Abstract:
A medical balloon includes at least one internal wall dividing the balloon into a plurality of separate chambers which may be separately inflatable and deflatable. The at least one internal wall is impregnated with heat conductive particles. The heat conductive particles enable heat produced during the balloon blowing process to pass through the polymer material of the balloon and specifically into the internal wall or walls, enabling these to soften and stretch during the process. This improves the integrity of the balloon and also balloon flexibility. The radiopaque particles embedded in the internal wall or walls of the balloon can also, in preferred embodiments, be of radiopaque material, providing the balloon with imaging visibility during deployment thereof in a patient.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. §119(a) to Great Britain Patent Application No. GB 1517831.2, filed Oct. 8, 2015, which is hereby incorporated by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to a medical balloon for use in a variety of medical treatments including, for example, for angioplasty procedures, medical device implantation, valvuloplasty, rehabilitation of airways, temporary vessel occlusion, and so on. 
     BACKGROUND ART 
     Medical balloons are well known in the art. A conventional balloon assembly includes an expandable balloon fitted at the distal end of a carrier catheter, the catheter having at least one lumen fluidically connected to the internal volume of the balloon and arranged to supply fluid to expand, or inflate, the balloon, and to exhaust fluid from the balloon so as to collapse the balloon at the end of the medical procedure. Medical balloons of this nature are generally circular in transverse cross-section and have their two ends fixed in fluid tight manner to the balloon catheter such that the internal volume, or chamber, of the balloon is sealed to the environment. Whilst it is relatively simple to form a balloon which has a varying diameter along its length, it is harder to alter the cross-sectional shape of the balloon as the inflation pressure causes the balloon wall to tend to a circle. Attempts to make a balloon with cross-sectional shapes other than round when inflated have met with practical difficulties, including increased stiffness of the balloon particularly when deflated, increased tendency to rupture, poor repeatability and stability of the inflated shape, and so on. 
     Examples of medical balloons and catheters having a plurality of chambers of non-round cross-sections can be found in US 2007/0010845, U.S. Pat. No. 5,501,667, US 2015/0094657, U.S. Pat. No. 5,304,135, US 2003/0032963 and WO 2006/037608. 
     SUMMARY OF THE PRESENT INVENTION 
     The present invention seeks to provide an improved medical balloon and specifically a multi-chamber medical balloon. 
     According to an aspect of the present invention, there is provided a medical balloon assembly including a balloon having a body portion, the body portion being formed of a balloon wall providing an expandable volume within the balloon, the expandable volume being divided into a plurality of chambers by a least one internal wall extending between opposing sides of the balloon wall, the balloon wall and internal wall being formed from a flexible polymer material, the polymer material of the internal wall having heat conductive particles embedded therein. 
     The heat conductive particles in the internal wall have the function of transferring heat during the balloon blowing process into the internal walls, allowing these to soften and expand, with the result that the balloon can be properly formed. This can also optimise the flexibility of the formed balloon, even though the balloon includes additional walls compared to a standard cylindrical single chamber balloon. The provision of a balloon with internal walls can also provide a balloon with multiple chambers, permitting the formation of a balloon with a non-round axial shape and also or in the alternative a balloon which can be selectively inflated. 
     The heat conductive particles have a thermal conductivity which is greater than the thermal conductivity of the material of the internal wall. In embodiments, the thermal conductivity of the heat conductive particles is at least 50 times greater than the thermal conductivity of the material of the internal wall. In some embodiments, the thermal conductivity of the heat conductive particles is at least 100, or at least 200, times greater than the thermal conductivity of the material of the internal wall. Preferably, the thermal conductivity of the heat conductive particles is at least 500 times greater than the thermal conductivity of the material of the internal wall. 
     In some embodiments, the thermal conductivity of the heat conductive particles is at least 20 W/(mK), at least 60 W/(mK), or preferably at least 150 W/(mK). 
     Advantageously, the balloon wall has exterior and interior surfaces and a wall thickness between the exterior and interior surfaces, the internal wall extending to the interior surface of the balloon body portion. In other words, the internal wall preferably does not extend to the outer surface of the balloon, enabling the balloon wall material to act as a barrier to the heat conductive particles relative to surrounding body tissue. 
     Preferably, the balloon body portion is substantially free of the heat conductive particles of the internal wall. In the preferred embodiments, the balloon wall is made of polymer material only. 
     The balloon wall may be made of a single layer of material or of multiple layers of material. The internal wall is preferably made of a single layer of material, and may be uniform in consistency throughout its volume. 
     The heat conductive particles may be of or include a metal or metal alloy. They may also be made of or include a radiopaque material. 
     In the preferred embodiment, the heat conductive particles are or include tungsten. Tungsten is a preferred material as it exhibits good heat conductive properties and is also radiopaque, which results in the balloon being visible to imaging during the deployment of the balloon in a patient. 
     In other embodiments, the heat conductive particles are or include at least one of: boron, gold, silver, platinum, palladium and copper. 
     Advantageously, the internal wall includes around or at least 50% by weight of heat conductive particles. 
     The density of heat conductive particles in the internal wall may be around 2 g/cc, in one example 1.92 g/cc, and the specific volume around 0.5 g/cc, in one example 0.521 g/cc. 
     Preferably, the heat conductive particles have an average particle size of less than one to tens of micrometres, in one embodiment in the region of 0.50 to 1.0 micrometres. They may have a substantially round or elongate shape, advantageously a rounded oblong shape. It has been found that such shape and size provide optimum characteristics in terms of conducting heat to the internal wall or walls during formation of the balloon from a raw tubing. 
     The heat conductive particles are preferably substantially evenly distributed throughout the internal wall or walls, although in other embodiments they may have a differing distribution, for instance to have a greater concentration or density further away from the external surfaces of the balloon or raw tubing. 
     In the preferred embodiments, the balloon wall and the internal wall or walls are made from the same polymer material. In some embodiments, the balloon wall and the at least one internal wall are made from a polyamide, for example of nylon, preferably nylon  12 . 
     The balloon may include a plurality of internal walls. The or at least two of said internal walls may be disposed substantially parallel to one another. In addition or in the alternative, they may be disposed to cross one another. 
     The body portion may be generally circular or non-circular in transverse cross-section. It may, for instance, be generally oval in transverse cross-section. 
     In some embodiments, the internal wall generates an external channel or depression in an exterior surface of the balloon on inflation of the balloon. This can be very useful in some medical applications, for instance where the balloon may be positioned adjacent an organ requiring protection from the pressure generated by the balloon. An example are the vocal cords for a balloon intended to treat the trachea. 
     The at least one internal wall advantageously divides the balloon into fluidically separate chambers. 
     Other features and advantageous of the invention taught herein will be apparent from the following description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic perspective view of an embodiment of raw tubing for forming a medical balloon according to the teachings herein; 
         FIG. 2  is a transverse cross-sectional view of an embodiment of raw tubing according to the teachings herein; 
         FIG. 3  shows in enlarged form a part of the raw tubing of  FIG. 2 ; 
         FIG. 4  is a schematic cross-sectional view of a medical balloon according to the teachings herein disposed in a balloon formation mold; 
         FIG. 5  is a side elevational view of a balloon catheter according to the teachings herein; 
         FIG. 6  is another side elevational view of the balloon catheter of  FIG. 5   
         FIG. 7  is a transverse cross-sectional view of the medical balloon of  FIGS. 5 and 6 ; 
         FIG. 8  is a transverse cross-sectional view of another embodiment of raw tubing for making a medical balloon; 
         FIG. 9  is a transverse cross-sectional view of a medical balloon in inflated condition formed from the raw tubing of  FIG. 8 ; and 
         FIG. 10  is a transverse cross-sectional view of another embodiment medical balloon in inflated condition and having four internal chambers. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Described below are various embodiments of medical balloon and balloon catheter assembly according to the teachings herein. The skilled person will appreciate that only some embodiments are described and that a medical balloon having additional features and characteristics over and above the described embodiments will be readily understandable to the person skilled in the art, such as having more chambers, different balloon shapes and so on. 
     The drawings shown are schematic and not to scale, and they depict only the major components of the device taught herein. The skilled person will be familiar with the typical characteristics in terms of dimensions and proportions of the various components. 
     In the described embodiments, the balloon is preferably formed from a raw tubing, typically made of a polymer material, which is inflated under pressure and at heat in order to cause the raw tubing to expand within a mold and to form a balloon shape. This is a technique which is well-known in the art. 
     A medical balloon is typically formed as a cylindrical structure having a body portion and at either end conical end portions. The end portions extend to necks which are bonded in fluid tight manner to a distal end of a carrier catheter. Generally, though not necessarily, the balloon wall is impermeable and forms a fluid tight chamber over the carrier catheter. The carrier catheter typically has one or more lumens extending through the length of the catheter, with at least one of these lumens having a port fluidically coupled to the internal chamber of the balloon. Fluid, typically saline liquid, can be fed into the balloon through the lumen in the carrier catheter so as to inflate, or expand, the balloon to its operating condition. Expansion fluid can also be exhausted through the lumen, so as to cause the balloon to collapse and preferably to wrap around the carrier catheter in order to permit easy withdrawal of the medical balloon from within vessel or other organ of a patient. 
     The wall of the balloon is preferably as thin as possible, in order to optimise the flexibility of the balloon and also reduce the footprint, that is the diameter, of the deflated balloon for endoluminal deployment. 
     As a result of the inflation pressures used, the balloon will typically expand to the most efficient shape, specifically round in axial cross-section, although it is known to have balloons having different diameters along its length in order to generate a profiled shape, such as an hourglass or tapering profile. 
     It is also known to have balloons with multiple layers, for instance for drug elution and for other purposes. The teachings herein apply also to such multi-layered balloon structures. 
     As it will become apparent from the description of the specific embodiments below, the teachings herein provide a balloon structure which is divided into a plurality of chambers by at least one internal wall extending between opposing sides of the balloon wall. Such an internal wall can divide the expandable volume of the balloon into a plurality of separate chambers, which in the preferred embodiments can be individually filled with or exhausted of inflation fluid, such that the balloon can be differentially inflated in dependence upon the medical procedure. 
     It is also important for the balloon to retain its structure during normal and expected operating conditions, without the balloon rupturing or losing its intended shape during the medical procedure. Whilst attempts have been made to form internal structures or partitions within a balloon for this purpose, the inventors have discovered that any internal device of this nature can compromise the integrity of the balloon and can result in loss of flexibility of the balloon, making known structures unsuitable for many medical applications. 
     Referring now to  FIG. 1 , this shows in schematic form a perspective view of a simple embodiment of raw tubing  10  for use in the manufacture of a medical balloon. In the example shown in  FIG. 1 , the raw tubing  10  includes a major portion  12  of generally cylindrical form and an internal wall  14  which extends throughout the length of the major portion  12  and is attached to or otherwise integral with opposing sides of the major portion  12 . The internal wall  14  divides the raw tubing into first and second chambers  16 ,  18  which are, in the preferred embodiment, fluidically separate from one another. 
     Typically, the raw tubing  10  will have a diameter which is consistent with that of the catheter upon which the balloon is to be fitted, such that the raw tubing  10  substantially at its original diameter can create the necks of the balloon. 
     The raw tubing  10  need not have a circular cylindrical shape and in many embodiments may have a different shape. Generally, the shape of the raw tubing will be related to the final desired shape of the balloon. 
     Referring now to  FIG. 2 , this shows a transverse cross-sectional view of raw tubing similar to that of  FIG. 1 . The raw tubing  20  of  FIG. 2  has a cylindrical outer wall  22  which in this embodiment is shown as being generally oval, having first and second opposing sides  24 ,  26  joined to one another by rounded sections  28 ,  30  and by an internal wall  32  described in further detail below. 
     In the example shown in  FIG. 2 , the raw tubing  20  has a first depth D 1  and a width W 2 , the width W 2  being greater than the depth D 1 . The balloon wall  22  has, in this example, a uniform wall thickness T 1 , although in other embodiments the balloon wall may have varying thicknesses across its extent. The balloon wall  22  can be made of any suitable material, typically a polymer material. A preferred material is a polyamide, preferably nylon  12 . Other materials include a medical grade polyurethane, PET or other polyester elastomer. An example is Hytrel®. 
     Integral with the opposing sides  24 ,  26  is the internal wall  32 , which extends throughout the length of the raw tubing  20 , in a manner similar to the example shown in  FIG. 1 . The internal wall  32 , in this embodiment, divides the balloon wall  22  into two equal components, so as to create two separate lumens or chambers  34 ,  36  of the same or similar dimensions. 
     The internal wall  32  has a width W 2  which is smaller than the depth D 1  of the cylindrical portion  22 , the difference being twice the thickness of the balloon wall  22 , that is twice T 1 . The width W 2  of the internal wall  32 , relative to the extent of the balloon wall extending from one end of the internal wall  32  to the other, shown as E 1  in  FIG. 2 , will in practice determine the amount by which each half of the cylindrical portion  22  will inflate beyond the width W 2  of the internal wall  32  upon inflation of the chambers  34 ,  36  and, as a result, the eventual shape of the balloon. This is explained in further detail below. In practice, a larger dimension E 1  will cause greater deviation beyond W 2  (and in practice D 1 ) than when E 1  is smaller. 
     With reference now to  FIG. 3 , its shows a cutaway section of the raw tubing  20 . The internal wall  32  is preferably made of a polymer material, advantageously but not necessarily the same material as that of the wall  22  of the raw tubing  20 . Within the material forming the internal wall  32  there is embedded a mass of heat conductive particles  34 , for the purposes described in further detail below. The heat conductive particles may be of metal or metal alloy and in the preferred embodiment are also of a radiopaque material. Examples include boron, gold, silver, platinum, palladium, copper, or other known radiopaque materials. The preferred material is tungsten, which the inventors have discovered has optimal heat conductive properties for this application and also good radiopacity. 
     The heat conductive particles have a thermal conductivity which is greater than the thermal conductivity of the material of the internal wall. In embodiments, the thermal conductivity of the heat conductive particles is at least 50 times greater than the thermal conductivity of the material of the internal wall. In some embodiments, the thermal conductivity of the heat conductive particles is at least 100, or at least 200, times greater than the thermal conductivity of the material of the internal wall. Preferably, the thermal conductivity of the heat conductive particles is at least 500 times greater than the thermal conductivity of the material of the internal wall. 
     In some embodiments, the thermal conductivity of the heat conductive particles is at least 20 W/(mK), at least 60 W/(mK), or preferably at least 150 W/(mK). 
     The internal wall  32  may have around 50% by weight of heat conductive particles, although other embodiments may have substantially more than 50% by weight. The concentration of heat conductive particles should be balanced between providing optimal conduction of heat without resulting in degradation of the structural integrity of the internal wall  32 , loss of flexibility and loss of ability to stretch during inflation of the raw tubing in order to form the medical balloon. In a practical embodiment using nylon for the polymer material and tungsten for the particles, the proportion of heat conductive particles within the internal wall was in the region of 52%. 
     The heat conductive particles preferably have a density in the region of 2 grams/cm 3 , in the practical embodiment indicated above a density of around 1.92 grams/cm 3 . The specific volume of the formulation may be in the region of 0.50 grams/cm 3 , in the specific example 0.521 grams/cm 3 . The heat conductive particles may have an average particle size of 0.50 to 2.0 micrometres. They preferably have an average particle size of between 0.50 and 0.99 micrometres, although in other embodiments may have an average particle size of from less than a micrometre to tens of micrometres, for instance up to 10 to 25 micrometres. 
     The heat conductive particles may be of a rounded or generally spherical shape, although it is preferred that they have an elongate shape. They could, for instance, be a very rounded oval shape which could be described as being somewhat like the shape of an asteroid. 
     The heat conductive particles are preferably even distributed throughout the material of the inner wall  32 , although in other embodiments their distribution may vary through the internal wall  32 . Varying the concentration of heat conductive particles can alter the heat transfer characteristics through the internal wall as will be apparent from the teachings below. 
     It is preferred that the heat conductive particles  34  are kept within the volume of the internal wall  32 , that is they do not extend into the wall  22  of the raw tubing  20 . Thus, and as will be apparent in particular from  FIG. 3 , it is preferred that the cylindrical wall  22  of the raw tubing  20  is uniformly, preferably solely, of polymer material, having no heat conductive particles within it. As a result, the heat conductive particles  34  of the internal wall  32  could be said to be separated from the external surface  40  of the raw tubing  20  and, as a consequence, of the formed balloon. 
     Referring now to  FIG. 4 , this shows in schematic form a transverse cross-sectional view of a mold chamber  50  used for forming a balloon from the raw tubing  10 ,  20  as taught herein. The mold  50  includes a mold chamber typically of heat conductive material which in practice is heated during the formation of the balloon. As a result, the internal surfaces  52  of the mold  50  become hot, for the purpose of imparting heat to the wall  22  of the raw tubing  20 , which forms the balloon wall. This heat causes the polymer material of the wall  22  of the raw tubing to soften, enabling it to stretch when inflation fluid is pumped into the lumens  34 ,  36  of the raw tubing  20 . As is known in the art, in practice, one end of the raw tubing  20  fitted within the mold  50  is sealed, while the other end is attached to a source of inflation fluid, such that inflation fluid will apply pressure from inside the raw tubing to cause it to inflate. It will be appreciated that the raw tubing  20  will typically be spaced from the internal surfaces  52  of the mold  50  at the start of the blowing operation and that the gap between the wall  22  and the internal surfaces  52  of the mold  50  will be heated by the heat from the mold  50 , thereby to transfer heat to the walls  22  of the raw tubing  20  in order to cause this to soften. 
     With reference specifically to  FIG. 4 , the internal wall  32  of the raw tubing  20  is disposed within the outer wall  22 . As a result of the poor thermal conductivity of the material of the outer tubing  24 , the material of the internal wall  32  would not normally be heated to the same extent as the material of the wall  22 . With an internal wall  32  made solely of a polymer material, this would not be sufficiently heated from heat from the mold  50  and consequentially will not soften or stretch. This can result in rupture of the structure (by separation of the internal wall from the external wall  22  or by tearing of the internal wall  22  or a combination of the two). Similarly, failure to heat and soften the internal wall  32  will cause it to retain its original dimensions and typically cause it to remain relatively thick, resulting in loss of flexibility of the formed balloon. 
     The provision of the heat conductive particles  34  within the internal wall  32  enables heat from the mold surfaces  52  to conduct through the particles  34  into the polymer material of the internal wall  32 , as depicted by the arrows  54  in  FIG. 4 . The heat conductive particles  34 , therefore, enable the polymer material of the remainder of the internal wall  32  to heat and soften, such as it stretches on expansion of the raw tubing, thereby maintaining structural integrity, as well as enabling the internal wall  32  to thin as it stretches. This makes the internal wall  32  more flexible, with a resultant optimisation of the flexibility of the formed balloon. 
     It should be appreciated that the shape of the internal surfaces  52  of the mold  50 , which will determine the overall shape of the formed balloon, will not necessarily be as depicted in  FIG. 4 , which is schematic only. The mold  50  will have a shape consistent with that desired for the specific balloon to be formed, of which some examples are given below. 
     Referring now to  FIGS. 5 and 6 , these show two views of a balloon catheter  60  formed from the raw tubing  20  of  FIG. 2  and by the method depicted in  FIG. 4 . With reference first to  FIG. 5 , the balloon  60  is fitted to a carrier catheter  62 , of conventional form and which in this example includes first and second lumens  64 ,  66  therein which are separate from one another and which have respective ports  68 ,  70  open to respective chambers  72 ,  74  of the balloon  60 . The chambers  72 ,  74  are separated from one another by the internal wall  76 , which is shown in dotted outline in  FIG. 5 . The respective chambers  72 ,  74  of the balloon  60  can be inflated together or separately. The expanded profile of the balloon  60  can thus be determined by the relative state of inflation of each of the chambers  72 ,  74 . 
     It is not necessary for the chambers  72 ,  74  to be separately inflatable and in some embodiments they could be inflated and deflated from a common lumen of the carry catheter  62 . 
     Reference is now made to  FIG. 6  in conjunction with  FIG. 7 , the latter showing a transverse cross-sectional view of the inflated balloon  60  shown in  FIG. 6 . In this particular embodiment, the lateral extent of the balloon material forming each chamber  72 ,  74  is such that when the balloon is expanded, that is inflated, the two halves of the balloon expand to a diameter D 4  which is greater than the width W 2  of the internal wall  76 , so as to create two depressions  80 ,  82  extending along the length of the balloon  60 . The walls of the balloon  60  form what could be described as lobes either side of the internal wall  76 . These depressions  80 ,  82  are useful in protecting parts of a patient&#39;s vessel or passageway which it is desired to protect from the inflation pressure of the balloon. A skilled person will appreciate that the depth of the depressions  80 ,  82  can be altered by altering the lateral extent (dimension) of the balloon wall forming each of the lobes  84 ,  86  of the inflated balloon  60 . More balloon wall material for the lobes  84 ,  86  will result in deeper depressions  80 ,  82 , whereas less material will result in the depressions being more shallow. In the case of a balloon made of conformable material, a similar effect can be achieved by changing the inflation pressure of the balloon. 
       FIG. 8  shows in schematic form a transverse cross-sectional view of an example of raw tubing  100  having an outer peripheral wall  110  and first and second internal walls  112 ,  114 , extending throughout the length of the cylindrical portion  110 , which form three internal chambers  116 - 120  within the raw tubing  100 . Each of the internal walls  112 ,  114  has heat conductive particles  34  embedded therewithin and have the same characteristics as described above. 
     With reference to  FIG. 9 , this shows a transverse cross-sectional view of a balloon  130  formed from the raw tubing  100 , in an expanded condition. The balloon has three internal chambers  136 ,  138 ,  140  each formed from a respected one of the chambers  116 - 120  of the raw tubing. The inflated balloon  130  shown in  FIG. 9  has two lobes  150 ,  152  either side of a central portion  154  which may, as desired, have a smaller expanded depth D 5  compared to the depth D 6  of the lobes  150 ,  152 . The skilled person will appreciate from the teachings herein that the relative dimensions of the three parts of the medical balloon  130  can be adjusted in the manner indicated above. 
     The balloon  130  can be fitted to a carrier catheter similar to that depicted in  FIGS. 5 and 6 , the catheter having one or more lumens with one or more ports extending into the chambers  136 - 140 . The carry catheter may include separate lumens in order to inflate the chambers  136 - 140  independently of one another, and in other embodiments may have a common lumen to two or three of the chambers  136 - 140  so that these may be inflated together. 
     Another embodiment is shown in  FIG. 10 , which is a transverse cross-sectional view of a medical balloon  170  in an expanded state. The balloon  170  includes two internal walls  172 ,  174  which, as with the previous embodiments extend for the length of the balloon  170  and which in this embodiment cross one another to form four separate chambers  176 - 182 . In the example of  FIG. 10 , the chambers  176 - 182  are of equal size, although other embodiments may have chambers of different sizes. 
     The raw tubing of all the embodiments disclosed herein can be formed by co-extrusion of the different parts. 
     The preferred embodiments, as described above, all seal the conductive particles  34  within the perimeter of the balloon, such that the heat conductive particles are not exposed to the patient&#39;s body. 
     It will be appreciated that the relative thicknesses T 2 , T 1  of the internal wall or walls and of the outer wall of the balloon may vary from the examples given above. It is advantageous for the walls to be as thin as possible in order to increase the flexibility of the balloon and to reduce its footprint when the balloon is deflated, which enhance the trackability of the balloon through a patient&#39;s vasculature. The internal wall T 2  may be of the same thickness, thicker or thinner than the peripheral wall T 1  of the balloon. 
     All optional and preferred features and modifications of the described embodiments and dependent claims are usable in all aspects of the invention taught herein. Furthermore, the individual features of the dependent claims, as well as all optional and preferred features and modifications of the described embodiments are combinable and interchangeable with one another. 
     The disclosures in British patent application number 1517831.2, from which this application claims priority, and in the abstract accompanying this application, are incorporated herein by reference.