Surgery – Means for introducing or removing material from body for... – Treating material introduced into or removed from body...
Reexamination Certificate
2001-05-25
2004-03-23
Lazarus, Ira S. (Department: 3749)
Surgery
Means for introducing or removing material from body for...
Treating material introduced into or removed from body...
C604S264000, C604S272000, C604S164070, C029S525000
Reexamination Certificate
active
06709428
ABSTRACT:
FIELD OF THE INVENTION
The present application is directed generally to cannulas and specifically to the securement of the cannula to a hub member.
BACKGROUND OF THE INVENTION
To be acceptable, processes for manufacturing cannula assemblies, which include a hub and cannula, must satisfy several requirements. For example, the process must have a low incidence of damaging the point of the cannula. Second, the process must have a low incidence of plugging the hollow passageway extending the length of the cannula. Third, the hub must hold onto the needle notwithstanding a film of lubricant such as silicone located on the needle. As will be appreciated, the film of lubricant is placed on the needle to reduce the resistance of skin to puncture by the needle. Fourth, the process must provide a cannula assembly in which the minimum force required to push the cannula out of the hub is greater than forces associated with its intended use, thereby precluding disassociation of the cannula from the hub.
The standard manufacturing process for cannula assemblies to be used in medical applications typically includes numerous steps. In a first step, the blunt end of the cannula is subjected to a grit blast to provide a roughened surface. A suitable epoxy is applied to the roughened surface, and the roughened surface is then placed into a cylindrical passage in a hub. The cylindrical passage has a number of peripherally disposed channels to contain the epoxy. The narrower sections of the passage (disposed between the peripheral channels) typically have a radius larger than that of the roughened surface of the cannula. The roughened surface permits the epoxy to form a strong bond between the peripherally disposed channels of the hub passage and the roughened end of the cannula. The epoxy is than cured by a suitable process, such as by exposure to ultraviolet light, elevated temperatures (via radiant heating or induction heating), and the like. Alternatively, the epoxy can use a one stage curing process with air curing or a two stage curing process in which the epoxy is mixed with a hardener or other reactant to cause curing of the epoxy. In another process, the hub is injection molded when the roughened surface is in the mold. Further, detail on conventional manufacturing processes is contained in U.S. Pat. Nos. 4,581,024; 4,655,764; 5,026,355; 5,215,621; and 5,207,853, each of which is incorporated herein by this reference.
These processes can have a number of drawbacks. First, there can be incompatability with the epoxies used to secure the cannula to the hub and the plastic material in the hub. Second, the need to cure some adhesives using ultraviolet curing requires a hub that is substantially transparent. This requirement imposes further substantial limitations on the types of plastics that can be used to form the hub. The use of a thermal cure of the adhesive can cause physical or chemical changes of the plastic which can undesirably alter the physical characteristics (e.g., strength) of the material. In addition, all the above processes require extra time in to manufacture a cannula assembly, which significantly increases costs.
SUMMARY OF THE INVENTION
These and other problems are addressed by the method and device configurations of the present invention. Generally, the present invention includes a cannula assembly having an interference fit between the cannula and a surface of a hub member. The interference fit has sufficient strength that adhesives are not required to secure the cannula to the hub member. In some cases, the ability to manufacture a cannula assembly without using adhesives represents an approximate 50% reduction in manufacturing costs and a significantly increased capacity for a given plant size compared to conventional manufacturing processes.
In a first embodiment of the present invention, a method for manufacturing a cannula assembly including a hub member and a cannula is provided. The method includes the steps of:
(a) forming (e.g., by grit blasting) a roughened exterior surface on a portion of the cannula to yield a roughened portion of the cannula such that the roughened portion is adjacent to an unroughened or substantially smooth (e.g., non-grit blasted) portion of the exterior surface of the cannula; and
(b) inserting the roughened portion of the cannula into a central bore of a hub (typically after the smooth portion is inserted into the central bore), wherein a radius of the smooth portion is substantially the same as a radius of the hub bore to form a line-to-line fit between the wall of the bore and the adjacent surface of the smooth portion of the cannula and the radius of the roughened portion is slightly larger than the bore radius to form an interference fit between the wall of the bore and the adjacent, roughened portion of the cannula. As used herein, a line-to-line fit refers to a relationship between the hub bore and adjacent portion of the cannula in which the outer diameter of the adjacent portion of the cannula is the same as or slightly less than the inner diameter of the bore, and an interference fit refers to a relationship between the hub bore and adjacent portion of the cannula in which the outer diameter of the adjacent portion of the cannula is greater than the inner diameter of the hub bore.
The cannula and hub member can take on any number of configurations. The cannula is typically elongated and can have any shape. The cannula is typically formed from a metal such as a stainless steel. The hub member can be in one or several pieces and can be of many differing shapes. A preferred hub member configuration is shown in U.S. Pat. Nos. 5,714,125 and 5,910,289, which are incorporated herein fully by this reference. The hub member is typically formed from a nontoxic plastic typically used for medical devices.
The forming step can be performed by any suitable process capable of roughening the outer surface of the cannula. Examples include (i) mechanical techniques such as grit blasting or contacting the outer surface with an abrasive medium; (ii) chemical techniques such as etching with an acid, and reacting the outer surface with an oxidant; and/or (iii) thermal techniques such as heating the outer surface to a softening temperature followed by deformation of the softened area to form a corrugated surface and the like.
When grit blasting is employed to roughen the outer surface of the cannula, the preferred depth of the grit blast creates an outer diameter of the grit blasted (roughened) portion of the cannula that is slightly greater than the inner diameter of the hub bore. Typically, the outer diameter of the roughened portion is at least about 0.0001 inches, more typically at least about 0.0002 inches, and most typically at least about 0.0003 inches more than the smooth portion of the cannula. The outer diameter of the roughened portion is typically no more than about 0.001 inches and more typically no more than about 0.0008 inches more than the smooth portion of the cannula. The grit blasting is typically more circumferential than conventional grit blasting processes. Preferably, the roughened (enlarged) portion of the cannula extends at least about 320° C. around the circumference of the cannula.
In one configuration, the roughened portion of the cannula has a length and the cannula a total length. The length of the roughened portion is from about 25 to about 50% of the total length. The length of the roughened portion typically ranges from about 5 to about 50 mm and more typically from about 10 to about 25 mm. The length of the smooth portion typically ranges from about 0.25 to about 0.75 inches. The total length of the cannula typically ranges from about 0.5 to about 1 inches.
To provide a strong interference fit, the tolerance between the radii of the roughened and smooth portions on the one hand and of the hub bore on the other is typically relatively small. In one configuration, the radius of the smooth portion is at least about 5% and more typically at least about 10% less than the radius of the roughened portion. In yet another c
Baxter International Inc.
Lazarus Ira S.
Mayo Michael C.
Nguyen Camtu Tran
Swartz Douglas W.
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