Drop and slide engagement for implantable medical device

An implantable medical device having a case with therapeutic componentry contained with the case. A module has a rail around at least a portion of a perimeter of the module and is adapted to be mechanically secured to the case. The case has a rigid fastening channel adapted to receive the rail of the module. The rigid fastening channel has an opening allowing the rail of the module to drop into the rigid fastening channel through the opening and then slide along the rigid fastening channel to be mechanically secured to the case.

FIELD OF THE INVENTION

The present invention relates generally to implantable medical devices and, more particularly, to engagement apparatus and techniques for components of implantable medical devices.

BACKGROUND OF THE INVENTION

Implantable medical devices for producing a therapeutic result in a patient are well known. Examples of such implantable medical devices include implantable drug infusion pumps, implantable neurostimulators, implantable cardioverters, implantable cardiac pacemakers, implantable defibrillators and cochlear implants. Some of these devices, if not all, and other devices either provide an electrical output or otherwise contain electrical circuitry to perform their intended function.

Such implantable medical devices, when implanted, are subjected to a harsh environment in contact with bodily fluids. Such bodily fluids can be corrosive to the implantable medical device. Typically, implantable medical devices are hermetically sealed, often in a titanium case, in order to protect the implantable medical device from the harmful effects of the bodily fluids with which the implantable medical device comes into contact.

Implantable medical devices often have components that may be assembled in separate, or at least separable, housings. An example is an implantable medical device containing a rechargeable power source, such as a chemical battery, which needs to be inductively charged transcutaneously from an external charging device. The external charging device typically has a primary charging coil which inductively stimulates a secondary coil associated with an implantable medical device. It may be desirable to locate the secondary coil away from, typically outside of, the housing containing the remaining components of the implantable medical device primarily in order to segregate the heat generating component of the secondary coil from the remainder of the implantable medical device. Thus, the secondary coil is sometimes contained in a separate assembly than the rechargeable power source and/or therapeutic componentry of the implantable medical device. It is still necessary to electrically connect the secondary coil to at least some of the remaining components. Further, it may be desirable to physically secure the internal antenna housing the secondary coil with the housing of the remainder of the implantable medical device.

It is difficult, however, to achieve a secure and reliable mechanical and electrical connection which is secure from the deleterious effects of body fluids into which the implantable medical device will come into contact following implantation.

BRIEF SUMMARY OF THE INVENTION

Thus, it is extremely desirable to be able to secure the components of an implantable medical device together and reliably protect the implantable medical device from the ravages of the body.

In one embodiment, the present invention provides an implantable medical device having a case with therapeutic componentry contained with the case. A module has a rail around at least a portion of a perimeter of the module and is adapted to be mechanically secured to the case. The case has a rigid fastening channel adapted to receive the rail of the module. The rigid fastening channel has an opening allowing the rail of the module to drop into the rigid fastening channel through the opening and then slide along the rigid fastening channel to be mechanically secured to the case.

In another embodiment, the present invention provides an implantable medical device having a case with therapeutic componentry contained with the case. A module has a rail around at least a portion of a perimeter of the module, the module adapted to be mechanically secured to the case. The case has a rigid fastening channel adapted to receive the rail of the module. The rigid fastening channel allows the rail of the module to slide along the rigid fastening channel to be mechanically secured to the case.

In a preferred embodiment, at least one detent is provided on at least one of the rail and the rigid fastening channel, the detent providing tactile feedback when the module is mechanically secured to the case.

In a preferred embodiment, at least one locking tab is provided on at least one of the rail and the fastening channel, the locking tab preventing the module from disengaging from the case once the module is mechanically secured to the case.

In a preferred embodiment, a chamber is created around a perimeter of the module between the module and the case and further comprising a sealant substantially filling the chamber.

In a preferred embodiment, the module has an opening allowing the chamber to be substantially filled with the sealant.

In another embodiment, the present invention provides a method of assembling an implantable medical device having a case with a rigid fastening channel, therapeutic componentry contained within the case and a module having a rail around at least a portion of a perimeter of the module. The rail of the module is dropped into an opening in the rigid fastening channel of the case. The rail of the module is slid along the rigid fastening channel until the module is mechanically secured to the case.

In another embodiment, the present invention provides a method of assembling an implantable medical device having a case with a rigid fastening channel, therapeutic componentry contained within the case and a module having a rail around at least a portion of a perimeter of the module. The rail of the module is slid along the rigid fastening channel until the module is mechanically secured to the case forming a chamber around a perimeter of the module between the module and the case. The chamber is substantially filed with a sealant.

In a preferred embodiment, feedback is provided to mechanically secure the module to the case through complementary mechanical detents on the rigid fastening channel and the rail of the module.

In a preferred embodiment, the module is locked in mechanical engagement with the case through at least one locking tab preventing the module from disengaging from the case once the module is mechanically secured to the case.

In a preferred embodiment, a chamber is created around a perimeter of the module between the module and the case and substantially filling the chamber with a sealant.

In a preferred embodiment, the substantially filling step is accomplished through an opening in the module.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows implantable medical device10for example, a drug pump, implanted in patient12. The implantable medical device10is typically implanted by a surgeon in a sterile surgical procedure performed under local, regional, or general anesthesia. Before implanting the medical device10, a catheter14is typically implanted with the distal end position at a desired location, or therapeutic delivery site16, in the body of patient12and the proximal end tunneled under the skin to the location where the medical device10is to be implanted. Implantable medical device10is generally implanted subcutaneously at depths, depending upon application and device10, of from 1 centimeter (0.4 inches) to 2.5 centimeters (1 inch) where there is sufficient tissue to support the implanted system. Once medical device10is implanted into the patient12, the incision can be sutured closed and medical device10can begin operation.

Implantable medical device10operates to infuse a therapeutic substance into patient12. Implantable medical device10can be used for a wide variety of therapies such as pain, spasticity, cancer, and many other medical conditions.

The therapeutic substance contained in implantable medical device10is a substance intended to have a therapeutic effect such as pharmaceutical compositions, genetic materials, biologics, and other substances. Pharmaceutical compositions are chemical formulations intended to have a therapeutic effect such as intrathecal antispasmodics, pain medications, chemotherapeutic agents, and the like. Pharmaceutical compositions are often configured to function in an implanted environment with characteristics such as stability at body temperature to retain therapeutic qualities, concentration to reduce the frequency of replenishment, and the like. Genetic materials are substances intended to have a direct or indirect genetic therapeutic effect such as genetic vectors, genetic regulator elements, genetic structural elements, DNA, and the like. Biologics are substances that are living matter or derived from living matter intended to have a therapeutic effect such as stem cells, platelets, hormones, biologically produced chemicals, and the like. Other substances may or may not be intended to have a therapeutic effect and are not easily classified such as saline solution, fluoroscopy agents, disease diagnostic agents and the like. Unless otherwise noted in the following paragraphs, a drug is synonymous with any therapeutic, diagnostic, or other substance that is delivered by the implantable infusion device.

Implantable medical device10can be any of a number of medical devices such as an implantable pulse generator, implantable therapeutic substance delivery device, implantable drug pump, cardiac pacemaker, cardioverter or defibrillator, as examples.

Electrical power for implantable medical device10can be contained in implantable medical device itself. Power source for implantable medical device10can be any commonly known and readily available sources of power such as a chemical battery, electrical storage device, e.g., capacitor, a mechanical storage device, e.g., spring, or can be transcutaneously supplied in real time, or some combination.

In order to achieve a transcutaneous transfer of energy, either to charge or recharge an implanted battery or to supply real time power supply, or some combination, an inductive charging technique using an external primary coil and an internal secondary coil can be utilized.

FIG. 2illustrates an embodiment of implantable medical device10situated under cutaneous boundary18. Charging regulation module20controls the charging of rechargeable power source22. Power source22powers electronics module24which, in turn, controls therapy module26. Again, charging regulation and therapy control is conventional. Implantable medical device10also has internal telemetry coil28configured in conventional manner to communicate through external telemetry coil30to an external programming device (not shown), charging unit32or other device in a conventional manner in order to both program and control implantable medical device and to externally obtain information from implantable medical device10once implantable medical device has been implanted. Internal telemetry coil28, rectangular in shape with dimensions of 1.85 inches (4.7 centimeters) by 1.89 inches (4.8 centimeters) constructed from 150 turns of 43 AWG wire, is sized to be larger than the diameter of secondary charging coil34. Secondary coil34is constructed with 182 turns of 30 AWG wire with an inside diameter of 0.72 inches (1.83 centimeters) and an outside diameter of 1.43 inches (3.63 centimeters) with a height of 0.075 inches (0.19 centimeters). Magnetic shield56is positioned between secondary charging coil34and housing or case38and sized to cover the footprint of secondary charging coil34.

Internal telemetry coil28, having a larger diameter than secondary coil34, is not completely covered by magnetic shield56allowing implantable medical device10to communicate with the external programming device with internal telemetty coil28in spite of the presence of magnetic shield56.

Rechargeable power source24can be charged while implantable medical device10is in place in a patient through the use of external charging device40. In a preferred embodiment, external charging device40consists of charging unit32and external antenna42. Charging unit32contains the electronics necessary to drive primary coil44with an oscillating current in order to induce current in secondary coil34when primary coil44is placed in the proximity of secondary coil34. Charging unit32is operatively coupled to primary coil by cable46. In an alternative embodiment, charging unit32and external antenna42may be combined into a single unit. Antenna42may also optionally contain external telemetry coil30which may be operatively coupled to charging unit32if it is desired to communicate to or from implantable medical device10with external charging device40. Alternatively, external antenna42may optionally contain external telemetry coil30which can be operatively coupled to an external programming device, either individually or together with external charging unit32.

Repositionable magnetic core48can help to focus electromagnetic energy from primary coil30to more closely be aligned with secondary coil34. Energy absorptive material50can help to absorb heat build-up in external antenna42which will also help allow for a lower temperature in implantable medical device10and/or help lower recharge times. Thermally conductive material52is positioned covering at least a portion of the surface of external antenna42which contacts cutaneous boundary18of patient12. Thermally conductive material52positioned on the surface of external charging device40in order to distribute any heat which may be generated by external charging device40.

Secondary coil34is located in internal antenna or module54that is separable from housing or case38. Magnetic shield56is positioned between secondary coil34and housing or case38and inside the diameter of internal telemetry coil28to help isolate the remainder of implantable medical device10from electromagnetic energy from external charging device40.

InFIG. 3andFIG. 4, construction of internal antenna or module54begins with base laminate58. Base laminate58is constructed of a plurality of layers, preferably three layers, of Metglas™ material59secured together by a suitable adhesive such as Pyralux® acrylic adhesive. Each layer of Metglas™ material59is approximately 0.001 inch (0.0254 millimeters) thick. Eight eddy current grooves60are radially etched by laser into one side of the layers of Metglas™ material59at approximately equal radial spacings. An insulative layer61of polyimide is adhesively secured to each side of Metglas™ laminate resulting in a base laminate58approximately 0.15 inches (3.8 millimeters) thick. Base laminate58is approximately 1.54 inches (39 millimeters) square with two rounded corners to facilitate subsequent assembly.

Lead wires62are placed (FIG. 5) onto base laminate58with ends positioned at locations adapted to connect with wires from a coil to added to base laminate58. Lead wires62are placed inboard and, generally, away from cutouts for hub64and feet66. Preferably, lead wires62are flat 0.004 inch (0.10 millimeters) and round 0.015 inch (0.38 millimeters) in locations70and72exiting base laminate58. Preferably, lead wires62are made from niobium ribbon wire. Once positioned, lead wires62are secured in place by adhesively securing another layer63of polyimide to the side of base laminate58onto which lead wires62have been positioned. The resulting structure forms a coil ready coreless laminate68ready to receive a coil of wire that forms secondary coil34. Pre-placing lead wires62onto base laminate58reduces stress from normal movement of lead wires62and aids in further assembly.

Prior to being placed onto the surface of coil ready coreless laminate68, secondary coil34is preferably coated in a siloxane coating process. Secondary coil34is placed in a vacuum chamber that is then evacuated to 0.10 torr vacuum and held for ten (10) minutes. 10 sccm of Hexamethyldisiloxane, 30 sccm of Nitrous oxide and 1 sccm of Argon are pumped into the chamber. Approximately 150 watts of power to ignite the plasma for thirty (30) seconds.

InFIG. 6, secondary coil34is then placed onto the surface of coil ready coreless laminate68and electrically connected to lead wires62at locations70and72by welding or, preferably, opposed welding. Cross-over copper wire74from secondary coil34makes electrical connection at location72. The resulting substrate80is then sandwiched between a cover sheet76of polyimide secured with a thermoset adhesive as illustrated inFIG. 7. Substrate80is placed into a press between polyimide cover sheets76which, of course, can be added either before or after substrate80is placed into the press. A thermoset adhesive, preferably Pyralux® acrylic adhesive, is located between substrate80and cover sheets76. A liquid thermoset polymer, such as liquid silicone rubber, is added to the press outside of cover sheets76. Heat, preferably approximately 340 degrees Fahrenheit, and pressure, preferably approximately 1,200 pounds per square inch (8,274 pascals), are applied in the press forcing liquid thermoset polymer again cover sheets76which are, in turn, pressed against substrate80. The use of a liquid material in the press allows the press to apply force evenly against the irregular upper surface of substrate80. The thermoset polymer is allowed to cure under heat and pressure for approximately five (5) minutes forming an at least partially cured silicone rubber sheet on either side of substrate80and allowed to cool for approximately twenty (20) minutes. The assembly can then be removed from the mold and the silicone rubber sheets removed (peeled) away and discarded leaving the laminated substrate80.

This process can increase the efficiency of laminating a plurality of articles. The press is only used during while the liquid thermoset polymer is being pressed to substrate80. Once the liquid thermoset polymer has cured, e.g., approximately five (5) minutes, the laminated substrate80may be removed from the press. The laminated substrate80can continue to be allowed to cool outside of the press, e.g., for approximately twenty (20) minutes. As soon as the first laminated substrate80is removed from the press, the press may be used again to produce a second laminated substrate80. Since the laminated substrate80need only remain in the press during the initial stages (first five (5) minutes) for curing, the press may be used to produce a second laminated substrate80while the first laminated substrate80continues to cool. The early re-use of the press, as compared with having to along laminated substrate to remain in the press for the entire cooling time, is a consider savings in equipment time and allows a greatly increased efficiency of operation.

Laminated substrate80is then overmolded to seal laminated substrate in an environment better able to withstand the harmful effects of bodily fluids after implantation. The overmolding takes place in two steps. In the first step shown inFIG. 8, a plurality of support feet82are placed on one side, preferably the underside, of laminated substrate80. Support feet82may be molded onto the underside of laminated substrate80using conventional molding techniques. Alternatively, support feet82may be adhesively attached, e.g., with glue, may be ultrasonically staked or may be otherwise mechanically attached, e.g., by threaded fastener. Support feet82may be equally spaced somewhat near each of the four corners of laminated substrate80. In a preferred embodiment, support feet have a circular cross-section. Preferably hub84is also molded, or otherwise mechanically attached, to laminated substrate surrounding a central hole in laminated substrate.

The second part of the overmolding process is illustrated inFIGS. 9A,9B,9C and9D. InFIG. 9A, laminated substrate90with support feet82and hub84is placed into an injection mold. Injection material85, preferably polysulfone, is introduced into the mold through five (5) injection holes (86A,86B,86C,86D and86E) from one side of the injection mold. Please note that theFIGS. 9A,9B,9C and9D represent a cross-sectional view of the injection mold. Although a total of five (5) injection holes are utilized, only three (3) are visible in the cross-sectional view. One (1) injection hole is used for the hub (injection hole86B). Four (4) injection holes are equally spaced as illustrated inFIG. 9E. Note that injection holes86D and86E are not visible in the cross-sectional view inFIG. 9A. Injection material85begins to flow into the underside of laminated substrate80through injection holes86A and86C. Injection material85also begins to flow through hub84and spreads out over the topside of laminated substrate80through injection hole86B. InFIG. 9B, injection material85continues to flow into the injection mold through the five (5) injection holes (86A,86B,86C,86D and86E) in a manner such that the amount of injection material85flowing over the topside of laminated substrate80and the amount of injection material85flowing over the underside of laminated substrate80is such that mechanical forces against laminated substrate80are evened out from topside and underside. Generally, this is expected to occur when injection material85flows at approximately the same rate over the topside of laminated substrate80as over the underside of laminated substrate90. That is, injection material85on the topside of laminated substrate80is forcing against the topside of laminated substrate80with about the same amount of force that injection material85is forcing against the underside of laminated substrate80. The general evening of molding forces for topside to underside helps stabilize laminated substrate80during the molding process and helps to eliminate warping of laminated substrate80. InFIG. 9C, injection material85continues to flow evenly over the topside and the underside of laminated substrate80. InFIG. 9D, injection material85has filled the injection mold essentially filling all of the cavity of the injection mold resulting in an overmolded laminated substrate80. Injection holes86A,86B,86C,86D and86E are chosen in size such to facilitate the even flow of injection material85. If injection material85does not flow evenly over both the topside and the underside of laminated substrate80, the resultant overmolded part can warp following cooling.

As shown inFIGS. 9A,9B,9C and9D, injection material85flows around support feet82and encircles each of circular support feet82. As injection material85cools following the injection molding process, injection material85has a tendency to shrink. Typically, shrinkage of injection material may create a crack or a gap which may create an area into which bodily fluids could subsequently gain entry following implantation. However, by encircling each of support feet82, such shrinkage of injection material85will actually cause injection material to form more tightly around support feet82creating an even stronger bond and helping to ensure that bodily fluids can not gain entry following implantation. This same technique holds true for hub84. Hub84has a circular cross-section and has surrounding a indentation which allow injection material85to surround hub84and shrink more tightly to hub84as injection material85cools creating a stronger bond and less likelihood of leaks.

FIG. 12shows housing or case38of portion of implantable medical device10holding power source22, electronics module24and other components. Power source (preferably a battery)22is located in area92in housing or case38. It is desirable that battery22be reasonably secured within housing or case38but at the same be allowed to expand and contract with use. Chemical batteries, such as battery22, may have a tendency to expand as the battery22is charged and subsequently contract as the battery22ceases to be charged. Such expansion and contraction in a battery22which is very tightly secured in housing or case38might cause battery22to either come loose from its attachments and/or compromise its electrical connections. Therefore, in a preferred embodiment battery22is held in a manner which allows battery22to expand, e.g., during charging, and subsequently contract, e.g., following charging, without compromising mechanical and/or electrical connections. Spacer94, seen more clearly inFIG. 13, supports battery22around the periphery of battery22while cutout96in the central portion of spacer94allows battery22to expand without compromise. In a preferred embodiment, battery22has a rectangular shape with major and minor sides. Preferably, spacer94supports aniajor side of battery22while allowing cutout96to allow expansion of the major side of battery22. In a preferred embodiment, spacer94is constructed with a layer of polyimide approximately 0.001 inch (0.0254 millimeters) thick. Preferably, spacer94is secured in an inside surface of housing or case38with a suitable adhesive (seeFIG. 14). As can be seen inFIG. 14, battery22, fits inside battery cup97supported by spacer94, is allowed to expand, e.g., during charge, as illustrated by expansion doted lines98. During a subsequent operation of assembly of implantable medical device10, epoxy100is introduced into housing or case38to help secure battery22. Battery cup97and spacer94will help to ensure that epoxy100does not fill the space created by spacer94.

FIG. 15 through 20illUstrate the mechanical connection of internal antenna or module54to housing or case38to achieve an integrated implantable medical device10that will be able to withstand the ravages of bodily fluids once implanted. Housing or case38has a recharge rail102extending around three sides that is adapted to slideably mate with a complementary rail104on internal antenna or module54. However, electrical connector wires106inhibit rail104of internal antenna or module54from engaging recharge rail102from the open end. While electrical connector wires could be bent and then reformed to the illustrated position following installation of internal antenna or module54onto housing or case38, this is not desirable from a reliability standpoint, due to the bending and straightening of wires106, it is also inefficient. Recharge rail102has a drop opening108allowing tab110of internal antenna or module54to drop into opening108and then allow rail104to slidably engage recharge rail102which are configured to slidably engage over a portion of the sliding distance. This “drop and slide” engagement allows internal antenna or module54to drop avoiding interference with electrical connection wires106and still slidably securely engage to housing or case38. Detent112provides tactile feedback to the installer to know when proper sliding engagement is achieved. Following engagement locking tab114may be purposely bent up to engage the rear of rail104preventing internal antenna or module54from disengaging with housing or case38. It is to be recognized and understood that all of these engaging and locking mechanisms preferably exist on both sides of implantable medical device10in complementary fashion even though the drawings illustrate only one side.

An adhesive channel116is formed around the perimeter of housing or case38. Fill hole118communicates through both internal antenna or module54and housing or case38to allow an adhesive needle120to be inserted. Adhesive needle120may then be used to fill adhesive channel116, through fill hole118, with adhesive providing another layer of sealing for implantable medical device10.

Once internal antenna or module54is secured to housing54, electrical connector wires106may be connected using connector block122as shown inFIGS. 21,22,23and24. Rigid polysulfone frame124provides structural rigidity to connector block122. Frame124is laid out in linear fashion so that all electrical connections are in a linear row. Wire frame126is stamped out of a conductive material, preferably a metal. Since rigid frame124is laid out linearly, wire frame126can be stamped with a plurality of linear connector areas. Wire frame126is joined with rigid flame124and mated with electrical connector wires106. Frame cover128fits over rigid frame124. Once assembled, a biocompatible thermoset polymer, such as silicone rubber, can be injected into connector block122substantially filling any voids in connector block122forming a thermoset polymer gasket helping to prevent infiltration of body fluids into implantable medical device10. The thermoset polymer (not shown) also provides electrical isolation between the electrical contacts of wire frame126.

Connector block122has a plurality of openings130allowing an external electrical connection with implantable medical device10. Chimneys132form a void near the external electrical contact openings allowing the thermoset polymer to at least partially fill chimney132to further seal and secure an electrical connection opening into implantable medical device10. Such thermoset polymer also provides a strain relief for the lead used for the external electrical connection. Grommets134, which are compatible with thermoset polymer, additionally secure and electrically isolate the external electrical connection. A set screw136may be used to mechanically secure the external wire to connector block122. As thermoset polymer substantially fills voids within connector block122, thermoset polymer forms a skirt, when cured, that is usually thinner than is reasonably possible to be created with rigid frame124or thermoplastic cover128. The thinner skirt achieved with the thermoset polymer allows an even stronger and more secure seal against the intrusion of body fluids.

In a preferred embodiment, rigid frame is treated before assembly with an adhesion promoter to create a stronger bond between rigid frame124and thermoset polymer. The surface of polysulfone rigid frame124is cleaned with a detergent, preferably Micro 90™ detergent, rinsed first in D.I. water and then rinsed in IPA. Polysulfone rigid frame124is plasma treated by first being placed in a vacuum chamber that is then evacuated to 0.10 torr vacuum and held for ten (10) minutes. 10 sccm of Hexamethyldisiloxane, 30 sccm of Nitrous oxide and 1 sccm of Argon are pumped into the chamber. Approximately 150 watts of power to ignite the plasma for thirty (30) seconds. Rigid frame124is then coated by being dipped into a twenty percent (20%) solution of RTV medical silicone adhesive and heptane by weight for approximately two (2) seconds. Rigid frame124is then removed from the dip and cured in an oven at 150 degrees Centigrade for eight (8) hours.

Thus, embodiments of the connector block for an implantable medical device are disclosed. One skilled in the art will appreciate that the present invention can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the present invention is limited only by the claims that follow.