1. Field of Invention
The present invention is directed to a lubricant system for medical devices. More particularly, the present invention is directed to a non-volatile lubricious coating for hypodermic needles, catheters, and the like.
2. Description of Related Art
It has become commonplace in the medical field to provide medical devices with lubricants for ease of use. For example, hypodermic needles are widely used in delivering and withdrawing fluids in medical practice. As originally used, hypodermic needles were used many times, the needles being sterilized between usages. A practitioner would sharpen the needles when they became dull, and then sterilize them prior to the next usage. Since the needles were reused, and often may have needed sharpening, the presence or absence of any lubrication on the outer surface of the needle had little effect on the penetration force or the pain perceived by the patient who was the recipient of the needle. With the development of commercially manufactured disposable needles that always have a fresh well-sharpened point, there was recognition that lubrication of the needle substantially reduced the pain perceived by the patient when a needle was administered to them.
A convention is followed in this disclosure wherein the portion of a device toward the practitioner is termed proximal and the portion of the device toward the patient is termed distal.
A tissue penetration by a hypodermic needle involves a sequence of events that collectively are perceived by the patient as whether or not the penetration causes pain. A distal point of the needle first touches the skin surface, stretches it, the point then cuts into the surface and begins penetration into the tissue. As the shaft of the needle passes through the original cut and into the tissue, there is also sliding friction of the tissue against the needle surface. In the hypodermic needle art when the forces for performing a hypodermic needle penetration are measured, the force measured prior to the needle point cutting the tissue is termed the “peak penetration force”, also called “F2” and the force required to continue the penetration into the tissue is called the “drag force” or “F4”. One primary component of the drag force is the sliding friction of the tissue against the surface of the needle shaft.
Insertion of intravenous (IV) catheters into a patient causes similar issues regarding ease of insertion and patient discomfort. For example, IV catheters are designed to infuse normal intravenous solutions, including antibiotics and other drugs, into a patient. These catheters are also used to withdraw blood from the patient for normal blood-gas analysis as well as other blood work. The most common type of IV catheter is an “over the needle” catheter, in which a catheter is disposed over an introducer needle or cannula, which is used to insert the IV catheter into a patient. The needle is typically stainless steel and is hollow. Its distal tip is ground to a sharp tip for easy insertion into the patient. The catheter is also hollow and is disposed such that the sharpened tip of the needle is extended from the catheter for piercing of the patient's skin during use. Once the skin and vein have been pierced, the catheter is advanced over the needle and the needle is removed from the catheter. The catheter is typically extruded out of suitable plastic material such as TEFLON material (polytetrafluoroethylene), polyvinyl chloride, polyethylene, polyurethane or polyether urethane.
The use of lubricants on the surface of such hypodermic needles and IV catheters significantly reduces both the peak penetration force and the drag force. As a result, almost all single-use sterile disposable needles and IV catheters are supplied with a lubricant already applied to substantially the entire outside surface. A number of lubricants have been developed for use in such applications. Typically, such lubricants involve a medical grade polydimethylsiloxane which is commonly applied to the surface through a volatile carrier solvent which rapidly evaporates. For example, U.S. Pat. No. 5,911,711 to Pelkey discloses a lubricant system for hypodermic needles which includes a first layer formed from an at least partially cured organosiloxane copolymer and a polydimethylsiloxane that has a viscosity greater than about 1000 centistokes, and a second layer over the first layer that includes a polydimethylsiloxane having a viscosity of 50-350 centistokes. The coating compositions of the first and second layers are applied through a volatile carrier solvent such as a chlorofluorocarbon (CFC), and the first layer is thermally cured by applying heat. Unfortunately, volatile solvents such as CFC's raise significant environmental concerns.
There is a need in the medical industry for lubricants for medical devices such as catheters and needles which are environmentally friendly, which are easy to apply, and which do not involve the use of volatile organic solvents such as CFC's.