Abstract:
A voice prosthesis comprising a tubular body portion, a valve and a valve seat disposed within the body portion. The valve seat is further comprised of a medical grade elastomer containing a dispersion of an antimicrobial agent. This valve seat extends the life of the prosthesis by retarding the growth of microorganisms. The body portion of the prosthesis may also contain an antimicrobial agent at a concentration that is non-toxic to the tissue it contacts.

Description:
This application is a continuation-in-part of pending U.S. patent application Ser. No. 09/833,961, filed Apr. 11, 2001 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to microbial-resistant medical devices and, more particularly, to a voice prosthesis having a valve seat which retards growth of microorganisms. 
     2. Prior Art 
     There are several options for restoring speech to patients who have had their larynx removed. One procedure is to surgically create a puncture or fistula between the trachea and the esophagus. A tracheoesophageal voice prosthesis containing a one-way valve such as a BLOM-SINGER® voice prosthesis is inserted into the tracheoesophageal fistula. The one-way valve protects the airway during swallowing but opens under positive pressure from the trachea. The voice prosthesis, thus, permits a patient to divert air from the lungs into the esophagus and out through the mouth. Speech is created during passage of air through the upper part of the esophagus. 
     The voice prosthesis maintains the patency of the fistula, transfers air from the trachea to the esophagus for voice production and prevents esophageal leakage into the trachea during swallowing. The oral cavity which extends into the throat can have a high microbial population. The prosthesis, being in contact with moisture in a warm, dark, nutrient rich environment, is subject to growth of commonly found micro-organisms, typically Candida, on the valve, valve seat and the retaining flange. The microbial growth on and into the soft silicone resin can interfere with function of the valve and can cause the valve seat to warp and the valve to leak. 
     A voice prosthesis has been developed that can remain in place in the tracheoesophageal fistula for months, depending on the patient and conditions of use. The patient can confidently use the prosthesis for longer periods than the non-indwelling voice prosthesis. The longer dwelling voice prosthesis is not removable by the patient. Trips to a health care specialist to remove and replace the prosthesis are greatly extended providing increased comfort and lower cost to the patient. 
     Blom, in U.S. Pat. No. 4,435,853 discribes a soft voice prosthesis for use over an extended period of time. This voice prosthesis does not include the use of an antimicrobial agent. 
     Persson, in U.S. Pat. No. 5,314,470 discloses a soft voice prosthesis that includes a rigid stiffening ring  14  inserted into a groove in the soft body of the prosthesis. 
     U.S. Pat. No. 5,578,083 issued Nov. 26, 1996, discloses the use of a stiff cartridge to support the soft silicone prosthesis and to provide a seat for the valve. However, microbial growth still proceeds to a point at which the valve can not be reliably sealed. 
     Although the rigid valve seat designs reduce microbial ingrowth into the valve seat material, they do not retard microbial growth. Leaking can be due to distortion of the valve body adjacent to the seat of the valve and to microbial growth on the seat. 
     Relevant prior art includes U.S. Pat. Nos. 3,932,627, 4,054,139, 4,483,688, 4,563,485, 4,581,028, 4,603,152, 4,612,337, 4,615,705, 5,019,096, 5,567,495, 5,624,704, 5,772,640, 5,902,283, 6,083,208 and 6,106,505. 
     SUMMARY 
     In accordance with the present invention, antimicrobial agents are compounded into either, or both, the valve and valve seat of a voice prosthesis. The antimicrobial parts remain free of microbial growth in situ for an extended period which contributes to longer use of the prosthesis in vivo. 
     The body of the voice prosthesis is formed of an elastomer and the valve seat is made with an antimicrobial agent incorporated therein. The body of the prosthesis may have some antimicrobial properties as long as the tissue-contacting surface of the body is not toxic to tissue. 
     The antimicrobial agent is preferably incorporated in the elastomer by mechanical dispersion into the uncured elastomer. The term “antmicrobial agent”, as used herein, means a chemical substance which retards the growth of microorganisms. For example, silicone elastomer can contain an antimicrobial agent such as silver or silver compounds such as silver oxide. Other suitable antimicrobial compounds that may be toxic to tissue such as gold, platinum, copper, zinc metal powder or oxides and salts thereof, can be used in the non-tissue contact regions of the prosthesis. Other antimicrobial agents include organic antimicrobial agents that can be dispersed throughout the raw material such as butyl paraben butyl p-hydroxy benzoate or an alkene carboxylic acid salts such as alkali metal sorbate salt or a halohydroxy aromatic ether such as triclosan (2,4,4′-trichloro-7′hydroxydiphenyl ether. 
     The features of the invention believed to be novel are set forth with particularity in the appended claims. However the invention itself, both as to organization and method of operation, together with further objects and advantages thereof may be best understood by reference to the following description taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a voice prosthesis installed in a tracheoesophageal fistula. 
         FIG. 2  is a longitudinal cross-sectional view of a preferred embodiment of a voice prosthesis of the present invention. 
         FIG. 3  is a cross-sectional view of the valve flap employed in the particularly preferred embodiment shown in  FIG. 2 . 
         FIG. 4  is a top view of the flap valve of  FIG. 3 . 
         FIG. 5   a  is a perspective view of a first embodiment of the valve seat used in the particularly preferred embodiment of  FIG. 2 . 
         FIG. 5   b  is a perspective view of a second embodiment of the valve seat used in the particularly preferred embodiment of  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Providing a voice prosthesis having a microbial-resistant valve seat according to the invention is desirable for extending the time that the prosthesis remains functional in its intended use. Since the growth of a biofilm layer will be retarded, warping of the valve seat is reduced. The microbial resistant surface can be provided by dispersing a microbial agent such as metal, metal oxide or salt or organic antimicrobial agent into the biocompatible elastomer. 
     The present invention provides an antimicrobial voice prosthesis and a method for producing the antimicrobial voice prosthesis, which can be applied to any size voice prosthesis. Referring now to  FIG. 1 , a voice prosthesis  100  is shown inserted into a fistula  10  with the front flange  107  engaging the outer wall  11  of the trachea, and the rear flange  106  engaging the wall  12  of the esophagus. The body portion  101  of the prosthesis  100  prevents the fistula  10  from closing. 
     With reference to  FIGS. 2-5 , the voice prosthesis of the present invention, indicated at numeral  100  in  FIGS. 1 and 2 , is similar in operation to the above-described prior art voice prostheses, but lacks a (rigid) cartridge and obviates the need for a stiffening ring around the cartridge as taught in the prior art. The voice prosthesis  100  includes a body portion  101 , a valve seat  102  and a flap valve  103 . A hinge portion  104  of the valve  103 , located on the periphery of the flap valve  103 , is located via locating posts  105  ( FIGS. 5   a  and  5   b ) projecting upwardly from the valve seat  102  and affixed to the valve seat, body wall, or both. The rear flange  106  is unitary with the body portion  101 , foldable and dimensioned to fit through the fistula  10  ( FIG. 1 ) and engage the inner wall  12  ( FIG. 1 ) of the esophagus when the device  100  is implanted. The front flange  107  is also unitary with the body portion  101  and has a strap  108  projecting outwardly therefrom that is employed to insert and stabilize the position of the device  100  within the fistula. The strap  108  may further have a section thereon for detachable joinder with an insertion tool. 
     The prior art devices have not recognized the problems caused by microbial growth on the valve seat and have not provided means for retarding microbial growth on the valve seat. In accordance with an embodiment of the present invention, the valve seat  102  and valve  103  are constructed at least in part from an elastomer, preferably medical grade silicone, having silver oxide dispersed in the elastomer. The lumen  110  in the body portion  101  has a step therein to provide a shoulder  111  in the lumen  110  operable for supporting the valve seat  102 . The antimicrobial valve seat  102  can be glued or insertion molded into the lumen  110  of the voice prosthesis body portion  101 , and the hinge portion  104  of the (preferably antimicrobial) flap valve  103  glued thereto. Alternatively, the valve seat  102  may be friction fit or physically locked by ledges, grooves, or abutments into the body portion  101  of the voice prosthesis  100  to achieve the same effect. 
     The important features of the present voice prosthesis are: (a) the valve seat  102  has an antimicrobial agent incorporated within the elastomer and is recessed within the lumen  110  of the body portion; (b) the valve seat  102  is nonreleasably attached to the body portion  101 ; and (c) the construction obviates the use of a stiffening ring disposed around the valve seat. The placement of the valve seat within the lumen of body portion of the voice prosthesis keeps the antimicrobial material away from tissue contact. The antimicrobial agent is preferably silver oxide (Ag 2 O) but could comprise other antimicrobial substances compounded into the silicone material. 
     The preferred manner of providing a surface resistant to microbial growth is to disperse an antimicrobial agent in the elastomer forming the portion of the device not in direct contact with body tissue. The agent can be inorganic such as a salt or oxide of silver, gold, platinum, zinc or copper, preferably silver oxide or organic materials soluble or dispersible in the resin forming the valve or the cartridge such as hydroxy aromatic carboxylic acids, esters thereof or halogenated phenols. The agent is present in the elastomer in an amount effective to deter microbial growth and at a concentration that can be toxic to tissue. The portions of the device in contact with tissue can contain a much lower concentration of the microbial agent at a level non-toxic and non-irritating to tissue. 
     For example, in the case of silver oxide as taught in the prior art (U.S. Ser. No. 09/833,961, filed Apr. 11, 2001 by two of the present inventors), the concentration of silver oxide in a silicone elastomer effective to deter growth of microbial biofilm is attainable. The body of the device which is in direct contact with tissue can be compounded to include silver oxide. 
     The construction of a voice prosthesis in accordance with the particularly preferred embodiment of the device  100  proceeds as follows. A valve seat  102  comprising a silicone elastomer having silver oxide dispersed therein is molded as shown in  FIG. 5   a  or  5   b , then placed on a core pin. The silicone body portion  101  is then insertion molded around the valve seat, and the flap valve  103  is glued, located by the posts  105 , on the valve seat  102 . The rear flange  106  on the body portion is foldable as shown in the discussion of the prior art devices. The rear flange  106  can be circular or oval. 
     The particularly preferred embodiment  100  of the voice, prosthesis of the present invention, unlike the cartridge design currently in use, can be made in any size. The valve, valve seat and body portion can be made by liquid injection molding (LIM), transfer molding, or compression molding processes. The voice prosthesis  100 , formed with a microbial resistant valve seat (and preferably a antimicrobial valve), will be able to be used for longer periods without the need to remove the prosthesis for cleaning. The body portion of the voice prosthesis can also be compounded with antimicrobial agents at a level acceptable to the FDA. 
     The voice prosthesis  100  of the present invention is designed for patients who are unable (or resistant) to changing the voice prosthesis as recommended for the non-indwelling, patient-removable low pressure prior art voice prostheses. The indwelling low pressure voice prosthesis  100  has been specifically designed to maintain the placement of the prosthesis in the tracheoesophageal fistula for extended periods of time so that routine changing of the device is not necessary. 
     While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. For example, antimicrobial agents other than Ag 2 O (such as triclosan, buytl paraben, etc.) can be incorporated into the elastomer comprising the valve and valve seat. Materials other than silicone can be employed to fabricate the valve seat seat, such as Kynar PDVF or a polyolefin like polypropylene. The valve and valve seat may be molded as a single, unitary body and insert molded into any French size voice prosthesis. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.