Abstract:
An improved implantable hearing aid apparatus and related method of manufacture are disclosed. The inventive apparatus and method utilize electrodeposition techniques to yield enhanced sealing of implanted componentry. In one embodiment an inventive apparatus comprises at least first and second implantable hearing aid component housing members having at least one electrodeposited layer overlapping adjacent portions of the housing members to provide a hermetic seal therebetween. In another embodiment an inventive apparatus comprises an implantable hearing aid component housing member formed via electrodeposition having a plurality of electrodeposited layers, wherein at least two adjacent ones of the layers comprise differing materials (e.g. to yield enhanced functional characteristics). By way of primary example, a hollow bellows of any implantable middle ear actuator may be formed via the sequential electrodeposition of multiple layers on a shaped mandrel which is then selectively removed (e.g., via a removal fluid).

Description:
RELATED APPLICATION 
     This application claims priority from U.S. Provisional Patent Application Ser. No. 60/325,844, filed on Sep. 28, 2001, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to the field of implantable hearing aid devices, and more specifically to the sealing of implantable hearing aid componentry housings and interconnections therebetween. The invention is particularly apt for use in conjunction with implantable hearing aid actuator bellows. 
     BACKGROUND OF THE INVENTION 
     Implantable hearing aid systems entail the subcutaneous positioning of various componentry on or within a patient&#39;s skull, typically at locations proximal to the mastoid process. Such componentry typically includes a receiver for receiving transcutaneous RF and/or acoustic signals and an interconnected processor to provide processed signals. Additionally, some form of actuator is employed to utilize the processed signals to stimulate the ossicular chain and/or tympanic membrane within the middle ear of a patient. 
     By way of example, one type of implantable actuator comprises an electromechanical transducer having a vibratory member positioned to mechanically stimulate the ossicular chain via axial vibrations. (see e.g., U.S. Pat. No. 5,702,342). In another approach, implanted excitation coils may be employed to electromagnetically stimulate magnets affixed within the middle ear. Additional implantable componentry may include one or more power storage components and associated recharging componentry. Components of the above-noted nature may be utilized in either semi-implantable systems which utilize additional external mounted componentry (e.g. microphones and transmitters located in behind-the-ear units) and fully-implantable systems which do not employ external componentry during normal usage. 
     As may be appreciated, reliable operation of implanted hearing aid componentry is extremely important to the long term viability and widespread utilization of implanted hearing aid systems. Such reliability is key from the perspective of not only achieving ongoing enhanced hearing, but additionally due to the high costs associated with surgical procedures attendant to the servicing/repair of implanted components. 
     In conjunction with achieving high reliability, the need to isolate implanted componentry from bodily fluids has been recognized (see e.g. U.S. Pat. No. 5,282,858). While significant advances have been made to enclose implanted componentry in sealed housings, the present inventors have devised further improved techniques to realize enhanced sealing in implantable hearing aid systems. Such techniques include the capability to achieve reliable sealing while allowing for relative movement between mechanically interconnected hearing aid componentry. In the later regard, the inventive techniques are particularly well-suited for implementation in implanted hearing aid systems that include a bellows to facilitate axial vibration of a vibratory member of an electromechanical transducer actuator. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, a general objective of the present invention is to provide an implantable hearing aid apparatus with improved sealing, thereby yielding enhanced reliability. 
     A further objective of the present invention is to provide an improved implantable hearing aid while maintaining or even reducing overall mass and complexity. 
     Another objective of the present invention is to provide an improved implantable hearing aid that can be produced in a highly consistent manner. 
     Yet a further objective of the present invention is to provide an improved implantable hearing aid apparatus that accommodates relative movement between implanted housing members while enhancing the sealing therebetween. 
     In relation to realizing the above-identified objectives, the present inventors have recognized that significant advances are achievable through the utilization of electrodeposition techniques. Specifically, it has been recognized that electrodeposition may be advantageously utilized to both sealably interconnect implanted hearing aid componentry housing members and in the fabrication of multi-layered implanted hearing aid housing members. 
     Based on such recognition, and in one aspect of the present invention, an implantable hearing aid apparatus is provided that comprises first and second implantable hearing aid component housing members, and at least one electrodeposited layer overlapping adjacent portions of the first and second housing members to provide an interconnection and hermetic seal therebetween. Preferably, the outer electrodeposited layer may comprise a biocompatible first material, such as a biocompatible metal selected from a first metals group consisting of gold, platinum and titanium. 
     In conjunction with this inventive aspect, an outer electrodeposited layer and a conformal underlying electrodeposited layer may be provided, wherein the outer layer comprises a first material that is different than a second material comprising the underlying layer. Preferably, the outer layer hermetically seals the underlying layer. Further, the underlying layer may be provided to have at least one of a modulus of elasticity, tensile strength and yield strength that is at least two times greater than that of the electrodeposited outer layer. By way of primary example, the underlying electrodeposited layer may comprise a second material selected from a second metals group consisting of nickel, iron, chromium, platinum, iridium, copper and aluminum. Such an arrangement may be of benefit where a degree of relative movement between the housing members is desired. 
     In addition to an outer layer and underlying layer, a conformal inner electrodeposited layer may also be provided to hermetically seal the underlying layer between the outer layer and inner layer. As with the outer layer, the inner layer may comprise a biocompatible metal selected from the noted first metals group. 
     Of note, the first and second housing members may be advantageously configured to define a substantially flush interface region therebetween. Further, the electrodeposited layers(s) overlapping the interface region may be provided to be substantially, continuously arcuate and/or flat. By way of example, opposing ends of tubular first and second cylindrical housing members may be disposed in abutting relation, wherein one or more electrodeposited layer(s) is disposed across and about the abutting ends of the first and second housing members. 
     In one embodiment, one of the first and second housing members may be in the form of a hollow bellows employed in an electromechanical transducer actuator with a vibratory member extending therethrough. The hollow bellows may comprise a plurality of undulations which allow the bellows to respond in an accordion-like fashion to axial vibrations imparted to one end thereof (e.g. via mechanical interconnection with the vibratory member). In such embodiment, the other one of the first and second housing members may be in the form of a sleeve member that is interconnected to one of an electromechanical transducer housing or to a distal end of the vibratory member that extends from the electromechanical transducer housing and through the hollow bellows and other housing member. Such sleeve member may advantageously comprise a biocompatible metal selected from the noted first metals group. 
     In another aspect of the present invention, an improved implantable hearing aid apparatus is provided that comprises first and second implantable hearing aid component housing members and a third implantable hearing aid component housing member interconnected therebetween. Specifically, the third housing member may be connected at a proximal end to the first housing member and at a distal end to the second housing member. Of importance, the third housing member may advantageously comprise a plurality of electrodeposited layers, wherein at least two adjacent ones of the plurality of electrodeposited layers comprise differing materials. 
     Preferably, an outer electrodeposited layer of the third housing member comprises a biocompatible material which substantially covers and thereby hermetically seals an underlying layer. Again, the underlying layer may be advantageously provided to have at least one of a modulus of elasticity, yield strength and tensile strength that is at least two times greater than that of the outer layer. By way of primary example, the outer layer may comprise a biocompatible metal selected from the first metals group identified above, and the underlying layer may comprise a metal selected from the second metals group noted above. The described, arrangement allows for relative axial movement of between the proximally/distally disposed first housing member/second housing member, respectively, while also yielding a reliably sealed structure. 
     In addition to the outer layer and underlying layer, an inner electrodeposited layer may also be provided to substantially cover and thereby hermetically seal the underlying layer. Preferably, the inner layer may comprise a biocompatible metal selected from the first metals group. As may be appreciated, the provision of a biocompatible inner layer that seals the underlying layer serves to preserve the functional integrity of the underlying layer in the event of bodily fluid leakage into the third housing member. 
     In conjunction with this inventive aspect, one or both of the first and second housing members, and the third housing member, may be configured to define a substantially flush interface region between adjacent portions thereof. Relatedly, at least one electrodeposited layer may be disposed in overlapping relation across the interface regions. By way of primary example, one end of each of the first and second housing members may be cylindrically configured to conformally abut opposing cylindrical ends of the third housing member, wherein biocompatible electrodeposited layers are disposed in a substantially continuous and arcuate manner over each of the two interface regions. 
     In one embodiment the third housing member may be in the form of a hollow bellows employed in an electromechanical transducer actuator with a vibratory member extending therethrough. The hollow bellows may comprise a plurality of undulations which allow the bellows to respond in an accordion-like fashion to axial vibrations imparted to one end thereof. More particularly, the proximal end of the bellows may be interconnected to (e.g. rigidly anchored) to an electromechanical transducer housing via a first housing member in the form of a tubular sleeve. The distal end of the bellows may be interconnected (e.g. rigidly) to the distal end of the vibratory member via a second housing member in the form of a tubular sleeve, wherein the vibratory member extends through all three housing members from the electromechanical transducer housing to communicate axial vibrations (e.g. to the ossicular chain within a patient&#39;s middle ear). 
     In view of the foregoing, it will be appreciated that an inventive method is also provided for use in the manufacture of implantable hearing aid apparatus. In one aspect, the inventive method includes the steps of positioning first and second implantable hearing aid component housing members in adjacent relation, and electrodepositing at least a first layer of a first material on adjacent portions of the first and second housing members to establish an interconnection and hermetic seal therebetween. The method may further provide for the electrodeposition of a second layer of a second material on the first layer, wherein the first and second materials are different. Additionally, a third electrodeposited layer may be disposed on the second layer. 
     Where a single layer is utilized to provide a hermetical seal and interconnection between the first and second implantable hearing aid component housing members, it is preferable for such layer to comprise a biocompatible metal selected from the noted first metals group. Where two electrodeposited layers of differing materials are utilized, the underlying layer may have at least one of a modulus of elasticity, tensile strength and yield strength that is at least two times greater than that of the outer layer. Again, the underlying layer may comprise a metal selected from the second metals group. 
     In another aspect of the inventive method a first implantable hearing aid component housing member may be formed by electrodepositing at least a first layer of a first material onto a supporting shaped mandrel, and by selectively removing the shaped mandrel from within the shaped first layer. As may be appreciated the shaped first layer may integrally define an internal space. For such purposes, the shaped mandrel may be of a hollow configuration. In turn, the removing step may be advantageously completed by contacting the shaped mandrel with a removal fluid (e.g. so that the mandrel material may be flowed away with the fluid), thereby facilitating the formation of complex housing configurations. In this regard, the removing step may comprise one of chemically removing, dissolving and melting the shaped mandrel away from the shaped first layer, e.g. by flowing the removal fluid through the hollow shaped mandrel. 
     More particularly, the removal fluid may be an appropriate reagent for leaching the shaped mandrel off of the shaped first layer. For such purposes, the electrodeposited first material comprising the first layer should be chemically inert to the removal fluid. In one example, the shaped mandrel may comprise aluminum, and the reagent may comprise sodium hydroxide. 
     Alternatively, the removal fluid may comprise a solvent for selectively dissolving the shaped mandrel apart from the shaped first layer. For example, the mandrel may comprise an electrically conductive plastic composite and the solvent may comprise tetraethylene. 
     In another option, the shaped mandrel may comprise a low-melting point metal, such as iridium. The shaped mandrel may be heated above its melting point and removed from the first shaped layer via a removal fluid that is flowed thereby. 
     In conjunction with this aspect of the inventive method, a second layer of a second material may also be electrodeposited on the first layer in the formation of the first housing member, wherein the first and second materials are different. Further, a third layer (e.g. comprising a first material) may be electrodeposited on to the second layer in the formation of the first housing member. 
     As may be appreciated, the first material may comprise a metal selected from the above-noted first metals group, while the second electrodeposited layer may comprise a material selected from the above-noted second metals group. Such an arrangement facilitates the above-noted sealing and relative movement functionalities. Preferably, the first, second, and third layers may be sequentially electrodeposited over the shaped mandrel prior to selective removal of the supporting shaped mandrel. 
     The inventive method may further provide for the positioning of a second implantable hearing aid component housing member in adjacent relation to one end of the first housing member, and the electrodeposition of at least one overlapping layer of a first material (e.g. selected from the above-noted first metals group) on abutting end portions of the first and second housing members to establish an interconnection and hermetic seal therebetween. Further, a third implantable hearing aid component housing member may be then positioned in adjacent relation to another end of the first housing member, wherein at least one overlapping layer of a first material (e.g. selected from the above-noted first metals group) is electrodeposited on abutting end portions of the first and third housing members to establish an interconnection and hermetic seal therebetween. 
     Preferably, a central portion of the first housing member, as well as the non-abutting end portions of the second and third housing members (i.e. not abutting the first housing member) may be covered prior to the electrodeposition of the noted overlapping layers. Further, the overlapping layers may be simultaneously formed prior to the selective removal of the shaped mandrel, wherein the second and third housing members each comprise a material(s) that is not subject to removal by a removal fluid. 
     In one embodiment, the inventive method may be employed in the manufacture of an implantable actuator arrangement having a bellows (e.g. comprising three electrodeposited layers) interconnected at a proximal end to an electromechanical transducer housing via a proximal tubular sleeve, wherein an electrodeposited layer overlaps the bellows and proximal sleeve. A distal end of the bellows is interconnected to a vibratory member (e.g. that extends from the transducer housing) via a distal tubular sleeve, wherein an electrodeposited layer overlaps the bellows and distal sleeve. Such an arrangement yields a highly reliable actuator. 
     In an additional aspect of the inventive method, one or more of the noted electrodeposited layers may be formed in a plurality of substeps, wherein the electrodeposition process is interrupted then restarted between each sub-step so as to affect a discontinuity in grain pattern formation and thereby reduce incidences of pore alignment. By way of example, such interruption and restarting may simply entail the application, discontinuance, and re-application of an electrical current to a metallic shaped mandrel in a submersion electrodeposition bath process. Additionally and/or alternatively, one or more of the above-noted electrodeposited layers may be established utilizing a pulsed current (e.g. as opposed to a direct current), wherein nucleation may occur between each pulse to reduce the likelihood of pore formation. 
     In yet a further related aspect of the inventive method, the above-noted, multi-layered first housing member may be subjected to hot isostatic pressing to improve the fatigue characteristics thereof. More particularly, the multi-layered first housing member may be subjected to an elevated temperature and pressure to enhance the microstructure of one or more of the electrodeposited layers. The temperature and pressure utilized should be selected so that the yield strength of the intended affected layer (e.g. the second of three layers) is less than the treatment pressure at the treatment temperature. HIP processing may also be utilized to treat the noted second and third housing members too. 
    
    
     Numerous additional aspects and advantages will become apparent to those skilled in the art upon consideration of the further description below. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional side view of an implantable hearing aid actuator embodiment comprising features of the present invention. 
     FIG. 2 is a cross-sectional side view of a bellows employable in the embodiment of FIG.  1 . 
     FIG. 3 is a process flow diagram directed to the manufacture/implementation of the bellows of FIG. 2 into the embodiment of FIG.  1 . 
     FIG. 4 is a process flow diagram for one embodiment directed to the sequential electrodeposition of layers to form the bellows of FIG.  2 . 
     FIG. 5 is a process flow diagram illustrating steps of an embodiment for removing a shaped mandrel in connection with the formation of the bellows of FIG.  2 . 
     FIG. 6 illustrates one embodiment of a hot isostatic technique employable in conjunction with the formation of the bellows of FIG.  2 . 
     FIG. 7 is a process flow diagram for one embodiment for interconnecting the bellows of FIG. 2 in the embodiment of FIG.  1 . 
     FIGS. 8A and 8B illustrate exemplary microstructures associated with the bellows of FIG. 2 prior to and after the utilization of the process refinement illustrated in FIG.  6 . 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates an implantable hearing aid actuator comprising one embodiment of the present invention. As may be appreciated, the embodiment may be employed in either semi-implantable or fully-implantable hearing aid systems. 
     The illustrated actuator includes an electrometrical transducer  10 , an elongated vibratory member  20  interconnected at a proximal end to the transducer  10 , and a hollow bellows  30  interconnected at its distal end to a distal end of the vibratory member  20 . In use, the distal end of vibratory member  20  may be positioned within the middle ear of a patient to stimulate the ossicular chain. More particularly, transducer  10  may selectively induce axial vibrations of vibratory member  20 , which vibrations are in turn communicated to the incus bone of the ossicular chain to yield enhanced hearing. Bellows  30  comprises a plurality of undulations  32  that allow bellows  30  to axially respond in an accordion-like fashion to axial vibrations of the vibratory member  20 . Of note, bellows  30  is sealed to provide for isolation of the internal componentry of transducer  10 . 
     In the latter regard, an electromechanical transducer  10  is shown that comprises a leaf  12  extending through a plurality of coils  14 . Coils  14  may be electrically interconnected to a cable  40  which provides signals that induce a desired magnetic field across coils  14  so as to affect desired movement of leaf  12 . In the illustrated embodiment, leaf  12  is connected to a stiff wire  16 , and vibratory member  20  is crimped onto the wire  16 . As such, movement of leaf  12  affects axial vibration of vibratory member  20 . 
     Transducer  10  is disposed within a housing  50 , comprising welded main body and lid housing members  52  and  54 . In order to affect the communication of axial vibrations, vibratory member  20  passes through an opening  56  of the lid housing member  54  and extends through the bellows  30  to the distal end interconnection therewith. To maintain isolation of transducer  10  within housing  50 , bellows  30  is hermetically sealed and hermetically interconnected to the housing  50  at its proximal end  32  and to the vibratory member  20  at its distal end  34 . 
     More particularly, a proximal sleeve  60  may be welded at its proximal end  62  to transducer lid housing member  54  about the opening  56 . Preferably, proximal sleeve  60  and housing members  52  and  54  all comprise the same biocompatible metal, such as titanium. An end portion, or tang  31 , of the proximal end  32  of bellows  30  is slidably and intimately disposed within a cylindrical distal end  64  of proximal sleeve  60 . As shown, the proximal end  32  of bellows  30  may be of a stepped-in, cylindrical configuration, wherein the distal end  64  of proximal sleeve  60  may abut the bellows  30  to define a substantially flush, annular interface region therebetween. Such an arrangement accommodates the application and reliability of an overlapping electrodeposited layer  70  (e.g., comprising a biocompatible material such as gold) disposed across and about the abutment region for interconnection and sealing purposes. 
     Similarly, a distal sleeve  80  may be slidably and intimately disposed about an end portion, or tang  33 , of the distal end  34  of bellows  30 . The distal end  34  may be of a stepped-in, cylindrical configuration, to define the tang  33 , wherein a cylindrical proximal end  82  of distal sleeve  80  may abut the bellows  30  to define a substantially flush, annular interface region therebetween. Again, a reliable overlapping electrodeposited layer  72  (e.g., comprising a biocompatible material such as gold) may be readily provided across and about the abutment region for interconnection and sealing purposes. 
     In the illustrated embodiment, a cylindrical distal end  84  of distal sleeve  80  receives a cylindrical bushing  90 , which locates the distal end of vibratory member  20  therewithin. As further shown, a wire member  92  may be provided within the distal end portion of vibratory member  20 , wherein the distal extreme of distal sleeve  80 , bushing  90 , vibratory member  20  and wire member  92  collectively provide a substantially uninterrupted surface for a fusion weld interconnection (e.g. as may be achieved by laser welding) therebetween, thereby sealing the distal end of distal sleeve  80  and bellows  30 . 
     The embodiment shown in FIG. 1 also includes a tip assembly  94  having an interconnected tip member  94   a  and cap member  94   b , and a ring member  94   c . The cap member  94   b  may be interconnected (e.g., via tack welding) about the distal end  84  of distal sleeve  80 . The ring member  94   c  locates the tip assembly  94  relative to the distal extreme of sleeve  80 . The tip member  94   a  may be particularly adapted for tissue attachment with the ossicular chain of a patient. 
     As noted above, bellows  30  functions to facilitate axial vibration of vibratory member  20  while maintaining isolation of transducer  10 . To further address such functionality, reference will now be made to FIG.  2 . As illustrated therein, bellows  30  may comprise a plurality of conformally disposed layers. Specifically, an inner layer  31 , intermediate layer  33  and outer layer  35  may be advantageously provided via electrodeposition on a shaped mandrel  200 , wherein adjacent ones of the inner layer  31 , intermediate layer  33  and outer layer  35  comprise dissimilar materials. Outer layer  35  may comprise a biocompatible material that is substantially chemically inert to bodily fluids, thereby protecting intermediate layer  33 . Similarly, inner layer  31  may be provided to display the same qualities. The provision of inner layer  31  serves to protect intermediate layer  33  in the event of undesired bodily fluid passage into bellows  30 . 
     Intermediate layer  33  may comprise a material that provides enhanced flexural and strength characteristics relative to the inner and outer layers  31  and  35 . More particularly, intermediate layer  33  may comprise a material that displays a relatively high modulus of elasticity, yet sufficient yield and tensile strength. As may be appreciated, such qualities are desirable in relation to bellows  30  ability to repeatedly and reliably respond in an accordion-like fashion to axial vibrations communicated thereto from the distal end of vibratory member  20 . 
     In this regard, intermediate layer  33  may be advantageously provided to have a modulus of elasticity which is at least about two times the modulus of elasticity of the inner layer  31  and/or outer layer  35 . Further, the intermediate layer  33  may be provided to display tensile and yield strengths which are otherwise at least about two times that of the inner layer  31  and/or outer layer  35 . 
     By way of example, intermediate layer  33  may preferably comprise one or more metal selected from a group consisting of: nickel, iron, chromium, platinum, iridium, copper and aluminum. Inner layer  31  and outer layer  35  may preferably comprise one or more conductive materials selected from a group consisting of gold, titanium and platinum. While less desirable, other materials may also be utilized for layers  31 ,  33  and  35 . 
     As will be further described, the inner layer  31 , intermediate layer  33  and outer layer  35  of bellows  30  may be advantageously defined by a sequential electrodeposition process. In conjunction with such processing, a preferred thickness range for each of the layers may be established between about 5 to 50 microns, and even more preferably between about 5 to 20 microns. Further, a preferred thickness range for the electrodeposited layers  70  and  72  may be established at between about 5 to 50 microns, and even more preferably between about 20 to 40 microns. 
     In one arrangement, thicknesses of about 8 to 15 microns for each of the layers  31 ,  33  and  35  provides satisfactory results. In such arrangement, nickel may be employed for the intermediate layer  33  to provide a modulus of elasticity (in tension) of at least about 200 gigapascals with yield and tensile strengths of at least about 60 megapascals and 320 megapascals, respectively. Gold may be utilized for the inner and outer layers  31  and  35  to provide a modulus of elasticity (in tension) of at least about 80 gigapascals and a tensile strength of about 100 megapascals. Similarly, gold may be utilized to define the electrodeposited layers  70  and  72 , with thicknesses of about 20 to 40 microns. 
     FIG. 3 generally illustrates one embodiment of a process for fabrication/implementation of bellows  30 . Such embodiment provides for the initial formation of bellows  30  via the sequential electrodeposition of a plurality of layers  31 ,  33  and  35  on a shaped mandrel  200  (step  100 ). Utilization of electrodeposition processing yields enhanced sealing of the various layers of bellows  30 . Following bellows  30  formation, the shaped mandrel  200  may be selectively removed therefrom (step  140 ), thereby facilitating complex configurations for bellows  30 . Then, in order to enhance the fatigue properties of bellows  30 , bellows  30  may be subjected to hot isostatic processing (step  160 ). Finally, bellows  30  may be interconnected to transducer  10  and vibratory member  20  in a manner that yields reliable sealing therebetween (step  180 ). 
     Referring now to FIG. 4, the electrodeposition formation of bellows  30  (i.e., step  100 ) is illustrated as comprising separate and sequential steps for the electrodeposition of inner layer  31  (step  110 ), intermediate layer  33  (step  120 ) and outer layer  35  (step  130 ), and correspondingly surface preparation steps (steps  108 ,  118  and  128 ). More particularly, inner layer  31  may be formed via the electrodeposition of an appropriate material (e.g., as noted above) on a supporting shaped mandrel  200 . As shown in FIG. 2, the shaped mandrel  200  may be configured to define the desired undulating configuration of bellows  30 . Preparation of the outer surfaces of mandrel  200  (step  108 ) may entail surface cleaning (e.g. with methylene chloride), striping trapped metals, surface preservation (e.g. using a zincate bath), and surface conditioning (e.g. striking the surface in an electroless nickel bath to enhance surface uniformity and/or striking the surface in an aluminum plating bath to yield an adherent layer). 
     The electrodeposition of inner layer  31  may be achieved via submersion of the shaped mandrel  200  in a plating bath (e.g. gold), wherein an electrical current is passed through the shaped mandrel to additively build up the inner layer  31  to a predetermined thickness. In this regard, it has been recognized that a pulsed current may be provided to the shaped mandrel (step  112 ), wherein the plating bath nucleates in conjunction with each pulse to reduce the likelihood of pore formation in inner layer  31 . Further, the electrodeposition of inner layer  31  may be completed in a plurality of substeps, wherein a corresponding plurality of inner layer  31  sublayers are successively formed. In conjunction with each such substep the electrodeposition process may be interrupted/resumed to affect grain boundary discontinuities (step  114 ). For example, the application of the electrical current may be stopped/restarted. Additionally or alternatively, the mandrel  200  may be removed from and then resubmerged into the plating bath. The formation of one or more sublayers of inner layer  31  during electrodeposition build-up further enhances the protective sealing function of inner layer  31 . In particular, the utilization of such an approach reduces bodily fluid access through undesired pores since, with multiple sublayers, it is unlikely that undesired pores in the different sublayers will be aligned to provide fluid access therethrough. 
     As shown by FIG. 4, intermediate layer  33  may be formed via the electrodeposition of an appropriate material (e.g., as noted above) on the inner layer  31 . Preparation of the surface of inner layer  31  (step  118 ) may entail surface cleaning, (e.g. using ultrasound techniques and surface activation (e.g. with a hot sulfuric acid bath). The electrodeposition of intermediate layer  33  may be achieved via submersion of the shaped mandrel  200  with inner layer  31  into a plating bath (e.g. nickel), wherein an electrical current is passed through the shaped mandrel  200  to additively build-up the intermediate layer  33  to a predetermined thickness. As with the formation of inner layer  31 , it has been recognized that a pulsed current may be utilized (step  122 ), wherein the plating bath nucleates in conjunction with each pulse to reduce the likelihood of pore formation in intermediate layer  33 . Further, electrodeposition of intermediate layer  33  may also be completed in a plurality of substeps, wherein a corresponding plurality of intermediate layer  33  sublayers are successively formed. In conjunction with such substeps, the electrodeposition process may be interrupted/resumed (step  124 ). Again, the formation of two or more sublayers of intermediate layer  33  during electrodeposition build-up may further enhance sealing. 
     Referring further to FIG. 4, the formation of the outer layer  35  may also be completed via electrodeposition of an appropriate material (e.g., as noted above) on the intermediate layer  33 . Preparation of the surface of intermediate layer  33  (step  128 ) may entail surface cleaning, surface smoothing (e.g. using an actane bath), surface activation (e.g. with a hot sulfuric acid bath) and surface conditioning (e.g. striking the surface with an aluminum plating bath to yield an adherent surface). The completion of layer  35  may be achieved via submersion of the shaped mandrel  200  with inner layer  31  and intermediate layer  33  in an appropriate plating bath (e.g. gold) wherein an electrical current is passed through the shaped mandrel  200  to additively buildup outer layer  35  to a predetermined thickness. Again, it has been recognized that a pulsed current may be provided to the shaped mandrel (step  132 ) wherein the plating bath nucleates in conjunction with each pulse to reduce the likelihood of pore formation in outer layer  35 . Further, electrodeposition of outer layer  35  may be completed in a plurality of substeps, wherein a corresponding plurality of sublayers portions are successively formed to define outer layer  35 . In conjunction with each such substep the process may be interrupted/resumed (step  134 ). Again, the formation of multiple sublayers of outer layer  35  during electrodeposition build-up enhances sealing. 
     As previously noted, the above-noted shaped mandrel  200  utilized in the formation of bellows  30  may be selectively removed. In this regard, a collapsible mandrel may be employed. Alternatively, and more preferably, a removal fluid and may be utilized. In this regard, and referring now to FIG. 5, the mandrel  200  and bellows  30  may be supported in a reservoir (step  142 ), and an appropriate reagent may be flowed through the shaped mandrel  200  to leach the shaped mandrel away from the formed bellows  30  (step  144 ). As will be appreciated, the utilization of such a leaching process entails the utilization of materials for the shaped mandrel and inner layer  31  of bellows  30  which are leachable and non-leachable, respectively, in the presence of the reagent utilized. By way of example, an inner layer  31  comprising gold and a hollow shaped mandrel  200  comprising aluminum have been satisfactorily utilized in conjunction with a sodium hydroxide reagent. Following removal of the shaped mandrel  200  from the formed bellows  30 , the bellows  30  may be washed (step  146 ) prior to further processing. Other embodiments may provide for dissolving the mandrel  200  in a selected solvent or melting the mandrel in a heated bath. 
     As noted in the process embodiment of FIG. 3, bellows  30  may be advantageously subjected to hot isostatic pressing (HIP). To further describe such processing, reference is now made to FIG.  6 . As illustrated, bellows  30  may be positioned in an appropriate processing chamber in which the atmosphere/temperature/pressure are selectively controllable (step  162 ). For example, an inert gas atmosphere (e.g. argon) may be established (step  164 ), and the temperature and pressure within the chamber may be increased (step  166 ) so that the yield strength of one or more layers of bellows  30  (e.g. layer  33 ) is less than the set pressure at the set temperature. The elevated pressure and temperature within the chamber may then be maintained for an appropriate time period (step  168 ) to close and diffusion bond internal pores within the intended affected layer. 
     By way of example, in an arrangement having a bellows  30  with an inner layer  31 , intermediate layer  33 , and outer layer  35 , comprising gold, nickel and gold, respectively, with each layer having a thickness of about 10 microns, HIP processing has been satisfactorily completed utilizing an argon atmosphere with elevated temperatures and pressures of at least about 400° C. and 15,000 psi for a predetermined period of at least about 30 minutes. The utilization of HIP processing functions to enhance the microstructure of the intermediate layer  33 . Such modification in turn yields enhanced fatigue characteristics. 
     In this regard, FIGS. 8A and 8B illustrate the microstructure of a bellows  30  comprising gold, nickel and gold layers prior to and after HIP processing. As can be seen in FIG. 8A, the intermediate nickel layer is of a columnar microstructure. After HIP processing, FIG. 2 illustrates how the nickel layer has been modified to a more relatively isotropic granular microstructure. 
     Referring now to FIG. 7, a further process diagram is illustrated showing key steps in one process embodiment for interconnection of bellows  30  in an actuator embodiment as per FIG.  1 . In particular, the above-noted tang  31  at the proximal end  32  of bellows  30  may be positioned (e.g. slidably inserted) into the proximal sleeve  70  (step  182 ). Then, the above-noted tang  33  at the distal end  34  of bellows  30  may be positioned (e.g. slidably inserted) within the proximal end of distal sleeve  80  (step  184 ) to define a 3-part assembly. Prior to such assembly, the outer layer  35 , intermediate layer  33  and a portion of the inner layer  31  may be selectively removed from the opposing ends of bellows  30  (e.g. via bead blasting with the undulating central portion of bellows  30  protectively shielded), wherein the noted tangs  31 ,  33  comprise only the remaining portion of inner layer  31 . Then, a proximal end of proximal sleeve  70 , a central portion of bellows  30  and a distal end portion of distal sleeve  80  may be covered (e.g. with inflatable silicon boots), leaving only the abutment regions therebetween exposed (step  184 ). Such exposed regions of the sleeves  70 ,  80  may be pretreated (e.g. gold-plated). Thereafter, the 3-part assembly may be submerged in a plating bath to electrodeposit a biocompatible metal (e.g. gold) onto the uncovered abutment regions (step  186 ), thereby simultaneously defining layers  70 ,  72  noted above. In one arrangement two successive gold plating baths have been utilized to define layers  70 ,  72 . 
     Preferably, steps  182 ,  184  and  186  are completed prior to removal of the shaped mandrel  200  from billons  30  described above. More particularly, mandrel  200  may be utilized to support the noted 3-part assembly during the electrodeposition step  186 . For such purposes mandrel  200  may be configured to slidably receive the sleeves  60 ,  80  at opposing ends with the formed bellows  30  interposed therebetween. 
     Following formation of layers  70 ,  72 , the proximal end of 62 proximal sleeve  60  may be laser welded to housing lid  54 , and housing lid  54 , may be laser welded to housing body  52  (step  187 ). As previously indicated, a bushing  90  may then be inserted into the distal end  84  of distal sleeve  80 , and a wire section  92  may be positioned within the end of vibratory member  20  (step  188 ). Thereafter, the distal sleeve  80 , vibratory member  20 , and wire member  92  may be putter welded together to hermetically seal the distal interconnections therebetween (step  190 ). Finally, a tip assembly  94  may be tack welded about the distal end of distal sleeve  80  and a bellows guard  96  may be positioned about the bellows  30  (step  192 ). 
     The embodiment descriptions provided above are for exemplary purposes only and are not intended to limit the scope of the present invention. Various modifications and extensions of the described embodiments will be apparent to those skilled in the art and are intended to be within the scope of the invention as defined by the claims which follow.