subject: Natural Silicone Foley Catheter [print this page] This invention relates to a natural rubber urinary silicone foley catheter having cholesterol incorporated therein. More particularly, this invention relates to improving the resistance of rubber Foley catheters to urinary salt calcification during long-term catheterizations.
Silicone Foley catheters have been used for many years in urethral catheterizations. However, continuous long-term catheterizations are often unsuccessful because of the severity of urinary salt deposits (calculus) which adhere to the outside and luminal surfaces of the rubber Foley catheter. Consequently, because recatheterizations become necessary, the attendant risks of urinary tract infection and tissue irritation are maximized.
In order to minimize the buildup of calculus and allow long-term catheterization to become a reality, catheters manufactured entirely of a plastic material such as disclosed in U.S. Pat. Nos. 3,528,869; 3,539,674 and 3,544,668 were developed. Another approach was to apply a surface layer coating of an elastomeric silicone material such as dimethylpolysiloxane to natural rubber catheters. This process and catheter are more fully described in U.S. Pat. No. 3,434,869. Although some plastic and coated natural rubber catheters are reasonably effective in minimizing calculus buildup, they lack the resiliency and superior handling characteristics of catheters made of natural rubber which urologists traditionally prefer.
Now it has been found that an anti-calcification property is conferred on an indwelling rubber urinary catheter by incorporating cholesterol into the rubber matrix, which constitutes the substance of the catheter, without impairing the essential properties of the natural rubber. The cholesterol can be incorporated throughout the entire catheter but for the purpose of this invention, must be incorporated in at least that portion of the shaft intended for insertion into the body cavity.
For the purpose of this invention, it is not necessary that the cholesterol be incorporated in a homogeneous manner. For example, while it is not desired to be bound by theory, there appears to be a migration of the incorporated cholesterol to the surfaces of the catheter after incorporation. Therefore, it is intended to include a coating of cholesterol on the natural rubber catheter surfaces within the scope of this invention.
More specifically, cholesterol can be incorporated into the rubber matrix by any convenient method, for example, by stirring a slurry of cholesterol in water into the natural rubber latex prior to manufacture or by impregnating the finished catheter by immersing in a solution of cholesterol in a rubber-swelling solvent. By "rubber-swelling solvent" is meant an organic solvent for which rubber has a natural affinity and, upon immersion, causes the rubber to expand.
More in detail in the latter process mentioned above, the catheter is immersed in the solution for a period of time sufficient to impart the desired percentage of cholesterol to the rubber. After the immersion period, the rubber-swelling solvent is removed by conventional drying techniques.
Some rubber-swelling solvents which can be employed in this process are benzene, chloroform, xylene, carbon tetrachloride or methylene chloride. Generally, an immersion of from 10-20 minutes in a 5-10 percent (w/v) of cholesterol in a dry, pure, rubber-swelling solvent is sufficient to impregnate a rubber catheter with from 2-20 percent by weight cholesterol, which concentrations have proven to be effective in reducing calculus buildup. By the term "(w/v)" is meant a weighed amount of solute per 100 ml. of solution, as in this instance 5-10 grams of cholesterol per 100 ml. of solution. A range of 10-12 percent by weight cholesterol in the rubber matrix is considered optimum. As previously indicated, the cholesterol must be present in at least that portion of the shaft intended for insertion into the body cavity.
