Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Breast prosthesis – Implantable
Reexamination Certificate
1994-06-14
2001-06-26
McDermott, Corrine (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Breast prosthesis
Implantable
C623S007000, C424S422000, C424S423000
Reexamination Certificate
active
06251137
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to surgical implants or prostheses, and more particularly to a filler material for implants comprising a flexible shell enclosing a filler material and implants containing the filler material.
BACKGROUND OF THE INVENTION
Surgical implants requiring a filler material, such as breast implants, penile implants, or musculature implants, have conventionally used a silicone gel or a saline solution as the filler material. One of the primary concerns in the design of an implant is to provide a tactile response that is comparable to the tactile response of normal human tissue. Silicone has been the filler material of choice primarily because silicone filled implants provided an adequate tactile response, but the very nature of the silicone filler material also limits the desirability of its tactile properties. Silicone filled implants typically comprise about 10-20% cross-linked silicone which forms an interconnected “sponge” in the implant with the remainder of the filler material being low molecular weight silicone oil. Because of this “sponge”, silicone filled implants are stiffer than human tissue, such as breast tissue, and do not provide the same feel as human tissue. Moreover, adverse medical consequences have recently become associated with the use of silicone gel filled implants because it has been discovered that the silicone oil can migrate through the implant shell and the silicone oil is not biocompatible with other human tissues. Therefore, the use of silicone based filler materials has been discontinued in the industry. Saline filled implants have not exhibited any adverse medical consequences when used as a filler material in an implant, but saline is not considered a preferred filler material because of the relatively low viscosity (~1 cp) of such a solution which renders undesirable its tactile properties.
In U.S. Pat. No. 4,995,882 issued to Destouet et al., the rights to which are owned by the assignee herein, naturally occurring, vegetable derived triglyceride oils were proposed for use as a filler material for a breast implant. This represented a dramatic break from the teaching of the prior art and is a good and valuable invention. One of the stated reasons for using a triglyceride oil composition was to take advantage of the radiolucent characteristics thereof so that a useful mammogram could be performed of an implanted breast. Although this radiolucency characteristic is important for mammograms, the naturally occurring triglyceride oil compositions disclosed by Destouet et al., such as peanut oil and sunflower seed oil, have a relatively low viscosity (~30 cps) and as such do not completely provide the desired tactile response of a normal breast. Furthermore, naturally occurring triglyceride oils typically contain unsaturated and/or polyunsaturated alkyl groups which are susceptible to oxidation. It is known that polyunsaturated fatty acid side chains of triglycerides will react with molecular oxygen to create unstable reduction products such as superoxide and hydrogen peroxide. This is known as lipid peroxidation or rancidification. The reaction forms peroxy lipid radicals and eventually results in the formation of shorter chain compounds such as malondialdehyde, ethane, pentane and 4-hydroxyalkenals, free fatty acids, and the unstable superoxide and peroxide moieties. The free radicals produced as a result of lipid peroxidation are capable of harming cells and cellular components as well as molecular structures essential to the organism. Because of the hydrophobic nature of lipid radicals, it is believed that membrane associated molecules would be most at risk, but other molecular species such as non-oxidized lipids, carbohydrates, lipoproteins and nucleic acids could be damaged. Thus, it is believed that the oxidation of unsaturated alkyl chains on a triglyceride may reduce over time the biocompatability of naturally occurring triglycerides in an implant.
There is, therefore, room for improvement with a filler material which retains the radiolucent characteristics of a naturally occurring triglyceride oil while also having an improved viscosity and biocompatability, and implants containing such a filler material.
SUMMARY OF THE INVENTION
The present invention is directed to a filler material for a surgically implantable prothesis that exhibits the radiolucent characteristics of naturally occurring triglycerides but which also has a greater viscosity and which provides a tactile response substantially the equivalent of the tactile response of normal human tissue, such as breast tissue. According to the invention, a synthetic triglyceride composition containing triglycerides having saturated alkyl chains of between 4 and 26 carbons in length in proportions such that the triglyceride composition has a viscosity substantially greater than naturally occurring triglyceride oils is provided. Preferably, the filler material provides a tactile response substantially the equivalent of the tactile response of normal human tissue, and has a viscosity of about 10,000 cps at a temperature of between about 32° C. and about 40° C. Its viscosity can be compared to that of a viscous paste over the extremes of physiologic temperature, i.e. 32° C. to 40° C. This is achieved by providing a triglyceride composition having alkyl chains of varying lengths in selected proportions to provide this increased viscosity characteristic.
In another aspect of the invention, the filler material is prepared in a manner which reduces its susceptibility to autoxidation to enhance its biocompatibility. This is achieved by utilizing triglycerides that have substantially all saturated alkyl groups or by the inclusion of antioxidants with the filler material.
In still another aspect of the invention, a surgically implantable prosthesis containing a filler material that can be provided in a range of viscosities, and a method for preparing such a filler material, is provided. This enables the provision and production of an implant having a pre-selected viscosity or tactile response.
In yet another aspect of the invention, a synthetic triglyceride composition containing triglycerides having fully saturated fatty acid (alkyl) side chains in proportions providing a composition that is a liquid at room temperature (~23° C.) is provided. This filler material has a viscosity similar to that of naturally occurring triglyceride oils, but is fully saturated to limit the possibility of oxidation and can be readily injected via a small diameter delivery tube into an already implanted device.
The present invention is further directed to surgically implantable prostheses containing this filler material within the sealed shell of the prosthesis.
REFERENCES:
patent: 4995882 (1991-02-01), Destouet et al.
patent: 5376117 (1994-12-01), Pinchuk et al.
patent: 5391203 (1995-02-01), Bartlett et al.
patent: 5407445 (1995-04-01), Taytvydas et al.
Andrews Winston A.
Dumlao Gloria R.
Knapp Terry R.
Koh Choon P.
McDermott Corrine
McGhan Medical Corporation
Milbank Tweed Hadley & McCloy LLP
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