Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
  • C08J9/28—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
  • A61L27/14—Macromolecular materials
  • A61L27/16—Macromolecular materials obtained by reactions only involving carbon-to-carbon unsaturated bonds
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61L—METHODS OR APPARATUS FOR STERILISING MATERIALS OR OBJECTS IN GENERAL; DISINFECTION, STERILISATION OR DEODORISATION OF AIR; CHEMICAL ASPECTS OF BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES; MATERIALS FOR BANDAGES, DRESSINGS, ABSORBENT PADS OR SURGICAL ARTICLES
  • A61L27/00—Materials for grafts or prostheses or for coating grafts or prostheses
  • A61L27/50—Materials characterised by their function or physical properties, e.g. injectable or lubricating compositions, shape-memory materials, surface modified materials
  • A61L27/507—Materials characterised by their function or physical properties, e.g. injectable or lubricating compositions, shape-memory materials, surface modified materials for artificial blood vessels
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C43/00—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
  • B29C43/02—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor of articles of definite length, i.e. discrete articles
  • B29C43/20—Making multilayered or multicoloured articles
  • B29C43/203—Making multilayered articles
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
  • B29C55/005—Shaping by stretching, e.g. drawing through a die; Apparatus therefor characterised by the choice of materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C43/00—Compression moulding, i.e. applying external pressure to flow the moulding material; Apparatus therefor
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2023/00—Use of polyalkenes or derivatives thereof as moulding material
  • B29K2023/04—Polymers of ethylene
  • B29K2023/06—PE, i.e. polyethylene
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2201/00—Foams characterised by the foaming process
  • C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
  • C08J2201/052—Inducing phase separation by thermal treatment, e.g. cooling a solution
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2201/00—Foams characterised by the foaming process
  • C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
  • C08J2201/054—Precipitating the polymer by adding a non-solvent or a different solvent
  • C08J2201/0542—Precipitating the polymer by adding a non-solvent or a different solvent from an organic solvent-based polymer composition
  • C08J2201/0543—Precipitating the polymer by adding a non-solvent or a different solvent from an organic solvent-based polymer composition the non-solvent being organic
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2201/00—Foams characterised by the foaming process
  • C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
  • C08J2201/054—Precipitating the polymer by adding a non-solvent or a different solvent
  • C08J2201/0545—Precipitating the polymer by adding a non-solvent or a different solvent from an aqueous solvent-based polymer composition
  • C08J2201/0546—Precipitating the polymer by adding a non-solvent or a different solvent from an aqueous solvent-based polymer composition the non-solvent being organic
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
  • C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
  • C08J2323/04—Homopolymers or copolymers of ethene
  • C08J2323/06—Polyethene

Definitions

• This invention relates to a novel ultra-high- molecular-weight polyethylene product, useful for vascular prosthesis devices and for both industrial and biomedical uses calling for high-impact/ low-friction, high wearresistance, high-porosity, and softness or for one or more of these qualities.
• the invention also relates to such devices. It further relates to a novel method for processing solution-grown ultra-high molecular weight polyethylene crystalline morphologies which may form pseudo-gel states when the polymer is dissolved in a suitable volatile or non-volatile solvent at an elevated temperature and the solution is cooled to or below the temperature at which the polymer crystals are grown. Additionally it relates to methods involving further processing of the pseudo-gel states and their products after solvent extraction into profiles and shapes with physical and mechanical properties that may be tailored to specific biomedical (e.g., vascular and orthopedic prosthesis and sutures) and industrial applications.
• biomedical e.g., vascular and orthopedic prosthesis and sutures
• vascular prostheses have been developed a subject of extensive work over the last 25 years.
• Most synthetic vascular prostheses have been products of the application of textile technology in this field and have been woven or knitted tubular structures designed to resemble the softness and flexibility of the natural blood vessels.
• the two major synthetic polymers used as vascular prostheses have been Dacron polyester and polytetra- fluoroethylene (PTFE). These woven or knitted tubular structures are porous and have been produced with smooth or veiour surfaces.
• the porosity which has been claimed to play a determinant role for the healing process of the arterial prostheses, can be controlled to some extent by adjusting the thread size, or the interstices size, and by the textur ization or knit pattern of the synthetic fabric. High degrees of porosity may lead to excessive blood loss after implantation; the veiour has been claimed to have the advantage that it fills the interstices of the underlying fabric, thus reducing implant bleeding without reducing the porosity of the implant.
• the DeBakey Ultra-light-weight Knitted Prosthesis (USCI, Inc.), the Cooley Graft and the Wesolowski Weavenit (Meadox, Inc.) and the Microknit (Golaski Lab, Inc.) are "smooth wall" commercial Dacron arterial prostheses of different geometric and compositional configurations; the Sauvage Filamentous Veiour Prosthesis (USCI, Inc.) is an example of a veiour Dacron vascular prosthesis material.
• Woven PTFE prostheses have low porosity and have not been used as much as the Dacron prostheses. Also, it has been suggested that their use should be temporary, their permanent use being “dangerous”. More recently, “expanded” PTFE, called “Gore-tex” (W. L. Gore & Assoc, Inc.) has become available. “Gore-tex” is a network of small nodules interconnected by thin fibrils and with an adjustable porosity from 0 to 96%, and it has been used with generally encouraging results.
• UHMWPE Ultra-high-molecular-weight polyethylene
• UHMWPE in contrast to the conventional high-density poly- ethylenes having average molecular weights up to approximately 400,000, has an extremely high molecular weight, typically 2 - 8 million, and is intractable.
• the polymer is supplied as fine powder and is processed into various profiles using compression molding and ram extrusion processes.
• the intractability of the polymer can be overcome by varying the degree of material cohesion and its initial morphology, more specifically by the formation of gel states and single-crystal mat morphologies and by heating the polymer melt to high temperature ranges, under inert conditions, in which the viscosity of the melt is reduced significantly for melt processing.
• the porosity of the resultant fiber is stated to be "no more than about 10% (preferably no. more than about 6% and more preferably no more than about 3%)".
• S_ummary of the Invention includes the formation and use of UHMWPE pseudo-gels.
• gel in the prior art referred to a macroscopically coherent structure, that (1) is spatially cross- linked, (2) comprises a major amount of low molecular-weight liquid, and (3) exhibits elastic properties not unlike those of solids.
• the terms "pseudo-gel” and “gel-like” refer to a concentrated solution of organic polymer which contains an entangled three-dimensional semicrystalline network the morphology of which may vary with the conditions of preparation or crystallization, for example, when the pseudo-gel of this invention is prepared under isothermal and quiescent conditions, the crystals in the pseudo-gel have predominantly a lamellar morphology, with single crystals on spherulitic crystals. The number of single crystals decreases, and the crystalline morphology becomes more complex as the solution concentration increases.
• the pseudo-gel of this invention when the pseudo-gel of this invention is prepared under non-isothermal and qu i e scent cond i tions , a large frac tion of ex tended chain crystals (shish-kebab crystals) are also present.
• a large frac tion of ex tended chain crystals (shish-kebab crystals) are also present.
• the molecular entanglements in this semicrystalline network are not permanent, such solutions undergo flow when a shear stress, no matter how small, is applied. Therefore, such pseudo-gels exhibit time-dependent elastic properties and are not true gels, as the term is properly used, because they do not possess an equilibrium shear modulus.
• the present invention provides for the preparation of an UHMWPE crystalline morphology with isotropic mechanical properties from a pseudo-gel precursor.
• This invention provides a method for the preparation of UHMWPE vascular prostheses by processing the UHMWPE in the pseudo-gel state.
• the pseudo-gel is prepared by dissolving a suitable concentration of the polymer in a suitable solvent, preferably a non-volatile solvent, at an elevated -temperature well above the temperature at which the pseudo-gel forms and then cooling to or below the temperature at which the polymer crystals grow and the pseudo-gel forms.
• the pseudo-gel is subsequently processed under compression or tension into products of different profiles. Extraction of the solvent from the shaped pseudo- gel products leads to semi-crystalline porous morphologies with geometrical configurations analogous to those of their pseudo-gel precursors. These morphologies may be processed further, at a temperature below or close to their melting point.
• This invention provides also a method for the construction of vascular prostheses by (a) compressing the pseudo-gels into thin films between hot plates, e.g., at
• This invention also provides for the preparation of anisotropic UHMWPE morphologies with enhanced mechanical properties, obtained by solid-state deforming, i.e., at a temperature near or below the melting point of UHMWPE, the semicrystalline polymer after extraction of the solvent, by extrusion, drawing, molding, and forging techniques.
• This invention also provides for the preparation of an UHMWPE semicrystalline material which has adjustable porosity from zero up to more than 90%.
• This material can be made with sufficient body to maintain its shape and cross- sectional area; it is uniformly expansive and readily deformable to generate products with bulk properties, in contrast to filamentary products.
• Fig. 1 is a flow sheet of a process embodying the principles of the invention.
• Fig. 2 is a flow sheet of another process embodying the principles of the invention.
• Fig. 3 is a flow sheet of a third process embodying the principles of the invention.
• Fig. 4 is an optical photomicrograph at about 100x of a UHMWPE pseudo-gel morphology prepared under non- isothermal and quiescent conditions (NIQ). The morphology was viewed with cross-polarized light.
• NIQ non- isothermal and quiescent conditions
• Fig. 5 is a reproduction of a scanning electron micrograph of a UHMWPE semicrystalline morphology obtained from the pseudo-gels after solvent extraction and drying, according to the invention, the pseudo-gel having been prepared under isothermal and non-quiescent conditions (INQ).
• Fig. 6 is a similar scanning electron micrograph reproduction of a greater enlargement of the same kind of UHMWPE semicrystalline morphology of this invention the pseudo-gel having been prepared under isothermal and non- quiescent conditions (INQ).
• Fig . 7 is an optical photomicrograph at about 100x of a UHMWPE pseudo-gel morphology obtained under i sothermal and non-quiescent condi tions ( INQ) . The morphology was viewed with cross-polar ized light.
• F ig . 8 is a similar scanning electron micrograph reproduction of a semicrystalline UHMWPE morphology of the invention obtained from the pseudo-gel after solvent extracting and drying, the pseudo-gel having been prepared under isothermal and quiescent conditions ( IQ) .
• Fig . 9 is an optical photomicrogr aph at about 100x of a UHMWPE pseudo-gel morphology obtained under isothermal and quiescent cond itions (IQ) .
• the morphology was v iewed with cross-polar ized light.
• Fig. 10 is a graph plotting Young's modulus versus draw ratio for a UHMWPE of this invention.
• the solid-line curve represents observed values and the broken-line curve shows estimated maximum values for the UHMWPE of this invention.
• an UHMWPE pseudo-gel according to this invention may be prepared from a raw UHMWPE powder 20 by dissolving the UHMWPE in a solvent at 21, preferably a non-volatile solvent such as paraffin oil, in a temperature range from 140 - 170°C, preferably in the high end of the temperature range in order to disrupt the thermally per s istent ex tended chain morphology of the raw UHMWPE powder and decrease the number of nucleation s i tes which allow for the prepar ation , upon cooling , of large lamellar single crystals .
• a solvent at 21 preferably a non-volatile solvent such as paraffin oil
• the polymer is preferably stabilized with approximately 0.5 wt. % (based on the polymer) of BHT antioxidant (butyl hydroxy toluene) and heated under inert conditions. The mixtures were stirred slowly under constant conditions at a temperature of 150°C. A solution 22 was obtained that appeared clear until it was cooled in step 23 to a temperature of approximately 123°C, where it became opaque as the pseudo-gel was formed.
• BHT antioxidant butyl hydroxy toluene
• the uniformity of a so-produced UHMWPE pseudo-gel 24 depends on the conditions of preparation.
• NIQ non-isothermal and quiescent conditions
• the UHMWPE pseudo-gel is non-uniform and is comprised of a mixture of single crystals and a fib ⁇ llar network in which the fibrils have a shish-kebab crystalline morphology; the shish kebab fibrils in the UHMWPE pseudo-gel can be up to 2 - 3 mm. long and 20 ⁇ m. wide.
• This non-uniform structure is shown in Fig. 4.
• the semicrystalline morphologies in Figs. 5 and 6 were obtained from the pseudo-gel shown in Fig.
• Fig. 7 which was prepared under isothermal and non-quiescent conditions, herein called INQ. These semicrystalline morphologies were prepared by solvent extraction of the pseudo-gel followed by drying.
• Fig. 5 is a scanning electron micrograph of such a semicrystalline morphology; the degree of magnification is shown by the white bar which corresponds to 0.1 mm. in the actual semicrystalline morphology. A further magnification is shown in Fig. 6, when the white bar corresponds to 10 ⁇ m.
• Fig. 7 is taken from an optical photomicrograph of the pseudo-gel at about 100x and shows a typical shish-kebab fibrillar structure surrounded by randomly oriented single crystals and stacks of single crystals, as viewed with cross-polarized light.
• the different crystalline morphologies of the UHMWPE pseudo-gels obtained under different conditions of preparation can be ascertained also by the thermal behavior of the semicrystalline UHMWPE products which are obtained by extracting, in step 25, the paraffin oil from the pseudo-gel precursor with a more volatile solvent such as hexane, and subsequently evaporating out, step 26, the volatile solvent off in a drying process, leaving a semicrystalline UHMWPE morphology 27.
• the results of the thermal analysis are summarized in Table I.
• the first column of Table I indicates the percent concentration of the gel-like precursor, the second column the melting temperature of the semicrystalline morphologies after the evaporation of the volatile solvent, and the third column the percent crystallinity of these semicrystalline morphologies.
• the melting endotherms were obtained at
• the thermal analysis results indicate that the melting temperature of the semicrystalline structures is independent of the concentration of the gel-like precursors which were obtained under non-isothermal non-quiescent conditions; however, it is lower when the gel-like precursor was prepared under isothermal and quiescent conditions.
• the higher melting endotherm of the crystalline structures at approximately 137°C. from pseudo-gels which were prepared under non-isothermal or non-quiescent conditions indicates that the crystals should have an extended chain configuration and is in agreement with the optical observations (e.g., Fig. 4) that so-produced pseudo-gels are comprised to a large extent of a shish kebab fibrillar network.
• Figs. 8 and 9 indicates that the crystals in this case have a chain-folded configuration, and, again, this is in agreement with the observation that the isothermally produced pseudo-gels under quiescent conditions are comprised of chain-folded crystals, like the stacks of single crystals and spherulites shown in Figs. 8 and 9. Also, it is clear from the data in Table I that the percent crystallinity of the semicrystalline structure is independent of the studied concentration range of its gel-like precursors as well as its processing history.
• a semicrystalline UHMWPE structure which is prepared from a pseudo-gel intermediate combines morphological features which cannot be exhibited by the morphologies obtained either by compacting the as-received fine powder stock or by melt crystallization. These morphological features arise from (a) the controlled material cohesion which is incomplete in the compacted powders and the meltcrystallized morphologies prepared by partial fusion.
• the intrinsic fibrillar networks of this invention have the advantage that their porosity can be adjusted by thermal and mechanical means.
• Thermal treatment may be brought about by heating the semicrystalline structure from a gel-like precursor to a temperature close to or above the melting point of the polymer and then cooling to ambient under modest compression ( ⁇ approximately 50 Atm). This treatment resulted in a significant porosity reduction.
• the porosity was calculated from density determination, assuming that the density of polyethylene is 960 kgm -3 .
• NIQ indicates that the gel-like precursor was prepared under non-isothermal and quiescent conditions
• INQ indicates that the gel-like precursor was prepared under isothermal and non-quiescent conditions
• iQ indicates that the gel-like precursor was prepared under isothermal and quiescent conditions.
• SSD indicates a semicrystalline morphology from an NIQ-pseudo-gel which was de formed in the sol id state by tens i le drawing at ambient temperature and at the indicated Draw Ratio (DR) de termined by the cross-sectional areas before and after drawing .
• DR Draw Ratio
• UHMWPE pseudo-gel states contain- ing preferably a non-volatile solvent can be processed by molding or rolling under compression in step 31 to obtain thin gel-like film 32, preferably in a temperature range close to or above the temperature at which the pseudo-gel is formed (approximately 123°C.).
• the thin pseudo-gel film 32 can be wrapped in step 33 with or without tension on a mandrel to give a multilayer tubular structure", a process which allows also for the build up of the tubular wall thickness. Cohesion of the successive pseudo-gel layers is achieved by a molecular reptation process which may occur between adjacent layers and result in a tubular wall with fraying resi.stance.
• the volatile solvent such as n-hexane replaced the non-volatile solvent in step 25 and is removed by evaporation in step 34, to give a moderately shrunk, hoop stressed structure 35, in a drying step.
• the evaporation of the volatile solvent from the pseudo-gel is accompanied by considerable shrinkage, which when constrained has the advantage of resulting in the development of hoop stresses which enhance (a) the molecular chain orientation in the circumferential direction and consequently the lateral strength of the tubular structures and (b) the molecular chain interpenetration in the overlapping pseudo-gel layers, thus resulting in a coherent tubular wall.
• tubular products 37 having a biaxially oriented fibrillar network structure with mechanical integrity along and across the draw direction. This integrity results from the superposition of the circumferential orientation, which is obtained by the constrained shrinkage during the evaporation of the volatile solvent, and the axial orientation during the solid-state deformation process on the mandrel.
• the solid-state deformation was performed at ambient temperature, and the draw ratio (DR) was calculated from the displacement of markers on the tubular wall after drawing.
• Fig. 10 shows in a solid line curve average experimental modulus values at different draw ratios.
• the variation of experimentally determined initial modulus with the draw ratio is non-linear for the solid-state-drawn UHMWPE semicrystalline morphologies of this invention to a draw ratio of 8, in contrast to the previously established linear relation for melt-crystallized, high-density (not ultra-high molecular weight) polyethylene resins shown in Fig. 11; the difference is presumably due to the high porosity of the UHMWPE semicrystalline morphologies, in comparison to the low-porosity, melt-crystallized, high- density polyethylenes, which diminishes and allows for effective load transmission at significantly higher draw- ratios.
• Fig. 10 shows in a solid line curve average experimental modulus values at different draw ratios.
• the variation of experimentally determined initial modulus with the draw ratio is non-linear for the solid-state-drawn UHMWPE semicrystalline morphologies of this invention to a draw ratio of 8, in contrast
• FIG. 10 shows in a broken-line curve a graph of experimentally determined maximum initial modulus values from my new material at different draw ratios.
• Fig. 3 shows a process much like that of Fig. 2.
• Pieces of pseudo-gel 40 are compressed at step 41 to make a gel-like sheet 42.
• the sheet 42 is wrapped around a mandrel 43 to produce a gel-like tube 44, which is then extracted at 45 to give a dry tube 46.
• This may be further processed, as at 47, as by drawing, or may be received from the mandrel 43 to give a vascular product 48.
• Alternative methods for the preparation of tubular products with a biaxially oriented fibrillar network structure include processes such as solid-state extrusion through inverted conical dies and blowing air through the tubes.
• Both processes are also suitable for the preparation of biaxially oriented UHMWPE films which can be obtained by splitting the biaxially oriented tubes along their length.
• some or most of the conventional thermoplastic processes such as rolling, extrusion, drawing, compression molding, forging, and extrudo-rolling are amenable to processing UHMWPE semicrystalline morphologies from gel-like precursors into products with different profiles and geometric configurations and with adjustable mechanical properties over a wide range. Tests in vivo indicate that artificial vascular prostheses made by this process can be handled conveniently and sutured to the natural vascular system readily.
• the vascular prostheses, isotropic UHMWPE semicrystalline tubes approximately 5 - 6 cm.
• the vascular prostheses of this invention can be fabricated in different geometric configurations, straight, crimped, smooth, or rough wall surfaces with adjustable porosities and mechanical properties over a wide range.
• this invention includes within its scope the use of isotropic and anisotropic UHMWPE morphologies from gel-like precursors in other biomedical application, such as orthopedic prostheses, sutures, and ligatures, in which a suitable combination of porosity and mechanical properties is necessary.
• Other polymers which fall in the same category and can be obtained from gel-like precursors are ultra-high- molecular-weight polypropylene, polyvinyl alcohol, and nylons (polyamides).
• Such embodiments may include the fabrication of UHMWPE knitted and woven vascular prostheses , sutures , and composite structures of UHMWPE filamentary and non- filamentary semicrystalline morphologies.
• the disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting. What is claimed is :

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• Health & Medical Sciences (AREA)
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• Engineering & Computer Science (AREA)
• Medicinal Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Public Health (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Oral & Maxillofacial Surgery (AREA)
• Transplantation (AREA)
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• 1985
  • 1985-10-22 EP EP19850905473 patent/EP0198904A1/de not_active Withdrawn
  • 1985-10-22 AU AU50172/85A patent/AU5017285A/en not_active Abandoned
  • 1985-10-22 WO PCT/US1985/002078 patent/WO1986002656A1/en unknown
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