News Column

"Laser System and Processing Conditions for Manufacturing Bioabsorbable Stents" in Patent Application Approval Process

June 26, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- A patent application by the inventors Harrington, Joel (Redwood City, CA); Vaughan, Ryan (Mountain View, CA); Jow, Kevin (San Mateo, CA); Pippey, William (San Jose, CA); Chen, Yung-Ming (San Jose, CA), filed on February 3, 2014, was made available online on June 12, 2014, according to news reporting originating from Washington, D.C., by VerticalNews correspondents.

This patent application has not been assigned to a company or institution.

The following quote was obtained by the news editors from the background information supplied by the inventors: "This invention relates to laser machining tubing to form stents.

"This invention relates to laser machining of devices such as stents. Laser machining refers to removal of material accomplished through laser and target material interactions. Generally speaking, these processes include laser drilling, laser cutting, and laser grooving, marking or scribing. Laser machining processes transport photon energy into a target material in the form of thermal energy or photochemical energy. Material is removed by melting and blow away, or by direct vaporization/ablation.

"When a substrate is laser machined energy is transferred into the substrate. As a result, a region beyond the cutting edge is modified by the energy, which affect the properties in this region. In general, the changes in properties are adverse to the proper functioning of a device that is being manufactured. Therefore, it is generally desirable to reduce or eliminate energy transfer beyond removed material, thus reducing or eliminating the extent of modification and size of the region affected.

"One of the many medical applications for laser machining includes fabrication of radially expandable endoprostheses, which 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, which 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 the diameter 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.

"The treatment of a diseased site or lesion with a stent involves both delivery and deployment of the stent. 'Delivery' refers to introducing and transporting the stent through a bodily lumen to a region, such as a lesion, in a vessel that requires treatment. 'Deployment' corresponds to the expanding of the stent within the lumen at the treatment region. Delivery and deployment of a stent are accomplished by positioning the stent about one end of a catheter, inserting the end of the catheter through the skin into a bodily lumen, advancing the catheter in the bodily lumen to a desired treatment location, expanding the stent at the treatment location, and removing the catheter from the lumen.

"In the case of a balloon expandable stent, the stent is mounted about a balloon disposed on the catheter. Mounting the stent typically involves compressing or crimping the stent onto the balloon. The stent is then expanded by inflating the balloon. The balloon may then be deflated and the catheter withdrawn. In the case of a self-expanding stent, the stent may be secured to the catheter via a retractable sheath or a sock. When the stent is in a desired bodily location, the sheath may be withdrawn which allows the stent to self-expand.

"The stent must be able to satisfy a number of mechanical requirements. First, the stent must be capable of withstanding the structural loads, namely radial compressive forces, imposed on the stent as it supports the walls of a vessel. Therefore, the stent must possess adequate radial strength and rigidity. Radial strength is the ability of a stent to resist radial compressive forces. Once expanded, the stent must adequately maintain its size and shape throughout its service life despite the various forces that may come to bear on it, including the cyclic loading induced by the beating heart. For example, a radially directed force may tend to cause a stent to recoil inward. Generally, it is desirable to minimize recoil.

"In addition, the stent must possess sufficient flexibility to allow for crimping, expansion, and cyclic loading. The stent should have sufficient resistance to fracture so that stent performance is not adversely affected during the crimping, expansion, and cycling loading.

"Finally, the stent must be biocompatible so as not to trigger any adverse vascular responses.

"The structure of a stent is typically composed of scaffolding that includes a pattern or network of interconnecting structural elements often referred to in the art as struts or bar arms. The scaffolding can be formed from wires, tubes, or sheets of material rolled into a cylindrical shape. The scaffolding is designed so that the stent can be radially compressed (to allow crimping) and radially expanded (to allow deployment).

"Stents have been made of many materials such as metals and polymers, including biodegradable polymeric materials. Biodegradable stents are desirable in many treatment applications in which the presence of a stent in a body may be necessary for a limited period of time until its intended function of, for example, achieving and maintaining vascular patency and/or drug delivery is accomplished.

"Stents can be fabricated by forming patterns on tubes or sheets using laser machining. Even though the basic laser-material interaction is similar, there are certain aspects among types of materials (such as metals, plastics, glasses, and ceramics), i.e. different absorption characteristics. To produce the desired results, it is critical in choosing a suitable wavelength. Once a suitable wavelength is selected, it is the combination of pulse energy and pulse duration that define the optimal process condition for the type of material. The properties of biodegradable polymers like PLLA and PLGA tend to be very sensitive to energy transfer such as that from laser machining. There are great efforts needed in understanding the laser parameters and laser-material interaction to help select a laser system and define processing parameters enabling faster laser machining of biodegradable stents which minimize the adverse effects on the properties."

In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventors' summary information for this patent application: "Various embodiments of the present invention include a method of laser machining a substrate to form a stent, comprising: providing a thin-walled polymer substrate; laser machining the thin-walled polymer substrate with a laser beam with a pulse width and wavelength that can cut through the wall of the substrate to form structural elements having a machined edge surface, wherein the laser beam modifies the substrate in a surface region adjacent to the machined edge surface in much less degree, wherein the modifications include voids, cracks that contribute to the variation in modulus of the polymer with distance from the edge surface, or a combination thereof, and selecting the pulse width and wavelength so that the voids or cracks are present at no greater than a depth of 2 microns or the modulus converges at no greater than 4 microns.

"Additional embodiments of the present invention include a method of laser machining a substrate to form a stent, comprising: providing a thin-walled PLLA polymer substrate; laser machining the thin-walled PLLA polymer substrate with a laser beam to cut through the wall to form structural elements having a machined edge surface, wherein the pulse width and wavelength of the laser beam are within the green range and the pulse width is 1-10 ps.

"Further embodiments of the present invention include a polymer stent body, comprising: a plurality of interconnected structural elements formed by laser machining a thin-walled PLLA polymer substrate with a laser beam that cuts through the wall to form the structural elements, wherein the structural elements have sidewalls corresponding to a machined edge surface, wherein a surface region adjacent to the sidewalls has damage caused by interaction of the laser beam with the substrate, wherein the damage comprises voids or cracks dispersed in the surface region to a depth of 2 microns or less from the edge surface.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1 depicts a stent.

"FIG. 2 depicts a machine-controlled system for laser machining a tube.

"FIG. 3 depicts a close-up axial view of a region where a laser beam interacts with a tube.

"FIG. 4A depicts a portion of a strut or structural element formed by laser machining a substrate.

"FIG. 4B depicts a cross-section of a portion of a strut normal to a machined edge surface.

"FIGS. 5-8 show SEM images of the surface region adjacent to a laser machined edge surface for combinations of pulse width and wavelength.

"FIGS. 9-13 show the modulus vs. displacement into the surface of a laser machined edge for combinations of pulse width and wavelength.

"FIGS. 14-17 depict SEM images showing the sidewall surfaces of stents machined with different combinations of pulse widths and wavelengths."

URL and more information on this patent application, see: Harrington, Joel; Vaughan, Ryan; Jow, Kevin; Pippey, William; Chen, Yung-Ming. Laser System and Processing Conditions for Manufacturing Bioabsorbable Stents. Filed February 3, 2014 and posted June 12, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=1487&p=30&f=G&l=50&d=PG01&S1=20140605.PD.&OS=PD/20140605&RS=PD/20140605

Keywords for this news article include: Patents, Surgery, Cardiology, Restenosis, Heart Disease, Cardiovascular, Risk and Prevention, Surgical Technology.

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Source: Politics & Government Week


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