Abstract:
A seal assembly adapted for use in conjunction with a trocar assembly includes a plurality of seal segments. Each seal segment includes a peripheral edge and a seam edge. At least a first seal segment and a second seal segment are connected along their respective peripheral edges to form a first seal layer having a seam defined by the seam edge of the first seal segment and the seam edge of the second seal segment. At least a third seal segment and a fourth seal segment are connected along their respective peripheral edges to form a second seal layer having a seam defined by the seam edge of the third seal segment and the seam edge of the fourth seal segment. The seam of the first seal layer has a first longitudinal axis and the seam of the second seal layer has a second longitudinal axis, and the first seal layer is oriented relative to the second seal layer such that the first longitudinal axis is angularly oriented relative to the second longitudinal axis.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to trocar assemblies. More particularly, the invention relates to a circumferential trocar sealing structure.  
         [0003]     2. Description of the Prior Art  
         [0004]     A trocar assembly is a surgical instrument that is used to gain access to a body cavity. A trocar assembly generally comprises two major components, a trocar sleeve, composed of a trocar housing and a trocar cannula, and a trocar obturator. The trocar cannula, having the trocar obturator inserted therethrough, is directed through the skin to access a body cavity. Once the body cavity is accessed, laparoscopic or arthroscopic surgery and endoscopic procedures may be performed. In order to penetrate the skin, the distal end of the trocar cannula is placed against the skin that has been previously cut with a scalpel and the trocar obturator is used to penetrate the skin and access the body cavity. By applying pressure against the proximal end of the obturator, the sharp point of the obturator is forced through the skin until it enters the body cavity. The trocar cannula is inserted through the perforation made by the trocar obturator and the trocar obturator is withdrawn, leaving the trocar cannula as an access way to the body cavity.  
         [0005]     The proximal end portion of the trocar cannula is typically joined to a trocar housing that defines a chamber having an open distal end portion in communication with the interior lumen defined by the trocar cannula. An obturator, or other elongate surgical instruments or tools, axially extend into and are withdrawn from the trocar cannula through the proximal end portion of the chamber defined by the trocar housing.  
         [0006]     Current trocar assemblies are commonly designed with a seal mechanism positioned within the chamber of the trocar housing. The sealing mechanisms are commonly a sealing grommet or gasket through which the obturator or other instruments extend. The sealing mechanism seals against the outer surface of the inserted instruments and thereby prevents fluids and insufflation gas from leaving or entering the body cavity through the trocar cannula. It is desired that such seals provide for good tear resistance, resistance to snagging and low friction with respect to insertion of a device such as a rod, shaft or cylinder.  
         [0007]     Seal assemblies are designed to maintain a seal before the insertion of an instrument and after the removal of the instrument. As a result, many trocar assemblies provide double sealing systems. That is, a top, or proximal, seal is used to seal around the tool/instrument when present and a flapper door or duckbill seal is requited below the top seal for sealing the trocar cannula when the instrument is not present.  
         [0008]     In contrast, other trocar assemblies employ a single sealing mechanism. Many of these trocar seal assemblies simply employ a silicone seal with a small hole slightly smaller than the smallest tool/instrument to be used in conjunction with the trocar assembly. This type of seal is often referred to as a lip seal. Surgical instruments of various diameters are passed through the lip seal. As such, these seals are often required to provide a seal for use with a full range of instruments. The opening diameter of the seals is, therefore, small relative the largest diameter instruments.  
         [0009]     In fact, it is not uncommon for lip seals to be pushed to 400% strain. By forcing these large diameter instruments through a relatively small diameter lip seal, these large diameter instruments are subjected to a significant increase in the normal force upon the instrument shaft. The surgeon feels this increased force as increased drag or resistance to instrument insertion/movement. It is also required that the material properties of the seal be such that the seal does not rip or tear as the seal is stretched to its limit. As a result, a need currently exists for an improved trocar seal assembly overcoming the deficiencies of the prior art.  
         [0010]     The present invention overcomes these deficiencies by providing a seal assembly which eliminates the hoop/high stress issues associated with prior art seals and provides a seal assembly which may be utilized either as a single sealing method (reducing the overall complexity of the trocar) or as a proximal seal assembly in a multiseal system.  
       SUMMARY OF THE INVENTION  
       [0011]     It is, therefore, an object of the present invention to provide a seal assembly adapted for use in conjunction with a trocar assembly. The seal assembly includes a plurality of seal segments. Each seal segment includes a peripheral edge and a seam edge. At least a first seal segment and a second seal segment are connected along their respective peripheral edges to form a first seal layer having a seam defined by the seam edge of the first seal segment and the seam edge of the second seal segment. At least a third seal segment and a fourth seal segment are connected along their respective peripheral edges to form a second seal layer having a seam defined by the seam edge of the third seal segment and the seam edge of the fourth seal segment. The seam of the first seal layer has a first longitudinal axis and the seam of the second seal layer has a second longitudinal axis, and the first seal layer is oriented relative to the second seal layer such that the first longitudinal axis is angularly oriented relative to the second longitudinal axis.  
         [0012]     It is also an object of the present invention a trocar assembly including a trocar cannula having a proximal end and distal end. The trocar assembly further includes a trocar housing coupled to the proximal end of the trocar cannula for receiving and guiding an obturator through the trocar cannula. The trocar housing includes an open proximal end portion defining an opening provided with a seal assembly. The seal assembly is constructed as described  
         [0013]     Other objects and advantages of the present invention will become apparent from the following detailed description when viewed in conjunction with the accompanying drawings, which set forth certain embodiments of the invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is an exploded view of a trocar assembly in accordance with the present invention.  
         [0015]      FIG. 2  is an exploded view of the seal assembly in accordance with the embodiment disclosed in  FIGS. 3, 4  and  5 .  
         [0016]      FIG. 3  is an exploded perspective view of first and second seal segments in accordance with the present invention.  
         [0017]      FIG. 4  is a perspective view of a seal layer composed of the first and second seal segments shown in  FIG. 3 .  
         [0018]      FIG. 5  is a cross sectional view of the seal layer shown in accordance with  FIG. 4 .  
         [0019]      FIG. 6  is an exploded perspective view of a further embodiment of first and second seal segments.  
         [0020]      FIG. 7  is a perspective view of a seal layer composed of the first and second seal segments shown in  FIG. 6 .  
         [0021]      FIG. 8  is a cross sectional view of the seal layer shown in accordance with  FIG. 7 .  
         [0022]      FIG. 9  is a perspective view of an alternate embodiment of a seal layer composed of first and second seal segments in accordance with a further embodiment.  
         [0023]      FIG. 10  is an exploded perspective view of the first and second seal segments shown in accordance with  FIG. 9 .  
         [0024]      FIG. 11  is a cross sectional view of the seal layer along the line  11 - 11  of  FIG. 9 .  
         [0025]      FIG. 12  is perspective view of a seal layer in accordance with a further embodiment.  
         [0026]      FIG. 13  is an exploded perspective view of the first and second seal segments shown in accordance with  FIG. 12 .  
         [0027]      FIG. 14  is a cross sectional view of the seal layer along the line  14 - 14  of  FIG. 12 .  
         [0028]      FIG. 15  is a perspective view of a seal layer in accordance with still another embodiment.  
         [0029]      FIG. 16  is an exploded perspective view of the first and second seal segments shown in accordance with  FIG. 15 .  
         [0030]      FIG. 17  is a cross sectional view of the seal layer along the line  17 - 17  of  FIG. 15 .  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]     The detailed embodiments of the present invention are disclosed herein. It should be understood, however, that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, the details disclosed herein are not to be interpreted as limiting, but merely as the basis for the claims and as a basis for teaching one skilled in the art how to make and/or use the invention.  
         [0032]     With reference to  FIGS. 1, 2 ,  3 ,  4  and  5 , a seal assembly  10  for a trocar assembly  12  is disclosed. The seal assembly  10  provides for improved resistance to tearing by reducing the likelihood for tenting to occur. As those skilled in the art will appreciate, tenting occurs when a seal is stretched and thinned out, for example, by an instrument passing through the seal, thus providing an area of weakness which may be easily punctured. As those skilled in the art will certainly appreciate, the present seal assembly  10  is adapted for use with a variety of trocar assemblies  10 .  
         [0033]     Apart from the seal assembly  10  in accordance with the present invention, the general structure of trocar assembly  12  does not form part of the present invention. For example, and by way of explaining the present seal assembly  10 , the trocar assembly  12  may take a variety of forms without departing from the spirit of the present invention.  
         [0034]     With that in mind, and by way of example, the trocar assembly  12  includes a trocar cannula  14 , a trocar obturator  16  and a trocar housing  18 . The trocar cannula  14  defines an interior lumen having an open distal end portion and an open proximal end portion. The proximal end portion extends into and is mounted in the distal end portion of trocar housing  18 . The trocar housing  18  has an open proximal end portion that defines an opening  20 . The opening  20  is provided with a proximal seal assembly  10  constructed in accordance with the present invention and described in detail hereinbelow. The opening  20  is further provided with a duckbill seal assembly  22  positioned beneath the proximal seal assembly  10 . While the present seal assembly  10  is disclosed as a proximal seal assembly  10  forming part of a dual sealing system, the present seal assembly may be utilized in a single seal system without departing from the spirit of the present invention.  
         [0035]     The trocar obturator  16  is slidably and removably extendable within the trocar cannula  14  and is inserted into the trocar housing  18  and the trocar cannula  14  through the proximal seal assembly  10 , the duckbill seal assembly  22  and the opening  20  of the trocar housing  18 . An obturator handle  24  is provided at the proximal end of the trocar obturator  16  and a sharpened point or blade (not shown) is formed at the distal end thereof. As is well known in the art, the seal assembly  10  cooperates with the trocar obturator  16 , or another surgical instrument extending through the trocar cannula  14 , to sealingly engage the outer surface thereof and thereby preclude the passage of fluids through the trocar housing  18 .  
         [0036]     With reference to the various embodiments in accordance with the present invention, the proximal seal assembly  10  is composed of multiple overlapping seal segments  26   a ,  26   b ,  26   a ′,  26   b ′ assembled so as to minimize leakage between the seal assembly  10  and the insertable rod, shaft or collar of various instruments. In particular, four seal segments  26   a ,  26   b ,  26   a ′,  26   b ′ are arranged to create the seal body  28  of the seal assembly  10 . While four seal segments are utilized in accordance with a preferred embodiment of the present invention, the seal assembly may ultimately be formed with different numbers of seal segments without departing from the spirit of the present invention.  
         [0037]     With reference to  FIG. 2 , a preferred embodiment of the present seal assembly  10  is disclosed. The seal assembly  10  employs several radial seal segments  26   a ,  26   b ,  26   a ′,  26   b ′ that fold around the shaft of an inserted instrument. In accordance with the proposed embodiment, hoop stress is eliminated by replacing the single hole of a prior art lip seal with multiple circumferentially positioned seal segments  26   a ,  26   b ,  26   a ′,  26   b ′. These seal segments  26   a ,  26   b ,  26   a ′,  26   b ′, when opened with a round probe, provide sealing similar to that provided by the round hole of a prior art lip seal. The present design also utilizes an angled edge feature for wrapping around an instrument shaft while yielding a design that is both easier to mold and inspect.  
         [0038]     As will be discussed below in greater detail, the present seal assembly  10  uses a series of interlocking seal segments  26   a ,  26   b ,  26   a ′,  26   b ′. The preferred embodiment disclosed herein employs four seal segments  26   a ,  26   b ,  26   a ′,  26   b ′, although more than four seal segments may be utilized without departing from the spirit of the present invention. All four seal segments  26   a ,  26   b ,  26   a ′,  26   b ′ are molded individually and then assembled into the final configuration.  
         [0039]     The hoop stress of the present seal assembly  10  is reduced by providing a single seal assembly  10  with multiple layers, that is, seal segments  26   a ,  26   b ,  26   a ′,  26   b ′, lapped over each other in a manner creating a through hole. The layers form contact zones with the inserted probe. The sum of the contact zones provides contact around the full diameter of the inserted instrument. Without a probe inserted, the seal segments  26   a ,  26   b ,  26   a ′,  26   b ′ remain in contact with each other so that the seal assembly  10  allows for no air passage.  
         [0040]     The proximal seal assembly  10  is composed of a seal body  28  constructed from two seal layers  34 ,  34 ′ respectively composed of a pair of seal segments  26   a ,  26   b ,  26   a ′,  26   b ′. Once the two seal layers  34 ,  34 ′ are properly constructed, the second seal layer  34 ′ is placed beneath the first seal layer  34  with the seal seam  36 ′ of the second seal layer  34 ′ rotated 90° from the seal seam  36  of the first seal layer  34 . In this way, the seal seams  36 ,  36 ′ of the first and second seal layers  34 ,  34 ′ create a double seamed seal providing for improved circumferential sealing within the trocar housing  18 .  
         [0041]     Apertures  37 ,  37 ′ are formed along a peripheral edges  35   a ,  35   b ,  35   a ′,  35   b ′ of the respective seal segments  26   a ,  26   b ,  26   a ′,  26   b ′ and are spaced such that the apertures  37 ,  37 ′ will align when the seal layers  34 ,  34 ′ are properly aligned and rotated 90 degrees. As such, a male retaining ring  44  and a female retaining ring  46  are positioned on opposite sides of the juxtaposed first and second seal layers  34 ,  34 ′. The male retaining ring  44  includes a series of connecting prongs  45  that extend through the apertures  37 ,  37 ′ of the seal layers  34 ,  34 ′ and are connected with the female openings  47  formed in the female sealing ring  46 . In this way, the seal body  28  composed of the first and second seal layers  34 ,  34 ′ is securely positioned between the male and female retaining rings  44 ,  46 , and ultimately supported for attachment to the trocar housing  18 .  
         [0042]      FIG. 2  illustrates an embodiment wherein a seal assembly  10  is provided with seal layers  34 ,  34 ′ comprising seal segments  26   a ,  26   b ,  26   a ′,  26   b ′. In accordance with this embodiment, the seal segments  26   a ,  26   b ,  26   a ′,  26   b ′ leaves no center hole. It is believed this arrangement provides for the best sealing prior to insertion and after removal of the rod. However, and in accordance with an alternate embodiment, an optional clearance opening  127 , such as shown in  FIGS. 6, 7  and  8 , may be utilized.  
         [0043]     In practice, when a device such as rod or shaft is inserted through the seal assembly  10 , the overlapping segments of the first and second seal layers  34 ,  34 ′ deflect both downward and around the device inserted. This deflection creates a cat-eye effect on the first seal layer  34 , leaving gaps between the inserted device and the first and second seal segments  26   a ,  26   b  making up the first seal layer  34 . The second seal layer  34 ′, with its seam  36 ′ rotated 90° from the seam  36 ′ of the first seal layer  34 ′, counters the gaps between the inserted device and the seal segments  26   a ,  26   b  of first seal layer  34 , creating a circumferential seal around the inserted device.  
         [0044]     As will be described below in substantial detail, various embodiments in accordance with the present invention are contemplated. The various embodiments describe the application of the concept underlying the present invention to flat seal segments with straight seam edges, flat seal segments with sigmoidal seam edges, cone shaped seal segments with straight seam edges and cone shaped seal segments with sigmoidal seam edges.  
         [0045]     While the present seal assembly  10  is specifically adapted for use in conjunction with trocar assemblies, it will be appreciated by those skilled in the art that the present seal assembly may be employed for different functions without departing from the spirit of the present invention.  
         [0046]     With reference to  FIGS. 3, 4  and  5 , a preferred embodiment of the seal layer  34  is disclosed. This is the same seal layer  34  disclosed with reference to  FIG. 2 . Each of the seal segments  26   a ,  26   b  in accordance with this embodiment are semi-circular and flat with straight seam edges  38   a ,  38   b . As is shown in  FIG. 3 , and as described below in greater detail, the use of straight seam edge  38   a ,  38   b  produces a seal seam  36  that follows along a substantially straight line.  
         [0047]     Referring to  FIGS. 3, 4  and  5 , each of these flat seal segments  26   a ,  26   b  includes a substantially flat semicircular disk having a substantially round peripheral edge  35   a ,  35   b  and a straight seam edge  38   a ,  38   b , which defines the straight seal seam  36 . In accordance with a preferred embodiment of the present invention, the outer peripheral edge  35   a ,  35   b  of each seal segment  26   a ,  26   b  defines an arc of approximately 200-220 degrees. The outer peripheral edges  35   a ,  35   b  further include a series of apertures  37  that function as a means of attachment for the seal segments  26   a ,  26   b . The seal segments  26   a ,  26   b  further include respective tapered angled sections  30   a ,  30   b  extending radially for connecting adjacent seal segments  26   a ,  26   b . The angled sections  30   a ,  30   b  are respectively tapered on one side. A matching taper  32   a ,  32   b  is also formed along the underside of each seal segment  26   a ,  26   b  opposite the angled section  30   a ,  30   b . The angled sections  30   a ,  30   b  of the seal segments  26   a ,  26   b  allow for increased contact between assembled seal segments.  
         [0048]     As mentioned above, the radially extending angled sections  30   a ,  30   b  are tapered as they extend toward the tip thereof. The underside of each seal segment  26   a ,  26   b  opposite the angled section  30   a ,  30   b  is similarly formed with a matching taper  32   a ,  32   b  to that of the angled section  30   a ,  30   b . In this way, the angled section  30   a  of the first seal segment  26   a  is seated within the matching taper  32   b  along the underside of the second seal segment  26   b  and the angled section  30   b  of the second seal segment  26   b  is seated within the matching taper  32   b  along the underside of the first seal segment  26   a . The matching tapers  32   a ,  32   b  permit the formation of a first seal layer  34  including no undesirable ridges or bumps along its underside due to the coupling of the first seal segment  26   a  to the second seal segment  26   b.    
         [0049]     In practice, and with reference to  FIGS. 3, 4  and  5 , two seal segments  26   a ,  26   b  are connected in an overlapping relationship to create a first seal layer  34 . As such, the resulting first seal layer  34  defines a complete circular outer periphery with a straight seal seam  36  extending between the first and second seal segments  26   a ,  26   b . As will be discussed below, the shape of the seam edges  38   a ,  38   b  of the seal segments  26   a ,  26   b  ultimately defines the shape of the seal seam  36  extending between the first and second seal segments  26   a ,  26   b  making up the first seal layer  34 .  
         [0050]     As was mentioned above, the concepts underlying the present invention may be practiced through the utilization of a variety of seal layer constructions without departing from the spirit of the present invention. Some of these contemplated constructions are disclosed below. Since it is believe those skilled in the art will appreciate the seal layer will be assembled in a manner similar to that described above with reference to  FIG. 2 , the details of constructing the complete seal assembly are not be repeated and the following disclosure focuses upon the construction of the individual seal layers.  
         [0051]     With reference to  FIGS. 6, 7  and  8 , a further embodiment in accordance with the present invention is disclosed. This embodiment is substantially similar to that disclosed with reference to  FIGS. 3, 4  and  5 , but includes a central clearance opening  127 . Each of the seal segments  126   a ,  126   b  in accordance with this embodiment is semicircular and flat with straight seam edges  138   a ,  138   b . As is shown in  FIG. 7 , and as described below in greater detail, the use of a straight seam edge  138   a ,  138   b  produces a seal seam  136  that follows along a substantially straight line.  
         [0052]     Referring to  FIGS. 6, 7  and  8 , each of these flat seal segments  126   a ,  126   b  includes a substantially flat semicircular disk having a substantially round peripheral edge  135   a ,  135   b  and a straight seam edge  138   a ,  138   b  which defines the straight seal seam  136 . Each seal segment  126   a ,  126   b  also includes a center clearance recess  127   a ,  127   b , which ultimately define the center clearance opening  127 .  
         [0053]     In accordance with a preferred embodiment of the present invention, the outer peripheral edge  135   a ,  135   b  of each seal segment  126   a ,  126   b  defines an arc of approximately 200-220 degrees. The outer peripheral edges  135   a ,  135   b  further include a series of apertures  137  that function as a means of attachment for the seal segments  126   a ,  126   b . The seal segments  126   a ,  126   b  further include respective tapered angled sections  130   a ,  130   b  extending radially for connecting adjacent seal segments  126   a ,  126   b  in the manner discussed above. The angled sections  130   a ,  130   b  are respectively tapered on one side. A matching taper  132   a ,  132   b  is also formed along the underside of each seal segment  126   a ,  126   b  opposite the angled section  130   a ,  130   b . The angled sections  130   a ,  130   b  of the seal segments  126   a ,  126   b  allow for increased contact between assembled seal segments  126   a ,  126   b.    
         [0054]     In practice, and with reference to  FIGS. 6, 7  and  8 , two seal segments  126   a ,  126   b  are connected in an overlapping relationship to create a first seal layer  134 . As such, the resulting first seal layer  134  defines a complete circular outer periphery with a straight seal seam  136  extending between the first and second seal segments  126   a ,  126   b . As will be discussed below, the shape of the seam edge  138   a ,  138   b  of the seal segments  126   a ,  126   b  ultimately defines the shape of the seal seam  136  extending between the first and second seal segments making up the first seal layer  134 .  
         [0055]     A further embodiment is disclosed with reference to  FIGS. 9, 10 ,  11 . This embodiment relates to a seal layer  234  composed of flat seal segments  226   a ,  226   b  having sigmoidal seam edges  238   a ,  238   b . As is shown in  FIG. 10  and is described below in greater detail, the use of sigmoidal seam edges  238   a ,  238   b  produces a seal seam  236  that is substantially S-shaped. Each of the flat seal segments  226   a ,  226   b  include a substantially flat semicircular disk having a substantially round peripheral edge  235   a ,  235   b  and a sigmoidal shaped edge that ultimately defines the seam edge  238   a ,  238   b . Ultimately, a seal body employing two of the present seal layer  224  as described above will create a seal assembly with an S-cut seal seam  236 .  
         [0056]     In accordance with a preferred embodiment of the present invention, the outer peripheral edges  235   a ,  235   b  of each of the seal segments  226   a ,  226   b  define an arc of approximately 200-220 degrees. The outer peripheral edges  235   a ,  235   b  further include a series of apertures  237  that function as a means of attachment for the seal segments  226   a ,  226   b . The seal segments  226   a ,  226   b  further include respective tapered angled sections  230   a ,  230   b  extending radially for connecting adjacent seal segments  226   a ,  226   b  in the manner discussed above. A matching taper  232   a ,  232   b  is also formed along the underside of each of the seal segments  226   a ,  226   b  opposite the angled sections  230   a ,  230   b . The angled sections  230   a ,  230   b  of the seal segments  226   a ,  226   b  allow for increased contact between assembled seal segments  226   a ,  226   b.    
         [0057]     In practice, and with reference to the figures, two seal segments  226   a ,  226   b  are connected in an overlapping relationship to create a first seal layer  234 . As such, the resulting first seal layer  234  defines a complete circular outer periphery with a sigmoidal seal seam  236  extending between the first and second seal segments  226   a ,  226   b . As will be discussed below, the sigmoidal shape of the seam edges  238   a ,  238   b  of the respective seal segments  226   a ,  226   b  ultimately define the shape of the seal seam  236  extending between the first and second seal segments  226   a ,  226   b  making up the first seal layer  234 .  
         [0058]     Still a further embodiment is disclosed with reference to  FIGS. 12, 13  and  14 . This embodiment relates to a seal layer  334  composed of cone shaped seal segments  326   a ,  326   b  having straight seam edges  338   a ,  338   b . As is shown in the figures and as described below in greater detail, the use of a straight seam edge  338   a ,  338   b  produces a seal seam  336  that is substantially straight. The cone shaped seal segments  326   a ,  326   b  each include a cone shaped structure that extends about only a portion of a circle. As such, the cone shaped seal segments  326   a ,  326   b  may be considered as constituting “a semicircular cone”. Each of the semicircular cones includes a flat, substantially round peripheral edge  335   a ,  335   b  and a straight seam edge  338   a ,  338   b.    
         [0059]     In accordance with a preferred embodiment of the present invention, the outer peripheral edge  335   a ,  335   b  of each of the seal segments  326   a ,  326   b  defines an arc of approximately 200-220 degrees. The outer peripheral edge  335   a ,  335   b  further includes a series of apertures  337  that function as a means of attachment for the seal segments  326   a ,  326   b . The seal segments  326   a ,  326   b  further include respective tapered angled sections  330   a ,  330   b  extending radially for connecting adjacent seal segments  326   a ,  326   b  in the manner discussed above. A matching taper  332   a ,  332   b  is also formed along the underside of each of the seal segments  326   a ,  326   b  opposite the angled portions  330   a ,  330   b . The angled portions  330   a ,  330   b  of the seal segments  326   a ,  326   b  allow for increased contact between assembled seal segments  326   a ,  326   b.    
         [0060]     In practice, and with reference to the figures, two seal segments  326   a ,  326   b  are connected in an overlapping relationship to create a first seal layer  334 . As such, the resulting first seal layer  334  defines a complete circular cone with a straight seal seam  336  extending between the first and second seal segments  326   a ,  326   b . As will be discussed below, the shape of the seam edge  338   a ,  338   b  of the seal segments  326   a ,  326   b  ultimately defines the shape of the seal seam  336  extending between the first and second seal segments  326   a ,  326   b  making up the first seal layer  334 .  
         [0061]     Yet a further embodiment is disclosed with reference to  FIGS. 15, 16  and  17 . This embodiment relates to a seal layer  434  composed of cone shaped seal segments  426   a ,  426   b  having sigmoidal seam edges  438   a ,  438   b . The cone feature of this embodiment reduces the potential for seal inversion upon instrument retraction and provides a natural “lead in” towards the center of the coned seal assembly.  
         [0062]     As is shown in  FIGS. 15, 16  and  17  and as described below in greater detail, a further embodiment of a seal layer  434  composed of seal segments  426   a ,  426   b  is disclosed. The use of sigmoidal seam edges  438   a ,  438   b  produce a seal seam  436  that is substantially S-shaped. Referring to the figures, each of the cone shaped seal segments  426   a ,  426   b  includes a cone shaped structure that extends about only a portion of a circle. As such, the cone shaped seal segments may be consider as constituting “a semicircular cone”. The semicircular cone includes a flat, substantially round peripheral edge  435   a ,  435   b  and a sigmoidal shaped edge that defines the seam edge  438   a ,  438   b.    
         [0063]     In accordance with a preferred embodiment of the present invention, the outer peripheral edges  435   a ,  435   b  of the seal segments  426   a ,  426   b  define an arc of approximately 200-220 degrees. The outer peripheral edges  435   a ,  435   b  further include a series of apertures  437  that function as a means of attachment for the seal segments  426   a ,  426   b . The seal segments  426   a ,  426   b  further include tapered angled sections  430   a ,  430   b  extending radially for connecting adjacent seal segments  426   a ,  426   b  in the manner discussed above. A matching taper  432   a ,  432   b  is also formed along the underside of each of the seal segments  426   a ,  426   b  opposite the angled sections  430   a ,  430   b . The angled sections  430   a ,  430   b  of the seal segments  426   a ,  426   b  allow for increase contact between assembled seal segments  426   a ,  426   b.    
         [0064]     In practice, two seal segments  426   a ,  426   b  are connected along their respective peripheral edges  435   a ,  435   b  in an overlapping relationship to create a first seal layer  434 . As such, the resulting first seal layer  434  defines a complete circular cone with a seal seam  436  extending between the first and second seal segments  426   a ,  426   b . As will be discussed below, the shape of the seam edge  438   a ,  438   b  of the seal segments  426   a ,  426   b  ultimately defines the shape of the seal seam  436  extending between the first and second seal segments  426   a ,  426   b  making up the first seal layer  434 .  
         [0065]     The cone feature of the seal assembly reduces the possibility of seal inversion upon instrument retraction. Seal inversion can cause binding of the instrument during retraction creating difficulty when removing instruments from the trocar. The cone feature also provides a natural lead in towards the center of the seal assembly. This guides the instrument inserted towards the center of the seal assembly and reduces the potential of puncturing through the seal at location towards the outer periphery of the cone.  
         [0066]     In accordance with a preferred embodiment of the present invention, the seal segments are composed of an elastomer or a cross-linked polymer such as, but not restricted to, silicone or a polyisoprene. However, those skilled in the art will appreciate the possibility that other materials may be employed without departing from the spirit of the present invention.  
         [0067]     While the preferred embodiments have been shown and described, it will be understood that there is no intent to limit the invention by such disclosure, but rather, is intended to cover all modifications and alternate constructions falling within the spirit and scope of the invention as defined in the appended claims.