Abstract:
A medical balloon, implantable in human tissue, of unitary silicone construction. The balloon is self-sealing upon removal of an inflation implement. The balloon device comprises a molded valve portion which is dip-coated in a silicone dispersion to create a balloon wall around and integral with the valve portion. Preferably, both the valve portion and the balloon wall are comprised of the same silicone material. The dipping process, combined with a vulcanizing process, creates a laminar wall which is strong and resistant to separation during inflation. The balloons may be used in for the treatement of urinary incontinence or vesicoureteral reflux, alternative procedures such as emboliztion or blocking of veins or arteries to accomplish the treatement of enlarged blood vessels in the brain or for treating severe uterine bleeding.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to U.S. provisional patent application No. 60/291,493, filed May 15, 2001 which is incorporated by reference herein. 

   BACKGROUND OF THE INVENTION 
   The present invention pertains generally to an implantable microballoon and a method of making such a microballoon. 
   Implantable microballoons provide a minimally invasive treatment for the urological condition of stress urinary incontinence resulting from Intrinsic Sphincter Deficiency (ISD). Treatment of the condition is completed through placement of one or more implantable balloons into the periurethral tissue of the bladder neck. Implantation of the balloons results in the coaptation of the urethra which improves or resolves the incontinence condition. 
   Delivery is completed by insertion of the microballoon into the tissue parallel to the urethra. The microballoon is then inflated and left in the bladder neck. 
   Microballoons can be similarly used for the treatment of vesicoureteral reflux (VUR—reflux of the urine from the bladder up the urethras to the kidneys) and alternative procedures such as embolization or blocking of veins or arteries to accomplish the treatment of enlarged blood vessels in the brain or for treating severe uterine bleeding. Slightly larger balloons may be used for fecal incontinence or gastrointestinal reflux. 
   Until now, the small size and numerous intricacies of microballoons have presented problems pertaining to performance and manufacture. The valves that are included in such microballoons are typically constructed using numerous parts and designed to be self-sealing once an inflation syringe is removed therefrom. In the assembled condition, an outsidewall of the valve is typically attached to the inside neck of a microballoon using adhesive or similar bonding procedure. 
   Such a manufacturing method is laborious and expensive. Moreover, when the balloons are inflated, there is a tendency for the adhesive to fatigue, separate and allow the fluid contained within the balloon chamber to leak. Even when the adhesive holds, however, the valve can leak due to manufacturing defects that can result from the complexity and size of the valve. 
   In view of the above, there is a need for a valve which is simple, reliable and relatively inexpensive. There is also a need for a method of manufacturing a microballoon which is repeatable, efficient, and relatively simple. 
   BRIEF SUMMARY OF THE INVENTION 
   Provided is a microballoon which is relatively simple in construction and manufacture and provides an increased level of reliability and cost efficiency. The microballoon generally comprises a valve portion of unitary construction, which is a molded valve body made of a material, such as silicone, capable of being punctured and resealed. The valve portion includes a cylindrical wall extending therefrom having an open end which is constructed and arranged such that when the open end is dipped into a solution of material, such as silicone, a meniscus forms over the end. 
   When the meniscus solidifies, it closes the end of the cylindrical wall, thereby creating a completely enclosed inner chamber. The valve portion is then dipped into the solution again and allowed to solidify in order to form another layer over substantially the entire valve portion. This process is repeated until the cylindrical wall is built up to a desired thickness, thereby creating the microballoon. 
   This method obviates the need for adhesives to bond the valve portion to the inner wall of a microballoon. Rather, the microballoon and the valve are integral and problems pertaining to separation between the valve portion and the balloon portion are avoided. 
   Additionally, the repeated dipping creates multiple layers of material in the formation of the balloon. Such a “laminate” balloon wall is significantly stronger than a wall formed in a single step. 
   Moreover, this method of manufacturing a microballoon is much simpler than conventional methods which require assembling intricate valve portions using a plurality of separate parts and subsequently adhering the valve portion to the balloon portion. The balloon designs and methods of manufacture of the present invention are also effective for creating balloons of various sizes. 
   Once the balloon is created, a piercing is placed through the valve body using a needle like instrument. This piercing defines a path through which an inflation member may be inserted without imparting damage to the valve body. Preferably, this piercing has a curved portion which improves the sealing characteristic of the piercing when subjected to back pressure, such as that created by the inflated balloon. This curved portion is created by bending the balloon midway through the piercing operation. 
   The term “piercing” is used to describe the channel created through the valve body and stem which remains substantially collapsed or closed unless forced open by an implement which is substantially rigid, relative to the soft material of the valve body. Though the piercing is created by piercing the valve body with a sharp, needle-like instrument, it is understood that the piercing could be created using other methods such as molding or the like. For example, if a threadlike sacrificial strand is held in place while the valve body is being molded, and pulled out and discarded once the body set, such a “piercing” would likely form and perform adequately. Due to the resiliency of the material used, however, best results are likely to be obtained by actually piercing the valve body with a fine, needle-like implement. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of the device of the present invention in an inflated state; 
       FIG. 2  is a sectional view of the device of the present invention in a deflated state; 
       FIG. 3  is a flow chart of a preferred method of the present invention; and, 
       FIGS. 4A ,  4 B,  4 C,  4 D,  41 E and  4 F are a series of sectional views of the device of the present invention in progressive stages of manufacture. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the Figures, and first to  FIG. 1 , there is shown a completed device  10  of the present invention in an inflated state. Device  10  generally comprises a valve portion  20  and a balloon portion  70 . 
     FIG. 2  provides a detailed depiction of the device  10  in a deflated state and prior to its first inflation. The valve portion  20  is of unitary construction and includes a valve body  22  and a valve stem  26 . The valve body  22  is preferably cylindrical and defines an inlet  24  in its lower side. The inlet  24  is cylindrical, frustoconical, conical, semispherical, or a similar suitable shape, and substantially concentric with the valve body  22 . 
   The valve stem  26  is integral with the valve body  22  and extends upwardly therefrom, opposite the inlet  24 . The valve stem  26  has at least one side  28  and a tip  30 . Preferably, the valve stem  26  is cylindrical and the tip  30  is rounded, thereby forming somewhat of a silo shape. The valve stem  26  is substantially concentric with the valve body  22  and the inlet  24 . It has an outside diameter which is smaller than the diameter of the body  22 . When the valve portion  20  is operably attached to the balloon portion  70 , the valve stem  26  extends into an inner chamber  72  of the balloon portion  70 . 
   The valve portion  20  is preferably molded from an elastomeric or similarly resilient material such as silicone. Such a material is advantageous because it can be pierced and remain fluid-tight after removing the piercing implement. Thus, a channel or piercing  32  is defined by the valve portion  20  and provides a path for a rigid inflation tube to follow when inserted into the balloon, thereby preventing the valve portion  20  from being damaged by the insertion of an inflation tube during an implantation operation. The piercing  32  leads from the inlet  24  to the inner chamber  72  through the valve body  22  and the valve stem  26 . Preferably, the piercing  32  begins in the inlet  24  along a longitudinal axis  34 , which is shared by the inlet  24 , the valve body  22 , and the valve stem  26 . The piercing  32  continues along this longitudinal axis  34  until it reaches a predetermined location in the valve stem  26  where a curved portion or bend  36  is formed in the piercing  32 , such that the piercing  32  exits the side  28  of the valve stem  26 . The bend  36  is advantageous in that it enhances the ability of the silicone to close the piercing  32 , thereby making the chamber  72  fluid-tight when the piercing  32  is not held open by a substantially rigid member. A close look at  FIG. 1  shows how the valve stem  26  stretches and flattens during inflation. It can be seen that bend  36  of the piercing  32  forms somewhat of a flap  37  which is held closed by the pressure contained within the inner chamber  72 . 
   A cylindrical sidewall  38  extends upwardly from the valve body  22  in a direction substantially parallel to that of the valve stem  26 . The cylindrical sidewall is laterally or radially displaced from the valve stem  26  and is substantially concentric therewith. The sidewall  38  has an inner diameter which is greater than an outer diameter of the valve stem  26 , thereby creating an annular space  39  between the valve stem  26  and the sidewall  38 . 
   The annular space  39  created between the valve stem  26  and the sidewall  38  is defined on its lower side by a curved portion or web  44 . Web  44  is concave and opens upwardly toward the inner chamber  72  of the balloon portion  70 . Web  44  functions to relieve stress from the union of the valve body  22  and the cylindrical sidewall  38  when the device  10  is inflated. Web  44  is also shaped to ease the molding process of the valve body  22 . 
   Referring briefly back to  FIG. 1 , it can be seen how the annular space  39  virtually disappears when the valve portion  20  stretches due to inflation. The web  44  creates a smooth transition between the sidewall  38  and the side  28  of the valve stem  26 . It can also be seen that the elastic properties of the cylindrical sidewall  38  and the balloon wall  74  are similar if not identical, acting in concert while stretching and forming the desired balloon shape. 
   Referring again to  FIG. 2 , an end portion  40  extends upwardly from the sidewall  38  and bends inwardly to define an opening  42 . Although the present invention may be practiced without the inwardly curving end portion  40 , it will be seen that the end portion  40  is advantageous in forming a meniscus  76  when the end portion  40  is inverted and dipped in a solution of silicone. This process will be described in more detail below. The opening  42  thus has an inner diameter which is less than an inner diameter of the cylindrical sidewall  38 . 
   Preferably, the outer surface of the cylindrical sidewall  38  comprises an upper sidewall  46  and a lower sidewall  48  connected by a taper  50 . Lower sidewall  48  has a greater outer diameter than upper sidewall  46 . The function of this taper  50  will become evident when the manufacturing method is described below. 
   For purposes of manufacture, a skirt  54  is provided that extends downwardly from the valve body  22 . The skirt  54 , preferably, has an outer diameter that is smaller than outer diameter of the valve body  22 . The skirt  54  provides an attachment area so that the valve body  22  may be more readily handled during manufacturing. The smaller outer diameter of the skirt  54  creates a ridge  56  which is used to provide a visual and tactile definition of a lower extent of the valve body  22  and an upper extent of the valve skirt  54  such that the skirt  54  may be removed without removing any material from the valve body  22 . The ridge  56  also creates a stop in the event that a dipping mandrel  80  (e.g.  FIGS. 4C and 4D ) is used to manufacture the device  10 . The mandrel  80  is preferably sized such that the skirt  54  frictionally fits within an open end of the mandrel  80 . The valve body  22 , however, is too large to fit within the mandrel  80 . The use of the mandrel  80  will be explained in more detail below. 
   The device  10  is completed when the balloon portion  70  is attached to, or more specifically formed on, the valve portion  20 . The balloon portion  70  comprises a balloon wall  74  which is preferably integral with the cylindrical sidewall  38 . The balloon wall  74  begins at approximately the ridge  56  and extends all the way over the end portion  40  and also over the opening  42 . Additionally, the balloon portion includes a meniscus plug  76  which fills in the opening  42  and prevents liquid silicone solution from entering the inner chamber  72  during the dipping procedure. Once the balloon portion  70  is attached to the valve portion  20 , the inner chamber  72  is defined by the cylindrical sidewall  38 , the meniscus plug  76 , the valve stem  26 , and the web  44 . 
   In a preferred embodiment, the material used to create the balloon wall  74  is the same as the material used to mold the valve portion  20 . Once the balloon portion is attached to the valve portion, the distinction between the balloon wall  74  and the cylindrical sidewall  38  disappears and an integral wall of unitary construction is created. 
   Attention is now drawn to  FIGS. 3 and 4 , which pertain to preferred methods of manufacturing the device  10  of the present invention.  FIG. 3  provides a flowchart depicting the steps of a preferred method.  FIG. 4  shows the device  10  of the present invention in various states of construction in accordance with the method of  FIG. 3 . 
   At  100  ( FIG. 3 ), a silicone dispersion is prepared and placed in a container having sufficient depth to provide a dipping pool into which a valve portion  20 , or many valve portions  20 , may be dipped. In a preferred embodiment, the dispersion is comprised of a solid silicone gum base or silicone paste mixed with xylene, which breaks down the intermolecular bonds of the solid silicone to form a self-leveling liquid dispersion. The dispersion should be thin enough to form a thin film across the opening  42  when the end portion  40  of the valve portion  20  is dipped into the dispersion. A large opening  42  may require a thicker dispersion than a smaller opening  42 . The dispersion becomes thinner as more xylene is used, as is understood by those skilled in the art. 
   At  110 , the valve portion  20  is molded. This may be done in a separate operation or the silicone dispersion from  100  may be used. Preferably the material used to mold the valve portion is the same as the material in the silicone dispersion.  FIG. 4A  shows a completed valve portion  20 . Notably, opening  42  in the end portion  40  of the valve portion  20  is formed by the mold member used to create the contours of the valve stem  26  and web  44 , and allows the mold member to be removed therethrough. 
   At  120 , the molded valve portion  20  is attached to a dipping mandrel or tube  80 , as shown in  FIG. 4B . The valve portion  20  is attached to the dipping mandrel  80  by inserting the skirt  54  into an open end of the dipping mandrel  80 . The skirt  54  is sized to frictionally fit within the opening of the mandrel  80  with enough resistance to movement to prevent the valve portion  20  from falling out of the dipping mandrel  80  when the mandrel  80  is inverted during the dipping operations. The use of a dipping mandrel  80  is preferred because several dipping mandrels  80  may be arranged in close proximity such that the dipping process can occur for several valve portions  20  at once. Other instruments to retain the skirt  54  would be acceptable, especially when the devices  10  are being constructed on an individual basis. Similarly, a dipping mandrel could be constructed and arranged to frictionally fit within the inlet and achieve similar results.  FIG. 4B  shows the skirt  54  of valve portion  20  inserted within an open end of dipping mandrel  80 . Notably, the skirt  54  is inserted until the ridge  56  abuts against the end of the dipping mandrel or tube  80 . 
   The valve portion  20  is now ready for the dipping process used to create the balloon portion  70 . At  130  ( FIG. 3 ), the meniscus plug  76  ( FIG. 4B ) is formed. Forming the meniscus plug  76  comprises inverting the valve portion  20  and dipping mandrel  80  and submerging the end portion  40  of the valve portion  20  into the silicone dispersion at  132 . The end portion  40  is submerged deeply enough to ensure that the entire opening  42  comes into contact with the silicone. The valve portion  20  is then removed from the dispersion pool at  134  and held in an inverted position above the dispersion while some of the xylene forming the meniscus  76  has a chance to evaporate, thereby somewhat solidifying the meniscus. The steps of dipping the valve portion and holding it above the dispersion pool are repeated until a plug  76  is formed at  136 . Determining the optimal number of times to repeat the process may require a visual inspection, at  134 , on the first plug  76  of a batch. It is important that the meniscus plug  76  is thick enough and strong enough to prevent the liquid silicone from entering the inner chamber  72  when the valve portion  20  is later fully dipped in the silicone dispersion in order to form the balloon portion  70 . One skilled in the art will see that there are a number of variables which may change the drying time or the number of cycles required to achieve a desired meniscus plug  76 . The factors include, but may not be limited to, the size of the opening  42 , the thickness of the end portion  40 , the length of the cylindrical sidewall  38 , the viscosity of the silicone dispersion, and the material used in creating the valve portion  20 . It has been found, however, that three to four cycles usually forms an adequate plug  76 . 
   Once the plug  76  has been formed at  130 , the plug  76  is partially vulcanized at  140  in order to expel the xylene from the plug  76 , thereby solidifying the entire end portion  40 . Partial vulcanization is accomplished by baking the valve portion  20  at between 150 C and 170 C, preferably 160 C, for between 5 and 20 minutes, preferably between 9 and 11 minutes. 
   The valve portion  20  now has a plug  76  which is strong enough to prevent the silicone dispersion from entering the inner chamber  72  when the valve portion  20  is fully dipped into the dispersion. At  150 , the balloon portion  70  is formed. This entails inverting the valve portion  20  and the mandrel  80 , as was done at  130  to form the plug  76 , and dipping the entire valve portion  20  into the dispersion, with the exception of the skirt  54 , which is contained within the mandrel  80 . This is step  152  of  FIG. 3 . 
   At  154 , the device  10  is removed from the dispersion and the xylene is allowed to evaporate. This evaporation process is preferably accelerated by spinning the mandrel  80  for approximately 15 minutes. At  156 , the thickness of the newly formed balloon wall  74  is examined and, if too thin, the decision is made at  158  to dip the device  10  again and spin for another 15 minutes. Preferably, this process is repeated at least two, more preferably three times, in order to build up the balloon wall  74  and also to create a laminar construction in the wall  74 , thereby significantly increasing its strength. In the embodiment, the desired wall thickness is 0.009″–011″. 
     FIG. 4C  shows the device  10 , attached to the mandrel  80 , with a newly formed balloon wall  74  extending over the end portion  40  and back to approximately the ridge  56  where the skirt  54  extends from the valve body  22 . Notably, the taper  50  still exists between the upper sidewall  46  and the lower sidewall  48 , as the balloon wall  74  closely follows the contours of the valve portion  20 . 
   Having achieved the desired thickness, the device  10  is ready to be fully vulcanized at  160 . This is accomplished by baking the device  10  at between 150 C and 170 C, preferably about 160 C, for approximately one hour. Doing so ensures a complete expulsion of the xylene from the wall  74  and the plug  76 , thereby leaving a solid device  10  of silicone. 
   The device  10  must now be pierced, at  170 , in order to form piercing  32 . Piercing  32  will provide a path for an inflation tube to follow from the inlet  24  to the inner chamber  72 . A piercing implement  82  is used having a sharp, needle-like point  84 . The piercing implement  82  is inserted through the mandrel  80 , which acts as a guide to keep the point  84  substantially travelling along the central axis  34  of the device  10 . The implement  82  passes through the mandrel  80 , entering the inlet  24  of the device  10 , and begins puncturing the valve body  22 . The implement continues through the valve body  22  and pierces the valve stem  26 , still along the common central axis  34 . This is shown in  FIG. 4D . For clarity, the piercing  32  shown in  FIG. 4D  is straight, exiting the valve stem  26  and entering the inner chamber  72  along the central axis  34 . However, as discussed above, a bend  36  in the piercing  32 , shown in  FIGS. 1 and 2 , is preferable. As the mandrel  80  limits lateral movement of the implement  82 , the bend  36  is formed by manually bending the valve stem  26  to one side prior to completing the piercing operation. Once the valve stem  26  is bent to one side, the implement  82  is pushed through the mandrel  80  until the point  84  exits a side  28  of the valve stem  26 . Whether or not a bend  36  is created in the piercing  32 , once the point  84  of the implement  82  enters the inner chamber  72 , the piercing  32  is complete and the implement  82  is removed from the mandrel  80 . 
   At  180 , the device  10  is substantially complete and cut from the mandrel  80 . The cut is made along the ridge  56 , thereby removing the skirt  54  while leaving the inlet  24  intact. The device  10  is complete but must be tested to ensure that no leaks occur. At  190 , an inflation test is performed. As seen in  FIG. 4E , an inflation tube  90  is inserted through the newly formed piercing  32 . Preferably, this is done manually so as to prevent damage to the valve body  22 . The balloon device  10  is then inflated to capacity with a fluid, such as saline or water. The inflation tube  90  is removed and the inflated device  10  is inspected for leaks. Once the fluid-tight integrity of the device  10  has been confirmed, the inflation tube  90  is reinserted and used to deflate the device  10 . The inflation tube  90  is again removed.  FIG. 4F  shows a deflated device  10 . Note that the taper  50  is now gone. A degree of hyperplasia occurs during the initial inflation, thereby increasing the deflated diameter of the upper sidewall  46  and the balloon wall  74  thereover. The taper  50  allows for this hyperplasia such that the exterior of the balloon device  10  becomes cylindrical upon completion of the initial inflation at  190 . If there is no taper  50 , the balloon device  10  would not become cylindrical after the inflation test and would, therefore not fit into transporter tubes, discussed below. 
   At  200  the balloons are oven dried to remove any remaining test fluid. Preferably the balloons are dried at 90 C for approximately 60 minutes. 
   Each balloon is then removed from the oven and loaded into a transporter tube at  210 . Transporter tubes are the preferred method for packaging and shipping because they are constructed and arranged for use with a linear balloon delivery system such as that disclosed in U.S. patent application Ser. No. 09/547,952, filed Apr. 12, 2000, incorporated by reference herein. The transporter tube is disclosed in U.S. Provisional Patent Application Serial No. (unassigned) filed by the common assignee of the present application on even date herewith and which is also incorporated by reference herein. These transporter tubes are metal tubes which have an inner diameter substantially equal to the outer diameter of the device  10 . They allow a physician to load the balloon device  10  into a linear delivery system easily and accurately. They also serve to protect the balloons during shipping and handling. 
   Those skilled in the art will further appreciate that the present invention may be embodied in other specific forms without departing from the spirit or central attributes thereof. In that the foregoing description of the present invention discloses only exemplary embodiments thereof, it is to be understood that other variations are contemplated as being within the scope of the present invention. Accordingly, the present invention is not limited in the particular embodiments which have been described in detail therein. Rather, reference should be made to the appended claims as indicative of the scope and content of the present invention. 
   Additionally, it is understood that terms such as “upper”, “lower”, “side”, “above”, “below”, and the like, as used herein, are terms of relationship rather than absolute orientation. These relative terms are used to enhance the clarity of description and are in no way limiting or implying that a certain orientation is required to practice the scope of the present invention.