Thermal forming of refractory alloy surgical needles

Abstract

A method of thermal forming of refractory alloy suture needles is disclosed. Needle blanks made from refractory alloys are used to form surgical needles, which are heated to a temperature above the ductile to brittle transition temperature but below the recrystallization temperature of the refractory alloy. The heated needle blanks are then mechanically formed into a surgical needle.

Description

[0001]This patent application is related to commonly-assigned patent application Ser. No. ______ entitled “Thermal Forming of Refractory Alloy Surgical Needles and Fixture and Apparatus” filed on evendate herewith and incorporated by reference.FIELD OF ART[0002]The field of art to which this invention pertains is surgical needles, in particular, methods of thermally forming refractory alloy suture needles.BACKGROUND OF THE INVENTION[0003]Surgical needles are well known in the surgical arts. Typically the surgical needles are mounted to sutures, and used in a variety of surgical procedures for approximating tissue. It is important that the surgical needles function under a variety of conditions encountered by surgeons when performing procedures on patients. Surgical needles can be used for delicate surgical procedures with relatively soft and fragile tissues such as liver or lung surgery and for more robust procedures involving harder and tougher tissues such as ophthalmic, plastic, ...

AI Technical Summary

Benefits of technology

[0027]As an additional benefit associated with the novel thermal forming methods of the present invention, alloys that may exhibit high DBTT can be formed into suture needles. For example, in the W—Re alloy system, alloys with high rhenium concentrations tend to have lower DBTT than alloys with low rhenium concentration. However, from a commercial perspective, rhenium has a high raw material cost and can be an exceedingly expensive component of the alloy. If the thermal forming methods of the present invention are used, low rhenium concentrations may be used in lieu of high rhenium concentrations to realize a substantial cost savings. An additional benefit is that the market price for the finished suture needle may in theory be reduced, as raw material costs no longer need to be passed on to the customer, and use of the tungsten alloys as suture needle materials may be expanded to a greater number of needle designs.

Problems solved by technology

However, the room temperature formability of many refractory alloys is limited and often substantially less than the formability of other metals typically used in the manufacture of suture needles.

Difficulties may thus arise in the manufacture of refractory alloy surgical needles as numerous steps in a conventional manufacturing process require substantial material ductility.

Conventional needle forming methods typically cannot be used with refractory alloys.

This method is deficient for use on refractory metals for several reasons.

If refractory metals are heated to near their melting point, recrystallization of the work hardened microstructure occurs and the alloy can be expected to lose essential properties and even exhibit brittle characteristics at room temperature due to the effect of microstructural changes on the ductile to brittle transition temperature, DBTT.

Secondly, such a process is applicable to oxidation resistant alloys, however, this is not the case for refractory alloys (especially those in the W—Re binary system) as these alloys will readily oxidize at temperatures far below their melting points.

The previously described needle forming methods may impart substantial stresses to the needle material, and if the material exhibits insufficient ductility, cracking and or splitting of the suture needle may occur.

Many refractory alloys exhibit ductile to brittle transition temperatures (DBTT) above room temperature, and consequently the ability to plastically deform these refractory alloys in the various surgical needle forming operations is substantially limited.

Excessively high temperatures may however lead to the recrystallization and growth of the grain structure of the alloy, leading to a substantial change in properties that may be deleterious to the performance of the suture needle.

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