Abstract:
The present invention is directed to a two-ply absorbent liner for use in a sterilization process and, more particularly, to an absorbent liner having a foam layer and a paper layer for cushioning sterilization trays and surgical instruments in a sterilization pack and providing advantageous moisture absorption functionality during and after completion of a sterilization process. The absorbent liner functions advantageously with steam or ethylene oxide gas as the sterilization agent. The absorbent liner is fabricated from a foam material, preferably a hydrophilic polymeric foam material, e.g., a hydrophilic polyurethane foam flame laminated to paper, preferably medical grade paper. The disclosed liner may be advantageously utilized in sterilizing surgical instruments and in conjunction with sterilizing trays such that potential residual moisture is eliminated from the surface of the instruments or trays and metal surfaces are cushioned.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to liners such as tray liners for use in a sterilization process, and more particularly to an absorbent two-ply liner providing an advantageous moisture absorption functionality during and after completion of a sterilization process. The liner may be used as a base pad, a tray corner guard, or for cushioning of surgical instruments during and after the sterilization process. 
       BACKGROUND OF THE INVENTION 
       [0002]    As is well known, surgical instruments used in the healthcare industry must be sterilized before and/or after each use. Sterilization, of course, frees instruments from microorganism contamination, to prevent infections and the spread of diseases among patients. All medical procedures rely upon a stringent program of sterilization. 
         [0003]    The medical device industry has addressed the sterilization requirements in the surgical field by offering two general types of surgical instruments: reusable instruments and single use, or disposable, instruments. Reusable instruments are typically composed of stainless steel and are typically sterilized before their initial use and then cleaned and resterilized prior to each subsequent use thereof. Single use or disposable instruments, on the other hand, are often fabricated primarily from plastic materials, thereby reducing costs associated with manufacture, and are discarded after use in a single procedure. 
         [0004]    With respect to reusable surgical instruments, e.g., forceps, graspers, dissectors, probes, hemostats, scissors and the like, sterilization and resterilization had historically been accomplished using various sterilization modalities. In a broad sense, these sterilization processes generally involve placing instruments to be sterilized in a tray, wrapping the instruments and the tray with a sterilization wrap, and placing the wrapped tray and instruments in a sterilization chamber, where the instruments are exposed to a sterilization medium. In order to protect the instruments, a tray liner is typically placed on the tray, and then the surgical instruments are placed on the tray liner. In order to protect the tray itself, the tray is typically placed on corner guards or a base pad before it is wrapped and placed in the sterilization chamber. 
         [0005]    One long and continuing problem encountered with sterilization, however, is the presence of moisture that remains on the sterilized instruments, i.e., within the sterile wrap, at the conclusion of the sterilization process. This residual moisture can range from slight levels of dampness to visible droplets on the surface of surgical instruments. Such residual moisture is both undesirable and is unacceptable because such moisture could permit migration of surface microorganisms, thereby penetrating the wrapped tray or basin and rendering its contents contaminated, and/or may cause rust or pitting of the surgical instruments. Also, the wrapped tray may become stained during sterilization or even torn during loading or removal from a sterilization chamber because of the damp condition of the sterilization wrap. 
         [0006]    Tray liners formed of a single material, such as open or closed cell foam or a cellulose based material have been employed in the past. For example, a hydrophilic polyurethane foam trayliner is disclosed in U.S. Pat. No. 6,902,712, incorporated herein by reference. This tray liner is comprised of a single foam layer. While effective, the evaporation rate and dispersing properties of foam liners could be improved to allow for more efficient moisture absorption and multiple applications within in a sterilization system. 
         [0007]    Two-ply liners comprised of foam backing are known in the art. Typically a foam layer is adhered to plastic or cloth. However, use of adhesive to join liners used for sterilization presents several problems. The adhesive may deteriorate when exposed to high heat, steam and/or various chemicals used in the sterilization process. The liners may delaminate or adhesive may come in contact with the sterile instruments or sterilizing equipment. The adhesive residue is often sticky and difficult to eliminate. 
         [0008]    In addition, laminated paper products which contain at least one layer of paper bonded to a foam layer have also been known for some time. See e.g. U.S. Pat. Nos. 3,687,797; 3,285,800; 3,530,030; 3,366,532. However, these multi-layered products are also adhered together with an adhesive or thermally fused with hot rollers. U.S. Pat. No. 4,276,339 discloses a more efficient lamination process via a gelling process; however it does not allow the paper and foam to be separately purchased. 
         [0009]    A two-ply liner comprised of foam and paper joined by flame lamination has never been taught for the purpose moisture trapping, and more specifically for use in sterilization of surgical instruments. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention is intended to obviate many of the problems associated with moisture remaining on or in the trays after a sterilization process. Rather than employing a tray liner formed of a single material, such as open or closed cell foam or a cellulose based material, as has been done in the past, the present invention employs a two-ply construction to provide padding as well as absorption. More specifically, the present invention combines the cushioning properties of foam with the absorbent properties of medical grade paper in order to protect delicate instruments from impact damage as well as preventing the adverse effects of moisture, and also to trap moisture and provide protection when used as a base pad or corner guard. 
         [0011]    As exemplified in the Figures and described in detail herein, when used as a tray liner, it has been found that positioning the inventive material with the foam layer adjacent to instruments, such that the instruments are in contact with the foam layer, provides excellent results. The instruments are well-protected and the moisture is retained in the paper layer, away from the instruments, where it spreads out through the paper in order to increase the surface area of the moisture and also thereby increase the rate of evaporation. 
         [0012]    When used as a base pad or corner guard, it has been found that positioning the inventive material with the paper layer adjacent to the tray, such that the tray is in contact with the paper layer, provides excellent results. The tray is well-protected, and the moisture is trapped in the paper layer before it reaches the sterile wrap. Also again, the moisture spreads out through the paper in order to increase the surface area of the moisture and also thereby increase the rate of evaporation. 
         [0013]    The inventive material may employ any of numerous types of foam material, although polyester polyurethane foam has exhibited excellent results. The inventive material may also employ any of numerous types of medical grade paper, as well. 
         [0014]    The foam layer and the paper layer are joined together using a flame lamination technique. As is known, such a technique involves passing the foam layer through an open flame, thereby creating a thin layer of hot polymer. The hot polymer is then used as an adhesive to bond the foam layer to the paper layer to create the inventive material. By employing this method, excellent results are achieved without the need for a separate adhesive, the use of which may have its own disadvantages. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    So that those having ordinary skill in the art to which the disclosed liner and associated methods pertain will more readily understand how to employ and use the same, reference may be had to the drawings wherein: 
           [0016]      FIG. 1 . is a perspective view of a two-ply liner according to the present invention; 
           [0017]      FIG. 2  depicts a perspective view of a sterilization system having various placements of an absorbent two-ply liner of the invention; 
           [0018]      FIG. 3  is a perspective view of a tray liner according to the present invention, lying beneath surgical instruments; 
           [0019]      FIG. 4  is a perspective view of a two-ply liner according to the present invention, lying beneath surgical instruments and lying below a sterilization tray; 
           [0020]      FIG. 5  is an alternate perspective view of tray liners according to the present invention; 
           [0021]      FIG. 6  is a perspective view of a corner guard according to the present invention; 
           [0022]      FIG. 7  is a perspective view of a corner guard according to the present invention positioned on the sterilization tray of  FIG. 4 ; 
           [0023]      FIG. 8  is top-down view of a cross section of a corner guard according to the present invention positioned on the sterilization tray of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    Referring to  FIGS. 1 and 5 , a two-ply liner of the present invention is illustrated. In particular, an absorbent liner  16  is provided for introduction into a sterilizing system in connection with the sterilizing process. Liner  16  is composed of two layers  11  and  12 . A paper layer  11  is composed of any type of paper that will allow moisture to be absorbed and dissipate. However, medical grade paper is preferred for use in sterilization systems. A foam layer  12  is preferably fabricated from hydrophilic polyurethane foam that is adapted for use in sterilization processes that utilize steam or ethylene oxide as the sterilizing agent. 
         [0025]    The foam layer  12  is joined to the paper layer  11  at interface  14  through flame lamination. Flame lamination overcomes problems of the adhesives of the prior art. First, flame lamination does not have a tendency to delaminate when exposed to high temperatures, such as those used in the sterilization process. Flame lamination also prevents adhesive from leaking onto or contacting a tray or sterile instruments and consequently leaving an undesirable residue. 
         [0026]    As shown, absorbent liner  16  is of rectangular configuration; however, alternative geometries are contemplated, e.g., as may be appropriate for specific sterilization tray configurations. Absorbent tray liners  16  may be dimensioned depending upon the application. Preferred absorbent liners  16  measure 9 to 15 inches in width and 0.1 inches to 1 inch in thickness. More preferred absorbent liners  16  measure 9, 12 or 15 inches in width, and are approximately ⅛ inch in thickness. Tray liner  16  preferred for use in separating basins measures 3×24 inches and may also be ⅛ inch in thickness. 
         [0027]    The liner  16  may also be supplied in roll form as depicted in  FIG. 5 . When provided as a continuous roll, a length of 35 to 40 feet is preferred. 
         [0028]    The liner  16  may, optionally, contain perforations  13 . Latitudinal perforations  13   a  and longitudinal perforations  13   b  may be provided. The latitudinal perforations  13   a  allow the liner  16  to sit flatly on a surface since it has a tendency to curl. Moreover, the latitudinal perforations  13   a  allow the liner to be torn off a continuous roll, as depicted in  FIG. 5 . The latitudinal perforations  13   a  may be placed at any suitable interval so that the length of the liner can be chosen to accommodate sterilization trays of different sizes. Preferably the perforations  13  are about 2 to 3 inches apart. Most preferably, the latitudinal perforations  13   a  are spaced about 2 inches apart. 
         [0029]    The liner  16  may also, optionally, contain surface cuts  15  in the paper layer  11  for purposes of corner relief, as discussed in more detail below. The cuts  15  are placed into the paper layer by any suitable means. 
         [0030]    The absorbent liner  16  of the present invention is particularly adapted for use in a steam sterilization system or ethylene oxide sterilization system. As is known, sterilization systems generally include a sterilization chamber that is adapted to receive instruments to be sterilized, and a source of sterilizing agent, e.g. steam or ethylene oxide, connected to the sterilization chamber. 
         [0031]    Preferably, the absorbent liner  16  is fabricated from a non-woven, lint free material that is compatible with both steam and ethylene oxide sterilization. The absorbent liner  16  is preferably fabricated from a hydrophilic polymeric foam plastic, e.g. a hydrophilic polyurethane foam that is clickable. 
         [0032]    Typical physical properties of the foam include the following: 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Physical Properties 
                 Minimum 
                 Average 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Density (lbs./ft 3 ) 
                 1.60 ± 10% 
                   
               
             
          
           
               
                   
                 Tensile strength (psi) 
                 17.0 
                 25.0 
               
               
                   
                 Elongation (%) 
                 80 
                 120 
               
               
                   
                 Tear resistance (pli) 
                 1.20 
                 1.90 
               
               
                   
                 Compression force Deflection (psi) 
               
               
                   
                 25% Deflection 
                 0.60 
                 0.85 
               
               
                   
                 50% Deflection 
                 0.70 
                 0.95 
               
             
          
           
               
                   
                 Retention of Tensile Strength after 3 
                 Minimum 70 
                   
               
               
                   
                 hours, 105° C., steam 
               
               
                   
                 autoclave (%) 
               
               
                   
                 Retention of Tensile Strength after 
                 Minimum 70 
               
               
                   
                 22 hours, 140° C., dry heat 
               
               
                   
                 aging (%) 
               
               
                   
                   
               
             
          
         
       
     
         [0033]    With reference to  FIGS. 2 ,  3  and  4 , a first embodiment of an absorbent liner  16  of the present invention is illustrated as a tray liner. The absorbent tray liner  16  of the present embodiment advantageously functions to prevent the presence of residual moisture on the surface of surgical instruments  20  at the conclusion of the sterilization process by absorbing such potential residual moisture. The surgical instruments  20  are positioned adjacent to the foam layer  12 . Since the paper layer  11  is not adjacent to the surgical instruments, but rather below the foam layer  12 , it pulls moisture from the foam layer  12  and retains any residual moisture. The moisture is free to spread out through the paper to increase the surface area of the moisture and thereby increase the rate of evaporation. Thus, the foam layer  12  advantageously cushions surgical instruments to be sterilized, e.g., forceps, graspers, dissectors, probes, hemostats, scissors and the like, both during and after the sterilization process and will not leave residual moisture on surgical instruments  20 . 
         [0034]    With reference to  FIGS. 2 and 3 , absorbent tray liner  16  generally comprises a sheet of absorbent material cut to substantially cover a base  32  of a sterilization tray  30 . The base  32  of the sterilization tray  30  may be solid or perforated, as is known in the art. 
         [0035]      FIG. 4  shows a second embodiment of an absorbent liner  16  of the present invention as a base pad. The absorbent liner  16  of the base pad embodiment advantageously functions to pull and retain moisture away from wrap  40  during and at the conclusion of the sterilization process by absorbing such potential and residual moisture. The paper layer  11  is positioned underneath and adjacent to the tray  30 . The paper layer pulls moisture away from the wrap  40  and retains any residual moisture toward the tray  30 . The moisture is free to spread out through the paper to increase the surface area of the moisture and thereby increase the rate of evaporation. The foam layer  12  advantageously cushions the tray and protects any sterilization wrap  40  or cart that may be used. 
         [0036]    A method for sterilizing instruments  20  according to the present invention includes positioning the tray liner  16  in the base of the tray  30  such that the paper layer  11  is adjacent to the tray base  32  and positioning instruments on the foam layer  12 . The types of instruments  20  that may benefit from sterilization method disclosed herein include all conventional surgical instruments composed of stainless steel. Determinations as to the types of surgical instruments to be placed on the tray  30 , the numbers/weights of such surgical instruments, sterilization cycles, and the like, are made according to conventional sterilization criteria. 
         [0037]    Tray  30  is then advantageously wrapped in a conventional sterilization wrap  40 . Sterilization wrap  40  may be fabricated from paper and, optionally, a second absorbent tray liner  16  or other cushioning member may be placed between tray  30  and sterilization wrap as a base pad, thereby reducing the risk that wrap  40  may be torn by the corners of tray  30 . Once wrapped in the sterilization wrap  40 , tray  30  is ready to be placed in a sterilization unit for sterilization of surgical instruments  20 . At the conclusion of the sterilization cycle, tray  30  is typically removed from the sterilization unit (not pictured), and the sterilized instruments  20  are, in due course, removed from the tray and made ready for subsequent surgical procedures. At the conclusion of the sterilization cycle, the absorbent tray liner  16  of the present invention is typically disposed of in a conventional waste container. 
         [0038]    A preferred method for sterilizing instruments  20  according to the present invention includes positioning the liner  16  underneath the outer base of the tray  30  such that the paper layer  11  is adjacent to the tray base  32  and the foam layer  12  is not in contact with the tray  30 . As such, the foam layer  12  may contact a sterilization wrap  40 , if utilized. The paper layer  11  will absorb moisture that leaks through perforations in the base  32  of the tray  30 . The paper layer  11  may also collect moisture that accumulates on the tray  30  surfaces. Moisture from the tray  30  or base  32  will be absorbed by the paper layer  11  and dissipate throughout its surface keeping the foam layer  12  appreciably dry, and in turn keeping sterilization wrap  40  dry and uncompromised. 
         [0039]    With reference to  FIG. 4 , in a particularly preferred method where the liner  16  functions as a base pad, the perforations  13  are adapted to meet the tray  30  edges. This allows the edges of the liner  16  to be folded upward so that paper layer  11  is adjacent and in contact with the face  33  of the tray  30 . This method allows for cushioning and moisture absorption from the face  33  of the tray as well as the base  32 . Moisture from the tray  30  will be absorbed by the paper layer  11  and dissipate throughout its surface keeping the foam layer  12  appreciably dry, and in turn keeping sterilization wrap  40  dry and uncompromised. 
         [0040]    Corner relief is provided through the perforations  13 . The intersection of the longitudinal perforations  13   a  and the latitudinal perforations  13   b  may provide a corner box  17  within a sheet of liner  16 . The corner box  17  may be easily removed through means of the perforations. Once the corner box  17  is removed, the sides of the liner  16  are more easily folded up and positioned adjacent to the tray face  33 . 
         [0041]    For additional corner relief, the liner of the invention may be provided with surface cuts  15 . Various size cuts  15  are embodied. The surfaces cuts  15  are positioned to accommodate the edges of a sterilization tray  30 , and most preferably the corners of the tray  30 . The cuts  15  also allow for stabilization of a tray  30  while seated on the liner  16 . 
         [0042]    The absorbent tray liner of the present invention provides significant benefits to the reliability and efficacy of conventional sterilization operations. Ideally, as is known in the art, when the sterilization system is operating at peak performance a sterilization system that utilizes steam or ethylene oxide as the sterilizing agent will be totally dry at the conclusion of the sterilization cycle. However, as discussed above due to ambient humidity, plumbing, etc., sterilization systems are highly variable in operation and such systems do not always operate at peak levels. As a result, without use of an absorbent tray liner, it is not uncommon for residual moisture to be found on the surface of sterilized instruments or the sterilization tray at the conclusion of the sterilization cycle. The absorbent tray liner of the present invention exhibits sufficient hydrophilicity to absorb an amount of moisture sufficient to address typical operative variability. 
         [0043]    The present invention, therefore, provides an absorbent liner  16  that functions to cushion trays and surgical instruments in connection with the sterilization process, and further functions to absorb potential excess moisture that might remain on the surgical instruments or on the tray at the conclusion of a steam or ethylene oxide sterilization process. The absorbent liner has been found to permit proper air removal, sterilant penetration/evacuation, and delivery of sterilized surgical instruments substantially devoid of residual moisture at the conclusion of a sterilization process. The absorbent tray liner has also been found to permit effective aeration of instruments sterilized with ethylene oxide. 
         [0044]    Another embodiment of the liner in accordance with the present invention is illustrated in  FIGS. 6-8 . In particular, a corner guard  50  is provided which is preferably composed of a polyurethane foam layer  12  and a paper layer  11  as described above in connection with the liner  16 . In addition, the corner guard is dimensioned for use with a sterilization tray such as that shown in  FIGS. 2 and 4 . 
         [0045]    As shown in  FIG. 6 , guard  50  contains a cavity  51  that is shaped to accommodate the corner of tray  30 . The paper layer  11  is exposed on the surface of the cavity  51 . The outer surface of the guard  50  is comprised of foam layer  12 . 
         [0046]    Referring now to  FIGS. 7 and 8 , the guard  50  is positioned adjacent to the surface  33  of tray  30  is such that the paper layer  11  is adjacent to the surface  33 . The corner guard  50  advantageously absorbs liquid while allowing the passage of the sterilization medium therethrough. The moisture is free to spread out through the paper to increase the surface area of the moisture and thereby increase the rate of evaporation. Thus, moisture is retained in the paper layer  11  before it reaches a sterile wrap or cart. Additionally, cushioning and protection are provided for the tray  30  and penetration of sterilization wrap by sharp corners is prevented. 
         [0047]    The principles, preferred embodiments and modes of operation of the presently disclosed absorbent liners, corner guards and methods of sterilizing surgical instruments have been described in the foregoing specification. The presently disclosed absorbent liners and methods of sterilization, however, are not to be construed as limited to the particular embodiments shown as these embodiments are regarded as illustrious rather than restrictive. Moreover, variations and changes may be made by those skilled in the art without departing from the spirit of the presently disclosed absorbent liners, guards and methods of sterilization.