Abstract:
A wound retractor comprising an outer ring, an inner ring, and a flexible sheath extending therebetween is described, wherein the inner ring has the strength, rigidity and bounce back characteristics of a solid injection-molded ring yet is manufactured by extrusion techniques described herein with a 20-30% reduction in materials, resulting in reduced manufacturing costs.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Application No. 62/037,501, filed Aug. 14, 2014, the entire disclosure of which is incorporated by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    This invention generally relates to medical devices and, more specifically, to a wound retractor having an improved inner ring. 
         [0004]    2. Discussion of the Related Art 
         [0005]    Wound retractors/protectors have been described in U.S. Pat. Nos. 7,650,887; 7,727,146; 7,883,461; 7,913,697; 8,235,054, and 8,267,858, the disclosures of which are hereby incorporated by reference in their entireties. The basic components of such wound retractors include an outer ring or rings, which may be flexible or rigid, an inner ring, and flexible sleeve attached at either end to the outer and inner ring. 
         [0006]    In use, the inner ring of the wound retractor is compressed for insertion through an incision. Once placed, the inner ring requires a particular “bounce back” force to ensure that while the device is retracted and in use during surgery, the inner ring does not collapse, which would result in loss of retraction. 
         [0007]    Because of the particular requirements for proper function of the inner ring, the inner ring is typically manufactured by injection molding and is fully dense. Such rings have the requisite stiffness and bounce back force to function properly in a wound retractor. To save manufacturing time and costs, it is desirable to manufacture the inner ring by extruding the ring material into tubes and then welding the tube to form a ring. This manufacturing process allows for material reduction, by introducing lumen(s) for example, thereby saving costs, but may produce unsatisfactory results when used in a wound retractor. Hollow tubing or tubing with one or more lumens are not generally as stiff as a fully dense tube of the same size, nor do they have the requisite bounce back to function in a wound retractor. 
         [0008]    What is needed, therefore, is an inner ring that can be manufactured using extrusion techniques with reduced material costs yet still maintains the rigidity and bounce back of a fully dense injection-molded ring, so that the final product costs less but maintains retraction when the wound retractor is deployed. 
       SUMMARY OF THE INVENTION 
       [0009]    A wound retractor incorporating an inner ring manufactured using extrusion techniques with reduced material costs yet still maintaining the rigidity and bounce back of a fully dense injection-molded ring is described. Although a ring with void spaces or lumens generally has less strength and bounce-back force than a fully dense molded ring, it was surprisingly discovered that a ring could be fashioned by more cost effective extrusion techniques, providing a substantial reduction in material costs, while maintaining the superior features of the fully dense ring, provided a stable internal wall structure is maintained within the ring cross-section. Moreover, it was determined that such rings provide the same performance as fully dense rings when incorporated into wound retractors. 
         [0010]    The inventive, more cost-effective wound retractor comprises a longitudinal axis defining an instrument access channel extending from a proximal end to a distal end, an outer ring, an inner ring, wherein the inner ring has a teardrop-shaped cross section, a first lumen, a second lumen, and a stable internal wall structure separating the first lumen from the second lumen, and a flexible, tubular sheath extending between the outer ring and the inner ring. In some embodiments, the outer ring comprises an annular axis around which the outer ring is rotatable. Optionally, the outer ring includes surfaces that are easy to grip and turn, allowing the user to roll the flexible ring over itself to provide the sheath with a radial retraction force sufficient to stretch an incision to a desired diameter. In some embodiments, the outer ring may be rolled over itself to provide the sheath with a radial retraction force sufficient to seal the sheath against the edges of a wound incision. 
         [0011]    Also described is a method for manufacturing an inner ring for use in a wound retractor, comprising the steps of providing a die having teardrop-shaped cross-section; providing tip tooling having a first tip and a second tip, wherein the second tip has a generally circular shape having a diameter R1 with a region of concavity having a radius R2, wherein the first tip and the second tip are separated by a distance L1; extruding a thermoplastic elastomer through the die and tip tooling to thereby produce a tube having a teardrop cross-section, a first lumen, a second lumen, and a stable internal wall structure separating the first lumen from the second lumen by the distance L2; cutting the tube into a length equal to the desired circumference of the inner ring to produce a first end and a second end; and welding the first end to the second end to produce the inner ring. 
         [0012]    In some embodiments of the method of manufacturing, the first tip has a generally triangular shape. In some embodiments, R1 is approximately 0.15 inches to approximately 0.2 inches; optionally, R1 is approximately 0.17 inches. In some embodiments, R2 is approximately 0.2 inches to approximately 0.3 inches; optionally, R2 is approximately 0.25 inches. In some embodiments, L2 is approximately 0.06 inches to approximately 0.10 inches; optionally L2 is approximately 0.06 inches. 
         [0013]    Inner rings for wound retractors manufactured by the above methods are also described. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  illustrates an isometric view of an adjustable wound retractor. 
           [0015]      FIG. 2  is a cross-sectional view of a wound retractor deployed in an incision. 
           [0016]      FIG. 3  is a photograph of die and tip tooling used to produce a tear-drop shaped ring with two lumens. 
           [0017]      FIG. 4  is a photograph of the cross-section of the ring produced using the tooling of  FIG. 3 . 
           [0018]      FIG. 5  is a perspective view of a 3-D model of a new tip tooling having a concavity in the tip. 
           [0019]      FIG. 6  is a cross-sectional view of the tip tooling of  FIG. 5 , shown with dimensions of one embodiment of the invention. 
           [0020]      FIG. 7  is a cross-sectional view of the lower tip of the tooling of  FIG. 5 , shown with dimensions of one embodiment of the invention. 
           [0021]      FIG. 8  is a cross-sectional view of the die and tip tooling used to produce an extruded tube having a teardrop-shaped cross section, two lumens and a stable internal wall structure, shown with dimensions of one embodiment of the invention. 
           [0022]      FIG. 9  is a cross-sectional of the die and tip tooling used to produce an extruded tube having a teardrop-shaped cross section, two lumens and a stable internal wall structure, shown without dimensions. 
           [0023]      FIG. 10  is a photograph of the cross-section of the ring produced using the tooling of  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION 
       [0024]      FIG. 1  illustrates an adjustable wound retractor  100  useful in a variety of surgical procedures. The wound retractor  100  includes an outer ring  102 , an inner ring  104 , and a distensible sleeve  106  coupling the outer ring and the inner ring. Outer ring  102  is shown as a single ring, but may also be a double ring or triple ring or multiples thereof. 
         [0025]    The sleeve  106  may be coupled to the outer ring  102  and the inner ring  104  by heat seal, adhesive, or other means that are well known in the art. The sleeve  106  may be made of a material that is flexible and impermeable to fluids and bacteria. 
         [0026]    The inner ring  104  may be made of materials of sufficient hardness to retain its shape after insertion into a body cavity  904  ( FIG. 2 ) but sufficiently flexible so as to allow the inner ring to be compressed for insertion through an incision. The materials of which the outer ring  102  is made must allow the outer ring to be turned around its annular axis as further described below. The shape of the outer ring  102  affects both its ability to grip and to provide stability during and after adjustment. 
         [0027]      FIG. 2  illustrates the wound retractor deployed in a wound opening  900 . To deploy the wound retractor, an incision in the shape of a slit is first made in the body wall  902  of a patient, such as the abdominal wall  902 . The inner ring  104  is compressed and the inner ring and sleeve  106  are manually inserted into the body cavity  904  through the incision with the outer ring  102  remaining external to the body cavity. Once the inner ring  104  is within the body cavity  904 , it expands around the inner surface of the incision  900  so as to be generally parallel to the outer surface of the abdominal wall  902 . The sleeve  106  provides a working channel from outside the body cavity  904  to inside the body cavity. 
         [0028]    The outer ring  102  initially rests above the abdominal wall  902  around the wound opening  900 . Since the upper end of the sleeve  106  is coupled to the outer ring  102 , the sleeve  106  can be drawn upwards and radially outward or inward, thereby drawing the inner ring  104  tightly against the inner surface of the abdominal wall  902 . Moreover, the intermediate portion of the sleeve  106  is drawn tightly against the sides and edges of the wound opening  900 , thereby retracting the adjacent tissue and producing a tightly sealed opening in the body cavity  904 . The sleeve  106  contacts the entire surface of the wound  900  and protectively covers and seals it from contamination and infection. Depending on the size and depth of the incision  900 , the user can roll up the sleeve  106  by gripping the outer ring  102  and rotating it until the sleeve  106  abuts the outer edge of the wound opening  900 . The inner ring  104  is adapted for juxtaposition with the inner surface of the abdominal wall  902  and the outer ring  102  is adapted for juxtaposition with the outer surface of the abdominal wall. Both the inner ring  104  and the outer ring  102  are adapted for disposition relative to the incision  900  in the abdominal wall  902 . The sleeve  106  is adapted to traverse the incision  900  in the abdominal wall  902 . 
         [0029]    In one embodiment of the invention, the outer ring is solid. Alternatively, the outer ring may have one or more lumens. In another embodiment of the invention, a small wire, such as a stainless steel wire, or other stiffening element is placed inside a lumen of the outer ring  102 . The wire provides retraction stability to the wound retractor  100 . 
         [0030]    After surgery, the wound retractor  100  may be retrieved by grabbing the inner ring  104  and the sleeve  106  and pulling them through the wound opening  900 . The use of the sleeve  106  and the ease of retracting the outer ring  102  provide higher compression between the inner and outer rings. As a result, the wound retractor  100  provides incremental adjustability to fit a wide range of incision sizes and isolates and protects the wound from bacterial infection as diseased body parts and contaminated instruments are passed through the wound. 
         [0031]    As noted above, the inner ring of the wound retractor must be sufficiently flexible to be compressed for insertion through an incision into a body wall, but able to return to its ring shape after insertion so that it can anchor the wound retractor against the inner wall. The inner ring must also be sufficiently rigid to maintain its shape during retraction and throughout the surgical procedure. Inner rings of suitable flexibility and strength may be formed from a variety of suitable materials, including thermoplastic polyurethane elastomers, such as PELLETHANE or IROGRAN. 
         [0032]    The inner and outer rings may be manufactured using a variety of techniques known in the art, including injection molding and extrusion. In forming a ring using the extrusion process, the plastic material is extruded as a tube, with or without lumen(s), and then welded to into a ring. Typically, the inner ring is produced as a fully dense tube, often using injection molding, so that it has the rigidity and bounce back required in a wound retractor. The present invention is directed at an inner ring that requires less material than a fully dense ring while maintaining all the functional advantages of a fully dense ring, preferably formed by extrusion rather than injection molding. Such an inner ring functions as well in a retractor as a fully dense ring, but is much less expensive to produce due to savings in materials and manufacturing. 
         [0033]    The plastic extrusion process is known, but in brief, raw material, often called resin, is fed into the hopper of an extruder. Additives, such as colorant, may be added to the resin prior to adding it to the hopper. From the hopper, the resin is fed into the extruder barrel and propelled forward through the barrel, typically by the action of a screw mounted to a screw drive motor. As the resin moves through the barrel, it is heated until the resin reaches a molten state. The molten resin is generally filtered through a screen after exiting the barrel; from there, it is fed into the head assembly and then the tip and die tooling, which gives the tubing its final profile, including lumens, surface features, etc. Pressurized air may be used to keep void spaces, such as lumens, open until the tubing cools. The product is cooled, for example, by pulling the extruded material through a water bath. 
         [0034]    In the present invention, a modification of the extrusion process was developed that resulted in manufacturing cost savings through a reduction in the amount of material required to produce rings while maintaining the strength and flexibility needed for the inner rings to function properly. Specifically, it was discovered that a ring having a tear-drop shaped cross-section could be produced with less material than a solid ring and still maintain the desirable attributes of a solid ring so long as the ring had a stable interior wall structure or bridge that spanned the width of the ring. Accordingly, tip and die tooling was designed in a particular geometry to introduce lumens into the inner ring while maintaining this bridge, thus maximizing material reduction while still maintaining the inner ring&#39;s required structure and force. 
         [0035]    Initially, two lumens were introduced into the inner ring using a triangular tip and a circular tip. During the extrusion process, positive air pressure was introduced through tip and die tooling  200 , seen in  FIG. 3 , having a teardrop-shaped die  218 , a generally triangular upper lumen tip  202  and a generally circular lower lumen tip  204 . However, when too much air pressure was applied, the lumens in the resulting ring, shown in  FIG. 4 , interfered with the inner ring&#39;s interior wall structure or bridge. The resulting ring had an inner wall structure  206  that was curved or “U” shaped. The upper lumen  208  was crescent-shaped, rather than the expected triangular shape, while the lower lumen  210  was distorted into a tear-drop shape rather than a circular shape. The end result was a ring that collapsed too easily, did not have the needed bounce back and was generally not suitable for functioning in a wound retractor. 
         [0036]    To solve this problem, tip and die tooling with unique geometries were tested to identify configurations that maintain a straight inner wall structure and thus maintain the requisite rigidity of the ring. It was determined that a region of concavity introduced onto the lower lumen tip stabilized the structure of the extrudate allowing for maximimum material reduction while not affecting the inner wall structure. 
         [0037]    A perspective view of a 3-D model of the new tip tooling  212  is shown in  FIG. 5 . The new tip tooling includes an upper generally triangular tip  202  and a lower tip  214 . The lower tip is generally circular with a region of concavity  216  on the edge of the lower tip closest to the upper tip. A close-up of the new tip tooling is shown with representative dimensions (in inches) in  FIG. 6 . A further close-up of the lower tip is shown in cross section with representative dimensions (in inches) in  FIG. 7 . A cross-section of the die and tip tooling is shown with dimensions (in inches) in  FIG. 8 . 
         [0038]    The illustrated tip tooling will produce a tubing having a 20-25% reduction in material, although ranges from 20% to 30% may be produced by varying the process parameters of the extrusion line and the axial position of the tip relative to the die. In general, the die and tip tooling is configured to produce a stable bridge or straight inner wall extending across the cross-section of the tube, the bridge having a thickness of no less than 0.060 inches. 
         [0039]    The newly designed die and tip tooling is shown in  FIG. 9 . This tooling was used to produce the tube shown in cross-section in  FIG. 10 . In this tube, the upper lumen  220  and the lower lumen  222  retain their general shape. Importantly, the interior wall structure or bridge  224  remains straight. The tubing was heat welded to form a ring and subjected to the testing described below. 
         [0040]    In order to determine if rings having a teardrop cross-section, two lumens and a straight internal wall structure performed as well as solid injection molded rings, a number of tests were conducted. Solid rings formed using an extrusion process were used as a control. Given that both injection molded rings and rings formed by extrusion without lumen are solid, one would expect them to behave similarly in the various tests. In fact, the extruded rings with lumens and a straight inner wall structure performed better than extruded solid rings, much closer to the performance of a solid injection molded ring. 
         [0041]    The first test was the “Inner Ring Force Test,” used to measure the bounce back force of the extruded rings (with and without lumens) compared to the injection molded solid rings. The results are shown in Table 1. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Inner Ring Force Test 
               
             
          
           
               
                 Spec 
                 Unit 
                 Force (lbs) 
                 Average (lbs) 
                 Difference 
               
               
                   
               
             
          
           
               
                 Injection 
                 1 
                 2.25 
                 2.23 
                 N/A 
               
               
                 Molded 
                 2 
                 2.28 
               
               
                   
                 3 
                 2.14 
               
               
                   
                 4 
                 2.24 
               
               
                   
                 5 
                 2.25 
               
               
                 Extruded 
                 1 
                 1.65 
                 1.71 
                 0.52 
               
               
                 without 
                 2 
                 1.77 
               
               
                 lumens 
                 3 
                 1.72 
               
               
                   
                 4 
                 1.75 
               
               
                   
                 5 
                 1.66 
               
               
                 Extruded 
                 1 
                 2.06 
                 2.06 
                 0.18 
               
               
                 with lumens 
                 2 
                 2.04 
               
               
                   
                 3 
                 2.08 
               
               
                   
                 4 
                 2.03 
               
               
                   
                 5 
                 2.03 
               
               
                   
                 6 
                 2.00 
               
               
                   
                 7 
                 2.05 
               
               
                   
                 8 
                 2.01 
               
               
                   
                 9 
                 1.99 
               
               
                   
                 10 
                 2.03 
               
               
                   
                 11 
                 2.10 
               
               
                   
                 12 
                 2.09 
               
               
                   
                 13 
                 2.03 
               
               
                   
                 14 
                 2.11 
               
               
                   
                 15 
                 2.10 
               
               
                   
                 16 
                 2.03 
               
               
                   
                 17 
                 2.13 
               
               
                   
                 18 
                 2.03 
               
               
                   
                 19 
                 2.05 
               
               
                   
                 20 
                 2.06 
               
               
                   
                 21 
                 2.10 
               
               
                   
                 22 
                 2.02 
               
               
                   
                 23 
                 2.04 
               
               
                   
                 24 
                 2.12 
               
               
                   
                 25 
                 2.05 
               
               
                   
               
             
          
         
       
     
         [0042]    Minimum Retraction Testing: This test is designed to determine if wound retractors with specific inner ring designs can sufficiently retract the minimum qualified incision compared to injection molded rings. The results are shown in Table 2. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Minimum Retraction Test 
               
             
          
           
               
                   
                   
                 Number 
                   
                   
                   
               
               
                   
                 Inci- 
                 of 
                   
                   
                 Difference 
               
             
          
           
               
                   
                   
                 sion 
                 Retrac- 
                 Length 
                 Width 
                 Length 
                 Width 
               
               
                 Spec 
                 Unit 
                 Size 
                 tions 
                 (in) 
                 (in) 
                 (in) 
                 (in) 
               
               
                   
               
               
                 Injection 
                 1 
                 11 
                 7 
                 4.40 
                 2.35 
                   
                   
               
               
                 Molded 
                 2 
                 11 
                 7 
                 4.30 
                 2.30 
               
               
                   
                 3 
                 11 
                 7 
                 4.30 
                 2.35 
               
               
                   
                   
                   
                 Average 
                 4.33 
                 2.33 
                 N/A 
                 N/A 
               
               
                 Extruded 
                 1 
                 11 
                 7 
                 4.35 
                 2.30 
               
               
                 without 
                 2 
                 11 
                 7 
                 4.40 
                 2.35 
               
               
                 lumens 
                 3 
                 11 
                 7 
                 4.40 
                 2.40 
               
               
                   
                   
                   
                 Average 
                 4.38 
                 2.35 
                 0.05 
                 0.02 
               
               
                 Extruded 
                 1 
                 11 
                 7 
                 4.30 
                 2.30 
               
               
                 with 
                 2 
                 11 
                 7 
                 4.40 
                 2.35 
               
               
                 lumens 
                 3 
                 11 
                 7 
                 4.35 
                 2.25 
               
               
                   
                   
                   
                 Average 
                 4.35 
                 2.30 
                 0.02 
                 0.03 
               
               
                   
               
             
          
         
       
     
         [0043]    Maximum Retraction Testing: The third test was used to determine if wound retractors with specific inner ring designs can sufficiently retract the maximum qualified incision compared to injection molded rings. The results are shown in Table 3. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Maximum Retraction Test 
               
             
          
           
               
                   
                   
                 Number 
                   
                   
                   
               
               
                   
                 Inci- 
                 of 
                   
                   
                 Difference 
               
             
          
           
               
                   
                   
                 sion 
                 Retrac- 
                 Length 
                 Width 
                 Length 
                 Width 
               
               
                 Spec 
                 Unit 
                 Size 
                 tions 
                 (in) 
                 (in) 
                 (in) 
                 (in) 
               
               
                   
               
               
                 Injection 
                 1 
                 17 
                 8 
                 6.30 
                 3.30 
                   
                   
               
               
                 Molded 
                 2 
                 17 
                 8 
                 6.40 
                 3.45 
               
               
                   
                 3 
                 17 
                 8 
                 6.40 
                 3.60 
               
               
                   
                   
                   
                 Average 
                 6.37 
                 3.45 
                 N/A 
                 N/A 
               
               
                 Extruded 
                 1 
                 17 
                 8 
                 6.40 
                 3.30 
               
               
                 without 
                 2 
                 17 
                 8 
                 6.40 
                 3.30 
               
               
                 lumens 
                 3 
                 17 
                 8 
                 6.30 
                 3.30 
               
               
                   
                   
                   
                 Average 
                 6.37 
                 3.30 
                 0.00 
                 0.15 
               
               
                 Extruded 
                 1 
                 17 
                 8 
                 6.30 
                 3.30 
               
               
                 with 
                 2 
                 17 
                 8 
                 6.40 
                 3.40 
               
               
                 lumens 
                 3 
                 17 
                 8 
                 6.40 
                 3.40 
               
               
                   
                   
                   
                 Average 
                 6.37 
                 3.37 
                 0.00 
                 0.08 
               
               
                   
               
             
          
         
       
     
         [0044]    Retraction Dwell Testing: Finally, the last test was used to determine if wound retractors with specific inner ring designs can sufficiently retract the nominal qualified incision for a four hour duration. The results are shown in Table 4. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Dwell Test 
               
             
          
           
               
                   
                   
                   
                   
                   
                 4 Hour 
                   
               
               
                   
                 Incision 
                   
                 Start 
                 4 Hours 
                 Difference 
                 Difference 
               
             
          
           
               
                   
                   
                 Size 
                 Number of 
                 Length 
                 Width 
                 Length 
                 Width 
                 Length 
                 Width 
                 Length 
                 Width 
               
               
                 Spec 
                 Unit 
                 (cm) 
                 Retractions 
                 (in) 
                 (in) 
                 (in) 
                 (in) 
                 (in) 
                 (in) 
                 (in) 
                 (in) 
               
               
                   
               
               
                 Injection 
                 1 
                 11 
                 8 
                 6.61 
                 5.73 
                 6.40 
                 5.56 
                 0.21 
                 0.17 
                 N/A 
                 N/A 
               
               
                 Molded 
               
               
                 Extruded 
                 1 
                 11 
                 8 
                 6.44 
                 5.66 
                 6.17 
                 5.24 
                 0.27 
                 0.42 
                 0.06 
                 0.25 
               
               
                 without 
               
               
                 lumens 
               
               
                 Extruded 
                 1 
                 11 
                 8 
                 6.46 
                 5.67 
                 6.26 
                 5.41 
                 0.20 
                 0.26 
                 0.01 
                 0.09 
               
               
                 with 
               
               
                 lumens 
               
               
                   
               
             
          
         
       
     
         [0045]    Results show that extruded tubing with lumens of the inventive design is more comparable to injection molded inner rings than extruded tubing without lumens. This demonstrates the inner wall running through the profile of the extruded inner ring with lumens provides more additional support than a fully dense extruded inner ring. The extruded inner ring with dual lumens of the inventive design is comparable to an injection molded inner ring and provides the requisite strength and flexibility to function in a wound retractor while providing cost savings in the manufacturing process through reduced material use. 
         [0046]    While certain embodiments have been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope thereof as defined by the following claims.