US 2193188 A
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Patented Mar. 12, 1940 v UNITED STATES NONCAPILLARYSILK SUTURE AND METHOD "OF PREPARING THE SAME Theodore F. Bradley, Stamford, Conn, assignor to American Cyanamid Company, New
N. Y., a corporation of Maine I NoDrawing. Application June 16, 1938, Serial No. 214,147
9 Claims. (Cl. 128-3355) The present invention relates to a method of making a noncapillary silk suture for surgical purposes and the suture per se. 7
Silkthreads, made by twisting or braiding a number of degummed and cleaned raw silk filaments, have been used in surgery as suture material for many years. However, when such a silk suture is embedded in infected tissue, bacteria are harbored in its interstices and the suture becomes a nidus of infection which does not subside until the silk sloughs out or is removed surgically. Because of its capillarity, there is always the possibility of the exposedend of a silk suture acting as a wick to carry infection into the tissue. Thematerial, therefore, has never come into general surgical use for this purpose.
It is a principal object of the invention to produce a silk suture made of a number of silk threads, twisted, braided, woven or otherwise associated together into a strand, which will be substantially noncap-illary, and this object can most effectively be accomplished by coating such suture material with a composition which will present an unbroken surface to moisture.
The proposal toreducethecapillarity of silk sutures is not a new one. Many attempts have been made to this end and while it has been found not particularly difficult to-treat a braided or twisted surgical silk so as to produce a satisfactory degree of noncapillarity, yet such treat-- ment resulted in lending undesirable characteristics to the product or was unsatisfactory for other reasons.
A surgical silk suitable for useas a suture must be soft, pliable, nonacidic, noncorrosive and physiologically harmless and be capable of withstanding heat or chemical sterilization. These factors have generally stood in the way of the production of a successful noncapillary surgeons silk, for any treatment which decreased capillarity was objectionable because such product did not meet the other necessary qualifications or because the stringent conditions of sterilizawithout detrimental effect.
silk suture by applying to the silk suture stock, hereinafter referred to as a strand, a composition including ethyl cellulose in a volatile solvent and then permitting or inducing the solvent to evaporate. Under these conditions, the ethyl cellulose forms an unbroken film on the exterior periphery of the suture strand and even penetrates the same to a desired extent, whereby the capillarity of the strand is reduced.
A noncapillary suture thus produced will withstand the usual heat and/or chemical st'erilization without substantial decrease in its noncapillarity. Where the sterilization treatment consists in contact with hot liquids, such as hot mineral 'oil, the suture will withstand the necessary high temperatures for the required periods Such heat sterilization treatment in oil is even beneficial in that it hasa tendency to maintain the pliability of the suture, and in use even when the excess oil is removed, a slight film thereof remains which, due to its water repellency, assists in maintaining the noncapillarity of the product.
The invention further contemplates a substantially noncapillary silk suture product in which the silk strand or strands are provided with one or more coatings of ethyl cellulose with or without an additional superficial coating of oil.
Alarge number of coatingand impregnating compositions were found to be satisfactory from the standpoint of actually reducing capillarity to the desired degree when applied to twisted or braided silk suture stock but resulted in lending stillness, u'npliability or other undesirable characteristics to the product, or the noncapillarity was materially destroyed when such products were subjected to heat and/or chemical sterilization or to other conditions to which sutures may be normally subjected.
Ethyl cellulose was found to be of outstanding value in that it met all of the stringent requirements without producing detrimental eifects while at the same time producing reduction in capillarity to the desired degree with optimum permanence.
In preparing the ethyl cellulose solution with which the silk stock is to be treated, ethyl cellulose of various viscosities and different solvents may be employed. While ethyl cellulose of viscosities of from 10 to centipoises has been 50 used for these compositions, such as the methyl 5 or ethyl ether of ethylene glycol, toluene, ethanol or mixtures thereof, as well as other known solvents, the proportions being varied to give the desired concentration of ethyl cellulose. Mis cible diluents may also be employed and where these are noninflammable, such as carbon tetra chloride, their use may be desirable under some circumstances.
The preferred coating composition comprises the following substances in substantially the proportions specified:
Solution A Grams Ethyl cellulose20 centipoise grade 40 Toluene 120 Ethanol 40 200 (20% solids) Solution B Grams Solution A 40 Ethanol 10 Toluene 50 100 (8% solids) Suture stock silk may then be immersed in, sprayed or otherwise contacted with, such a solution for from one to two minutes, the excess solution removed and then the coated strand airdried or preferably at some elevated temperature to remove all of the volatile solvent. This operation may be repeated as many times as necessary in order to produce a coating of the desired thickness or Weight, dependent upon the circumstances. In order to reduce fire hazard due to the infiammability of the above solvents, requisite amounts of carbon tetra chloride may be added thereto as desired.
After the silk has thus been treated to render it noncapillary, it may be out into the required lengths, wound into small coils, placed in glass tubes, which are filled with a light mineral oil and then sealed by fusion of the glass, the sealed tubes may then be placed in an autoclave and heat sterilized. When this is complete, the tubes are ready for packaging. While the above method of sterilization is preferred, other standardized procedures may likewise be employed.
While the invention has been described with specific reference to certain embodiments, it is to be understood that it is not to be limited thereto but is to be construed broadly and restricted solely by the scope of the claims.
"coated with ethyl cellulose and having a superficial exterior coating of oil.
3. A substantially noncapillary non-water absorptive silk suture comprising a silk strand coatedwith ethyl cellulose and having a superficial exterior coating of mineral oil.
4. A method of making a substantially noncapillary silksuture which includes the following steps: contacting a silk strand with a solution of ethyl cellulose in an organic solvent, removing the strand from the solution and evaporating the solvent from the ethyl cellulose so as to produce an adherent coating of the latter on the strand.
5. A method of'making a substantially noncapillary silk suture which includes the following steps: immersing a silk strand in a solution of ethyl cellulose in an organic solvent, removing the strand from the solution, removing the excess solution from the strand and drying the strand.
6. A method of making a substantially noncapillary silk suture which includes the following steps: immersing the silk strand in ethyl cellulose dissolved in a mixture of toluene and ethyl alcohol, removingthe strand from the solution and drying the strand.
7. A method of making a substantially noncapillary silk suture which includes the following steps: immersing the silk strand in a solution of 20 centipoise viscosity ethyl cellulose in an organic solvent, removing the strand from the solution anddrying the strand.
8. A method of making a substantially noncapillary silk suture which includes the following steps: immersing a silk strand in an 8% solution of 20 centipoise viscosity ethyl cellulose in an organic solvent, removing the strand from the solution and drying the strand.
9. A method of making a substantially noncapillary silk suture which includes the following steps: immersing a silk strand in a solution of ethyl cellulose in an organic solvent, removing the strand from the solution and evaporating the solvent from the ethyl cellulose so as to produce an adherent coating of the latter on the strand and sterilizing the coated strand in mineral oil.
THEODORE F. BRADLEY.