Abstract:
A penile prosthesis beneficially includes components coated with parylene in order to increase product life and reduce wear. In particular, components of the inflatable cylinder benefits from having been coated with parylene. The parylene-coated cylinder components are resistant to wear generated by pinching of the cylinder when the cylinder is in a flaccid state. The parylene-coated cylinder may be formed by masking a tube of silicone (or other appropriate material) and vapor coating the silicone tube with parylene. Further, where a double walled cylinder is used, each of two tubes making up the double wall cylinder can have their surfaces coated with parylene, thus increasing cylinder life and avoiding wear.

Description:
This application is a continuation of U.S. application Ser. No. 09/526,051 filed Mar. 15, 2000, now U.S. Pat. No. 6,558,315 (May 6, 2003), which is hereby incorporated by reference in its entirety. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to penile prostheses and more specifically to parylene-coated components used therefor. 
   2. Description of the Related Art 
   The implantation of a penile prosthesis is one known treatment for the condition in human males known as erectile dysfunction or ED. Once implanted, the penile prosthesis is used to artificially create an erection, thus allowing the patient to be sexually active. 
   Such prosthesis generally includes a pair of inflatable cylinders which are implanted, in parallel, in the patient&#39;s corpus cavernosae. The prosthetic also includes a pressurized reservoir of fluid that is implanted elsewhere in the patient&#39;s body, usually in the abdomen. A pump and valve assembly is fluidly coupled to the reservoir via reservoir tubing and the pair of inflatable cylinders are then fluidly coupled, via fluid passageways, to the pump and valve assembly. Upon actuation of the pump and valve assembly, the cylinders become pressurized due to fluid transfer from the reservoir to the pump and valve assembly and from the pump/valve to the cylinders which, in turn, causes the cylinders to become rigid. This rigidity thereby causes the desired erection. 
   There are several variations of such a prosthetic. For example, the cylindrical members can expand as they are pressurized, or in another variation, they may simply go from an empty, flaccid state to a full, rigid state, with no expansion of the cylinder(s). The reservoir and/or the pump assembly can also be made integral with the cylinder(s). 
   In order to adapt the prosthetic to the patient&#39;s anatomy, the cylinders have arcuate front and rear cap portions which mate well with the ends of the corpus cavernosae. Moreover, the caps serve to form a sealed chamber within the cylinder thus enabling the cylinder to inflate. 
   In order to control the expansion of the cylinder as it is inflated, a sleeve of fabric or other cloth-like material is placed around an inner tube of the cylinder. Thus, the diameter of the cylinder can only expand to a size congruent with the fabric sleeve. The use of a fabric sleeve also effectuates a uniform inflation. Typically, a second sealed outer tube is placed around the inner tube and the fabric sleeve. Thus, a typical cylinder wall includes two tubes, one within the other. Consequently, proper functioning is dependent on the correct operation of the inner tube and, in some embodiments, on the correct operation of the outer tuber as well. That is, in some cases, the area around the outer tube is used for fluid transfer and/or storage. A fabric sleeve may also be used with those types of cylinders that do not expand when filled, but simply become rigid. 
   The double walled structure is an efficient arrangement. One potential issue is the continuous contact between each of the tubes and the fabric. The prosthetic exists in a relaxed or flaccid state a majority of the time and thus the inner and outer tubes are in contact with the fabric a majority of the time. The specifics of this situation are elaborated below. 
   In order to provide comfort and a better sense of normalcy to the patient, the prosthetic is made from materials that allow the prosthetic to bend and be flexible when in the flaccid state. Such bending, however, may lead to the formation of a crease in the walls of the double-walled or single-walled device. This crease terminates in bend corners that are areas of stress and highly localized areas of contact between the cylinder&#39;s inner and outer tubes and the fabric sleeve. Consequently, as the flaccid cylinder is bent from side to side or generally moved about a central axis due to normal movement of the patient, the bend corners will likewise travel thus resulting in pockets of the cylinder contacting and moving across each other. This results in a movement of the corners which causes portions of the tubes to contact (and move across) each other. There is also a potential element of material fatigue as the various materials are repeatedly stressed and unstressed. 
   Moreover, since the crease generally occurs in the same location on the cylinder, the same areas of contact are repeatedly moved across each other. Over time, this repeated contact and movement may lead to wear, abrasion, and fatigue. 
   Typically, the tubes are formed from a versatile material such as silicone or polyurethane which are medically safe and provides the necessary degree of structural reliability. It has been found that silicone has a high coefficient of friction and can be somewhat tacky. As a result, when silicone contacts itself or some other surface, it can bind and resist movement. Indeed, this frictional engagement could cause the contacting surfaces to wear at these contacting locations and eventually could potentially cause the tubing to wear and fatigue. 
   For the same reasons, similar situations may be encountered with other components of the prosthesis. The fluid passageways, the reservoir, the housing for the pump and valve assembly are all typically made from silicone. Thus, in any instance where the silicone surfaces of these components are caused to bend, to contact other silicone surfaces, or to fatigue, similar situations of wear may be encountered. 
   SUMMARY OF THE INVENTION 
   The present invention provides a penile prosthesis which has components formed from silicone or similarly flexible material which are coated with a material that increases the strength of the component while also reducing its coefficient of friction. When corners are formed in the flaccid cylinder, for example, increased wear tolerances are exhibited by allowing the components of the cylinder to smoothly move against each other. The coating material allows one surface of the cylinder to slide smoothly against another surface. Thus, wear due to abrasion is significantly diminished. Furthermore, the coating material minimizes fatigue and resists contact stresses. 
   In a preferred embodiment, both the inner-and outer surfaces of the tube(s) of the cylinder are coated with a very thin layer of parylene. Parylene is an ideal material for this purpose in that it provides a very strong and wear resistant surface, is relatively slippery, is fatigue resistant, and allows for repeated expansion and contraction with no negative effects. 
   To form the components of the cylinder (or any other tubular component) of the preferred embodiment of the present invention, a silicone tube is sized. Both the inner and outer surfaces of each end portion are then masked. The masking can be done by inserting sections of rigid silicone into the ends of the silicone tube. This rigid insert has an outer diameter approximately equal to the inner diameter of the silicone tube. A wrapping, such as shrink-wrap (heat shrink tubing), is then placed over the outer diameter of the silicone tube, to correspond with the rigid insert. The shrink-wrap is then heated causing it to shrink. This, in turn, causes the silicone tube to compress the rigid insert, thus generating a portion of the silicone tube that is sealed between the rigid insert and the outer wrapping. 
   The masked tube is then placed in a vapor deposition chamber where vaporized parylene is introduced into the environment. In a known way the vaporized parylene simultaneously coats both the inner and outer surfaces of the silicone tube to a predetermined thickness. The coated silicone tube is then removed from the deposition chamber and the rigid inserts and shrink-wrap are removed from the coated silicone tube. Appropriate end caps are attached and adhered to the non-coated portions, thus forming a complete cylinder. Alternatively, coating just the inner or the outer surface will also lead to increased wear characteristics. 
   In addition, any of the other components of the penile prosthesis could likewise be coated, thus realizing increased wear characteristics. 
   For those cylinders utilizing a double wall structure, it is optimal to coat the inner and outer surfaces of both tubes forming the completed cylinder. Increased wear characteristics are achieved, however, even when just the inner or outer surfaces are coated. 
   The present invention includes applying a coating of a material such as parylene to one or more components of a penile prosthesis. This is applicable to virtually any type or style of prosthesis. Namely, whether a single or double walled cylinder is utilized, whether expandable or non-expandable cylinders are utilized, or whether the components (cylinders, pump assembly, reservoir, etc.) are separate or integral, the coating will be advantageous. 
   Yet another aspect of the present invention is the application of parylene, or a similar material to a variety of implantable devices, commonly formed from silicone or a like material. As specifically detailed herein as the preferred embodiment, a penile prosthesis having connected but separate components (cylinders, reservoir, pump) will benefit greatly by having a coating of a material such as parylene applied to one or more of those components. In addition, many penile prosthetics come in different configurations. A reservoir may be made integral with the cylinder, or all of the components may be made from one integral unit. As referred to herein, the penile prosthesis is meant to include any and all of these various forms, as they may all benefit from the application of a material such as parylene. 
   In addition to the penile prosthesis, other implantable devices are commonly formed from silicone or other flexible materials and can benefit from the application of a coating of parylene. For example, testicular implants are sometimes implanted into a male patient to return a sense of normalcy to that patient. Such implants may be implanted during the implantation of the penile prosthesis to minimize surgical exposure. Testicular implants can be formed as elliptical or oval silicone blocks. These blocks are generally solid, but could be fluid filled. In either event, the application of parylene of a like material will reduce the effects of frictional engagements as the implants are moved about. In addition, the coating may serve to contain the material forming the implant, thus preventing leakage into the patients. For this reason, it is also desirable to apply parylene to silicone breast implants. The parylene will serve to contain the fluid filled implant and will reduce the abrasive effects cause by the normal movement of the implant. 
   Another type of implantable device within the scope of the present invention is an artificial sphincter. An artificial sphincter is somewhat similar in form and function to the penile prosthesis. Namely, a reservoir and a pump are provided and are coupled to an inflatable member. The inflatable member is positioned so that when inflated, it exerts pressure on the urethra or bladder neck, in the case of artificial urinary sphincters, or the rectum in the case of artificial bowel sphincters. As pressure is applied, the rectum or the urethra is effectively sealed, thus preventing incontinence. These devices can come in various forms; i.e., those with separate components connected by tubing or those having certain parts combined into an integral unit (pump combined with reservoir). Whatever their form, it is advantageous to coat the various components with parylene or a like material. The coating serves to minimize the effects of frictional engagement and will increase the life expectancy of the product. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side-elevational view of a penile prosthesis system including a reservoir, a pump and valve assembly, and a cylinder. 
       FIG. 2  is a side-elevational view of a penile prosthesis cylinder in its flaccid state. 
       FIG. 3  is a side-elevational view of a cylinder with a parylene-coated silicone tube with end caps in place. 
       FIG. 4  is a side-elevational view of a silicone tube used to make the cylinder of the penile prosthesis, which has been coated with parylene. 
       FIG. 5  is a side-elevational view of a silicone tube used to make a cylinder in a penile prosthesis wherein front and rear rigid inserts are being inserted inside the tube to form a mask. 
       FIG. 6  is s side-elevational view of a silicone tube used to form a cylinder in a penile prosthesis wherein front and rear inserts have been inserted into the tube and front and rear shrink wrappings are being placed over the outer circumference of the ends of the tube. 
       FIG. 7  is a schematic diagram illustrating a masked silicone tube within a vapor deposition chamber. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring to  FIG. 1 , the penile prosthesis of the present invention includes a pair of cylinders  18  that are selectively inflated by actuating pump and valve assembly  14  thus transferring fluid from reservoir  10 , through pump and valve assembly  14 , and into cylinder  18  under pressure. (Only one cylinder of the pair is illustrated). As such, cylinder  18  will inflate thus producing the desired effect. When the user desires to deflate cylinder  18 , pump and valve assembly  14  is opened, thus allowing the pressurized fluid to retreat from cylinder  18  back into reservoir  10 . This returns cylinder  18  to its flaccid state. In-previous penile prostheses, cylinder  18  has usually been composed solely of polyurethane, silicone or a combination of the two. 
   It is to be understood that the prosthesis illustrated is only meant to be representative of the variety of penile implants currently used. That is, the illustrated implant will expand upon inflation and has separate components interconnected by tubing. Other types of implants provide for cylinders that do not expand (in any direction) but simply become rigid. There are also implants having a reservoir formed integrally with one or both of the cylinders. Likewise, the pump can be formed integrally with the reservoir and/or the cylinders. It is to be understood that all of these variations are within the scope of the present invention and are referred to generally and collectively as a penile prosthesis. 
   Referring to  FIG. 3 , cylinder  18  is shown to be formed from silicone and has a layer of parylene deposited over a substantial portion of its inner and outer surfaces. The parylene coating is represented by hatched lines (in  FIGS. 3 and 4 ).  FIG. 3  illustrates the completed cylinder  18  having front and rear end caps  20  and  22  attached thereto. As shown, the end caps  20  and  22  are not coated with parylene. These portions of cylinder  18  are less likely to contact other portions of the cylinder  18 , thus minimizing the frictional engagement which leads to wear. The end caps  20  and  22  are also thicker and more rigid than the tubing, again reducing the risk of wear. However, to provide the highest level of security and wear resistance, end caps  20  and  22  (or a portion thereof) could likewise be coated. 
   Often, double walled cylinders are used wherein each tube of the cylinder (inner and outer) may have its inner and outer surfaces coated. Though not illustrated, double walled cylinders will have a layer of fabric between the two wall portions. This fabric could also be coated on one or both sides with parylene, reducing the coefficient of friction of the material. This coated fabric could then be utilized in the same fashion. Alternatively, the coated fabric could eliminate the need for the outer tube. 
   Referring to  FIG. 4 , cylinder  18  is shown having end caps  20  and  22  removed. The silicone tube  32  has had parylene deposited on its inner and outer surfaces on all portions except front end section  36  and rear end section  38  which have no parylene deposited on either the inner or outer surfaces. Front and rear end sections  36  and  38  are left uncoated so that end caps  20  and  22  can be firmly secured to the silicone tube  32 . (Likewise, if caps  20  and  22  were to be coated, a corresponding portion of the caps  20  and  22  would be left uncoated.) If parylene were applied in these areas, the strength of the bond between the tube  32  and the end caps  20  and  22  would be greatly reduced as parylene does not work well with many of the silicone adhesives. This assumes an end cap structure which is bonded to the silicone tube  32 . Many variations are conceivable, thus altering the masking parameters. For example, if the end cap is only bonded to an inner surface of the tube  32 , the entire outer surface of the tube  32  could be coated in parylene. Similarly, if the cap is only bonded to the outer surface, the entire inner surface can be coated. In the preferred embodiment, the tube  32  is masked as illustrated and the caps  20  and  22  are bonded to tube  32 . 
   Various other adhesion techniques could be employed, bonding the caps  20  and  22  to the parylene coating. This may include coating the end caps  20  and  22  with parylene prior to bonding. When handling any other component, appropriate masking should be employed. Any tubular structure could be masked as described below. Larger components such as reservoir  10  or pump and valve assembly  14  have different requirements, thus the coating and masking characteristics will vary. For example, all surfaces of the reservoir  10  can be coated except where the reservoir tubing  12  will be connected. This is due to the same parylene/silicone adhesive issues described above. 
   When the parylene-coated silicone tube  32  illustrated in  FIG. 3  is in the condition shown in  FIG. 2 , i.e. flaccid, corners  30  are formed at the pinch points. (It is noted that any or all of the components shown in  FIGS. 1 and 2  could be coated with parylene, thus the coating is not separately shown by hatched lines.) In the flaccid state, a crease line is created extending across the cylinder terminating in a pair of bend corners  30 . As the cylinder naturally moves (in its flaccid condition) the crease line changes its location and orientation, thus causing the bend corners  30  to be translated or moved along the cylinder due to normal movement of the patient. However, the parylene coating slides smoothly over itself or any adjacent component it may come into contact with, thus greatly reducing frictional wear. In addition, parylene also has greater strength than silicone to better resist contact and fatigue stresses. 
   Parylene is a unique material forming a high molecular weight, linear, crystalline polymer coating having an all carbon backbone. During the vapor deposition process, parylene never enters the liquid state, thus an extremely continuous and even coating occurs. Parylene has excellent dry film lubricant characteristics as indicated by its coefficient of friction, which approaches polytetrafluoroethylene. Parylene will have a coefficient of friction approximately 1/10 that of silicone, when the parylene exists in a 2 μm layer. Parylene is superior in its ability to resist wear and abrasion. While various parylene variations are available and each is applicable herein, parylene N seems to be the most advantageous to use, as a preferred embodiment. 
   When inflated, the cylinder  18  is caused to expand or at least become rigid. As such, the layers of parylene on or within cylinder  18  must likewise expand. Parylene is ideal in this situation in that it will expand without breaking and once the cylinder  18  is deflated, will return to its original configuration. In actuality, tiny structures appear in the parylene that resemble cracks in the coating. These are not actually cracks, but areas of local yielding and this characteristic allows the coating to be very effective. While parylene is ideally suited for this application, a wide variety of other materials could be used equally welt. Such alternate materials need to produce a relatively smooth coating having a sufficiently high degree of dry film lubricity, which will not bind when it is caused to contact other portions of the tube and is able to be repeatedly expanded and then returned to its original configuration. The material should be relatively strong, to withstand the repeated contact, and have good wear characteristics so that a long lifetime is achieved. 
   Any suitable method of application may be used to apply the parylene or an alternative material to any of the components of the prosthesis. In a preferred form (for tubular components), the silicone tube is first masked as shown in  FIG. 5 . Silicone tube  32  is cut to length and front and rear silicone inserts  40  and  42  are inserted within the inner circumference of silicone tube  32 . The front and rear inserts  40  and  42  are sized to create the appropriate area for the adhesion of the end caps  20  and  22 . As shown in  FIG. 6 , the silicone tube then has front and rear wrappings  44  and  46  placed over the outer ends of the silicone tube  32 . Any such suitable wrappings are appropriate. For example shrink wrapping or heat shrink tubing is used and after application to the ends, the shrink-wrapping is heated thus conforming closely to the size and shape of the silicone tube  32 . The compression of the shrink-wrap also clamps the silicone tube  32  around the inserts  40  and  42 , thus forming a barrier which prevents vapor deposition. Forming inserts  40  and  42  from silicone is advantageous in that parylene bonds extremely well to silicone. Thus, when inserts  40 ,  42  are removed, a clean break is formed in the parylene coating. 
   Previous masking techniques usually include applying a layer of liquid latex as a mask, then peeling off the latex after the application of parylene. This is unacceptable in some cases, due to the likelihood of a patient having an allergic reaction to the latex. The latex will also discolor the silicon, giving an inferior appearance. It is possible to use a synthetic liquid latex as the mask. It is also possible to use synthetic latex as the outer mask and the tubular inserts  40  and  42  as the inner mask. Since synthetic latex is water based, it will shrink upon drying, thus sealing the silicone tube  32  against the inserts  40  and  42 . 
   The masked silicone tube  32  is then placed into a vapor deposition chamber  48  as shown in  FIG. 7 . Parylene or any other suitable material is then vaporized in the vaporization chamber  50  and caused to enter the deposition chamber  48 . In a known way, the vaporized parylene is caused to deposit itself on the silicone tube  32 . The vaporized parylene evenly coats both the inner and outer circumference of the silicone tube  32  and all areas that are unmasked. The thickness of the parylene coating is dependent on the time the silicone tube  32  remains in deposition chamber  48 . The parylene should be coated on the silicone tube  32  to a thickness of between 0.000040–0.000120″. Ideally, the parylene should be about 0.000040–0.000080″ with a layer of 0.000060″ being optimal in the preferred embodiment. Too thin of a layer will not yield the desired wear characteristics nor will it yield the desired lubricity. Too thick of a layer will make the tube too stiff and will also reduce the wear characteristics. 
   Once the appropriate level of vapor deposition has occurred, the silicone tube  32  is then removed, the masking elements are removed, and end caps  20  and  22  are appropriately adhered to each end. The completed cylinder  18  is then attached to the remaining components of the penile prosthesis and is ready for implantation. If a double walled cylinder is desired, the completed tube  18  is then inserted into another coated tube  32 . End caps  20  and  22  are then affixed to the ends of the outer tube  32 , thus forming the double walled structure. Optimally, all of the major surfaces of each tube  32  (excluding any desired masked areas) will be coated with parylene or a like material. However, various surfaces can be left uncoated to reduce cost and material issues. For example, coating the cloth barrier between the inner and outer cylinders may be sufficient to prevent wear, without those surfaces being coated. This will depend on the particular materials and configurations chosen. 
   Though cylinder  18  has been described as being coated with parylene or a like material, any of the components of the penile prosthesis would benefit by having a similar coating. In particular, fluid passageways  16  and reservoir tubing  12  could be optimized by such a coating. It is within the scope of the present invention to apply parylene to fluid passageways  16 , reservoir tubing  17 , reservoir  10 , pump assembly  14 , and of course cylinders  18 . Namely, it is advantageous to apply parylene to any of the components of the implant. As previously described, these components are often subjected to frictional wearing. Currently, a portion of these smaller diameter components are covered in polytetrafluoroethylene to assist the surgeon in implantation. A parylene coating would increase the wear characteristics of these components and could be applied in a similar fashion to that described above for the cylinders  18 . The pump and valve assembly  14  and/or the reservoir  10  can also benefit from being coated. This will reduce wear when any of the components contact any other component, when the components are being manipulated by the patient, and when the tubes or reservoir are flexing against themselves or the surrounding tissue. 
   Though not separately illustrated, the above described process is also applicable to other implantable devices. For example, artificial sphincters, testicular implants, and breast implants can benefit from having a coating of material, such as parylene applied thereto. 
   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.