Abstract:
A method of forming an implantable medical device includes providing an implantable microstimulator. The microstimulator includes a body with a first end and an opposing second end. The microstimulator further includes internal circuitry that is disposed in the body and that provides stimulation energy. The microstimulator additionally includes a first microstimulator electrode that is electrically coupled to the internal circuitry and that is disposed along the first end portion of the body. The method further includes providing a first lead assembly that includes an insulated conductor with at least one first remote electrode disposed at a distal end of the insulated conductor, and a first connector disposed at a proximal end of the insulated conductor. The first connector is disposed over the first microstimulator electrode to completely cover the first microstimulator electrode. The first connector also electrically couples the insulated conductor to the first microstimulator electrode.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is a continuation of U.S. patent application Ser. No. 10/503,281 filed on Mar. 11, 2005, which is a National Stage Entry of PCT/US03/02784 filed Jan. 29, 2003, all of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to small implantable medical devices, and in particular to lead assemblies for such devices. Such small devices are easily implantable, and provide stimulation and/or sensing functions. The lead assembly is removably electrically connectable to an existing electrode of the device, thereby providing means to stimulate tissue, or sense physiological parameters, at some distance from the device. 
     Implantable electrical stimulation devices have proven therapeutic in a wide variety of diseases and disorders. Pacemakers and Implantable Cardiac Defibrillators (ICDs) have proven highly effective in the treatment of a number of cardiac conditions arrhythmias). Spinal Cord Stimulation (SCS) systems have long been accepted as a therapeutic modality for the treatment of chronic pain syndromes. Deep Brain Stimulation (DBS) has been applied in areas such as movement disorders. Functional Electrical Stimulation (FES) systems, such as the Freehand system by NeuroControl Corporation (Cleveland, Ohio), have been applied to restore some functionality to paralyzed extremities in spinal cord injury patients. 
     Current implantable electrical stimulation systems typically consist of a leaded system wherein the electrodes are on a lead and are separate from but connected to a System Control Unit (SCU) that contains the power source and the stimulation electronics. A number of these systems have the advantage of having fixation devices for the electrodes, so that the electrodes remain proximal to or even attached to their target sites of stimulation. For example, some pacemaker electrode leads have tines that act as barbs to hook Into the tissue, thereby anchoring the electrodes in place. As another example, the electrode used in the Neuro Cybernetic Prosthesis (NCP®) manufactured by Cyberonics (Houston, Tex.) is a helical electrode that is wound around the vagus nerve in order to remain attached to its stimulation target. In addition, several companies and research institutions, such as Neuro Stream Technologies, Inc. (Anmore, British Columbia, Canada) are investigating cuff electrodes, which wrap around the nerve like a cuff, thereby fixing an electrode(s) in close approximation to a nerve. 
     A microminiature electrical stimulator known as the BION® microstimulator has been developed to overcome some of the disadvantages of a large SCU-based (a.k.a. IPG-based) system. The BION® microstimulator is a leadless device, wherein the SCU and the electrodes have been combined into a single microminiature package. The current embodiment of the BION® microstimulator is a cylinder that is approximately 3 mm in diameter and between about 2 and 3 cm in length. This form factor allows the BION® microstimulator to be implanted with relative ease and rapidity, e.g., via endoscopic or laparoscopic techniques. Thus, the BION® microstimulator may easily be implanted subcutaneously, and in such a configuration, it is unlikely to demonstrate problems with cosmesis or erosion. 
     A known microminiature electrical stimulator, a microstimulator, is described in U.S. Pat. No. 5,193,539 issued May 16, 1993 for “Implantable Microstimulator.” A method for manufacturing the microstimulator is described in U.S. Pat. No. 5,193,540 issued May 16, 1993 for “Structure and Method of Manufacturing of an Implantable Microstimulator.” Further teaching is included in U.S. Pat. No. 5,324,316 issued Jun. 28, 1994 for “Implantable Microstimulator.” The &#39;539, &#39;540, and &#39;316 patents are incorporated herein by reference. 
     In some applications, e.g., pudendal nerve stimulation for the treatment of incontinence, the leadless BION® microstimulator system has proven sufficient. In such applications, the BION® microstimulator is surgically placed near an easily identifiable landmark(s), e.g., the pudendal canal. Additionally, in such applications the stimulator is surrounded by soft tissue and is not embedded in or located very close to large muscles or other structures that may demonstrate significant motion or varying pressure. 
     However, for other applications, a leadless BION® microstimulator may prove insufficient or inappropriate. For example, it may be desirable to implant a BION® microstimulator close to the skin, to facilitate power and/or data transfer, and/or to facilitate removal and/or replacement, while a lead assembly removably attached to the BION® microstimulator may stay in place, with the electrode(s) positioned for appropriate tissue stimulation, possibly deep within the body. 
     What is needed are lead assemblies for microdevices which facilitate removal and/or replacement of the microdevice by reducing or eliminating the ingress of fluids into the assemblies. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the above and other needs by providing a lead assembly for small implantable medical devices (e.g., microdevices). Such microdevices may provide either or both tissue stimulation and sensing functions. Known microdevices include spaced apart electrodes on the outer surface of the microdevice. In some cases, the microdevice may not be locatable in contact with tissue targeted for stimulation or sensing, and the electrodes on the outer surface of the microdevice are not able to provide the intended stimulation or sensing. A connector of the lead assembly is over an electrode on the microdevice case, and electrically connects to an electrode(s) on a lead, thus providing a capability to stimulate or sense tissue not in contact with the microdevice. The lead assembly connector may partially or completely cover the electrode, wherein by completely covering the electrode, the electrode is Insulated from adjacent tissue. 
     The lead assembly includes an electrode(s), an insulated lead, and connector, The electrode is constructed from a biocompatible material, and may be in a variety of shapes. The electrode lead includes one or more wires to carry signals between the electrode(s) and the microdevice. The connector is removably connectable to the microdevice, and preferably provides a low resistance electrical connection between the wires and an electrode on the microdevice case. 
     In accordance with the invention, there is provided an electrode lead assembly that may be removably attached to a microstimulator or microsensor, for purposes of allowing stimulation or sensing at sites distal from the microdevice, in applications where the microdevice may not reside proximal to such sites. It is an object of the present invention to provide an assembly that inhibits fluid ingress white the assembly is not attached to a microstimulator or microsensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
         FIG. 1  shows a side view of a typical microdevice (a microstimulator of a microsensor), including electrodes at each end of the device; 
         FIG. 2  depicts a microdevice and a lead assembly according to the present invention; 
         FIG. 3  shows the lead assembly connected to the microdevice; 
         FIG. 4   a  illustrates a cross sectional view of an embodiment of a lead assembly of the invention; 
         FIG. 4   b  shows the lead assembly of  FIG. 4   a  with a microdevice inserted into the lead assembly; 
         FIG. 5   a  illustrates a cress sectional view of an embodiment of a lead assembly of the invention which assembly includes a circumferential spring; 
         FIG. 5   b  shows the lead assembly of  FIG. 4   a  with a microdevice inserted into the lead assembly; 
         FIG. 6   a  illustrates a cross sectional view of an embodiment of a lead assembly of the invention which assembly Includes a seal; 
         FIG. 6   b  shows an and view of the lead assembly of  FIG. 6   a;    
         FIG. 6   c  shows the lead assembly of  FIG. 4   a  with a microdevice inserted Into the lead assembly; 
         FIG. 7   a  illustrates a cross sectional view of an embodiment of a lead assembly of the invention which assembly Includes leaf springs; 
         FIG. 7   b  shows the lead assembly of  FIG. 4   a  with a microdevice inserted into the lead assembly; and 
         FIG. 8  illustrates a cross sectional view of an embodiment of a lead assembly of the invention which assembly includes a plug. 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims. 
     Implantable microdevices may serve many useful purposes through stimulating nerves, muscles, or other tissue (a microstimulator), or through sensing various physiological conditions (a microsensor) within a patient. Such a microdevice  10  is shown in  FIG. 1 . The microdevice  10  includes Internal circuitry to receive and process signals, and to provide either sensing or stimulation through a first microdevice electrode  120  at one end, and a second microdevice electrode  12   b  at an opposite end. The microdevice  10  is very small to allow minimally invasive implantation. A representative microdevice  10  is about 2 to 3 cm in length, and about 3 mm in diameter. The characteristics, employment, and manufacturing of one example of a microdevice  10  are described in U.S. Pat. No. 6,193,539 issued May 16, 1993 for “Implantable Microstimulator,” U.S. Pat. No. 5,193,540 issued May 16, 1993 for “Structure and Method of Manufacturing of an Implantable Microstimulator,” and U.S. Pat. No. 5,324,316 issued Jun. 26, 1994 for “Implantable Microstimulator.” 
     A lead assembly  20  according to the present invention is shown in  FIG. 2  detached from the microdevice  10 . The lead assembly comprises at least one remote electrode  14 , a lead  16  including at least one wire (or conductor), and a connector  18 . The remote electrode  14  provides stimulation or sensing at sites where the microdevice  10  would not normally reside due to a variety of reasons. The remote electrode  14  is fabricated from a biocompatible material(s) with a relatively low impedance, e.g., platinum, iridium, titanium, and alloys and preparations thereof. The remote electrode  14  may be fabricated to have a number of different shapes, e.g., a ball electrode, a cylindrical electrode, a disc electrode, a flat rectangular electrode, or an electrode curved around a surface of a nerve cuff. The remote electrode  14  preferably has sufficient surface area so as to ensure that safe level electric current density and electric charge density are maintained during chronic stimulation. 
     The remote electrode  14  may additionally or alternatively provide a means for sensing nerve signals (e.g., EEG, ENG), muscle signals (e.g., EMG), cardiac signals (e.g., ECG), or other state of the patient. In such embodiment, at least one electrode may be dedicated for recording and may have a surface area that is smaller than that used for stimulation, in order to provide a higher degree of spatial localization for recording. Additionally, the remote electrode  14  may be coated with materials such as platinum black, titanium nitride, carbon, or iridium oxide to increase the effective sensing area of the remote electrode  14  without increasing the geometric surface area. 
     The lead  16  connecting the remote electrode  14  to the connector  18  is fabricated from a biocompatible material(s), and the lead  14  insulates at least one wire that runs from the connector  18  to the remote electrode  14 . Preferable materials include polymers such as silicone, and polyurethane, or preparations thereof. In the case where there is more than one remote electrode  14 , the wires electrically connected to each electrode must be insulated from each other. The individual wires may be insulated from each other using a coating such as TEFZEL® (ethylene tetrafluoroethylene), TEFLON® (polytetrafluoroethylene), KYNAR® (polyvinylidene fluoride), PFA (perfluoralkoxy), FEP (fluorinated ethylene propylene), or HYTREL® (thermoplastic elastomer). Coating the outer surface of the lead and/or the outer surface of a guidewire during implantation may facilitate placement of the lead. For example, the outer insulation of the lead may be coated with a hydrophilic agent such as polyvinylperolydone (PVP). 
     Connector  18  is located at the proximal end of electrode lead  16  and electrically connects the wire(s) in the electrode lead  16  to at least one of the electrodes  12   a ,  12   b  of the microdevice  10 , while mechanically attaching to the microdevice  10 . In a preferred embodiment, connector  18  attaches a single stimulating remote electrode  14  at the distal end of the lead  16  to a single microdevice electrode  12   a  or  12   b  located on the microdevice  10 . Preferably, the connector  18  completely covers the electrode  12   a  or  12   b  and ideally provides a watertight seal, thereby ensuring that most or all stimulation current is directed to the remote electrode  14 . Connector  18  preferably provides good contact between the electrode  12   a  or  12   b  and the wire in the lead  18 , ensuring a low electrical resistance connection between the electrode  12   a  or  12   b  and the wire. 
     Lead assembly  20  is shown connected to microdevice  10  in  FIG. 3 . As shown, the end of microdevice  10  is inserted into connector  18 , which connector entirely covers and provides a seal around electrode  12   a  in order to prevent current from leaking from electrode  12   a  into nearby tissue. Lead assembly  20  may alternatively be connected to the second electrode  12   b . Further, two lead assemblies  20  may be attached to a single microdevice  10  to provide two remote electrodes. The lead and/or remote electrode  14  may further Include a means of fixation to anchor the lead and/or electrode adjacent to a target site. 
     The lead assembly electrical/mechanical connection method allows for relatively easy attachment of lead assembly  20  to microdevice  10 . The electrical/mechanical connection method may comprise one or more of a multiplicity of connecting methods including: a threaded connection, such as a set-screw mechanism; a clip connection; a ball bearing connection; a spring loaded connection; a conductive adhesive connection; a collet connection; a ball seal connection; and an interference fit connection. 
     In accordance with the invention, connector  18  preferably collapses or closes when a microdevice  10  is not inserted into connector  18 , ensuring minimal fluid ingress into the portion of the connector  18  that makes electrical contact with the electrode  12   a  or  12   b , i.e., electrical contact  22 . In an alternative embodiment, a plug may be Inserted into the connector  18  when a microdevice  10  is not attached. 
       FIGS. 4   a  and  4   b  show one embodiment of the invention. Connector  18  comprises an elastic pouch  24  that expands from a collapsed position, shown in  FIG. 4   a , as microdevice  10  is inserted at opening  26 .  FIG. 4   b  shows connector  18  with microdevice  10  inserted, so that electrode  12   a  makes electrical contact with contact  22 . In this embodiment, connector  18  inhibits fluid ingress while in a collapsed state due to the properties of the material of pouch  24 . For instance, pouch  24  may be made of a biocompatible elastic material(s) such as silicone or polyurethane which collapses when not expanded by microdevice  10 , and seals as a result of the high coefficient of friction of the material, which causes the material to adhere to itself to form closure  30 . 
     Additionally or alternatively, suture material or the like (not shown) may be provided at closure  30 . For instance, sutures built into pouch  24  may encircle closure  30  so the ends of the sutures may be pulled and secured, in a draw-string manner. Thus, a surgeon may further tighten the seal at closure  30 , when collapsed or when a microdevice  10  is inserted into connector  18 . Suture material may additionally or alternatively be applied around pouch  24  at closure  30 , rather than being provided therein. 
     As depicted in  FIGS. 4   a  and  4   b , the material of pouch  24  may extend around contact  22  and over a portion of lead  16 . This portion  32  insulates surrounding tissue from contact  22  and provides stress relief and strength to the connection made between lead  16  (i.e., the wire in lead  18 ) and contact  22 . This connection may be made via laser welding or other methods known to those of skill in the art. Insulation portion  32  may alternatively conform to the shape of contact  22 , or may be otherwise configured to insulate surrounding tissue from contact  22 . 
     As is also shown in  FIGS. 4   a  and  4   b , contact  22  may be configured with edges  23  that extend at least partly around electrode  12   a  when microdevice  10  is inserted, and which may also aid in sealing pouch  24  when collapsed. For instance, contact  22  and/or edges  23  may be made, at least in part, of a conductive material with resilient properties, such as 316 SS, 304 SS, or inconel. Edges  23  may, in a relaxed state, bend inward, aiding pouch  24  to seal at closure  30 . Upon insertion of microdevice  10 , edges  23  bend outward with pouch  24 , allowing microdevice  10  to make electrical contact with contact  22 . 
     In the embodiment illustrated in  FIGS. 5   a  and  5   b , closure  30  may include a circumferential spring  36  (such as manufactured be Bal Seal Engineering Company of Santa Ana, Calif.). To aid in sealing connector  18  when collapsed, spring  36  ray be coated with, for instance, silicone. In  FIG. 5   a , closure  30  is partially closed, and spring  36  is partially sealed. When connector  18  is collapsed and fully closed, the coils of spring  36  compress against each other to form a seal. Spring  36  may be positioned via attachment to pouch  24  via a medical adhesive or the like at one or more attachment points  37 , and preferably three or more points  37 . 
     As with the other closure embodiments herein, the closure, in this case spring  36 , aids in capturing and retaining microdevice  10  in place when inserted in connector  18 . Furthermore, closure  30  may aid in sealing connector  18  around electrode  12   a  in order to prevent current from leaking from electrode  12   a  into nearby tissue. 
     In this or other embodiments of the invention, contact  22  may be made of a spring, such as a circumferential spring, or other useful configuration. In addition or alternatively to contact  22 , electrical contact with electrode  12   a  (or other electrode) may include a portion or portions of connector  18 , such as a portion or portions of pouch  24  that make electrical contact with the electrode and are electrically connected to the wire(s) in lead  16 . Any such electrical connection may further aid in retaining microdevice  10  and/or in sealing connector  18  around electrode  12   a.    
     In the embodiment shown in  FIGS. 6   a ,  6   b , and  6   c , closure  30  may include a seal  38 , which seal may be positioned at opening  26  or other position on connector  18 . As can be seen in  FIG. 8   b , seal  38  may preferably include three or more flaps  39 , which allow insertion and removal of microdevice  10 , and which, when microdevice  10  is not present, fit closely together to inhibit ingress of fluids into connector  18 . Any suitable seal design made of biocompatible materials, such as silicone or polyurethane, as known to those of skill In the art, may be used. As with other embodiments herein, seal  38  may be provided in addition or as an alternative to the pouch  24  being made of a biocompatible elastic material(s) such as silicone or polyurethane, which collapses when microdevice  10  is not present, and seals as a result of the inherent adhesive properties of the high coefficient of friction material, which adheres to itself to form closure  30 . 
     As shown in the embodiment of  FIGS. 7   a  and  7   b , closure  30  may include leaf spring(s)  42 , preferably Incorporated longitudinally in the walls of pouch  24 . As with other embodiments herein, leaf springs  42  aid in sealing closure  30  and inhibiting ingress of fluids when connector  18  is collapsed and may also aid in retaining microdevice  10  when inserted and/or in sealing connector  18  around electrode  12   a.    
     Connector  18  may be made by conventional methods known in the art. For instance, connector  18  of  FIGS. 7   a  and  7   b  may be made by placing contact  22 , springs  42 , and possibly also the proximal end of lead  16  in a mold and injection molding (i.e., insert molding) the pouch  24  material (and/or portion  32 ), such as silicone, polyurethane, TEFLON® (polytetrafluoroethylene), or the like, around the inserts, thus forming the connector  18  with leaf springs  42  and contact  22  integral thereto. Other methods known in the art may be used for this or other embodiments herein, such as blow molding and/or securing closure devices, such as leaf springs  42  or circumferential spring  36 , to connector  18  with a medical adhesive or the like, as described and shown earlier. 
     In an alternative embodiment, as shown in  FIG. 8 , a plug  44  may be used to protect contact  22  from fluids when microdevice  10  is not present in connector  18 . Such plug  44  configuration and size may be similar to microdevice  10 , or may include features to aid in insertion, removal, and/or sealing of connector  18 . For instance, plug  44  may be slightly larger than microdevice  10 , which may improve the seal created when plug  44  is inserted into connector  18 . As another example, plug  44  may include features such as surface texturing to aid in sealing and/or handling of plug  44 . Plug  44  may be made of any suitable biocompatible material(s), such as silicone, polyurethane, or TEFLON® (polytetrafluoroethylene). 
     Those skilled in the art will recognize variations of the embodiments described herein. For instance, various closure embodiments may be combined to further inhibit ingress of fluids into connector  18 . The heart of the present invention is a lead assembly that may be removably attached to a microdevice, which lead assembly inhibits fluid ingress when the microdevice is removed from the connector of the lead assembly. Any lead assembly which provides this capability to a small implantable microdevice is intended to come within the scope of the present invention. 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.