Patent Publication Number: US-2021187137-A1

Title: Method for sterilizing water-filled devices

Description:
TECHNICAL FIELD 
     The present disclosure relates to a method of steam-sterilizing liquid-filled medical devices, e.g., filtration and/or diffusion devices like ultrafilters and capillary dialyzers. 
     BACKGROUND OF THE INVENTION 
     The steam-sterilization of liquid-filled medical devices, for instance, filtration and/or diffusion devices, poses a particular challenge. The temperature increase during steam-sterilization causes a pressure increase within the closed liquid-filled device, which in turn brings about deformation of components and can cause leaks or the formation of stress cracks in the housing of the device. 
     It would be desirable to have a steam sterilization process which is suitable for liquid-filled medical devices. 
     SUMMARY 
     The present disclosure provides a method of steam-sterilizing a liquid-filled medical device. The process uses a cannulated stopper comprised of an elastomer to seal a fluid port of the medical device. The cannulated stopper acts as a pressure relief valve to limit over-pressure within the medical device. The stopper is self-sealing, so that no liquid leaks from the medical device at ambient pressure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of two versions of a setup for measuring internal pressure of a medical device being heated; 
         FIG. 2  shows a side view and a cross-sectional view of a stopper for a liquid port of a medical device; 
         FIG. 3  shows several pressure curves obtained during heating experiments. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure provides a process for steam-sterilizing a liquid-filled medical device, e.g., a filtration and/or diffusion device, for instance, an ultra-filter or a capillary dialyzer. 
     The process comprises providing a liquid-filled medical device featuring at least one open liquid port. A liquid port is a port on the medical device that is configured for liquid transport into or out of the medical device, i.e., an inlet or outlet for a liquid. Usually, the liquid-filled medical device will have more than one liquid port, but most of them will be closed to prevent the liquid from flowing from the device. In one embodiment, all but one of the liquid ports of the liquid-filled medical device are closed. In another embodiment, all but two of the liquid ports of the liquid-filled medical device are closed. 
     At least one open liquid port of the liquid-filled medical device is closed with a cannulated stopper comprised of an elastomeric material. Any remaining open ports of the liquid-filled medical device are closed before sterilization; and the closed liquid-filled medical device then is steam-sterilized. 
     In one embodiment, the liquid-filled medical device is a filtration and/or diffusion device. In one embodiment, the medical device is a dialyzer, an ultrafilter, or a plasma filter, or an adsorber column, for instance, a hemocathartic column. In one embodiment, the medical device comprises hollow fiber membranes. In a further embodiment, the medical device comprises particulate material, e.g., polymer beads or carbon particles. In a particular embodiment, the liquid-filled medical device is a filtration and/or diffusion device filled with water or physiological saline and comprising hollow fiber membranes. In another particular embodiment, the medical device is a liquid-filled filtration and/or diffusion device comprising hollow fiber membranes and particulate material. In one embodiment, the particulate material is located in the space surrounding the hollow fiber membranes. 
     The liquid-filled medical device features at least one liquid port. In one embodiment, the liquid-filled medical device features a plurality of liquid ports, e.g., two, three or four liquid ports. 
     In one embodiment, the liquid-filled medical device comprises two compartments separated by a semipermeable membrane, and at least one of the two compartments features an inlet port and an outlet port for a liquid, e.g., blood. In a further embodiment, both compartments each feature an inlet port and an outlet port for a liquid. In another embodiment, one of the compartments only has an inlet port for a liquid. In another embodiment, one of the compartments does not feature liquid ports; or only ports which have been permanently sealed. In one embodiment, the liquid ports are connectors of a filtration and/or diffusion device for hemofiltration, hemodiafiltration, or hemodialysis, as described in DIN EN ISO 8637 (2014). 
     In the process of the present disclosure, the opening of at least one liquid port of the medical device to be steam-sterilized is closed with a cannulated stopper. In one embodiment, the opening of the port is closed by inserting a cannulated stopper into the opening of the port. In one embodiment, the stopper has a conical shape, its minimum diameter being smaller than the diameter of the opening of the port and its maximum diameter being larger than the diameter of the opening of the port. After insertion, part of the plug protrudes from the opening of the port. In another embodiment, the stopper features a section of cylindrical or conical shape, the maximum diameter of this section being smaller than or equal to the inner diameter of the port; and a head section having a diameter which is equal to or larger than the outer diameter of the port. After insertion, the head section of the plug covers the opening and the rim of the port. 
     The cannulated stopper is comprised of an elastomeric material. Examples of suitable elastomeric materials include silicone rubber, natural rubber (NR), butadiene rubber (BR), chloroprene rubber (CR), butyl rubber (IIR), styrene-butadiene rubber (SBR), nitrile rubber (NBR), ethylene propylene diene rubber (EPDM), and polyurethane elastomers. In one embodiment, the stopper is comprised of a silicone rubber. In one embodiment, the stopper has been produced by injection molding. 
     The cannulated stopper features a cannulation extending from the top of the stopper to its bottom and providing a through conduit from the interior of the liquid-filled medical device to the outside when the cannulation is in an expanded state. At ambient pressure, the cannulation is closed by the elastic restoring force of the elastomeric material. In one embodiment, the cannulation is produced by piercing a stopper comprised of an elastomeric material with a cannula having an outer diameter in the range of from 0.4 to 1.0 mm, for instance, 0.6 to 0.8 mm. 
     In case the medical device to be steam-sterilized comprises more than one liquid port, all liquid ports have to be closed before sterilizing the device. In one embodiment, all but one liquid port are closed by non-cannulated stoppers. In another embodiment, two or more of the liquid ports are closed by cannulated stoppers. It is generally sufficient to use a cannulated stopper in only one of the liquid ports of the medical device. However, for medical devices having two compartments separated by a semipermeable membrane, it may be advantageous to use a cannulated stopper in one liquid port of each compartment. 
     After all liquid ports of the liquid-filled medical device have been closed, the opening of at least one liquid port having been closed with a cannulated stopper, the liquid-filled medical device is steam-sterilized. Steam sterilization is a procedure well known in the art, and the person skilled in the art is familiar with the equipment and parameters to be used. In one embodiment, the medical device is sterilized with steam at a temperature in the range of from 119 to 121° C. for a time period of at least 20 minutes. 
     The present disclosure also is directed to the use of a cannulated stopper comprised of an elastomeric material in the steam-sterilization of a liquid-filled medical device. In one embodiment, the elastomeric material comprises silicone rubber. In one embodiment, the cannulation in the cannulated stopper has been produced by piercing a non-cannulated stopper with a cannula having an outer diameter in the range of from 0.4 to 1.0 mm, in particular, from 0.6 to 0.8 mm. 
     In one embodiment, the medical device is a filtration and/or diffusion device comprising hollow fiber membranes. In a further embodiment, the medical device comprises particulate material located in the space surrounding the hollow fiber membranes. 
     EXAMPLES 
       FIG. 1  shows two versions a) and b) of a setup for measuring internal pressure of a medical device being heated. In both versions of the setup, a filtration and/or diffusion device  11 , for instance, a dialyzer, having a lower blood port  12 , an upper blood port  13 , a lower dialysate port  14 , and an upper dialysate port  15  is present. Lower blood port  12  is sealed by a stopper  16 . Lower dialysate port  14  has been welded shut. Upper dialysate port  15  is connected to a pressure gauge  18  which indicates the pressure P within the device  11 . Upper blood port  13  is closed by cannulated stopper  17 . The device  11  is partially immersed into a heated bath  19  that is used to control the temperature within the device  11 . The second version of the setup ( FIG. 1 b   ) additionally comprises a syringe  20  connected to the cannulation of stopper  17 . The syringe  20  allows collecting and measuring liquid emerging from the device  11 . 
     Stoppers  16  comprised of silicone rubber were produced by injection molding of a two-component liquid silicone rubber (ELASTOSIL® LR 3003/60 A/B, Wacker Chemie AG, D-81737 Munich). The design of the stoppers  16  is shown in  FIG. 2 . After 5 min at 165° C. in the mold and 4 hours of post-curing at 200° C. in ventilated air, the material has a density of 1.13 g/cm 3  (ISO 1183-1 A), and a hardness of 60 Shore A (DIN 53505). It has a viscosity, measured according to DIN 53019 at a shear rate of 0.9 s −1 , of 1,100,000 mPa·s. Its tensile strength is 9.40 N/mm 2  and the elongation at break is 340% (both measured according to DIN 53504 S 1). The material shows a rebound resilience of 67%, measured according to DIN 53512. 
     Comparative Example 1 
     A medical device  11  comprising hollow fiber membranes having a surface area of 2.3 m 2  with lower dialysate port  14  welded shut was filled with water, blood ports  12  and  13  were closed with stoppers  16 ; and upper dialysate port  15  was connected to a pressure gauge  18 . The device  11  was immersed into a water bath  19  kept at a temperature of (80±2)° C. and the pressure P inside the device  11  was monitored. 
     The resulting pressure curve (pressure P over time t) is shown in  FIG. 3  (curve  1 ). After immersion of the device  11 , the pressure P inside the device  11  quickly rose to values exceeding 2 bar (g). When the pressure P had reached 3.9 bar (g), the experiment was stopped. No water had leaked from the device  11 . 
     Example 2 
     A stopper  16  comprised of silicone rubber was pierced with a cannula having an outer diameter of 0.45 mm to produce a cannulated stopper  17 . 
     A medical device  11  comprising hollow fiber membranes having a surface area of 2.3 m 2  and lower dialysate port  14  welded shut was filled with water, lower blood port  12  was closed with a stopper  16 , upper blood port  13  was closed with the cannulated stopper  17 ; and upper dialysate port  15  was connected to a pressure gauge  18 . The device  11  was immersed into a water bath  19  kept at a temperature of (80±2)° C. and the pressure P inside the device  11  was monitored (Setup according to  FIG. 1 a   ). 
     The resulting pressure curve is shown in  FIG. 3  (curve  2 ). After immersion of the device  11 , the pressure P inside the device  11  rose to a maximum of 1.59 bar (g) and then tapered off. At the end of the experiment, the pressure P was 1.17 bar (g), and 7.5 g of water had leaked from the device. 
     Example 3 
     A stopper  16  comprised of silicone rubber was pierced with a cannula having an outer diameter of 0.60 mm to produce a cannulated stopper  17 . 
     A medical device  11  comprising hollow fiber membranes having a surface area of 2.3 m 2  and lower dialysate port  14  welded shut was filled with water, lower blood port  12  was closed with a stopper  16 , upper blood port  13  was closed with the cannulated stopper  17 ; and upper dialysate port  15  was connected to a pressure gauge  18 . The device  11  was immersed into a water bath  19  kept at a temperature of (80±2)° C. and the pressure P inside the device  11  was monitored (Setup according to  FIG. 1 a   ). 
     The resulting pressure curve is shown in  FIG. 3  (curve  3 ). After immersion of the device  11 , the pressure P inside the device  11  rose to a maximum of 1.50 bar (g) and then tapered off. At the end of the experiment, the pressure P was 1.26 bar (g), and 7.0 g of water had leaked from the device. 
     Example 4 
     A stopper  16  comprised of silicone rubber was pierced with a cannula having an outer diameter of 0.80 mm to produce a cannulated stopper  17 . 
     A medical device  11  comprising hollow fiber membranes having a surface area of 2.3 m 2  and lower dialysate port  14  welded shut was filled with water, lower blood port  12  was closed with a stopper  16 , upper blood port  13  was closed with the cannulated stopper  17 ; and upper dialysate port  15  was connected to a pressure gauge  18 . The device  11  was immersed into a water bath  19  kept at a temperature of (80±2)° C. and the pressure P inside the device  11  was monitored (Setup according to  FIG. 1 a   ). 
     The resulting pressure curve is shown in  FIG. 3  (curve  4 ). After immersion of the device  11 , the pressure P inside the device  11  rose to a maximum of 1.15 bar (g) and then tapered off. At the end of the experiment, the pressure P was 0.5 bar (g), and 6.5 g of water had leaked from the device. 
     Example 5 
     A stopper  16  comprised of silicone rubber was pierced with a cannula having an outer diameter of 0.90 mm to produce a cannulated stopper  17 . 
     A medical device  11  comprising hollow fiber membranes having a surface area of 2.3 m 2  and lower dialysate port  14  welded shut was filled with water, lower blood port  12  was closed with a stopper  16 , upper blood port  13  was closed with the cannulated stopper  17 ; and upper dialysate port  15  was connected to a pressure gauge  18 . The device  11  was immersed into a water bath  19  kept at a temperature of (80±2)° C. and the pressure P inside the device  11  was monitored (Setup according to  FIG. 1 a   ). 
     The resulting pressure curve is shown in  FIG. 3  (curve  5 ). After immersion of the device  11 , the pressure P inside the device  11  rose to a maximum of 0.08 bar (g) and then tapered off. At the end of the experiment, the pressure P was 0.0 bar (g), and 7.5 g of water had leaked from the device. 
     Example 6 
     A stopper  16  comprised of silicone rubber was pierced with a cannula having an outer diameter of 0.45 mm to produce a cannulated stopper  17 . 
     A medical device  11  comprising hollow fiber membranes having a surface area of 2.3 m 2  and polymer beads in the space surrounding the hollow fiber membranes was used for the experiment. The lower dialysate port  14  of the device  11  had been welded shut. The device  11  was filled with water, lower blood port  12  was closed with a stopper  16 , upper blood port  13  was closed with the cannulated stopper  17 ; and upper dialysate port  15  was connected to a pressure gauge  18 . The device  11  was immersed into a water bath  19  kept at a temperature of (80±2)° C. and the pressure P inside the device  11  was monitored (Setup according to  FIG. 1 a   ). 
     The resulting pressure curve is shown in  FIG. 3  (curve  6 ). After immersion of the device  11 , the pressure P inside the device  11  rose to a maximum of 1.8 bar (g) and then tapered off. At the end of the experiment, the pressure P was 1.05 bar (g), and 5.6 g of water had leaked from the device. 
     Example 7 
     A stopper  16  comprised of silicone rubber was pierced with a cannula having an outer diameter of 0.45 mm to produce a cannulated stopper  17 . A 30 ml syringe  20  was connected to the cannula which had a length of 10 mm. 
     A medical device  11  comprising hollow fiber membranes having a surface area of 2.3 m 2  and lower dialysate port  14  welded shut was filled with water, lower blood port  12  was closed with a stopper  16 , upper blood port  13  was closed with the cannulated stopper  17  connected to the syringe  20 ; and upper dialysate port  15  was connected to a pressure gauge  18 . The device  11  was immersed into a water bath  19  kept at a temperature of (80±2)° C. and the pressure P inside the device  11  was monitored (Setup according to  FIG. 1 b   ). 
     The resulting pressure curve is shown in  FIG. 3  (curve  7 ). The maximum of the pressure P inside the device  11  reached during the experiment was 0.18 bar (g). The plunger of the syringe began to move when the pressure P reached 0.05 bar (g). During the experiment, a maximum volume of 7.5 ml water was displaced into the syringe  20 . After removing the water bath  19  and cooling the device to room temperature, a residual volume of 1 ml remained in the syringe  20 . 
     LIST OF REFERENCE SIGNS 
       10  Testing setup 
       11  filter 
       12  lower blood port 
       13  upper blood port 
       14  lower dialysate port 
       15  upper dialysate port 
       16  stopper 
       17  cannulated stopper 
       18  pressure gauge 
       19  heated bath 
       20  syringe 
     P pressure