Abstract:
A method of making absorbable surgical threads consists in treating cellulose threads with nitrogen oxides, then treating these threads with a protophilic solvent for 1 to 2 hours at a room temperature and holding them at a temperature of 70° to 90° C. for 1 to 2 hours.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of making absorbable surgical threads and can be used in medicine biology and veterinary science. 
     At present absorbable threads are widely used in medical practice. They do not require such a manipulation as thread removal and provide for a proper cosmeticability of the cicatrices resulting from surgical operations. 
     In order to be successfully used, the absorbable threads should possess a sufficient strength. However, conventional absorbable threads are of inadequate mechanical strength. Therefore efforts are constantly undertaken to develop novel methods of making absorbable threads based on cellulose which are characterized by a higher mechanical strength. 
     2. Description of the Prior Art 
     There is known in the art a method of making surgical threads (U.S. Pat. No. 2,537,979) which consists in oxidizing cellulose with nitrogen dioxide. However, as distinct from the method described above, the oxidation here is carried out till the content of carboxyls is 4 to 12.5%. The time of making said surgical sutures is 64 hours. The process is carried out at a temperature of 25° C. Having been treated with nitrogen dioxide, the threads are washed with distilled water and dried. The ratio between the value of the tensile strength of the absorbable threads produced due to the treatment of the initial threads and the value of the tensile strength of the initial threads prior to the treatment is 36.8 to 43.5%. 
     As a result of the oxidation of the cellulose threads with nitrogen oxides there occurred a destruction of the supermolecular structure of the cellulose threads because of inculation of large molecules of N 2  O 4 , rupture of intermolecular hydrogen bonds cellulose-cellulose and cellulose-water-cellulose, substitution of a part of C 6  H 2  OH-groups by larger C 6  OOH-groups. Therefore, the surgical absorbable threads produced by said method are of a low mechanical strength and of a high swelling property in biological media. 
     As noted in the above Patent, such a thread completely lost its strength within 5 days. The testing was carried out in a phosphate buffered solution having a pH of 7.5 at a temperature of 37° C. where a thread is absorbed slower than in living tissues. No testing of the thread placed in living tissues was carried out. 
     Thus, the above-described method does not provide for the manufacture of absorbable surgical threads having a high mechanical strength and a low swelling property in beological media. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a method of making absorbable surgical threads based on oxidized cellulose, which method makes it possible to upgrade the quality of the absorbable surgical threads, i.e. to improve their mechanical strength and to reduce their swelling property both in water and in biological media. 
     Other objects and advantages of the present invention will be clear from the following description. 
     The above and other objects of the invention are attained by that there is provided a method of making absorbable surgical threads consisting in treating cellulose threads with nitrogen oxides, wherein, according to the invention, the threads treated with the nitrogen oxides are further treated with a protophilic solvent for 1 to 2 hours at a room temperature and then held at a temperature of 70° to 90° C. for 1 to 2 hours. 
     The above treatment of the oxidized cellulose threads provides for a higher degree of ordering of their supermolecular structure, for a larger amount of hydrogen bonds between macromolecules of the oxidized cellulose as well as between the latter and water bonded with cellulose. As a result, the mechanical strength of the oxidized threads improves and the selling property of these same threads in water and biological media decreases. 
     It is expedient to use as the protophilic solvent a 2 to 10% water solution of ionogenic compound selected from the group consisting of sodium chloride, calcium chloride, calcium acetate and acetic acid; a 2 to 10% aqueous solution of an amphiprotonic polyhydric alcohol selected from the group consisting of glycerol, pentaerytritol, mannite, sorbitol, glucose, saccharose and dextrose; an organic solvent selected from the group consisting of dimethyl formamide, dimethyl sulfoxide and dimethyl acetamide. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Absorbable surgical sutures according to the invention were produced in the following way. 
     Cellulose threads are oxidized with nitrogen oxides in a conventional manner. The cellulose threads may be threads from cotton, flax, viscose, high-module viscose, polynose etc which are characterized by a wide range of thickness and an amount of additions. 
     The oxidized threads are thoroughly washed with water, whereupon wet threads are placed into a stainless steel reaction vessel having a capacity of 20 liters and filled with a preliminarily prepared protophilic solvent. The threads are held in this reaction vessel for 1 to 2 hours. 
     The protophilic solvent may be a 2 to 10% water solution of ionogenic compounds such as sodium chloride, calcium chloride, calcium acetate and acetic acid; a 2 to 10% aqueous solution of an amphiprotic polyhydric alcohol such as glycerol, pentaerytritol, mannite, sorbitol, glucose, saccharose and dextrose as well as an organic solvent such as dimethyl formamide, dimethyl sulfoxide, or dimethyl acetamide. 
     Thereupon the threads are withdrawn from the reaction vessel and placed into a stainless steel chamber having a capacity of 20 liters and blown through with air heated up to a temperature of 70° to 90° C. In this chamber the threads are held for 1 to 2 hours. 
     The method of the present invention makes it possible to produce absorbable surgical threads whose mechanical strength is 83 to 105% of cellulose threads before oxidation. 
     The swelling property of the sutures produced according to the invention is reduced down to 20 to 60% as compared with the swelling property of the initial non-oxidized cellulose threads. 
    
    
     EXAMPLE 1 
     Absorbable surgical sutures were produced according to the invention in the following way. 
     2.4 kg of complex viscose threads having a size of 60/18 and a tensile strength of 4.75 kg were oxidized with nitrogen oxides in a conventional manner. The oxidized threads were thoroughly washed with water and then tested to determine the content of carboxyls, fixed nitrogen, relative humidity, tensile strength, and degree of swelling in water. 
     The results of the testing were the following: 
     
         ______________________________________content of carboxyls, %                6.5content of fixed nitrogen, %                0.12relative humidity, % 12.8tensile strength, kg 3.35degree of swelling in water, %                59.5______________________________________ 
    
     Thereupon, the wet threads were placed in a reaction vessel having a capacity of 20 liters and filled with a 10% of an aqueous solution of sorbitol in an amount of 15 liters. The threads were held in the reaction vessel for 2 hours, whereupon they were withdrawn therefrom, and placed into a chamber blown through with air heated to a temperature of 80° C., in which chamber the threads were again held for 1.5 hours. 
     Thus treated threads were again tested to determine the tensile strength and degree of swelling. 
     The results of the testing are given below: 
     
         ______________________________________tensile strength, kg             5.0degree of swelling, %             31.1______________________________________ 
    
     The ratio between the value of the tensile strength of the oxidized treated threads to the value of the tensile strength of the oxidized non-treated threads was 154%, and the ratio between the value of the degree of swelling of the oxidized treated threads to the value of the degree of swelling of the oxidized non-treated threads was 52.3%. 
     The ratio between the value of the tensile strength of the oxidized treated threads to the value of the tensile strength of the initial viscose threads was 105.3%. 
     EXAMPLE 2,3 
     Absorbable surgical threads according to the invention were produced in the following way. 
     Complex viscose threads having initial properties similar to those described in Example 1 were subjected to oxidation and then to treatment according to the procedure described in Example 1. 
     The properties of the oxidized non-treated threads are similar to those of Example 1. 
     
         ______________________________________Teatment conditions                       Temperature                                DurationNo of  Protophilic            Time of hold-                       of treat-                                of treat-Example  solvent   ing, hours ment, °C.                                ment, hours______________________________________2      2% sodium 2          80       1.5  chloride3      2% calcium            2          80       1.5  chloride______________________________________ 
    
     
         ______________________________________Properties of the oxidized treated threads          Ratio between the          indices of oxidized                        Ratio between          treated threads and                        the value of the          the indices of oxi-                        tensile strength    Degree          dized non-treated                        of oxidized non-    of    threads       treated threadsNo of Tensile  swel-   Tensile                         Degree and the tensileExam- strength,          ling,   strength,                         of swel-                                strength of ini-ple   kg       %       %      ling, %                                tial threads, %______________________________________2     4.95     36.0    152.0  60.2   104.23     4.60     36.0    141.6  60.5   96.8______________________________________ 
    
     EXAMPLES 4-12 
     Absorbable surgical threads according to the invention were produced in the following way. 
     2.4 kg of viscose threads having a size of 60/18 and a tensile strength of 4.75 kg were oxidized and further treated in accordance with the procedure described in Example 1. 
     The properties of the oxidized non-treated threads are similar to those of Example 1. 
     
         ______________________________________Treatment conditions                          Temper-                                 Time of              Time duration                          ature of                                 treat-No of  Protophilic of holding, treat- ment,Example  solvent     hours       ment, °C.                                 hours______________________________________4      6% sodium   1.5         80     1.5  chloride5      10% calcium 1.0         70     2.0  chloride6      6% glycerol 1.5         80     1.57      6% penta-   1.5         80     1.5  erytritol8      2% sorbitol 2.0         90     1.09      10% sorbitol              1.0         70     2.010     2% glucose  2.0         90     1.011     6% saccharose              1.5         80     1.512     10% dextrose              1.0         70     2.0______________________________________ 
    
     
         ______________________________________Properties of the oxidized treated threads          Ratio between the                        Ratio between          indices of oxidized                        the value of the          treated threads and                        tensile strength          the indices of oxi-                        of oxidized non-    Degree          dized non-treated                        treated threads    of    threads       and the valueNo of Tensile  swel-   Tensile                         Degree of the tensileExam- strength,          ling,   strength,                         of swel-                                strength if ini-ple   kg       %       %      ling, %                                tial threads, %1     2        3       4      5      6______________________________________4     4.95     35.5    152.5  59.6   102.05     4.70     36.0    145.0  60.5   99.06     4.15     42.5    128.0  71.4   87.47     4.15     43.0    128.0  72.3   87.48     5.0      31.1    154.0  52.3   105.09     5.0      31.2    154.0  52.4   105.010    4.5      44.5    138.0  74.8   94.611    4.3      42.0    132.0  70.6   90.512    4.2      42.5    129.0  71.4   88.5______________________________________ 
    
     EXAMPLE 13 
     Absorbable surgical threads according to the invention were produced in the following way. 
     2.4 kg of complex viscose threads having a size of 60/18 and a tensile strength of 5.95 kg were oxidized and further treated in accordance with the procedure described in Example 1. 
     Properties of the oxidized non-treated threads: 
     
         ______________________________________content of carboxyls, %                9.0content of fixed nitrogen, %                0.1relative humidity, % 9.0tensile strength, kg 4.05degree of swelling in water, %                57.6______________________________________ 
    
     The conditions of the treatment were as follows: 
     
         ______________________________________protophilic solvent    4% acetic acidtime of holding, hours 2temperature of heat treatment, °C.                  80time of heat treatment, hours                  1.5______________________________________ 
    
     The properties of the oxidized treated threads were as follows: 
     
         ______________________________________tensile strength, kg  5.35degree of swelling, % 45.0ratio between the value of the ten-sile strength of the oxidizedtreated threads to the value ofthe tensile strength of the oxi-dized non-treated threads, %                 132.0ratio between the value of thedegree of swelling of the oxidizedtreated threads and the valueof the degree of swelling of theoxidized non-treated threads, %                 78.0ratio between the value of the ten-sile strength of the oxidizedtreated threads to the valueof the tensile strength of theinitial threads, %    90.0______________________________________ 
    
     EXAMPLES 14-23 
     Absorbable surgical threads were produced according to the method of the present invention. 
     2.4 kg of high-modull viscose having a size of 20/6 and a tensile strength of 5.60 kg were oxidized and further treated in accordance with the procedure described in Example 1. 
     The properties of the oxidized non-treated threads were the following: 
     
         ______________________________________content of carboxyls, %                5.5content of fixed nitrogen, %                0.1relative humidity, % 7.6tensile strength, kg 4.45degree of swelling in water, %                61.0______________________________________ 
    
     
         ______________________________________Treatment conditions                       Temperature                                Time ofNo of  Protophilic            Time of hold-                       of treat-                                treatment,example  solvent   ing, hours ment, °C.                                hours______________________________________14     dimethyl  2.0        80       2.0  sulfoxide15     dimethyl  2.0        90       1.0  formamide16     dimethyl  1.5        80       1.5  formamide17     dimethyl  1.0        70       2.0  formamide18     dimethyl  2.0        90       1.0  sulfoxide19     dimethyl  1.5        80       1.5  sulfoxide20     dimethyl  1.0        70       2.0  sulfoxide21     dimethyl  2.0        90       1.0  acetamide22     dimethyl  1.5        80       1.5  acetamide23     dimethyl  1.0        70       2.0  acetamide______________________________________ 
    
     
         ______________________________________Properties of the oxidized treated threads:                        Ratio between          Ratio between the                        the value of          indices of oxidized                        the tensile          treated threads and                        strength of          the indices of oxi-                        oxidized non-    Degree          dized non-treated                        treated threads    of    threads       and theNo of Tensile  swel-   Tensile                         Degree tensile strengthExam- strength,          ling,   strength,                         of swel-                                of initialple   kg       %       %      %      threads, %______________________________________14    5.85     38.0    131.5  62.2   104.515    5.2      42.0    127.0  68.8   93.716    5.3      42.0    119.0  68.8   94.717    5.25     43.0    118.0  70.5   94.518    5.85     38.0    131.5  62.3   104.519    5.8      38.5    130.2  63.1   103.520    5.85     38.0    131.5  62.3   104.521    5.25     42.0    118.0  68.8   94.522    5.4      40.0    121.5  65.6   96.623    5.3      41.5    119.0  68.0   94.7______________________________________ 
    
     While particular embodiments of the invention have been shown and described, various modifications thereof will be apparent to those skilled in the art and therefore it is not intended that the invention be limited to the disclosed embodiments or to the details thereof and the departures may be made therefrom within the spirit and the scope of the invention as defined in the claims.