Syringe with two-stage sealing pressure

Abstract

A syringe includes a barrel, a plunger, and a sealing member creating a seal between the plunger and the barrel. The barrel includes a first portion with a first inner diameter and a second portion with a second inner diameter that is larger than the first inner diameter. The sealing member engages the first portion of the barrel to give rise to a first contact pressure when the barrel is filled with product. The first contact pressure is sufficient to maintain a gas-tight seal over the expected temperature ranges −25° C. to 40° C. A first force is applied to the plunger to overcome the first contact pressure and move the plunger out of the first portion and into the second portion to dispense product. The sealing member engages the second portion of the barrel to give rise to a second contact pressure that is lower than the first contact pressure. A second force lower than the first force is sufficient to overcome the second contact pressure and move the plunger in the second portion to continue dispensing product. The syringe may include a restraining element for accommodating expansion of the product during freezing.

What is claimed is: 
     
         1 . A syringe for use in a drug infusion system, the syringe comprising:
 a barrel having a cylindrical wall, the cylindrical wall having a first portion with a first inner diameter and a second portion with a second inner diameter that is larger than the first inner diameter;   a plunger within the barrel;   wherein a sealing member of the plunger engages the first portion of the barrel with a first contact pressure when the barrel is filled with product, such that a first force is required to move the plunger with respect to the barrel;   wherein a portion of the plunger engages the second portion of the barrel with a second contact pressure that is lower than the first contact pressure, such that a second force is required to move the plunger in the second portion; and   wherein the second force is lower than the first force.   
     
     
         2 . The syringe of  claim 1 , wherein the first contact pressure gives rise to a seal between the plunger and the first portion of the barrel, which seal is gas-tight through a temperature range of −25° C. to 40° C. 
     
     
         3 . The syringe of  claim 1 , wherein the plunger includes at least one o-ring; and wherein the o-ring gas-tightly seals against the cylindrical wall of the barrel in both of the first and second portions. 
     
     
         4 . The syringe of  claim 1 , wherein the sealing member gas-tightly seals against the first portion of the barrel; and does not gas-tightly seal against the second portion of the barrel. 
     
     
         5 . The syringe of  claim 1 , wherein the plunger includes a plunger head with at least one rim in addition to the sealing member; wherein the sealing member does not engage the second portion of the barrel; and wherein the at least one rim engages the inner surface of the second portion of the barrel. 
     
     
         6 . The syringe of  claim 1 , wherein the first portion of the barrel includes a reduced diameter member inserted into the barrel. 
     
     
         7 . The syringe of  claim 1 , wherein the sealing member of the plunger includes a flexible wiper. 
     
     
         8 . The syringe of  claim 1 , wherein a step is defined between the first and second portions of the barrel; and wherein the sealing member engages the step to resist movement of the plunger in a rearward direction with respect to the barrel. 
     
     
         9 . A method for storing and dispensing a product having a high content of water, the method comprising:
 providing a syringe barrel having a cylindrical wall, the cylindrical wall having a first portion with a first inner diameter and a second portion with a second inner diameter that is larger than the first inner diameter;   providing a plunger having a sealing member;   inserting the plunger into the barrel;   filling the syringe with product such that the plunger is positioned within the first portion of the barrel;   engaging the first portion of the barrel with the sealing member to give rise to a first contact pressure when the barrel is filled with product;   applying a first force to overcome the first contact pressure and move the plunger out of the first portion and into the second portion to dispense product;   engaging the second portion of the barrel with a portion of the plunger to give rise to a second contact pressure that is lower than the first contact pressure; and   applying a second force lower than the first force to overcome the second contact pressure move the plunger in the second portion to continue dispensing product.   
     
     
         10 . The method of  claim 9 , wherein giving rise to the first contact pressure includes creating a gas-tight seal between the plunger and barrel through a temperature range of −25° C. to 40° C. 
     
     
         11 . The syringe of  claim 9 , wherein providing a plunger having a sealing member includes providing a plunger with at least one o-ring as the sealing member; wherein engaging the second portion of the barrel with a portion of the plunger includes engaging the second portion of the barrel with the at least one o-ring; and wherein the o-ring gas-tightly seals against both of the first and second portions. 
     
     
         12 . The syringe of  claim 9 , wherein engaging the first portion of the barrel with the sealing member includes gas-tightly sealing the plunger with respect to the first portion of the barrel with the sealing member; and wherein engaging the second portion of the barrel with a portion of the plunger does not include gas-tightly sealing the plunger with respect to the second portion of the barrel with the sealing member. 
     
     
         13 . The syringe of  claim 9 , wherein providing a plunger having a sealing member includes providing a plunger head having a sealing member and at least one rim; and wherein engaging the second portion of the barrel with a portion of the plunger includes engaging the second portion of the barrel the at least one rim and not with the sealing member. 
     
     
         14 . The syringe of  claim 9 , further comprising inserting a reduced diameter member into the barrel to create the first portion of the barrel. 
     
     
         15 . The syringe of  claim 9 , wherein providing a plunger having a sealing member includes providing the plunger having a flexible wiper as the sealing member. 
     
     
         16 . The syringe of  claim 9 , further comprising defining a step between the first and second portions of the barrel; and engaging the step with the sealing member to resist movement of the plunger in a rearward direction with respect to the barrel. 
     
     
         17 . A method for storing and dispensing a product having water content, the method comprising:
 providing a syringe barrel having a front end, a rear end, and a cylindrical wall having an inner surface, the rear end being open, and the front end including an orifice;   providing a plunger adapted to fit within the syringe barrel with a sliding seal against the inner surface, a product chamber being defined between the inner surface of the barrel and the plunger;   filling the product chamber with the product having water content;   attaching a restraining element to the syringe;   freezing the product-filled syringe such that the water content of the product freezes and expands;   restraining displacement of the plunger with the restraining member during expansion of the water content during freezing;   storing the frozen product-filled syringe until an approximate time of use; and   at the approximate time of use, thawing the frozen product-filled syringe and actuating the plunger to dispense the thawed product from the syringe through the orifice.   
     
     
         18 . The method of  claim 17 , wherein restraining displacement of the plunger includes abutting the restraining element with the plunger; the method further comprising: pressing the plunger against the restraining element with a force in response to expansion of the water content during freezing. 
     
     
         19 . The method of  claim 18 , further comprising accommodating expansion of the water content during freezing by deflecting the restraining element when the force exceeds a restraining element deflection threshold. 
     
     
         20 . The method of  claim 18 , further comprising accommodating expansion of the water content during freezing by deflecting the plunger when the force exceeds a plunger deflecting threshold. 
     
     
         21 . The method of  claim 17 , wherein attaching a restraining element includes affixing an end cap to the syringe. 
     
     
         22 . The method of  claim 17 , wherein providing a syringe barrel includes forming a mounting structure at the rear end, the mounting structure adapted for mounting the syringe to a pump; and wherein attaching the restraining element includes attaching the restraining element to the mounting structure. 
     
     
         23 . The method of  claim 17 , wherein attaching a restraining element includes inserting the syringe into a case and affixing a cap to the case; and wherein restraining displacement of the plunger includes abutting the plunger against the cap. 
     
     
         24 . The method of  claim 17 , wherein restraining displacement of the plunger includes accommodating expansion of the freezing water content with deflection of at least one of the plunger and restraining element. 
     
     
         25 . The method of  claim 17 , further comprising permitting displacement of the plunger toward the restraining element during freezing of the product-filled syringe, prior to restraining displacement of the plunger with the restraining element.