US 3754069 A
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Aug. 21, 1973 D M ET AL 3,754,069
METHOD 01- FABRICATINQPLIABLE POLYFILAMENTOUS PLASTIC STRANDS Original Filed July 23, 1969 LEONARD D. KURTZ JOSEPH H. ADAMS I BY 07.36 QO /W ATTORNEY 5 Qj INVENTOR United States Patent Ice 3 754 069 METHOD OF FABRICATING PLIABLE POLY- FILAMENTOUS PLASTIC STRANDS Joseph H. Adams, Vernon, Conn., and Leonard D. Kurtz,
Woodmere, N.Y., assignors to Sutures, Inc., Coventry, Conn.
Continuation of abandoned application Ser. No. 843,987,
July 23, 1969. This application Aug. 23, 1971, Ser. No. 174,142
Int. Cl. B29c 17/02; A611 17/00 U.S. Cl. 264-131 8 Claims ABSTRACT OF THE DISCLOSURE This application is a continuation of Ser. No. 843,987, filed July 23, 1969, now abandoned.
This invention relates to an improvement in the fabrication of pliable plastic polyfilamentous strands such as pliable sutures.
Plastic strands, for example, braided or twisted polyethylene terephthalate threads, have certain physical and chemical properties superior to naturally occurring materials for many applications. Polyfilamentous polyethylene terephthalate threads, for example, are suitable for use as surgical sutures because of the high tensile strength and inertness thereof. However, the thread is very stiff relative to, for example, silk of equal tensile strength and/or dimension and this lack of pliability causes the knotting characteristics of the thread to be quite poor for surgical use. To this end, various methods have been disclosed in the art for modifying the lubricity and pliability of plastic threads such that the knotting properties are similar to those of silk threads.
Moreover, to make the polyfilamentous strand suitable for use, including surgical use, it has been necessary to reduce the elasticity and memory (tendency to return to original length) of the plastic polyfilamentous strand by hot-stretching the strand.
A method for providing a polyfilamentous plastic strand of improved softness and pliability has been described in copending application Ser. No. 78,174 to Joseph H. Adams and Leonard D. Kurtz, filed Oct. 2, 1970, now abandoned. In accordance with that invention, a polyfilamentous plastic strand is first impregnated with an oil of lubricating viscosity and then hot-stretched while maintaining the strand at least at the heat-setting temperature thereof. The hotstretched strand is then permitted to cool and the impregnated strand is found to possess a greater pliability and softness than non-treated strands. In a preferred embodiment of that invention, the lubricating oil impregnant is removed as by solvent extraction after heat-stretching and the strand is then water-washed, dried and then impregnated with inert, polymeric particles such as Teflon. It has now been unexpectedly found that in this preferred process for improving the softness and pliability of polyfilamentous strands, omission of the drying step provides a final product of improved softness. Apparently, drying of the strand, after water-washing and before impregnation with the polymeric particles, causes some return of the stiffness originally found in the material. Consequently, when the material is subsequently impregnated with the polymeric particles, no further softening is obtained; this small return of stiffness persists and remains a permanent 3,754,069 Patented Aug. 21, 1973 part of the product. If, however, after the water-wash step, the strand is impregnated with the polymeric particles before drying, there is no return of stitfness and the product remains dead soft. Furthermore, wetting and drying after impregnation, in accordance with the process of this invention, does not cause return of stiliness.
Without being bound by any explanation or theory, we believe that the return of stiffness to the material is due to internal cohesions. If the individual filaments in the polyfilamentous strand are permitted to dry against each other, internal attractions between the adjacent filaments are probably being introduced causing a degree of stiffness. When the strand is wet with water, however, water is interposed between filaments eliminating the cohesive effect. Then, when the strand is subsequently impregnated with the polymeric particles, the latter interposes a mechanical barrier between filaments preventing close contact and the strand remains soft.
In a preferred embodiment of the invention, further pliability and softness is endowed the polyfilamentous strand by subjecting it, after cooling, to repeated flexion in order to cause relative movement between adjacent filaments of the strand. By this embodiment of the invention, there is produced an unusually soft and pliable strand.
By the term polyfilamentous plastic strand as used herein and in the appended claims is meant a unitary structure of a plurality of plastic filaments and includes plastic monofilaments and polyfilaments which have been twisted, braided, entangled, spun and the like. Illustrative of such strands are braided and twisted threads, sutures, strings and rope, spun and continuous synthetic filament yarns, etc. Plastic materials from which the strands may be made include any of the fiber-forming synthetic material as, for example, polyesters such as polyethylene terephthalate; polyolefins such as polyethylene, polypropylene, and the like; the acrylics such as polymethacrylate, polyacrylonitrile, etc.; polycarbonates; polyamides such as nylon; cellulose esters; vinyl polymers such as copolymers of viny choride and vinyidene chloride and coploymers and vinyl chloride and vinylacetate; and like fiberforming plastic materials.
The oils employed in the method of the invention are oils of lubricating viscosity, stable toward the high hotstretching temperatures to which the polyfilamentous strand is subjected and include mineral and synthetic oils. Generally, such oils have viscosities from about 35 to 250 SUS at 210 F. In the case of polyfilamentous surgical sutures, the oil selected from the impregnation should, of course, be physiologically inert.
The mineral oils may be solvent-extracted or solventrefined mineral oils obtained in accordance with conventional methods of solvent refining petroleum lubricating oils. The base oil from which these lubricating fractions are obtained may be derived from parafiinic, naphthenic, asphaltic or mixed base crudes.
Synthetic oils which may be used include those of the ester type, for instance, the complex esters, diesters, monoesters and polyesters, prepared from aliphatic or aromatic acidic and alcoholic compounds. Various useful ester base oils are disclosed in U.S. Pat. Nos. 2,499,- 983; 2,499,984; 2,575,195; 2,575,196; 2,703,811; 2,705,- 724; and 2,723,286. Generally, the synthetic base oils consist essentially of carbon, hydrogen and oxygen, i.e. the essential nuclear chemical structure is formed by these elements alone. However, these oils may be substituted with other elements such as halogens, e.g. chlorine and fluorine. Some representative components of ester lubricants are ethyl palmitate, ethyl stearate, di-(Z-ethylhexyl) sebacate, ethylene glycol di-laurate, di-(2-ethylhexyl) phthalate, di (1,3 methylbutyl) adipate, di-(2- ethylbutyl) adipate, di (1 ethylpropyl) adipate, diethyl oxylate, glycerol tri-n-octoate, dicyclohexyl adipate, di- (undecyl) sebacate, tetraethylene glycol di (ethylene hexoate), dicellosolve phthalate, butyl phthallyl butyl glycolate, di-n-hexyl fumarate polymer, di-benzyl sebacate and diethylene glycol bis (2 n butoxy ethyl carbonate). 2-ethylhexyl-adipate-neopentyl glycyl-adipate-Z- ethylhexyl is a representative complex ester.
Preferred synthetic oils are the silicone oils of lubricating viscosity. The silicone oils are liquid organic siloxane polymers in which the siloxane structure, fi9i-Ofi9i, occurs successively along the polymer chain and in which the major number of residual valences of the silicone atoms are not satisfied by the substitution thereon of monovalent organic essentially hydrocarbon radicals such as aromatic and aliphatic radicals. For the purpose for which such silicone oils are used in the present invention, the aliphatic substituents of the polymers are preferably low molecular weight alkyl radicals (i.e., those not having more than about carbon atoms per radical) such as methyl, ethyl and butyl radicals, and the aromatic substituents are preferably phenyl, halogen-substituted phenyl radicals, and alkyl-substituted phenyl radicals in which the alkyl group is halogenated. The aromatic siloxane polymers are preferably those in which a major proportion of the silicone atoms are bonded to aliphatic radicals such as methyl radicals, and in which the remaining number of organic radicals are aromatic radicals. Typical examples of specific silicone oils which may be used are the dimethyl siloxane polymers having a viscosity of at least centistokes at 25 C. (77 F.) and preferably a viscosity of at least 20 centistokes at 25 C. Such methyl-substituted siloxanes are commercially known as the Dow Corning Silicone Type 200 fluids and are mixtures of polymers of the homologous series of trimethyl end-blocked dimethyl siloxane polymers having a viscosity at 25 C. ranging up to about 12,500 centistokes. Other suitable siloxane polymers which may be used in accordance with the present invention are the aliphaticand aromatic-substituted siloxane polymers such as the methyl phenyl siloxane polymers of medium aromaticity commercially available as Dow Corning DC-SOO silicone oil, and those containing a low ratio of phenyl to methyl groups commercially available as Dow Corning DC-SlO silicone oils. Further examples of suitable aliphaticand aromatic-substituted siloxane polymers are the methyl phenyl siloxanes in which the phenyl radical is substituted with halogen such as in methyl-p bromophenyl siloxane polymer, methyl-pchlorphenyl siloxane polymer, methyl m trifluoromethyl phenyl siloxane polymer and methyl 3,4-dichlorophenyl siloxane polymer. It is within the scope of the present invention to employ any admixture of the above-mew tioned silicone oils as an ingredient of the presently described novel compositions.
It is to be understood that the term siloxane polymer as used herein includes silicone oils having the following general formula:
LR J. l.
wherein R R and R are the same or different hydrocarbon radicals such as straight or branched chain alkyl, aryl, alkaryl, arylalkyl, halogen-substituted aryl or halo gen-containing alkyl-substituted aryl radicals and n is an integer of at least 2. Such silicones are also referred to in the literature as organo polysiloxanes.
impregnation of the polyfilamentous strands may be effected in any convenient manner, for instance, by simply immersing the strand in the oil for a short period of time suflicient to saturate and thoroughly impregnate and coat the strand. Ordinarily, complete saturation is effected in a matter of minutes.
The hot-stretching step of the invention comprises stretching the strand at a temperature above its glass transition temperature, which will permit a change in configuration without the introduction of internal stresses. Conveniently, the strand may be heated to its softening point. Tension is applied to the heated strand such that the strand is stretched, for example, up to its breaking point. Elongation of over 10% and particularly from about 20% up to about, but not including, the breaking point are suitable to reduce the elasticity and memory of the strand sufliciently. The temperature necessary to reduce or eliminate elasticity and memory is called the heat-setting temperature which is known for various plastic materials. For instance, in the case of polyesters of terephthalic acid, a temperature of 320 F. or above will suffice, although temperatures of about 390 F. to 450 F. are preferred.
The flexion to which the strand may be subjected after cooling in the preferred embodiment of the invention may be accomplished, for instance, by subjecting the strands to repeated flexion as described in US. Pat. No. 3,257,702 hereby incorporated by reference. Alternatively and preferably, the fiexion may be induced by passing the impregnated strand under tension after hot-stretching and cooling over a plurality of sharp edges, each edge being positioned to efliect at least about a 30 change in direction of the passing strand. Treatment of the hot-stretched strand in this manner induces a consistent flexing uniformly throughout the entire strand. There is consequently provided a strand of particularly improved softness and pliability since no area of this strand escapes flexing. In addition, the improvement of the invention offers reproducibility advantages since it enables repeated preparation of strands of like softness and pliability. Furthermore, the improved method of the invention permits easy adjustment of the degree and the rapidity of flexion applied so as to enable optimization of conditions with respect to whatever type strand is being flexed.
The edge over which the strand is passed may be any suitable element having a relatively sharp edge. By sharp edge as used in the specification and claims is meant an edge that provides a sharp flex to the strand over which it is passed in accordance with the methods of the invention that breaks free or loosens adhering or cohering filaments of the strand. Thus, the edge of the element, over which the strand is passed, should not be so sharp as to cause severing, cutting, or abraiding of the strand; nor should the edge have a radius of curvature so large as not to provide the desired sharp flex. Included within the sharp edges contemplated by the method of the invention are sharp angular elements which can be considered as having essentially a zero radius of curvature and cylindrical elements having a very small radius of curvature of say up to inch as is found in edges having a diameter of up to ,5 inch. The sharp edged-elements over which the strand is passed may be constructed out of any suitable solid, hard material resistant to wear such as steel, ceramic and the like. The number of edges in the series over and around which the strand passes will vary depending upon the nature of the particular polyfilamentous strand, the tension applied, and the rate at which the strand is drawn around the elements. Use of too many edges in the series, however, should be avoided since an excess of edges will often cause the strand to break. A series of three edges has been found to provide satisfactory results.
Any arrangement of the edges that provides the desired degree in change of direction can be employed. Although an arrangement which gives a 30 change of direction as the strand passes around each edge provides suificient flexion, an arrangement which effects at least about a change is preferred. The rate at which the strands are passed around the edge is not critical and, during passage, the strand may be drawn either partially around or completely around each of the elements as long as it is passed over the flex-inducing edge. The strands should be under sufiicient tension as they are passed over the edges in order to induce the desired flex. Any tension which keeps the strand taut without breaking the strand can be employed. Tensioning devices known to the art may be used for this purpose, if desired. The drawing of the strand may be accomplished manually or, if desired, any suitable automatic or mechanical means may be employed. It may be necessary to repeat the passage of the thread around the plurality of edges to achieve the desired degree of softness and pliability.
Removal of the oil of lubricating viscosity from the final product may be effected by any of the techniques well known to the art. For example, the oil may be conveniently removed by washing the product with a suitable solventvfor the oil. The particular solvent selected will depend upon the lubricating oil employed. For instance, in the case of the silicone oils and ester-type synthetic lubricants, suitable solvents include, for example, the alkyl and aryl monoethers of alkylene glycols such as ethylene glycol, propylene glycol, etc. Illustrative of these solvents are those of the Dowanol series. In the case of mineral lubricating oils, on the other hand, the aromatic solvents including benzene, xylene, toluene and the like are satisfactory.
After extraction of the lubricant from the strand, the strand is water-washed in any convenient manner and then while still wet impregnated with inert, insoluble synthetic polymeric particles small enough to penetrate into the interstices of the strand. The inert, polymeric particles may be any of those known in the art for endowing polyfilamentous strands with improved softness and flexibility such as those disclosed in US. Pat. Nos. 3,390,681 and 3,322,125, hereby incorporated by reference. Other suitable inert, insoluble synthetic resins which can be used include polyolefins such as polyethylene, polypropylene and the like; diolefins such as polymers of butadiene and isoprene; polystyrene; polyamides and silicone waxes such as are disclosed by US. Pat. 3,187,752, hereby incorporated by reference. A particularly preferred particle is polytetrafluoroethylene (Teflon). Aqueous dispersions of these materials such as aqueous dispersions of Teflon described in Berry, US. Pat. No. 2,478,229, are suitable to incorporate the particles into the strands. Saturated aqueous dispersions are particularly suitable. Ordinarily, the inert particles employed will have a particle size of up to 1 micron.
If desired, the strand may also be subjected to any of the conventional treatments known in the art. For instance, the polyfilamentous strand may be provided with polytetrafluoroethylene to improve knottability and flexibility 5's described in U.S. Pat. Nos. 3,390,681 and 3,322,- 125.
The following example is included to further illustrate the present invention. In the example, reference is made to the attached figures wherein:
FIG. 1 is a perspective view of an apparatus for eflecting the flexing in accordance with a preferred embodiment of the invention and,
FIG. 2 is an enlarged perspective view of one of the sharp edged-elements employed in the apparatus of FIG. 1.
EXAMPLE A five/zero polyethylene terephthalate thread is immersed in silicone fluid (Dow Corning 710 a polyphenylsiloxane having an average molecular weight of 2600, approximately 20 silicon atoms per molecule, and a phenyl to methyl ratio of 1.0) for approximately one minute. The excess silicone fluid is wiped off the thread and the thread is stretched at approximately 390 F. to an elongation of approximately 50%. The hot-stretched thread is drawn from a supply 1 and manually threaded through an introductory guide 3, entrance opening 5, over the wick 7 of applicator indicated generally as 9, thropgh exit opening 11, and around guides 13, 15 and 17, respectively, in the manner illustrated in FIG. 1. The thread is then attached to take-up spool 9. The guides, each containing a sharp ceramic edge shown, for instance, in FIG. 2 as 19, are arranged in a manner which will effect at least a change of direction of the passing thread at each edge. The applicator 9 is composed of a container 21 provided with wick 7 and a guide structure 23 provided with the aforementioned entrance opening 5 and exit opening 11. The wick 7 is immersed in a cooling medium such as water. When take-up spool 9 is rotated, the hot-stretched thread is pulled over wick 7 of the applicator 9 where it is cooled by the application of the liquid cooling medium and then over the sharp edges of guides 13, 15 and 17.
The silicone fluid is then removed from the thread by washing with Dowanol 508 (dipropylene glycol monomethyl ether) after which the thread is water-washed. The water-washed thread is gathered into a skein and immersed before it has had a chance to dry into an aqueous solution of Teflon. Du Pont blend 2510, containing water and about 58% by weight of Teflon (polytetrafluoroethylene) particles having an average particle size of 0.5 micron diluted with water to a concentration, is used. A surfactant Triton X-lOO, an alkylaryl polyether alcohol having the general formula R(O-CH -CH OH where R is an alkylaryl radical and n is an integer from 5 to or more (Rohm and Haas) and agitation are used to keep the blend well dispersed.
The skein of thread is kept immersed in the Teflon dispersion for 15 minutes to permit the particles of Teflon lubricant to permeate into the interstices of the thread. While the immersion time can vary widely, it has been found that 15 minutes is adequate for skeins weighing up to 50 pounds as determined by measuring the amounts of Teflon picked up after final processing. Excess Teflon is then removed to provide a thread which is extremely pliable and has knotting characteristics substantially identical to that of silk sutures.
It is claimed:
1. A method for fabricating a braided polyester suture of improved softness and pliability which comprises thoroughly impregnating a braided polyester suture having elastic memory with a lubricating oil which is physiologically inert and is inert with respect to the suture, stretching the impregnated suture while maintaining the suture at the heat-setting temperature above the glass transition temperature of the polyester to reduce the clastic memory thereof, contacting the stretched suture with a solvent for said oil to remove said oil from the suture, water-washing the solvent-treated suture, and impregnating the water-washed suture while wet with water from the water washing step with inert, synthetic, polymeric particles of a resin selected from the group consisting of polyolefins, polystyrene, polyamides, silicone waxes, and polytetrafluoroethylene, said particles having a size sufliciently small to enter into the interstices of said braided suture.
2. The method of claim 1 wherein the lubricating oil is a silicone fluid.
3. The method of claim 1 wherein the inert, synthetic, polymeric particles are polytetrafluoroethylene.
4 The method of claim 1 wherein the stretched suture is subjected to repeated flexion to cause relative movement between adjacent filaments of the suture.
5. The method of claim 4 wherein the repeated flexion is effected by passing the suture under tension over a plurality of sharp edges, each edge being positioned to eflect at least about a 30 change in direction of the passing strand.
6. The method of claim 5 wherein a series of three edges a e employed.
7. The method of claim 5 wherein each edge effects at least about a 90 change in direction of the passing strand.
sharp edge of a guide pin.
Strohmaier et a1. 264-290 N FOREIGN PATENTS Great Britain 264-210 ROBERT F. WHITE, Primary Examiner I. B. LOWE, Assistant Examiner U.S. C1. X.R.
28-75 R; 117-7, 138.8 F, 139.5 A, 161 UZ; 128- 7 8. The method of claim 7 wherein each edge is the 3,113,369 3,140,957 3,257,702 References Cited 3,3 4,2 9 UNITED STATES PATENTS 5 7/1964 Tanabe et a1 -7 117-6 5/1970 Strohmaier et a1. 264-290 N 6/1966 Kurtz 28-72 12/1963 Barrett at al. 28-75 10 19694596 1/1968 Campbell -1 264-290 8/1963 Heighten 264-290 T 7/1969 Amok! 264-210 F 4/1968 Kurtz 12s 33s.s 11/1960 K161 2s 72.13 15 8/1963 Heighten 264-290 11/1963 Bergeijk 61 a1 264-210 F 335.5; 264-233, 290 T, DIG 73