Textiles: manufacturing – Thread finishing – Surface modification of running length
Reexamination Certificate
2002-04-25
2004-07-20
Vanatta, A. (Department: 3765)
Textiles: manufacturing
Thread finishing
Surface modification of running length
C028S220000, C264S210800
Reexamination Certificate
active
06763559
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of drawing polymeric yarns and more particularly, to a cold drawing process that produces polytetrafluoroethylene (PTFE) yarns suitable for use in medical devices.
BACKGROUND OF RELATED TECHNOLOGY
PTFE is used in numerous demanding applications due to its excellent physical properties, which include excellent high and low temperature performance, chemical resistance and lubricious properties. PTFE is particularly useful in medical devices such as vascular prostheses. Use of PTFE yarns for textile vascular prostheses has been limited because finished PTFE yarns suitable for use in medical devices are often not commercially available to medical device manufacturers. Unfinished PTFE yarns that are available, however, typically do not possess the physical characteristics, such as sufficient orientation, i.e. molecular alignment of the fibers, and the requisite uniform linear density necessary for such medical device uses. Unfinished PTFE yarns also typically have poor molecular orientation and uneven linear densities within the same strand of yarn. This creates problems when processing such yarns into a textile prosthesis. For instance, unfinished yarns may accumulate in the machine during the textile prosthesis manufacturing process or stretch to create a non-uniform prosthesis. Additionally, problems may occur when such prostheses made with unfinished yarns therein are placed in a body lumen because such yarns may unexpectedly and undesirably stretch. Thus, the prostheses will not perform in a consistent and predictable manner. As such, these yarns are not suitable for use in medical devices without further processing.
Conventional means to finish PTFE yarns typically involve a heat drawing process. Heat drawing results in yarns with good orientation and uniform linear density which when incorporated into a textile vascular prosthesis exhibit predictable and consistent behavior, both in the textile manufacturing process and in vivo. However, heat drawing yarns requires a heat drawing apparatus that can maintain the yarn at an elevated temperature. Thus, heat drawing is less than satisfactory since it may be expensive and difficult to control and maintain the elevated temperatures.
Accordingly, it is desirable to provide a convenient and inexpensive method for producing PTFE yarns suitable for use in medical devices that have a uniform linear density and a highly oriented molecular structure.
SUMMARY OF THE INVENTION
The present invention provides for a method of cold drawing PTFE yarn. The cold drawing method of the present invention can be performed at room temperature and does not require the use of a heat drawing apparatus. Thus, the present invention overcomes some of the disadvantages of conventional PTFE drawing techniques by providing an inexpensive and convenient method of producing PTFE yarns suitable for use in implantable medical devices, such as vascular grafts.
The method of the present invention produces cold drawn PTFE yarns that have a substantially uniform linear density and good molecular orientation as well as good lubricity, non-thrombogenicity and biocompatibility. Yarns made by the method of the present invention behave in a consistent and predictable manner thereby minimizing the in vivo problems associated with textile prosthesis manufacturing having unfinished yarns therein. Additionally, the yarns produced by the inventive methods reduce the problems associated with textile manufacturing and can be processed into textile vascular prostheses, such as woven, knitted or braided prostheses.
In one embodiment of the present invention, there is provided a method of cold drawing polymeric yarns suitable for use in implantable medical devices including the steps of maintaining the polymeric yarn at a temperature below the glass transition temperature of the yarn, drawing the yarn at such temperature over a first roller rotated about its axis at a first speed and a second roller rotated about its axis at a speed faster than the speed of the first roller, to a selected denier and to increase molecular orientation; and twisting the drawn yarn to form a yarn with a substantially uniform linear density.
In another embodiment of the present invention, there is provided a method of cold drawing multi-filament PTFE yarns suitable for use in implantable medical devices including the steps of maintaining the PTFE yarn at a temperature below the glass transition temperature of the yarn, drawing the yarn at such temperature over a first roller rotated about its axis at a first speed and a second roller rotated about its axis at a speed faster than the speed of the first roller, to a selected denier and to increase molecular orientation; and twisting the drawn yarn to form a yarn with a substantially uniform linear density.
One aspect of the present invention provides for twisting the multi-filament yarn, which encourages the multiple filaments to behave as a coherent unit. Twisting the filaments binds the filaments together and increases the tensile strength of the yarn. Additionally, twisting the yarns helps minimize filament separation and yarn static processing problems.
The present invention also contemplates providing for PTFE yarn produced by the inventive methods.
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Hoffmann & Baron , LLP
Sci-Med Life Systems, Inc.
Vanatta A.
LandOfFree
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