Metallic silver is deposited upon the surface of a nonconducting substrate using a multi-step wet deposition process. The surface is cleaned, and then activated in an aqueous solution containing stannous tin. The silver is deposited as a colloidal material from an aqueous solution of a silver-containing salt, a reduction agent that reduces the salt to form the metallic silver, and a deposition control agent that prevents the silver from nucleating throughout the solution. After the substrate is coated, the coating is stabilized in an aqueous solution of a salt of a metal from the platinum group of gold, dissolved in dilute hydrochloric acid. The process is particularly effective for depositing uniform films of 2 to 2000 Angstroms thickness, which strongly adhere to the substrate.

Apparatus having an antimicrobial surface includes a medical device and a plurality of metals, at least one of which is in contact with a surface of the device and in contact with a different metal. The invention includes a method to use the apparatus to treat a living body wherein the antimicrobial surface of the apparatus is contacted with a body electrolyte thereby inhibiting growth of microorganisms in the body consequent to the use of the apparatus.

A double lumen catheter made up of an elongated integral flexible plastic thin-walled tubular body extending from a proximal end part, through an intermediate part, to a distal end part, terminating in a tip. The intermediate part has an outer wall and an internal septum wall containing juxtaposed arterial and venous lumens. The terminal end of each lumen in the proximal part is adapted for connection to an access tube to hemodialysis apparatus. At the junction of the intermediate part and the distal part, the arterial lumen is terminated and the venous lumen continued at least part way to the tip of the distal part. The outside surface of the outer walls are continuous and smooth to offer minimum resistance to insertion into the body of a patient. The walls are also relatively thin to provide for lumens of relatively large cross-section compared to the total cross-section of the catheter body. Removable obturators are inserted in the lumens to prevent the catheter from buckling. The inner surface of the outer walls and the surfaces of the septum wall are continuous and smooth and any change of direction in the lumen wall is in a gradual curve to accommodate negotiation by a flexible obturator. Alternatively, the catheter may be made from tubing sufficiently resistant in itself to buckling for the catheter to be inserted without the use of obturators. One such form of tubing is made of alternating hard and soft plastic rings welded together. Another form employs wire reinforcing within the walls. Welding and molding methods for making the catheters are disclosed.

Catheters and other medical devices include plural layers of metals applied to the outer surfaces, which tend to close minuscule cracks through which corrosion may attack the underlying support. In some avatars, the initial layer of material is preferably silver, applied following specific preparation steps. In other embodiments, succeeding layers of metal completely cover the initial layer, and are also of silver. The succeeding layers are deposited after deposition of the prior layer, and tend to reduce the incidence of microscopic pores or cracks and are less prone to delamination. The succeeding layers are preferably of mutually different metals between layers. In a particular avatar, in which the exposed metals are oligodynamic silver and more noble platinum, the exposed silver layer lies over a portion of the platinum layer, to thereby prevent corrosion of the silver layer from disconnecting portions of the silver layer. Fabrication methods include deposition of successive layers by means of sputtering in a longitudinal array of cylindrical magnetron sections, in which each section applies one layer of the coating over the coating applied by the preceding section. The magnetron sections may be energized and deenergized in a temporal pattern associated with the progress of the workpiece material through the array, to thereby cover or expose particular longitudinal layers. In some embodiments, a first layer of electrically conductive material is deposited by electroless methods particularly in the lumen, following which additional layers may be applied by conventional electrolytic deposition. An electroless method according to the invention includes preparation steps which may include ultrasonically cleaning the surface with a solution of isopropyl alcohol, then drying the surface with a stream of dry gas, and etching the surface with a solution of sodium naphthalene in diethylene glycol dimethyl ether.

The needle assembly consists of a plastic cannula (11) with a hollow hub (12) at its dital end, a steel needle (16) adapted for insertion into the plastic cannula (11) and having a ground tip (17) and a needle head (15) adapted for being detachably coupled with the hollow hub (12), and of a tube-like protecting cap for the elongated parts. According to the inventon the protecting cap (22) has a closed, thick-walled bottom (23) into which the ground tip (17) of the steel needle (16) is clampingly pierceable, thus providing a reliable connection between these two parts. The steel needle (16) can be thrown into the commonly used waste containers without the protecting cap (22) falling off.