Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis
Reexamination Certificate
1995-05-22
2001-11-06
Prebilic, Paul B. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
C623S007000, C623S008000
Reexamination Certificate
active
06312466
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to medical prostheses, particularly those medical prostheses used for a breast or testicular prosthesis.
Silicone-gel implants have fallen into disfavor in recent years which has created a need for new implants that can be used as medical prostheses. Medical prostheses from a safety standpoint should be chemically inert, noninflammatory, nonallergenic, and noncarcinogenic. In the case of breast implants, they ideally should also simulate the viscoelastic properties of the normal human breast, and be radiolucent to mammography. It is further important that breast implants create a natural “feel” and desirable aesthetics.
Much research has been directed toward finding alternative prostheses fitting this description. Although saline filled prostheses in large measure meet the criteria outlined above, saline prostheses create an unnatural feel and less than optical aesthetics. When implanted, for example, they tend to result in wrinkling of the overlying skin. In addition, Ersek et al. in U.S. Pat. No. 5,067,965 disclosed in column 1 that a prosthesis filled with saline alone undergoes accelerated breakdown of the outer shell of the prosthesis due to friction of the inner shell rubbing against itself. Due to this accelerated breakdown, the implants must be surgically replaced periodically, typically on the order of every four to five years. Ersek et al. further state that saline is a poor lubricating agent. Because of the relatively high amount of motion of the saline in the implant, the implant is also prone to fold-crease failure resulting in a rupture of the implant.
There is also a continuing need for implants that are radiolucent. It is therefore desirable that breast prostheses not unduly interfere with the ability to perform X-ray mammograms. Breast protheses that are radiographically dense can be serious impediments to effective mammography.
In addition, implants filled with saline alone may oftentimes not be usable for breast cancer patients who have undergone radiation therapy. Since the radiation weakens the tissue, the movement of the saline in the implant may be very painful to the patient such that the saline filled implant is not used.
SUMMARY OF THE INVENTION
The present invention concerns prostheses which address one or more of the problems described above.
In one broad respect, the present invention is a prosthesis useful for implantation into soft tissue, comprising an envelope that forms a hollow sealed shell defining an enclosed volume, wherein the enclosed volume of the hollow shell contains an aqueous solution of polyethylene glycol. In another broad respect, the present invention comprises a sealed, compliant envelope or capsule which is filled with an aqueous solution of polyethylene glycol.
Preferably, the polyethylene glycol will have a molecular weight of about 6,000 to about 20,000, and the viscosity of the aqueous solution will be from about 300 centistokes to about 450 centistokes, and the polyethylene glycol will preferably be present in the aqueous solution in an amount of from about 50 to about 85 weight/volume percent.
In a second broad respect, this invention is a method of making an implantable prosthesis, comprising filling an elastomeric envelope that forms a hollow sealed shell defining an enclosed volume with an aqueous solution of polyethylene glycol. In another broad respect, this invention is directed to a method of making an implantable prosthesis which comprises filling an elastomeric envelope with an aqueous solution of polyethylene glycol, and sealing the envelope to define an enclosed volume.
The envelope may be made of any of a number of elastomers which are employed in medical implants. The envelope may also be configured or otherwise shaped to conform to the shape of a body-organ or part upon being filled with a fluid or gel or the invention. It is important that the envelope be of a medical grade—i.e., that it be biocompatible, non-allergenic, noncarcinogenic and so forth. Particularly suitable envelopes or shells are fabricated from silicone elastomers and are available from McGhan Medical Corporation and other suppliers.
The prosthesis of this invention provides an implant that alleviates one or more of the problems discussed above. The present prosthesis employs a mixture of a saline solution and polyethylene glycol which possesses increased viscosity relative to saline alone. Advantageously, the saline/PEG blends of the present invention provide implants with a viscosity which enable the implants to possess characteristics simulating those of the body parts which they supplant. In general, saline solutions at best by themselves have viscosities which are too low for this purpose. Accordingly, the relative volumes and viscosities of the PEG components of the saline/PEG blends are selected to produce blends which possess the desired viscosities. Thus a saline/PEG blend having a viscosity of about 350 centistokes (cs) has been found to provide an implant which closely approaches the compliance and feel of breast tissue. The saline component alone had a viscosity of about 40 cs.
The prostheses of this invention that not only approximate the feel of human breast tissue, but the polyethylene glycol employed in the prostheses is considered to be a nontoxic, nonimmunogenic, and noncarcinogenic material. In that regard, PEG is routinely used in products ranging from cosmetics and food additives to bowel prep solutions. The prostheses of this invention, accordingly, are useful as an implant to augment or reconstruct human tissue, especially breast tissue.
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Hawley's Condensed Chemical Dictionary, 11th Edition, (1987), p. 936, 1987.
Friedman Ronald M.
Robinson, Jr. Jack B.
Rohrich Rod J.
Board of Regents University of Texas System
Fulbright & Jaworski
Prebilic Paul B.
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