News Column

Patent Application Titled "Post Electron Beam Conditioning of Polymeric Medical Devices" Published Online

May 15, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- According to news reporting originating from Washington, D.C., by VerticalNews journalists, a patent application by the inventors Wang, Yunbing (Sunnyvale, CA); Ma, Xiao (San Jose, CA); Tang, Fuh-Wei (Temecula, CA); Ding, Ni (San Jose, CA), filed on December 23, 2013, was made available online on May 1, 2014.

The assignee for this patent application is Abbott Cardiovascular Systems Inc.

Reporters obtained the following quote from the background information supplied by the inventors: "This invention relates to methods making stents from bioabsorbable polymers.

"This invention relates to radially expandable endoprostheses that are adapted to be implanted in a bodily lumen. An 'endoprosthesis' corresponds to an artificial device that is placed inside the body. A 'lumen' refers to a cavity of a tubular organ such as a blood vessel. A stent is an example of such an endoprosthesis. Stents are generally cylindrically shaped devices that function to hold open and sometimes expand a segment of a blood vessel or other anatomical lumen such as urinary tracts and bile ducts. Stents are often used in the treatment of atherosclerotic stenosis in blood vessels. 'Stenosis' refers to a narrowing or constriction of a bodily passage or orifice. In such treatments, stents reinforce body vessels and prevent restenosis following angioplasty in the vascular system. 'Restenosis' refers to the reoccurrence of stenosis in a blood vessel or heart valve after it has been treated (as by balloon angioplasty, stenting, or valvuloplasty) with apparent success.

"Stents are typically composed of scaffolding that includes a pattern or network of interconnecting structural elements or struts, that may be formed from wires, tubes, or sheets of material rolled into a cylindrical shape. This scaffolding gets its name because it physically holds open and, if desired, expands the wall of the passageway, or lumen. Typically, stents are capable of being compressed, or crimped, onto a catheter so that they can be delivered to and deployed at a treatment site. Delivery includes inserting the stent through small lumens, such as blood vessels, using a catheter and transporting it to the treatment site. Deployment includes expanding the stent to a larger diameter once it is at the desired location. Mechanical intervention with stents has reduced the rate of restenosis as compared to balloon angioplasty. Yet, restenosis remains a significant problem. When restenosis does occur in the stented segment, the treatment of it can be challenging, as clinical options are more limited than for those lesions that were treated solely with a balloon.

"Stents are used not only for mechanical intervention but also as vehicles for providing biological therapy. Biological therapy uses medicated stents to locally administer a drug. A medicated stent may be fabricated by coating the surface of either a metallic or polymeric scaffolding with a polymeric carrier that includes a drug. Polymeric scaffolding may also serve as a carrier of a drug.

"It may be desirable for a stent to be biodegradable. In many treatment applications, the presence of a stent in a body may be necessary for a limited period of time until its intended function of, for example, maintaining vascular patency and/or drug delivery is accomplished. Therefore, stents fabricated from biodegradable, bioabsorbable, and/or bioerodable materials such as bioabsorbable polymers should be configured to completely erode only after the clinical need for them has ended.

"One of the challenges of making medical devices out of polymers is that the properties of a polymer can change both during processing and after processing. These properties include mechanical properties such as strength and toughness as well as bioresorption kinetics. The processing steps in a fabrication process of a stent may be designed to maintain or instill in the stent particular ranges of the strength, toughness, and bioresorption, that are crucial for treatment with the stent. In some cases, properties of the polymer can change during additional processing operations and/or as a function of time during storage. Therefore, methods are needed that reduce, or eliminate undesirable changes in properties, and/or ameliorate their impact."

In addition to obtaining background information on this patent application, VerticalNews editors also obtained the inventors' summary information for this patent application: "Various embodiments of the present invention include a method for conditioning a polymeric stent. The method may include the operations of: exposing a polymeric stent with a polymeric scaffolding to a temperature equal to, approximately equal to, or greater than 30.degree. C. and not more than about 15.degree. C. less than the glass transition temperature of the polymeric scaffolding for a duration of time. The duration of time may be at least 8 hours. The polymeric stent may have been crimped onto a delivery device, packaged, and sterilized prior to the exposure. The polymeric scaffolding may be formed from a polymeric article that has been deformed by the application of stress at a temperature greater than that of the glass transition temperature of the polymeric article, and the polymeric article may have a glass transition temperature greater than 25.degree. C. The exposure temperature may be controlled to within .+-.3.degree. C.

"In an aspect of the invention, the polymeric article may be a polymer tube and the deformation under stress may comprise radial expansion of the polymer tube.

"In another aspect of the invention, the polymeric scaffolding may include a polymer selected from the group consisting of poly(L-lactide), polymandelide, poly(DL-lactide), polyglycolide, poly(L-lactide-co-glycolide), and all combinations thereof in all proportions.

"In another aspect of the invention, the exposure temperature may be not higher than 20.degree. C. below the glass transition temperature of the polymeric scaffolding.

"In another aspect of the invention, the duration of exposure may be from about 8 hours to about 20 days and the exposure temperature may be from about 32.degree. C. to about 40.degree. C.

"In other aspects of the invention, the duration of exposure may be from about 1 day to about 10 days, or from about 2 days to about 6 days.

"In another aspect of the invention, the exposure temperature may be in the range of about 35.degree. C. to about 40.degree. C.

"In another aspect of the invention, the method may also include exposing the polymeric stent to a temperature equal to or greater than 35.degree. C. and not more than about 10.degree. C. greater than the glass transition temperature of the polymeric scaffolding for a duration of time where the duration of time may be in the range of from about 4 hours to about 10 days, and where the exposure may occur after the polymeric stent has been crimped onto a delivery device, but before the polymeric stent has been sterilized. The temperature of the exposure after crimping and before sterilization may be controlled to within .+-.3.degree. C.

"In another aspect of the invention, the duration of the exposure after crimping and before sterilizing may be from about 16 hours to about 48 hours, and the temperature of the exposure after crimping and before sterilization is from about 45.degree. C. to about 65.degree. C.

"In another aspect of the invention, the duration of the exposure after crimping and before sterilizing may be from about 16 hours to about 32 hours, and the temperature of the exposure after crimping and before sterilization may be from about 50.degree. C. to about 65.degree. C.

"In another aspect of the invention, the polymeric stent may be crimped onto a delivery device and the crimping may be performed at a temperature in the range of about 45.degree. C. to about 50.degree. C.

"In another aspect of the invention, the polymeric stent may be crimped in the range of about 40.degree. C. to about 55.degree. C., and the post-sterilization exposure temperature may be about 33.degree. C. and not more than about 37.degree. C. and the duration of the exposure may be in the range of about 32 hours to about 84 hours.

"In another aspect of the invention, the polymeric stent may be crimped onto a delivery device and the crimping may be performed at a temperature in the range of about 48.degree. C., and the post-sterilization exposure temperature may be about 35.degree. C. and the duration of the exposure may be in the range of about 48 hours to about 72 hours.

"Various embodiments of the present invention include a method for conditioning a polymeric stent. The method includes the operations of: exposing a polymeric stent with a polymeric scaffolding consisting essentially of poly(L-lactide) to a temperature equal to, approximately equal to, or greater than 30.degree. C. and not more than about 55.degree. C. for a duration of time. The duration of time may be at least 8 hours. The polymeric stent may have been crimped onto a delivery device, packaged, and sterilized prior to the exposure. The polymeric scaffolding may be formed from a polymeric tube consisting essentially of poly(L-lactide) that has been deformed by the radial expansion of the polymeric tube at a temperature greater than that of the glass transition temperature of the polymeric tube. The exposure temperature may be controlled to within .+-.3.degree. C.

"In an aspect of the present invention, the duration of exposure after sterilization may be from about 8 hours to about 20 days and the exposure temperature may be from about 32.degree. C. to about 40.degree. C.

"In an aspect of the present invention, the duration of exposure after sterilization may be from about 1 day to about 10 days.

"In an aspect of the present invention, the duration of exposure after sterilization may be from about 2 days to about 6 days, and wherein the exposure temperature may be in the range of about 35.degree. C. to about 40.degree. C.

"An aspect of the present invention, the method of exposing a poly(L-lactide) scaffolding also may include exposing the polymeric stent with the polymeric scaffolding to a temperature equal to or greater than 35.degree. C. and not more than about 70.degree. C. for a duration of time, where the duration of time may be from about 4 hours to about 6 days, after the polymeric stent has been crimped onto a delivery device, but before the polymeric stent has been sterilized. The temperature of the exposure after crimping and before sterilization may be controlled to within .+-.3.degree. C.

"In an aspect of the invention, for a polymeric stent with a poly(L-lactide) scaffolding, the duration of the exposure after crimping and before sterilizing may be from about 16 hours to about 48 hours, and the temperature of the exposure after crimping and before sterilization may be from about 45.degree. C. to about 65.degree. C.

"In an aspect of the invention, for a polymeric stent with a poly(L-lactide) scaffolding, the duration of the exposure after crimping and before sterilizing may be from about 16 hours to about 32 hours, and the temperature of the exposure after crimping and before sterilization may be from about 50.degree. C. to about 65.degree. C.

"In an aspect of the invention, for a polymeric stent with a poly(L-lactide) scaffolding, the polymeric stent may be crimped onto a delivery device at a temperature in the range of about 45.degree. C. to about 50.degree. C.

"In an aspect of the invention, for a polymeric stent with a poly(L-lactide) scaffolding, the post-sterilization exposure temperature may be in the range from about 33.degree. C. and not more than about 37.degree. C., and the duration of the exposure may be in the range of about 32 hours to about 84 hours.

"In an aspect of the invention, for a polymeric stent with a poly(L-lactide) scaffolding, the polymeric stent may be crimped onto a delivery device at a temperature of about 48.degree. C., and the post-sterilization exposure temperature may be about 35.degree. C., and the duration of the exposure after sterilization may be in the range of about 48 hours to about 72 hours.

"Various embodiments of the present invention include a method for conditioning a polymeric stent. The method may include the operations of: exposing a polymeric stent with a polymeric scaffolding to a temperature equal to, approximately equal to, or greater than 30.degree. C. and not more than about 55.degree. C. for a duration of time until the radial strength is reduced by at least 10%. The duration of time may be at least 30 minutes, and the polymeric stent may have been crimped onto a delivery device, packaged, and sterilized prior to the exposure. The polymeric scaffolding may be formed from a polymeric tube that has been deformed by the radial expansion of the polymeric tube at a temperature greater than that of the glass transition temperature of the polymeric tube, and the exposure temperature may be controlled to within .+-.3.degree. C. The glass transition temperature of the polymeric scaffolding may be greater than 25.degree. C.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 depicts an exemplary stent.

"FIG. 2 depicts the specific volume of a polymer as a function of temperature.

"FIG. 3 depicts the relative free radical concentration of a polymeric stent with heat treatment and the stent with no heat treatment.

"FIG. 4 depicts the relative free radical concentration of a polymeric stent with heat treatment and the stent with no heat treatment.

"FIG. 5 depicts the number-average molecular weight of a polymer of a polymeric stent as a function of time after electron beam sterilization.

"FIG. 6 depicts the radial strength of a polymeric stent as a function of time after electron beam sterilization.

"FIG. 7 depicts the heat capacity of a polymer as a function of temperature."

For more information, see this patent application: Wang, Yunbing; Ma, Xiao; Tang, Fuh-Wei; Ding, Ni. Post Electron Beam Conditioning of Polymeric Medical Devices. Filed December 23, 2013 and posted May 1, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=4858&p=98&f=G&l=50&d=PG01&S1=20140424.PD.&OS=PD/20140424&RS=PD/20140424

Keywords for this news article include: Surgery, Therapy, Cardiology, Restenosis, Blood Vessels, Cardio Device, Heart Disease, Medical Devices, Surgical Technology, Abbott Cardiovascular Systems Inc..

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