Abstract:
A process of making a tack-free gel is disclosed comprising the steps of providing a mold defining a mold cavity, the mold cavity comprising a plastic material; pouring or injecting a molten gel having a high molding temperature into the mold cavity; and forming the tack-free gel as a thin layer of plastic of the mold cavity is melted over the gel. The forming step further comprises cooling the gel from the molten state to a solidified state. The melting temperature of the plastic material is lower than the molding temperature of the gel; and the higher the temperature differential, the greater the melting of the plastic material and the thicker the layer of the plastic material on the surface of the gel. The mold may be formed of low-density polyethylene (LDPE).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 13/215,432, filed Aug. 23, 2011, which is a continuation of U.S. application Ser. No. 10/913,565, filed on Aug. 5, 2004, now abandoned, which claims the benefit of U.S. Provisional Application No. 60/492,949, filed on Aug. 6, 2003, now expired, and is a continuation-in-part of U.S. application Ser. No. 10/776,387, filed on Feb. 10, 2004, now U.S. Pat. No. 7,727,255, which is a continuation of International Application No. PCT/US02/15696, filed on May 14, 2002, now expired, which claims the benefit of U.S. Provisional Application No. 60/312,683, filed on Aug. 14, 2001, now expired, all of which are fully incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention generally relates to gels having tacky surfaces and, more specifically, to surface treatments which will render the gel tack-free. 
         [0004]    2. Discussion of Related Art 
         [0005]    A “gel” is often defined as a semisolid condition of a precipitated or coagulated colloid. Within this definition, gels can differ widely. On one end of the spectrum gels are more fluid in nature but have some solid properties. An example of such a gel might be a gel toothpaste. At the opposite end of the spectrum, the gels are considered solids with some fluid properties. 
         [0006]    It is toward this end of the spectrum that gels are commonly used to facilitate load distribution. Gels enhance this function by offering a high degree of compliance which basically increases the amount of area available to support a load. With an increased area of support, the load is accommodated at a considerably reduced pressure. Particularly where the human body is involved, a reduced pressure is desirable in order to maintain capillary blood flow in body tissue. It is with this in mind that gels are commonly used for bicycle seats, wrist pads, insole supports, as well as elbow and shoulder pads. 
         [0007]    While the advantageous properties of gels have made them candidates for many applications, one disadvantage has seriously limited their use. Most gels are extremely tacky. This characteristic alone makes them difficult to manufacture and aggravating to use. 
         [0008]    Attempts have been made to produce gels that are naturally non-tacky. But such attempts unfortunately have resulted in an intolerable sacrifice of the advantageous properties. Attempts have been made to enclose the gels in a non-tacky pouch. This has also tended to mask the advantageous properties and to significantly increase manufacturing costs. Powders and lubricants have been applied to the tacky surfaces with results limited in both duration and effect. 
         [0009]    Gels have also been of particular interest in the formation of seals where the high compliance and extensive elongation of the gel are of considerable value. Such is the case with seals used in trocars and other surgical access devices, where a seal must be formed both in the presence of a surgical instrument and in the absence of a surgical instrument. 
         [0010]    In general, a trocar is a surgical device intended to provide tubular access for surgical instruments across a body wall, such as the abdominal wall, and into a body cavity, such as the abdominal cavity. Often, the body cavity is pressurized with a gas, typically carbon dioxide, to enlarge the operative volume of the working environment. Under these conditions, the trocar must include appropriate seals to inhibit loss of the pressurizing gas through the trocar. Thus, a zero seal must be provided to seal the working channel of the trocar in the absence of the instrument, and an instrument seal must be provided to seal the working channel in the presence of the instrument. 
         [0011]    Most recently, both zero seals and instrument seals have been provided by a pair of rollers disposed on opposing sides of the working channel. The rollers have been formed of a gel material providing a high degree of compliance, significant tear strength and exceptional elongation. As noted, however, the best gel materials tend to exhibit surfaces that are very tacky. The use of a tacky gel can make the processes of manufacturing and using the gel seals extremely difficult. The disadvantages are increasing in this application, where a tacky gel also produces significant drag forces during instrument insertion. Furthermore, the tacky surfaces tend to draw and retain particulate matter during the manufacturing and handling processes. For these reasons it has been even more desirable to render the highly tacky gel surfaces non-tacky in the case of medical devices such as trocars. 
         [0012]    Many attempts have been made to facilitate handling the rollers during manufacture and to lower instrument drag forces during use. For example, use of lubricants such as silicone oil, KY jelly, and Astroglide, have been applied to the surface to reduce tackiness. Unfortunately, these lubricants tend to dry out over time leaving the gel in its natural tacky state. Non-tacky gels have also been investigated. The non-tacky gels, however, are not particularly heat tolerant, as low amounts of heat can rapidly cause the materials to take a set and distort particularly under compressive loads. This can occur over an extended period of time, for example, even at normal room temperatures. 
       SUMMARY OF THE INVENTION 
       [0013]    In accordance with the present invention, a gel material having all of the advantageous properties previously discussed is further blessed with a non-tacky surface that can be provided at the earliest possible opportunity, during the molding step of the manufacturing process. From the time when the molten gel material first achieves its solid characteristics, it is provided with a non-tacky surface. In the case of a trocar seal, significant drag forces are avoided during the process of instrument insertion. Moreover, the advantages of high compliance, significant tear strength, and exceptional elongation are maintained without any of the disadvantages associated with a tacky device. 
         [0014]    In a first aspect of the invention, a process of making a tack-free gel is disclosed comprising the steps of providing a mold defining a mold cavity, the mold cavity comprising a plastic material; pouring or injecting a molten gel having a high molding temperature into the mold cavity; and forming the tack-free gel as a thin layer of plastic of the mold cavity is melted over the gel. More specifically, the forming step further comprises cooling the gel from the molten state to a solidified state. The mold providing step may further comprise the step of injecting or spraying the mold cavity with the plastic material. It is appreciated that the melting temperature of the plastic material is lower than the molding temperature of the gel and, in this aspect, the difference in the melting temperature of the plastic material and the molding temperature of the gel is in a range of about 20° F. to about 100° F. It should be noted that the higher the temperature differential, the greater the melting of the plastic material and the thicker the layer of the plastic material on the surface of the gel. 
         [0015]    The mold may be formed of low-density polyethylene (LDPE) and has a melting temperature of about 240° F. With the process of the invention, the heat of the molten gel at its molding temperature is transferred to the surface of the LDPE mold so as to melt a thin layer of the LDPE. The solidified gel may be a cylindrical shape having a first opposing end, a second opposing end and a cylindrical body. The mold may comprise a mold base having a plurality of mold holes forming a plurality of mold cavities, each of the mold holes comprising an axial pin to mold an axial hole through a center of the gel, an LDPE cylinder providing a predetermined inside diameter for the mold, and an LDPE disc mounted on the axial pin and disposed at the bottom of each mold cavity in the mold base. After each molding process, the LDPE cylinder may be replaced. The process of the invention may further comprise the step of dabbing at least one of the opposing ends in a low-friction powder such as polytetrafluoroethylene (PTFE) and a lubricant. In another aspect, the mold may further comprise a mold top disposed axially of the mold base and comprises a plurality of holes forming a plurality of cavities, each of the mold top holes is adapted to receive the LDPE cylinder, and a second LDPE disc disposed at the top of each mold cavity of the mold top. 
         [0016]    In another aspect of the invention, the plastic material may be formed from at least one of PVC, ABS, acrylic, polycarbonate, clear polycarbonate, Delrin, acetal, polypropylene and high-density polyethylene (HDPE). The process of the invention may further comprise the step of tumbling or coating the gel in a lubricious material, applying a lubricious coating to the gel in a vacuum deposition process, dipping the gel in a lubricious material, or spraying the solidified gel with a lubricious material to further facilitate the non-tackiness surface of the gel. The lubricious material includes Parylene. 
         [0017]    In yet another aspect of the invention, a process of making a tack-free gel by co-extrusion is disclosed comprising the steps of extruding an elongate sleeve formed of a plastic material around a molten gel having a high molding temperature, the elongate sleeve having an axis and a diameter; pressurizing the molten gel to control the diameter of the filled elongate sleeve; and cooling the filled elongate sleeve to form the tack-free gel. The plastic material of the elongate sleeve may be low-density polyethylene (LDPE). The process may further comprise the step of radially cutting the elongate sleeve into individual segments having predetermined lengths, and removing the gel by squeezing the sleeve and pulling the gel from the sleeve. With this aspect of the invention, the gel may have a cylindrical shape having a first opposing end, a second opposing end and a cylindrical body. The process may further comprise the step of dabbing at least one of the opposing ends in a low-friction powder, which may include at least one of polytetrafluoroethylene (PTFE) and a lubricant, tumbling or coating the gel in a lubricious material, applying a lubricious coating to the gel in a vacuum deposition process, dipping the gel in a lubricious material, or spraying the gel with a lubricious material. The lubricious material includes Parylene. 
         [0018]    Another aspect of the invention is directed to a trocar being adapted to provide access for a surgical instrument through a body wall and into a body cavity, the trocar comprising a cannula having a proximal end and a distal end, a seal housing communicating with the cannula to define a working channel, a seal assembly disposed within the seal housing, at least one roller included in the seal assembly and having an axle supported by the seal housing, and the roller having a tack-free surface and properties for forming a zero seal in the absence of the instrument, and an instrument seal in the presence of the instrument. With this aspect, the roller is pivotal with the axle relative to the seal housing. The tack-free surface may be formed of LDPE, and the roller may further comprise a lubricious coating including at least one of polytetrafluoroethylene (PTFE) low-friction powder or a lubricant including Parylene. 
         [0019]    In a final aspect, a medical access device is disclosed comprising a tubular member having an elongate configuration, at least one wall defining with the tubular member a working channel sized and configured to receive an instrument, and a gel disposed in the working channel and being adapted to form a seal with any instrument disposed in the working channel, wherein the gel includes a non-tacky film to facilitate movement of any instrument through the working channel. It is appreciated that the film may be formed by a fluoropolymer including polytetrafluoroethylene (PTFE). The non-tacky film may be applied as a powder or as a tape over the gel. It is further appreciated that the gel and non-tacky film may have properties including an elongation up to about 1500 percent, and that the gel may be coated with a lubricant including Parylene. 
         [0020]    These and other features of the invention will become more apparent with a description of the various embodiments and reference to the associated drawings. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0021]    The accompanying drawings, which are included in and constitute a part of this specification, illustrate the embodiments of the invention and, together with the description, explain the features and principles of the invention. In the drawings: 
           [0022]      FIG. 1   a  is a side elevation view partially in cross-section of a trocar with a roller seal assembly; 
           [0023]      FIG. 1   b  is a side elevation view of the trocar illustrated in  FIG. 1   a;    
           [0024]      FIG. 2   a  is a perspective view of a plastic mold with multiple mold cavities; 
           [0025]      FIG. 2   b  is a perspective view of a gel roller with an outer layer of mold plastic; 
           [0026]      FIG. 2   c  is a perspective view of a metal mold and multiple cylinders and discs each associated with an individual mold cavity; 
           [0027]      FIG. 2   d  is a perspective view showing the mold cylinders disposed in the mold base; 
           [0028]      FIG. 3  is a side elevation view illustrating a step of dabbing a tacky gel surface into powder; 
           [0029]      FIG. 4  is a side elevation view similar to  FIG. 1   b  and illustrating a single low friction disc mounted between a tacky roller surface and the seal housing; 
           [0030]      FIG. 5  is a schematic view illustrating co-extrusion of an LDPE sleeve and a gel; 
           [0031]      FIG. 6  is a perspective view of base and top molds used in an injection molding operation; 
           [0032]      FIG. 7  illustrates a method for applying a coating by vacuum deposition; 
           [0033]      FIG. 8  is a perspective view illustrating application of a coating in a dipping process; 
           [0034]      FIG. 9  is a perspective view illustrating application of a coating by spraying; 
           [0035]      FIG. 10  is a perspective view illustrating an application of a coating by tumbling; 
           [0036]      FIG. 11  is a perspective view of a hand port wherein a gel seal is overlayed with a fluoropolymer film; and 
           [0037]      FIG. 12  is a cross-section view taken along lines  12 - 12  of  FIG. 11 . 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0038]    A trocar is illustrated in  FIG. 1  and designated by the reference numeral  10 . The trocar  10  is an access device commonly used in surgeries to provide a working channel  12  across a body wall and into a body cavity. The working channel  12  in this case is defined by a cannula  14  and a seal housing  16 . Within the seal housing, a seal apparatus  18  is formed by a pair of opposing rollers  21  and  23 . These rollers  21  and  23  are typically formed of a gel material  30  that provides the seal apparatus  18  with a high degree of compliance, significant tear strength and exceptional elongation. In this case, the gel rollers  21  and  23  are merely representative of any gel structure adapted for use in a medical device, such as the trocar  10 . 
         [0039]    The gel materials contemplated for the rollers  21  and  23  typically have a high melting temperature and exhibit a tacky surface as previously discussed. These two properties, normally considered disadvantages, become advantages in a method of manufacture of the invention. In this case, the gel at a high molding temperature and liquid state, is brought into contact with a plastic molding material having a melting temperature less than the molding temperature of the gel  30 . 
         [0040]    A roller mold  25  is illustrated in  FIG. 2   a  with a plurality of mold cavities or holes  27 . In this case, the mold  25  is formed entirely of a plastic material  26  which defines each of the cylindrical mold cavities  27 . The gel  30  in its high temperature liquid state is poured into each of the mold holes  27  to form one of the rollers  21 ,  23 . At the high molding temperature, the gel  30  initially melts a thin layer  32  of the mold plastic  26  which cools onto the gel surface as illustrated in  FIG. 2   b . In this process, it is believed that the tacky properties of the gel  30  attract and hold this thin layer  32  of plastic thereby resulting in a non-tacky surface on the gel  30 . 
         [0041]    With the process of the invention, it is desirable that the melting temperature of the plastic material  26  be only slightly lower than the molding temperature of the gel  30 . In one aspect, the differential in temperature is in a range of about 20° F. to about 100° F. It is anticipated that the higher this temperature differential, the greater the melting of the plastic material, thereby resulting in a thicker layer of the plastic material on the surface of the gel. 
         [0042]    In one example, a gel can be chosen with a gel molding temperature of about 450° F. A mold  25  formed of a non-metal, plastic material such as low-density polyethylene (LDPE) having a melting temperature of about 240° F. is particularly suited for this process. With the mold at room temperature, and the liquid gel heated to its molding temperature, the gel can be poured into the mold cavities. During and after this molding step, the heat of the liquid gel at its molding temperature is transferred to the surface of the plastic mold and in fact melts a thin layer of the LDPE. At this point, the mold  25  and gel  30  rapidly cool and the melted LDPE forms the thin layer  32  on the outer surface of the solidified gel  30 . As the gel solidifies, its naturally tacky surface attracts and holds the thin LDPE layer  32  to the outer surface. This thin layer  32  of LDPE provides the resulting gel roller  21  with a non-tacky surface. 
         [0043]    Using the mold formed entirely of the LDPE plastic will gradually increase the size of the mold cavities  27  as succeeding interior layers  32  of the LDPE are removed from the mold cavities  27 . One way of addressing this problem is to provide a mold base  41  having a plurality of mold holes  43  as illustrated in  FIG. 2   c . In this case, the mold holes  43  are formed with an axial pin  45  which can be used to mold an axial hole through the center of the roller  21 . Each of the mold holes  43  in the base  41  can then be lined with an LDPE cylinder  47  providing a predetermined inside diameter for the mold. In addition, an LDPE disc  50  can be mounted on the pin  45  and disposed in the bottom of each mold cavity  43  in the base  41 . In this case, the cylinder  47  and disc  50  provide the preferred mold cavities  27  formed of LDPE and ready to receive the gel  30 . 
         [0044]    With this mold base  41  appropriately filled with the LDPE cylinders  47  and discs  50 , the molten gel  30  can be poured into the top of each cylinder  47  to mold each roller  21  with a cylindrical outer surface  52  and an axial pin  45 . In the manner previously discussed, the high temperature of the molten gel will melt a layer off the inside of the LDPE cylinder  47  and disc  50  to provide a non-tacky surface on each roller  21 . One advantage provided by the method illustrated in  FIG. 3  is that the LDPE cylinders  47  can be discarded after each molding process and replaced with new LDPE cylinders  47  having the predetermined diameter. 
         [0045]    It will be noted that in the absence of an LDPE disc on the top of the mold cavity, one end  56  of the roller  21  will maintain its tacky properties. Although the single tacky end  56  may not be particularly detrimental in use, there are several methods that can be implemented to make the tacky end  56  less tacky. For example, this end  56  can be dabbed in a low friction powder  57 , such as PTFE, as shown in  FIG. 3 . Also, the tacky end  56  can be lubricated to make it less tacky. As a third alternative, the tacky end  56  of the roller  21  can be mounted in the trocar  10  adjacent to a low friction disc  58  as illustrated in  FIG. 4 . 
         [0046]    An alternative method for constructing the rollers  21 ,  23  with a non-tacky surface might involve the use of co-extrusion techniques. In such a process, illustrated in  FIG. 5 , an elongate sleeve  61  of LDPE can be extruded around the molten gel  30 . In this case, the gel  30  can be pressurized to control the diameter of the filled sleeve  61 . After the filled sleeve  61  is permitted to cool, it can be radially cut into individual segments  62  having a predetermined length as illustrated in  FIG. 5 . The gel  30  can be removed by merely squeezing the sleeve  61  and pulling the gel  30  from the sleeve. Once removed, the gel roller  21  will have an outer cylindrical surface  63  with an LDPE coating  65 , and a pair of opposing ends  67  and  70 . In this process, both of the ends  67  and  70  of the roller  21  will be uncoated and will therefore have tacky surfaces. These two ends  67 ,  70  can be addressed in the manner previously discussed with reference to the roller end  56  in  FIG. 3 . 
         [0047]    Another process which might be used to eliminate the tacky ends of the roller  21 , might be an injection molding process such as that illustrated in  FIG. 6 . In this case both a mold base  72  and a mold top  74  are provided to receive an LDPE cylinder  74  and a pair of LDPE discs  76  and  78 , one on each end of the cylinder  74 . Rather than pouring the molten gel  30  into the open top of the cylinder as illustrated in  FIG. 2 , the molten gel  30  in this process would be injected into the LDPE mold cavity  43 . The resulting gel roller  21  would have all of its surfaces, including both ends, coated with a thin layer of LDPE. 
         [0048]    The foregoing processes have been discussed with respect to a single plastic, namely low density polyethylene. It is apparent that other types of plastics might be similarly used to provide the desired non-tacky surface for the gel compounds. Other plastics which might be of advantage in this process could include for example, PVC, ABS, acrylic, polycarbonate, clear polycarbonate, “Delrin” (a trademark of Dupont), acetyl, polypropylene, and high density polyethylene (HDPE). Of this group of plastics, the HDPE appears to reduce the tackiness of the gel surface to the greatest extent. 
         [0049]    Other types of coatings can be applied to either a tacky or non-tacky surface of the roller  21 . One highly lubricious coating is that manufactured and sold by Para Tech Coating, Inc. under the trademark “Parylene”. It has been found that this material can be applied to the surface of the roller  21  by processes including vacuum deposition in a chamber  81  ( FIG. 7 ), dipping on a tray  83  ( FIG. 8 ) and spraying on a shelf  85  ( FIG. 9 ). A highly lubricious coating, such as Parylene may also be applied in a tumbler  87  as illustrated in  FIG. 10 . In this case, the rollers  21 ,  23  being tumbled must already have a non-tacky surface in order to remain separate during the tumbling process. 
         [0050]    Another apparatus and method for addressing the natural tacky properties of a gel seal is discussed with reference to  FIG. 11 . In this view, a medical device in the form of a hand port is adapted to overlay a body wall, such as an abdominal wall  92 , and to provide sealed access to a body cavity, such as an abdominal cavity  93 , for a surgical instrument, such as a surgeon&#39;s hand  94 . 
         [0051]    In this embodiment, the hand port  90  includes a rigid or semi-rigid base structure  96  in the form of a ring  98 . A gel material  101 , of the types previously discussed, can be molded into the ring  98  with portions  103  of the gel  101  defining a slit  105 . This slit  105 , which is of particular interest in one aspect of the invention, forms part of a working channel  107  that extends through the abdominal wall  92  and into the abdominal cavity  93 . 
         [0052]    In this embodiment, the ring  98  is similar to the cannula  14  and seal housing  16  discussed with reference to  FIG. 1   a , in that it is disposed around the working channel  107  and is adapted to form a seal  110  with the abdominal wall  92 . 
         [0053]    A second seal  112  is formed between the gel material  101  and the ring  98  so there is no communication between the abdominal cavity  93  and regions exterior of the abdominal wall  92  as long as the slit  105  remains closed. In this manner, the hand port  90  functions as a zero seal in the absence of the surgeon&#39;s hand  94 , or any other medical instrument. 
         [0054]    The highly advantageous properties of the gel material  101  are particularly beneficial in the hand port  90 , where they provide a high degree of compliance together with elongation or stretch as great as 1500 percent. Thus, the gel material  101  is ideally suited to form a zero seal in the absence of the surgeon&#39;s hand  94 , or an instrument seal in the presence of the surgeon&#39;s hand  94 . It can be seen that the gel material  101  is similar to that previously discussed with respect to the rollers  21  and  23  in  FIG. 1   a . In that regard, the gel material  101  is disposed in the base structure and forms the second seal  112  with the base structure. The gel material  101  will typically have the tacky properties in its natural state, as previously discussed. 
         [0055]    In order to address these tacky properties in the hand port  90 , and also with respect to the trocar  10  of  FIG. 1   a , a film  14  can be applied to the surface of the gel material  101 . This is particularly advantageous with respect to the portions  103  where the film  114  lines the working channel  107  through the hand port  90 . When the film  114  is applied to any surface of the gel material  101 , it functions to mask the tacky properties of the gel material  101  greatly facilitating handling of the hand port  90  during manufacture. But in the particular location where the film  114  is applied to the portions  103  defining the slit  105 , the gel not only masks the tacky properties, but also facilitates movement of the medical instrument such as the surgeon&#39;s hand  94  into and through the working channel  107 . In certain preferred embodiments, the film  114  is formed by a fluoropolymer, such as polytetrafluoroethylene (PTFE). In one method of manufacture, the film  114  is applied as a PTFE powder. In other processes, the film  114  can be applied as a PTFE tape. 
         [0056]    One advantage associated with the PTFE film  114  is the adhesive properties which this material exhibits with respect to the gel material  101 . Although not fully understood, it is believed that the mineral oil present in a typical gel  101  is highly attracted to the PTFE where it facilitates adhesion between the gel material  101  and the film  114 . 
         [0057]    Another advantage associated with the PTFE film  114  is associated with its stretchability or elasticity. While the film  114  is desirable to mask the tacky properties of the gel  105 , it is important that the elongation properties of the gel be maintained. It has been found that the elongation of the gel material  101 , up to 1500 percent, is generally matched by the elongation or stretchability of the PTFE film  114 . Thus, the gel  101  and PTFE film  114  can be stretched about 1000 percent, and perhaps as much as 1500 percent, from an original state to a stretched state without breaking the film  114 , and returned from the stretched state to the original state. 
         [0058]    Although the PTFE film  114  masks the tacky properties of the gel, it is not necessarily lubricious. If this lubricious property is desired in addition to the non-tacky properties, the film  114  can be coated with a lubricant  116 , such as the Parylene and other lubricants previously discussed. 
         [0059]    It will be understood that many other modifications can be made to the various disclosed embodiments without departing from the spirit and scope of the invention. For these reasons, the above description should not be construed as limiting the invention, but should be interpreted as merely exemplary of embodiments.