Patent Publication Number: US-2023142866-A1

Title: Determining Effectiveness of Sterilization Procedure from Outside the Sterilization Package

Description:
TECHNICAL FIELD 
     The present application is related to articles, systems, and techniques for determining the effectiveness of a sterilization procedure from outside the sterilization package. 
     BACKGROUND 
     Medical instruments are cleaned, assembled, processed, packaged, stored, and issued for patient care from the central sterilization department or Sterile Processing Department of a hospital. Typically, once opened in the operating room or other point of use, sterilization indicators placed inside sterilization packages prior to sterilization are used to determine whether instruments inside the sterilization package were properly sterilized. 
     SUMMARY 
     The disclosure is related to articles, systems, and techniques for determining, by an indicator disposed on an exterior of a sterilization package, the effectiveness of a sterilization procedure. The described articles, systems, and techniques include externally visible, internally sampling sterilization indicators configured to enable assessment of the presence and state of a chemical indicator prior to taking medical instruments to the operating room. 
     In some examples, the disclosure is directed to a sterilization indicator including a cover, an indicator, and a seal. The cover defines at least a portion of a cavity. The indicator is disposed within the cavity. The indicator is configured to fluidly couple with an internal cavity of a sterilization package and indicate an exposure to a sterilant. The seal is configured to form a microorganism barrier between an exterior of the cover and an internal cavity of a sterilization package. 
     In some examples, the disclosure is directed to a sterilization package including an enclosure, and a sterilization indicator disposed on the exterior surface of the enclosure. The enclosure includes an exterior surface and defines an internal cavity. At least a portion of the enclosure comprises a sterilant-permeable region. The sterilization indicator includes cover, an indicator, and a seal. The cover defines at least a portion of a cavity. The indicator is disposed within the cavity and is fluidly coupled to the internal cavity of the enclosure. The indicator is configured to indicate an exposure to a sterilant within the internal cavity. The seal is configured to form a microorganism barrier between an exterior of the enclosure and the internal cavity of the enclosure. 
     In some examples, the disclosure is directed to a method of forming a sterilization indicator. The method includes forming a cover defining at least a portion of a cavity. The method also includes positioning an indicator within the cavity. The indicator is configured to fluidly couple with an internal cavity of a sterilization package and indicate an exposure to a sterilant. The method also includes disposing a seal adjacent the cover. The seal is configured to form a microorganism barrier between an exterior of the cover and the cavity of the sterilization package. 
     In some examples, the disclosure is directed to a method of using a sterilization indicator. The method includes positioning the sterilization indicator on an exterior surface of an enclosure, which defines an internal cavity. At least a portion of the exterior surface comprises a sterilant-permeable region. The method also includes exposing the sterilization indicator and the enclosure to a sterilant for a selected duration of time, at a selected temperature, and/or at a selected sterilant concentration. The method also includes determining, by the indicator, whether the internal cavity of the enclosure was exposed to at least one of a threshold exposure duration, a threshold sterilant temperature, or a threshold sterilant concentration. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a conceptual cross-sectional view of an example sterilization package that includes a sterilization indicator positioned on an exterior surface of an enclosure. 
         FIGS.  2 A- 2 C  are conceptual diagrams illustrating several views of an example sterilization indicator. 
         FIGS.  3 A and  3 B  are conceptual diagrams illustrating perspective views of an example sterilization indicator including a process challenge device. 
         FIG.  4    is a conceptual diagram illustrating an example sterilization package that includes a sterilization indicator positioned on an exterior surface of an enclosure. 
         FIG.  5    is a conceptual diagram illustrating a perspective view of an example sterilant indicator. 
         FIGS.  6 A and  6 B  are conceptual diagrams illustrating perspective views of an example sterilization indicator. 
         FIG.  7    is a conceptual diagram illustrating a plan view of a portion of an example sterilization package including a clamshell sterilization indicator. 
         FIGS.  8 A through  8 E  are conceptual diagrams illustrating example components of a sterilization package. 
         FIG.  9    is a conceptual diagram illustrating a perspective view of a soft pack sterilization package including a plurality of sterilization indicators adhered to the sterilization package. 
         FIG.  10    is a flow diagram illustrating an example technique of forming a sterilization indicator. 
         FIG.  11    is a flow diagram illustrating an example technique of using a sterilization indicator. 
     
    
    
     Like symbols in the drawings indicate like elements. 
     DETAILED DESCRIPTION 
     The present disclosure describes articles, systems, and techniques for assessing the presence and condition of sterilization inside a closed sterilization package from outside the closed sterilization package. Such sterilization indicators include externally visible, internally sampling sterilization indicators (hereinafter, sterilization indicators). An example sterilization indicator system may include, for example, a chemical or biological sterilization indicator, a housing surrounding the sterilization indicator, a conduit fluidly coupled to an interior of the housing via a sample port, one or more seals configured to provide a sterile barrier between the interior of the housing and an environment exterior to the housing and sterilization package, and an optional locking mechanism configured to secure the sterilization indicator to the sterilization package in a tamper-resistant manner. 
     A variety of products and articles, including, for example, medical instruments, devices, bandages, and equipment, must be sterilized prior to use to prevent biocontamination of a wound site, a sample, an organism, or the like. Used medical instruments received from the operating room in the decontamination area of the Sterile Processing Department undergo a sterilization procedure. The used medical instruments are processed by manual and/or automated cleaning and disinfecting procedures, followed by packaging in a soft pack or a rigid container (e.g., a sterilization package). The sterilization package materials and sterilization methods allow for penetration of sterilant through a sterilant-permeable, microorganism-impermeable material during the sterilization process. The sterilization package materials protect the instruments from microorganism contamination during storage and handling. 
     Typically, internal sterilization indicators (e.g., not externally visible) are placed in the sterilization package prior to sealing the sterilization package. After sealing, the sterilization package is sterilized using a sterilant, such as, for example, steam, ethylene oxide, dry heat, or hydrogen peroxide vapor. After sterilization, instruments are stored, e.g., from a few minutes to several weeks, until needed in the operating room. The internal sterilization indicator provides a visual indication of the effectiveness of a sterilization procedure. Because materials of some sterilization packages are not transparent, visualization of internal sterilization indicators requires opening of the pack or container. 
     A method for viewing and obtaining information about the functioning of a sterilizer is to use a test pack. A test pack may include a model package constructed to simulate air removal and the penetration of a sterilant in a sterilization package containing instruments. Since the test pack does not usually contain instruments that are to be used in medical procedures, the test pack can be placed in the same sterilization cycles as the instrument sterilization packages, and can be opened and examined following sterilization without compromising any instruments intended for medical procedures. However, a sterilization load often contains a mixture of different types of sterilization packaging, such as wrapped instrument sets, rigid containers, and other sterilization package forms. Each sterilization package may also contain a different amount of materials within the sterilization packaging, thereby limiting the use and construction of a universal test pack. Additionally, varying the number or orientation of sterilization packages in a given sterilization load can also affect sterilization effectiveness for certain types of sterilization packages. The use of multiple test packs designed to simulate a wider range of packaging types and loading conditions may be limited by available space within a sterilizer and/or procedural complexity for a sterilization technician, e.g., in determining which test packs to use for the various combinations of packaging and load levels, which may lead to increased operator error. 
     One method for viewing and obtaining information from the interior environment of a sterilization package is to place the indicator inside a sterilization package, then open the sterilization package and inspect the sterilization indicator following a sterilization procedure. For example, during set-up of the operating room for a surgical operation, the sterilization package including designated instrument sets are moved into the operating room. Once inside the operating room, the sterilization package may be opened and inspected for the presence of one or more internal sterilization indicators. The internal sterilization indicators may be used to assess whether the sterilization procedure was effective. For example, the internal sterilization indicators may be used to assess whether the internal cavity of the enclosure was exposed to the sterilant for at least one of a threshold exposure duration, a threshold sterilant temperature, or a threshold sterilant concentration. As used herein, the threshold exposure duration, the threshold sterilant temperature, or the threshold sterilant concentration may include commonly accepted threshold values for respective sterilization procedures. 
     Unless the internal sterilization indicator provides a visual indication that the sterilization procedure was effective, the set of instruments is considered contaminated and must be reprocessed before use. Reprocessing a sterilization package can have undesired consequences, including decreased productivity in the Sterile Processing Department and delayed surgeries. In an emergency situation, hospitals may use immediate-use sterilization, a process which may be less effective than other sterilization procedures. Thus, reducing reprocessing may be advantageous. 
     Another method for viewing and obtaining information from sterilization indicators regarding the interior environment of a sterilization package is to introduce a transparent or sheer element, such as a window, within the container or wrap through which the indicator can be visualized. Such modification, however, may add significant costs and complexity to manufacture of the sterilization package. 
     The described sterilization indicator (e.g., externally visible, internally sampling) articles, systems, and techniques allow an operator (e.g., a technician or clinician) to determine, without opening the sterilization package, whether the interior contents of a closed sterilization package have been exposed to a sterilant for a threshold time, a threshold temperature, and/or a threshold concentration. This enables assessing effectiveness of sterilization within the Sterile Processing Department, e.g., before the sterilization package is moved into the operating room. The described articles, systems, and techniques may reduce the cost and/or the delays associated with contaminated sterilization packages being staged in the operating room. Additionally, or alternatively, the described articles, systems, and techniques may reduce the cost and/or improve processing throughput by eliminating use of test packs. Additionally, or alternatively, the described articles, systems, and techniques may reduce sterilization package cost associated with introducing transparent windows in sterilization packages. Additionally, or alternatively, by fluidically connecting a sterilization indicator outside of the tray to contents inside the tray using a sample port, the described articles, systems, and techniques provide externally visible sterilization indicator that may reduce or prevent operator error in not placing internal sterilization indicator(s) inside a sterilization package prior to sterilization. 
       FIG.  1    is a conceptual cross-sectional view of an example sterilization package  100  that includes a sterilization indicator  102  positioned on an exterior surface  106  of an enclosure  104 . Enclosure  104  is configured to receive articles, such as medical instruments, for sterilization. Sterilization indicator  102  is configured to provide an externally visible indication of whether sterilization parameters were met during the sterilization process for the articles. 
     Enclosure  104  may define one or more of a base, one or more sidewalls, and/or a top or a removable lid. Enclosure  104  includes an exterior surface  106  and interior surface  108 . Interior surface  108  defines an internal cavity  110 . Internal cavity  110  is size and shaped to receive one or more articles for sterilization. In some examples, internal cavity  110  may be shaped to receive one or more sterilization trays. The sterilization trays may be configured to retain the articles and reduce contact of the articles with interior surface  108  and/or sterilant, such as condensate, that may remain within internal cavity  110  after sterilization. 
     Enclosure  104  may include a rigid container, a soft pack, or a wrapped sterilization tray. Generally, enclosure  104  may include any material suitable for sterilizing and storing sterilized articles. In examples in which enclosure  104  includes a rigid container, enclosure  104  may include a rigid material, such as, for example, aluminum, stainless steel, or other metals or polymers compatible with steam, ethylene oxide, dry heat, and/or vaporized hydrogen peroxide sterilization. In examples in which enclosure  104  includes a soft pack, enclosure  104  may include a flexible material, such as, for example, a woven or nonwoven fabric, a spunbond-meltblown-spunbond material, a synthetic fabric, a natural fabric, polyethylene, polypropylene, or combinations thereof. In some examples, the flexible material may be selected to have a selected permeability to a selected sterilant, such as steam, ethylene oxide, dry heat, vaporized hydrogen peroxide, or other sterilant. In some examples, the flexible material may include a microorganism barrier layer. For example, the flexible material may be substantially impermeable to microorganisms, such as bacteria, fungi, viruses, or the like. Substantially impermeable may include impermeable or nearly impermeable in accordance with generally accepted sterilization procedure guidelines. For the purposes of this disclosure, rigid materials may include materials that are stiffer (e.g., a greater Young&#39;s modulus) relative to flexible materials. 
     At least a portion of enclosure  104  comprises a sterilant-permeable region  112 . The sterilant-permeable region  112  may include at least a region including the flexible material described above in reference to the soft pack enclosure  104 . In examples in which enclosure  104  includes a soft pack flexible material, the entirety of enclosure  104  or at least a portion of enclosure  104  may define sterilant-permeable region  112 . In examples in which enclosure  104  includes a rigid material, as illustrated in  FIG.  1   , sterilant-permeable region  112  may include a plurality of apertures  114  and a filter  116 . For example, a portion of enclosure  104 , such as a sidewall, base, or removable lid of enclosure  104 , may define a plurality of apertures  114 . Plurality of apertures  114  may be bored or otherwise mechanically formed in enclosure  104 . Filter  116  includes a sterilant-permeable, microorganism barrier material. For example, filter  116  may include the flexible material described above in reference to the soft pack enclosure  104 . In this way, during sterilization, sterilant may move from sterilization chamber  118  into internal cavity  110  through apertures  114  and filter  116 , as illustrated by dashed arrow  120 . From internal cavity  110 , the sterilant may move into sterilization indicator  102 , as illustrated by dashed arrow  121 . 
     Sterilization indicator  102  may include an article containing a sterilant exposure indicator  128  (indicator  128 ) configured to provide an indication of an exposure to a sterilant from internal cavity  110  (e.g., via dashed arrow  121 ). Sterilization indicator  102  may include a layered or laminate structure, a molded structure, or combinations thereof. For example, as illustrated in  FIG.  1   , sterilization indicator  102  may include cover layer  122  and base layer  132  adjacent to indicator  128 , and intermediate layer  130  extending between cover  122  and base  132 . In some examples, intermediate layer  130  may be integrally formed with either of cover  122  or base  132 . In some examples, sterilization indicator  102  may include cover  122  and intermediate layer  130 , optionally integrally formed with cover  122 , without base  132 . In some examples, sterilization indicator  102  may include only cover  122  configured to couple with/to exterior surface  106  of enclosure  104 , e.g., using an adhesive or the like. 
     In some examples, cover  122  may have a rectilinear shape defining an upper surface  124  and a lower surface  126  opposing surface  124  and extending in a plane substantially parallel to a plane of surface  124 . Cover  122  may include any material suitable for use in steam, ethylene oxide, dry heat, or vaporized hydrogen peroxide sterilization procedures. In some examples, cover  122  may include a metal, aluminum, anodized aluminum, stainless steel, glass, a polymeric material, polyethylene, polypropylene, polycarbonate, a polyether sulfone, a polyamide-imide, a polyamide, polytetrafluoroethylene, or combinations thereof. At least a portion of cover  122  includes a transparent or semi-transparent material configured to allow visualization of sterilant exposure indicator  128 . For example, the entirety of cover  122  may include a transparent material, or a portion, e.g., window, of cover  122  may include a transparent material. 
     In some examples, base  132  may include a rectilinear shape defining an upper surface  134  and a lower surface  136  opposing surface  134  and extending in a plane substantially parallel to a plane of surface  134 . Base  132  may include any one or more of the materials described above in reference to cover  122 . In some examples, base  132  may include any one or more of the materials described above in reference to cover  122 . In some examples, base  132  may include an adhesive layer and/or a release liner. The adhesive layer may include, for example, a pressure sensitive adhesive, a hot-melt adhesive, a structural adhesive, a thermoplastic, a thermoset polymer, an epoxy, or an adhesive suitable for use in steam, ethylene oxide, dry heat, or vaporized hydrogen peroxide sterilization procedures and selected to adhere to an external surface of a rigid container or a soft pack. In some examples, the adhesive layer may define a seal configured to form a microorganism barrier between an exterior of enclosure  104  and internal cavity  110  of enclosure  104 . The release liner may be removable, e.g., from the adhesive layer, prior to positioning sterilization indicator  102  on enclosure  104 . For example, cover  122  may be peripherally bonded to base  132  defining a release liner such that indicator  128  is disposed between the release liner and cover  122 . 
     In some examples, intermediate layer  130  may extend between cover  122  and base  132 , defining a rectilinear annulus in the plane of surface  126  and surface  134 . For example, intermediate layer  130  may define a cavity  138  configured to receive at least a portion of indicator  128 . In some examples, at least a portion of intermediate layer  130  may extend between at least a portion of cover  122  and at least a portion of indicator  128 , between at least a portion of base  132  and at least a portion of indicator  128 , or both. 
     As one example, indicator  128  may be dimensionally smaller than cover  122  and base  132 . In this way, one or more perimeter edges of both cover  122  and base  132  may extend beyond a perimeter of indicator  128 . Indicator  128  may be disposed on surface  126  of cover  122  and/or surface  134  of  132 . In some examples, indicator  128  may be disposed directly on surface  126  and/or surface  134 . In some examples, one or more additional intermediate layers may be disposed between indicator  128  and surface  126  and/or surface  134 . For example, the one or more additional intermediate layers may include an adhesive, a filter material, or a fluid. 
     By extending beyond a perimeter of indicator  128 , the one or more perimeter edges of cover  122  and base  132  may be adhered or otherwise fastened to intermediate layer  130  to substantially encapsulate indicator  128 . In some examples, intermediate layer  130  may include any one or more of the materials described above in reference to cover  122 . In some examples, intermediate layer  130  may include a sterilant impermeable layer, a microorganism barrier layer, and/or a color-enhancing layer. The color-enhancing layer may include any suitable material configured to improve visualization of a color change of at least a portion of indicator  128  in response to exposure to a sterilant during sterilization. In some examples, a color enhancing layer may be adjacent one or more of cover  122  and/or base  132 . 
     In some examples, intermediate layer  130  may define an adhesive configured to adhere cover  122  to base  132 . The adhesive may include, for example, a pressure sensitive adhesive, a hot-melt adhesive, a structural adhesive, a thermoplastic, a thermoset polymer, an epoxy, or an adhesive suitable for use in steam, ethylene oxide, dry heat, or vaporized hydrogen peroxide sterilization procedures. In some examples, at least one of cover  122  and/or base  132  may be fastened to at least a portion of intermediate layer  130  using other fastening methods, such as, for example, thermal welding, sonic welding, heat-sealing, mechanical fasteners, or other suitable fastening techniques. In some examples, substantially encapsulating indicator  128  may prevent a sterilant in sterilization chamber  118  from contacting indicator  128  without the sterilant first entering internal cavity  110  of enclosure  104 . 
     Indicator  128  may include at least one of a chemical indicator, a biological indicator, or an indicator configured to provide an indication of an exposure to a sterilant. In some examples, indicator  128  may include an Attest VH202 Tri-Metric Indicator available from 3M, St. Paul, Minn. or a 3M Comply SteriGage steam chemical integrator available from 3M, St. Paul, Minn. Although described herein as a visual indication, in some examples, the indication may include, for example, a change in an electrical signal, a change in an optical signal, or a change in physical phenomena. 
     Indicator  128 , e.g., cavity  138 , is fluidly coupled to internal cavity  110  of enclosure  104 . For example, base  132  may define one or more apertures  140  fluidly coupling cavity  138  with internal cavity  110  of enclosure  104  of sterilization package  100 . In examples in which enclosure  104  includes a soft pack, apertures  140  may allow sterilant to pass from internal cavity  110  into cavity  138  during sterilization. In examples in which enclosure  104  includes a rigid container, apertures  140  may allow sterilant to pass from internal cavity  110 , through at least a portion of filter  116  and one or more apertures of apertures  114 , into cavity  138  during sterilization. 
     In some examples, indicator  128  may be fluidly coupled to internal cavity  110  via a sample port  144 . For example, sample port  144  may define lumen  146  fluidly coupling internal cavity  110  to cavity  138 . Sample port  144  may be coupled to or extending through aperture  140 . For example, sample port  144  may extend from a proximal end coupled to aperture  140  of base  132  to a distal end configured to extend into internal cavity  110  of enclosure  104  of sterilization package  100 . In some examples, sample port  144  may include a proximal end defining a disc from which lumen  146  extends to a distal end extending into internal cavity  110 . The disc may have a diameter larger than a diameter of aperture  140 . At least a portion of base  132  adjacent to the disc may be configured to engage the disc. 
     In some examples, an external surface of at least a portion of sample port  144  may define a neck. The neck of sample port  144  may be configured to engage a locking mechanism. The locking mechanism may be configured to secure sample port  144  to enclosure  104  in a tamper-resistant manner. For example, in examples in which enclosure  104  includes a rigid container having a removable lid, sample port  144  may be positioned to extend through aperture  140 . The locking mechanism may be engaged with sample port  144  to secure sample port  144  to the lid. Once the lid is closed on the rigid container, the locking mechanism is disposed within internal cavity  110 . Hence, sample port  144  may not be disengaged without opening the rigid container. As discussed above, sterilization indicator  102  may be adhered to or otherwise fastened to sample port  144 . In this way, sample port  144  may be used to secure sterilization indicator  102  to exterior surface  106  of enclosure  104  of sterilization package  100 . 
     In some examples, sample port  144  may include a sterilant-permeable microorganism barrier disposed within lumen  146 . The sterilant-permeable microorganism barrier may be configured to allow sterilant to pass from internal cavity  110  to cavity  138  and prevent microorganisms from passing from cavity  138  into internal cavity  110 . The sterilant-permeable microorganism barrier may include, for example, one or more of the flexible materials describe above in reference to the soft pack enclosure  104 . In this way, the sterilant-permeable microorganism barrier may reduce potential contamination of internal cavity  110  from sterilization indicator  102 . 
     In some examples, the distal end of sample port  144  may define an incisive tip configured to puncture enclosure  104 . For example, the incisive distal end of sample port  144  may be configured to puncture exterior surface  106  of a soft pack enclosure  104 . Forming sample port  144  to define an incisive tip may enable, after wrapping articles in a soft pack enclosure  104 , sterilization indicator  102  to be affixed to enclosure  104  by puncturing enclosure  104  with sample port  144  and adhering base  132  to exterior surface  106  of enclosure  104 . 
     In some examples, sterilization indicator  102  may include a seal  142  configured to form a sterilant barrier and/or microorganism barrier between an exterior of sterilization indicator  102  and cavity  110  of sterilization package  100  and/or cavity  138  of sterilization indicator  102 . The exterior of sterilization indicator  102  may include, for example, any one or more of surface  124  of cover  122 , surface  134  of base  132 , or another surface of cover  122 , intermediate layer  130 , and/or base  132  exterior to cavity  138 . In some examples, seal  142  may be disposed on a surface of cover  122  or base  132 . Seal  142  may extend at least around a perimeter of aperture  140 , such as a perimeter of cover  122  and/or base  132 . In examples in which cover  122  is integrally formed with intermediate layer  130 , seal  142  may be disposed on a lower surface (e.g., surface  126 ) of cover  122  such that at least a portion of the edges of cover  122  are configured to couple with exterior surface  106  of enclosure  104  of sterilization package  100 . In examples in which the proximal end of sample port  144  defines a disc, seal  142  may be disposed on the disc, e.g., between the disc and exterior surface  106  of enclosure  104 . 
     Seal  142  may include any suitable material configured to form a sterilant barrier and/or microorganism barrier between an exterior of sterilization indicator  102  and cavity  110  of sterilization package  100  and/or cavity  138  of sterilization indicator  102 . For example, seal  142  may include a pressure sensitive adhesive, an elastomeric material, silicone, polytetrafluoroethylene, nitrile, neoprene, ethylene propylene diene monomer rubber, fluorocarbon, or combinations thereof. 
     In some examples, sterilization indicator  102  may include a process challenge or be part of a process challenge device. The process may be configured to resist passage of a sterilant from internal cavity  110  to cavity  138  during sterilization. The process challenge may include, for example, a channel fluidly coupling internal cavity  110  to cavity  138 . The channel may define a tortuous path that, relative to a substantially straight lumen or a non-tortuous lumen, may slow movement of the sterilant, thereby limiting exposure of indicator  128  to the sterilant. In some examples, the process challenge may be configured to represent a path of travel of sterilant through one or more lumens of a medical device. In some examples, lumen  146  of sample port  144  may define the process challenge. 
       FIGS.  2 A- 2 C  are conceptual diagrams illustrating several views of an example sterilization indicator  202 . Sterilization indicator  202  may be the same as or substantially similar to sterilization indicator  102  described above in reference to  FIG.  1   , except for the differences described herein. 
     Sterilization indicator  202  includes a cover  222 , an indicator  228 , an intermediate layer  230 , and a base  232 . As discussed above in reference to  FIG.  1   , cover  222  and base  232  extend in substantially parallel planes. At least one of cover  222  or base  232  may be integrally formed with, adhered to, or otherwise fastened to at least a portion of intermediate layer  230  to define a cavity  238  that is configured to receive indicator  228 . 
     In some examples, indicator  228  may be adhered to or otherwise fastened to a surface of cover  222  or a surface of base  232  ( FIG.  2 C ). In some examples, indicator  228  may include a coating applied to a surface of cover  222  or a surface of base  232 . In some examples, indicator  228  may be removable or replaceable. For example, as illustrated in  FIG.  2 B , cover  222  may be removable. After removing cover  222 , indicator  228 , which may include a spent indicator having been exposed to a sterilant, may be replaced with a fresh indicator that has not been exposed to a sterilant. In this way, sterilization indicator  202  may define a housing and a replaceable indicator. By enabling replacement of indicator  228 , indicator  202  may reduce operating costs for a Sterile Processing Department compared to using sterilization indicators without replaceable indicators. 
     Although not illustrated in  FIGS.  2 A- 2 C , in examples in which cover  222  is removable, cover  222  may be fixable to base  232  and/or intermediate layer  230  by one or more hinges, clips, or other mechanical fasteners. Additionally, or alternatively, sterilization indicator  202  may include one or more seals between cover  222  and base  232  and/or intermediate layer  230 . The one or more seals may be substantially the same as or similar to seal  142  described above in reference to  FIG.  1   . 
     In some examples, base  232  may include an adhesive bottom layer (e.g., opposing the surface of base  232  that is adjacent to intermediate layer  230  and indicator  228 ). The adhesive layer of base  232  may be configured to adhere to a sterilization package (e.g., exterior surface  106  of enclosure  104 ). For example, the adhesive layer may include a pressure sensitive adhesive, a hot-melt adhesive, a structural adhesive, a thermoplastic, a thermoset polymer, an epoxy, or an adhesive suitable for use in steam, ethylene oxide, dry heat, or vaporized hydrogen peroxide sterilization procedures and selected to adhere to an external surface of a sterilization package. 
     In examples in which the sterilization package includes a soft pack, the adhesive may be selected to migrate into the flexible material of the soft pack during the sterilization process. Migrating may include a first portion of the adhesive remaining adhered to base  232  and an exterior surface of the soft pack and a second portion of the adhesive moving through the flexible material (e.g., between fibers of the flexible material) toward an interior surface of the soft pack. In this way, the adhesive may form a more sterilant-impermeable barrier and a more microorganism-impermeable barrier (e.g., between an exterior of the soft pack and an interior of the soft pack) compared to sterilization indicator  202  including an adhesive that does not migrate into the flexible material of the soft pack during the sterilization process. Additionally, or alternatively, the adhesive may prevent, or at least reduce an amount of, sterilant from traversing only the flexible material of the soft pack to enter cavity  238 . That is, the adhesive may force sterilant entry into cavity  238  via aperture  240  of base  232  from an interior cavity of the soft pack. 
       FIGS.  3 A and  3 B  are conceptual diagrams illustrating perspective views of an example process challenge device  300  containing a sterilization indicator  302  including a process challenge  350 . Sterilization indicator  302  may be the same as or substantially similar to sterilization indicator  102  and/or  202  described above in reference to  FIGS.  1 - 2 C , respectively, except for the differences described herein. Process challenge  350  is configured to restrict the flow of a sterilant to indicator  328  using a tortuous path from aperture  340  of base  332  to cavity  338 . The tortuous path may be configured to represent a path of sterilant through one or more lumens of a medical device. For example, endoscopes often include a long, narrow channel through which the sterilant must pass in order to expose all surfaces to the sterilant for a time sufficient to cause sterilization. The tortuous path of process challenge  350  may be configured to represent a path of sterilant through the long, narrow channel of the endoscope. 
     In some examples, process challenge  350  may be integrally formed with one or more components of process challenge device  300 , such as sterilization indicator  302 . For example, process challenge device sterilization indicator  302  includes a cover  322 , a first intermediate layer  330  adjacent cover  322 , a second intermediate layer  331 , and a base  332  adjacent second intermediate layer  331 . At least one of cover  322 , first intermediate layer  330 , a second intermediate layer  331 , or a base  332  may define a cavity  352  that includes a tortuous path from aperture  340  of base  332  to cavity  338 . In some examples, cavity  352  may be formed in at least one of cover  322 , first intermediate layer  330 , a second intermediate layer  331 , or a base  332  by milling, laser etching, lithography, or subtractive manufacturing techniques suitable for use with the materials of process challenge device  300  and resolution required for cavity  352 . In other examples, process challenge  350  may be separately formed from, and attachable to, process challenge device  300 . For example, process challenge  350  may be adhered to or otherwise mechanically coupled to sterilization indicator  302  to fluidly coupled aperture  340  to an internal cavity of an enclosure. 
     As illustrated in  FIGS.  3 A and  3 B , second intermediate layer  331  may define cavity  352 , whereas first intermediate layer  330 , together with cover  322  and second intermediate layer  331 , may define cavity  338 . The tortuous path of cavity  352  may include any suitable shape. For example, a shape of the tortuous path may include a serpentine shape, one or more necks or narrowed portions, or zigzags. Cavity  352  may extend entirely within a plane defined by cover  322 , first intermediate layer  330 , a second intermediate layer  331 , or a base  332 , or may extend between two or more of cover  322 , first intermediate layer  330 , a second intermediate layer  331 , or a base  332 . 
     In some examples, the process challenge  350  may include a heat-transfer modulating body adjacent indicator  328 . The heat-transfer modulating body may be configured to slow a rate at which indicator  328  comes to the temperature of a given sterilization process. The heat-transfer modulating body may be integrally formed with at least a portion of process challenge device  300 , e.g., base  332 , or a separate component that can be included with process challenge device  300  or added or removed from process challenge device  300 . In some examples, at least a portion of the heat-transfer modulating body may surround at least a portion of indicator  328 . In some examples, the heat-transfer modulating body may increase the time required for the sterilant to contact the indicator sufficiently to bring about an indication that sterilization conditions have been achieved, at least with respect to a temperature of the sterilization conditions. 
     In some examples, process challenge  350  and/or cavity  338  may include a selected volume of gas, for example, air, nitrogen, carbon dioxide, or another inert gas. The volume of gas contained within process challenge  350  and/or cavity  338  may provide a resistance to the sterilant to contribute, at least in part, to an operation of process challenge  350 . The resistance may correlate with sterilization of a variety of products and articles and quantities thereof. In some examples, displacement of the gas may enable the sterilant to fill cavity  338  and contact indicator  328 . 
     In some examples, process challenge device  300  may include a port in fluid communication with the internal cavity of the enclosure, such that condensate can exit out of cavity  338  through the port. Additionally, or alternatively, process challenge device  300  may include an absorbent material within cavity  338 , e.g., adjacent indicator  328 . The absorbent material may be configured to absorb condensate. Reducing the amount of condensate, when present, that may contact indicator  328  may increase the reproducibility of an indication by indicator  328  that sterilizing conditions have or have not been achieved. 
       FIG.  4    is a conceptual diagram illustrating an example sterilization package  400  that includes a sterilization indicator  402  positioned on an exterior surface of an enclosure  104 . Sterilization indicator  402  may be the same as or substantially similar to sterilization indicators  102 ,  202 ,  302 , and/or process challenge device  300  described above in reference to  FIGS.  1 - 3 B , respectively, except for the differences described herein. 
     Enclosure  404  defines an internal cavity  410 . Sterilization indicator  402  includes cover  422  and base  432  adjacent to indicator  428 , and intermediate layer  430  extending between cover  422  and base  432 . Intermediate layer  430  may define a cavity  438  configured to receive at least a portion of indicator  428 . Indicator  428 , e.g., cavity  438 , may be fluidly coupled to internal cavity  410  via lumen  446  defined by sample port  444  and aperture  440  defined by base  432 . Sample port  444  may be tapered. During sterilization, sterilant may move from the sterilization chamber into internal cavity  410  as illustrated by dashed arrow  420 . From internal cavity  410 , the sterilant may move into sterilization indicator  402 . 
       FIG.  5    is a conceptual diagram illustrating a perspective view of an example sterilization indicator  502 . Sterilization indicator  502  may be the same as or substantially similar to sterilization indicators  102 ,  202 ,  302 ,  402 , and/or process challenge device  300 , described above in reference to  FIGS.  1 - 4   , respectively, except for the differences described herein. 
     Sterilization indicator  502  includes a cover  522 , an indicator  528 , and a base  532 . In some examples, sterilization indicator  502  may include an intermediate layer, as discussed above. At least one of cover  522  or base  532  may define a cavity  538  that is configured to receive indicator  528 . Cover  522  may be movable between a closed position and, as illustrated in  FIG.  5   , an opened position that allows removal of indicator  528 . For example, after opening cover  522 , indicator  528 , which may include a spent indicator having been exposed to a sterilant, may be replaced with a fresh indicator that has not been exposed to a sterilant. By enabling replacement of indicator  528 , sterilization indicator  502  may be fixed to a sterilization package. 
     In some examples, sample port  544  may include a proximal end  547  defining a disc  545  from which lumen  546  extends to a distal end  549  extending into internal cavity  110 . The disc may have a diameter larger than a diameter of aperture  540 . At least a portion of base  532  adjacent to the disc may be configured to engage disc  545 . 
       FIGS.  6 A and  6 B  are conceptual diagrams illustrating perspective views of an example sterilization indicator  602 . Sterilization indicator  602  may be the same as or substantially similar to sterilization indicators  102 ,  202 ,  302 ,  402 ,  502 , and/or process challenge device  300 , described above in reference to  FIGS.  1 - 5   , respectively, except for the differences described herein. 
     Sterilization indicator  602  defines aperture  640  and cavity  638 . As illustrated in  FIG.  6 B , aperture  640  is configured to fluidly couple cavity  638  to an internal cavity of enclosure  604  of sterilization package  600 . For example, a shape and size of aperture  640  may be selected to be the same as or substantially similar to a shape and size of a lumen of a sample port and/or positionable over one or more of apertures  614  defined by enclosure  604 . Cavity  638  is configured to receive indicator  628 . As discussed above, sterilization indicator  602  may include a multi-layer laminate structure including a plurality of polymeric films housing indicator  628  in cavity  638  into which sterilant can be passed only through a sample port via aperture  640 . 
       FIG.  7    is a conceptual diagram illustrating a plan view of a portion of an example sterilization package  700  including a sterilization indicator  702 . Sterilization indicator  702  may be the same as or substantially similar to sterilization indicators  102 ,  202 ,  302 ,  402 ,  502 ,  602 , and/or process challenge device  300 , described above in reference to  FIGS.  1 - 6 B , respectively, except for the differences described herein. 
     For example, sterilization package  700  includes an enclosure  704  defining a plurality of apertures  714 . Sterilization indicator  702  is positioned on enclosure  704 . Sterilization indicator  702  includes two layers of flexible polymeric film. Perimeter edges of the two layers of the flexible polymeric film may be sealed together, e.g., as discussed above, to form a clamshell construction. The clamshell construction may define cavity  738 , which is configured to receive indicator  728 . Aperture  740  is configured to fluidly couple cavity  738  to an internal cavity of enclosure  704 . In some examples, the clamshell construction of sterilization indicator  702  may be less expensive and/or less time consuming to manufacture compared to other sterilization indicators, such as a sterilization indicator having a laminate structure. 
       FIGS.  8 A through  8 E  are conceptual diagrams illustrating example components of a sterilization package  800 . Sterilization package  800  may be the same as or substantially similar to sterilization packages  100 ,  400 ,  600 , and/or  700 , except for the differences described herein. For example, sterilization package  800  may include one or more components of sterilization indicators  102 ,  202 ,  302 ,  402 ,  502 ,  602 ,  702 , and/or process challenge device  300  sterilization indicators. 
     As illustrated in  FIG.  8 A , sample port  844  includes an elongate tube  843  and a disc  845 . Sample port  844  extends from a proximal end  847  to a distal end  849 . Proximal end  847  includes disc  845  from which elongate tube  843  extends to distal end  849 . 
     Elongate tube  843  defines lumen  846  and neck  851 . Lumen  846  is configured to extend into an internal cavity of enclosure  804  of sterilization package  800 . Neck  851  is configured to engage a locking mechanism  860 , as illustrated in  FIG.  8 B . 
     In some examples, locking mechanism  860  may include a frame  862 . As illustrated in  FIG.  8 C , frame  862  may be configured to secure a sterilant-permeable, microorganism barrier  870  (filter  870 ) to a portion of enclosure  804 . For example, frame  862  when engaged with an interior surface of enclosure  804  may secure filter  870  to sterilant-permeable region  812  of enclosure  804  defining apertures  814  ( FIG.  8 E ). In this way, frame  862  may enable enclosure  804  to define one or more sterilant-permeable and microorganism-impermeable pathways from an exterior to an interior of enclosure  804 . 
     As illustrated in  FIG.  8 B , locking mechanism  860  may define an aperture  864 . Aperture  864  is configured to receive at least a portion of elongate tube  843  of sample port  844  therethrough. For example, elongate tube  843  may be passed through aperture  864  until neck  851  engages locking member  866  of locking mechanism  860 . In some examples, locking member  866  may include one or more protrusions shaped to fit within neck  851 . Locking mechanism  860  may include one or more springs coupled to locking members  866 . The one or more springs may be configured to urge locking members toward a locked configuration. For example, the locked configuration may include a position of locking members  866  that engage neck  851  of sample port  844 . In some examples, locking mechanism may include one or more levers  868  mechanically coupled to respective locking members  866 . Levers  868  may be configured to move locking members  866  from a locked configuration to an open configuration. The open configuration may include a position of locking members  866  that allow elongate tube  843  to pass through aperture  864 . For example, as illustrated in  FIG.  8 D , levers  868  may be manipulated to allow elongate tube  843  to be inserted into aperture  864  of locking mechanism  860  and/or to disengage locking members  866  from neck  841 . 
     In some examples, disc  845  may define a recess configured to receive a seal, such as o-ring seal  853 . Seal  853  may be configured to, when engaged with enclosure  804 , such as by a locking mechanism  860 , provide a sterilant barrier and/or microorganism barrier between an exterior and an interior of enclosure  804 . In some examples, locking mechanism  860  may be configured to engage neck  851  when o-ring seal  853  is compressed a sufficient amount to form the sterilant barrier and/or microorganism barrier. 
       FIG.  8 E  is a plan view of sterilant-permeable region  812  of enclosure  804  that defines apertures  814  and disc  845  of sample port  844  engaged, as discussed above, with an exterior surface of enclosure  804 . In this way, locking mechanism  860 , elongate tube  843 , and seal  853  enable a sterilant to travel from an interior of enclosure  804  into a sterilization indicator and reduce or prevent sterilant from traveling into the interior of enclosure  804  from a point external to enclosure  804 . Additionally, or alternatively, by positioning locking mechanism  860  within an interior of enclosure  804 , sample port  844  and microorganism barrier  870  may be disengaged only once a lid of enclosure  804  is removed, such as, for example, during instrument set-up for a surgical operation. 
     As discussed above, in some examples, a sterilization indicator may be adhered to a surface of a soft pack sterilization package.  FIG.  9    is a conceptual diagram illustrating a perspective view of a soft pack sterilization package  900  including a plurality of sterilization indicators  902 A and  902 B (collectively, sterilization indicators  902 ) adhered to enclosure  904  of sterilization package  900 . Sterilization package  900  may be the same as or substantially similar to sterilization packages  100 ,  400 ,  600 ,  700 , and/or  800 , except for the differences described herein. For example, sterilization package  900  may include one or more components of sterilization indicators  102 ,  202 ,  302 ,  402 ,  502 ,  602 ,  702 ,  802 , and/or process challenge device  300 . 
     Enclosure  904  includes folded flexible material taped at seams to define an interior cavity  910 . As discussed above, enclosure  904  may define a sterilant-permeable microorganism barrier between interior cavity  910  and sterilization chamber  918  (e.g., external to enclosure  904 ). Sterilization indicators  902  are configured to adhere to an exterior surface  906  of enclosure  904 . For example, as illustrated in the cross-section, sterilization indicators include a cover  922  and base  932  configured to retain indicator  928 . Base  932  includes an adhesive layer  933  on a surface of base  932  adjacent to enclosure  904 . Adhesive  933  may be configured to migrate at least partially through flexible material of enclosure  904 . For example, adhesive layer  933  may be configured to migrate into flexible material of enclosure  904  when exposed to heat, moisture, or pressure. At least a first portion of adhesive layer  933  may remain adhered to base  932  and exterior surface  906  of enclosure  904 . At least a second portion of adhesive layer  933  may migrate into the flexible material (e.g., between fibers of the flexible material) toward interior surface  908  of enclosure  904 . In this way, adhesive layer  933  may be configured to form a more sterilant-impermeable barrier and a more microorganism-impermeable barrier (e.g., between an exterior  918  of enclosure  904  and interior cavity  910 ) compared to sterilization indicator  902  including an adhesive that does not migrate into the flexible material of enclosure  904  before or during the sterilization process. Additionally, or alternatively, the adhesive may prevent, or at least reduce an amount of, sterilant from traversing only the flexible material of enclosure  904  to contact indicator  928  without first entering cavity  910 . 
       FIG.  10    is a flow diagram illustrating an example technique of forming a sterilization indicator. Although the technique illustrated in  FIG.  10    will be described in reference to sterilization indicator  102  described in reference to  FIG.  1   , the technique may be used to form other sterilization indicators, such as any one or more of sterilization indicator  202 ,  302 ,  402 ,  502 ,  602 ,  702 ,  802 ,  902 , and/or process challenge device  300 . 
     The technique illustrated in  FIG.  10    includes forming a cover  122  defining at least a portion of a cavity  138  ( 1002 ). In some examples, sterilization indicator  102  may include a laminate structure, including, for example, cover  122 , intermediate layer  130 , and base  132 . In examples in which the sterilization indicator includes a laminate structure, forming cover  122  may include laminating base  132  to cover  122 , or laminating one or more intermediate layers  130  to cover  122  and laminating base  132  to the one or more intermediate layers  130 . As used herein, laminating may include fixing at least a portion of two or more layers by adhering, ultrasonic welding, thermal welding, or other suitable fastening technique. 
     In some examples, forming cover  122  may include molding cover  122 . For example, molding may include injection molding, vacuum forming, or other molding process to produce a selected shape of cover  122 . For example, molding cover  122  may include molding cover  122  to define at least a portion of cavity  138 . In some examples, forming cover  122  may include molding one or more of intermediate layer  130  and base layer  132 . 
     In some examples, forming cover  122  may include removing material from cover  122 . Removing material from cover  122  may include, for example, milling, laser etching, chemical etching, or other substantive manufacturing technique. For example, forming cover  122  may include machining at least a portion of cover  122  to form at least a portion of cavity  138 . In some examples, forming cover  122  may include laser etching at least a portion of cover  122 , intermediate layer  130 , and/or base  132  to form one or more process challenges (e.g., process challenge  350 ). In some examples, forming cover  122  may include removing material from intermediate layer  130 , e.g., to define cavity  138 , and/or removing material from base  132 , e.g., to define aperture  140 . 
     The technique illustrated in  FIG.  10    may include positioning indicator  128  within cavity  138  ( 1004 ). Positioning indicator  128  may include positioning indicator  128  into cavity  138 , or into a location of cavity  138 , before or after forming cover  122  and/or cavity  138 . In some examples, positioning indicator  128  within cavity  138  may include placing indicator  128  into cavity  138 , or into a location of cavity  138 , without adhering or otherwise fixing indicator  128  within cavity  138 . In some examples, positioning indicator  128  within cavity  138  may include removing cover  122 , positioning indicator  128  within cavity  138 , and replacing cover  122 . In some examples, positioning indicator  128  within cavity  138  may include adhering indicator  128  to surface  126  of cover  122 , surface  134  of base  132 , or a surface of intermediate layer  130 . In examples in which indicator  128  includes a coating, positioning indicator  128  may include coating surface  126  of cover  122 , surface  134  of base  132 , or a surface of intermediate layer  130 . As used herein, coating to position indicator  128  may include any suitable coating process, such as, for example, spray coating, brush application, ink jet printing, or other additive manufacturing process. 
     The technique illustrated in  FIG.  10    may include disposing seal  142  adjacent the cover ( 1006 ). Disposing seal  142  may include disposing an adhesive or an elastomeric material on a surface of one or more of cover  122 , intermediate layer  130 , or base  132 . In some examples, disposing seal  142  may include disposing an adhesive or an elastomeric material on a surface of sample port  144 . 
     In some examples, the technique may include forming sample port  144 . Forming sample port  144  may include any suitable additive manufacturing process, e.g., three dimensional printing, and/or subtractive manufacturing process, e.g., milling or machining, to form sample port  144 . In some examples, forming sample port  144  may include positioning seal  142  on at least a portion of sample port  144 . In some examples, forming sample port  144  may include positioning a sterilant-permeable, microorganism barrier within lumen  146  of sample port  144 . In examples in which sample port  144  includes an incisive distal end, forming sample port  144  may include removing material to define the incisive distal end. In examples in which sample port  144  includes a proximal disc (e.g., disc  845 ) and elongate tube (e.g., elongate tube  843 ), disc  845  may be integrally formed with elongate tube  843 , or separately formed and subsequently fixed, e.g., using an adhesive, welding, or the like. In examples in which sample port  144  includes a neck (e.g., neck  851 ), forming sample port  144  may include forming neck  841  by, for example, removing material from elongate tube  843 . 
     In some examples, the technique also may include forming enclosure  104  including at least one sterilant-permeable region  112 . In some examples, the technique also may include positioning sterilization indicator  102  on at least a portion of the sterilant-permeable region  112 . In examples in which enclosure  104  includes a soft pack, positioning sterilization indicator  102  on enclosure  104  may include adhering sterilization indicator  102  to exterior surface  106  of enclosure  104 . In examples in which sterilization indicator  102  includes an incisive distal end, positioning sterilization indicator  102  may include piercing, with the incisive distal end, enclosure  104 . In examples in which enclosure  104  includes a rigid container, positioning sterilization indicator  102  may include extending at least a portion of sample port  144  through aperture  140  of enclosure and, in some examples, engaging neck  851  with a locking mechanism (e.g., locking mechanism  860 ) to secure sample port  144  to enclosure  104 . 
       FIG.  11    is a flow diagram illustrating an example technique of using a sterilization indicator. Although the technique illustrated in  FIG.  11    will be described in reference to sterilization package  100  described in reference to  FIG.  1   , the technique may be used with other sterilization packages and sterilization indicators, such as, any one or more of sterilization indicator  202 ,  302 ,  402 ,  502 ,  602 ,  702 ,  802 ,  902 , and/or process challenge device  300 . 
     The technique illustrated in  FIG.  11    includes positioning sterilization indicator  102  on exterior surface  106  of enclosure  104  ( 1102 ). At least a portion of exterior surface  106  includes sterilant-permeable region  112 . In examples in which enclosure  104  includes a soft pack, positioning sterilization indicator  102  on enclosure  104  may include adhering sterilization indicator  102  to exterior surface  106  of enclosure  104 . In examples in which sterilization indicator  102  includes an incisive distal end, positioning sterilization indicator  102  may include piercing, with the incisive distal end, enclosure  104 . In examples in which enclosure  104  includes a rigid container, positioning sterilization indicator  102  may include extending at least a portion of sample port  144  through aperture  140  of enclosure and, in some examples, engaging neck  851  with a locking mechanism (e.g., locking mechanism  860 ) to secure sample port  144  to enclosure  104 . 
     The technique illustrated in  FIG.  11    includes exposing sterilization indicator  102  and enclosure  104  to a sterilant at least one of for a selected duration of time, at a selected temperature, or at a selected sterilant concentration ( 1104 ). In some examples, exposing sterilization indicator  102  to the sterilant may include using a vacuum to remove air from sterilization chamber  118 . Exposing sterilization indicator  102  to the sterilant includes introducing the sterilant into cavity  110 , e.g., as illustrated by arrow  120 , such that sterilant travels into cavity  138  via lumen  146 , e.g., as illustrated by arrow  121 . In some examples, at least one of the selected duration of time, the selected temperature, or the selected sterilant concentration may be based, at least in part, on one or more of the type or types of articles to be sterilized, common sterilization practices, the type of enclosure  104  (e.g., rigid container or soft pack), the type of sterilant, or the like. 
     The technique illustrated in  FIG.  11    includes determining, by indicator  128 , whether internal cavity  110  of enclosure  104  was exposed to at least one of a threshold exposure duration, a threshold sterilant temperature, or a threshold sterilant concentration ( 1106 ). In some examples, determining the exposure of indicator  128  may include comparing a color change of indicator  128  to a legend or a key. For example, a threshold color change of indicator  128  may indicate at least one of the threshold exposure duration, the threshold sterilant temperature, or the threshold sterilant concentration. In some examples, the indication may include, for example, a change in an electrical signal, a change in an optical signal, or a change in physical phenomena. In this way, determining the exposure of indicator  128  may include determining, by processing circuitry coupled to indicator  128 , based on a change in an electrical signal or an optical signal, whether internal cavity  110  of enclosure  104  was exposed to at least one of a threshold exposure duration, a threshold sterilant temperature, or a threshold sterilant concentration. 
     Various embodiments of the invention have been described. These and other embodiments are within the scope of the following claims.