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Patent Issued for Coatings for the Manufacture and Application of Polyhydroxyalkanoate Medical Devices

June 24, 2014



By a News Reporter-Staff News Editor at Life Science Weekly -- From Alexandria, Virginia, NewsRx journalists report that a patent by the inventors Martin, David P. (Arlington, MA); Rizk, Said (Salem, NH); Montcrieff, Jon I. (Boston, MA); Connelly, Dennis W. (Arlington, MA), filed on March 23, 2011, was published online on June 10, 2014 (see also Tepha, Inc.).

The patent's assignee for patent number 8747468 is Tepha, Inc. (Lexington, MA).

News editors obtained the following quote from the background information supplied by the inventors: "There is a need for absorbable braided sutures with improved performance. In particular, these sutures should have high initial tensile strength, prolonged strength retention in vivo, good knot security and tie down (with a small knot bundle), good handling characteristics, and be biocompatible. The braided sutures should also have a low tissue drag that minimizes trauma to the sutured tissues. Biocompatible braided polyhydroxyalkanoate ('PHA') sutures, or those having a braided component, can be made with high tensile strength, prolonged strength retention in vivo, and good knot security; however, it would be advantageous if the tissue drag resulting from the braided structure of the suture could be reduced.

"A number of different types of coatings have been applied to braided sutures to lower tissue drag. These coatings must: impart good lubricity to the fiber/braid, have a reasonable shelf life, be biocompatible, and be compatible with the physical and chemical structure of the fiber. For example, the coating must not react with the suture fiber, dissolve the fiber, or adversely alter the mechanical and thermal properties of the fiber. Thus, it is desirable to identify coatings that can be applied to PHA braided sutures to reduce tissue drag by imparting good lubricity to the braid and fill the braid interstices without adversely altering the inherent properties of the fiber/braid. Moreover, it is particularly desirable to identify coatings that can be applied to braided sutures, or sutures containing braided components, made from P4HB polymers and copolymers thereof.

"In addition to providing coatings for PHA fibers that reduce tissue drag, it is desirable to identify spin finishes that can be applied to PHA fibers to facilitate their manufacture and, optionally, their conversion to other products, including medical textiles. Spin finishes are applied during extrusion of multifilaments to keep the fiber bundle protected and intact, and to impart lubricity to the fiber bundle so that it may be manipulated in subsequent processing steps without damaging the fiber. Spin finishes are also applied to monofilament to facilitate textile processing without damaging the fiber. Spin finishes for medical applications must satisfy a number of conditions. These include compatibility with the fiber (similar to that described for suture coatings), and effectiveness under the process conditions, for example, in processes such as spinning and orienting of the fiber, and in knitting or weaving of the fiber. In addition, it must be easy to apply the spin finish, and easy to remove the spin finish without damaging the fiber or adversely impacting any component in the fiber such as dye, using conditions that are compatible with the fiber's subsequent use in a medical device. Residues of the spin finish should also be easily detectable, and any spin finish left on the device, even residues, needs to be biocompatible. The spin finish should also be stable with a long shelf life, and any spin finish left on the final product should not adversely impact the properties or the shelf life of the final product.

"It is also desirable to provide multifilament with a lower denier per filament (dpf) and improved tenacity compared to uncoated multifilament. Such fibers can be used to prepare higher strength medical devices as well as reduce the device profile.

"It is an object of the present invention to provide methods to produce coated PHA braids for use as sutures and in other medical devices, wherein the coating provides the device with good lubricity to minimize trauma to tissues, and good knot strength (in the case of a suture), without adversely impacting the properties of the PHA polymer.

"It is a further object of the present invention to provide processes to produce PHA multifilament fiber using spin finish, and process PHA monofilament and multifilament fibers into other forms, such as textiles, with the aid of spin finish such that the fibers may be processed without damage, and the spin finish imparts lubricity to aid in the subsequent processing of the fiber.

"It is another object of the present invention to provide coated PHA multifilament and monofilament fibers, coated PHA braided sutures, coated PHA braided structures as components of other devices, and other coated PHA medical devices and textiles, including monofilament and multifilament knitted and woven meshes, and vascular grafts, which are biocompatible and can be used in medical applications, for example, as implants for soft tissue repair and reconstruction, temporary wound support, cosmetic, breast, facial, and plastic surgery, and for the regeneration and replacement of tissues. Such devices and textiles may be further coated or encapsulated by or contain collagen.

"It is yet another object of the invention to provide PHA multifilament fibers with low filament denier and higher tenacity.

"It is still another object of the invention to provide coatings and spin finishes that can be used in processing PHA polymers to yield materials with excellent physical and mechanical properties, and biocompatibility."

As a supplement to the background information on this patent, NewsRx correspondents also obtained the inventors' summary information for this patent: "Biocompatible coatings and spin finishes that can be applied to polyhydroxyalkanoate (PHA) polymers, and medical devices made from PHA polymers, have been developed. The spin finishes can be applied to PHA fibers to facilitate their manufacture, and also for their conversion to other products, including medical textiles. The spin finishes protect the multifilament fiber bundles, keeping them intact following extrusion, and imparting lubricity to the fiber bundles and monofilament fibers so that they are not damaged in subsequent processing steps, particularly in textile processing. In the preferred embodiment, the coatings and spin finish are applied to a polyhydroxyalkanoate polymer, and in the most preferred embodiment, the PHA polymer comprises 4-hydroxybutyrate. In a preferred embodiment, the coating or spin finish is a polymer or oligomer of an alkylene oxide, such as ethylene oxide or propylene oxide, or a copolymer thereof.

"The spin finish is preferably a liquid at the fiber processing temperature. For example, if P4HB is processed at or near room temperature, the spin finish is preferably a liquid at room temperature. In other embodiments, the polyalkylene oxides can be wetted with water or solvent to provide a liquid solution at the processing temperature. A particularly preferred embodiment is where the spin finish is polyethylene glycol (PEG) with an average molecular weight of approximately 400 Daltons (PEG 400) to 2000 daltons (PEG 2000) applied to a poly-4-hydroxybutyrate polymer or copolymer thereof. PEG with an average molecular weight of approximately 400 Daltons (PEG 400) to 1000 daltons (PEG 1000) is preferred for PHAs being processed at or near room temperature. Higher molecular weights can be preferable for PHAs being processed at higher temperatures.

"In another preferred embodiment for the processing of monofilament PHA fibers into textiles, the spin finish is polyethylene glycol sorbitan monolaurate (e.g., a polysorbate detergent available under the brand Tween.RTM. 20). A particularly preferred embodiment is where the spin finish, Tween.RTM. 20, is applied to monofilament PHA fiber and knitted or woven into a textile construct, and the PHA fiber comprises 4-hydroxybutyrate.

"The preferred coating weight for a spin finish will depend on the fiber being processed. Monofilaments require less spin finish than multifilaments, due to the smaller total surface area of a monofilament fiber. So a preferred coating weight on a monofilament may be less than 2 wt %, preferably less than 1 wt %, while for multifilament it may be less than 10 wt %, preferably less than 8 wt %. Spin finishes can be removed by a scouring process to prevent cytotoxicity. In preferred embodiments, the residual content of Tween.RTM. 20 after scouring is less than about 0.5 wt %, including less than about 0.4, 0.3, 0.2, 0.1, 0.09, 0.08, 0.07, 0.06, 0.05, 0.04, or 0.03 wt %. In preferred embodiments, the residual content of PEG 400 after scouring is less than about 2 wt %, including less than about 1, 0.5, 0.4, 0.3, 0.2, or 0.1 wt %.

"The textile construct produced from the coated PHA fibers may be further coated, impregnated, covered, or encapsulated by or contain collagen.

"The coatings impart good lubricity to PHA polymers, particularly to fibers and braids made from these materials, making the coatings ideal for use on medical devices such as PHA braided sutures. Braided monofilament fibers or multifilament yarns are provided that are coated with polymers or oligomers of ethylene oxide, polymers or oligomers of propylene oxide, polyvinyl alcohol, or combinations thereof. These braided fibers or yarns have an average tissue drag force at least 10% lower than the uncoated braid, including at least 20, 30, 40, 50, 60, 70, 80, 90, 100% lower than the uncoated braid.

"The polyhydroxyalkanoate of the braided fiber or yarn preferably has a molecular weight between 50,000 and 1,200,000. In preferred embodiments, the polyhydroxyalkanoate is 4-hydroxybutyrate.

"In a preferred embodiment, the coating is polyethylene glycol (PEG) with an average molecular weight of approximately 1000 Daltons (PEG 1000) to 10,000 daltons (PEG 10000) applied to devices, such as braided sutures, derived from poly-4-hydroxybutyrate or copolymers thereof.

"In another embodiment, the coating is polyvinyl alcohol (PVOH). A particularly preferred embodiment is where the coating is polyvinyl alcohol applied to a poly-4-hydroxybutyrate polymer or copolymer thereof or applied to devices, such as braided sutures, derived from poly-4-hydroxybutyrate or copolymers thereof.

"In preferred embodiments, the biocompatible coating is present on the PHA polymers or the medical devices made from PHA polymers in a coating weight of about 0.1 wt % to 10 wt %, including about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 wt %. For example, PEG2000 is preferably present on the PHA polymers or the medical devices made from PHA polymers in a coating weight of less than 10 wt %, more preferably less than 7 wt %, even more preferably less than 5 wt %. For example, PVA is preferably present on the PHA polymers or the medical devices made from PHA polymers in a coating weight of less than 6 wt %, more preferably less than 4 wt %, even more preferably less than 3 wt %.

"A method of reducing the tissue drag force of a braided suture formed from polyhydroxyalkanoate filaments is also provided. This method can involve coating the braided suture with polymers or oligomers of ethylene oxide, polymers or oligomers of propylene oxide, polyvinyl alcohol, or combinations thereof."

For additional information on this patent, see: Martin, David P.; Rizk, Said; Montcrieff, Jon I.; Connelly, Dennis W.. Coatings for the Manufacture and Application of Polyhydroxyalkanoate Medical Devices. U.S. Patent Number 8747468, filed March 23, 2011, and published online on June 10, 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=8747468.PN.&OS=PN/8747468RS=PN/8747468

Keywords for this news article include: Alkenes, Polyenes, Tepha Inc., Hydrocarbons, Vinyl Compounds, Carboxylic Acids, Hydroxybutyrates, Organic Chemicals, Polyvinyl Alcohol, 3-Hydroxybutyric Acid.

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Source: Life Science Weekly


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