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Patent Issued for Crosslinked Polyolefins for Biomedical Applications and Method of Making Same

July 18, 2014



By a News Reporter-Staff News Editor at Health & Medicine Week -- According to news reporting originating from Alexandria, Virginia, by NewsRx journalists, a patent by the inventors Zhou, Yonghua (Miami, FL); Pinchuk, Leonard (Miami, FL), filed on June 25, 2008, was published online on July 1, 2014 (see also Innolene LLC).

The assignee for this patent, patent number 8765895, is Innolene LLC (Miami, FL).

Reporters obtained the following quote from the background information supplied by the inventors: "This invention relates to polymeric materials. The polymeric materials are particularly suitable for biomedical applications, such as a component of an intraocular lens.

"Polymers have been used in biomedical applications for a long time. Early in vivo studies on polymeric implants revealed that the polymers are susceptible to degradation in physiological environment and lose integrity over time. A close scrutiny of the structure and bio-properties relationship led to Pinchuk's discovery of the superior biostability of polyisobutylene-based materials. The biomedical application of polyisobutylene-based materials is disclosed in U.S. Pat. Nos. 5,741,331; 6,102,939; 6,197,240; 6,545,097; and 6,855,770, all of which are herein incorporated by reference in their entirety. The first commercial application of such materials is the use of SIBS in the TAXUS.RTM. Stent of Boston Scientific Corporation, which is regarded as the most successful launch of a biomedical device in history.

"SIBS is a thermoforming triblock copolymer consisting of polyisobutylene (PIB) as the rubbery center block and polystyrene (PS) as the hard side blocks. Due to the immiscibility of PIB and PS, the SIBS material has microphase-separated morphology in which PS phase forms physical crosslinks in the matrix of rubbery PIB phase. Due to the thermoplastic nature of the crosslinking, SIBS material creeps and can lose its dimension. SIBS doesn't withstand the high temperature of autoclave sterilization due to limitation by the glass transition temperature of PS. As a result, SIBS sterilization is difficult, because gamma-sterilization breaks down SIBS and ethylene oxide sterilization is cumbersome.

"PIB is commonly crosslinked through vulcanization. First, isobutylene is copolymerized with a small fraction (1-5%) conjugated dienes such as butadiene, so that there are carbon-carbon double bonds in the backbone providing sites for vulcanization; second, the isobutylene/butadiene copolymer is heated with sulfur and crosslinked by the sulfur. To accelerate the vulcanization process, either the polymer is activated as in the case of halo-butyl rubber, or accelerators are added such as resins, zinc oxide, xanthates and quinoid systems. An extremely fast vulcanization process involves mixing butyl rubber solution with sulfur monochloride at room temperature (Erman et al, Macromolecules, Vol. 33, 2000, 4822-4827). The chemicals used for vulcanization of butyl rubber are toxic to human body. Extraction by solvent is necessary for removal of toxic residuals, but complete extraction is difficult and time-consuming.

"PIB can be crosslinked utilizing silicone chemistry. Kaneka developed telechelic functional PIB (trade name: Epion) with silyl or allyl end groups, which can be crosslinked by moisture or adding silanes. Faust et al disclosed a virtually telechelic silyl PIB, which undergoes room temperature crosslinking as described in U.S. Pat. No. 6,268,451.

"Benzocyclobutene derivates and 1-hexene were analyzed in Fishback et al., 'A New Non-Toxic, Curing Agent for Synthetic Polyolefins,' Bio-Medical Materials and Engineering, Vol. 2, pp. 83-87 (1992), herein incorporated in reference in its entirety. Fishback prepared polymers containing 1-hexene, allyl-benzocyclobutene, and a diene, either 7-methyl-1,6-octadiene or 5-methyl-1,4-hexadiene, using free-radical polymerization techniques. While the polymer showed improved properties, it requires carbon black as a filler, and is polymerizable only through free-radical chemistry techniques that necessitate the use of free radical initiators. Additionally, there is a need to extract the non-crosslinked polymers to rid the system of the initiators as the initiators, if not removed, would leave the polymer with an undesirable purple color."

In addition to obtaining background information on this patent, NewsRx editors also obtained the inventors' summary information for this patent: "The present invention provides a polymeric composition including alkenes and benzocyclobutene-functional olefins that is polymerizable using living carbocationic chemistry.

"The present invention provides such a polymeric composition that is biostable, exhibits increased tensile strength, and does not require a filler.

"The present invention provides such a polymeric composition that is suitable for many applications.

"The present invention provides such a polymeric composition that is crosslinked in a manner such that it has improved creep resistance and/or dimensional stability, especially when stressed or at elevated temperatures.

"The present invention provides such a polymeric composition that does not release a small molecule to the environment.

"The present invention provides such a polymeric composition that can withstand high temperature sterilization.

"The present invention provides such a polymeric composition that is chemically crosslinked at elevated temperatures (e.g., greater than 180.degree. C.) without addition or evolution of small molecules.

"A copolymer composition of the present invention includes, in polymerized form, a branched alkene which is cationically polymerizable as well as a glass-forming comonomer and/or a vinyl comonomer containing benzocyclobutene (herein called 'BCB') as the pendant group. The structure of the copolymer composition can take various forms: linear random copolymer, linear block copolymer, star random copolymer, star block copolymer, and other hyperbranched polymers and copolymers. The copolymer composition preferably undergoes crosslinking reaction at elevated temperatures (preferably above 180.degree. C.).

"It will be appreciated that the material of the present invention has improved structural characteristics and thus superior physical properties (such as creep resistance, heat resistance, dimensional stability and solvent resistance). By changing the copolymer composition and structure, materials with variable hardness and crosslinking density can be obtained for various biomedical applications. Examples of such uses include implantable medical devices such as synthetic heart valves, pharmaceutical closure devices, vertebral disks, joint menisci, artificial ligaments, artificial meniscuses, vascular grafts, pacemaker headers and lead insulators, glaucoma drainage tubes, intraocular lenses, and the like.

"The material of the present invention also avoids the release of molecules that can cause inflammation when introduced in the body, which is characteristic of the silyl-terminated PIB of the prior art as it releases inflammation-introducing small molecules such as methanol, ethanol, acetic acid, chlorine and the like when cured.

"Additional objects and advantages of the invention will become apparent to those skilled in the art upon reference to the detailed description taken in conjunction with the provided figures."

For more information, see this patent: Zhou, Yonghua; Pinchuk, Leonard. Crosslinked Polyolefins for Biomedical Applications and Method of Making Same. U.S. Patent Number 8765895, filed June 25, 2008, and published online on July 1, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8765895.PN.&OS=PN/8765895RS=PN/8765895

Keywords for this news article include: Chemicals, Chemistry, Inflammation, Innolene LLC.

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Source: Health & Medicine Week


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