical pattern. 
     In some embodiments, the polymer tube is comprised of silicone, a polymer dispersion, parylene, a polyurethane. In some embodiments, an inner diameter of the polymer tube is greater than an outer diameter of the portion of the supporting structure wound in the helical pattern. 
     In various embodiments, a method of manufacturing a monolithic thin-film lead assembly is provided that includes: obtaining an initial structure comprising: (i) a cable comprising: a proximal end, a distal end, a supporting structure that extends from the proximal end to the distal end, and a plurality of conductive traces formed on a portion of the supporting structure; and (ii) an electrode assembly formed on the supporting structure at the distal end of the cable, where the electrode assembly comprises one or more electrodes in electrical connection with one or more conductive traces of the plurality of conductive traces; winding the portion of the supporting structure in a helical pattern on a mandrel; removing the mandrel from the portion of the supporting structure; treating the portion of the supporting structure with oxygen plasma; diluting a liquid prepolymer or polymer with a solvent to form a solution; applying the solution on the supporting structure to form an intermediate structure comprising one or more coats of polymer; and heating the intermediate structure to form the monolithic thin-film lead assembly. The polymer encases the portion of the supporting structure wound in the helical pattern. 
     In some embodiments, the polymer is comprised of silicone, a polymer dispersion, parylene, or a polyurethane. In some embodiments, the applying the solution comprises applying the solution using a dip coating process, a spin coating process, or a spray coating process. 
     In various embodiments, a lead assembly is provided comprising: a cable comprising: a proximal end, a distal end, a supporting structure that extends from the proximal end to the distal end, and a plurality of conductive traces formed on a portion of the supporting structure, where the supporting structure is comprised of one or more layers of dielectric material; and an interface formed on the supporting structure at the distal end of the cable, where the interface comprises a plurality of electrodes and/or a plurality of sensors in electrical connection with one or more conductive traces of the plurality of conductive traces, the plurality of electrodes comprise a first set of electrodes and a second set of electrodes and/or the plurality of sensors comprise a first set of sensors and a second set of sensors, the supporting structure at the distal end of the cable comprises at least one curved portion; and (i) the at least one curved portion of the supporting structure is disposed between the first set of electrodes and the second set of electrodes, and/or (ii) the at least one curved portion of the supporting structure is disposed between the first set of sensors and the second set of sensors. 
     In some embodiments, the supporting structure at the distal end of the cable is thermoformed into a curved structure comprising the at least one curved portion. 
     In some embodiments, the at least one curved portion is a single curved portion and the curved structure has a shape of a “U” or a “J”. 
     In some embodiments, the at least one curved portion is multiple curved portions and the curved structure has a shape of a “S”, a helix, or a involute spiral. 
     In some embodiments, the plurality of conductive traces have a thickness from 0.5 μm to 100 μm. 
     In some embodiments, the cable has a spiral shape comprising two or more turns and a pitch between each of the turns from 10 μm to 1 cm. 
     In some embodiments, the plurality of conductive traces extend from the proximal end to the distal end. 
     In some embodiments, a length of the supporting structure is from 5 cm to 150 cm, and a width of the supporting structure is from 25 μm to 5 mm. 
     In some embodiments, the dielectric material is polyimide, liquid crystal polymer, parylene, polyether ether ketone, or a combination thereof. 
     In some embodiments, the plurality of conductive traces are comprised of one or more layers of conductive material, and the conductive material is copper (Cu), gold (Au), silver (Ag), gold/chromium (Au/Cr), platinum (Pt), platinum/iridium (Pt/Ir), titanium (Ti), gold/titanium (Au/Ti), or any alloy thereof. 
     In some embodiments, a coefficient of thermal expansion for the plurality of conductive traces is approximately equal to a coefficient of thermal expansion for the supporting structure. 
     In some embodiments, the lead assembly further comprises a multiplexer chip formed on the supporting structure at the proximal end or the distal end, the multiplexer chip in electrical connection with the plurality of electrodes and/or the plurality of sensors via the plurality of conductive traces. 
     In various embodiments, a method of manufacturing a monolithic thin-film lead assembly is provided that comprises: forming a cable comprising: forming a first polymer layer; and forming a plurality of conductive traces on a first portion of the first polymer layer, where the forming the plurality of conductive traces comprises depositing a conductive material on the first portion of the first polymer layer; forming an interface comprising: forming a wiring layer on a second portion of the first polymer layer, where the forming the wiring layer comprises depositing the conductive material in electrical contact with the plurality of conductive traces; depositing a second polymer layer on the wiring layer and the second portion of the first polymer layer; forming a plurality of electrodes and/or a plurality of sensors on the second polymer layer such that the plurality of electrodes and/or the plurality of sensors are in electrical contact with at least a portion of a top surface of the wiring layer; where the plurality of electrodes comprise a first set of electrodes and a second set of electrodes and/or the plurality of sensors comprise a first set of sensors and a second set of sensors; forming at least one curved portion in the second portion of the first polymer layer and the second polymer layer, where the at least one curved portion is formed by wrapping the interface around a mandrel or placing the interface in a mold, and where: (i) the at least one curved portion is disposed between the first set of electrodes and the second set of electrodes, and/or (ii) the at least one curved portion is disposed between the first set of sensors and the second set of sensors; and heating the interface while wrapped around the mandrel or placed in the mold to thermoform the second portion of the first polymer layer and the second polymer layer into a curved structure comprising the at least one curved portion. 
     In some embodiments, the at least one curved portion is a single curved portion and the curved structure has a shape of a “U” or a “J”. 
     In some embodiments, the at least one curved portion is multiple curved portions and the curved structure has a shape of a “S”, a helix, or a involute spiral. 
     In some embodiments, the method further comprises: inserting a guidewire having a stylet though the interface causing the at least one curved portion to straighten, which forces the curved structure into a linear structure. 
     In various embodiments, a method for deploying a monolithic thin-film lead assembly is provided that comprises: obtaining the lead assembly comprising: a cable comprising: a proximal end, a distal end, a supporting structure that extends from the proximal end to the distal end, and a plurality of conductive traces formed on a portion of the supporting structure, where the supporting structure is comprised of one or more layers of dielectric material; an interface formed on the supporting structure at the distal end of the cable, where the interface comprises a plurality of electrodes and/or a plurality of sensors in electrical connection with one or more conductive traces of the plurality of conductive traces, where the plurality of electrodes comprise a first set of electrodes and a second set of electrodes and/or the plurality of sensors comprise a first set of sensors and a second set of sensors; and a guidewire comprising a stylet inserted through the interface, where while the stylet is inserted through the interface, the interface has a first profile, and where the first profile is straight with the first set of electrodes and the second set of electrodes and/or the first set of sensors and the second set of sensors provided in a linear array; inserting, with the guidewire, the lead assembly into a cavity (such as an endovascular cavity) of a subject; moving, with the guidewire, the lead assembly through the cavity to position the interface at a target location (such as a target location for brain computer interfacing); and removing the guidewire and stylet from the cavity while leaving the lead assembly in place with the interface positioned at the target location, where removal of the stylet from the interface allows for the interface to take a second profile having at least one curved portion, where: (i) the at least one curved portion is disposed between the first set of electrodes and the second set of electrodes, and/or (ii) the at least one curved portion is disposed between the first set of sensors and the second set of sensors. 
     In some embodiments, the at least one curved portion is a single curved portion and the curved structure has a shape of a “U” or a “J”. 
     In some embodiments, the at least one curved portion is multiple curved portions and the curved structure has a shape of a “S”, a helix, or a involute spiral. 
     In some embodiments, the method further comprises: connecting the cable to a computing device and using the computing device to send a single through the interface to tissue at the target location or receive a signal from the tissue at the target location. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be better understood in view of the following non-limiting figures, in which: 
         FIG.  1    shows a neuromodulation system in accordance with various embodiments; 
         FIGS.  2 A- 2 H  show a lead assembly in accordance with various embodiments; 
         FIGS.  3 A and  3 B  show an alternative lead assembly in accordance with various embodiments; 
         FIGS.  4 A,  4 B, and  4 C  show an alternative lead assembly in accordance with various embodiments; 
         FIGS.  5 A,  5 B, and  5 C  show an alternative lead assembly in accordance with various embodiments; 
         FIGS.  6 A,  6 B,  6 C, and  6 D  show alternative lead assemblies in accordance with various embodiments; 
         FIG.  7    shows an alternative lead assembly in accordance with various embodiments; 
         FIGS.  8 A- 8 G  show cross-sectional side views and a lead assembly view illustrating a method of forming a lead assembly in accordance with various embodiments; 
         FIGS.  9 A- 9 D  show lead assembly views illustrating a method of forming a lead assembly in accordance with various embodiments; 
         FIGS.  10 A- 10 J  show lead assembly views illustrating a method of forming a lead assembly in accordance with various embodiments; 
         FIGS.  11 A- 11 F  show lead assembly views illustrating a method of forming a lead assembly in accordance with various embodiments; 
         FIGS.  12 A- 12 G  show lead assembly views illustrating a method of forming a lead assembly in accordance with various embodiments; 
         FIGS.  13 A- 13 F  show lead assembly views illustrating a method of forming a lead assembly in accordance with various embodiments; and 
         FIGS.  14 A- 14 F  show lead assembly views illustrating a method of forming a lead assembly in accordance with various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     I. Introduction 
     The following disclosure describes monolithic thin-film lead assemblies and methods of microfabricating monolithic thin-film lead assemblies. As used herein, the phrase “monolithic” refers to a device fabricated using a same layer of base material. The device may be fabricated using microfabricating techniques. As used herein, the phrase “microfabrication” refers to the process of fabricating miniature structures on micrometer scales and smaller. The major concepts and principles of microfabrication are microlithography, doping, thin films, etching, bonding, and polishing. As used herein, the phrase “thin films” refers to a layer of material ranging from fractions of a nanometer (monolayer) to several micrometers in thickness (e.g., between a few nanometers to about 100 μm, or the thickness of a few atoms). Thin films may be deposited by applying a very thin film of material (e.g., between a few nanometers to about 100 μm, or the thickness of a few atoms) onto a substrate surface to be coated, or onto a previously deposited layer of thin film. In various embodiments, a thin film lead assembly is provided comprising a base polymer body (e.g., a supporting structure) and at least one conductive trace formed on the base polymer body. 
     Limitations associated with conventional thin film cables such as flexible printed circuits, flexible foil circuits or flexible flat cables is that the cable length is restricted by a size of the wafer or panel used to fabricate the cable, the base polymer typically has a small elastic elongation (e.g., an elastic elongation of &lt;20%), and the cables are overall stiff with a relatively high Young&#39;s modulus (e.g., &gt;1.0 GPa). All of these limitations create challenges for using thin film cables in electrical neuromodulation systems where the cables need to extend deep within the patient while allowing for freedom of movement by the patient with very little to no irritation or damage to surrounding tissues. Moreover, as discussed herein, conventional cables used in electrical neuromodulation systems have connectors on both ends for connecting the cable to additional components such as a lead conductor, electrode, and neurostimulator. The use of connectors and the presence of multiple conductive components to supply electrical signals between the neurostimulator and the electrodes results in an overall bulky electrical neuromodulation system and provide multiple connection points that are susceptible to disconnections and fractures of system components. 
     To address these limitations and problems, the thin film cable of various embodiments disclosed herein is a monolithic structure, which results in less connection points, a smaller footprint, and greater design flexibility. One illustrative embodiment of the present disclosure is directed to a monolithic thin-film lead assembly that comprises a cable having a proximal end, a distal end, a supporting structure that extends from the proximal end to the distal end, and a plurality of conductive traces formed on a portion of the supporting structure. The supporting structure may include one or more layers of dielectric material. The monolithic thin-film lead assembly may further include an electrode assembly formed on the supporting structure at the distal end of the cable. The electrode assembly may include one or more electrodes in electrical connection with one or more conductive traces of the plurality of conductive traces. 
     In other embodiments, a monolithic thin-film lead assembly is provided directed to a specific application (e.g., a deep brain neurostimulation). The monolithic thin-film lead assembly comprises a cable having: a first helical portion at a proximal end of the cable, the first helical portion having a pitch from 200 μm to 400 μm, a second helical portion at a distal end of the cable, the second helical portion having a pitch from 200 μm to 400 μm, a third helical portion that extends between the first helical portion and the second helical portion, the middle portion being a third helical portion with a pitch from 600 μm to 1600 μm, a supporting structure that extends from the proximal end to the distal end, and a plurality of conductive traces formed on a portion of the supporting structure. The monolithic thin-film lead assembly may further include an electrode assembly formed on the supporting structure at the distal end of the cable. The electrode assembly may comprise one or more electrodes in electrical connection with one or more conductive traces of the plurality of conductive traces. 
     In other embodiments, a monolithic thin-film lead assembly is provided directed to a specific application (e.g., vagus nerve or artery/nerve plexus). The monolithic thin-film lead assembly comprises a cable having: a helical portion that extends between a proximal end and a distal end of the cable, the helical portion having a pitch from 600 μm to 1600 μm, a supporting structure that extends from the proximal end to the distal end of the cable, and a plurality of conductive traces formed on a portion of the supporting structure. The monolithic thin-film lead assembly may further include an electrode assembly formed on the supporting structure at the distal end of the cable. The electrode assembly may comprise one or more electrodes in electrical connection with one or more conductive traces of the plurality of conductive traces. 
     In other embodiments, a monolithic thin-film lead assembly is provided comprising: a cable comprising: a proximal end, a distal end, a supporting structure that extends from the proximal end to the distal end, and a plurality of conductive traces formed on a portion of the supporting structure, where the supporting structure is comprised of one or more layers of dielectric material; and an interface formed on the supporting structure at the distal end of the cable, where the interface comprises a plurality of electrodes and/or a plurality of sensors in electrical connection with one or more conductive traces of the plurality of conductive traces. The plurality of electrodes comprise a first set of electrodes and a second set of electrodes and/or the plurality of sensors comprise a first set of sensors and a second set of sensors. The supporting structure at the distal end of the cable comprises at least one curved portion. The at least one curved portion of the supporting structure is disposed between the first set of electrodes and the second set of electrodes, and/or the at least one curved portion of the supporting structure is disposed between the first set of sensors and the second set of sensors. 
     To further address these limitations and problems, a method of manufacturing the thin film cable of various embodiments disclosed herein includes process steps for creating a monolithic structure, which results in less connection points, a smaller footprint, and greater design flexibility. One illustrative embodiment of the present disclosure is directed to method of manufacturing a monolithic thin-film lead assembly that comprises forming a first polymer layer on a wafer or panel of substrate, and forming a plurality of conductive traces on a first portion of the first polymer layer. The forming the plurality of conductive traces may comprise depositing a conductive material in a spiral pattern with two or more turns on the first portion of the first polymer layer. The method further comprises forming a wiring layer on a second portion of the first polymer layer. The forming the wiring layer may comprise depositing the conductive material in electrical contact with the plurality of conductive traces. The method may further comprise depositing a second polymer layer on the wiring layer and the second portion of the first polymer layer, forming at least one electrode on the second polymer layer such that the at least one electrode is in electrical contact with at least a portion of a top surface of the wiring layer, and cutting the monolithic thin-film lead assembly from the first polymer layer. The monolithic thin-film lead assembly may comprise the plurality of conductive traces in the spiral pattern on the first polymer layer and the at least one electrode on the second polymer layer electrically connected to the plurality of conductive traces. 
     In other embodiments, a method of manufacturing a monolithic thin-film lead assembly is provided that comprises obtaining an initial structure comprising: (i) a cable comprising: a proximal end, a distal end, a supporting structure that extends from the proximal end to the distal end, and a plurality of conductive traces formed on a portion of the supporting structure; and (ii) an electrode assembly formed on the supporting structure at the distal end of the cable. The electrode assembly may comprise one or more electrodes in electrical connection with one or more conductive traces of the plurality of conductive traces. The method further comprises winding the portion of the supporting structure in a helical pattern on a mandrel, inserting the mandrel with the portion of the supporting structure into a polymer tube to form an intermediate structure, heating the intermediate structure with the portion of the supporting structure wound in the helical pattern on the mandrel to form the monolithic thin-film lead assembly, and removing the mandrel from the monolithic thin-film lead assembly. The polymer tube may completely encase the portion of the supporting structure wound in the helical pattern. 
     In other embodiments, a method of manufacturing a monolithic thin-film lead assembly is provided that comprises obtaining an initial structure comprising: (i) a cable comprising: a proximal end, a distal end, a supporting structure that extends from the proximal end to the distal end, and a plurality of conductive traces formed on a portion of the supporting structure; and (ii) an electrode assembly formed on the supporting structure at the distal end of the cable. The electrode assembly may comprise one or more electrodes in electrical connection with one or more conductive traces of the plurality of conductive traces. The method further comprises winding the portion of the supporting structure in a helical pattern on a mandrel, heating the initial structure with the portion of the supporting structure wound in the helical pattern on the mandrel to form a first intermediate structure, removing the mandrel from the intermediate structure, inserting the mandrel into a polymer tube, winding the portion of the supporting structure in the helical pattern on the polymer tube and the mandrel to form a second intermediate structure, inserting the second intermediate structure into a heat shrink tube, heating the second intermediate structure with the heat shrink tube to form the monolithic thin-film lead assembly, and removing the heat shrink tube and the mandrel from the monolithic thin-film lead assembly. The heating may embed the supporting structure wound in the helical pattern into the polymer tube. 
     In other embodiments, a method of manufacturing a monolithic thin-film lead assembly is provided that comprises forming a cable comprising: forming a first polymer layer; and forming a plurality of conductive traces on a first portion of the first polymer layer, where the forming the plurality of conductive traces comprises depositing a conductive material on the first portion of the first polymer layer; forming an interface comprising: forming a wiring layer on a second portion of the first polymer layer, where the forming the wiring layer comprises depositing the conductive material in electrical contact with the plurality of conductive traces; depositing a second polymer layer on the wiring layer and the second portion of the first polymer layer; forming a plurality of electrodes and/or a plurality of sensors on the second polymer layer such that the plurality of electrodes and/or the plurality of sensors are in electrical contact with at least a portion of a top surface of the wiring layer; where the plurality of electrodes comprise a first set of electrodes and a second set of electrodes and/or the plurality of sensors comprise a first set of sensors and a second set of sensors; forming at least one curved portion in the second portion of the first polymer layer and the second polymer layer, where the at least one curved portion is formed by wrapping the interface around a mandrel or placing the interface in a mold, and where: (i) the at least one curved portion is disposed between the first set of electrodes and the second set of electrodes, and/or (ii) the at least one curved portion is disposed between the first set of sensors and the second set of sensors; and heating the interface while wrapped around the mandrel or placed in the mold to thermoform the second portion of the first polymer layer and the second polymer layer into a curved structure comprising the at least one curved portion. 
     In other embodiments, a method for deploying a monolithic thin-film lead assembly is provided that comprises: obtaining the lead assembly comprising: a cable comprising: a proximal end, a distal end, a supporting structure that extends from the proximal end to the distal end, and a plurality of conductive traces formed on a portion of the supporting structure, where the supporting structure is comprised of one or more layers of dielectric material; an interface formed on the supporting structure at the distal end of the cable, where the interface comprises a plurality of electrodes and/or a plurality of sensors in electrical connection with one or more conductive traces of the plurality of conductive traces, where the plurality of electrodes comprise a first set of electrodes and a second set of electrodes and/or the plurality of sensors comprise a first set of sensors and a second set of sensors; and a guidewire comprising a stylet inserted through the interface, where while the stylet is inserted through the interface, the interface has a first profile, and where the first profile is straight with the first set of electrodes and the second set of electrodes and/or the first set of sensors and the second set of sensors provided in a linear array; inserting, with the guidewire, the lead assembly into a cavity (such as an endovascular cavity) of a subject; moving, with the guidewire, the lead assembly through the cavity to position the interface at a target location (such as a target location for brain computer interfacing); and removing the guidewire and stylet from the cavity while leaving the lead assembly in place with the interface positioned at the target location, where removal of the stylet from the interface allows for the interface to take a second profile having at least one curved portion, where: (i) the at least one curved portion is disposed between the first set of electrodes and the second set of electrodes, and/or (ii) the at least one curved portion is disposed between the first set of sensors and the second set of sensors. In some instances, the cable is connected to a computing device and the computing device is used to send a single through the interface to tissue at the target location or receive a signal from the tissue at the target location. 
     Advantageously, these approaches provide a monolithic thin-film lead assembly, which has less connection points, a smaller footprint, and greater design flexibility. More specifically, these approaches enable continuous electrode(s) and conductor(s) on a single cable or lead body. This solution is scalable to connecting several electrodes using a multi flex chip, and thus enabling several therapeutic opportunities for neurostimulation. Furthermore even for applications where multiple electrodes are not required, various embodiments can be miniaturized to make the implant minimally invasive, additionally may make invasive anatomies to become accessible (or navigable) due to the miniaturization. It should be understood that although deep brain neurostimulation and vagus nerve or artery/nerve plexus device applications are provided as examples of some embodiments, this solution is applicable to all leads and devices that need electrodes/sensors that need to be attached to long lengths of conductors. 
     II. Neuromodulation Devices and Systems with a Lead Assembly 
       FIG.  1    shows a neuromodulation system  100  in accordance with some aspects of the present invention. In various embodiments, the neuromodulation system  100  includes an implantable neurostimulator  105  and a lead assembly  110 . The implantable neurostimulator  105  may include a housing  115 , a feedthrough assembly  120 , a power source  125 , an antenna  130 , and an electronics module  135  (e.g., a computing system). The housing  115  may be comprised of materials that are biocompatible such as bioceramics or bioglasses for radio frequency transparency, or metals such as titanium. In accordance with some aspects of the present invention, the size and shape of the housing  115  may be selected such that the neurostimulator  105  can be implanted within a patient. In the example shown in  FIG.  1   , the feedthrough assembly  120  is attached to a hole in a surface of the housing  115  such that the housing  115  is hermetically sealed. The feedthrough assembly  120  may include one or more feedthroughs (i.e., electrically conductive elements, pins, wires, tabs, pads, etc.) mounted within and extending through the surface of the housing  115  or a cap from an interior to an exterior of the housing  115 . The power source  125  may be within the housing  115  and connected (e.g., electrically connected) to the electronics module  135  to power and operate the components of the electronics module  135 . The antenna  130  may be connected (e.g., electrically connected) to the electronics module  135  for wireless communication with external devices via, for example, radiofrequency (RF) telemetry. 
     In some embodiments, the electronics module  135  may be connected (e.g., electrically connected) to interior ends of the feedthrough assembly  120  such that the electronics module  135  is able to apply a signal or electrical current to conductive traces of the lead assembly  110  connected to exterior ends of the feedthrough assembly  120 . The electronics module  135  may include discrete and/or integrated electronic circuit components that implement analog and/or digital circuits capable of producing the functions attributed to the neuromodulation devices or systems such as applying or delivering neural stimulation to a patient. In various embodiments, the electronics module  135  may include software and/or electronic circuit components such as a pulse generator  140  that generates a signal to deliver a voltage, current, optical, or ultrasonic stimulation to a nerve or artery/nerve plexus via electrodes, a controller  145  that determines or senses electrical activity and physiological responses via the electrodes and sensors, controls stimulation parameters of the pulse generator  140  (e.g., control stimulation parameters based on feedback from the physiological responses), and/or causes delivery of the stimulation via the pulse generator  140  and electrodes, and a memory  150  with program instructions operable on by the pulse generator  140  and the controller  145  to perform one or more processes for applying or delivering neural stimulation. 
     In various embodiments, the lead assembly  110  is a monolithic structure that includes a cable or lead body  155 . In some embodiments, the lead assembly  110  further includes one or more electrode assemblies  160  having one or more electrodes  165 , and optionally one or more sensors. In some embodiments, the lead assembly  110  further includes a connector  170 . In certain embodiments, the connector  170  is bonding material that bonds conductor material of the cable  155  to the electronics module  135  of the implantable neurostimulator  105  via the feedthrough assembly  120 . The bonding material may be a conductive epoxy or a metallic solder or weld such as platinum. In other embodiments, the connector  170  is conductive wire, conductive traces, or bond pads (e.g., a wire, trace, or bond pads formed of a conductive material such as copper, silver, or gold) formed on a substrate and bonds a conductor of the cable  155  to the electronics module  135  of the implantable neurostimulator  105 . In alternative embodiments, the implantable neurostimulator  105  and the cable  155  are designed to connect with one another via a mechanical connector  170  such as a pin and sleeve connector, snap and lock connector, flexible printed circuit connectors, or other means known to those of ordinary skill in the art. 
     The cable  155  may include one or more conductive traces  175  formed on a supporting structure  180 . The one or more conductive traces  175  allow for electrical coupling of the electronics module  135  to the electrodes  165  and/or sensors of the electrode assemblies  160 . As described herein in detail, the supporting structure  180  may be formed with a dielectric material such as a polymer having suitable dielectric, flexibility and biocompatibility characteristics. Polyurethane, polycarbonate, silicone, polyethylene, fluoropolymer and/or other medical polymers, copolymers and combinations or blends may be used. The conductive material for the traces  175  may be any suitable conductor such as stainless steel, silver, copper or other conductive materials, which may have separate coatings or sheathing for anticorrosive, insulative and/or protective reasons. 
     The electrode assemblies  160  may include the electrodes  165  and/or sensors fabricated using various shapes and patterns to create certain types of electrode assemblies (e.g., book electrodes, split cuff electrodes, spiral cuff electrodes, epidural electrodes, helical electrodes, probe electrodes, linear electrodes, neural probe, paddle electrodes, intraneural electrodes, etc.). In various embodiments, the electrode assemblies  160  include a base material that provides support for microelectronic structures including the electrodes  165 , a wiring layer, optional contacts, etc. In some embodiments, the base material is the supporting structure  180 . The wiring layer may be embedded within or located on a surface of the supporting structure  180 . The wiring layer may be used to electrically connect the electrodes  165  with the one or more conductive traces  175  directly or indirectly via a lead conductor. The term “directly”, as used herein, may be defined as being without something in between. The term “indirectly”, as used herein, may be defined as having something in between. In some embodiments, the electrodes  165  may make electrical contact with the wiring layer by using the contacts. 
     III. Lead Assemblies 
       FIG.  2 A  shows a lead assembly  200  (e.g., the monolithic lead assembly  110  described with respect to  FIG.  1   ) in accordance with aspects of the present disclosure. In various embodiments, the lead assembly  200  comprises a cable  205  having a proximal end  210  and a distal end  215 . As used herein, the term “proximal end” refers to a first end of the main body, while the term “distal end” refers to a second end opposing the first end. For example, the proximal end may be an end of the main body, which is closest to the user, and the distal end may be an end of the main body, which is furthest from the user. The cable  205  may comprise a supporting structure  220  and one or more conductive traces  225  formed on a portion of the supporting structure. As used herein, the term “formed on” refers to a structure or feature that is formed on a surface of another structure or feature, a structure or feature that is formed within another structure or feature, or a structure or feature that is formed both on and within another structure or feature. In some embodiments, the supporting structure  220  extends from the proximal end  210  to the distal end  215 . In some embodiments, the supporting structure  220  may be made of one or more layers of dielectric material (i.e., an insulator). The dielectric material may be selected from the group of electrically nonconductive materials consisting of organic or inorganic polymers, ceramics, glass, glass-ceramics, polyimide-epoxy, epoxy-fiberglass, and the like. In certain embodiments, the dielectric material is a polymer of imide monomers (i.e., a polyimide), a liquid crystal polymer (LCP) such as Kevlar®, parylene, polyether ether ketone (PEEK), or combinations thereof. In other embodiments, the supporting structure  220  may be made of one or more layers of dielectric material formed on a substrate. The substrate may be made from any type of metallic or non-metallic material. 
     As shown in  FIG.  2 B , in various embodiments, the supporting structure  220  comprising the one or more layers of dielectric material, and optionally the substrate, has a thickness (t) from the proximal end  210  to the distal end  215 . In some embodiments, the thickness (t) is from 10 μm to 150 μm, for example about 50 μm or about 60 μm. As used herein, the terms “substantially,” “approximately” and “about” are defined as being largely but not necessarily wholly what is specified (and include wholly what is specified) as understood by one of ordinary skill in the art. In any disclosed embodiment, the term “substantially,” “approximately,” or “about” may be substituted with “within [a percentage] of” what is specified, where the percentage includes 0.1, 1, 5, and 10 percent. In some embodiments, the supporting structure  220  has a length (l) of 5 cm to 150 cm or 50 cm to 100 cm, e.g., about 75 cm (see, e.g.,  FIG.  2 A ). In some embodiments, the supporting structure  220  has a width (w) from a first side  230  to a second side  235 . In some embodiments, the width (w) is from 25 μm to 5 mm, for example about 400 μm or about 1000 μm (see, e.g.,  FIG.  2 A ). 
     In various embodiments, the one or more conductive traces  225  are a plurality of traces, for example, two or more conductive traces or from two to twenty-four conductive traces. The plurality of conductive traces  225  are comprised of one or more layers of conductive material. The conductive material selected for the one or more conductive traces  225  should have good electrical conductivity and may include pure metals, metal alloys, combinations of metals and dielectrics, and the like. For example, the conductive material may be copper (Cu), gold (Au), silver (Ag), gold/chromium (Au/Cr), etc. In some embodiments, it is also desirable that the conductive material selected for the one or more conductive traces  225  have thermal expansion characteristics or a coefficient of thermal expansion (CTE) that is approximately equal to that of CTE of the supporting structure  220 . Matching the CTE of components that contact one another is desirable because it eliminates the development of thermal stresses, which may occur during fabrication and the operation of the cable, and thus eliminates a known cause of mechanical failure in the components. 
     The one or more conductive traces  225  may be deposited onto a surface of the supporting structure  220  by using thin film deposition techniques well known to those skilled in the art such as by sputter deposition, chemical vapor deposition, metal organic chemical vapor deposition, electroplating, electroless plating, and the like. In some embodiments, the thickness of the one or more conductive traces  225  is dependent on the particular impedance desired for conductor, in order to ensure excellent signal integrity (e.g., electrical signal integrity for stimulation or recording). For example, if a conductor having a relatively high impedance is desired, a small thickness of conductive material should be deposited onto the supporting structure  220 . If, however, a signal plane having a relatively low impedance is desired, a greater thickness of electrically conductive material should be deposited onto the supporting structure  220 . In certain embodiments, each of the one or more conductive traces  225  has a thickness (d). In some embodiments, the thickness (d) is from 0.5 μm to 100 μm or from 25 μm to 50 μm, for example about 25 μm or about 40 μm. In some embodiments, each of the one or more conductive traces  225  has a length (m) of about 5 cm to 200 cm or 50 cm to 150 cm, e.g., about 80 cm. In certain embodiments, each of the one or more conductive traces  225  extends from the proximal end  210  to the distal end  215 . In some embodiments, each of the one or more conductive traces  225  has a width (y) from 2.0 μm to 500 μm, for example about 30 μm or about 50 μm. 
     As shown in  FIG.  2 C , the lead assembly  200  may be formed with a predetermined shape in accordance with aspects of the present disclosure. In particular, as described in greater detail herein, the lead assembly  200  may be formed with a predetermined shape from a prefabricated wafer or panel of dielectric material or optionally a substrate. For example, the lead assembly  200  may be laser cut from a prefabricated wafer or panel in a spiral shape. The spiral shape may include characteristics designed to maximize the length of the lead assembly  200  that can be fabricated from a single wafer or panel. Conventionally, wafers or panels have a diameter, length, and/or width of less than 10 cm. In some embodiments, the characteristics of the spiral shape include a predetermined number of turns 240 and a predetermined pitch (p) between each of the turns 240 to maximize the overall length obtainable for the lead assembly  200 . In certain embodiments, the spiral shape has 2 or more turns, for example from 2 to 25 turns, and a pitch (p) between each of the turns from 10 μm to 1 cm or from 250 μm to 2 mm, for example about 350 μm. Accordingly, the spiral shape can maximize the length of the lead assembly  200  that can be fabricated from a single wafer or panel. For example, a single wafer or panel with a limited diameter, length, and/or width of less than 10 cm, can be used to fabricate a lead assembly  200  with a length of 5 cm to 150 cm, 10 cm to 100 cm, or 25 cm to 75 cm, e.g., about 15 cm, using the spiral shape. 
     As shown in  FIG.  2 D , the lead assembly  200  may further comprise an electrode assembly  245  comprising a supporting structure  220 ′ that provides support for microelectronic structures including one or more electrodes  250 , a wiring layer  255 , and optional contact(s)  260  (shown in  FIG.  2 F ). The electrode assembly  250  may be located at the distal end  215  of the lead assembly  200 . In various embodiments, the supporting structure  220 ′ of the lead assembly and the supporting structure  220  of the electrode assembly are the same structure (i.e., the supporting structure is continuous from the proximal end  210  to the distal end  215 ), which thus creates a monolithic cable. In some embodiments and as shown in  FIG.  2 E , the supporting structure  220 ′ for the electrode assembly  245  comprising the one or more layers of dielectric material, and optionally the substrate, has a thickness (r) of from 10 μm to 150 μm, from 15 μm to 70 μm, from 30 μm to 60 μm, or from 40 μm to 60 μm. In some embodiments, the supporting structure  220  has a width (v) from a first side  225  to a second side  230 . In some embodiments, the width (v) is from 25 μm to 10 mm, for example about 50 μm or about 5000 μm. 
     The wiring layer  255  may be formed on the supporting structure  220 ′. In various embodiments, the wiring layer  255  is formed continuously of the one or more conductive traces  225 , and is comprised of various metals or alloys thereof, for example, copper (Cu), gold (Au), silver (Ag), gold/chromium (Au/Cr), platinum (Pt), platinum/iridium (Pt/Ir), titanium (Ti), gold/titanium (Au/Ti), or any alloy thereof. The wiring layer  255  may have a thickness (x) of from 0.5 μm to 100 μm, from 0.5 μm to 15 μm, from 0.5 μm to 10 μm, or from 0.5 μm to 5 μm (see, e.g.,  FIG.  2 F ). In some embodiments, a top surface of the wiring layer  255  is coplanar with a top surface of the supporting structure  220 ′ (see, e.g.,  FIG.  2 F ). In other embodiments, the wiring layer  255  is embedded within the supporting structure  220 ′. In yet other embodiments, the wiring layer  255  is formed on the top surface of the supporting structure  220 ′ and the top surface of the wiring layer  255  is raised above the top surface of the supporting structure  220 ′. 
     In some embodiments, the one or more electrodes  250  are formed on the supporting structure  220 ′ and in electrical contact with the wiring layer  255 . The one or more electrodes  250  may be comprised of conductive material such as copper (Cu), gold (Au), silver (Ag), gold/chromium (Au/Cr), platinum (Pt), platinum/iridium (Pt/Ir), titanium (Ti), gold/titanium (Au/Ti), or any alloy thereof, for example. The one or more electrodes  250  may have a thickness (z) of from 0.1 μm to 50 μm, from 0.3 μm to 30 μm, from 0.5 μm to 20 μm, or from 1 μm to 15 μm (see, e.g.,  FIG.  2 E ). The one or more electrodes  250  may be formed directly on the supporting structure  220 ′ (see, e.g.,  FIG.  2 E ). Alternatively, the one or more electrodes  250  may be formed indirectly on the supporting structure  220 ′. In some embodiments, the contact(s)  260  are formed on the supporting structure  220 ′ and provide electrical contact between the one or more electrodes  255  and the wiring layer  260  (see, e.g.,  FIG.  2 E ). The contact(s)  260  may be comprised of conductive material such as copper (Cu), gold (Au), silver (Ag), gold/chromium (Au/Cr), platinum (Pt), platinum/iridium (Pt/Ir), titanium (Ti), gold/titanium (Au/Ti), or any alloy thereof, for example. 
     In various embodiments, the lead assembly  200  may further comprise one or more additional supporting structures that may support one or more additional electronic structures of the assembly such as an electrode, conductor, and/or connector. In some embodiments, as shown in  FIG.  2 H , the lead assembly  200  further comprises supporting structure  225 ″ for a connector  265 . In certain embodiments, the connector  265  is bonding material that bonds the one or more conductive traces  225  of the cable  205  to an electronics module of the implantable neurostimulator. The bonding material may be a conductive epoxy or a metallic solder or weld such as platinum. In other embodiments, the connector  265  is conductive wire, conductive traces, or one or more bond or contact pads  270  formed on the supporting substrate  225 ″ and bonds the one or more conductive traces  225  of the cable  205  to the electronics module of the implantable neurostimulator. In alternative embodiments, the implantable neurostimulator and the cable  205  are designed to connect with one another via a mechanical connector  265  such as a pin and sleeve connector, snap and lock connector, flexible printed circuit connectors, or other means known to those of ordinary skill in the art. 
     The properties of the supporting structures and electronic structures (e.g., thickness, material, position, contact, etc.) may be the same or different from those of the structures previously discussed herein with reference to  FIGS.  2 A- 2 G . However, it should be understood the lead assembly  200  is an exemplary embodiment, and that the lead assembly  200  is to be construed with the broadest sense to include variations of the specific design and/or performance need described herein, as well as other variations that are well known to those of skill in the art. In particular, the shape and location of components and layers in the lead assembly  200  may be adjusted or modified to meet specific design and/or performance needs. Furthermore, it is to be understood that other structures may have been omitted from the description of the lead assembly  200  for clarity. The omitted structures may include, for example, sensor structures, insulating layers, interconnect components, passive devices, etc. 
       FIGS.  3 A and  3 B  show a lead assembly  300  in accordance with aspects of the present disclosure. In various embodiments, the lead assembly  300  comprises a cable  305  having a proximal end  310  and a distal end  315  (e.g., lead assembly  200  as described with respect to  FIGS.  2 A- 2 H ). In some embodiments, at least a portion  320  of the cable  305  is helical. As used herein, the phrases “helical” refer to a device fabricated with plural helixes or helices, which are a type of smooth space curve, i.e. a curve in three-dimensional space. The helixes may be wound clockwise direction or anti-clockwise direction. The helixes have the property that a tangent line at any point makes a constant angle with a fixed line called the axis. The helical portion  320  of the cable  305  may be the portion of the cable including substantially the entire length (m) of the one or more conductive traces  325 . Alternatively, the helical portion  320  of the cable  305  may be the portion of the cable  305  extending between the proximal end  310  and the distal end  315  but not including the electrode assembly and/or the connector. In certain embodiments, the helical portion  320  of the cable  305  comprises one or more characteristics including a radius  330 , a helix angle  335 , a pitch  340  (rise of the helix for one turn), a helix length  345 , and/or a total rise  350  of the helix (see, e.g.,  FIG.  3 B ). The radius  330  may be from 200 μm to 900 μm, from 250 μm to 700 μm, or from 400 μm to 650 μm, for example, about 580 μm. The helix angle  335  may be from 10° to 85°, from 40° to 65°, or from 42° to 60°, for example, about 55°. A pitch  340  may be from 100 μm to 2 mm, from 200 μm to 400 μm, or from 600 μm to 1600 μm, for example, about 720 μm. The helix length  345  may be from 5 cm to 150 cm or 50 cm to 100 cm, e.g., about 75 cm, from the proximal end  310  to the distal end  315 . The total rise  350  may be from 5 cm to 125 cm or 25 cm to 75 cm, e.g., about 50 cm, from the proximal end  310  to the distal end  315 . 
     In various embodiments, it is desirable that one or more of the characteristics of the helix are selected such that the cable  305  is capable of achieving an elastic elongation % of &gt;20%. The term “elastic”, as used herein, may be defined as a material (e.g., the cable) that returns to its original size/shape when force is removed and the “elongation %”=change in total rise*100/original total rise). Achieving an elastic elongation % of &gt;20% is desirable because it allows the cable to stretch and move during and after implantation in the patient. In some embodiments, it is desirable that one or more of the radius, the helix angle, and the pitch are selected such that the cable is capable of being stretched to a stretched total rise of greater than 20% of its original total rise but the cable will return to its original size/shape when the force causing the stretch is removed. In other embodiments, it is desirable that one or more of the radius, the helix angle, and the pitch are selected such that the cable is capable of being stretched to a stretched total rise of greater than 40% of its original total rise but the cable will return to its original size/shape when the force causing the stretch is removed. 
       FIGS.  4 A- 4 C  show a lead assembly  400  in accordance with aspects of the present disclosure. In various embodiments, the lead assembly  400  comprises a cable  405  having a proximal end  410  and a distal end  415  (e.g., lead assembly  200  as described with respect to  FIGS.  2 A- 2 H ). In some embodiments, the cable  405  includes a supporting structure  420  with one or more conductive traces  425  and a housing  430 . In some embodiments, the lead assembly  400  further includes one or more additional supporting structures that may support one or more additional electronic structures of the assembly such as an electrode, conductor, and/or connector. For example, the lead assembly  400  may further include an electrode assembly  435  comprising one or more electrodes  440 . The electrode assembly  435  may be connected to the one or more conductive traces  425  via a wiring layer  445 . In some embodiments, the distal  415  end of the lead assembly  400  carries the electrode assembly  435  (e.g., book electrodes, split cuff electrodes, spiral cuff electrodes, epidural electrodes, helical electrodes, probe electrodes, linear electrodes, neural probe, paddle electrodes, and intraneural electrodes). In other embodiments, the distal end  415  of the lead assembly  400  carries a plurality of the electrode assemblies  435 . In certain embodiments, the housing  430  completely encases at least a portion of the supporting structure  420  and the one or more conductive traces  425  (see, e.g.,  FIGS.  4 B and  4 C ). In other embodiments, the housing  430  completely encases at least a portion of the supporting structure  420  and the one or more conductive traces  425 , and extends to partially encase the electrode assembly  440  (e.g., the surfaces of the electrodes are exposed). The housing  430  may be comprised of a medical grade polymer material. In some embodiments, the medical grade polymer is thermosetting or thermoplastic. For example, the medical grade polymer may be a soft polymer such as silicone, a polymer dispersion such as latex, a chemical vapor deposited poly(p-xylylene) polymer such as parylene, or a polyurethane such as Bionate® Thermoplastic Polycarbonate-urethane (PCU) or CarboSil® Thermoplastic Silicone-Polycarbonate-urethan (TSPCU). 
       FIGS.  5 A- 5 C  show a lead assembly  500  in accordance with aspects of the present disclosure. In various embodiments, the lead assembly  500  comprises a cable  505  having a proximal end  510  and a distal end  515  (e.g., lead assembly  200  as described with respect to  FIGS.  2 A- 2 H ). In some embodiments, the cable  505  includes a supporting structure  520  with one or more conductive traces  525  and a housing  530 . In some embodiments, the lead assembly  500  further includes one or more additional supporting structures that may support one or more additional electronic structures of the assembly such as an electrode, conductor, and/or connector. For example, the lead assembly  500  may further include an electrode assembly  535  comprising one or more electrodes  540 . The electrode assembly  535  may be connected to the one or more conductive traces  525  via a wiring layer  545 . In some embodiments, the distal end  515  of the lead assembly  500  carries the electrode assembly  535  (e.g., book electrodes, split cuff electrodes, spiral cuff electrodes, epidural electrodes, helical electrodes, probe electrodes, linear electrodes, neural probe, paddle electrodes, and intraneural electrodes). In other embodiments, the distal end  515  of the lead assembly  500  carries a plurality of electrode assemblies  535 . In certain embodiments, the housing  530  is formed coplanar with at least a portion of the supporting structure  520  and the one or more conductive traces  525  (see, e.g.,  FIGS.  5 B and  5 C ) and encases only a portion of the supporting structure  520  and the one or more conductive traces  525 . In other embodiments, the housing  530  is formed coplanar with at least a portion of the supporting structure  520  and the one or more conductive traces  525 , and encases only a portion of the supporting structure  520 , the one or more conductive traces  525 , and the electrode assembly  535 . The housing  530  may be comprised of a medical grade polymer material. In some embodiments, the medical grade polymer is thermosetting or thermoplastic. For example, the medical grade polymer may be a soft polymer such as silicone, a polymer dispersion such as latex, a chemical vapor deposited poly(p-xylylene) polymer such as parylene, or a polyurethane such as Bionate® Thermoplastic Polycarbonate-urethane (PCU) or CarboSil® Thermoplastic Silicone-Polycarbonate-urethan (TSPCU). 
       FIG.  6 A  shows a lead assembly  600  in accordance with aspects of the present disclosure. In various embodiments, the lead assembly  600  comprises a cable  605  having a proximal end  610  and a distal end  615  (e.g., lead assembly  200  as described with respect to  FIGS.  2 A- 2 H ). In some embodiments, the cable  605  includes: (i) a supporting structure  620  with one or more conductive traces  625 , and (ii) a first housing  630 . The housing  630  may be comprised of a medical grade polymer material, as described herein. In accordance with various aspects of the present disclosure, the cable  605  and the housing  630  may be designed for a number of applications. For example, the cable  605  and the housing  630  may be designed for deep brain stimulation, as shown in  FIG.  6   . 
     In some embodiments, a first portion  635  of the cable  605  has a first helical structure. The first portion  635  may be defined as the last 1 cm to 15 cm of the cable  605  on the proximal end  610  of the cable  605 . In certain embodiments, the first portion  635  comprises tight helixes (e.g., for tissue penetration as with deep brain stimulation or connection to a device such as a neurostimulator) with characteristics including a radius from 200 μm to 900 μm, a helix angle from 10° to 85°, and a pitch from 200 μm to 400 μm. In some embodiments, at least a first portion of the housing  630  completely encases the first portion  635 . In other embodiments, at least a first portion of the housing  630  is formed coplanar with the supporting structure  620  and the one or more conductive traces  625  of the first portion  635 . In some embodiments, the first portion of the housing  630  is formed coplanar with the first helical portion  535 , and the first portion of the housing  630  is comprised of thermosetting polymer such as polyurethane. 
     In some embodiments, a second portion  640  of the cable  605  has a second helical structure. The second portion  640  may be defined as the last 1 cm to 15 cm of the cable  605  on the proximal end  610  of the cable  605 . In certain embodiments, the second portion  640  comprises tight helixes (e.g., for tissue penetration as with deep brain stimulation or connection to a device such as a neurostimulator) with characteristics including a radius from 200 μm to 900 μm, a helix angle from 10° to 85°, and a pitch from 200 μm to 400 μm. In some embodiments, at least a second portion of the housing  630  completely encases the second portion  640 . In other embodiments, at least a second portion of the housing  630  is formed coplanar with the supporting structure  620  and the one or more conductive traces  625  of the second portion  640 . In some embodiments, the second portion of the housing  630  is formed coplanar with the second helical portion  540 , and the first portion of the housing  630  is comprised of thermosetting polymer such as polyurethane. 
     In some embodiments, a third portion  645  of the cable  605  has a third helical structure. The third portion  645  may be defined as the middle 5 cm to 150 cm of the cable  605  between the first portion  635  and the second portion  640 . In certain embodiments, the third portion  645  comprises loose helixes with characteristics including a radius from 200 μm to 900 μm, a helix angle from 10° to 85°, and a pitch from 600 μm to 1600 μm. In some embodiments, at least a third portion of the housing  630  completely encases the second portion  640 . In other embodiments, at least a third portion of the housing  630  is formed coplanar with the supporting structure  620  and the one or more conductive traces  625  of the third portion  645 . In some embodiments, the third portion of the housing  630  encases the third helical portion  645 , and the third portion of the housing  630  is comprised of silicone. 
     In some embodiments, the lead assembly  600  further includes one or more additional supporting structures that may support one or more additional electronic structures of the assembly such as an electrode, sensor, conductor, and/or connector. In certain embodiments, the lead assembly  600  further includes a portion of the supporting structure  620  that is formed as an electrode assembly  650  at the distal end  615 . In other embodiments, the lead assembly  600  further includes: (i) a portion of the supporting structure  620  that is formed as an electrode assembly  650  at the distal end  615 , and (ii) a multiplexer chip (not shown) formed on the supporting structure  620  at the proximal end  610  or the distal end  615 . The multiplexer chip (not shown) may be in electrical connection with one or more electrodes (optionally one or more sensors) of the electrode assembly via the one or more conductive traces  625 . In yet other embodiments, the lead assembly  600  further includes: (i) a portion of the supporting structure  620  that is formed as an electrode assembly  650  at the distal end  615 , (ii) a multiplexer chip (not shown) formed on the supporting structure  620  at the proximal end  610  or the distal end  615 , and/or (iii) a connector formed on the supporting structure  620  at the proximal end  610  of the cable  605  and in electrical connection with the one or more conductive traces  625 . The multiplexer chip (not shown) may be in electrical connection with one or more electrodes (optionally one or more sensors) of the electrode assembly via the one or more conductive traces  625 . 
       FIGS.  6 B,  6 C, and  6 D  show the distal end  615  and electrode assembly  650  of the lead assembly  600  in various configurations. The distal end  615  has at least one curved portion of the supporting structure that is disposed between a first set of electrodes and a second set of electrodes of the electrode assembly  650 , and/or (ii) the at least one curved portion of the supporting structure that is disposed between a first set of sensors and a second set of sensors of the electrode assembly  650 . In some instances, disclosed herein are monolithic thin-film lead assemblies that can be implanted in biological structures such as veins using a guidewire or a stylet. These lead assemblies can be made isodiametric and under ˜1.3 mm outer diameter to be compatible with standard implant tools. Additionally, different distal end lead configurations may be used that allow the lead assemblies to be implanted through a biological structure and deployed in a manner that will not allow the lead assemblies to become dislodged from a given implant location. These shapes or configurations are enabled because of the thermoforming ability of the thin-film lead assembly design. As shown in  FIG.  6 B , the distal end  615  of the lead assembly  600  is straight when a stylet of guidewire is inserted during which allows for the lead to be navigated through the biological structure (e.g., veins) to a target implant location. Upon situation of the lead at the target implant location, the guidewire or stylet is retracted which is when the distal end  615  of the lead assembly  600  starts to take shape into one or more of the following form factors comprising at least one curved portion: (i) the at least one curved portion is a single curved portion and the curved structure has a shape of a “U” or a “J”, or (ii) the at least one curved portion is multiple curved portions and the curved structure has a shape of a “S”, a helix, or a involute spiral (see, e.g.,  FIGS.  6 B,  6 C, and  6 D ). This shape at the distal end allows the electrodes and/or sensors of the electrode assembly  650  to be positioned against a biological structure such as a venous wall for sensing and allows for stability. 
       FIG.  6 B  shows the “J” or “U” shape on the distal end  615  allowing electrodes and/or sensors of the electrode assembly  650  to be deployed on both sides of a biological structure for better contact. Distal end  615  straightens with stylet or guidewire  655  and takes shape upon retraction. For example, the top portion  660  shows the stylet/guidewire  655  extended which straightens the lead assembly  600  with the electrodes and/or sensors of the electrode assembly  650 . The bottom portion  670  shows the stylet/guidewire  655  retracted which allows the lead assembly  600  to take “U” or “J” shape on the distal end  615 . This shape acts like a wedge and provides stability to the lead assembly  600 , at the same time will not block or occlude the biological structure completely, while allowing enough surface area against the biological structure that can have multiple electrodes and/or sensors in contact with the biological structure. 
       FIG.  6 C  shows the helical shape on the distal end  615  allowing electrodes and/or sensors of the electrode assembly  650  to be deployed on both sides of a biological structure for better contact. Distal end  615  straightens with stylet or guidewire  655  and takes shape upon retraction. For example, the top portion  660  shows the stylet/guidewire  655  extended which straightens the lead assembly  600  with the electrodes and/or sensors of the electrode assembly  650 . The bottom portion  670  shows the stylet/guidewire  655  retracted which allows the lead assembly  600  to take the helical shape on the distal end  615 . This shape acts like a wedge and provides stability to the lead assembly  600 , at the same time will not block or occlude the biological structure completely, while allowing enough surface area against the biological structure that can have multiple electrodes and/or sensors in contact with the biological structure. 
       FIG.  6 D  shows the spiral shape on the distal end  615  allowing electrodes and/or sensors of the electrode assembly  650  to be deployed on both sides of a biological structure for better contact. Distal end  615  straightens with stylet or guidewire  655  and takes shape upon retraction. For example, the top portion  660  shows the stylet/guidewire  655  extended which straightens the lead assembly  600  with the electrodes and/or sensors of the electrode assembly  650 . The bottom portion  670  shows the stylet/guidewire  655  retracted which allows the lead assembly  600  to take the spiral shape on the distal end  615 . This shape acts like a wedge and provides stability to the lead assembly  600 , at the same time will not block or occlude the biological structure completely, while allowing enough surface area against the biological structure that can have multiple electrodes and/or sensors in contact with the biological structure. 
     In some embodiments, a method for deploying a monolithic thin-film lead assembly is provided that comprises: obtaining the lead assembly comprising: a lead comprising: a proximal end, a distal end, a supporting structure that extends from the proximal end to the distal end, and a plurality of conductive traces formed on a portion of the supporting structure, where the supporting structure is comprised of one or more layers of dielectric material; an interface formed on the supporting structure at the distal end of the cable, where the interface comprises a plurality of electrodes and/or a plurality of sensors in electrical connection with one or more conductive traces of the plurality of conductive traces, where the plurality of electrodes comprise a first set of electrodes and a second set of electrodes and/or the plurality of sensors comprise a first set of sensors and a second set of sensors; and a guidewire comprising a stylet inserted through the interface, where while the stylet is inserted through the interface, the interface has a first profile, and where the first profile is straight with the first set of electrodes and the second set of electrodes and/or the first set of sensors and the second set of sensors provided in a linear array; inserting, with the guidewire, the lead assembly into a cavity (such as an endovascular cavity) of a subject; moving, with the guidewire, the lead assembly through the cavity to position the interface at a target location (such as a target location for brain computer interfacing); and removing the guidewire and stylet from the cavity while leaving the lead assembly in place with the interface positioned at the target location, where removal of the stylet from the interface allows for the interface to take a second profile having at least one curved portion, where: (i) the at least one curved portion is disposed between the first set of electrodes and the second set of electrodes, and/or (ii) the at least one curved portion is disposed between the first set of sensors and the second set of sensors. In some instances, the method further comprises connecting the cable to a computing device and using the computing device to send a single through the interface to tissue at the target location or receive a signal from the tissue at the target location. 
       FIG.  7    shows a lead assembly  700  in accordance with aspects of the present disclosure. In various embodiments, the lead assembly  700  comprises a cable  705  having a proximal end  710  and a distal end  715  (e.g., lead assembly  200  as described with respect to  FIGS.  2 A- 2 H ). In some embodiments, the cable  705  includes: (i) a supporting structure  720  with one or more conductive traces  725 , and (ii) an housing  730 . The housing  730  may be comprised of a medical grade polymer material, as described herein. In accordance with various aspects of the present disclosure, the cable  705  and the housing  730  may be designed for a number of applications. For example, the cable  705  and the housing  730  may be designed for vagus nerve/artery plexus stimulation, as shown in  FIG.  7   . 
     In some embodiments, a first portion  735  of the cable  705  has a helical structure. The first portion  735  may be defined as the middle 5 cm to 150 cm of the cable  705  between the proximal end  710  and the distal end  715 . In certain embodiments, the first portion  735  comprises loose helixes with characteristics including a radius from 200 μm to 900 μm, a helix angle from 10° to 85°, and a pitch from 600 μm to 1600 μm. In some embodiments, at least a portion of the housing  730  completely encases the portion  735 . In other embodiments, at least a portion of the housing  730  is formed coplanar with the supporting structure  720  and the one or more conductive traces  725  of the first portion  735 . In some embodiments, the housing  730  completely encases the helical portion  735 , and the housing  730  is comprised of silicone. 
     In some embodiments, a second portion  740  of the cable  705  has an electrode assembly  745 . The second portion  740  may be defined as the last 1 cm to 15 cm of the cable  705  on the distal end  715 . In certain embodiments, the second portion  740  comprises a portion of the supporting structure  720  that is thermoformed into book electrodes, split cuff electrodes, spiral cuff electrodes, epidural electrodes, helical electrodes, probe electrodes, linear electrodes, neural probe, paddle electrodes, and intraneural electrodes. In some embodiments, the supporting structure  720  at the distal end  715  of the cable  705  having the electrode assembly  745  formed thereon is thermoformed into a cuff structure. Additionally, a multiplexer chip  750  may formed on or within the supporting structure  720  at the proximal end  710  or the distal end  715 . The multiplexer chip  750  may be in electrical connection with one or more electrodes (optionally one or more sensors) of the electrode assembly  745  via the one or more conductive traces  725 . In some embodiments, at least a portion of the housing  730  partially encases the second portion  740 . In other embodiments, at least a portion of the housing  730  is formed coplanar with one or more electrodes (optionally one or more sensors) of the electrode assembly  745 . 
     In some embodiments, a third portion  755  of the cable  705  has another helical structure. The third portion  755  may be defined as the last 1 cm to 15 cm of the cable  705  on the proximal end  710 . In certain embodiments, the third portion  755  comprises tight helixes (e.g., for connection to a device such as a neurostimulator) with characteristics including a radius from 200 μm to 900 μm, a helix angle from 10° to 85°, and a pitch from 200 μm to 400 μm. In some embodiments, at least a portion of the housing  730  completely encases the third portion  755 . In other embodiments, at least a portion of the housing  730  is formed coplanar with the supporting structure  720  and the one or more conductive traces  725  of the third portion  755 . 
     In other embodiments, the third portion  755  of the cable  705  includes one or more additional supporting structures that may support one or more additional electronic structures of the assembly such as an electrode, sensor, conductor, and/or connector. The third portion  755  may be defined as the last 1 cm to 15 cm of the cable  705  on the proximal end  710 . In certain embodiments, the third portion  755  comprises a connector formed on the supporting structure  720  at the proximal end  710  of the cable  705  and in electrical connection with the one or more conductive traces  725 . In some embodiments, at least a portion of the housing  730  completely partially encases the third portion  755 . In other embodiments, at least a portion of the housing  730  is formed coplanar with the supporting structure  720  and the connector (e.g., a bond pad) of the third portion  755 . 
     While the lead assemblies have been described at some length and with some particularity with respect to a specific design and/or performance need, it is not intended that the lead assemblies be limited to any such particular design and/or performance need. Instead, it should be understood the lead assemblies described herein are exemplary embodiments, and that the lead assemblies are to be construed with the broadest sense to include variations of the specific design and/or performance need described herein, as well as other variations that are well known to those of skill in the art. In particular, the shape and location of components and layers in the lead assemblies may be adjusted or modified to meet specific design and/or performance needs. Furthermore, it is to be understood that other structures have been omitted from the description of the lead assemblies for clarity. The omitted structures may include sensor structures, insulating layers, interconnect components, passive devices, etc. 
     IV. Methods For Fabricating a Lead Assembly 
       FIGS.  8 A- 8 H  show structures and respective processing steps for fabricating a thin-film lead assembly  800  (e.g., as described with respect to  FIG.  2 A- 2 H,  3 A,  4 B,  4 A,  4 B,  4 C,  5 A,  5 B,  5 C,  6   , or  7 ) in accordance with various aspects of the invention. It should be understood by those of skill in the art that the thin-film lead assembly can be manufactured in a number of ways using a number of different tools. In general, however, the methodologies and tools used to form the structures of the various embodiments can be adopted from integrated circuit (IC) technology. For example, the structures of the various embodiments, e.g., supporting structure, conductive traces, electrodes, sensors, wiring layers, bond/contact pads, etc., may be built with or without a substrate and realized in films of materials patterned by photolithographic processes. In particular, the fabrication of various structures described herein may typically use three basic building blocks: (i) deposition of films of material on a substrate and/or previous film(s), (ii) applying a patterned mask on top of the film(s) by photolithographic imaging, and (iii) etching the film(s) selectively to the mask. 
     As used herein, the term “depositing” may include any known or later developed techniques appropriate for the material to be deposited including but not limited to, for example: chemical vapor deposition (CVD), low-pressure CVD (LPCVD), plasma-enhanced CVD (PECVD), semi-atmosphere CVD (SACVD) and high density plasma CVD (HDPCVD), rapid thermal CVD (RTCVD), ultra-high vacuum CVD (UHVCVD), limited reaction processing CVD (LRPCVD), metalorganic CVD (MOCVD), sputtering deposition, ion beam deposition, electron beam deposition, laser assisted deposition, thermal oxidation, thermal nitridation, spin-on methods, physical vapor deposition (PVD), atomic layer deposition (ALD), chemical oxidation, molecular beam epitaxy (MBE), plating (e.g., electroplating), or evaporation. 
       FIG.  8 A  shows a beginning structure (a supporting structure) comprising a first polymer layer  805  overlying an optional substrate  810  (e.g., a backer). In various embodiments, the beginning structure may be provided, obtained, or fabricated as a single wafer or panel having a diameter, length, and/or width of less than 15 cm. The substrate  810  may be comprised of any type of metallic or non-metallic material. For example, the substrate  810  may be comprised of but not limited to silicon, germanium, silicon germanium, silicon carbide, and those materials consisting essentially of one or more Group III-V compound semiconductors having a composition defined by the formula AlX1GaX2InX3AsY1PY2NY3SbY4, where X1, X2, X3, Y1, Y2, Y3, and Y4 represent relative proportions, each greater than or equal to zero and X1+X2+X3+Y1+Y2+Y3+Y4=1 (1 being the total relative mole quantity). Substrate  810  may additionally or alternatively be comprised of Group II-VI compound semiconductors having a composition ZnA1CdA2SeB1TeB2, where A1, A2, B1, and B2 are relative proportions each greater than or equal to zero and A1+A2+B1+B2=1 (1 being a total mole quantity). The processes to provide, obtain, or fabricate substrate  810 , as illustrated and described, are well known in the art and thus, no further description is provided herein. 
     The first polymer layer  805  may be comprised of dielectric material (i.e., an insulator). The dielectric material may be selected from the group of electrically nonconductive materials consisting of organic or inorganic polymers, ceramics, glass, glass-ceramics, polyimide-epoxy, epoxy-fiberglass, and the like. In certain embodiments, the dielectric material is a thermoplastic or thermosetting polymer. For example, the polymer may be a polyimide, a LCP, parylene, a PEEK, or combinations thereof. The forming of the first polymer layer  805  may include depositing and curing a dielectric material directly on the substrate  810  without an adhesion promoter. For example, a solution comprised of an imidizable polyamic acid compound dissolved in a vaporizable organic solvent without an adhesion promoter may be deposited (e.g., spin coated) onto the substrate  810 . The solution may then be heated at a temperature, preferably less than 250° C., to imidize the polyamic acid compound to form the desired polyimide and vaporize the solvent. The first polymer layer  805  may then be thinned to a desired thickness by planarization, grinding, wet etch, dry etch, oxidation followed by oxide etch, or any combination thereof. This process can be repeated to achieve a desired thickness for the first polymer layer  805 . In some embodiments, the first polymer layer  805  may have a thickness from 10 μm to 150 μm. In some embodiments, the first polymer layer  805  may have a thickness from 25 μm to 100 μm. In some embodiments, the first polymer layer  805  may have a thickness from 35 μm to 75 μm. 
       FIG.  8 B  shows conductive traces  815  formed in a pattern on a first portion (e.g., region) of the first polymer layer  805 . In some embodiments, forming the conductive traces  815  may include depositing a seed layer (e.g., a copper (Cu) seed layer, a gold (Au) seed layer, a silver (Ag) seed layer, a gold/chromium (Au/Cr) seed layer, platinum (Pt) seed layer, platinum/iridium (Pt/Ir) seed layer, etc.) over the first polymer layer  805 . The seed layer may be configured to enable forming of a conductive trace on the first polymer layer  805  (e.g., through Cu electroplating, Au electroplating, Sn electroplating, Ag electroplating, Au/Cr electroplating, platinum (Pt) electroplating, platinum/iridium (Pt/Ir) electroplating, etc.). Optionally, and prior to forming of the seed layer, an adhesion layer may be deposited over the first polymer layer  805  to enable adequate application of the seed layer. Deposition of either or both of the adhesion layer and seed layer may include sputter deposition 
     Following deposition of the seed layer, a resist pattern may be formed above the first polymer layer  805 . The resist pattern may include openings that align over at least a portion of the first polymer layer  805  for forming of a plurality of conductive traces  815  (e.g., a conductive layer with a cross-sectional thickness of 0.5 μm to 100 μm or from 25 μm to 50 μm) on the first polymer layer  805 . For example, the resist may be patterned with openings to form: (i) a first conductive trace  815  over a first region  817  of the first polymer layer  805 , (ii) a second conductive trace  815  over a second region  818  of the first polymer layer  805 , and (iii) a third conductive trace  815  over a third region  819  of the first polymer layer  805 . In various embodiments, the openings of the resist pattern may have a spiral pattern such that the formed plurality of conductive traces  815  have a spiral shape, e.g. as shown in  FIG.  2 C . The spiral shape may include characteristics designed to maximize the length of the lead assembly  800  that can be fabricated from a single wafer or panel. In some embodiments, characteristics of the spiral shape include a predetermined number of turns and a predetermined pitch (p) between each of the turns to maximize the overall length obtainable for the lead assembly  800 . In certain embodiments, the spiral shape has greater than 2 turns, for example from 2 to 25 turns, and a pitch between each of the turns from 10 μm to 1 cm or from 250 μm to 2 mm, for example about 250 μm. Accordingly, the spiral shape can maximize the length of the lead assembly  800  that can be fabricated from a single wafer or panel. For example, a single wafer or panel with a limited diameter, length, and/or width of less than 10 cm, can be used to fabricate a lead assembly  800  with a length of 5 cm to 150 cm or 50 cm to 100 cm, e.g., about 75 cm, using the spiral shape. It should be understood by those of skill in the art that different patterns and shapes are also contemplated by the present invention to maximize the length of the lead assembly  800 . 
     In various embodiments, the conductive traces  815  may be deposited through electroplating (e.g., through Cu electroplating, Au electroplating, Sn electroplating, Ag electroplating, Au/Cr electroplating, etc.) and may be positioned over at least a portion of the first polymer layer  805  (e.g., the first region  817 , the second region  818 , and the third region  819 ). The electroplating maybe performed at a current density of about 4.0 mA/cm2 to about 4.5 mA/cm2. In some embodiments, the exposed area or portion of the first polymer layer  805  may encompass about 8 cm 2  to about 10 cm 2 . The current may be about 14 mA to about 18 mA and the duration may be from about 110 minutes to about 135 minutes to form the conductive traces  815  having a thickness of about 8 μm to about 10 μm. In other embodiments, the exposed area or portion of the first polymer layer  805  may encompass about 10 cm 2  to about 18 cm 2 . The current may be about 18 mA to about 28 mA and the duration may be from about 35 minutes to about 50 minutes to form the wiring layer  815  having a thickness of about 2 μm to about 5 μm. 
     Following the deposition of the conductive traces  815 , the intermediate structure may be subjected to a strip resist to remove the resist pattern and expose portions of the seed layer (portions without wire formation), and optionally the adhesion layer. The exposed portions of the seed layer, and optionally the adhesion layer, may then be subjected to an etch (e.g., wet etch, dry etch, etc.) to remove those portions, thereby isolating the conductive traces  815  over at least a portion of the first polymer layer  805 . 
       FIG.  8 C  shows an optional second polymer layer  820  formed over the conductive traces  815  and the first portion of the polymer layer  805 . The second polymer layer  820  may be comprised of dielectric material (i.e., an insulator). The dielectric material may be selected from the group of electrically nonconductive materials consisting of organic or inorganic polymers, ceramics, glass, glass-ceramics, polyimide-epoxy, epoxy-fiberglass, and the like. In certain embodiments, the dielectric material is a thermoplastic or thermosetting polymer. For example, the polymer may be a polyimide, a LCP, silicone, parylene, a PEEK, or combinations thereof. The second polymer layer  820  may be comprised of the same material or a different material from that of the first polymer layer  805 . 
     The forming of the second polymer layer  820  may include depositing and curing of a polymer material directly on the conductive traces  815  and the first polymer layer  805 . For example, a solution comprised of an imidizable polyamic acid compound dissolved in a vaporizable organic solvent may be applied to the conductive traces  815  and the first polymer layer  805 . The solution may then be heated at a temperature, preferably less than 250° C., to imidize the polyamic acid compound to form the desired polyimide and vaporize the solvent. The second polymer layer  820  may then be thinned to a desired thickness by planarization, grinding, wet etch, dry etch, oxidation followed by oxide etch, or any combination thereof. This process can be repeated to achieve a desired thickness for the second polymer layer  820 . In some embodiments, the second polymer layer  820  may have a thickness from 1.0 μm to 50.0 μm. In some embodiments, the second polymer layer  820  may have a thickness from 4.0 μm to 15.0 μm. In some embodiments, the second polymer layer  820  may have a thickness from 5.0 μm to 7.0 μm. 
     In various embodiments, the lead assembly  800  may further comprise one or more additional supporting structures that may support one or more additional electronic structures of the assembly such as an electrode, sensor, conductor, and/or connector.  FIG.  8 D  shows forming an electrode assembly on the supporting structure  805 / 810  formed in  FIG.  8 A  that is electrically connected to the conductive traces  815  formed in  FIG.  8 B . In some embodiments, forming the electrode assembly comprises forming a wiring layer  822  in a pattern on a second portion of the first polymer layer  805 . The wiring layer  822  may be formed at the same time as forming the conductive traces  815 , or may be formed subsequent to forming the conductive traces  815 . For example, the wiring layer  822  and the conductive traces  815  may be deposited as a continuous layer of conductive material, or may be deposited as two separate metallization layers of conductive material that are in electrical contact with one another. The wiring layer  822  may be formed in the same manner as described in detail with respect to the conductive traces  815 . 
     In some embodiments, forming the electrode assembly further comprises forming the second polymer layer  820  over the wiring layer and the second portion of the first polymer layer  805 . As described herein, the second polymer layer  820  may be comprised of dielectric material (i.e., an insulator) selected from the group of electrically nonconductive materials consisting of organic or inorganic polymers, ceramics, glass, glass-ceramics, polyimide-epoxy, epoxy-fiberglass, and the like. In certain embodiments, the dielectric material is a thermoplastic or thermosetting polymer. For example, the polymer may be a polyimide, a LCP, parylene, silicone, a PEEK, or combinations thereof. The second polymer layer  820  may be comprised of the same material or a different material from that of the first polymer layer  805 . 
     In some embodiments, forming the electrode assembly further comprises forming contact vias  825  in the second polymer layer  820  to the wiring layer  822 . The contact vias can e.g. be formed using conventional lithographic, etching, and cleaning processes, known to those of skill in the art.  FIG.  8 E  shows electrodes (optionally one or more sensors)  830  and contacts  835  formed on and within the contact vias  825  to the portion of the top surface the conductive traces  815 . In various embodiments, the electrodes  830  (optionally one or more sensors) and contacts  835  may be formed using conventional processes. For example, a conductive material may be blanket deposited on the second polymer layer  820 , including within the contact vias  825  and in contact with the portion of the top surface the wiring layer  822 . The conductive material may be copper (Cu), gold (Au), silver (Ag), gold/chromium (Au/Cr), platinum (Pt), platinum/iridium (Pt/Ir), titanium (Ti), gold/titanium (Au/Ti), or any alloy thereof, for example. Once the conductive material is deposited, the conductive material may be patterned using conventional lithography and etching processes to form at least one electrode  830  or a pattern of electrodes  830  as shown in  FIG.  8 E , for example. In some embodiments, at least one electrode  830  is formed on the second polymer layer  820  such that the at least one electrode  830  is in electrical contact with at least a portion of a top surface of the wiring layer  822 . In some embodiments, the pattern of electrodes  830  may include each electrode  830  spaced apart from one another via a portion or region  840  of the second polymer layer  820 . It should be understood by those of skill in the art that different patterns are also contemplated by the present invention. 
       FIG.  8 F  shows an intermediate structure  845  of the thin-film lead assembly  800  including the first polymer layer  805 , the conductive traces  815 , the wiring layer  822 , the second polymer layer  820 , the electrodes  830 , and the contacts  835  detached from the substrate  810 . In some embodiments, detaching the thin-film lead assembly  800  from the substrate  810  may include removal of the substrate (e.g., selective etching), and cleaning (e.g., a step-wise rinsing process) at least top surfaces of the electrodes  830  and the second polymer layer  820  with acetone, isopropyl alcohol, non-ionic surfactant, a liquid detergent system, and/or deionized water to remove residual material such as remaining adhesive material. 
       FIG.  8 G  shows a final monolithic structure  850  of the thin-film lead assembly  800  including a cable  855 , optionally an electrode assembly  860 , and optionally a connector  865  that is cut from the first polymer layer  805 . For example, the thin-film lead assembly  800  may be cut from the first polymer layer  805 , and comprises the plurality of conductive traces  815  in the spiral pattern on the first polymer layer  805  and the at least one electrode  830  (optionally one or more sensors) on the second polymer layer  820  electrically connected to the plurality of conductive traces  815 . In some embodiments, the cutting is accomplished using a laser and known techniques. As should be understood,  FIGS.  8 A- 8 C and  8 F  shows steps for forming a portion of the cable  855  denoted by line G-G, whereas  FIGS.  8 A- 8 F  shows steps for forming a portion of the electrode assembly  860  denoted by line H-H. 
     In some instances, the electrode assembly  860  is an interface comprising a plurality of electrodes and/or a plurality of sensors in electrical connection with one or more conductive traces of the plurality of conductive traces. The plurality of electrodes comprise a first set of electrodes and a second set of electrodes and/or the plurality of sensors comprise a first set of sensors and a second set of sensors. The supporting structure at the distal end of the cable comprises at least one curved portion. The at least one curved portion of the supporting structure is disposed between the first set of electrodes and the second set of electrodes, and/or the at least one curved portion of the supporting structure is disposed between the first set of sensors and the second set of sensors. The interface may be formed by: forming a wiring layer on a second portion of the first polymer layer, where the forming the wiring layer comprises depositing the conductive material in electrical contact with the plurality of conductive traces; depositing a second polymer layer on the wiring layer and the second portion of the first polymer layer; forming a plurality of electrodes and/or a plurality of sensors on the second polymer layer such that the plurality of electrodes and/or the plurality of sensors are in electrical contact with at least a portion of a top surface of the wiring layer; where the plurality of electrodes comprise a first set of electrodes and a second set of electrodes and/or the plurality of sensors comprise a first set of sensors and a second set of sensors; forming at least one curved portion in the second portion of the first polymer layer and the second polymer layer, where the at least one curved portion is formed by wrapping the interface around a mandrel or placing the interface in a mold, and where: (i) the at least one curved portion is disposed between the first set of electrodes and the second set of electrodes, and/or (ii) the at least one curved portion is disposed between the first set of sensors and the second set of sensors; and heating the interface while wrapped around the mandrel or placed in the mold to thermoform the second portion of the first polymer layer and the second polymer layer into a curved structure comprising the at least one curved portion. 
     In some instances, the at least one curved portion is a single curved portion and the curved structure has a shape of a “U” or a “J”. In some instances, the at least one curved portion is multiple curved portions and the curved structure has a shape of a “S”, a helix, or a involute spiral. In some instances, the method further comprises: inserting a guidewire having a stylet though the interface causing the at least one curved portion to straighten, which forces the curved structure into a linear structure. 
       FIGS.  9 A- 9 D  show structures and respective processing steps for fabricating an alternative thin-film lead assembly  900  (e.g., a lead assembly having a helical portion) in accordance with various aspects of the invention.  FIG.  9 A  shows a beginning structure  905  for a cable including a plurality of conductive traces  910  formed on or within a supporting structure  915 . The cable  910  may further include an electrode assembly  920  comprising a multi-electrode array  925  (optionally one or more sensors) formed at a distal end of the cable. The beginning structure  905  may be formed in accordance with the processes describe herein with reference to  FIGS.  8 A- 8 F . For example, the beginning structure  905  may be laser cut in a spiral design from a wafer or panel fabricated with electroplated traces. 
       FIG.  9 B  shows a portion of the cable wound (clockwise direction or anti-clockwise direction) into a helical pattern on a mandrel  930  to form an intermediate structure  935  with a helical portion  940 . In various embodiments, the mandrel  930  is selected and the winding is controlled such that the helical portion  940  comprises one or more characteristics including a radius, a helix angle, a pitch, a helix length, and a total rise of the helix. The radius is dictated by the outer diameter of the mandrel  930  and may be from 200 μm to 900 μm, from 250 μm to 700 μm, or from 400 μm to 650 μm, for example, about 580 μm. The helix angle is dictated by controlling the winding and may be from 10° to 85°, from 40° to 65°, or from 42° to 60°, for example, about 55°. The pitch is dictated by controlling the winding and may be may be from 100 μm to 2 mm, from 250 μm to 1100 μm, or from 400 μm to 950 μm, for example, about 720 μm. The helix length is dictated by controlling the winding and may be from 5 cm to 150 cm or 50 cm to 100 cm, e.g., about 75 cm, from the proximal end to the distal end. The total rise is dictated by controlling the winding and may be from 5 cm to 125 cm or 25 cm to 75 cm, e.g., about 50 cm, from the proximal end to the distal end. In some embodiments, the mandrel  930  comprises a coating such as polytetrafluoroethylene (PTFE) for easier removal of the cable  910  from the mandrel  930 . 
       FIG.  9 C  shows the intermediate structure  935  with a helical portion  940  being heated to thermoform intermediate structure  935  with a helical portion  940  into a final structure  945 . The heating process may include baking the structure in an oven, use of a heat gun, application of hot air, like methods, or any combination thereof. In various embodiments, the intermediate structure  935  is heated at 135° C. to 165° C., for example about 150° C., for 25 to 40 minutes, for example 30 minutes. Thereafter, the intermediate structure  935  is cooled (e.g., at ambient temperature) and withdrawn from the mandrel to obtain the final structure  945  shown in  FIG.  9 D . 
       FIGS.  10 A- 10 J  show structures and respective processing steps for fabricating an alternative thin-film lead assembly  1000  (e.g., a portion of a lead assembly encased in a housing) in accordance with various aspects of the invention.  FIG.  10 A  shows a beginning structure  1005  for a cable including a plurality of conductive traces  1010  formed on or within a supporting structure  1015 . The cable may further include an electrode assembly  1020  comprising a multi-electrode array  1025  (optionally one or more sensors) formed at a distal end of the cable  1010 . The beginning structure  1005  may be formed in accordance with the processes describe herein with reference to  FIGS.  8 A- 8 F  and  FIGS.  9 A- 9 C . For example, the beginning structure  1005  may be laser cut in a spiral design from a wafer or panel fabricated with electroplated traces. Thereafter, a portion of the cable may be wound into a helical pattern on a mandrel and heated to form beginning structure  1005  with a helical portion  1030 . 
       FIG.  10 B  shows a polymer tube  1035  being soaked in a solution and swelled to an enlarged size. In various embodiments, the polymer tube is comprised of a medical grade polymer material, for example, a soft polymer such as silicone, a polymer dispersion such as latex, or a polyurethane. In certain embodiments, the inner diameter of the polymer tube  1035  is selected to be slightly smaller (5 μm to 25 μm smaller) than the outer diameter of the helical portion  1030 . For example, the inner diameter of the polymer tube  1035  may be selected to be from 375 μm to 1775 μm, from 475 μm to 1375 μm, or from 750 μm to 1275 μm, for example, about 1145 μm. The inability of medical grade polymers to expand or stretch without mechanical or chemical assistance coupled with its tacky surface makes assembly with rigid parts, such as the cable, difficult. Accordingly, the polymer tube  1035  may be soaked in a solution for predetermined amount of time to temporarily enlarge the size (e.g., the inner diameter and the outer diameter) of the polymer tube  1035  and allow for insertion of the cable into the polymer tube  1035 . In some embodiments, the medical grade polymer material is a silicone. In some embodiments, the solution includes heptane. In some embodiments, the predetermined time is between three and ten minutes, for example, five minutes. In some embodiments, the size of the polymer tube  1035  is enlarged by about 15% to 45%, for example 30%. 
       FIG.  10 C  shows the beginning structure  1005  on the mandrel  1040  being inserted into the enlarged polymer tube  1035  to form an intermediate structure  1045 .  FIG.  10 D  shows intermediate structure  1045  being heated to recover the original size of the polymer tube  1035 . The heating process may include baking the structure in an oven, use of a heat gun, application of hot air, like methods, or any combination thereof. In various embodiments, the intermediate structure  1045  is heated at 80° C. to 115° C., for example about 100° C., for 5 to 20 minutes, for example 10 minutes. Thereafter, the intermediate structure  1045  is cooled (e.g., at ambient temperature) and the mandrel  1040  is withdrawn to obtain the intermediate structure  1050  shown in  FIG.  10 E . In some embodiments, the heating process results in at least a portion  1055  of the helical portion  1030  embedding into the silicone wall since the inner diameter of the polymer tube  1035  is selected to be smaller than the outer diameter of the helical portion  1030 . 
       FIG.  10 F  shows the mandrel  1040  withdrawn from the intermediate structure  1050  to obtain the final structure  1060 . Optionally, the final structure  1060  may be treated to increase wettability of the thin-film lead assembly  1000 . In various embodiments, the final structure  1060  is treated with oxygen plasma  1065 , as shown in  FIG.  10 G . The processes to provide oxygen plasma treatment to a polymer are well known in the art and thus, no further description is provided herein. Optionally, the final structure  1060  may be sealed. In various embodiments, both ends of the polymer tube  1035  are filled with liquid prepolymer  1070  (e.g., silicone liquid prepolymer), as shown in  FIG.  10 H .  FIG.  10 I  shows the final structure  1060  being heated to thermally cure the liquid prepolymer on and seal the polymer tube  1035 . The heating process may include baking the structure in an oven, use of a heat gun, application of hot air, like methods, or any combination thereof. In various embodiments, the final structure  1060  is heated at 80° C. to 115° C., for example about 100° C., for 5 to 20 minutes, for example 10 minutes. Thereafter, the final structure  1060  is cooled (e.g., at ambient temperature) to obtain the thin-film lead assembly  1000  shown in  FIG.  10 J . 
       FIGS.  11 A- 11 F  show structures and respective processing steps for fabricating an alternative thin-film lead assembly  1100  (e.g., a portion of a lead assembly embedded in a housing) in accordance with various aspects of the invention.  FIG.  11 A  shows a beginning structure  1105  for a cable including a plurality of conductive traces  1110  formed on or within a supporting structure  1115 . The cable may further include an electrode assembly  1120  comprising a multi-electrode array  1125  (optionally one or more sensors) formed at a distal end of the cable. The beginning structure  1105  may be formed in accordance with the processes describe herein with reference to  FIGS.  8 A- 8 F  and  FIGS.  9 A- 9 D . For example, the beginning structure  1105  may be laser cut in a spiral design from a wafer or panel fabricated with electroplated traces. Thereafter, a portion of the cable may be wound into a helical pattern on a PTFE-coated mandrel to form beginning structure  1105  with a helical portion  1130 , the beginning structure  1105  with the helical portion  1130  is then heated, and the PTFE-coated mandrel may be withdrawn. 
       FIG.  11 B  shows a polymer tube  1135  inserted into a mandrel  1140 . In various embodiments, the polymer tube is comprised of a medical grade polymer material, for example, a soft polymer such as silicone, a polymer dispersion such as latex, or a polyurethane. In certain embodiments, the outer diameter of the polymer tube  1135  is selected to be smaller (5 μm to 25 μm smaller) than the inner diameter of the helical portion  1130 . For example, the outer diameter of the polymer tube  1135  may be selected to be from 375 μm to 1775 μm, from 475 μm to 1375 μm, or from 7750 μm to 1275 μm, for example, about 1145 μm. In some embodiments, the mandrel  1140  is the same mandrel used in the fabrications steps discussed with respect to  FIGS.  9 A- 9 C  (e.g., a PTFE-coated mandrel). In some embodiments, the medical grade polymer material is a polyurethane. 
       FIG.  11 C  shows the helical portion  1130  of the beginning structure  1105  being wrapped onto the polymer tube  1135  to form an intermediate structure  1145 .  FIG.  11 D  shows intermediate structure  1145  being inserted into a heat shrink tube  1150  to form an intermediate structure  1155 . In various embodiments, the heat shrink tube is comprised of one or more polymer resins, for example, a fluoropolymer such as the FluoroPEELZ® peelable heat shrink tubes, fluorinated ethylene propylene (FEP), etc.  FIG.  11 E  shows intermediate structure  1155  being heated to heat shrink the tube  1150  to define an outer diameter of the helical portion  1130  of the intermediate structure  1155 , and at the same time melt and reflow the polymer tube  1135  to embed the helical portion  1130  in the polymer tube  1135 . The heating process may include baking the structure in an oven, use of a heat gun, application of hot air, like methods, or any combination thereof. In various embodiments, the intermediate structure  1155  is heated at 170° C. to 210° C., for example about 190° C., for 15 to 40 minutes, for example 25 minutes. Thereafter, the intermediate structure  1155  is cooled (e.g., at ambient temperature), the heat shrink tube  1150  is peeled away, and the mandrel  1040  is withdrawn to obtain the final structure  1160  of the thin-film lead assembly  1100  shown in  FIG.  11 F . In some embodiments, the heating process embeds the helical portion  1130  into the polymer tube  1135 , which results in the conductive traces  1110  and the supporting structure  1115  of the helical portion  1130  being coplanar with the polymer tube  1135 . In some embodiments, the heating process results in the helical portion  1130  and the polymer tube  1135  forming a conjoined hollow tube or a conjoined tube with a lumen. 
       FIGS.  12 A- 12 G  show structures and respective processing steps for fabricating an alternative thin-film lead assembly  1200  (e.g., a portion of a lead assembly encased in a housing) in accordance with various aspects of the invention.  FIG.  12 A  shows a beginning structure  1205  for a cable including a plurality of conductive traces  1210  formed on or within a supporting structure  1215 . The cable may further include an electrode assembly  1220  comprising a multi-electrode array  1225  (optionally one or more sensors) formed at a distal end of the cable  1210 . The beginning structure  1205  may be formed in accordance with the processes describe herein with reference to  FIGS.  8 A- 8 F  and  FIGS.  9 A- 9 C . For example, the beginning structure  1205  may be laser cut in a spiral design from a wafer or panel fabricated with electroplated traces. Thereafter, a portion of the cable may be wound into a helical pattern on a mandrel and heated to form beginning structure  1205  with a helical portion  1230 . 
       FIG.  12 B  shows the beginning structure  1205  being inserted into a heat shrink tube  1235  to form an intermediate structure  1240 . In various embodiments, the heat shrink tube is comprised of one or more polymer resins, for example, a fluoropolymer such as the FluoroPEELZ® peelable heat shrink tubes, fluorinated ethylene propylene (FEP), etc.  FIG.  12 C  shows intermediate structure  1240  being heated in an oven to heat shrink the tube  1235  to define an outer diameter of the helical portion  1230  of the intermediate structure  1240 . The heating process may include baking the structure in an oven, use of a heat gun, application of hot air, like methods, or any combination thereof. In various embodiments, the intermediate structure  1240  is heated at 170° C. to 210° C., for example about 190° C., for 15 to 40 minutes, for example 25 minutes. Thereafter, the intermediate structure  1240  is cooled (e.g., at ambient temperature), and the mandrel is withdrawn to obtain the intermediate structure  1245  shown in  FIG.  12 D . 
       FIG.  12 E  shows a polymer  1250  being injected into the tube  1235  of the intermediate structure  1245 . In various embodiments, the polymer is comprised of a medical grade polymer material, for example, a soft polymer such as silicone, a polyurethane, a copolymer thereof, or a blend thereof. In some embodiments, the polymer is a thermosetting polymer. In certain embodiments, the polymer is comprised of a medical grade polymer material with a Shore durometer measured on a Shore 00 Scale of less than 50 or extra soft. (Shore durometer is defined as a material&#39;s resistance to indentation). The polymer  1250  may be injected into the tube  1235  one or more times in order to fill the entire length of the tube  1235  or a portion of the length of the tube  1235  to obtain the intermediate structure  1255 .  FIG.  12 F  shows intermediate structure  1255  being heated to thermally cure (e.g., thermoset) the polymer  1250 . The heating process may include heating the structure in an oven, use of a heat gun, application of hot air, like methods, or any combination thereof. In various embodiments, the intermediate structure  1255  is heated at 80° C. to 115° C., for example about 100° C., for 5 to 20 minutes, for example 10 minutes. Thereafter, the intermediate structure  1255  is cooled (e.g., at ambient temperature) and the heat shrink tube  1235  is peeled away to obtain the final structure  1260  of the thin-film lead assembly  1200  shown in  FIG.  12 G . In some embodiments, the injection and heating processes result in at least a portion of the helical portion  1230  embedding into the polymer  1250 . In some embodiments, the injection and heating processes embeds the helical portion  1230  into the polymer  1250 , which results in the conductive traces  1210  and the supporting structure  1215  of the helical portion  1230  being coplanar with the polymer  1250  (forms a housing with the polymer  1250 ). In some embodiments, the heating process results in the helical portion  1230  and the polymer  1250  forming a conjoined solid tube without a lumen. 
       FIGS.  13 A- 13 F  show structures and respective processing steps for fabricating an alternative thin-film lead assembly  1300  (e.g., a portion of a lead assembly encased in a housing) in accordance with various aspects of the invention.  FIG.  13 A  shows a beginning structure  1305  for a cable including a plurality of conductive traces  1310  formed on or within a supporting structure  1315 . The cable may further include an electrode assembly  1320  comprising a multi-electrode array  1325  (optionally one or more sensors) formed at a distal end of the cable  1310 . The beginning structure  1305  may be formed in accordance with the processes describe herein with reference to  FIGS.  8 A- 8 F  and  FIGS.  9 A- 9 C . For example, the beginning structure  1305  may be laser cut in a spiral design from a wafer or panel fabricated with electroplated traces. Thereafter, a portion of the cable may be wound into a helical pattern on a mandrel and heated to form beginning structure  1305  with a helical portion  1330 . 
       FIG.  13 B  shows a polymer tube  1335  having a slit  1340  cut along an entire length of the polymer tube  1335 . In various embodiments, a slit  1340  is cut into the polymer tube  1335  such that a lumen  1342  of the polymer tube  1335  is exposed along an entire length of the polymer tube  1335 . In some embodiments, the polymer tube is comprised of a medical grade polymer material, for example, a soft polymer such as silicone, a polymer dispersion such as latex, or a polyurethane. In certain embodiments, the inner diameter of the polymer tube  1335  is selected to be slightly larger (5 μm to 25 μm smaller) than the outer diameter of the helical portion  1330 . For example, the inner diameter of the polymer tube  1335  may be selected to be from 475 μm to 2075 μm, from 575 μm to 1775 μm, or from 850 μm to 1375 μm, for example, about 1245 μm. The inability of medical grade polymers to expand or stretch without mechanical or chemical assistance coupled with its tacky surface makes assembly with rigid parts, such as the cable, difficult. Accordingly, the polymer tube  1335  has a slit  1340  cut into it to temporarily open the polymer tube  1035  and allow for insertion of the cable into the lumen  1342  of the polymer tube  1335 . In some embodiments, the medical grade polymer material is a silicone. 
       FIG.  13 C  shows the beginning structure  1305  on the mandrel  1345  being inserted into the slit  1340  of the polymer tube  1335  to form an intermediate structure  1350 .  FIG.  13 D  shows the mandrel  1345  withdrawn and the intermediate structure  1350  being sealed. In various embodiments, both ends of the polymer tube  1335  are filled with liquid prepolymer  1355  (e.g., silicone liquid prepolymer) to form an intermediate structure  1360 .  FIG.  13 E  shows the intermediate structure  1360  being heated to thermally cure the liquid prepolymer on and seal the polymer tube  1335 . The heating process may include baking the structure in an oven, use of a heat gun, application of hot air, like methods, or any combination thereof. In various embodiments, the intermediate structure  1360  is heated at 80° C. to 115° C., for example about 100° C., for 5 to 20 minutes, for example 10 minutes. Thereafter, the intermediate structure  1360  is cooled (e.g., at ambient temperature) to obtain a final structure  1365  of the thin-film lead assembly  1300  shown in  FIG.  13 F . In some embodiments, the polymer tube  1335  encases (but for the slit between the sealed ends) portion of the supporting structure wound in the helical pattern. In other embodiments, the polymer tube  1335  completely encases (the slit is sealed, for example, using the liquid prepolymer) the portion of the supporting structure wound in the helical pattern. 
       FIGS.  14 A- 14 F  show structures and respective processing steps for fabricating an alternative thin-film lead assembly  1400  (e.g., a portion of a lead assembly encased in a housing) in accordance with various aspects of the invention.  FIG.  14 A  shows a beginning structure  1405  for a cable including a plurality of conductive traces  1410  formed on or within a supporting structure  1415 . The cable may further include an electrode assembly  1420  comprising a multi-electrode array  1425  (optionally one or more sensors) formed at a distal end of the cable  1410 . The beginning structure  1405  may be formed in accordance with the processes describe herein with reference to  FIGS.  8 A- 8 F  and  FIGS.  9 A- 9 D . For example, the beginning structure  1405  may be laser cut in a spiral design from a wafer or panel fabricated with electroplated traces. Thereafter, a portion of the cable may be wound into a helical pattern on a mandrel to form beginning structure  1405  with a helical portion  1430 , the beginning structure  1405  with the helical portion  1430  is then heated, and the mandrel may be withdrawn. 
       FIG.  14 B  shows the beginning structure  1405  is treated with oxygen plasma  1435  to form intermediate structure  1440 . In various embodiments, the oxygen plasma treatment is provided to create hydroxyl groups on a surface of the supporting structure  1415 . The processes to provide oxygen plasma treatment to a polymer are well known in the art and thus, no further description is provided herein. 
       FIG.  14 C  shows diluting a liquid prepolymer or polymer  1445  (e.g., silicone liquid prepolymer) with a solvent  1447  to adjust the viscosity for use as a dip or spray solution  1450  in a dip coating, spin coating, or spray coating process. In various embodiments, the liquid prepolymer or polymer  1445  is comprised of silicone, a polymer dispersion, parylene, or a polyurethane. In some embodiments, the solvent is an organic solvent. In some embodiments, the solvent is a fluorinated organic solvent. In some embodiments, the fluorinated organic solvent is selected from the group consisting of: perfluoroarylalkanes, perfluoro-tert-amines, perfluoropolyethers, and hydrofluoropolyethers. In some embodiments, the fluorinated organic solvent comprises perfluoropolyether or hydrofluoropolyether. In some embodiments, the fluorinated organic solvent comprises ethoxy-nonafluorobutane. In some embodiments, the fluorinated organic solvent consists essentially of ethoxy-nonafluorobutane. The solution  1450  may be provided comprising the solvent at a wt % in the range from 50 to 90 wt %, more particularly from 60 to 85 wt %, for example 75 wt % based on a total weight of the dip solution. In some embodiments, the solution  1450  is provided comprising the solvent at 75 wt %. 
       FIG.  14 D  shows applying the solution  1450  on the intermediate structure  1440  to form the intermediate structure  1455  comprising one or more coats of the polymer. In various embodiments, the applying comprising dip coating, pin coating, or spray coating the intermediate structure  1440  with the solution  1450  to form the intermediate structure  1455  comprising one or more coats of the polymer. In some embodiments, the dip coating process includes immersion and dwell time, deposition and drainage, and evaporation. In the first step, immersion and dwell time, the intermediate structure  1440  is immersed in the solution  1450 . Sufficient time is required for the solution  1450  to interact and fully wet the intermediate structure  1440 . In the second step, deposition and drainage, the intermediate structure  1440  is withdrawn from the solution  1450 . The moving intermediate structure  1440  entrains the liquid polymer. The entrained thickness of the deposited polymer is related to various competing factors. For example, higher viscosity and withdraw speed result in a thicker housing; whereas surface energy and gravity drive a lower housing thickness. In the third step, evaporation, the solvent evaporates from the liquid polymer, and the viscosity of the polymer increases such that bulk flow of the polymer is no longer possible. Change in housing thickness at the third step may be facilitated by further evaporation of the solvent from the liquid polymer. 
       FIG.  14 E  shows the intermediate structure  1455  being heated to cure (e.g., thermoset) the polymer. The heating process may include baking the structure in an oven, use of a heat gun, application of hot air, like methods, or any combination thereof. In various embodiments, the intermediate structure  1455  is heated at 80° C. to 115° C., for example about 100° C., for 5 to 20 minutes, for example 10 minutes. Thereafter, the intermediate structure  1455  is cooled (e.g., at ambient temperature) to obtain the final structure  1460  of the thin-film lead assembly  1400  shown in  FIG.  14 F . In some embodiments, the heating process results in at least a portion of the helical portion  1430  embedding into the polymer since the solution  1450  is capable of dispersing in between the helixes of the helical portion  1430 . In some embodiments, the polymer encases the portion of the supporting structure wound in the helical pattern. 
     While the manufacturing processes of lead assemblies have been described at some length and with some particularity with respect to a specific steps, it is not intended that the processes be limited to any such particular set of steps. Instead, it should be understood the manufacturing processes described herein are exemplary embodiments, and that the manufacturing processes are to be construed with the broadest sense to include variations of the steps to meet specific design and/or performance need described herein, as well as other variations that are well known to those of skill in the art. For example, the various intermediate and final structures described may be adjusted or modified with treatments to increase wettability of the thin-film lead assembly or to seal the ends of the lumens to meet specific design and/or performance needs. Furthermore, it is to be understood that other steps have been omitted from the description of the manufacturing processes for simplicity and clarity. The omitted steps may include obtaining or fabricating the polymer tubes, obtaining or fabricating the heat shrink tubes, waiting predetermined amounts of time for curing or thermosetting, etc. 
     While the invention has been described in detail, modifications within the spirit and scope of the invention will be readily apparent to the skilled artisan. It should be understood that aspects of the invention and portions of various embodiments and various features recited above and/or in the appended claims may be combined or interchanged either in whole or in part. In the foregoing descriptions of the various embodiments, those embodiments which refer to another embodiment may be appropriately combined with other embodiments as will be appreciated by the skilled artisan. Furthermore, the skilled artisan will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention.