Air tolerant implantable piston pump

Abstract

An implantable infusion device includes a reservoir for housing an infusion medium and a drive mechanism having an inlet chamber, a piston and a piston channel. The inlet chamber is in fluid communication with the reservoir. The piston channel is in fluid communication with the inlet chamber, and has a distal end and a proximal end, the proximal end being closer to the inlet channel than the distal end. The piston is axially moveable within the piston channel to drive infusion medium out of the distal end of the piston channel. The clearance between the piston and the channel is sufficiently small to prevent undissolved gas in the inlet chamber from passing through the clearance. The inlet chamber may be sufficiently large to allow undissolved gas to accumulate without adversely affecting the performance of the infusion device.

1 - 23 . (canceled) 
     
     
         24 . An implantable infusion device, comprising:
 a reservoir for housing an infusion medium;   a drive mechanism having an inlet chamber, a piston and a piston channel,
 wherein the inlet chamber is in fluid communication with the reservoir, 
 wherein the piston channel is in fluid communication with the inlet chamber, the piston channel having a distal end and a proximal end, the proximal end being closer to the inlet channel than the distal end, 
 wherein the piston is axially moveable within the piston channel to drive infusion medium out of the distal end of the piston channel, 
 wherein the piston is positioned and moveable within the channel such that a clearance between the piston and the piston channel is sufficiently small to prevent undissolved gas in the inlet chamber from passing through the clearance; 
   a filter disposed between the inlet chamber and the reservoir, wherein the filter is hydrophilic and is configured to prevent microorganisms from entering the inlet chamber from the reservoir, wherein the filter is configured to allow dissolved gas to pass from the reservoir to the inlet chamber such that over time, the dissolved gas comes out of solution as undissolved gas in the inlet chamber, and wherein the filter is configured to prevent the undissolved gas from passing from the inlet chamber to the reservoir;   an outlet in fluid communication with the piston channel, the outlet being closer to the distal end of the piston channel than the proximal end of the piston channel; and   a valve in fluid communication with, and disposed between, the outlet and the piston channel.   
     
     
         25 . The implantable infusion device of  claim 24 , wherein the clearance between the piston and the piston channel is sufficiently small such that the infusion medium is retained in the piston channel via capillary action. 
     
     
         26 . The implantable infusion device of  claim 24 , wherein the average clearance between the piston and the piston channel is between 3 micrometers and 10 micrometers. 
     
     
         27 . The implantable infusion device of  claim 24 , wherein the filter is configured to filter particles larger than 0.22 microns in diameter. 
     
     
         28 . The implantable infusion device of  claim 24 , wherein the volume of the inlet chamber is between 100 microliters and 300 microliters. 
     
     
         29 . The implantable infusion device of  claim 24 , wherein the reservoir is maintained at a pressure of greater than 5 psia. 
     
     
         30 . The implantable infusion device of  claim 24 , wherein the reservoir is maintained at a pressure of greater than 10 psia. 
     
     
         31 . The implantable infusion device of  claim 24 , wherein the reservoir is maintained at a pressure of between 15 psia and 16 psia. 
     
     
         32 . The implantable infusion device of  claim 24 ,
 wherein the valve has a cracking pressure that is between 5 psi less than the pressure of the reservoir and 5 psi more than the pressure of the reservoir.   
     
     
         33 . The implantable infusion device of  claim 24 , wherein the valve has a cracking pressure that is at least 2 psi greater than the difference of the reservoir pressure minus the outlet pressure at the lowest ambient atmospheric pressure that the device is designed to be subjected. 
     
     
         34 . The implantable infusion device of  claim 24 , wherein the valve has a cracking pressure that is equal to or greater than the reservoir pressure minus 6.3 psia. 
     
     
         35 . The implantable infusion device of  claim 24 , wherein the drive mechanism is capable of continued operation without undissolved gas exiting the distal portion of the piston channel when 70% of the volume of the inlet chamber is occupied by undissolved gas. 
     
     
         36 . The implantable infusion device of  claim 24 , wherein the reservoir is maintained at a pressure of greater than 8 psia. 
     
     
         37 . The implantable infusion device of  claim 24 , wherein the reservoir is maintained at a pressure of greater than 10 psia. 
     
     
         38 . The implantable infusion device of  claim 24 , wherein the reservoir is maintained at a pressure of between 14 psia and 19 psia. 
     
     
         39 . The implantable infusion device of  claim 24 , wherein the reservoir is maintained at a pressure of greater than 0 psia.