Patent Publication Number: US-2022225940-A1

Title: Low profile medical device with integrated flexible circuit and methods of making the same

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to medical devices. More specifically the invention relates medical devices using flexible circuit technologies to create thin walled structures, having simplified manufacturability along with complex functionality. 
     Background Art 
     Medical devices, such as catheters, guidewires, and sheaths are generally introduced into a patient through a needle inserted into a blood vessel such as an artery or vein and navigated to the area of interest or disease using fluoroscopy, MRI, ultrasound or similar tracking or visualization technology for guidance. Once at the area of interest these devices are used to diagnose and treat a variety of disease such as cardiac electrical arrhythmias, coronary artery blockages, neurovascular artery aneurysms, as examples. The devices have dimensional requirements that require them to be small enough navigate in human vessels, organs, and cavities, in conjunction with other devices, while incorporating a growing number of sensors such as those needed for sensing pressure, temperature, location, movement, impedance, velocity, cell electrical activity, blood chemistry, images, acoustics and the like. In addition, the devices typically include conductors, pull wires, fiber optics, lumens, fluid lumens, stiffeners, braiding, structural elements and many other components typically found in such devices. In general, over several decades, these devices have developed, through clinical need, to be more sophisticated with more complex diagnostic and therapeutic capabilities and have also needed to be made in smaller sizes to fit into more complex, distal, and smaller anatomical regions, allowing for the treatment of significantly more tissue volume. 
     However, the smaller the size of the device, the more difficult and expensive it is to manufacture, especially if it is made with an increasingly high density of electronic components, and other sophisticated elements. Complex assembly processes can be very complex and time consuming, especially when they are not automated, and as a result these medical devices are a relatively expensive burden on the health care system. There remains a need for a small, high performance medical device that is low in cost. 
     Devices using flexible circuit technologies to create thin walled medical device structures, having simplified manufacturability along with the desired complex functionality, with pre-mounted smaller profile components, and less assembly time, would be well received in the medical marketplace. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention solves this need by providing a medical device that includes an elongated lumen shaft that includes a shaft body having a shaft wall. The device also includes a cylindrical flexible circuit made of a dielectric layer in a cylindrical form, a conductive trace layer, a medical device element; and an open, unfilled lumen. In some embodiments the flexible circuit is integral to the shaft&#39;s mechanical structure. The cylindrical flexible circuit can have two or more substantially cylindrical flexible substrate layers and a via. 
     The via can provide fluid or electrical communication through one of the flexible substrate layers. The medical device element can be a sensor located on the interior of the cylindrical flexible circuit, and if so the device further includes an electrical connection between the sensor and the conductive trace layer through the via. The medical device element can be an electrode located on the exterior of the cylindrical flexible circuit, and if so the device further includes an electrical connection between the electrode and the conductive trace layer through the via. The medical device can have multiple medical device elements, one is located on the interior of the cylindrical flexible circuit, and a second medical device element located on the exterior of the cylindrical flexible circuit. 
     The medical device can include a flexible circuit edge joint that is sealed to form the cylindrical flexible circuit into a full cylinder. The joint can be longitudinally linear. The joint can also be longitudinally helical. 
     In one embodiment of the medical device the cylindrical flexible circuit is inside the lumen shaft, and the open, unfilled lumen is inside the cylindrical flexible circuit. Likewise, while the flexible circuit edge joint is sealed in one embodiment, in another the flexible circuit edge joint is not sealed, and the lumen shaft is adapted to hold the flexible circuit in a substantially cylindrical form. 
     In another embodiment the lumen shaft includes a sensor opening adapted to expose the medical device element to the exterior of the medical device. 
     In another embodiment the cylindrical flexible circuit is outside the lumen shaft, and the open, unfilled lumen is inside the lumen shaft. 
     In some embodiments the open, unfilled lumen has a pull wire or a fluid lumen. In some embodiments of the cylindrical flexible circuit it includes a cylindrical primary portion and a flat proximal portion. The medical device may also include a solder pad or a connector adapted to connect the cylindrical flexible circuit to external medical equipment. 
     In another embodiment the medical device includes an elongated lumen shaft that includes a shaft body having a shaft wall. The device also includes a cylindrical flexible circuit made of a dielectric layer in a cylindrical form, a conductive trace layer, and an open, unfilled lumen. 
     The invention also includes a method of manufacturing a medical device that includes providing a flat flexible circuit that includes a dielectric layer, a conductive trace layer, and a medical device element; rolling the flat flexible circuit into a substantially cylindrical form; sealing the cylindrical flexible circuit into the substantially cylindrical form by substantially filling its lumen with an adhesive; providing an open lumen shaft on the exterior of the cylindrical flexible circuit; and removing the adhesive from the cylindrical flexible circuit to provide an open lumen. In one embodiment the method further includes the step of providing a sensor opening to expose the medical device element to the exterior of the medical device. In another embodiment the method further includes the step of soldering a proximal portion of the flexible circuit to a connector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of a flexible circuit used for the invention; 
         FIG. 2  is a sectional view of a flexible circuit cross section which may be used for the invention; 
         FIG. 3  is a cross section of a flexible circuit configured as part of an elongated open lumen body with the flexible circuit disposed on the inside; 
         FIG. 4  is a cross section of a flexible circuit configured as part of an elongated open lumen body with the flexible circuit disposed about the outside diameter; 
         FIG. 5  is a cross section of a flexible circuit configured into an elongated open lumen body; 
         FIG. 6  is an isometric view of the manufacturing of the device; 
         FIG. 7  is a schematic drawing showing one embodiment of a manufacturing tool; 
         FIG. 8  is a view showing the flexible circuit batch; 
         FIG. 9  shows a perspective view of manufacturing; 
         FIG. 10  shows an isometric view of manufacturing; 
         FIG. 11  shows a cross section of one embodiment of the manufacturing process for constructing the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In general, the invention comprises a medical device used for diagnostic and/or therapeutic surgical procedures. For example, the device could be a guidewire, a catheter, a sheath, or other medical device to be inserted into a patient. 
     The device includes an elongated open lumen body. An elongated open lumen body is an elongated tubular structure which is not filled with structural material. It is open so that other elements, e.g., pull wires, fibers, conductors, additional lumens, stiffeners, or fluid, and may be run from one end of the medical device to the other or a portion of the device. An “open” lumen can be capped or sealed at the ends or in a portion thereof. 
     As part of this invention, the device has a structure that includes a flexible circuit comprising one or more dielectric layers (such as polyimide, silicone, parylene, LCP, ceramic, reinforced composites, for example); and one or more electrically conductive layers (such as copper, silver, carbon, conductive inks, for example); and possibly one or more mounted electronic components (such as electrodes, thermistors, capacitive micromachined ultrasonic transducers, pressure sensors, for example), which may be mounted in, on or within the elongated open lumen body over part or the whole of its length. Flexible circuits are known in the industry under a variety of names, including flexible printed wire boards (PWB), flexible electronics, flexible printed wiring, flexible printed circuit board (PCB), flexible printed wire assembly (PWA), flexible printed circuit assembly (PCA), or flexible printed circuit board assembly (PCBA). While in some settings there are slight differences between these terms, for purposes of this invention the term flexible circuit board will be used to encompass flexible or conforming boards with a wiring and with or without mounted sensors or other components. 
     As an alternative to or in addition to the electrically conductive layer, the flexible circuit may comprise a flexible integrated photonics layer, a flexible silicon photonics layer for use, for example, as an interferometer or resonator. Alternatively the photonic and electronic layers may be combined into one layer. 
     Instead of lying flat, one or more of the flexible circuit layers is rolled or partially rolled so that at least a portion of its edges abut each other or overlap (with each other or the ends of a another flexible circuit) to give the elongated open lumen body a seam or a joint, for example a lap joint. These joints may be held together with an adhesive, a reflowed substrate made of a thermoplastic, encapsulation within other layers, or by a mechanical means. In some embodiments the ends have a substantial gap between them that is filled or held in place by a thermoplastic, for example. 
     This lumen body can contain electrical conductors and sensors but also may have strengthening members within its layer (such as carbon fiber, stainless wire, for example), and also may contain pull wires, optical fibers, fluid lumens, and electrical wires. These components may lie at the center of the rolled layer, e.g. within an open lumen and over at least part of the length from proximal and distal ends. In this configuration of the invention the flexible circuit acts as a structural component carrying the device&#39;s mechanical load such that the balance of the medical device construction can be reduced in cross-section and thus reducing total wall thickness and total device diameter, allowing for less traumatic procedures and exponentially improved access to distal tissues of interest. 
     In an exemplary embodiment of the invention, a flexible circuit, over all or part of its length is rolled into a tubular, or partial tubular, shape such that the seam or edges run longitudinally down the length of the shaft, covering all or part of the circumference of an open lumen tubular shaft material such as a stainless hypo tube, a polymer catheter shaft, for example. The seam or edges are affixed together by means of an adhesive or a thermoplastic reflow process, for example. Alternatively a thermoset dielectric may be induced to hold a tubular or partial tubular shape through use of a stress relieving process. The latter may serve to hold the edges of the flexible circuit together over its length, but both the flexible circuit or the open lumen tubular shaft material may comprise the load bearing structure of the invention. In this embodiment it can be advantageous if both flexible circuit dielectric material and the tubular shaft material are made of a thermoplastic and reflowed together, for additional strength. In an alternative mode of this and other embodiments, the seam or edges may run in a spiral configuration about the shaft. Likewise, the seam or edges may be circumstantially offset at different portions of the shaft. That is, in a first proximal portion of the shaft the seam may be at  12 : 00  as looking at the cross-section of the shaft, in a middle portion the seam may be at  4 : 00 , while in a distal portion of the shaft the seam may be at  8 : 00 . This pattern may happen once or be repeated, as needed to either distribute the seam to reduce weakness or biasing in any one direction, or to increase weakness or bias in a direction at a particular location. 
     In another embodiment of the invention, a flexible circuit, over all or part of its length, is rolled into a tubular, or partial tubular shape such that the seam or edges run longitudinally down the length of the shaft, is placed inside of an additional tubular shaft material made of a metal tube or braided polymer shaft, as an example. The latter may serve to hold the edges of the flexible circuit together over its length. In one embodiment the flexible circuit does not cover the whole circumference of the tube. In one mode of this embodiment both the flexible circuit and the additional shaft material comprise the load bearing structure of the invention. The flexible circuit may be fitted into an existing tubular shaft and held in place by mechanical force, adhesive, thermoplastic reflow, extrusion, or shrink tubing, for example. A similar design may be achieved by first creating the tubular flexible circuit structure then dip coating or spray coating the flexible circuit structure. Alternatively or in combination with the above a thermoset dielectric may be shaped with a stress relieving process. 
     The previously described embodiments may also be combined as needed over the length of the device to create a hybrid or composite device. 
     The device has a greatly simplified construction compared to the prior art devices. Briefly, a flexible circuit is manufactured having on it the necessary traces, electrodes, connections, sensors, and vias for the device. This flexible circuit may then be wrapped around a core and the seam sealed (or not, as discussed above). It may be affixed, e.g., glued, to the core or to a portion of the core, giving the assembly a cylindrical shape. The core may then be removed to open up the lumen. Likewise, the flexible circuit can be wrapped around a removable core, placed inside a second tube and then have the core removed to open up the lumen. The removable core may be coated with a lubricious coating or stretchable such that upon stretching the core&#39;s OD shrinks allowing it to be removed from the assembly exposing the open lumen. In an alterative the flexible circuit can be wrapped around a hollow open lumen and glued to itself or the tube. 
       FIG. 1  shows an exemplary (flat) flexible circuit  100  for use as a basic building block of the medical devices of the present invention. A flexible circuit  100  utilizes a flexible substrate  105 , typically made with a thin flexible plastic or metal foil as the substrate. The flexible circuit  100  is advantageously long, thin and narrow. Often, the flexible substrate  105  utilizes an insulating material or a dielectric. The substrate can be made for example from thermoset or thermoplastic polymers. The substrate can be made from polymers such as liquid-crystal polymers (LCP), polyether ether ketone (PEEK), polyester (PET), polyimide (PI), polyethylene napthalate (PEN), polyetherimide (PEI), polyefine, Kapton, various fluropolymers (FEP), PTFE, silicone, parylene, reinforced composites and copolymer Polyimide films or a transparent conductive polyester film or other dielectrics. One non-limiting example of the latter is the product Topas® COC (TOPAS Advanced Polymers GmbH, Oberhausen, Germany or Ticona GmbH, Kelsterbach, Germany). 
     Advantageously the material for the flexible circuit  100  is biologically-inert or bio-compatible. The flexible circuit  100  may also be covered with a layer of biocompatible hydrogel, silicone, PTFE, for example on the outside to reduce the friction and for improved biocompatibility, e.g. to avoid blood coagulation. 
     The measures of the flexible circuit  100  may in one advantageous embodiment be 100 cm long, 1.5 mm wide and 50 micrometer thick. The length, as well as the thickness and the width, may vary depending on the application. The width may be in the interval of 0.5-10 mm, more advantageously 1-5 mm, and the thickness may be in the interval of 2-200 micrometer, more advantageously 3-50 micrometer, in one particular embodiment 50 micrometer is used. Generally a greater thickness results in a more rigid device and a smaller thickness results in a less rigid one. A thinner material, e.g. a laminate below 25 microns with conductive traces thinner than 25 microns, is typically more flexible, but in embodiments where increased rigidity is required the thickness is increased along all or a portion of the substrate  105 . 
     In addition, the similar medical devices described in the prior art can become too stiff when the diameter becomes large, as it does not have an open lumen. In this case, the stiffness of a cylindrically shaped device is proportional to the fourth power of the diameter. Thus, the larger the device&#39;s diameter, the substantially larger the stiffness will be. For a diameter below 1 mm the catheter is soft and flexible. However, for such a closed lumen device it is very difficult to make it very flexible. The present invention solves this difficulty by creating an open lumen and using the flexible circuit  100  as all or part of the structural element, reducing or eliminating the need for bulky polymer walls. Notably, it may be desired to create a region of the medical device that is more susceptible to bending or other faults, and accordingly such a region may have a thinner or otherwise modified flexible circuit substrate 
     Conductive traces  110  are formed onto substrate  105 . For example, a metal foil layer may be applied to or adhered to the substrate  105 . Conductive traces  110  may be etched from this foil layer. Most commonly a copper foil is used, but a wide variety of foils of varying materials (metals, alloys, conductive polymers) thicknesses, conductivities, and cost are available. A thin polymer coating (not shown) may be applied over the conductive traces. The conductive traces may be formed of a metal such as silver or copper, conductive inks and adhesives, conductive fiber such as carbon. They may be constructed by photolithography, conductive ink aerosol ink jet printing, vapor deposition or other methods known in the art. 
     Conductive traces  110  may be arranged on both sides of the substrate  105 . At certain points there are holes, called via holes  140  (see  FIG. 2 ) in the substrate  105 . Conductive traces  110  on opposite sides of the substrate  105  are electrically connected through the via holes  140 , In the via holes  140  there are electrical conductors, via conductors (not shown), connecting the electrically conductive traces  110  on both sides of the substrate  105 . Advantageously the via conductors comprise electrically conductive material on the walls of the via holes. The conductive traces  110  may comprise a suitable metal, e.g. copper or an electrically conductive polymer or another electrically conductive material. 
     The flexible circuits utilized in the present invention may be single sided, double sided, double access, sculptured, or multilayer flexible circuits. Single sided circuits have the advantage of being easy to manufacture. They have a single conductive trace layer formed on one side of the substrate. 
     Double access flexible circuits likewise typically have a single conductive trace layer, but are further processed so that portions of the conductive trace layer are accessible from both sides for ease of connection to a sensor, electrode, or the like. Double sided flexible circuits typically have two conductive trace layers, one on each side of one or more substrate layers. They are often advantageously constructed with through holes, or vias, to provide connection features for the conductive traces on one or both sides of the substrate. The present invention also contemplates the use of multilayer flexible circuits, which may have any number of substrate layers and conductive trace layers, the latter of which may be interconnected by vias. Likewise, the present invention may take advantage of a stretchable flexible circuit, allowing the device to take on various curvilinear shapes, bends, and motions during use. Such a stretchable flexible circuit can be especially useful for a catheter that must conform to physical anatomy, or for use in a catheter portion that is inflated and deflated during use. When a stretchable dielectric is used the conductor material is also ideally stretchable, such as an elastic conductive filled polymer, or a metal shaped in such a way to be stretchable. 
     The proximal end of the conductive traces  110  may be terminated in a connective means such as a solder pad  120 , connectors, or similar structure, for connecting the trace to other medical equipment, such as a power source, diagnostic equipment, or monitoring equipment. The distal end of the conductive traces  110  are terminated in medical device elements, such as sensors  125 , electrodes  130  or distal solder pads  121 , for example. Parameters that may be measured include pressure, temperature, flow, pH, partial pressure of oxygen, mapping with ultra sound etc. It is also possible to combine different electronic components and/or microelectromechanical systems to achieve multi functionality or to integrate several electronic components or microelectromechanical systems of one kind to get extended functionality. One such example could be several pressure sensors in order to improve diagnosis of stenosis in the coronary arteries. 
     When the medical device elements have been mounted, the flexible circuit  100  is at least partly rolled up into a tube and may be simultaneously filled with adhesive or glue that holds the flexible circuit  100  in a tube shape. Formation of the flexible circuit  100  at least partly into a tube is advantageously done by feeding the flexible circuit  100  through a hole with a funnel-like opening where the circumference of the hole matches the width of the flexible circuit  100 . When a single sided flexible circuit  100  is used it is advantageous that the width of the flexible circuit  100  is the same as the circumference of the hole. When a double sided flexible circuit  100  is used it is advantageous that the width of the flexible circuit  100  is slightly smaller than the circumference of the hole. This is necessary because elements on the second side of the flexible circuit  100 , such as the medical device elements or the conductive traces  110  need some space in the hole. After feeding the flexible circuit  100  through the hole, the first and second side of the flexible circuit  100  have respectively become inside and outside of the substantially cylindrical flexible circuit  100 . 
     After processing, the flexible circuit  100  is, alone or with other flexible circuit(s)  100 , in a substantially cylindrical shape. That is, the boundaries of the flexible circuit  100 —while not necessarily contiguous or closed—define a generally hollow tubular shape that is substantially cylindrical. A cylinder is the surface generated by a straight line intersecting and moving along a closed plane curve, the directrix, while remaining parallel to a fixed straight line that is not on or parallel to the plane of the directrix. An exemplar cylinder is bounded on the top and bottom by flat circular ends and by a single curved side. However, the cylindrical shapes of the present invention, because they are real world devices and not pure mathematical constructs, will not have perfectly circular tops and bottoms, but in fact may be irregular or in another form, e.g., an oval. Likewise, the single curved side may not be straight, even during manufacturing. During use of the medical device it is required to bend and twist to reach its target. Viewed in two dimensions one side may not match the other. While the cylindrical shape may be a right circular cylinder in some embodiments, in others it will be an oblique cylinder. As befitting an open lumen device, the flexible circuit  100  may have a closed top and bottom, but in a preferred embodiment the cylinder is an annular cylinder or a tube, and the top and bottom are in fact open allowing the passage of fluids, wires, and the like. Within this understanding, the flexible circuit  100  is formed from a flat flexible circuit into a substantially cylindrical shape for use in the medical device. 
       FIG. 2  shows a lateral cross section of one embodiment of a flexible circuit  100  suitable for use in the present invention. As shown therein, flexible circuit  100  comprises multiple flexible substrate layers  105 , which can be comprised of one or more similar or different polymers or other dielectrics which are flexible enough to be used in a medical device. The flexible circuit  100  also contains multiple conductive trace layers  110 . These layers may or may not be held together with an adhesive  115 . Likewise, an adhesive  115  or polymer may fill any gaps between traces. The proximal end of the conductive traces  110  are ideally terminated into a connector by means of a solder pad, connector, or similar (not shown). The distal end of the conductive traces  110  are terminated into distal medical device elements such as sensors  125 , electrodes  130 , solder pads, diagnostic devices (e.g., thermistors, pressure sensors, glucose monitors, etc.), or therapy devices (e.g., an ultrasound array, and ablation element, laser, cryogenic fluid delivery, etc.) The distal end of the conductive traces  110  may terminate to the distal element ( 125 ,  130 ,  121 ) by means of vias  140 , for example. The vias  140  may act as pathways through a dielectric layer  105  for a continuance of a conductive trace  110 , a connection to an electrode  130 , a connection to a sensor  125 , connection to a solder pad  121 , for fluid transmission between layers, inflation of a balloon, or a combination of these. For example, a via  140  may provide a pathway through the dielectric layer  105  for an electrical connection between sensor  125  and one of the conductive trace  110 , and also serve as a fluid lumen for one or more purposes, such as irrigating tissue, cooling a sensor  125  or an ultrasound array (not shown), or balloon inflation and deflation. The medical device elements may be clamped or secured to the flexible circuit using a collar (not shown). The medical device elements may also be attached to the flexible circuit substrate using bond pads (not shown). 
     The flexible circuit  100  may be comprised of one or more dielectric layers  105  and one or more conductive trace layers  110 . Each layer may be fractions of a micron thick as long as they satisfy the electrical requirements of the device. Distal elements (e.g., electrodes, solder pads and sensors, etc.) may be disposed on any layer of the flexible circuit  100  and on either side of the dielectric layers  105 . While three dielectric layers  105  are shown, and two conductive trace layers  110  are shown, it is understood that other combinations are within the scope of the invention. 
       FIG. 3  shows a medical device  151  used for diagnostic and/or therapeutic procedures, in the form of an elongated body  150 , such as a guidewire or catheter body. Elongated body  150  has an open lumen  155 . The elongated body  150  may be constructed of a polymer extrusion with or without reinforcement, a shrink tube such as polyester or PTFE, a polymer structure formed through dip coating, a polymer structure formed from reflowing of a polymer, or a metal tubular structure such as a hypo-tube. 
     Flexible circuit  100  is mounted inside of lumen body  150 , in open lumen  155 . In one embodiment lumen body  150  is formed around a cylindrical flexible circuit  100 . For example, lumen body  150  may be reflowed over the already rolled and cylindrical flexible circuit  100  (as discussed above). Likewise, a shrink tube may be placed over the cylindrical flexible circuit  100  and shrunk to fit in place. 
     In the alternative, flexible circuit  100  may slid into lumen body  150  and adhered into place by one or more mechanisms, such as an adhesive, a filler polymer, shrinking lumen body  150 , crimping, and the like. The flexible circuit  100  may be “over rolled” as discussed above, e.g., it may be rolled to a smaller diameter than desired in the end product. It may then be slid into the lumen body  150 , and the adhesive holding the edges of flexible substrate  105  together may be removed, allowing it to expand into the desired cylindrical shape. 
     In one embodiment, the flexible circuit  100  is placed onto a mandrel or rod and glued into place. It can also be heat formed or mechanically held on the mandrel. It is then placed inside the lumen body  150 . At this point the mandrel is removed by melting the glue. In the alternative the mandrel may be elongated to decrease its diameter, and then removed. For example, the mandrel may be coated with a lubricious surface like PTFE or silicon. Likewise, the mandrel can be made from a material that can handle high temperatures, can be stretched, and necked down in OD, such as an annealed stainless steel, copper, etc. 
     In some embodiments the flexible circuit  100  is formed into its cylindrical shape without the mandrel. For example, it can be heat shaped into the tubular or semi-tubular shape and then possibly glued or mechanically held in position. As needed, the glue and mechanical constraints can be removed once flexible circuit  100  is inside the lumen body  150 . Likewise, the flexible circuit  100  can be drawn or pulled into the lumen body  150  and held in place by a mechanical bias outward, with adhesives, by reflowing the outer shaft material to adhere or hold the flexible circuit  100 , or any combination thereof. 
     Flexible circuit  100  may include one or more flexible substrates  105 , for example, and one or more electrically conductive layers or elements  110 , such as copper, silver, carbon, conductive inks, for example, and possibly one or more mounted electronic elements, such as electrodes  130 , thermistors  125 , capacitive micromachined ultrasonic transducers  160 , pressure sensors, for example, which may be mounted in, on or within the elongated open lumen body over part or the whole of its length. The edges of the flexible circuit layers  105  may or may not meet or overlap to form a flexible circuit edge joint  165 , e.g., with a lap joint or butt joint. The flexible circuit edges may be held together with an adhesive, a reflowed substrate made of a thermoplastic, or by mechanical means. The flexible circuit  100  may be held in place within the open lumen  155  using one or more of the following; an adhesive, melting of a thermoplastic polymer dielectric to the id of the medical device, melting the open lumen  155  to the flexible circuit, or by strain from the flexible circuit  100  against the id of the open lumen  155 . 
     The flexible circuit  100  may be formed of multiple or variable widths, as to fill the inner circumference of the open lumen  155  as the inner diameter of the open lumen  155  may vary over its length and require both edges of the medical device meet at a flexible circuit edge joint  165 , and also to accommodate non-fully circumferential solutions where the requirement is for flexible circuit edges have a gap between then. The lumen  155  is depicted as being round in cross section, but may have other shapes as well, such as an oval or an irregular shape where needed. The flexible circuit  100  may be placed into the open lumen  155  such that the flexible circuit edge runs in a helix pattern over the length of the medical device lumen or in a single nonrotating fashion over its length. The mounted electronic components may be mounted on either side of the flexible circuit as shown in  FIG. 3  by the sensor  125  on the inner portion of the flexible circuit (in the open lumen  155 ) and the electrode  130  on the outer portion. Irrigation ports  141  may facilitate fluid or pressure communication from the inner diameter to the outer diameter of the elongated lumen body  150 . Sensor openings  142  may also be sued to facilitate communication between sensors  125 , electrodes  130 , and a target, such as a portion of a patient. 
     In this embodiment the elongated open lumen body  150  with inner mounted flexible circuit  100  may be used as the main medical device structure which not only contains electrical conductors and sensors but also may have strengthening members within its layer, such as carbon fiber or stainless wire. It also may contain pull wires, optical fibers, fluid lumens, and electrical wires and over at least part of the length from proximal and distal ends. In this configuration of the invention the flexible circuit  100  acts as part of the structural component carrying all of the device&#39;s mechanical loads such that the balance of the medical device construction can be reduced in cross-section, thus reducing total wall thickness and total device diameter, allowing for less traumatic procedures and exponentially improved access to distal tissues of interest. 
     In addition, the lumen body  150  may be the entirety of or a part of a single lumen catheter shaft. It may be one shaft and lumen of a multiple lumen catheter shaft, a sheath lumen, a guidewire lumen, a lumen forming part of an diagnostic or therapeutic assembly at the distal end of a device such as a catheter, or other medical device to be inserted into a patient, for example. The lumen body  150  may be a portion of an ultrasound catheter, a guidewire, an endoscope, a therapy catheter, a diagnostic catheter, or an OCT/OCR catheter or guidewire. 
       FIG. 4  depicts another embodiment of the invention,  152 . In the embodiment shown in  FIG. 4  the cylindrical flexible circuit  100  is outside open lumen shaft  157 . The medical device  152  of this embodiment is used for diagnostic and/or therapeutic surgical procedures. It has the cylindrical flexible circuit  100  placed onto the open lumen shaft  157  and includes an open lumen  155 . The cylindrical flexible circuit  100  is adhered to an open lumen shaft  157 , for example using an adhesive, melting a thermoplastic polymer dielectric to the open lumen shaft  157 , laser welding, or melting the open lumen shaft  157  to the flexible circuit. 
     The medical device  152  may be a single lumen catheter shaft, a lumen of a multiple lumen catheter shaft, a sheath lumen, a guidewire lumen. The medical device  152  may serve as a part of a diagnostic or therapeutic assembly at the distal end of a device such as a catheter, sheath or guidewire, with the remainder of the device formed by conventional means. The open lumen  155  may contain electrical conductors and sensors, strengthening members, such as carbon fiber, stainless wire, for example, and also may contain pull wires, optical fibers, fluid lumens, and electrical wires, within the open lumen and over at least part of the length from proximal and distal ends. One or more of these elements may be embedded in the shaft ( 150  or  157 ) or flexible circuit  100  as well. 
     The structure of the open lumen shaft  157  material may be constructed of one or more of the following; a polymer extrusion with or without reinforcement, a shrink tube such as polyester or PTFE, a polymer structure formed through dip coating, a polymer structure formed from reflowing of a polymer, a metal tubular structure such as a hypo-tube, for example. The flexible circuit  100  may be formed of multiple or variable widths, and placed on the outer circumference of the open lumen shaft  157 , as the outer diameter may vary over its length and may require both flexible circuit edges  165  to meet, and to also accommodate non-fully circumferential solutions where the flexible circuit edges have a gap between then. The cylindrical flexible circuit  100  may be placed onto the open lumen shaft  157  such that the flexible circuit edge runs in a helix pattern over the length of the medical device lumen or in a single nonrotating fashion over its length. The cylindrical flexible circuit may have sensors  125 , electrodes  130 , or transducers  160  mounted on either side of the flexible circuit. Sensor openings  142  may facilitate communication to sensors and electrodes or contact with a target. 
     Manufacturing such a structure may be accomplished by either; first mounting the open lumen shaft  157  onto a removable carrier then mounting the flexible circuit  100  to the open lumen shaft  157  then removing the carrier, or by placing the flexible circuit  100  onto the open lumen shaft  157  without a carrier. The flexible circuit  100  can be glued into place, or it can be held in place by reflowing the lumen shaft  157  to hold the flexible circuit  100 . Vias  140 , irrigation ports  141 , or sensor openings  142  may be mechanically formed, or created by use of a laser, before or after the flexible circuit  100  is mounted. 
       FIG. 5  shows another embodiment of the present invention in which the flexible circuit  100  itself forms the length of the elongated open lumen body  154 , without the support of additional structural elements (beyond that of a non-structural seal or biocompatible coating). In this embodiment the flexible circuit edges  165  of the flexible circuit  100  are joined by one or more of the following; gluing a butt or lap joint together, laser welding, reflowing a thermoplastic dielectric, joining edges made of an interlocking pattern. 
     The elongated open lumen body  154  may form a single lumen catheter shaft, a multiple lumen catheter shaft, a sheath lumen, a guidewire lumen, or a lumen forming part of a diagnostic or therapeutic assembly at the distal end of a device such as a catheter, sheath or guidewire, for example. The flexible circuit  100  may be formed of multiple or variable widths, as the outer diameter of the elongated open lumen body  154  may be required to vary over its length. The flexible circuit  100  may be oriented over the length of the elongated open lumen body  154  such that the flexible circuit edge runs in a helix pattern over the length of the elongated open lumen body or in a single nonrotating fashion over its length, or in combination. Elements such as flexible circuit sensors  125 , electrodes  130 , or transducers  160  may be mounted on either side of the flexible circuit. Vias  140  may facilitate communication from the inner diameter to outer diameter of the elongated open lumen body  154 , or between any given layers of flexible circuit  100 . 
     The open lumen  155  may contain electrical conductors and sensors, strengthening members, such as carbon fiber, stainless wire, for example, and also may contain pull wires, optical fibers, fluid lumens, and electrical wires, within the open lumen and over at least part of the length from proximal and distal ends. 
     The open lumen  155  may be formed by wrapping a flexible circuit  100  around a mandrel and or gluing the joint together, e.g., a lap joint glued together. Likewise, it may be formed by reflow or melting the edges together with a thermoplastic polymer substrate. The mandrel or glue may be removed as described above, as needed, to form the open lumen. Likewise, in each of the embodiments disclosed, there could be a combination of layers and embodiments, for example a flexible circuit layer inside an shaft layer, and a second flexible circuit layer outside of the shaft layer. 
     It is also anticipated that hybrid or composite devices may be made by combining the structure described in these individual embodiments, such that the structure of the open lumen body varies over its length and diameter to fit specific needs of the designer, manufacturer, and user. 
       FIGS. 6 and 7  show a method for forming the flexible circuit  100  into a substantially cylindrical shape. Generally, when manufacturing the flexible circuit  100 , an elongated substrate  105  is at least partly brought into a cylindrical shape along all or a portion of its length and the inside of the cylindrically shaped flexible circuit  100  may be at least partly sealed from the outside. The flexible circuit  100  has at least one electrical conductor  110  on one or both sides of the substrate  105  and may advantageously be equipped with at least one medical device element. It may be an advantage to mount medical device elements on the inside of the flexible circuit  100  but it may also be advantageous to mount the medical device elements to the outside, especially if it is integrated in the flexible substrate  105 . Advantageously, the medical device elements can be mounted on the substrate  105  before the flexible circuit  100  is formed into a cylindrical shape. 
     In one embodiment the flexible circuit  100  is provided with a tip  107  (see  FIG. 8 ) on at least one of the ends of the flexible circuit  100 . The tip  107  is narrower than the rest of the support member and may have a length of approximately 10 to 50 mm, preferably 15 to 30 mm. When forming the flexible circuit  100  at least partly into a cylindrical shape, a jig or tool  600  made out of a block of material like metal or plastic is used. The metal used may for example be steel, brass, copper or any other alloy. A suitable plastic may for example be polymethacrylate, known as Plexiglass™. 
     The jig or tool  600  is provided with a small hole  601  having a funnel-like opening  611 . The hole  601  and the funnel-like opening  611  are adapted not to damage the flexible circuit  100  or the other elements provided on the flexible circuit  100 . For example may a lining be provided in the hole  601  and/or funnel-like opening  611 . 
     The tip  103  of the flexible circuit  100  is threaded through the funnel-like opening  611  and the small hole  601 . The opening  611  is filled with an adhesive or glue, it may be advantageous to use PolyCaproLacton (PCL) which has a good adhesion to polyimide. The adhesive or glue may be distributed by means of a dispenser. Generally, an adhesive is selected that has a good adhesion to the material of the flexible substrate  105 . The adhesion between the adhesive and the flexible substrate  105  needs to be good to maintain the flexible substrate  105  in a tube shape. The adhesive is melted and fills the flexible substrate  105 . When the flexible substrate  105  is pulled through the lower part of the hole, it is cooled and the PCL crystallizes (it becomes solid) and forms a reinforcing or rigidifying element  103 . The reinforcing or rigidifying element  103  may comprise the solidified adhesive material, a separate reinforcing or rigidifying element or a combination of the solidified adhesive material and the separate reinforcing or rigidifying element. 
     If there are via holes  140  in the flexible substrate  105  these will filled with adhesive material as the flexible substrate  105  being fed through the tool  600 . The adhesive material will fill the via holes  140  completely and will substantially be in line with the outside surface of the flexible substrate  105 . If the flexible circuit  100  is not covered with a biocompatible material, like a biocompatible hydrogel, it is advantageous that the adhesive material used is biocompatible. Further details can be found in United States Patent Publication No. US20090143651, published Jun. 4, 2009 and incorporated herein by reference. 
     It is as well possible to use welding, for example laser welding, to weld the adjacent edges of the flexible circuit  100  to each other. In this case the jig or tool  600  may be provided with welding equipment that welds the edges of the flexible circuit  100  to each other as the substrate  105  is drawn through the jig or tool  600 . In this case the flexible circuit  100  may also be provided with a separate reinforcing or rigidifying element  103  as the substrate  105  is drawn through the jig or tool  600 . The reinforcing or rigidifying element  103  may advantageously be provided on the inside of the cylindrical flexible circuit  100 . 
     It is possible to produce medical devices in great numbers efficiently. The flexible circuit  100  may be manufactured simultaneously in great numbers. In one example, shown in  FIGS. 8-10 , flexible circuits  100  are manufactured from sheets or panels of a suitable material. Common widths of the panels or sheets are 30 or 45 cm, which allows hundreds of flexible circuits  100  (approximately 1-2 mm wide) to be manufactured simultaneously. The flexible circuits  100  are separated by perforations (done for example by milling or laser ablation) to make it easy to separate them. This allows simultaneous formation of several flexible circuits  100  as depicted in  FIG. 9 . 
     It is also possible to make the production continuous as indicated in  FIG. 10 . The flexible circuits  100  are preferably separated from one another by a suitable perforation or other suitable technologies. The perforation may be added before the perforated sheet or panel enters the tool or jig  600 . Here two standard methods are combined with the flexible circuit  100  described herein in a continuous production process. First, the substrate  105  is subjected to standard process steps used today by manufacturers of flexible printed wire boards, such as via drilling, pattern formation by lithography and etching. Conductors may also be formed by ink jet printing or in other ways. Next, the medical device elements are attached by standard pick-and-place equipment using conducing glue, soldering or some other method. Finally, the sheet or panel is fed into a tool or jig  600  with several parallel holes  609  with funnel-shaped openings  611 . The feeding mechanism is omitted in the figure. This would constitute a fully continuous process. Flexible circuits  100  can be cut off in batches after passage of the tool or jig  600 . 
     One advantage with the device described herein is that the construction is relatively simple. Thereby reliability can be improved. Basically the flexible circuit  100  itself constitutes a device suitable for invasive use. Since the construction is relatively simple the device may also be manufactured relatively inexpensively which facilitates the use of the device as a single use article. 
     The manufacturing process brings advantages for example in terms of automation. The manufacturing process is also easy to implement in a bigger scale since several devices can be manufactured in parallel. 
       FIG. 11  shows a cross section of one embodiment of the invention. In manufacturing flexible circuit  100  is formed with a closed lumen. Flexible circuit  100  is formed on a removable carrier  200  with its lumen filled with adhesive  210  to seal it into a cylindrical form. Manufacturing the structure in  FIG. 3  may be accomplished by first mounting the flexible circuit  100  into or onto a carrier  200 , then inserting the carrier  200  into the open lumen  155  then mounting the flexible circuit  100  to the open lumen  155 . Carrier  200  and adhesive  210  are then removed, leaving lumen  155  open. The carrier  200  removal may be facilitate by heating the adhesive, by having a lubricious PTFE surface on the carrier, or pulling on the carrier such that it elongates in and reduces in diameter, for example. Irrigation ports  141  may be mechanically formed, or created by use of a laser, before or after the flexible circuit  100  is mounted. 
     The medical device of the present invention can be formed from multiple flexible circuits  100 . Each flexible circuit  100  can be substantially cylindrical in its own right. Alternatively, each flexible circuit  100  can comprise a portion of the cylinder, e.g., a first flexible circuit that comprises half of the circumference of the cylinder, while a second flexible circuit comprises the other half of the circumference. In this case there may be two or more flexible circuit edge joints  165  to join the flexible circuits together. Alternatively the flexible circuit  100  may contribute structural characteristics to the medical device for only part of its length.