Patent GB-750325-A (GB)
Title: Absorbable cellulose ether products
IPC: A61L15/64
Filed: 1953-06-05
Abstract: A cellulose glycolic acid ether in free acid state is produced with a degree of polymerization indicated by a viscosity of a 0.50 per cent by weight solution of the free acid in a 0.50 N. NaOH solution at 25.5 DEG  C., in the range of 5.7 to not more than 17.4 seconds as determined in a modified Ostwald-Fenske viscosimeter pipette A.S.T.M. D-445-46T-300, as compared with a zero reading of 5.0 seconds for a 0.50 N. NaOH solution at the same temperature.  The compound is completely absorbable by the body, and it may be used for making filaments, films, sutures, sponges, powders, or other articles or preparations for surgical purposes.  It has haemostatic properties. Preferably the cellulose ether has a degree of substitution between 0.5 and 2.0 and a degree of neutralization in the range of 0-60 per cent. For obtaining the desired degree of polymerization a cellulose glycolic acid ether may be heated at an elevated temperature in presence of water or steam or in dry condition so as to reduce the length of the cellulose chain.  A minimum temperature of 180 DEG  F. is usually required, but in presence of strong mineral acid the process may be performed at room temperature.  Temperatures above 350 DEG  F. are undesirable.  The cellulose ether may be treated in the free acid state or in the form of its sodium salt.  When treated in dry condition at 180 DEG  F. the duration of the heating may be one day or longer, but at 300 DEG  F. it may be only 2 hours. A cellulose ether (having a degree of polymerization indicated by 15 seconds viscosity) in a 5 per cent aqueous solution, purified by electrodialysis, may be heated at 200-210 DEG  F. for 16 hours to reduce its degree of polymerization to a value indicated by 7.6 seconds viscosity.  If desired the de-polymerization may be carried out in an autoclave with the cellulose ether in free acid state dissolved in an aqueous solution.  Such treatment may be effected at 250 DEG  F. for 20 minutes.  Treatment with water under pressure may be carried out on initially insoluble forms of the cellulose ether which are rendered soluble or partially soluble by the treatment, forming thin solutions, smooth pastes, or thick gels.  Reduction in the length of the cellulose chain may also be effected by treatment of the cellulose ether, as free acid or in the form of its sodium or ammonium salt, with a cellulose enzyme. The action of the enzyme may be stopped by heating or by adding excess of ammonia.  Inorganic ionic impurities in the cellulose glycolic acid ether may be removed by subjecting it in solution to electrodialysis and if this is carried out at temperatures above 100 DEG  F. the degree of polymerization may be reduced at the same time.  The degree of polymerization may be reduced by fractionating a solution of the cellulose ether by incremental precipitation.  In the production of filaments, films, and other articles, the cellulose glycolic acid ether or a salt thereof may be dissolved in water or other solvent to form a liquid or plastic mass.  Sodium, potassium, or ammonium salts, may be used. Provided the cellulose ether has a sufficiently high degree of substitution, the free acid form of it may be transformed into a gelatinous state or even dissolved in water at elevated temperature and pressure.  The solution or plastic mass may be shaped, e.g. by extrusion or casting and solidified by treatment with an acid solution or with alcohol or other coagulating agent. Pore formers such as soluble salts or substances capable of generating gas may be incorporated in the mass when it is desired to make a spongy material.  An alternative procedure for making spongy material is to freeze a solution of the cellulose glycolic acid ether and remove the solvent by drying in a vacuum.  The solution to be frozen should contain at least 0.5 per cent of solids.  The filaments, films, sutures, sponges, or other articles are preferably subjected to a treatment to effect a substantial decrease in the solubility of the acid ether in water.  For this purpose they may be heated at 150-350 DEG  F., if desired in the presence of gaseous formaldehyde.  Before use, the articles are sterilized, e.g. by open steam treatment at 212-250 DEG  F. for 15-60 minutes, or by treatment at lower temperatures in presence of ethylene oxide or formaldehyde.  Pieces of the cellulose glycolic acid ether in sponge form may be compressed into pellets which retain their compressed form when dry but swell rapidly when treated with water.  These pellets may be used in dentistry.  The various operations of purification, solution, formation of the desired article, dehydration, insolubilization, adjustment of the degree of polymerization, and adjustment of the degree of neutralization may be carried out in various orders, and if desired, some of the steps may be combined.  In an example, an aqueous solution of the sodium salt of a cellulose glycolic acid ether having a degree of substitution of 1.2 and a degree of polymerization corresponding with a viscosity of 26.8 seconds as measured by the specified method is electrodialized to a limiting pH of 2.35, corresponding with the completely free acid state of the ether.  The electrolized solution is refluxed on a steam bath at 210 DEG  F. for 10 hours at the end of which time its D.P. is indicated by a viscosity of 7 seconds.  Ethyl alcohol is incorporated in the solution and the mix is frozen while being agitated.  Cooling is continued until the mixture assumes the consistency of a smooth sherbet of fine crystals.  The sherbet is then transferred to moulds and quickly frozen at -70 DEG  C.  The frozen bricks are freeze dried and then insolubilized by heating in air at 180 DEG  F. for 3 hours. Haemostatic absorbable sponges of uniform pore size are obtained. Instead of ethyl alcohol, there may be used methyl or propyl alcohol or a polyhydric alcohol such as ethylene glycol or glycerol.  If desired, ionic impurities may be removed and the free acid form of the cellulose ether may be obtained from its salts by passing a solution of a salt of the ether through a layer of an ion exchange resin.ALSO:Filaments, films, sutures, sponges, powders, and other articles or preparations for surgical purposes are made of a cellulose glycolic acid ether which is in the free acid state and has a degree of polymerization indicated by a viscosity of a 5,0 per cent by weight solution of the free acid in a 0,50 N. NaOH solution at 25,5 DEG C. in the range of 5,7 to not more than 17,4 seconds as determined in a modified Ostwald-Fenske viscosimeter pipette A.S.T.M. D-445-46T-300, as compared with a zero reading of 5,0 seconds for a 0,50 N. NaOH solution at the same temperature.  The cellulose ether is completely absorbable by the body and it has haemostatic properties.  For obtaining a compound of the required degree of polymerization a cellulose ether as originally obtained may be subjected to the action of heat or mineral acid, or other methods may be used (see Group IV(a)).  Films made of the cellulose ether may be used as barrier layers or liners in brain surgery.  Fine filaments may be obtained and spun to form suture threads, or coarser filaments may be produced and used directly for suturing.  The cellulose ether may be formed into cellular or spongy material (see Group IV(a)) which may be used as such or may be comminuted to form a dusting powder or haemostatic powder, or the sponge material, preferably after comminution, may be compressed into absorbable pellets, particularly suitable for use in dental surgery.  The pellets retain their compressed form, without application of external pressure, when dry, but when they are treated with water they rapidly expand to many times their original volume while still retaining their general shape and without appreciable disintegration.  After the cellulose ether has been obtained in the desired form e.g. powder, sponge, film, or suture, it may be subjected to a heat treatment e.g. at 150-350 DEG F., preferably in presence of formaldehyde vapour, so as to convert it into a water-insoluble state while still retaining the property of being absorbable by the body.  The material may be sterilized by steam treatment, by treatment with ethylene oxide, or by heating in a moist atmosphere containing formaldehyde vapour.