Encapsulated Non-permeable Piezoelectric Powered Pacesetter

Abstract

An encapsulated non-permeable piezoelectric self-powered pacesetter for implantation in an in vivo, or living, system in which the pacesetter is sealed and enclosed in an envelope formed of medical grade silicone rubber and preferably natural or synthetic animal, plant or insect wax, in which a piezoelectric poly-crystalline ceramic is completely embedded, enclosed or housed to function as a mechanical to electrical energy converter, when implanted near moving muscle in a living system, and without connection with a separate source of electrical energy either within or without the living system.

Description

THE INVENTION

This invention relates to pacesetters and more particularly to the encapsulated type enclosing a piezoelectric poly-crystalline ceramic mechanical to electrical energy converter wherein the enclosure consists of a non-permeable envelope formed of medical grade silicone rubber and natural or synthetic animal, plant or insect wax to provide a compatible ion obstructing or excluding interface between living tissue and the implant.

The invention embodies two forms, one of which may consist of a material of uniformly integrated medical grade silicone rubber and one or more natural or synthetic waxes of the type disclosed, or another form consisting of a moulded wax providing a highly non-permeable coating to prevent transfer of relatively highly reactive electrolytes or other conductive moisture from entering the areas in which the piezoelectric unit and its associated electrical components are enclosed. The outer cover or envelope of medical grade silicone rubber must be compatible with living tissue, while the inner envelope provides a non-permeable coating for the implantable electrical devices associated with the piezoelectrical generator.

THE DRAWING

FIG. 1 is an enlarged longitudinal section illustrating diagrammatically a form of pacesetter embodying the present invention, in which the enclosure is an integrated envelope of medical grade silicone rubber and a wax.

FIG. 2 is an end view of the same, and,

FIG. 3 is a modified form of the invention in which an enclosing envelope is formed of an inner body of moulded wax and an outer covering layer of medical grade silicone rubber.

DESCRIPTION

The figures illustrate forms of the invention which include an encapsulation constructed of materials compatible with living tissue with which they come into contact by implantation in a living system. While the invention is especially useful as a heart pacesetter for implantation in the chest cavity or adjacent to the heart left ventricle, it is equally useful in other muscular areas of the living system by implantation to stimulate and regulate muscular activity as, for instance, pacing the bladder, blood pressure control centers of the circulatory system, gastro-intestinal tract, the pancreas and other electrically controlled organs of the living system.

Due to its miniature size and compactness, relatively light weight, non-permeability to body fluids and its ability to obstruct or exclude ion passage therethrough, it is readily adaptable to these many uses.

In the drawing, first referring to FIGS. 1 and 2, illustrating a simplified and preferred form of the invention. In this embodiment, which is shown somewhat enlarged for clearness, the encapsulation is indicated generally at 10 and is formed of a mass composed of substantially uniformly and intimately integrated medical grade silicone rubber and one or more natural waxes of the type herein disclosed, imparting a material having high non-permeable qualities to prevent transfer of highly reactive electrolytes or other conductive moisture from entering the areas in which the piezoelectric generator unit and its associated electrical components are enclosed, yet possessing flexibility sufficient to react to muscular movement in the area of its implantation in a living system. Such material is found to be compatible with living tissue with which it comes into contact.

A transducer comprising elements 12 extend longitudinally along and within the encapsulation 10 and have imput electrical connection with a conventional piezoelectric generator unit 16 through electrodes of platinum or other suitable tissue-compatible conductors 18 and 20. Electrodes 18' and 20', respectively, are electrically connected with the output side of the unit 16 for purposes of delivering electrical impulses to the specific part of the body or living system in which the electrodes are implanted.

It is essential that the piezoelectric generator which is of very high impedance have a relatively slight ability to flex or bend in use to actively generate electrical energy. This is ensured by its encapsulation in a moulded or formed envelope 14 as disclosed herein.

The encapsulation 14 is preferably formed of either plant, insect or animal wax as distinguished from synthetic wax materials, to provide a highly non-permeable housing for the piezoelectric unit 16 and the transducer element 12 to prevent transfer of highly reactive electrolytes or other conductive moisture from entering the interior of the encapsulation 10.

Electrical generators such as piezoelectric bimorphs 12 have internal impedances of approximately 20 megohms and are adequate, for instance, for implantation in beeswax. Spermaciti, a mammal wax, also provides suitable non-permeable qualities and such waxes are compatible with living tissue. I have found that a thickness of non-permeable wax of the group referred to, when applied in a thickness of from 0.15 to 0.50 inch, is quite satisfactory.

I have found that the use of synthetic waxes as encapsulants are permeated by ions under the conditions of use in a living system and they do not maintain sufficient dielectric properties over a long period of implantation.

In FIG. 3 is illustrated an embodiment 10a which in many respects is similar to that described above in connection with the description of FIGS. 1 and 2, but differs in that an outer envelope of medical grade silicone rubber 22 completely encloses the inner core or encapsulation surrounding the piezoelectric unit and transducer elements 12a and provides a compatible, non-toxic interface between the implant and the living tissue in contact therewith.

The thickness of the envelope 22 may vary from 0.30 to 0.10 inch, depending upon the location of the implant or the mechanical requirements. The outer cover 22 also serves as a protective layer over the inner wax encapsulation 14a against abrasion that otherwise could occur in the presence of moving muscle or tissue.

Claims

I claim:

1. An encapsulated pacesetter implantable in a living system and responsive to movement of an organic muscle to which it is applied to stimulate and pace the natural movement of the muscle, said pacesetter comprising a piezoelectric unit, a transducer, input electrodes electrically connecting said transducer with said generator unit, generator output electrodes for implantation in the muscle tissue, an encapsulating envelope completely enclosing said pacesetter, said envelope formed of a living tissue compatible material consisting of medical grade silicone rubber and a natural wax substantially uniformly and intimately integrated together as a material possessing flexibility sufficient to respond to movement of the muscle tissue in which it is implanted.

2. The invention as defined in claim 1 in which said envelope comprises a natural wax inner enclosure for the generator and the transducer and a medical grade silicone rubber, outer, living tissue compatible envelope.

3. The invention defined in claim 1 in which the material forming the capsule consists of a natural wax and medical grade silicone rubber intimately and uniformly dispersed throughout the total mass to form an envelope.

4. An encapsulated pacesetter comprising an elongate capsule enclosing a piezoelectric generator unit at one end of the capsule, a transducer unit enclosed in the capsule and extending in a direction from said capsule end enclosing said generator to provide a flat flexing portion responsive to movement of organic muscle tissue in which the device is implanted in close proximity thereto, input electrodes within the capsule electrically connecting said transducer with said generator unit and generator output electrodes for implantation in the muscle tissue, said capsule comprising a mass consisting of medical grade silicone rubber and a natural wax.

5. The invention of claim 4 in which said encapsulation consists of an inner core of natural wax enclosing said generator, transducer and input electrodes, and an outer relatively thin interface of medical grade silicone rubber completely enclosing the core.