U.S. patent number 4,516,820 [Application Number 06/461,617] was granted by the patent office on 1985-05-14 for cochlear prosthesis package connector.
This patent grant is currently assigned to The Commonwealth of Australia. Invention is credited to Janusz Kuzma.
United States Patent |
4,516,820 |
Kuzma |
May 14, 1985 |
Cochlear prosthesis package connector
Abstract
A cochlear prosthetic package having an electronics part and an
electrode part. The two parts have ceramic plates with aligned,
hermetically-sealed hollow-pin feedthroughs therein. The parts are
connected by a Silastic sheet having individual metal foil pieces
extending therethrough, each piece of metal foil having its two
ends bent over to lie flush against respective faces of the
Silastic sheet. The metal foil ends contact the feedthroughs to
establish the electrical connections.
Inventors: |
Kuzma; Janusz (Stanmore,
AU) |
Assignee: |
The Commonwealth of Australia
(AU)
|
Family
ID: |
23833286 |
Appl.
No.: |
06/461,617 |
Filed: |
January 27, 1983 |
Current U.S.
Class: |
439/289; 439/278;
439/364; 439/591; 439/271; 439/292; 439/909; 607/137 |
Current CPC
Class: |
A61N
1/3754 (20130101); H05K 7/1061 (20130101); A61N
1/36038 (20170801); Y10S 439/909 (20130101) |
Current International
Class: |
A61N
1/375 (20060101); A61N 1/372 (20060101); H05K
7/10 (20060101); H04R 25/00 (20060101); H01R
025/00 () |
Field of
Search: |
;3/1,1.1 ;128/419,784
;339/48,49B,17LM,17M,92,193,194,59M,DIG.3 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Weidenfeld; Gil
Assistant Examiner: Pirlot; David L.
Attorney, Agent or Firm: Gottlieb, Rackman & Reisman
Claims
I claim:
1. A connector arrangement for connecting to each other first and
second parts of a cochlear prosthesis, said first part having an
hermetically sealed case adapted to contain an electronic circuit
therein and said second part having a plurality of conductors
extending therefrom; each of said first and second parts having a
carrier with a plurality of noble-metal conducting hollow-tube
feedthroughs extended therethrough and hermetically sealed thereto
by reaction bonds; the two pluralities of feedthroughs having
alignable patterns; a deformable sheet permanently adhered to the
carrier of said first part and having a plurality of noble-metal
foil contacts extending through respective slits each having its
two ends bent over so that they lie flush against respective faces
of said sheet, said plurality of contacts having a pattern which is
alignable with the patterns of the feedthroughs in said two
pluralities; each of said feedthroughs being open at that end which
faces said deformable sheet and the face of each of said carriers
which is disposed adjacent to said deformable sheet being lapped to
a mirror finish; a screw extending outwardly of the carrier of said
first part and passing through a central hole in the carrier of
said second part for securing said sheet between said first and
second parts to allow said plurality of contacts to establish
electrical connections between respective ones of the feedthroughs
in said two pluralities; said second part including a backing plate
having a central hole therein, and said securing means further
including a nut screwable onto the end of said screw which extends
through said backing plate hole; and a plurality of conductors
connected to respective ones of the feedthroughs in said second
part, said plurality of conductors being wound in the form of a
spiral and exiting said second part through an additional hole in
said backing plate.
2. A connector arrangement in accordance with claim 1 wherein the
carriers of said first and second parts are substantially
identical.
3. A connector arrangement in accordance with claim 2 further
including Silastic material surrounding the conductors in said
second part between the carrier and backing plate thereof.
4. A connector arrangement in accordance with claim 3 further
including mating means on said first and second parts for ensuring
the proper alignment thereof.
5. A connector arrangement for connecting to each other first and
second parts of a cochlear prosthesis, said first part having an
hermetically sealed case adapted to contain an electronic circuit
therein and said second part having a plurality of conductors
extending therefrom; said first part having a carrier with a
plurality of conducting means extended therethrough and
hermetically sealed thereto; characterized by said second part
having a carrier with a plurality of conducting means extended
therethrough, the two pluralities of conducting means having
alignable patterns; a deformable sheet having a plurality of
contacts each having one end on each respective face of said sheet,
said plurality of contacts having a pattern which is alignable with
the patterns of the conducting means in said two pluralities; a
screw extending outwardly of the carrier of said first part and
passing through a central hole in the carrier of said second part
for securing said sheet between said first and second parts to
allow said plurality of contacts to establish electrical
connections between respective ones of said conducting means in
said two pluralities; said second part including a backing plate
having a central hole therein, and securing means further including
a nut screwable onto the end of said screw which extends through
said backing plate hole; and a plurality of conductors connected to
respective ones of the conducting means in said second part, said
plurality of conductors being wound in the form of a spiral and
exiting said second part through an additional hole in said backing
plate.
6. A connector arrangement in accordance with claim 5 further
including Silastic material surrounding the conductors in said
second part between the carrier and backing plate thereof.
7. A connector arrangement for connecting to each other a first
part having an hermetically sealed case adapted to contain an
electronic circuit therein and a second part having a plurality of
conductors extending therefrom; said first part having a carrier
with a set of hollow-tube feedthroughs hermetically-sealed thereto
by reaction bonds; said second part having a carrier with a set of
hollow-tube feedthroughs, the two sets of feedthroughs having
alignable patterns; a deformable sheet having a set of contacts
each having one end on each respective face of said sheet, said set
of contacts having a pattern which is alignable with the patterns
of the feedhtroughs in said two sets and each of said feedthroughs
being open at that end which faces said deformable sheet; a screw
extending outwardly of the carrier of said first part and passing
through a central hole in the carrier of second second part for
securing said sheet between said first and second parts to allow
said set of contacts to establish electrical connections between
respective ones of the feedthroughs in said two sets; said second
part including a backing plate having a central hole therein, and
securing means further including a nut screwable onto the end of
said screw which extends through said backing plate hole; and a set
of conductors connected to respective ones of the feedthroughs in
said second part, said set of conductors being wound in the form of
a spiral and exiting said second part through an additional hole in
said backing plate.
8. A connector arrangement in accordance with claim 7 further
including Silastic material surrounding the conductors in said
second part between the carrier and backing plate thereof.
9. A connector arrangement for connecting to each other a first
part having an hermetically sealed case adapted to contain an
electronic circuit therein and a second part having a plurality of
conductors extending therefrom; said first part having a carrier
with a set of hermetically-sealed, hollow-tube feedthroughs;
characterized by said second part having a carrier with a set of
hollow-tube feedthroughs; the two sets of feedthroughs having
alignable patterns; a deformable sheet having a set of contracts
each having one end on each respective face of said sheet, said set
of contacts having a pattern which is alignable with the patterns
of the feedthroughs in said two sets; a screw extending outwardly
of the carrier of said first part and passing through a central
hole in the carrier of said second part for securing said sheet
between said first and second parts to allow said set of contacts
to establish electrical connections between respective ones of said
feedthroughs in said two sets; a backing plate in said second part
having a central hole therein; a nut screwable onto the end of said
screw which extends through said backing plate hole; and a set of
conductors connected to respective ones of the feed-throughs in
said second part, said set of conductors being wound in the form of
a spiral and exiting said second part through an additional hole in
said backing plate.
10. A connector arrangement in accordance with claim 9 further
including Silastic material surrounding the conductor in said
second part between the carrier and backing plate thereof.
Description
DESCRIPTION
This invention relates to implantable medical electronic devices
such as pacemakers and cochlear prostheses, and more particularly
to a cochlear prosthesis in which a plurality of connections are
made between the assembly containing the electronic circuits, and
an electrode or other conductor-type device.
In its usual form, a cochlear prosthesis consists of two parts
implanted into the skull of the patient. The first part is an
"electronics" package which is implanted in the mastoid bone behind
the ear. The second part consists of an electrode assembly which is
inserted into the cochlea in order to apply electrical stimulation
to auditory nerve fibers. The electrode array or assembly must be
electrically connected to the electronics package. In addition, an
internally-worn transmitter/receiver device is used to transfer
both information and power to the implanted unit, and may receive
information telemetered back from the implant.
A major problem with a cochlear prosthesis is that entire
replacement of the device is probably not feasible with present-day
technology. The electrode assembly, once it has been implanted into
the cochlea, probably cannot be explanted without damage to the
cochlea itself. The electrode assembly must thus be designed to
have a long life (in the order of fifty years, or the expected life
of the patient). However, it may be necessary or desirable to
replace the electronics package, for example, due to a circuit
failure, or to substitute a compatible assembly of more advanced
design at some time in the future. Thus, permanent connections
between the electronics package and the electrodes are not
appropriate.
In a cochlear prosthesis, the connection problem is much more
severe than in the case of a pacemaker for several reasons. First,
a pacemaker usually requires only a small number of connections to
electrodes (up to four in existing designs), whereas 22 connections
are required between the electronics package and the electrodes in
a cochlear prosthesis such as that of the illustrative embodiment
of the invention. Second, because of the confined space in the
skull where the cochlear prosthesis is required to fit, the space
constraints are much more severe than with a pacemaker. In
addition, it is desirable for surgical convenience and safety to be
able to make all connections between the electronics package and
the electrodes simultaneously, with one procedure, which contrasts
with a typical pacemaker design for which the small number of
connections required allows each one to be made individually, for
example, with grub screws.
Furthermore, as is the case with pacemakers and other implantable
devices, the re-connection process must take place in an
environment where fluid ingress cannot be prevented; since the
electrode assembly remains permanently in the skull, each
re-connection of the electodes to a new electronics package must
take place inside the patient's head.
It will be apparent to those skilled in the art that this type of
connector problem is not confined to medical prostheses. In fact,
there are a variety of situations in the electronics field where it
is necessary to make a connection or connections to an electronics
assembly in a hostile or difficult environment, such as in marine,
petrochemical, industrial or automotive applications. The subject
invention is applicable to fields other than medical
prostheses.
Several cochlear prostheses have been described in the prior art,
including some where a connector is provided. See, for example,
reports under NIH Contract No. N01-NS-7-2367, "Development of
Multichannel Electrodes for an Auditory Prosthesis". Connectors for
use with implantable medical electronic devices have also been
described. See, for example, U.S. patent application Ser. No.
237,090, entitled "Bone Growth Stimulator Connector", filed on Feb.
23, 1981 in the name of John B. Dickson. The prior art connector
techniques, however, suffer from disadvantages which are solved by
the subject invention.
The present invention relates to the design of a package for a
cochlear prosthesis as described in my copending patent application
entitled "Cochlear Prosthesis Package and Method for Making Same",
Ser. No. 402,227, filed on July 27, 1982, which application is
hereby incorporated by reference. The connection problem in my
earlier design was solved by providing a two-part connector. One
part consists of a ceramic plate or sheet containing a number of
tubular platinum feedthroughs which form the electrical paths
between the internal electronic circuits and the outside. These
platinum feedthroughs are inserted into holes made in the ceramic
while it is still in the green or unfired state. The platinum and
ceramic are fired together and, as the ceramic sinters, it shrinks.
The shrinking process exerts a force evenly around and along each
platinum tubular feedthrough, with the result that an hermetic,
high-strength reaction body is formed between the platinum and the
ceramic. After firing, the surface of the ceramic plate is lapped
to a mirror finish, and this assembly is then attached to the
electronics assembly and a titanium housing using conventional
soldering, welding and brazing techniques.
The second part of the connector consists of a Silastic sheet
containing preformed platinum parts to which are welded wires
connected to the electrodes. To this Silastic sheet is attached
another Silastic sheet which acts as an insulating material, and
due to its elasticity evenly distributes the force applied over the
contact area. This force is applied by means of a titanium backing
part, through the middle of which passes a screw attached to the
other side of the connector.
Although this connector performs satisfactorily, it has been found
to have some drawbacks. First, the elasticity of the connector is
derived from the Silastic sheet in the connector part which is
attached to the electrodes and thus remains inside the body. The
long-term performance of this Silastic material is not fully known.
Any deficiencies in the mechanical properties of the material which
might be uncovered with the passage of time cannot be overcome
without replacing the electrodes.
Second, the connector presents some difficulties in manufacture
because of the difficulty of forming the small platinum preformed
connector parts with a correctly shaped nail or conical head, with
consistent shape and quality, and additionally because of the
problem of welding the very fine platinum wires from the electrodes
to the platinum parts.
It was also found that the process of tightening up the connector
had the potential for stressing the very fine wires from the
electrode array to the connector parts to such an extent that the
welds might break or the wires fracture.
Finally, it is now thought that the small size of the head of each
preformed platinum part might allow it to deform the Silastic sheet
to such an extent that the platinum part could become so deeply
embedded in the Silastic sheet that adequate pressure is not
maintained, resulting in a loss of contact.
The present invention overcomes these limitations, and offers some
other significant improvements and advantages to be described. It
is an object of my invention to produce a connector suitable for
use in implantable medical electronic devices, and in particular a
cochlear prosthesis, and which is easily manufacturable; allows for
reliable disconnection and re-connection without compromising the
electrode array which is required to remain in the body; is not
subject to degradation in mechanical performance over time;
maintains both a high electrical resistance between different
connected circuits, and a low-resistance, reliable contact between
individual connector parts of the same electrical circuit; allows
the opportunity to take advantage of new materials which may be
developed in the future with more advantageous mechanical or
electrical properties; is suitable for multiple, independent
electrical connections in a small space; is designed such that the
part of the connector which remains in the body attached to the
electrodes has no elastic components which affect the performance
of the connector or components which might suffer from degradation
of properties with the passage of time; allows modularity of
component selection such that one of a family of cochlear implant
devices may be connected to one of a family of electrodes (e.g., of
different size); and permits different types of electronic modules
to be utilized with the same connector (e.g., an all ceramic
package), and in particular allows advantage to be taken of new
technology, materials, and manufacturing methods as they are
developed.
Further objects, features and advantages of the invention will
become apparent upon consideration of the following detailed
description in conjunction with the drawing, in which:
FIG. 1 is an exploded perspective view of the connector parts of a
cochlear implant package made in accordance with the principles of
my invention;
FIG. 2 is a detailed cross-sectional view of the connector parts
showing them assembled together;
FIG. 3 is an enlarged view of a single connection point; and
FIGS. 4A-4C illustrate the steps of the preferred method of
manufacturing the intervening Silastic sheet containing the
platinum contacts.
Referring to FIG. 1, one side of the connector arrangement consists
of a cochlear implant device such as that described in my copending
application. In fact, one of the advantages of the present
invention is that one side of the connector need not be changed.
The electronics assembly is contained in a titanium housing or case
10, to which is attached, by welding and brazing in the
conventional way, a plate (preferably ceramic) 12 containing
hermetic platinum feedthroughs 14, as previously described above. A
titanium screw 16 projects from the center of the ceramic plate.
The surface of the ceramic plate is lapped to a mirror finish. The
titanium housing contains hermetic feedthroughs 11 to a two-ended
tube 13 (shown only partially), through which a coil (not shown)
passes, as described in my copending application.
The other side of the connector consists of a plate (preferably
ceramic) 30 with identical feedthroughs 34, shown end on in FIG. 1
and illustrated in cross-section in FIG. 2. Ceramic plate 30 is
made of identical components and with an identical process as the
ceramic plate 12 containing the feedthroughs which is used in the
electronics package. Some minor machining operations are used to
convert the ceramic plate with feedthroughs which is used in the
electronics package for use in the electrode side of the
connector.
As shown in FIG. 1, ceramic plate 30 is backed by a titanium plate
38. A titanium piece 8 is accurately welded to the inside of the
circumference of the titanium housing 10 to act as a locating pin
or lug. This locating lug fits into a depression 50 machined into
the titanium backing piece 38 to ensure that the connector is
assembled while correctly aligned.
The titanium locating lug 8 is shown in one position in FIG. 1, and
in a different position in FIG. 2. The exact position of the
locating lug is not critical. In fact, the locating lug can be
looked upon not only as a locating lug but also a keying system.
That is to say, future generations of cochlear implants and/or
electronic packages may use a different number of locating lugs in
different positions such that it is not possible to mix elements
from imcompatible families. For example, the connector technique
described herein could be used to make a connector with, for
example, 50 connection points in the same area, and a different
locating and keying arrangement could be used to prevent mix-up of
incompatible components.
In the center of the titanium backing piece 38 is a hole 40 through
which the screw 16 attached to the other part projects. The
assembly is completed by a titanium nut 46 screwed onto screw 16. A
predetermined torque is applied to the screw via a special tool 48
used with any conventional torque spanner (not shown). A slot or
cutout 38a is machined in the titanium backing piece to allow exit
of the cable to be described below.
In the illustrative embodiment of the invention, the force holding
the connector together is applied by the centrally located screw
and nut. Other arrangements centrally located (e.g., a clip, or a
screw passing entirely through the package) are also suitable.
Alternatively, or in addition, the force could be applied by a
collar, ring or band outside the connector, where in this case
there would not be a need for a central hole in the connector.
The electrode leads 36 are formed into a spiral 36a inside a
Silastic tube 32 as it exits the connector. The tube is also filled
with Silastic (MDX 4-4210). The purpose of the spiralling is to
provide stress relief of the electrode cable so that fracture due
to fatigue resulting from flexing is prevented. The Silastic is
transparent, allowing visual inspection of the cable after
manufacture.
Between the two ceramic plates containing feed-throughs there is
disposed a thin Silastic sheet 20. Into this Silastic sheet are
placed small pieces of platinum foil 22, each passing from one side
of the sheet, through a small respective cut or slit, to the other
side. A central hole 24 in the Silastic sheet allows passage of the
screw 16. Thus, connection between paired feed-throughs is made via
a platinum foil piece pressed against and between the Silastic
sheet and the platinum feed-throughs in the ceramic plates on both
sides of the connector. In the preferred embodiment, the
interconnecting Silastic sheet is glued in a couple of spots to the
ceramic plate with platinum feedthroughs in the electronics
package, with the correct alignment being established visually at
the time of gluing; in this manner, the sheet can be held in place
during assembly. However, a larger Silastic sheet could be used
with cut-outs for alignment with the locating lug 8.
After assembly of the complete cochlear prosthesis, the entire
implantable device is surrounded by a silicon rubber (Silastic
4515, Type A) protective coating or shield (not shown). The purpose
of this shield is to act as a protective coating for the implant to
prevent tissue growth into cavities and corners in the implant
which might make removal of the implant more difficult, to protect
the body from sharp edges or corners on the implant and to protect
the implant during handling such as during surgical implantation
and electrode insertion.
The performance of the device is not dependent upon the integrity
of the shield as the electronics package is hermetically sealed.
Nor is the performance of the connector dependent upon fluids being
excluded by the shield, as it is designed to perform even if
connection is made totally immersed in saline, or other
physiological fluids.
Referring to FIG. 2 which shows the connector arrangement in
cross-sectional detail, it can be seen that the electronics
component of the implant is constructed as described in my
copending application. A ceramic sheet or plate 12 contains
platinum feedthroughs 14. The plate is attached to a machined or
pressed titanium flange 60 by a high-temperature brazing process
using a braze 62 capable of hermetically joining ceramic and
titanium. The flange and ceramic assembly with feedthroughs have
the electronic components attached (not shown), and the entire
assembly is TIG-welded using conventional techniques, shown by the
numeral 64, to the titanium bottom part 10 of the appropriate
dimensions.
In the center of the ceramic plate 12 is attached a titanium screw
16 using one of several methods. As illustrated, a platinum tube 66
is bonded to the ceramic plate at the same time as the
feedthroughs. The titanium screw 16 is then embedded firmly into
the platinum tube, and hermeticity is ensured by braze 68 between
the platinum tube and the titanium screw. The head 70 of the screw
is appropriately shaped for location, sealing, and force transfer,
as will be apparent to those skilled in the art.
Ceramic plate 30 with platinum feedthroughs 34 is used on the other
side of the connector. Instead of a central platinum tube, the
central hole is enlarged to accommodate an extension of the
tightening nut 46.
In fact, an advantage of the subject connector design is that the
ceramic plate on the electrode side of the connector is almost
identical to the ceramic plate on the electronics package side; the
two are made with the same components and processes. Defects in
components or manufacturing processes will produce a number of
ceramic assemblies with platinum tube feedthroughs which are not
hermetic, and therefore unsuitable for use in the electronics
package. However, these components are perfectly suitable for use
on the electrode side of the connector since feedthrough
hermeticity is not a requirement on this side. Thus, provided the
reject rate of the platinum-to-ceramic sintering process remains
below 50%, all parts manufactured may be used. It is anticipated,
however, that advances in technology and materials may result in
different materials being used for the connector plates, where both
sides are not the same. My invention is also useful in applications
where it is necessary to join two hermetically sealed parts with
electrical connections; in such a case, both sides of the connector
would need to be made from hermetic assemblies.
The ceramic plate 30 on the electrode side of the connector has the
fine wires 36 from the electrodes welded to the platinum
feedthroughs 34, as shown by the numeral 72. These wires are
mechanically supported after welding by Silastic glue (Type A),
shown by the numeral 74. All 22 electrode wires exit as a bundle
36a which is wound in a spiral supported in Silastic tube 32
embedded with Silastic 76. The purpose of the spiraling of the
electrode wire bundle is to act as a strain relief and prevent
electrode wire fracture due to fatigue as a result of flexing,
stetching or other movement while in the body, during insertion, or
during manufacture or transport. The electrode cable exits the
connector via a cutout 78 in the titanium backing plate 38.
The titanium backing plate 38 is shaped so that it makes contact
with the ceramic plate 30 at the periphery and circumferentially,
and also in the center where the nut 46 is located. There is a thin
film 74 of Silastic between the titanium backing plate 38 and the
ceramic plate 30. Thus, as the titanium nut is tightened, force is
transmitted from the nut, through the titanium backing plate, via
the thin film of Silastic to the ceramic connector plate. The hole
in the center of the ceramic plate fits snugly around the nut and
centrally locates the connector around the screw. This arrangement
of tightening ensures that forces transmitted to the electrode side
of the connector are evenly distributed over the entire surfaces of
the ceramic plates.
The other function of the titanium backing plate 38 is to protect
the delicate electrode wires embedded in the soft Silastic as they
pass from the electrode bundle 36a to where they are welded to the
connector feedthroughs. The backing plate in the preferred
embodiment is titanium, but other materials are suitable as long as
the forces holding the connector together with a central screw are
transmitted via a metal part against the ceramic feed-through
plate.
Because the cavity between the titanium backing plate and the
ceramic plate with feedthroughs to which the electrode wires are
attached is filled with Silastic 74, additional support for the
electrode wires is provided. Thus, the entire electrode side of the
connector is solid and contains no parts or components which may be
subject to fatigue or creep failure over the expected life of the
electrodes, or will be otherwise adversely affected by the passage
of time.
Between the two ceramic plates 12 and 30 there is disposed Silastic
sheet 30, containing a number of platinum foil parts 22 inserted
through slits cut into the Silastic sheet and then bent over. An
enlarged view of the Silastic sheet in the region of the platinum
feed-through parts is shown in FIG. 3. The thickness of the
platinum foil and the Silastic sheet should be accurately
controlled. I have found that 25-micron thick platinum foil and a
500-micron thick Silastic sheet give satisfactory results.
The platinum foil 22 makes contact in the form of a ring with each
feedthrough platinum part. Since there is a thickness of the
Silastic sheet, and twice the thickness of the platinum foil
between each pair of platinum connector feedthroughs, the Silastic
sheet in the region of contact is more deformed than elsewhere;
thus, the force pressing the platinum foil onto the platinum
feedthroughs can be accurately controlled. Even if there is a
misalignment of parts such that the platinum feedthroughs are not
coaxial, there will always be a region where two thicknesses of
platinum foil, and one thickness of Silastic, lie between
feedthrough platinum tubes (provided, of course, that the axes of
the tubes do not stray more than one diameter from each other).
However, since the platinum feedthroughs are preferably hollow (for
reasons explained in my copending application), there is only
little force tending to deform the Silastic sheet in the center of
the feedthroughs, and thus the Silastic tends to bulge in this
region, as shown by the numeral 80. The space 82 in the middle of
each platinum feedthrough is important. The purpose of this hole or
space is to allow plastic deformation of the Silastic sheet into
the hole, and there is thus a transition zone between Silastic
under high pressure outside the area of the hole, and Silastic
under no pressure. Therefore, there is always a region of Silastic
between the two extremes where the elastic limit is not exceeded
and, even if the Silastic sheet deforms plastically due to creep,
the platinum foil will be pressed against the platinum feedthroughs
with a fairly constant force by the Silastic still within the
elastic limit. In addition, the inside edge 84 of the hole in each
platinum feedthrough is fairly sharp, so the contact pressure is
high. Since platinum is a fairly ductile material, the foil tends
not to be cut by these forces, but deforms to make an excellent
contact around the entire circumference of each platinum
feedthrough.
The Silastic and platinum interconnecting part is designed to be
replaced at each re-connection. Thus, if there is any creep of the
Silastic material during the expected life of the implant, a new
Silastic sheet may be inserted when re-connection is performed. In
addition, this design has the option to take advantage of new
materials which may be developed or become available in future
years without modifying the intrinsic design or nature of the
connector, as discussed above.
In the preferred embodiment, the interconnecting Silastic sheet
containing the platinum foil pieces is supplied attached by glue
(Silastic, Type A) in a couple of spots to the electronics package,
but it is possible to supply it separately.
Referring to FIG. 2, the entire assembly is located by a small
titanium lug 8 which is resistance welded to the electronics
package after TIG-welding of the titanium sections together. This
locating lug is designed to fit inside a complementary shaped slot
50 machined into the titanium backing piece 38. The geometrical
arrangement of the components, with particular regard to the
locating lug and the electrode exit point, is designed to ensure
that correct alignment is maintained during assembly.
FIGS. 4A-4C illustrate diagrammatically the method of construction
of the Silastic interconnection sheet with the platinum foil parts.
In the upper part of the figure, a Silastic sheet 30 is depicted;
the sheet is molded from the appropriate Silastic (Type 4210)
between two sheets of optically flat glass separated by a precisely
known distance. A central hole 24 to allow passage of the screw is
punched or cut in the Silastic sheet. Additionally, 22 slits shown
by the numeral 88, are punched or cut in the sheet to one side of
the positions where the feedthrough platinum pieces are to be
inserted. Preformed platinum (or other noble metal) foil pieces 22
are punched or cut from a platinum foil sheet of a known and
controlled thickness. These pieces are inserted into the slits in
the Silastic sheet, as shown in the middle part of the figure, so
that equal amounts protrude from either side of the Silastic sheet.
Each foil piece is then folded over as shown in the lower part of
the figure, to form the interconnection. The foil pieces are shown
in the drawing to be of approximately rectangular shape with
rounded ends, but other shapes (e.g., kidney or figure eight) are
possible.
It is important that the surfaces of the two ceramic plates be
lapped to a mirror finish. A high electrical resistance between
adjacent contacts is assured because no path for conductive fluid
exists between adjacent connections except in the spaces between
each ceramic plate and the Silastic sheet. With smooth surfaces on
the ceramic plates and the Silastic sheet, and a known and
controlled tightening torque, high interconnection resistances are
routinely observed, even when the connection is made entirely under
saline. The process of tightening the connector tends to force out
any fluid which may have been inside the connector prior to
tightening.
Disconnection of the connector is made by cutting around the
perimeter of the protective Silastic shield (not shown) with a
blade and removing the Silastic shield over the electrode side of
the connector. The nut is then unscrewed, and the connector opened.
The electronics package with interconnecting sheet can then be
removed.
During replacement of the electronics package, the connection is
made and the nut is tightened so that the correct torque is
applied. Then a pre-molded Silastic covering part may be attached
over the electrode side of the connector, and attached to the
Silastic covering over the electronics assembly with Silastic
Medical Grade adhesive, Type A.
Although the invention had been described with reference to a
particular embodimenet, it is to be understood that this embodiment
is merely illustrative of the application of the principles of the
invention. Numerous modifications may be made therein and other
arrangements may be devised without departing from the spirit and
scope of the invention.
* * * * *