Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61F—FILTERS IMPLANTABLE INTO BLOOD VESSELS; PROSTHESES; DEVICES PROVIDING PATENCY TO, OR PREVENTING COLLAPSING OF, TUBULAR STRUCTURES OF THE BODY, e.g. STENTS; ORTHOPAEDIC, NURSING OR CONTRACEPTIVE DEVICES; FOMENTATION; TREATMENT OR PROTECTION OF EYES OR EARS; BANDAGES, DRESSINGS OR ABSORBENT PADS; FIRST-AID KITS
  • A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents
  • A61F2/02—Prostheses implantable into the body
  • A61F2/04—Hollow or tubular parts of organs, e.g. bladders, tracheae, bronchi or bile ducts
  • A61F2/06—Blood vessels
• • D—TEXTILES; PAPER
  • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
  • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
  • D06M13/00—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with non-macromolecular organic compounds; Such treatment combined with mechanical treatment
  • D06M13/08—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with non-macromolecular organic compounds; Such treatment combined with mechanical treatment with halogenated hydrocarbons
• • D—TEXTILES; PAPER
  • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
  • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
  • D06M13/00—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with non-macromolecular organic compounds; Such treatment combined with mechanical treatment
  • D06M13/10—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with non-macromolecular organic compounds; Such treatment combined with mechanical treatment with compounds containing oxygen
  • D06M13/144—Alcohols; Metal alcoholates
• • D—TEXTILES; PAPER
  • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
  • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
  • D06M13/00—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with non-macromolecular organic compounds; Such treatment combined with mechanical treatment
  • D06M13/10—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with non-macromolecular organic compounds; Such treatment combined with mechanical treatment with compounds containing oxygen
  • D06M13/152—Treating fibres, threads, yarns, fabrics or fibrous goods made from such materials, with non-macromolecular organic compounds; Such treatment combined with mechanical treatment with compounds containing oxygen having a hydroxy group bound to a carbon atom of a six-membered aromatic ring
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S8/00—Bleaching and dyeing; fluid treatment and chemical modification of textiles and fibers
  • Y10S8/21—Nylon

Definitions

• ABSTRACT Knitted flat stock or tubing fabric material of a suitable polyester material such as polyethylene terephthalate is treated to reduce its porosity.
• the resulting product is useful as a synthetic inter-cardiac (e.g., vascular) prosthesis.
• Treatment is performed by immersing the knitted fabric material in a compacting solution containing a minor amount of an acidic organic component and a major amount of a halogenated aliphatic hydrocarbon having up to about 6 carbon atoms for a time sufficient to reduce the porosity of the knitted fabric material at least about 30 percent in the wale direction.
• a compacting solution containing about 90 to 98 percent by weight of methylene chloride and about 10 to 2 percent by weight of hexafluoroisopropanol is an example of a suitable compacting solution.
• Synthetic vascular prostheses have been made from tubing materials such as'extruded plastic tubing, seamless braided and knitted tubing, cut. and Jacquardwoven tubing, as well as seamless woven tubing. Each of these has been found lacking in one or more of these essential characteristics. Extruded plastic tubing has lacked porosity and attempts to deliberately perforate the tubing have proved unsuccessful. Woven tubing made with a Jacquard-woven seam has a selvage edge which makes a suture between natural and synthetic materials. Seamless woven tubing, while better in some respects, has proved to be unsatisfactory in all areas where good tissue ingrowth is necessary. Also, woven tubing is subject to unraveling. Knitted seamless tubing, while sufficiently flexible, has been found to have undue leakage at the necessary thin wall thicknesses. Also, the porosity of knitted seamless tubing often is not constant along its length.
• the porosity of the prosthesis precursor is a function both of the size and multifilament nature of the yarn, as well as the close proximity of the yarns as laid in the knitting step.
• the body heals by fibrosis. That is, the body will react to the implantation of a synthetic graft such as a vascular graft by encapsulating the graft with fibers or scar tissue forming both an outer layer and an inner layer offibrous tissue.
• the healing process begins very shortly after implantation with the deposit of a fibrous layer on the inside of the graft in contact with the blood stream. Eventually, a mature layer of scar tissue will be formed.
• the inner fibrous layer is, however, believed to originate by migration of fibroblasts from the outer capsule through the mesh or interstices of the vascular prosthesis.
• an important factor in the determination of the ease of formation of the fibrous layers and the biological fate of the synthetic prosthesis is the porosity of the prosthesis material.
• Knitted tubing offers many advantages of strength, flexibility adn ease of handling.
• knitted tubing is relatively inexpensive to produce at the desired wall thickness.
• the knitted structure locks the yarns in a very stable manner.
• Knitting also provides a fabric material with more numerous interstices per unit of material and larger numbers of interstices may be advantageous for certain conditions of use.
• such knitted flat'stock or tubing is produced at a porosity in excess of that which is suitable for the effective utilization of the tubing as an intercardiac prosthesis. Even the finest knitted fabric material has this excessive porosity.
• polyester materials which are suitable for use as synthetic vascular prostheses.
• ter-cardiac prosthesis comprising the steps of: (a) providing a knitted polyester fabric material having a po rosity in excess of that suitable for long-term healing without undue hemorrhaging at implantation; (b) immersing said porous knitted polyester fabric material in a compacting solution consisting essentially of from about 2 to about percent by weight of an acidic organic component and about 98 to about 90 percent by weight of a halogenated aliphatic hydrocarbon having up to about 6 carbon atoms until said fabric material shrinks at least about 30 percent measured in the wale direction and the porosity of the said fabric material is reduced to that suitable for long-term healing effects without undue hemorrhaging at implantation; (c) removing said compacted fabric material from said compacting solution; and (d) forming said compacted fabric material into a vascular prosthesis.
• the objects of this invention are achieved by a solution for compacting a knitted polyester fabric material at least about 30 percent measured in the wale direction of the fabric consisting essentially -of from about 2 to about 10 percent by weight of an acidic organic component and from about 98 to about 90 percent by weight of a halogenated aliphatic hydrocarbon having up to about 6 carbon atoms.
• the knitted fabric material useful as a starting point in the preparation of a synthetic inter-cardiac prosthesis by the process of the present invention may be made from fine-denier synthetic yarns of materials selected for desired inter-cardiac implant properties such as discussed before.
• the yarn material found most satisfactory to date is a terephthalic acid-ethylene glycol polyester such as that which is commercially produced by E. I. duPont de Nemours Co. under the trademark Dacron.”
• Such polyester yarn is compatible with human tissue and wettable by blood so as to promote the starting of clotting and attendant growth of a layer of collagen on the wall of the prosthesis after implantation.
• the yarn has suitable strength, flexibility and resiliency properties accompanied by appropriate water-absorptivity and capacity to withstand sterilization.
• the yarn may have any denier which will result in the desired thin thickness of flat stock or tubing wall.
• the yarn can have a denier of from about 20 to about 250, preferably from about 30 to about 150. It has been found that multi-filament yarns give superior results in implantation use as compared with solid or monofilament yarn.
• Preferred for use in the formation of the knitted material herein is a'multi-filament Dacron polyester yarn of a denier of from about 40 to about 70 denier.
• the yarn may be knitted into flat stock or tubing by any suitable technique.
• a preferred method of forming knitted tubing is disclosed in copending U.S. Pat. application Ser. No. 865,326, filed Oct. l0, 1969 now abandoned, assigned to the same assignee as the present invention and herein incorporated by reference.
• the tubing may be produced on a fine (56) gauge double needle bar Raschel machine in which the yarn is warp-knitted with a tricot or lock stitch.
• the resulting knitted product has a smooth, hard surface and a standard, uniform porosity.
• Other suitable knitting techniques known to those skilled in the art which will provide a similar product may also be utilized. Similar fine gauge knitting may be utilized to form lengths of knitted flat stock material. It should be understood that knitted tubing suitable for use in the present invention includes bifurcated tubing.
• the porosity of such known knitted products are, however, too high for successful implantation use, that is, the porosity of the knitted material is in excess of that necessary to provide good long-term healing characteristics and that preventing undue hemorrhaging at implantation.
• Porosity of the knitted material is measured on the Wesolowski scale and by the procedure of Wesolowski. In the Wesolowski test, the fabric r test piece is clamped flatwise and subjected to a column of water at a constant pressure head of 120 mm. of mercury. Readings are obtained which express the number of milliliters of water permeating per minute through each square centimeter of fabric. The meter scale reads in units expressive of such water porosity ranging from absolute impermeability of zero upwardly through the range of 1,000, 2,000, etc., to a value of 20,000 as equivalent to free flow.
• the porosity of the synthetic inter-cardiac graft should be from about 30 to about 5,000, preferably from about 2,000 to about 4,000, on the Wesolowski scale.
• Knitted fabric material e.g., tubing or flat stock
• Knitted fabric material e.g., tubing or flat stock
• Knitted fabric material e.g., tubing or flat stock
• Knitted fabric material e.g., tubing or flat stock
• the knitted fabric material therefore must be compacted or shrunk, generally at least about 30 and preferably at least about 40 percent in the wale direction, in order to provide a synthetic inter-cardiac prosthesis having the requisite characteristics.
• the knitted polyester fabric material is thus immersed in a compacting solution for a time sufficient to compact the fabric material at least about 30, preferably at least about 40 percent measured in the wale direction.
• the compacting solution can be any solution, liquid, mixture or single solvent which will compact or shrink the knitted fabric material the amount necessary to provide the product having the desired characteristics.
• the compacting solution is a mixture of two or more components which yield, in combination, a suitable solution.
• the compacting solution may consist essentially of a minor proportion, e.g., 2 to 10 percent, of an acidic organic component and a major proportion, e.g., 98 to percent, of a liquid halogenated aliphatic hydrocarbon having up to 6 carbon atoms.
• the compacting solution contains a mixture of from about 4 to about 8 percent by weight of the total solution of the solvent and from about 96 to about 92 of the shrinking agent.
• the mixed solution should preferably have a solubility parameter about that of the polyester tubing material.
• the solubility parameter is a measure of the cohesive energy of a substance. Solubility parameters for liquids can be calculated from the heats of vaporization and molar volumes of the liquids in a manner known to those skilled in the art- Solubility parameters of many liquids have been published or may be derived from the known physical characteristics of these liquids. Solubility parameters for synthetic polymeric materials such as polyesters are usually determined experimentally by measuring the swelling of the polymer in various solvents of known solubility parameters. The solubility parameter of polyethylene terephthalate (Dacron) has been determined to be l0.7. The compacting solution should have a solubility parameter of from about 9.1 to about 11.0 in order to shrink the polyethylene terephthalate fabric material at least about 30 percent in the wale direction.
• the acidic organic component may be any liquid or solid organic material having acidic (i.e., esterforming) properties, which is soluble in the liquid halogenated aliphatic hydrocarbon material and which will function in solution to compact the polyester fabric material the necessary amount. Often the acidic organic component is a liquid which is a solvent for the polyester fabric material.
• Typical acidic organic components useful in a polyethylene terephthalatecompacting solution include organic acids such as benzoic acid and trichloroacetic acid, phenolic compounds such as phenol meta-cresol, parachlorophenol, halogenated lower alkanols such as hexafluoroisopropanol and also compounds such as hexafluoroacetone propylene adduct and hexafluoroacetone sesquihydrate.
• the liquid halogenated aliphatic hydrocarbon component can have up to 6 carbon atoms.
• Typical liquid halogenated aliphatic hydrocarbons useful as components for compacting the polyethylene terephthalate include methylene chloride, chloroform, tetrachloroethane and ethylene dichloride.
• liquid halogenated aliphatic hydrocarbon materials are known shrinking agents for the polyester. None of these materials, however, is known to shrink the knitted polyester fabric materials at least about 30 percent in the wale direction.
• Preferred compacting solutions for use with knitted polyethylene terephthalate fabric materials include solutions of from about 4 to about 8 percent by weight of either hexafluoroisopropanol or trichloroacetic acid and from about 96 to about 92 percent by weight of methylene chloride.
• the solubility parameter of the solution is determined by the volume fraction of each component, that is,
• S is the solubility parameter of the mixture
• V is the volume fraction of the first component
• S is the solubility parameter of the first component
• V is the volume fraction of the second component
• S is the solubility parameter of the second component
• the knitted tubing is immersed in the compacting solution for a time sufficient to compact the tubing at least about 30, preferably at least 40, percent measured in the wale direction.
• the compacted knitted tubing has a porosity sufficient to impart good,.long-term healing effects to the prosthesis without substantial hemorrhaging at time of implantation.
• the tubing is immersed in the compacting solution for from about l5 seconds to about 30 minutes, preferably from about immersion is peiffifia'i a temperature of f ro rn about I 6 l to about 5 minutes.
• the compacted knitted tubing generally will have a porosity, measured on the Wesolowski scale, of from about 30 to about 5,000, preferably from about 2,000 to about 4,000.
• Immersion of the knitted tubing in the compacting solution can generally be performed at a temperature of from above the freezing point of the solution up to about the boiling point of the solution.
• the temperature of the knitted tubing in the compacting solution can generally be performed at a temperature of from above the freezing point of the solution up to about the boiling point of the solution.
• the tubing may be suitably immersed into the' compacting solution in any suitable bath-type apparatus.
• Solution to sample ratios may vary from about 10:! to about 50:1 or more, e.g., up to about 100:1 (by weight).
• the tubing may be removed from the compacting solution, washed and dried (preferably at or near ambient temperatures) to remove all traces of the compacting solution and wash liquid.
• the tubing may then be prepared for use as intercardiac implants.
• the compacted knitted tubing may then be micro-crimped to improve flexibility and handling and sterilized. Suitable micro-crimping procedures are known in the art and are shown, for example, in U.S. Pat. No. 3,096,560, which patent is assigned to the same assignee as the present invention and which is herein incorporated by reference and in U.S. Pat. No. 3,337,673.
• ExAMPLE i A large number of solutions are prepared. Samples'of 40-denier knitted polyethyleneterephthalate (solubility parameter of 10.7) bifurcated tubing are immersed in the liquid systems for 10 minutes at room temperature (i.e., 20C.) except as indicated. A 20:1 liquid to sample ratio is used.
• the treated samples are removed, quenched in a water bath containing 1 weight percent of a watersoluble surfactant Triton X-l00, (an ethoxylated octyl phenol) sold by the Rohm and Haas Co., rinsed in tap water and dried at.lO0C. for 5 minutes.
• Triton X-l00 an ethoxylated octyl phenol sold by the Rohm and Haas Co.
• HFAPMA Hexafluoroacctone propylene monoadduct clv HFA Hcxatluoroacctonc scsquihydrate
• a number of other common solvents such as benzene (solubility parameter of 9.15), methanol (solubility parameter of 14.5), ethanol, dichloroethylene, trichloroethylene and 1,2,4-trichlorobenzene under the same conditions of use cause less than (some less than 10) percent shrinkage in the wale direction.
• liquid systems such as 6% l-lFlP-Valclene one (a fluorinated hydrocarbon solvent composed primarily of trichlorotrifluoroethane, 6% l-llFlP-methanol (solution solubility parameter of 14.3) and 6%-l-lFlP benzene (solution solubility parameter of 9.12) all cause less than 12 percent shrinkage in the wale direction.
• the system of 6% HFlP-tetrachloroethane is not miscible and 6% l-IFIP- carbon tetrachloride stiffens the fabric without shrinking.
• EXAMPLE II The hexafluoroisopropanol-methylene chloride system is studied in more detail in this Example.
• Methylene chloride is a known shrinking agent for polyesters such as polyethylene terephthalate (see, for example U.S. Pat. No. 2,981,978) and hexafluoroisopropanol is a known solvent for polyesters such as polyethylene terephthalate (see, for example, U.S. Pat. No. 3,418,337.
• Samples of 40denier polyethylene terephthalate tubing (wall thickness of 0.2 mm.) are immersed in methylene chloride solutions containing 3, 5, 6, 7, 7.5, 8 and i Table II below.
• the amount of shrinkage in the wale direction is relatively constant for both 40- and 70-denier tubing samples for all the solutions containing hexafluoroisopropanol and methylene chloride.
• measurement of the treated samples show that the wall thickness of each sample has increased.
• the wall thickness of the compacted 40-denier samples is about 0.3 mm. and 70-denier samples show about 0.4 mm. wall thickness.
• EXAMPLE Ill The effect of immersion time on the amount of shrinkage of a particular compacting solution is investigated by immersing 40- and 70-denier polyethylene terephthalate tubing samples of the type used in Example ll in a mixed solution of 6 percent by weight of hexafluoroisopropanol and 94 percent by weight of methylene chloride for l, 5, l and 30 minutes at room temperature (C.) and a 10:1 solutionzsample ratio. The compacted samples are rinsed, dried and measured as in Example I. As shown in Table III below, essentially all of the shrinkage occurs within5hiinutesandfufilief changes essentially do not occur beyond 5 minutes.
• Example IV The 40-denier, 5-minute immersion sample of Example III is crimped in accordance with the teachings of US. Pat. No. 3,337,673. The resulting, crimped tubing is cooled, dried and sterilized and is suitable for use as a vascular prosthesis.
• Example II is repeated for the trichloroacetic acidmethylene chloride system. Optimum results are again obtained with a solution containing about 6 to about 8 percent by weight of trichloroacetic acid and from about 94 to about 92 percent by weight of methylene chloride.
• Example III A 6 percent by weight solution of trichloroacetic acid in 94 percent by weight of methylene chloride is used as the compacting solution and Example III is repeated. It is again found that essentially all of the shrinkage occurs within 5 minutes.
• EXAMPLE v1 Flat stock material samples of knitted polyethylene terephthalate made from 40- and 70-denier filaments are immersed in compacting solutions of 6 percent hexafluoroisopropanol-94 percent methylene chloride and 6 percent trichloroacetic acid-94 percent methylene chloride at 20C. for 5 minutes (40:1 solution to sample ratio). Examination of the treated samples shows that the flat stock has shrunk essentially the same amount in the wale direction as comparable knitted samples.
• ADVANTAGES OF THE INVENTION present invention compacts or shrinks the material to a porosity which provides suitable long-term healing effects without undue hemorrhaging at implantation.
• the compacted knitted material produced by the present invention remains smooth-surfaced and has small, uniform interstices.
• the preclotting efficiency of the compacted material is high. Preclotting of the compacted material prior to implantation in a manner known to those skilled in the art substantially fills these small interstices making the implant device substantially impervious.
• a process for preparing a synthetic vascular prosthesis comprising the steps of:
• a knitted synthetic linear polyester fabric tubing material having a uniform porosity, measured on the Wesolowski scale, above about 7,500 up to about 20,000 and in excess of that suitable for long-term healing effects without undue hemorrhaging at implantation;
• a compacting solution consisting essentially of from about 2 to about 10 percent by weight of an acidic organic component selected from the group consisting of hexafluoroisopropanol, phenol, meta-cresol, hexafluoroacetone propylene adduct, trichloroacetic acid, parachlorophenol and hexafluoroacetone sesquihydrate and about 98 to about percent by weight of a halogenated aliphatic hydrocarbon selected from the group consisting of methylene chloride, chloroform, tetrachloroethane and ethylene dichloride until said fabric material uniformly shrinks at least about 30 percent measured in the wale direction and the porosity of the said fabric material is, measured on the Wesolowski scale,
• a process for preparing a synthetic vascular prosthesis which comprises the steps of: V w
• a process for reducing the porosity of a uniformly porous knitted synthetic linear polyester fabric material which comprises contacting said fabric with a compacting solution containing a minor proportion of a solvent for the polyester and a major proportion of a shrinking agent for the polyester for a time sufficient to uniformly compact said fabric at least about 30 percent measured in the wale direction of the fabric, said solvent being selected from the group consisting of hexafluoroisopropanol, phenol, meta-cresol, hexafluoroacetone propylene adduct, trichloroacetic acid, parachlorophenol and hexafluoroacetone sesquihydrate, and said shrinking agent being selected from the group consisting of methylene chloride and chloroform, said solution having a solubility parameter approximately that of the polyester, said solubility parameter of the solution being defined in accordance with the following:
• S is the solubility parameter of the solution
• V is the volume fraction of the solvent component
• S is the solubility parameter of the solvent component
• V is the volume fraction of the shrinking agent component
• S is the solubility parameter of the shrinking agent component
• said compacting solution contains from about 2 to about 10 percent by weight of the solution of the solvent for the polymer and from about 98 to about 90 percent by weight of the shrinking agent for the polymer.
• a process for reducing the porosity of a uniformly porous, relatively smooth-surfaced knitted synthetic linear polyester tubing which comprises immersing said tubing in a compacting solution for a time sufficient to uniformly compact said tubing at least about 30 percent measured in the wale direction of the tubing without appreciable distortion of the smooth surface of the tubing, said compacting solution containing a mixture of from about 2 to about 10 percent by weight of hexafluoroisopropanol and from about to about 98 percent by weight of methylene chloride; and removing all traces of said compacting solution from said compacted fabric.
• a process for preparing a synthetic inter-cardiac prosthesis comprising the steps of:
• a compacting solution consisting essentially of from about 2 to about 10 percent by weight of an acidic organic component selected from the group consisting of hexafluoroisopropanol, phenol, meta-cresol, hexafluoroacetone propylene adduct, trichloroacetic acid, parachlorophenol and hexafluoroacetone ses quihydrate and about 98 to about 90 percent by weight of a halogenated aliphatic hydrocarbon selected from the group consisting of methylene chloride, chloroform, tetrachloroethane and ethylene dichloride until said fabric material uniformly shrinks at least about 30 percent measured in the wale direction and the porosity of the said fabric material is, measured on the Wesolowski scale, from about 30 to about 5,000 and suitable for longterm healing effects without undue hemorrhaging at implantation;
• an acidic organic component selected from the group consisting of hexafluoroisopropanol, phenol, meta-cresol
• Claim 8 line 13, delete "5 to about 15'' and insert therefor -l5 seconds to about 30-- Claim 14, line 3, delete '30" first occurence and insert therefor -l5-- Claim 15, line 3, delete "5 to about 15” and insert therefor --l to about 5- Signed and sealed this 30th day of June 1975.

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• Engineering & Computer Science (AREA)
• Health & Medical Sciences (AREA)
• Textile Engineering (AREA)
• Biomedical Technology (AREA)
• Vascular Medicine (AREA)
• Cardiology (AREA)
• Oral & Maxillofacial Surgery (AREA)
• Transplantation (AREA)
• Gastroenterology & Hepatology (AREA)
• Heart & Thoracic Surgery (AREA)
• Pulmonology (AREA)
• Life Sciences & Earth Sciences (AREA)
• Animal Behavior & Ethology (AREA)
• General Health & Medical Sciences (AREA)
• Public Health (AREA)
• Veterinary Medicine (AREA)
• Materials For Medical Uses (AREA)
• Prostheses (AREA)
• Treatments For Attaching Organic Compounds To Fibrous Goods (AREA)

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Cited By (37)

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Citations (6)

• 1972
  • 1972-02-23 US US00228722A patent/US3853462A/en not_active Expired - Lifetime
• 1973
  • 1973-02-16 CA CA163,912A patent/CA1002708A/en not_active Expired
  • 1973-02-19 GB GB812173A patent/GB1370293A/en not_active Expired
  • 1973-02-22 DE DE19732308729 patent/DE2308729A1/de active Pending
  • 1973-02-22 JP JP48020750A patent/JPS4893793A/ja active Pending
  • 1973-02-23 FR FR7306454A patent/FR2173234B1/fr not_active Expired

Patent Citations (6)

Non-Patent Citations (1)

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