Patent Application
20090270795
The invention relates to implantable drug delivery devices, and more specifically implantable drug delivery devices including a solenoid driven piston pump.
An implantable drug delivery device can be implanted by a clinician into a patient at a location appropriate for the therapy that interferes as little as practicable with patient activity, such as subcutaneously in the lower abdomen. Typically, a drug delivery catheter is connected to a drug pump outlet and implanted to infuse the drug, infusate or other therapeutic substance at a programmed infusion rate and predetermined location to treat a medical condition. Reliable and accurate operation of the drug pump is important because both inadequate and unintended therapeutic substance delivery can create patient complications. Many drug pumps are configured so the pump can be replenished with drug through a refill port or septum while the pump is implanted, so the period of time in which the pump is implanted is not limited by drug capacity. In electrically powered implantable drug pumps, the period the pump can be implanted can be limited by factors such as battery consumption, corrosive damage, and mechanical wear. The relatively large size of some implantable drug pumps can limit locations where the device can be implanted in a patient.
In general, the disclosure is directed to a method for welding a barrier to a housing as a part of a solenoid-driven piston pump and an implantable drug delivery device including features that facilitate the welding of the barrier. In some embodiments, the barrier may include a titanium foil of a thickness of less than about 0.004 inches, about 0.002 inches, or less than about 0.002 inches.
In one aspect, the disclosure is directed to a method including providing an implantable drug delivery device including a housing defining a depression. The housing comprises a first surface. The method further includes inserting a bore housing including a coil cup and a sleeve in the depression. The coil cup includes a coil cup base plate having a first major surface and a second major surface opposite the first major surface. The coil cup base plate defines a coil cup perimeter and a coil cup orifice located substantially centered in the coil cup base plate. The coil cup also includes a coil cup perimeter wall including a perimeter wall top surface, attached to the first major surface of the coil cup base plate along the coil cup perimeter, and projecting substantially perpendicular to the first major surface of the coil cup base plate. The coil cup further includes a coil cup inner wall attached to the first major surface of the coil cup base plate along a perimeter of the coil cup orifice and projecting substantially perpendicular to the first major surface of the coil cup base plate. The coil cup inner wall further defines the coil cup orifice, and an outer surface of the coil cup inner wall, an inner surface of the coil cup perimeter wall and the first major surface of the coil cup base plate define a bore housing cavity. The sleeve includes a sleeve top surface and a sleeve inner surface. The sleeve is press fit into the coil cup orifice and defines a bore housing orifice. When the bore housing is inserted in the depression, the first surface of the housing, the perimeter wall top surface and the sleeve top surface are substantially co-planar. The method also includes placing a solenoid in the bore housing cavity, placing a pin in the bore housing orifice, and placing a barrier over the bore housing. The barrier defines a barrier perimeter and a barrier orifice substantially centered in the barrier. The pin substantially centers the barrier orifice over the bore housing orifice and the barrier substantially covers the bore housing cavity. The method further includes clamping the barrier against the bore housing with a clamping structure and spot welding the barrier perimeter to at least one of the first surface of the housing and the perimeter wall top surface at a plurality of spot weld locations with a laser. The method also includes removing the clamping structure, removing the pin, welding a remaining section of the barrier perimeter to the first surface of the housing with the laser, and welding a perimeter of the barrier orifice to the sleeve top surface with the laser.
In another aspect, the disclosure is directed to an implantable drug delivery device including a housing. The housing includes a depression and a first surface. The drug delivery device also includes a bore housing inserted in the depression, and the bore housing includes a coil cup and a sleeve. The coil cup includes a coil cup base plate having a first major surface and a second major surface opposite the first major surface. The coil cup base plate defines a coil cup perimeter and a coil cup orifice located substantially centered in the coil cup base plate. The coil cup also includes a coil cup perimeter wall that includes a perimeter wall top surface, attached to the first major surface of the coil cup base plate along the coil cup perimeter and projecting substantially perpendicular to the first major surface of the coil cup base plate. The coil cup further comprises a coil cup inner wall attached to the first major surface of the coil cup base plate along a perimeter of the coil cup orifice and projecting substantially perpendicular to the first major surface of the coil cup base plate. The coil cup inner wall further defines the coil cup orifice, and an outer surface of the coil cup inner wall, an inner surface of the coil cup perimeter wall and the first major surface of the coil cup base plate define a bore housing cavity. The sleeve includes a sleeve top surface and a sleeve inner surface. The sleeve is press fit into the coil cup orifice and the sleeve inner surface defines a bore housing orifice. The first surface of the housing, the perimeter wall top surface and the sleeve top surface are substantially co-planar.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
As discussed above, many implantable drug delivery devices are relatively large and must be implanted in locations such as the abdomen, which may be undesirable in some embodiments. For example, implanting an implantable drug delivery device in a location remote from the therapy site may require the use of a relatively long catheter. This may increase the strain on the catheter, which may lead to premature failure of the catheter and require more frequent replacement than is desired. For example, implanting the drug delivery device in an abdomen of a patient and routing the catheter to a location along the patient's spinal cord proximate the patient's neck may require the use of a long catheter, and may lead to significant strain on, and even premature failure of, the catheter due to movement of the patient.
In order to enable the implantable drug delivery device to be implanted in a wider range of locations within a patient, it may be desirable to reduce the size of the implantable drug pump. Existing drug delivery devices typically use a peristaltic pump to pump the drug at a prescribed rate. Peristaltic pumps typically operate by a battery-powered electric motor that drives peristaltic rollers over a flexible tube having one end coupled to a therapeutic substance reservoir and the other end coupled to an infusion outlet to pump the therapeutic substance from the therapeutic substance reservoir through the infusion outlet. In an implantable therapeutic substance delivery device including a peristaltic pump, the peristaltic pump is typically one of the largest components in the device and can consume 90% or more of the available battery power. Additionally, the flexible tube used in a peristaltic pump is typically permeable to some therapeutic substance components such as water that can then infiltrate into the hermetically sealed housing and cause corrosion. Further, the flexible tube can expand resulting in decreased accuracy.
As implantable drug delivery devices are made smaller, the peristaltic pump may be larger than desirable for the housing of the implantable drug delivery device or may consume too much energy, and a new type of pump may be desired or necessary. One alternative pump for an implantable drug delivery device includes a solenoid-driven piston pump. The piston pump may comprise a piston that includes a permanent magnet, and a solenoid that produces a magnetic field that induces motion in the piston.
While
Coil cup perimeter wall 112 and sleeve 116 may include a perimeter wall top surface 113 and a sleeve top surface 117, respectively. In some embodiments, perimeter wall top surface 113 and sleeve top surface 117 may be substantially co-planar and provide support for barrier 104.
Barrier 104 defines a barrier perimeter 105 and a barrier orifice 107, which may be substantially centered in barrier 104. That is, a perimeter of barrier orifice 107 may be substantially concentric with barrier perimeter 105. In other embodiments, barrier perimeter 105 may define another geometry, such as a square or rectangle, for example. Barrier orifice 107 may define the same geometry as barrier perimeter 105, or may define a different geometry than barrier perimeter 105. Barrier orifice 107 may substantially align with bore housing orifice 118 when barrier 104 is placed on perimeter wall top surface 113 and sleeve top surface 117.
Referring again to
When a current is passed through the solenoid 106, a magnetic field is generated, which exerts a force on the permanent magnet 109. The direction of the flow of current in the solenoid 106 determines the direction of the magnetic field, and thus the direction of the force applied to the permanent magnet 109. Thus, by changing the direction of current flow, the piston 108 may be made to move from the raised position to the lowered position and vice versa.
Although not illustrated in
As is well known, a magnetic field at any given point is inversely proportional to distance squared (e.g., B□1/r2, where B is the magnetic field and r is distance). In this case, the magnitude of the magnetic field produced by the solenoid 106 at the permanent magnet 109 is proportional to the square of the distance form the solenoid 106 to the permanent magnet 109. Accordingly, it may be desirable to minimize the distance that separates the permanent magnet 109 from the solenoid 106 to reduce the strength of the magnetic field that is necessary to move the piston 108 a desired amount or at a desired rate. For a solenoid 106, the magnetic field is also linearly proportional to the current passing through the solenoid 106 (e.g., B□I, where B is the magnetic field and I is the current). Thus, reducing the necessary magnetic field reduces the necessary current. This is desirable for an implantable drug delivery device, as a battery typically powers the device. Any reduction in current may improve battery life, reduce battery power (and size), or both.
In order to minimize the distance between permanent magnet 109 and solenoid 106, it may be desirable to decrease the thickness of barrier 104. For example, each reduction of thickness of barrier 104 to half the original thickness of barrier 104 may reduce the necessary magnetic field by a factor of four. Along with the physical thickness of barrier 104, any non-planarity in barrier 104 may increase the distance between permanent magnet 109 and solenoid 106. Barrier 104 may be more likely to deviate from planarity as the thickness of barrier 104 is reduced, because the stiffness of the barrier 104 is reduced as the barrier is made thinner. Thus, manufacturing a thin barrier 104 (e.g., about 0.002 in. or less), such as stamping barrier 104 from a sheet of metal, can result in a barrier 104 that deviates from planarity.
While it may be desirable to minimize the thickness of the barrier 104 to improve the efficiency of the pump 100, it is also important to maintain a hermetic seal of the cavity 110. The materials used in constructing the solenoid 106 are typically not biocompatible, and may corrode in the presence of bodily fluids or the therapeutic agent dispensed by the pump 100. Accordingly, it is important to provide a hermetic seal around solenoid 106. In some embodiments, the attachment of barrier 104 to bore housing 102 may be the structure most likely to compromise the hermetic seal.
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As
Further, laser welding joins the material(s) together by melting the material(s) to form a weld without introducing any new material. This results in less material being available to make the weld 328 as the barrier 304 is made thinner, and may result in discontinuities in the weld if the melted material flows away from the welding point. These discontinuities may destroy the hermetic seal that barrier 304 is designed to provide and render the drug delivery device 300 unsuitable for implantation in a patient.
For example, the manufacturing tolerances of the size of the outer perimeter of barrier 404, the size of the barrier orifice, and the relative location of orifice with respect to the outer perimeter of barrier 404 may be more relaxed. As one example, barrier 404 may be shifted to the left or right a certain distance in
Additionally, the use of a lap weld alleviates the concern over a lack of material for the laser weld when the thickness of barrier 404 is reduced. For example, because the weld is no longer between two pieces of material that are aligned end-to-end, but is instead between two pieces of material, with one piece overlying the other piece, the weld effectively can utilize more material.
First, an implantable drug delivery device housing 624 is provided (502). The housing 624 may include a first surface 627 and may define a depression 640. The housing 624 may comprise a variety of biocompatible materials, including, for example, titanium, stainless steel, and the like. While not shown in
As shown in
Bore housing 602, including at least one of sleeve 616 and coil cup 601, may comprise a biocompatible material. For example, bore housing 602 may comprise stainless steel, titanium or the like. In some embodiments, sleeve 616 and coil cup 601 may comprise different materials. For example, in some embodiments, sleeve 616 may comprise titanium and coil cup 601 may comprise stainless steel. Bore housing 602 may include one or more additional orifices in, for example, base plate 614. The additional orifices may allow a negative pressure (e.g., vacuum) to be applied to bore housing cavity 610. This may be desired in order to secure the barrier 604 over the cavity 610 during at least part of the welding process 500.
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Barrier 604 is placed (510) over bore housing 602, as shown in
For example, when orifice 607 is not precisely centered in barrier 604, pin 626 may align the perimeter of orifice 607 with sleeve top surface 617 so that welding of barrier 604 to top surface 617 is facilitated. In some embodiments, the location of orifice 607 with respect to orifice 618 may be more important that the location of perimeter 605 with respect to perimeter wall top surface 613. For example, in some embodiments, perimeter 605 of barrier 604 may be welded to coil cup 601, housing 624, or both. Accordingly, there may be larger tolerances for the size and placement of barrier perimeter 605 than the tolerances for the placement of barrier orifice 607.
Barrier 604 may include a biocompatible material such as, for example, titanium, stainless steel, or the like, and titanium is preferred. Barrier 604 may include a thickness of less than about 0.004 inches, and in some embodiments may include a thickness of about 0.002 inches. In other embodiments, barrier 604 may include a thickness of less than about 0.002 inches.
Once barrier 604 is placed over the bore housing 602, the barrier 604 is clamped (512) against the bore housing 602 and, in some embodiments housing 624, with clamping structure 630. For example, in some embodiments, clamping structure 630 includes a base (not shown) that receives housing 624 and a moveable portion (e.g., the portion of clamping structure 630 shown in
Clamping structure 630 may also assist in producing or maintaining a substantially planar barrier 604. For example, clamping structure 630 may exert sufficient force against barrier 604 to correct some non-planarity in barrier 604 and/or may prevent any non-planarity from being introduced into barrier during the welding process 500.
Once the clamping structure 630 is engaged to retain barrier 604 in position against bore housing 602, a low-pressure source, or vacuum, may optionally be engaged to further restrain barrier 604 against bore housing 602. For example, as described briefly above, bore housing 602 may include one or more additional orifice (not pictured) which may be used to fluidically couple cavity 610 to a vacuum source. The vacuum source may produce a low pressure in cavity 610, which may assist in restraining barrier 604, and may also reduce or eliminate any non-planarity in barrier 604, either alone or in conjunction with clamp 630.
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In some embodiments, such as the embodiment shown in
Once the laser 638 completes spot welds at spot weld locations 741-748, the clamp 630 may be removed (516), the pin 626 may be removed (518), and the laser 638 may weld (520) the remainder of the perimeter 603, as shown in
In the embodiment shown in
In the embodiments illustrated in
Various embodiments of the invention have been described. These and other embodiments are within the scope of the following claims.
