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.

1 . A syringe for use in a drug infusion system, the syringe comprising:
 a barrel having a cylindrical wall having an inner surface and an outer surface, the cylindrical wall having a first portion with a first inner diameter and a circumferentially continuous inner surface and a second portion with a second inner diameter that is larger than the first inner diameter, the first portion and the second portion configured to hold a pharmaceutical product, the first portion and the second portion having a substantially same outer diameter, and the inner surface of the cylindrical wall separating the first portion and the second portion of the barrel defining a step substantially perpendicular to a longitudinal axis of the barrel; and   a plunger within the barrel having a contact surface facing and contacting the pharmaceutical product within the barrel, the plunger including a sealing member configured to engage the first portion of the barrel with a first contact pressure such that a first force is required to move the plunger with respect to the barrel, and a portion of the plunger is configured to engage the second portion of the barrel with a second contact pressure that is lower than the first contact pressure, such that a second force lower than the first force is required to move the plunger in the second portion, the plunger configured to move rearwardly along at least a portion of the longitudinal axis of the barrel in response to application of a force exerted on the contact surface of the plunger by expansion of the pharmaceutical product during a transition from a non-frozen state to a frozen state, the plunger maintaining a gas tight seal between the inner surface of the barrel and the plunger during expansion of the pharmaceutical product.   
     
     
         2 - 25 . (canceled) 
     
     
         26 . The syringe of  claim 1 , wherein the first contact pressure provides a seal between the plunger and the first portion of the barrel, wherein the seal is gas-tight through a temperature range of about −25° C. to 40° C. 
     
     
         27 . The syringe of  claim 1 , wherein the plunger includes at least one o-ring; and wherein the o-ring is configured to gas-tightly seal against the cylindrical wall of the barrel in both of the first and second portions. 
     
     
         28 . The syringe of  claim 1 , wherein the sealing member is configured to gas-tightly seal against the first portion of the barrel and does not gas-tightly seal against the second portion of the barrel. 
     
     
         29 . The syringe of  claim 1 , wherein the plunger includes a plunger head with at least one rim;
 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.   
     
     
         30 . The syringe of  claim 1 , wherein the first portion of the barrel includes a reduced diameter member disposed in the barrel. 
     
     
         31 . The syringe of  claim 1 , wherein the sealing member of the plunger includes a flexible member. 
     
     
         32 . The syringe of  claim 1 , wherein the sealing member engages the step to resist movement of the plunger in a rearward direction with respect to the barrel. 
     
     
         33 . The syringe of  claim 1 , wherein the plunger is configured to interface with an actuator of a pump to dispense the product through an orifice in the syringe. 
     
     
         34 . The syringe of  claim 33 , wherein the pump includes a battery pack, and wherein less power from the battery pack is required to move the plunger after the sealing member is in the second portion.