NL8700229A - POly L- or DL-lactide fibres of high tensile strength - useful for surgical sutures which are re-absorbed by the body - Google Patents

Abstract

Polylactide yarns comprising an oriented lactide polymer which is derived from at least 60%, pref. at least 85% L-lactide or DL-lactide and up to 40 wt.% of a hydroxyacid or aminocarboxylic acid with at most 8C, the yarns having a tensile strength of 1.3-4 GPa and in a WAXD X-ray exposure, the reflection in the first stage of the diffractogram corresp. to the beta-structure at 2 theta = 19.8 deg. has a greater intensity than the reflection in the diffractogram corresp. to the alpha-structure at 2 theta = 19.2 deg.

Description

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Polylactide yarn with a tensile strength between 1.3 and 4 GPa and method for the manufacture of such a yarn

The invention relates to polylactide yarn comprising an oriented lactide polymer derived from at least 60% by weight of L-lactide and / or DL-lactide and up to 40% by weight of a hydroxy acid or amino carboxylic acid with at most S carbon atoms as well as a method of manufacturing such a yarn.

The manufacture of polylactide yarns is described, inter alia, in U.S. Patent 3,636,956. The yarns described therein appear to be deficient in a number of respects, in particular of which the tensile and knot strength are inadequate.

Polylactide yarns of much higher strength have been obtained by Gogolewski et al. and described in Journal of Appl. Pol. Sci. Full. 28, 1045-1061 (1983). The polylactide yarn spun from chloroform is drawn 20x, after which a tensile strength of 1.2 GPa is measured.

For a number of applications, especially in the medical field, there appears to be a great need for yarns with not only an even greater tensile strength but also other improved physical properties.

This is provided by the invention by providing a polylactide yarn, mentioned in the preamble, whose tensile strength is between 1.3 and 4 GPa and of which, in a WAXD image, the reflection corresponding to the B structure on the first floor of the diffractogram at 2Θ = 19.8 "has a greater intensity than the reflection corresponding to the a-structure on the first floor of the diffractogram at 2Θ = 19.2".

The latter property can be determined using a Statton camera, in which a WAXD X-ray image is taken with a CuKc radiation source (λ * 1.5421). The intensity of the reflections is determined in the known manner with the aid of a densitometer.

Polylactide yarns of the aforementioned strength possessing the latter structural parameter are ideally suited for use in medical technology. Indeed, they are strong enough to take the place of the non-biocompatible polyester or polyamide yarns used hitherto, yet they can be reabsorbed by the body so that their function can be gradually taken over by the more natural ones during the repair process. the body itself formed materials.

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Applicant has found that there is a direct relationship between polylactide yarns of> 1.3 GPa strength and the ratio of the 8 to ot structure therein. In addition, the knot strength with polylactide yarns with a predominantly 8 structure is also surprisingly high,

In the context of the invention, preference is given to polylactide yarn, of which the lactide polymer is at least 85% by weight derived from L-lactide and / or DL-lactide.

Examples of other monomers that can be used in addition to D-lactide or DL-lactide are glycolide, B-propiolactone, tetramethylglycolide, B-butyrolactone, γ-butyrolactone, pivalolactone and intermolecular cyclic esters of ö-hydroxybutyric acid, α-hydroxyisobutyric acid, a- hydroxyvaleric acid, α-hydroxyisovaleric acid, α-hydroxycaproic acid, α-hydroxyethylbutyric acid, oi-hydroxyisocaproic acid, oi-hydroxyoctanoic acid, caprolactam, p-hydroxybenzoic acid and depsipeptides.

The polylactides from which the yarns of the invention are made generally have a molecular weight to viscosity average of at least 3 x 105 and preferably more than 5.0 x 1CP kg / kmol, calculated by the formula; [η] = 5.45 x ΙΟ "* Mv °> 73, the viscosity being measured at 25 ° 0 in chloroform.

When preferred is a yarn of the highest strength and / or a yarn whose absorption time is relatively long, preference is given to polylactide yarn which is entirely derived from L-lactide and / or DL-lactide.

In the manufacture of the polylactide yarns according to the invention, use can be made of a Leenslag e.m. in Journal of Appl. Pol. Sci. Full. 29, 2829-2842 (1984), wherein a lactide polymer having an intrinsic viscosity of at least 5.5 dl / g is spun from a solvent mixture of an aliphatic chlorinated hydrocarbon of a polar character and a light aromatic hydrocarbon.

Table I on page 2833 of this article lists the result of a number of tensile and knot strengths of a poly (L-lactide), PLLA, yarn obtained by spinning PLLA of molecular weight to viscosity. - r; V - P 189 - 3 - average Mv * 4.6 x 103 from an 18% solution (w / v) of a mixture of 70 parts by volume chloroform and 30 parts by volume toluene. Although, according to the aforementioned table, yarns with a knot strength which can reach up to 70% of the tensile strength can be obtained by the known method, the strength figures of the PLLA yarns mentioned therein are relatively low.

The invention now provides a method by which poly-lactide yarns with the properties mentioned in the preamble can be obtained.

The invention consists in that in a method of the aforementioned known type the volume percentage of the solvents present in the mixture is chosen such that it is at most 154 away from the percentage where the intrinsic viscosity reaches a maximum after a gradual decrease.

The aliphatic chlorinated hydrocarbons to be used in the present invention generally have no more than three carbon atoms, while the light aromatic hydrocarbons which may be used in the present invention generally have a boiling point at atmospheric pressure of at most i 50'C.

Examples of polar character aliphatic chlorinated hydrocarbons which can be used in the context of the invention are ethylidene chloride, trans-1,2-dichloroethylene, 1,2-dichloropropane, cis-1,2-dichloroethylene, trichlorethylene and chloroform.

Examples of light aromatic hydrocarbons which can be used in the context of the invention are benzene, toluene, o-, m-, p-xylene and vinyl toluene.

It goes without saying that mixtures of aliphatic chlorinated hydrocarbons and mixtures of light aromatic hydrocarbons can also be used.

In particular, when a polylactide, which preferably consists wholly or mainly of poly L-lactide or poly DL-lactide, is spun from a solvent of chloroform and toluene, the volume ratio of chloroform to toluene is chosen, unlike the above-mentioned known process. between 55:45 and 25:75.

It has been found that when using the method according to the invention poly (L-lactide) yarns can be obtained with a strength up to at least 4 GPa.

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This should be considered particularly surprising since the aforementioned article by Gogolewski e.m. on page 1059 it is expressly stated that of the PLLA fibers made from PLLA with the same molecular weight, those spun from a good solvent for PLLA have a higher strength than those spun from a bad solvent for PLLA, while furthermore the figures given in Table I of the first mentioned article clearly tend towards a lower tensile strength when using a mixture of chloroform and toluene,

In the context of the invention, a method is preferred in which the volume ratio of chloroform to toluene is chosen between 45:55 and 35:65.

Optimal results are obtained when 2 parts by volume of chloroform are taken for 3 parts by volume of toluene for the solvent mixture.

Furthermore, it has been found that the method of preparation of the polylactide solution is of great importance in the final result to be obtained. Preferred herein is a process in which the solvent mixture is prepared by first dissolving the lactide polymer in the aliphatic chlorinated hydrocarbon and then adding the light aromatic hydrocarbon until the required volume ratio and concentration are obtained.

In general, good results can be obtained when the solvent mixture is spun at a temperature between 20 and 40OT. However, preference is given to a method in which the spin temperature is selected between 55 and 65 ^ 0,

The filaments thus formed are then drawn with a draw ratio of between 4 and 30 at a temperature of between 45 and 210 ° C. Preference is given to using a draw ratio of between 10 and 25 at a temperature between 190 and 208 ° C.

The concentration of the polylactide in the solvent mixture will generally be between 1 and 20 (w / v). The concentration to be used depends, inter alia, on the solution viscosity of the. polylactide in the respective solvent mixture. In practice, the optimal concentration will usually be between 1.5 and 15 (w / v).

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The polylactide yarns according to the invention can be woven, braided, knitted or used as such in the form of monofilaments in surgery as, for example, sewing thread, but also as reinforcing material in the manufacture of prostheses as artificial veins. As a result of the absorption of the polylactide in the body, gradual replacement can take place by natural materials produced by the body.

When spinning the polylactide according to the invention, use is preferably made of spinnerets with openings of 0.2 to 1 mm and a length of the capillary of 10 mm. By drawing the filaments after spinning under the conditions indicated above, ultimately filaments with a strength of 1.3 GPa or more are obtained. The diameter of the individual filaments will generally be between 0.3 x 10 "* and 1 x 10" * m. The filaments preferably have a diameter between,, 4 x 10 "m and 1 x 10 "" m.

For example, hot stretching of the fibers can be done in an electric tube furnace 60 cm long in a dry, oxygen-free atmosphere.

The invention will now be elucidated by means of the following examples. It goes without saying that these are exemplary embodiments to which the invention is not limited.

In the examples below, use was made of PLLA with Mv = 6.5 x 10 and 9 x 105 obtained by polymerization for 24 hours at 130 ° C and 112 hours at 110 ° C, respectively, according to a method as described in the aforementioned article by Gogolewski et al.

Viscosity was determined with an Ubbelohde viscometer (type Qa, ASIM D 445) in chloroform and chloroform / toluene mixtures at 25 and 6QVC. The average molecular weight to the viscosity average Mv was calculated after determining the intrinsic viscosity in chloroform at 25VC using the formula; inj * 5.45 x 10 "1 $ 7 0 8 Ρ 189 ν'1 · >> - ό -

The mechanical properties of the fibers were determined at room temperature on an Instron tensile tester (4301) at a drawing speed of 12 mm / minute. The length of the samples to be tested was 25 mm.

Example I

Poly (L-lactide) (PPLA) with Mv (molecular weight to viscosity average) 9 x 103 was dissolved in chloroform and then diluted with toluene until a solution was obtained with 4 (g dl-1) / o PLLA. The solution contained equal parts by volume of chloroform and toluene and was spun at 60 ° C and then drawn at 204 ° C. The draw ratio was 10.5. The filaments thus produced had a tensile strength of 1.45 GPa.

In a WAXD X-ray image, the β-reflection appeared to have a greater intensity than the ó-reflection.

Example II

The experiment of Example I was repeated, except that the spinning solution now contained 4 parts by volume of chloroform and 6 parts by volume of toluene. At a maximum draw ratio of about 20, a yarn having a tensile strength of 2.1 GPa was obtained. In a WAXD X-ray image, the pollactide was found to be entirely present in the β-structure.

Example III

The experiment of Example II was repeated, except that a PLLA with Mv = 6.5 x 103 was now started at a polymer concentration of 5.1 (g dl-1)%, at a maximum draw ratio a yarn was obtained with a tensile strength of 1.8 GPa. In a WAXD X-ray image, the 8 reflection was found to have a greater intensity than the o reflection.

Example IV

The experiment of Example I was repeated, except that the spinning solution now contained 7 parts of toluene and 3 parts of chloroform. At a draw ratio of 14.5, a yarn having a strength of 1.4 GPa was obtained. In a WAXD X-ray exposure, the β-refraction showed a greater intensity than the α-reflection. n * "<v f \ * / y t '~ £ · Ρ 189 T- -¾

Example V {Retaliation Example)

The experiment of Example I was repeated except that the spinning solution now consisted of a solution of 4 g PLLA in 100 ml chloroform. Spinning Sa at 60 ° C and maximum drawing at 204 ° C yielded a yarn with a tensile strength of 0.75 GPa.

Example VI (comparative example;

The experiment of Example I was repeated except that the spin solution now consisted of a solution of 4 g PLLA in 100 ml toluene.

Spinning Sa at hQ'C and maximum drawing at 204'JC yielded a yarn with a tensile strength of 1.05 GPa.

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Claims (12)

Polylactide yarn comprising an oriented latetide polymer derived from at least 60% by weight of L-lactide and / or DL-lactide and up to 40% by weight of a hydroxy acid or aminocarboxylic acid having up to 8 carbon atoms, characterized in that the yarn has a tensile strength between 1.3 and 4 GPa and, in a WAXD image, the reflection corresponding to the β-structure on the first floor of the diffractograra at 2Θ = 19.8U shows a greater intensity than that with the a-structure corresponding reflection on the first floor of the diffractogram at 2Θ = 19.2 °. Polylactide yarn according to claim 1, characterized in that the lactide polymer is at least 85% by weight derived from L-lactide and / or DL-lactide. Polylactide yarn according to claim 1, characterized in that the lactide polymer is entirely derived from L-lactide and / or DL-lactide. The method of manufacturing a polylactide yarn according to claim 1, wherein a lactide polymer having an intrinsic viscosity of at least 5.5 dl / g is spun from a solvent mixture of an aliphatic chlorinated hydrocarbon of a polar character and a light aromatic hydrocarbon, and then provided that the percentage by volume of the solvents contained in the mixture is chosen so that it does not exceed 15 .; is removed from the percentage where the intrinsic viscosity reaches a maximum after a gradual decrease. 5. V \ - f * '"« «P 189 - 9 - The process according to claim 4, wherein a lactide polymer is spun from a solvent of chloroform and toluene, characterized in that the volume ratio of chloroform to toluene is selected between 55:45 and 25:75. Process according to claim 5, characterized in that the volume ratio of chloroform to toluene is chosen between 45:55 and 35:65. ?> n *; ' Process according to claim 5, characterized in that 40 parts by volume of chloroform to 60 parts by volume of toluene are taken for the solvent mixture. Process according to claim 4, characterized in that the solvent mixture is prepared by first dissolving the lactide polymer in the aliphatic chlorinated hydrocarbon and then adding the light aromatic hydrocarbon until the required volume ratio and concentration are obtained. Method according to claim 4, characterized in that the spin temperature is selected between 55 and 65 ^ 0. Method according to claim 4, characterized in that the yarn is drawn with a draw ratio between 4 and 30 at a temperature between 45 and 21 ° C. Method according to claim 10, characterized in that. the yarn is drawn with a draw ratio of between 10 and 25 at a temperature of between 190 and 208 ° C. Process according to claim 4, characterized in that the lactide polymer is spun at a concentration of 1 to 20 (w / v) i. i>. Process according to claim 12, characterized in that the lactide polymer is spun at a concentration of 1.5 to 15 (w / v) 8 7 0 5; 5