Compaction Of Polyester Fabric Materials

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 mixture 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.

Description

BACKGROUND OF THE INVENTION

It is often desirable for synthetic textile materials to have a stable, controlled porosity structure. A particularly demanding end use for such compact synthetic textile structures is as flat stock or tubing material adapted to replace human arteries or to be used as patches in repairing hernias or the like. Materials of these types are otherwise known as synthetic inter-cardiac grafts or prostheses. Synthetic vascular prostheses, an important type of inter-cardiac prostheses, for use in the repair and replacement of vessels and tracts in human and animal bodies are shown, for example, in U.S. Pat. Nos. 2,978,787 and 3,096,560.

There are certain necessary characteristics essential to the successful performance of a synthetic inter-cardiac or vascular prosthesis in an animal or human body. These characteristics include a porosity sufficient to promote optimum healing while preventing undue hemorrhaging at implantation, a relatively thin thickness of the fabric material (e.g., about 0.1 mm. to 0.3 mm., wall thickness of the tubing, about the same wall thickness as the average wall of a natural blood vessel of about the same diameter), flexibility, strength and resilience sufficient to withstand body stresses, compatibility with human tissues and sterilization capability.

Synthetic vascular prostheses have been made from tubing materials such as extruded plastic tubing, seamless braided and knitted tubing, cut and Jacquard-woven 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.

Similar disadvantages have occurred with the manufacture and use of flat stock material for use as an inter-cardiac prosthesis. e.g., as a hernia patch or ligature or in general surgical or orthodontical use.

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.

As known in the art, 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 of fibrous 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. Thus, 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.

It is also known, however, that implantation of a synthetic prosthesis having a high porosity generally more suitable for long-term healing effects may result in undesirable hemorrhaging as the blood stream is allowed to pass through the graft following the initial implantation. The porosity of the synthetic prosthesis thus should be balanced between that necessary to provide good long-term healing characteristics and that preventing undue hemorrhaging at implantation.

Knitted tubing offers many advantages of strength, flexibility adn ease of handling. In addition, 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. However, as noted before, 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 inter-cardiac prosthesis. Even the finest knitted fabric material has this excessive porosity.

It is an object of this invention to provide a process for the production of knitted flat stock or tubing of synthetic material suitable for use as synthetic inter-cardiac prostheses.

It is a further object of this invention to provide a relatively rapid and inexpensive process for the production of knitted flat stock or tubing of fine filamentary polymeric materials which tubing has porosity characteristics to allow for good healing.

It is also an object of this invention to provide a process for the production of knitted fabric material having a constant porosity throughout the length of the material.

It is another object of this invention to provide a process for producing a synthetic inter-cardiac prosthesis having excellent physical and handling characteristics.

It is another object of this invention to provide a process for producing knitted tubing of fine filamentary polyester materials which are suitable for use as synthetic vascular prostheses.

It is another object of this invention to provide a process for producing synthetic knitted polyester patches for use as synthetic intercardiac prostheses.

It is another object of this invention to provide a compacting solution suitable for use in a process for the production of knitted polyester fabric material having uniform, fine porosity throughout the material.

It is another object of this invention to provide a compacting solution suitable for use in a process for the production of knitted polyester inter-cardiac prostheses.

It is still another object of this invention to provide a compacting solution suitable for use in a process producing a synthetic intercardiac prosthesis having good long-term healing characteristics while preventing undue hemorrhaging at implantation.

SUMMARY OF THE INVENTION

These and other objects of the invention are achieved in one aspect by a process for preparing a synthetic inter-cardiac prosthesis comprising the steps of: (a) providing a knitted polyester fabric material having a porosity 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 10 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.

In another aspect, 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.

DETAILED DESCRIPTION OF THE INVENTION

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. In addition, 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. 10, 1969 now abandoned, assigned to the same assignee as the present invention and herein incorporated by reference. As disclosed therein, 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 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.

It has been found that 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), even that knitted on the finest gauge double needle bar Raschel machine commercially available, however, generally has a porosity of above about 7,500, often above about 8,500, on the Wesolowski scale.

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. Generally, 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 90 percent, of a liquid halogenated aliphatic hydrocarbon having up to 6 carbon atoms. Preferably, 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 10.7. 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., ester-forming) 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 terephthalate-compacting 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.

Often, the 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.

Each of the acidic organic components and liquid halogenated aliphatic hydrocarbon components has its own solubility parameter. The solubility parameter of the solution is determined by the volume fraction of each component, that is,

S.sub.s = V.sub.1 S.sub.1 + V.sub.2 S.sub.2

where S.sub.s is the solubility parameter of the mixture, V.sub.1 is the volume fraction of the first component, S.sub.1 is the solubility parameter of the first component, V.sub.2 is the volume fraction of the second component and S.sub.2 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. Generally, the tubing is immersed in the compacting solution for from about 15 seconds to about 30 minutes, preferably from about 1 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. Preferably, the immersion is performed at a temperature of from about 0 to about 40, most preferably from about 15 to about 30.degree.C. The tubing may be suitably immersed into the compacting solution in any suitable bath-type apparatus. Solution to sample ratios may vary from about 10:1 to about 50:1 or more, e.g., up to about 100:1 (by weight).

After the knitted tubing has been compacted, 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. For example, 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.

Although the invention has been described with reference to knitted polyester fabric materials (such as "Dacron" polyethylene terephthalate), it will be apparent to those skilled in the art that the present invention may also be used to compact knitted fabric materials of other synthetic polymeric materials such as the polyamides (e.g., nylon 66) and polyacrylonitriles (some of which are commercially available as "Orlon" and "Acrilan").

The invention is additionally illustrated in connection with the following examples which are to be considered as illustrative of the present invention. It should be understood, however, that the invention is not limited to the specific details of the examples.

EXAMPLE I

A large number of solutions are prepared. Samples of 40-denier knitted polyethylene terephthalate (solubility parameter of 10.7) bifurcated tubing are immersed in the liquid systems for 10 minutes at room temperature (i.e., 20.degree.C.) 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 water-soluble surfactant "Triton X-100", (an ethoxylated octyl phenol) sold by the Rohm and Haas Co., rinsed in tap water and dried at 100.degree.C. for 5 minutes. Each of the treated samples is examined to determine the amount of shrinkage in the wale direction. The systems which cause 20 percent or greater shrinkage in the wale direction are shown below in Table I.

TABLE I __________________________________________________________________________ Shrinkage Percent System Solubility Parameter in Wale Direction __________________________________________________________________________ Dichloroethane 9.8 21 Dichloromethane 9.7 26-28 Chloroform 9.3 24-26 Dibromomethane 10.4 25 Tetrachloroethane 10.4 21 6% HFIP-methylene chloride.sup.a 9.62 39-40 6% HFIP-chloroform 9.24 35 6% HFIP-dichloroethane 9.72 26 6% Phenol-methylene chloride 10.05 35 10% m-Cresol-methylene chloride 10.08 38 10% HFAPA-methylene chloride.sup.b 38 10% HFAPMA-methylene chloride.sup.c 32 6% Phenol-tetrachloroethane 10.76 34 6% m-Cresol-tetrachloroethane 10.6 34 6% Benzoic acid-tetrachloroethane 10.55 33 6% Trichloroacetic acid-methylene chloride 9.67 40-41 6% p-Chlorophenol-methylene chloride 9.83 36 6% Phenol-chloroform 9.73 36 6% Trichloroacetic acid-chloroform 9.29 35 6% 2-Chloroethanol-chloroform 9.51 30 6% m-Cresol-dichloroethane 10.0 26 6% m-Cresol-chloroform 9.59 33 6% p-Bromophenol-methylene chloride 9.81 33 3% HFA-methylene chloride.sup.d 39 6% HFIP-methylene chloride at 0.degree.C. 9.62 39 3% Trichloroacetic acid-methylene chloride 9.68 36 5% Trichloroacetic acid-methylene chloride 9.67 39 __________________________________________________________________________ a. HFIP - Hexafluoroisopropanol b. HFAPA - Hexafluoroacetone propylene adduct c. HFAPMA - Hexafluoroacetone propylene monoadduct d. HFA - Hexafluoroacetone sesquihydrate

As may be seen from the above data, only systems containing mixtures of methylene chloride (solubility parameter of 9.7) or chloroform solubility parameter of 9.3) with hexafluoroisopropanol (solubility parameter of 8.2), phenol, meta-cresol (solubility parameter of 12.7), hexafluoroacetone propylene adduct (HFAPA), trichloroacetic acid (solubility parameter of 9.1), parachlorophenol (solubility parameter of 11.7), or hexafluoroacetone sesquihydrate, with the acidic organic component being present in minor proportions, e.g., from about 2 to 10 percent by weight of the mixture, cause shrinkages above about 35 percent.

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 20 (some less than 10) percent shrinkage in the wale direction. Also, liquid systems such as 6% HFIP-Valclene one (a fluorinated hydrocarbon solvent composed primarily of trichlorotrifluoroethane, 6% HFIP-methanol (solution solubility parameter of 14.3) and 6%-HFIP benzene (solution solubility parameter of 9.12) all cause less than 12 percent shrinkage in the wale direction. The system of 6% HFIP-tetrachloroethane is not miscible and 6% HFIP-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 40-denier polyethylene terephthalate tubing (wall thickness of 0.2 mm.) are immersed in methylene chloride solutions containing 3, 5, 6, 7, 7.5, 8 and 10 percent by weight of the solution of hexafluoroisopropanol for 1 minute at room temperature (10:1 liquid to sample ratio). A 40-denier sample of the same polyethylene terephthalate tubing is immersed in 100 percent methylene chloride for 20 minutes at room temperature for comparison purposes.

Samples of 70-denier polyethylene terephthalate tubing (0.3 mm. wall thickness) are immersed in the 5, 6, 7.5 and 10 percent hexafluoroisopropanol-containing methylene chloride solutions in the same manner as the 40-denier samples. The samples are rinsed, dried and measured as in Example I. The results are shown in Table II below.

TABLE II ______________________________________ 40-denier 70-denier Hexafluoroisopropanol/ tubing, tubing, methylene chloride by percent shrinkage percent shrinkage weight percent in wale direction in wale direction ______________________________________ 0/100 26.5 -- 3/97 33 -- 5/95 36.5 31 6/94 40 31 7/93 40 -- 7.5/92.5 39 33 8/92 41 -- 10/90 40 33 ______________________________________

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. In addition, 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 III

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 II in a mixed solution of 6 percent by weight of hexafluoroisopropanol and 94 percent by weight of methylene chloride for 1, 5, 15 and 30 minutes at room temperature (20.degree.C.) and a 10:1 solution:sample 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 within 5 minutes and further changes essentially do not occur beyond 5 minutes.

TABLE III ______________________________________ Percent Shrinkage in the Wale Direction Time, minutes 40-denier tubing 70-denier tubing ______________________________________ 1 40 31 5 40 33 15 40 34 30 40 33 ______________________________________

The porosity of the 40-denier sample prior to the above treatment is 8800 on the Wesolowski scale (i.e., 8800 cc water/cm.sup.2 min.) After 5 minutes immersion in the compacting solution as described above, the porosity is 2500 on the Wesolowski scale.

EXAMPLE IV

The 40-denier, 5-minute immersion sample of Example III is crimped in accordance with the teachings of U.S. Pat. No. 3,337,673. The resulting, crimped tubing is cooled, dried and sterilized and is suitable for use as a vascular prosthesis.

EXAMPLE V

Example II is repeated for the trichloroacetic acid-methylene 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.

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 VI

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 20.degree.C. 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

The present invention offers a number of significant advantages. Knitted flat stock or tubing may be economically manufactured in the wall thicknesses suitable for use as a vascular prosthesis. While the smooth-surfaced, uniformly porous knitted material possesses superior flexibility, handling and resiliency characteristics, it has a porosity too high to be suitable for long-term healing effects without undue hemorrhaging at implantation.

Treatment of the porous, synthetic knitted polyester material with the compacting solution as defined in the 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.

The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein, however, is not to be construed as limited to the particular forms disclosed, since these are to be regarded as illustrative rather than restrictive. Variations and changes may be made by those skilled in the art without departing from the spirit of the present invention.

Claims

I claim:

1. A process for preparing a synthetic vascular prosthesis comprising the steps of:

a. providing 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;

b. immersing said porous knitted synthetic linear polyester fabric tubing material in 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 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 long-term healing effects without undue hemorrhaging at implantation;

c. removing said compacted fabric material from said compacting solution;

d. washing said compacted fabric material to remove all traces of said compacting solution; and

e. forming said compacted fabric material into a vascular prosthesis.

2. The method of claim 1 wherein said acidic organic component is hexafluoroisopropanol and the said halogenated aliphatic hydrocarbon is methylene chloride.

3. The process of claim 2 wherein said compacting solution contains from about 4 to about 8 percent by weight of hexafluoroisopropanol and about 96 to about 92 percent by weight of methylene chloride.

4. The method of claim 1 wherein said polyester is polyethylene terephthalate.

5. The method of claim 1 wherein said compacting includes a shrinkage of at least about 40 percent in the wale direction.

6. The process of claim 1 wherein said forming of the prosthesis includes crimping of the compacted tubing.

7. The process of claim 1 wherein said fabric material is immersed in the said compacting solution for a time of from about 15 seconds to 30 minutes.

8. A process for preparing a synthetic vascular prosthesis which comprises the steps of:

a. providing a uniformly porous, knitted polyethylene terephthalate tubing having a wall thickness between about 0.1 and 0.3 mm. and a porosity, measured on the Wesolowski scale, above about 7,500 up to about 20,000;

b. immersing said porous, knitted polyethylene terephthalate tubing in a compacting solution consisting essentially of from about 4 to about 8 percent by weight hexafluoroisopropanol and from about 96 to about 92 percent by weight of methylene chloride for from about 5 to about 15 minutes to uniformly compact the tubing, said compacted tubing having a porosity, measured on the Wesolowski scale, of from about 30 to about 5,000;

c. removing said compacted tubing from the compacting solution;

d. washing and drying said compacted tubing to remove all traces of the compacting solution and wash liquid; and

e. crimping said dried compacted tubing.

9. 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.sub.s = V.sub.1 S.sub.1 + V.sub.2 S.sub.2

where S.sub.s is the solubility parameter of the solution, V.sub.1 is the volume fraction of the solvent component, S.sub.1 is the solubility parameter of the solvent component, V.sub.2 is the volume fraction of the shrinking agent component and S.sub.2 is the solubility parameter of the shrinking agent component; and removing all traces of said compacting solution from said compacted fabric.

10. The process of claim 9 wherein 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.

11. The process of claim 10 wherein said compacting solution contains from about 4 to about 8 percent by weight of the solution of the solvent for the polymer and from about 96 to about 92 percent by weight of the shrinking agent for the polymer.

12. The process of claim 9 wherein said polyester is polyethylene terephthalate.

13. 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 90 to about 98 percent by weight of methylene chloride; and removing all traces of said compacting solution from said compacted fabric.

14. The process of claim 13 wherein said tubing is immersed in the said compacting solution for from about 30 seconds to about 30 minutes.

15. The process of claim 14 wherein said tubing is immersed in the said compacting solution for from about 5 to about 15 minutes.

16. The process of claim 13 wherein said solution contains from about 4 to about 8 percent by weight of hexafluoroisopropanol and from about 96 to about 92 percent by weight of methylene chloride.

17. The process of claim 13 wherein the polyester is polyethylene terephthalate.

18. The process of claim 13 wherein the yarn in said tubing has a denier of 40.

19. The process of claim 13 wherein the yarn in the tubing has a denier of 70.

20. A process for preparing a synthetic inter-cardiac prosthesis comprising the steps of:

a. providing a knitted synthetic linear polyester fabric 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;

b. immersing said porous knitted synthetic linear polyester fabric material in 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 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 long-term healing effects without undue hemorrhaging at implantation;

c. removing said compacted fabric material from said compacting solution; and

d. washing said compacted fabric material to remove all traces of said compacting solution.