As previously mentioned, the present invention is directed to the task of improving the surface morphology of silicone foley catheters to provide a smooth surface which has a lower coefficient of friction and may thus be inserted in the bodycavity without causing abrasion and the problems resulting therefrom.

The invention is particularly directed to silicone rubber urethral catheters, e.g. those per se known in the art, where the abrasive action resulting from insertion of these indwelling catheters may cause urinary tract infections. However, itwill be appreciated by those skilled in the art that the invention is equally applicable to any catheters, whether indwelling or of the intermittent variety, where abrasion can be a source of concern. For example, it is envisioned that the abrasiveforce of a catheter inserted into the circulatory system, e.g. a cardiac or central venous catheter, may damage the endothelial lining of the vessel and may accordingly be a potential source of blood clotting.

In accordance with invention, the surface morphology of silicone rubber catheters is substantially improved by bonding to the surface of at least that portion to be inserted in a body cavity, a coating comprising the reaction product of acomposition comprising:

(1) at least one crosslinkable polysiloxane; (2) an innocuous medical grade lubricating oil; and (3) a crosslinking catalyst.

The coating may be applied to the silicone foley surface from a liquid vehicle, preferably a volatile organic solvent, followed by heating to drive off the organic solvent or other liquid vehicle and to effect crosslinking. The manner ofapplication, whether by dipping, flowing, spraying, etc. is a matter of individual choice and per se comprises no part of this invention.

As used herein, the term "crosslinkable" refers to a polysiloxane having reactive or functional groups which may be crosslinked. Silicone polymers of this description are generally known and commercially available. By way of illustration,mention may be made of dimethyl polysiloxane, methylphenyl polysiloxane, cyanoalkylmethyl polysiloxane, and fluoroalkylmethyl siloxane. A particularly preferred crosslinkable polysiloxane is dimethyl polysiloxane which is characterized as possessinghigh strength and elasticity.

As used herein with respect to the lubricating oil, the term "innocuous" means that the oil will not adversely react with the polysiloxane, e.g. preclude its ability to crosslink and thereby bond to the surface of the silicone foley catheter . It will beappreciated that the lubricating oil must also be medical grade for its intended use of insertion into a body cavity. It will also be appreciated that the lubricating oil should also be compatible with the polysiloxane. Lubricating oils of thisdescription will be readily apparent to those skilled in the art and also per se comprises no part of this invention.

The preferred lubricating agents are those within the class know in the art as medical fluids, the most preferred being silicone oils, e.g. DC-360 (trade designation of Dow Corning.)

In addition to the crosslinking catalyst, the coating composition will preferably also contain a crosslinking accelerator. While in theory, any silicone crosslinking agent and accelerator may be employed, applicants have determined that a lowtemperature fast cure paper release coating formulation commercially available from Silicone Products Department, General Electric Company is ideally suited. This formulation consists of a crosslinkable polysiloxane (sold under product designation:SS4191): a crosslinking catalyst (SS4192C); and an accelerator (SS4259C).

The crosslinkable polysiloxane, SS4191, is understood in fact to be a blend of about 94% polydimethylsiloxane with about 6% methyl, hydrogen polysiloxane.

The catalyst for the system, SS4192C is dibutyltin diacetate [(C4 H9)2 Sn(OCOCH3)2 ].

The accelerator, 554259C, is a polysiloxane having pendant amino groups.

The ratios or amounts of reagents in the coating composition will vary and will be apparent to those skilled in the art.

In general, the ratios (solids content) of crosslinkable polysiloxane to lubricating oil will be on the order of about 8:1 to about 3:1.

The levels of catalyst and accelerator are readily determined by starting with given levels and ascertaining whether the cure is complete or incomplete. Obviously, no more of the curatives than are necessary should be employed. On the otherhand, when the cure is incomplete, the levels can be then be increased in slow increments until the cure is complete.

While the levels will vary in accordance with the particular reactants employed, with the particular G.E. formulation described above, optimum results were found using levels (dry weight) of 100 parts of the crosslinkable polysiloxane and about6.5 parts for each of the catalyst and accelerator.

The solvent for the coating solution is not critical and will be readily suggested to the skilled worker. Preferably, low boiling organic solvents are employed. Useful solvents include the Freons, i.e. halogenated hydrocarbons such as1,1,2-trichlorotrifluormethane; heptane, etc.

The coating composition of this invention is readily prepared by mixing the ingredients under ambient temperature and pressure. The silicone foley catheter may be coated by per se known techniques, dipping in the coating solution being more efficacious.

Crosslinking as well as solvent removal is effected by heating at a temperature and for a time to effect complete cure as well as solvent removal. Since there is a time--temperature relationship to effect cure, the time and temperature are notsusceptible to precise quantitative statements. As will be seen from the following illustrative example, on a laboratory level, heating at about 350° F. (150° C.) for about one minute is effective. However, with production equipmentemploying higher temperature a shorter time will be required.