Metal working – Method of mechanical manufacture – Spring making
Patent
1996-06-04
1998-06-02
Hughes, S. Thomas
Metal working
Method of mechanical manufacture
Spring making
72128, 72130, 72137, 72275, 723428, 72364, 72371, 72700, 140 82, 148670, 148671, 606157, B21F 300, B21K 2900, B21D 700
Patent
active
057584206
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates generally to a process of manufacturing aneurysm clips and, more particularly, to a process of manufacturing a titanium or titanium alloy aneurysm clip incorporating the steps of cold drawing, coining, and bending a single, continuous, solid, elongated, resilient, cylindrical member to form the clip.
BACKGROUND OF THE INVENTION
A cerebral aneurysm clip is a surgical instrument which clamps the base part of a cerebral aneurysm to temporarily or permanently isolate it from the cerebral artery. For this purpose, the clip must maintain the clamping pressure with high reliability as long as desired without injury to the wall of the blood vessel. Such injury might be caused, for example, by a shearing action of the clamping jaws, which results from improper jaw alignment; improper clamping pressure; foreign material trapped in cracks and crevices formed in the clip design; surface imperfections on the clip material which can tear tissue; or the use of unsuitable materials to manufacture the clip.
A number of different materials are used to manufacture cerebral aneurysm clips. Such materials include, for example, stainless steel and chrome-cobalt alloy steel. These materials interfere with important diagnostic techniques such as magnetic resonance imaging (MRI or NMR), MRA, and CT-Scanning due to image degradation (haloing, starbursts, and "Black-Hole" obscuring) caused by the magnetic characteristic and high density of the materials. Furthermore, the significant magnetic susceptibility of these materials presents the danger that such clips will move in the intense magnetic fields created.
Titanium and some titanium alloys (specifically, the Ti 6-4 alloy of about 6% aluminum, 4% vanadium, and the remainder titanium ) are most desirable for implants because they are inert, are compatible with body fluids, are non-magnetic, and do not degrade the image. Having such qualities, CP (Chemically Pure) Titanium (ASTM F64-89) and the Ti 6-4 alloy have been widely acknowledged in medical literature and have been approved by the Federal Drug Administration for implants in human beings. The great difficulty in forming CP Titanium and Ti 6-4 alloys, however, has prevented their wide-spread use in aneurysm clips.
To provide satisfactory and prolonged service when properly implanted, a cerebral aneurysm clip should satisfy most, and preferably all, of the following criteria: isolate the aneurysm but not so high as to damage the blood vessel wall during either temporary or permanent implantation; prevent displacement or slipping of the clip; implantation in the brain; low density to prevent interference with MRI and CT-scan imaging; implantation; clip should be smooth and jagged edges should be absent; similar defects which trap foreign matter and contamination and which are susceptible to propagation by stress corrosion; and shearing of the vascular tissue between the jaws.
These criteria are extremely important to the performance of the clip. Consequently, the clip design must ensure that the above criteria are met. In addition to the clip design, the process of manufacturing the clip also must ensure that the above criteria are met.
Some prior art designs require that holes be drilled, components be welded or riveted, or recesses be formed. Machining processes are often required. Such manufacturing procedures introduce unacceptable microcracks, voids, and crevices into the clip. Defects such as these are especially detrimental when titanium or titanium alloys are used to fabricate the clip because titanium is notch sensitive, susceptible to phase separation when machined, and prone to embrittlement and microcracking.
Specifically, sharp corners of recesses and the machining process used to form prior art clips can create and propagate microcracks in the metal surface, producing a clip undesirable for use as a cerebral implant. Drilled holes and riveted components render the clip susceptible to microcracks emanating radially from the holes and in the region of riveting. The con
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Maughan Kevin P.
Schmidt Ferenc J.
Florida Hospital Supplies, Inc.
Hughes S. Thomas
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