Bulk metallic glass medical instruments, implants, and methods of using same

Abstract

MRI-compatible medical instruments and appliances are made using bulk metallic glass alloys. MRI-guided methods include the use of articles that include bulk metallic glass alloys.

Description

[0001] This application is a divisional application of U.S. patent application Ser. No. 09 / 799,445, filed on Mar. 5, 2001, the entirety of which is incorporated herein by reference.[0003] The present invention relates to medical, surgical, and dental hardware, especially medical instruments and biomedical appliances, and particularly to those instruments and appliances at least partially constructed of a bulk metallic glass (BMG), and to methods of using the same.[0004] The concept of magnetic susceptibility is central to many current research and development activities in magnetic resonance imaging (MRI). For example, the development of MR-guided surgery has created a need for surgical instruments and other devices with susceptibility tailored to the MR environment; susceptibility effects can lead to position errors of up to several millimeters in MR-guided stereotactic surgery; and the variation of magnetic susceptibility on a microscopic scale within tissues contributes to MR con...

AI Technical Summary

Benefits of technology

[0013] provision of new and improved medical instruments and biomedical appliances having at least one of: desirably high elastic limit, hardness, strength, toughness, and ability to hold a cutting edge;

[0015] provision of new and improved surgically implantable appliances (e.g., orthopedic, endodontic, etc.) with mechanical properties compatible with those of bone, low corrosion rate, and good biocompatibility (lack of rejection by human or animal tissue);

[0031] It has been discovered that certain bulk metallic glass (BMG) alloys have a very low MRI signature. BMG materials have high hardness, tensile strength, and toughness. The present invention is based on the discovery that the unique properties of BMG alloys make them especially suitable for biomedical implant applications as well as for medical instruments.

[0035] Because of the unique atomic structure in an amorphous metallic glass, this material possesses unique magnetic properties that allow the excellent MRI signature.

[0036] The composition tested contains substantial amounts of a ferromagnetic element, Ni. In a crystalline structure, the presence of Ni produces substantial blooming in an MRI image. All of the other elements in this alloy, namely Zr, Ni, Ti, and Al all have susceptibilities substantially higher than that of human tissues thereby producing a positional error in the MRI image. Only copper has susceptibility similar to human or animal tissues. Comparison images show that the image of the BMG is better even than a copper alloy. All bulk metallic glasses that are not expressly designed for good soft or hard ferromagnetic properties are expected to have this good MRI signature.

[0037] BMG alloys have a lower modulus and an extremely high elastic limit of about 2% as compared to that of a typical metal, namely about 0.2%. Bone has an elastic limit of about 1%. BMGs are unique in their ability to flex elastically with the natural bending of bones and so distribute stresses more uniformly. Faster healing rates result from reduced stress shielding effects while minimizing stress concentrators. Because of the unique mechanical properties of the BMGs, screws can have a thinner shank and deeper threads yielding greater holding power. Compared to the lowest modulus developmental titanium alloy, for a given load, the BMG will require 1 / 4 the cross section to carry the load and will undergo twice the deflection. Compared to stainless steel, the area will be 1 / 3 to carry the load and the BMG will have 5 times the deflection. Potential applications include fracture fixation screws, rods, pins, hip joint wear surfaces and shafts, aneurysm clips, endodontic files and orthodontic arch wires as well as components of devices such as pacemakers, neurostimulators, medicine-metering pumps, and equipment for remotely-viewed microsurgery.

Problems solved by technology

Because of demagnetizing effects, the shape and orientation, as well as the susceptibility, of articles within and adjacent to the imaging region is important in MRI, but the use of literature values for the susceptibility of materials is often difficult because of inconsistent traditions in the definitions and units used for magnetic parameters--particularly susceptibility.

Current implant materials produce a distortion or blooming (enlargement) in the MRI image.

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