IE83694B1 - Spring loaded implantable drug infusion device - Google Patents

Description

SPRING LOADED IMPLANTABLE DRUG INFUSION DEVICE Field of The Invention The present invention relates to an implantable drug delivery device for infusing a therapeutic agent into an organism. and more particularly, relates to an improved peristaltic implantable pump with improved occlusion along a fluid tube.

Description of the Related Art Implantable drug infusion devices are well known in the art. These devices typically include a medication reservoir within a generally cylindrical housing. Some form of fluid flow control is also provided to control or regulate the flow of fluid medication froth the reservoir to the outlet ofthe device for delivery ofthe medication to the desired location in a body, usually through a catheter. These devices are used to provide patients with a prolonged dosage or infusion ofa drug or other therapeutic agent.

Active drug infusion devices feature a pump or a metering system to deliver the drug into the patients system. An example of such a drug infusion pump Currently available is the Medtronic Synchro;VIed programmable pump. Additionally, U.S. Pat. Nos. 4,692,147 (Duggan). 5,840,069 (Robinson), and 6,036,459 (Robinson), assigned to l\/ledtronic, Inc., Minneapolis, Minn. disclose body-implantable electronic drug administration devices comprising a peristaltic (roller) pump for metering a measured amount of drug in response to an electronic pulse generated by control circuitry associated within the device. Each of these patents is incorporated herein by reference in their entirety for all purposes. Such pumps typically include a drug reservoir, a fill port, a peristaltic pump having a motor and a pumphead to pump out the drug from the reservoir, ‘ and a Catheter port to transport the drug from the reservoir via the pump to a patient’s anatomy, The drug reservoir, fill port, peristaltic pump, and catheter port are generally held in a housing, or bulkhead. The bulkhead typically has a series of passages extending from the drug reservoir and through the peristaltic pump that lead to the catheter port, which is typically located on the side ofthe housing. The peristaltic pumps use rollers which move along a pump tube, thereby moving liquid through the tube.

The prior art delivery devices, however, are limiting in that the load that the rollers piaee on the tube can vary as the rollers move along the tube. lfthe load is excessive, excess energy will be consumed and the tube life will be shortened, resulting in increased replacement costs. lfthe load is insufficient, inadequate occlusion ofthe tube will result in leakage of fluid past the roller, reducing the accuracy of the pump. Variation in the load is caused by variations in the gap between the rollers and the race in which the pump tube lies, the gap variance being due to manufacturing tolerances associated with the tube. the race and the pumphead. Prior art solutions to the load variance problem include tight manufacturing tolerances. sorting and matching ofcomponents, and placing shims of appropnatethicknessbenveentherohersandthetube,eadiof\vhichincreases manufacturing costs and reduces manufacturing flexibility.‘ ltnanomemofmemewnfinwnnmnopmvmemflnmhnmwednginfifion deficewhkhrmhmesorwhoflyovmcomessmneorahofmedfificuhksinhaeminpnor known devices. Particular objects and advantages ofthe invention will be apparent to those skilled in the art, that is, those who are knowledgeable or experienced in this field of technology, in view ofthe following disclosure of the invention and detailed description of preferred embodiments.

Summarv of The Invention The present invention provides an implantable drug infusion device which features a peristaltic pump having a new configuration, in which a spring biases a roller assembly against a pump tube, thereby minimizing the variation in the load that the roller assembly places on the pump tube. There is provided an implantable drug infusion device as claimed in Claim 1. ,_4 '.II |\) (J! From the foregoing disclosure, it will be readily apparent to those skilled in the art. that is, those who are knowledgeable or experienced in this area oftechnology, that the present invention provides a significant advance over the prior art. Preferred embodiments of the implantable infusion device of the present invention can significantly reduce the variation in load placed by the roller assembly on the pump tube. This will allow for less stringent manufacturing tolerancesfincreased manufacturing flexibility, increased tube life, and improved performance. These and additional features and advantages ofthe invention disclosed here will be further understood from the following detailed disclosure of preferred embodiments.

Brief Description of The Drawings Preferred embodiments are described in detail below with reference to the appended drawings.-The accompanying drawings, which are incorporated into and form a pan ofthis specification. together with the description, serve to explain the principles of the invention. The drawings are not drawn necessarily to scale, are only for the purpose of illustrating a preferred embodiment ofthe invention. and are not to be construed as limiting the invention. Some features of the implantable drug infusion device depicted in the drawings have been enlarged or distorted relative to others to facilitate explanation and understanding. The above mentioned and other advantages and features of the invention will become apparent upon reading the following detailed description and referring to the accompanying drawings in which like numbers refer to like parts throughout and in which: p‘.

‘J1 l\) L/I FIG. 1 is an exploded perspective view of an implantable drug infusion device in accordance with the present invention: FIG. 2 is an exploded perspective view of a pumphead assembly of the implantable device ofFIG. 1: FIG. 3 is perspective view, partially cut away, of the implantable device ofFig. 1, shown in its assembled state; FIG, 4 is a section view, taken along lines 4-4 ofFig. 3. ofthe implantable device ofFig. 1; FIG. 5 is a section view, taken along lines 5-5 ofFig. 2. ofa trailing arm of the implantable device ofFig. l; FIG. 6 is an exploded perspective view of an altemative embodiment ofthe roller arm assembly ofFig. l: FIG. 7 is a plan view ofthe geometry of the race and inlet and outlet ramps ofthe implantable device ofFig. l: FIG. 8 is a section view of an alternative embodiment of the roller arm assembly of Fig. 1; FIG. 9 is a plan view of the roller arm assembly of Fig. 8; FIG. 10 is a plan view of the roller ann assembly ofFig. 8, showing the roller artn assembly before and after being compressed; and FIG, 1 I is a perspective view of an alternative embodiment of the roller arm assembly ofFig. 8.

Description of the Preferred Embodiments As shown in Fig. 1, an implantable drug infusion device 2 in accordance with the invention comprises a bulkhead 4 containing a number of chambers and cavities sized and configured to house various subsystems ofthe implantable drug infusion device. In particular, bulkhead 4 has a first chamber 6 sized and configured to house a peristaltic pumphead assembly 8. A second chamber 10, sized and configured to house a motor assembly 12 which drives pumphead assembly 8, is positioned adjacent first chamber 6 and separated therefrom by a wall 13. Other chambers of bulkhead 4 house a battery and the electronic circuitry (not shown) used to operate implantable drug infusion device 2 and to control the dosage rate of the medication into the body.

Pumphead assembly 8 includes a compression member. such as roller ann .__.

(JI Ix) LII assembly 20, for compressing a pump tube l4 having an inlet 16 and an outlet 18. First chamber 6 has a generally circular wall 24 defining a pump race 19. Pump tube 14 is placed in first chamber 6 in close proximity to wall 24 so that roller amt assembly 20 may force the tube against the wall, thereby forcing medication to move through the tube in a known peristaltic manner. Flanges 21 extending outwardly from pumphead assembly 8 are received in recesses 23 formed in first chamber 6, supporting pumphead assembly 8 in first chamber 6. Inlet l6 is placed in a pump inlet cavity 26 formed in bulkhead 4. Pump inlet cavity 26 is connected to the pump race 19 by a pump inlet race ramp 28. Pump tube outlet 18 is placed in a pump outlet cavity 30 formed in bulkhead 4. Pump tube outlet cavity 30 is connected to the pump race 19 by a pump outlet race ramp 32. In a preferred embodiment, both pump inlet race ramp 28 and pump outlet race ramp 32 have an arcuate geometry to reduce pumphead torque. as described in greater detail below. A cover (not shown) is also provided for bulkhead 4 to provide protection for the components ofdrug infusion device 2. Motor assembly 12 includes a motor (not shown) which drives a four— stage gear assembly 11, only the fourth stage of which is visible. Teeth 15 are formed on the periphery of the fourth stage ofgear assembly 1 l.

Bulkhead 4 has an integral fill port cavity 34, sized and configured to house a septum and components to retain the septum. Drugs are injected through the septum to fill a reservoir (not shown) contained within a lower portion of bulkhead 4. A pathway is formed between the reservoir and pump inlet cavity 28, through which drugs are introduced into pump tube 14. The drugs exit pump outlet cavity 30 and travel through another pathway formed in bulkhead 4 to a catheter port on the periphery of bulkhead 4 from which the drug exits the device 2 and enters the anatomy of the individual. The structure of the septum, retaining components, pathways, and catheter port are known to one of skill in the art and are not shown here.

Referring now to Fig. 2, pumphead assembly 8 is shown in exploded form.

Pumphead assembly 8 includes a drive gear 40 with teeth 44 formed about its periphery.

A support plate 42 is positioned below drive gear 40. Flanges 21 extend outwardly from support plate 42 and, as described above, are received in recesses 23 of bulkhead 4, and preferably welded thereto. Roller arm assembly 20 is positioned below support plate 42.

Drive shaft 46 extends axially through apertures in roller arm assembly 20, support plate , and drive gear 40, and is retained by retaining screw 48. Drive shaft 46 is supported ,_ ‘Ji I\.) U: for rotation at its lower end by lower bearing 50, and at a central location. between roller arm assembly 20 and support plate 42. by upper bearing 52.

Roller ami assembly 20 comprises a central hub 53 having an apemire 55 through which drive shaft 46 extends. Flat 57 on drive shaft 46 mates with flat 59 ofaperture 55 such that roller ami assembly 20 rotates as drive shaft 46‘rotates. A plurality of trailing arms 54 are each pivotally secured by a pin 56 to hub 53. Trailing arm 54 comprises upper plate 51 and lower plate 61. A roller 58 is pivotally secured to each trailing arm 5-1 by an axle 60. As seen in Fig. 5, axle 60 extends between upper and lower plates 51, 61.

Axle 60 passes through an inner race 63 of roller 58. Inner race 63 is extended vertically to provide clearance between an outer race 65 of roller 58 and upper and lower plates 51, 61. In the illustrated embodiment. roller arm assembly 20 is shown with three trailing arms 54 and three corresponding rollers 5?. however. the number of trailing arms 54 and rollers 58 may be greater or lesser than three.

As seen in Figs. 3 and 4. teeth 15 of gear assemblj.‘ ll drivingly engage teeth 44 of drive gear 42, thereby causing rollers 58 to move about race 19. compressing and occluding tube 14 as they move and forcing the drug therethrough in known peristaltic fashion. As noted above, inlet race ramp 28 and outlet race ramp 32 each have an arcuate geometry, which reduces the torque required as each roller 58 engages pump tube 14 during rotation of roller arm assembly 20.

Referring back to Figure 2, each trailing arm 5-1 and its corresponding roller 58 is adjustably biased outwardly by a biasing member, such as spring 62. In a preferred embodiment, spring 62 is a coil spring. As seen in Fig. -1, spring 62 is oriented to facilitate the occlusion, or compression, of tube 14 by roller 58. Since manufacturing tolerances on the system components, i.e., roller 58, tube 14 and race 19, can result in variations in the gap A between roller 58 and race 19, the biasing action of spring 62 can advantageously minimize the variation in load placed by roller 58 on tube 14, greatly increasing the compliance of the system. Thus, for an incremental change in the gap between roller 58 and race 19, the incremental load required is reduced. For example, in prior art devices, where the system compliance is accounted for by the tube itself, a 0.001" decrease in a radial direction ofthe race could incur a 150g load increase on roller 58. With the present invention. however, spring 62 may be sized with a spring rate such that for a 0.001" decrease in the race, a 1.5g increase in load is realized. In a preferred embodiment, spring ,._.

‘J: is formed of a highly corrosion resistant and fatigue resistant alloy. Suitable mateiials include cobalt alloys and stainless steel. ln other preferred embodiments. a nitinol shape memory alloy may be used for spring 62.

The biasing member provides numerous advantages over the prior an devices.

Reducing the variation in load prevents excessive loading, thereby providing increased tube life; minimizes the force needed to occlude the pump tube. thereby minimizing the torque requirement for occlusion; improves occlusion and, therefore, reducing leakage and improving the performance ofthe peristaltic pump; allows for looser manufacturing tolerances and minimizes the need for sorting and matching components, providing increased manufacturing flexibility and reducing costs. ln a preferred embodiment. as seen in Fig. 2, roller ann assembly 20 further includes a tube guide 66. In the illustrated embodiment, tube guide 66 is connected to trailing arm 54 and is formed ofan upper plate 68 and a lower plate 70. In another preferred embodiment, tube guide 66 ma)‘ be connected directly to hub 53. Tube guide 66 serves to help keep pump tube l4 properly aligned to ensure that rollers 58 are centered with respect to pump tube 14.

Another embodiment of a roller arm assembly 80 is shown in Fig. 6. Roller arm assembly 80 comprises three trailing arms 82 pivotally secured to a hub 84. Hub 84 comprises upper plate 86, lower plate 88, and center plate 90. Rods 92 extend through apertures 94, 96 formed in upper plate 86 and lower plate 88, respectively. Pivot pins 98 extend between upper plate 5 l‘ and lower plate 61’ of each trailing arm 82. Hooks 100. lO2 formed on upper plate 86 and lower plate 88, respectively, of hub 84, capture pivot pins 98. The force of springs 62 acting on trailing arms 82 helps maintain trailing arms 82 in position on hub 84. lt is to be appreciated that other roller arm assembly constructions will be suitable, and are considered within the scope ofthe present invention. Suitable roller arm assembly constructions will provide a biasing member to ensure that a roller, or other suitable compression member, is biased against a pump tube, thereby minimizing the variation in load required to occlude the pump tube.

Other suitable biasing members include, for example, leaf springs and springs of other constructions, elastomeric members, closed or open cell elastomeric foam members, torsion bars, magnetic members, and solenoids.

‘J I In a preferred embodiment, inlet and outlet ramps 28 and 32 have exit and entry ramps transitioning smoothly into and from race 19 in order to minimize drag torque on pumphead assemb1)'8. As seen in Fig. 7. inlet ramp 28 transitions smoothly from a radius R of approximately 3.947 mm (01554 in) through point B to point A of race 19. Race 19 then transitions from point A’ to point B and then through a radius R’ of approximately 4.02mm (o.1583mm). The angles D, D’ between points A and B, and A’ and B’, respectively are approximately 35.5". Shown in the table below are the dimensions for the radius of race 19 along the arc between points A and B, and A’ and B’, in 0.5" increments.

It is to be appreciated that the radius varies smoothly along race 19.

Angle A Radius Angle Radius Angle Radius Angle Radius " 11.0000 4.0 110432 8.0 110864 12.0 11.1296 .5 11.0054 4.5 11.0486 8.5 11.0918 12.5 11.1350 11.0108 5.0 11.0540 9.0 11.0972 13.0 11.1404 1.5 11.0162 5.5 11.0594 9.5 11.1026 13.5 11.1458 2.0 11.0216 6.0 11.0648 10.0 11.1080 140 _11.1512 2.5 11.0270 6.5 11.0702 105 11.1134 14.5 11.1566 3.0 110324 7.0 11.0756 11.0 11.1188 15.0 11.1620 3.5 11.0378 7.5 11.0810 11.5 11.1242 15.5 11.1674 Angle Radius Angle Radius Angle Radius Angle Radius .0 1 1.1728 21.0 11.2268 260 11.2808 310 11.3348 16.5 11.1782 21.5 112322 26.5 11.2862 31.5 11.3402 17.0 11.1836 22.0 11.2376 27.0 11.2916 32.0 11.3456 17.5 11.1890 22.5 112430 27.5 11.2970 32.5 11.3510 18.0 11.1944 23.0 11.2484 28.0 11.3024 ' 33.0 11.3564 18.5 11.1998 23.5 12538 28 5 11.3078 33.5 11.3618 19.0 11.2052 240 11.2592 29.0 11 3132 34 0 11.367: 19.5 11.2106 24.5 11.2646 29.5 11.3186 34.5 11.3726 .0 11.2160 25.0 11.2700 30.0 11.3240 350 11.3780 .5 11.2214 25 5 11.2754 30.5 11.3294 35.5 11.3834 Another preferred embodiment is shown in Figs. 8 and 9, in which the biasing member is formed as an arm 112. Arm 1 12 is formed of a length of wire bent into a desired shape. Roller 58 is secured to a hub 110 via an arm 112. Arm 1 12 has a substantially U shaped profile forming upper and lower arms 113, 1 15 and extends through roller 58. An end 114 of upper arm 113 is bent and received in an aperture 1 16 in an upper surface ofhub 1 10, and an end 118 oflower arm 115 is bent and received in an aperture 120 in a lower surface ofhub 1 10. The upper and lower arms 1 13, 115 are of unequal length L1 and 1.2, respectively, such that apertures 1 16 and 120 are offset from one another in a radial direction with respect to hub 1 10 by a distance S1. Ends 114 and may also be offset from one another in an axial direction with respect to hub 110 by a distance S2. In an equilibrium state, there is no stress on am 1 12, and. therefore, no stress placed on roller 58.

As seen in Fig. 10. as arm 112 is rotated an angular amount 9 with respect to hub l 10 (to the position shown in dashed lines), the upper and lower arms 1 13, 1 15 become misaligned, placing stress on arm 1 12 and exerting a torque, and, therefore, a biasing effect on rollers 58. The amount of torque can be Varied by selecting appropriate lengths and diameters for upper and lower arms 1 13, l 15, varying the height of arm 1 12, and varying the offsets S1 and S2 between upper and lower arms 113. 115.

Another embodiment is shown in Fig. 1 1, wherein three arms 122, 124, 126, each having a configuration similar to that described above with respect to Figs. 8, 9, are ' formed from a single wire 128. As illustrated, wire 128 extends through a hub 110, however, it is to be appreciated that hub l 10 is not required, and the arms 122, 134, 126 may act as biasing members without the use ofa hub.

In light ofthe foregoing disclosure ofthe invention and description ofthe preferred embodiments, those skilled in this area oftechnology will readily understand that various modifications and adaptations can be made without departing from the scope and spirit of the invention. All such modifications and adaptations are intended to be covered by the following claims.

Claims (14)

Claims:

1. An implantable drug infusion device comprising, in combination: a pump tube for holding a liquid to be pumped; a race configured to support the tube along a path; a roller assembly configured to compress the tube against the race at one or more points along the path, the roller assembly including at least one roller; and a drive assembly to drive the roller assembly relative to the tube along the path so as to move the liquid through the tube; wherein the roller assembly comprises at least one trailing arm pivotally connected to the roller assembly, each trailing arm having a roller pivotally secured at one end of the trailing arm, a biasing member to bias the roller against the pump tube, and a tube guide extending from the other end of the trailing arm to align the pump tube with respect to a corresponding roller.

2. The implantable drug infusion device of claim 1, wherein the biasing member comprises a coil spring.

3. The implantable drug infusion device of claim 1, wherein the race includes an inlet ramp and an outlet ramp.

4. The implantable drug infusion device of claim 3, wherein the inlet ramp has an arcuate geometry.

5. The implantable drug infusion device of claim 3, wherein the outlet ramp has an arcuate geometry.

6. The implantable drug infusion device of claim 1, wherein the roller assembly comprises three trailing arms .

7. The implantable drug infusion device of claim 1, wherein each biasing member comprises a coil spring.

8. The implantable drug infusion device of claim 7, wherein the coil spring is formed of a nitinol shape memory alloy.

9. The implantable drug infusion device of claim 1, wherein the drive assembly comprises a drive shaft and a drive gear, the drive gear configured to be rotatably driven by a motor, the drive shaft rotatably driven by the drive gear and rotatably driving the roller assembly.

10. The implantable drug infusion device of claim 9, wherein the drive gear includes a plurality of teeth about a periphery of the drive engageable by a gear of a motor assembly.

11. The implantable drug infusion device of claim 1, wherein the biasing member comprises an arm formed of a length of wire. l0

12. The implantable drug infusion device of claim 1, wherein the biasing member comprises an arm formed of a length of wire and operably connected to three rollers.

13. The implantable drug infusion device of any of the proceeding claims further comprising a bulkhead, the race being provided on the bulkhead.

14. The implantable drug infusion device of claim 13 in which the bulkhead further defines a first chamber and a second chamber, the race being defined by a wall of the second chamber, the motor assembly being positioned within the first chamber, and the roller assembly being positioned within the second chamber.