NO137261B - TWINED SURGICAL MULTIFILAMENT SUT. - Google Patents

Description

The present invention relates to surgical sutures and more particularly to multifilament sutures. Twisted polyester monofilament sutures have been widely used by surgeons because of their strength and because they do not react with tissue. Other surgeons prefer to use wax-treated silk when there is a need for a non-absorbable suture because of this material's good properties when it comes to handling, it is easy to criy-te and that. passes easily through tissues.

An important feature of sutures for use in connection with deep wounds is the ease with which a simple knot can be passed in place down the suture. This property, which is often referred to as "tying ability<11>, can be judged subjectively by tying a suture around a suitable spindle. A single knot is formed and while pulling on one of the two free ends, the knot is forced to slide along the suture. The unevenness or The smoothness of this sliding action is an important criterion when it comes to performance or properties.

Uncoated braided tapes such as a braided polyethylene terephthalate suture behave very unevenly, while sutures coated with "Teflon" as described in US Patent No. 3,527,650 and wax-coated braided silk sutures are very smooth and even. ■ The unevenness or smoothness with respect to "bonding ability" can be measured and given a numerical value which enables the appearance and behavior in the hands of the surgeon to be predicted without having to rely on the subjective test discussed above. In the following, one method is described in which an "Instron Universal Testing Instrument" is used to determine "binding properties".

The present invention is aimed at improving the binding properties of a twisted suture by applying a surface coating of a non-toxic and physiologically inert polymer which has no adverse effect on the handling or strength properties of the suture.

It has now been discovered that the bonding properties of twisted or coated multifilament sutures can be improved (unevenness reduced) by applying to their surfaces polyesters derived from the polymerization of lactones or obtained by esterification of low molecular weight glycols with a dimer acid.

According to the present invention, a twisted multifilament surgical suture with improved binding ability is thus provided,

and the suture is characterized in that its surface is coated with 0.5-5% by weight of the suture with a polyester of the formula:

where n is an integer greater than 1 and less than 13, m is an integer greater than 1 and less than 9 and x is the degree of polymerization, or of the formula:

where R is a polymethylene group and x is the degree of polymerization,

in that the polyester has a molecular weight in the range 1500-5000.

One can condense stoichiometric amounts of succinic,, glutaric, adipic, pimelic, subering, azelaic and sebacic acid or mixtures thereof with ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, nonanediol, decanediol, undecanediol, dodecanediol or mixtures thereof, to obtain a polyester suitable for application as a surface coating. Polyesters of the above formula with a molecular weight in the range of .1,500 to 5,000

and characterized by at least two carbon atoms between the ester bonds in the polymer chain, has been found to give the best lubrication and handling properties on silk and polyester sutures. Particularly preferred polyesters are those derived from 1,4-butanediol (n = it) and adipic acid (m = 4-) with a molecular weight of 2,000 - 3,000.

It will be understood that acids with branched chains such as an a,a,g-trimethylsuberic acid of the formula: 3,7-dimethyloctadienonic acid-, 1,4-cyclohexanecarboxylic acid, mesaton-. acid, 8,fr-dimethylglutaric acid and dimer acid, as well as diols with branched chains such as diisononyl glycol with the formula:

and glycols with a secondary hydroxyl group, such as .1,.2-propylene glycol, can be added to the reaction mixture in small amounts as /comonomers Tor production of polyesters -suitable as coating materials and with a melting point above room temperature. The addition of larger amounts of such comonomers to the reaction mixture will result in polyesters with low melting points and which are unsuitable for use for the purposes of the invention.

Particularly preferred are the above-mentioned polyesters with a molecular weight of around 2,000 and which are obtained by polymerization of α-caprolactones in the presence of a polymethylenediol and as here with the formula: where R is a polymethylene group derived from polymethylenediol and x is the degree of polymerization.

The polyester coating compositions discussed above are non-toxic and can be applied, on. the multifilament suture from dissolution. The multifilament suture can have a braided, twisted or wrapped construction. The construction of - en-.ompunnet. suture is described in US Patent No. 3,791,388. The suture is then • air-dried to remove solvent and a continuous surface coating is obtained. The surface coating composition (0.5 to about 5%

based on the weight of the suture) has no adverse effect on the strength properties or stability. While application of over 5% by weight of the surface coating composition provides improved lubricity, this may impair other physical properties of the suture, particularly knot stability.

A numerical value can be assigned the "binding capacity" of which

any twisted suture when tested ■ in accordance with the following method. When describing:-' the' test for "binding capacity", reference is made to the attached drawings, where:

Figure 1 is a schematic representation of an "Instron Tester"

and shows two braided sutures placed for testing; Figure 2 is an enlarged perspective view of the knot indicated in figure-. 1; "-.'■■-' ■'• •' ' i -...<:>■•■•■---' Figure '3 is a curve plot obtained from one ' oscillographic ■ printer-. -

All bond measurements given in the tables were measured on a "Table-Mo"del Instron Tensile -Tester" using a "type B" cell -in the range of 100 to 2,000 g.- A "Sanborn" oscillographic high speed printer is used instead of the usual "Instron" printer which would be<:> too slow to follow the rapid force changes which result as the sutures under test slide against each other. One high gain DC amplifier is "used" and this is used to interface the printer with the "Instron" inverter and a low voltage DC power source is provided to energize the inverter. The measurements are made in an air-conditioned laboratory at a temperature of 21°C and 50% relative humidity. A contact jaw is used to hold the suture test threads. ■ The "Instrori" machine is operated at a crosshead speed of 125 cm per minute and the paper speed of the oscillographic printer is 20 mm per second.

Subjective tests for "tying ability" involve the suture configuration 11 shown in Figure 2 (a single tied knot). The same configuration is achieved by means of a pulley arrangement carried by a steel plate 10 shown in Figure 1'.. The steel plate is attached to the crosshead 12 of the "Instron" tester..

To perform "binding capacity" measurements, two threads 8 and 9 of the same suture are attached at one end to the "B-cell" transducer 14: on an "Instron tester". The sutures are threaded through the waist device as shown in Figures 1 and 2. The other end of the suture threads is passed around the waists 15 and 16 and attached to a plumb bob 18 which provides a tensile effect or tension similar to that exerted in a subjective attempt. With the "standard method" a weight of 1,125 g is used.

Figure. 3 shows current printer curves for a braided polyethylene terephthalate suture before and after coating with a polymer to improve bonding. The roughness values are measured along the ordinate and given in kilograms (roughness). When relatively smooth or even samples are compared, the oscillographic recorder's amplitude can be increased by a factor of 20.

In the following, the invention shall be illustrated by means of

the given examples illustrating preferred embodiments of the invention.

Example 1 I

A condensation polymer is prepared by reacting 42.5% by weight of 1,4-butanediol with 57.5% by weight of adipic acid. The polymer thus obtained is a waxy solid with a viscosity of 1475 eps. at 6o°C, a molecular weight of 2150 and an acid number of 1.7, as well as a hydroxyl number of 52.1.

The polyester thus produced (4.84 parts by weight) is dissolved

in 95.16 parts by weight toluene and the solution is applied to a braided size 2/0 polyethylene terephthalate suture using an "Atlab Yarn Finish Applicator". The braided thread is coated

under the following conditions:

The coated, braided wire is dried using blowing air at a temperature of 21-27°C to evaporate the solvent and is then wound up on a drum. No curing of the adipic acid ester is necessary. The coating is continuous over the entire surface of the suture and is present in an amount of 1% by weight (based on the weight of the untreated suture). The coated braided wire is sterilized by exposure to cobalt-60 irradiation without significant loss of straightness or knot strength. The physical properties of the braided polyethylene terephthalate suture before and after coating are given in table 1.

Similar results are obtained when the polyester resin indicated in this example is used to coat braided silk, cotton and collagen sutures. However, a larger amount of coating solid should be used on hydrophilic substrates such as cotton and silk. The coated sutures prepared according to this example have excellent knot-holding properties.

Example II

A linear polymer of ε-caprolactone with an average molecular weight of approx. 2,000 and with the structural formula:

where R is a polymethylene group derived from a polymethylenediol and where n is the degree of polymerization, was used. This polycaprolactone has a molecular weight of approx. 2,000 - and it is traded under the trade name "Niax Polyol D-56O".

The polycaprolactone was dissolved in toluene to obtain a 3.8% by weight solution. This solution is applied to a braided, size 2/0 polyethylene terephthalate suture using an "Atlab Yarn Finish Applicator". The braided thread is coated under the same conditions as stated in example I and dried by blowing air at a temperature of 24°C. The coated braided thread is wound on a drum after evaporation of the solvent. No curing of the polycaprolactone is necessary. The coating is continuous over the entire surface of the suture and is applied in amounts of 1% by weight (based on the weight of the untreated suture). The coated braided wire is sterilized by means of cobalt-60 irradiation without particular loss of straightness and knot strength.

The physical properties of the polyethylene terephthalate suture before and after coating are given in table 2.

Similar results are obtained when the polycaprolactone is used to coat braided silk, cotton and collagen sutures of sizes from 2/0 to 6/0." The polyesters used can also be used to coat absorbable synthetic sutures such as those described in US Patent Nos. 3-297,033 and 3-636,956 with a resulting improvement in bonding properties.

Claims (5)

1. Twisted surgical multifilament suture with improved tie eye, characterized in that the surface of the suture is coated with 0.5-5% by weight of the suture with a polyester of the formula: where n is an integer greater than 1 and less than 13, m is an integer greater than. ,1 and less than 9 and x is the degree of polymerization,. or by the formula: where R. is a polymethylene group and x is the degree of polymerization, the polyester having a molecular weight in the range 1500-5000. 2. Suture according to claim 1, characterized in that the polyester is a condensate of adipic acid and 1,4-butanediol with a molecular weight of 2000-3000. 3. Suture according to claims 1 and 2, characterized in that the suture consists of silk and that the polyester coating is present in an amount of 5% by weight of the untreated suture. 4. Suture according to claims 1-3, characterized in that the suture consists of polyethylene terephthalate and that the polyester coating is present in an amount of 1 weight-5 of the untreated suture. 5. Suture according to claims 1-4, characterized in that the polyester coating has a molecular weight of approx. 2000.