Hemostatic Material

Abstract

A new and improved hemostatic material formed of an oxidized cellulosic material and method for its preparation wherein an oxidized cellulosic material is treated with a borohydride under alkaline conditions.

Description

This invention relates to materials for the control of bleeding, and more particularly to hemostatic material formed of oxidized cellulose.

It is known that cellulosic material may be selectively oxidized with nitrogen dioxide to convert more than 90 percent of the methylol groups in the cellulosic molecule to yield a product which may be referred to as an oxycellulose or polyuronic acid. It is similarly known, as illustrated by U.S. Pat. Nos. 1,197,400 and 2,232,990, that oxidized cellulose may be used as a hemostatic material for the control of bleeding. The use of oxycellulose as compared to other hemostatic materials heretofore known, such as conventional gauze pads and the like treated with ferric chloride, thrombin, etc., represents a significant improvement since oxycellulose may be left in a closed wound without the result of a severe local tissue reaction in response to the presence of foreign material.

However, the primary disadvantage of hemostatic materials formed of oxidized cellulose heretofore known is that they lack stability whereby they must be used within a short time after manufacture, or they must be stored under refrigeration. Various attempts to overcome this disadvantage, such as by the washing of oxidized cellulose after oxidation with an anhydrous alcohol as suggested by U.S. Pat. No. 3,364,200, have been made. However, such attempts have generally been unsuccessful in that the use of an anhydrous alcohol is expensive, and does not significantly increase the stability of the resulting oxidized cellulose.

It is accordingly an object of the present invention to provide a new and improved hemostatic material formed of oxidized cellulose which is stable at room temperatures, and need not be stored under refrigeration.

It is another object of the present invention to provide a simple and inexpensive method for treating oxidized cellulose to improve the thermal stability of oxidized cellulose for use in hemostatic materials.

These and other objects and advantages of the present invention will appear hereinafter, and, it will be understood that the following specific examples are provided by way of illustration, and not by way of limitation, of the concepts of the present invention.

The present invention is addressed to a method for the treatment of an oxidized cellulosic material in order to improve the thermal stability of the oxidized cellulosic material when used as a hemostatic material. The oxidized cellulose to be treated in accordance with the practice of the present invention may be derived from any of a wide variety of cellulosic material, including but not limited to wood pulp, cotton, cotton linters, ramie, jute, paper, hemp, regenerated cellulose or rayon as well as a wide variety of others known to those skilled in the art. However, it is generally preferred to make use of cellulose in the form of cotton or regenerated cellulose, such as that prepared by the viscose process, because of their greater purity. The oxidized cellulosic material may be in the form of a knit or a woven fabric, such as gauze or in a fibrous thread or film form.

The oxidized cellulosic material may be prepared by the selective oxidation using nitrogen dioxide, using a wide variety of techniques. For example, it is possible to form the oxidized cellulosic material by treatment of the raw cellulosic material with liquid nitrogen dioxide in the ratio of 1 part by weight cellulose per 5-1,000 parts by weight liquid nitrogen dioxide, and preferably 1 part by weight cellulosic material to 25-50 parts by weight of the liquid nitrogen dioxide, as disclosed in copending application, Ser. No. 745,221, filed July 16, 1968, now U.S. Pat. No. 3,516,416, issued June 23, 1970. The reaction described therein is carried out at a temperature of 15.degree.-65.degree. C., and at autogenous pressure when the reaction temperature exceeds 21.degree. C., the boiling point of nitrogen dioxide. Another method for effecting this oxidation is disclosed in copending application, Ser. No. 745,135, filed July 16, 1968, now U.S. Pat. No. 3,491,766, issued Jan. 27, 1970, wherein the oxidation reaction, including reaction rate and amount of conversion, is materially improved by formulation of the oxidation reaction mixture to contain up to 8 percent by weight water in the liquid nitrogen dioxide system and by carrying out the reaction at elevated temperatures, generally about 15.degree. C., and preferably within the range of 20.degree.-45.degree. C., depending somewhat upon the amount of moisture present in the reaction medium, whereby the reaction medium is rendered relatively non-electrically conductive so that the presence of water in the reaction medium will not result in attack or degradation of the cellulosic material to be oxidized, and wherein the formulation to include aqueous medium in the reaction mixture of liquid nitrogen dioxide also operates to adjust the specific gravity of the reaction mixture in the direction toward the specific gravity of the cellulosic material whereby suspension of the cellulosic material in the reaction medium is easier to achieve and maintain. The result is a more rapid and uniform oxidation reaction of the cellulosic material to produce a higher quality product at a more rapid rate.

It is also possible, and frequently preferred in accordance with the practice of the present invention, to employ an oxidized cellulose which has been prepared by the selective oxidation of cellulose with gaseous nitrogen dioxide or a mixture of gaseous nitrogen dioxide and nitric oxide. The reaction may be conveniently carried out by contacting the cellulose to be oxidized with the gaseous nitrogen oxide or oxides at a temperature within the range of 30.degree.-220.degree. C. for a period of up to 40 hours to oxidize at least 80 percent of the methylol groups present in the cellulose molecule.

A further method for effecting the gaseous phase oxidation of cellulose is disclosed in copending application, Ser. No. 774,064, filed Nov. 7, 1968, now U.S. Pat. No. 3,577,994, issued May 11, 1971, wherein the cellulosic material is first wetted with a liquid nitrogen dioxide, which may optionally contain up to 8 percent by weight water, and then is exposed to hot gaseous nitrogen dioxide. This particular method can be advantageously used in the form of a continuous process for the production of large quantities of oxidized cellulosic material.

The concepts of the present invention reside in a process for the treatment of oxidized cellulosic material, independent of the method by which the cellulosic material is oxidized, with a borohydride under alkaline conditions to improve the thermal stability of the treated oxidized cellulose during storage. In accordance with the practice of the present invention, an oxidized cellulosic material is treated with a borohydride, such as ammonium borohydride, an alkali metal borohydride (e.g., lithium borohydride, sodium borohydride, potassium borohydride, etc.) or an alkaline earth metal borohydride (e.g., magnesium borohydride, calcium borohydride, etc.) at an alkaline pH. Thereafter the treated oxidized cellulose is washed with dilute acid to destroy the borohydride, and then washed again with alcohol to remove any remaining acid and dried. It has been found that oxidized cellulosic materials treated in this manner may be used as hemostatic materials which are completely stable at room temperatures, and can be stored for long periods of time without the need to store under refrigeration conditions.

The treatment of the oxidized cellulosic material with the borohydride may be conveniently carried out by placing the oxidized cellulosic material in contact with a water-alcohol mixture, and then raising the pH of the resulting mixture to at least 8.5, and preferably to a pH within the range of 9-12 by adding thereto a base, such as an alkali metal hydroxide or an ammonium hydroxide. Thereafter, the borohydride may be added to the basic oxycellulose-water-alcohol mixture to provide a ratio of 1 part by weight borohydride for every 1-100 parts by weight of oxidized cellulose. The resulting solution containing the borohydride may then be allowed to stand at a temperature within the range of 0.degree.-70.degree. C. for a period of 0.1 to 5 hours.

The water-alcohol mixture preferably comprises a mixture of water and an alkanol having one to five carbon atoms, such as methanol, ethanol, isopropanol, etc., wherein the alcohol is present in an amount constituting at least 20 percent by weight, and preferably 50-85 percent by weight, of the water-alcohol mixture. After the treatment with the borohydride has been completed, the treated oxidized cellulose may then be removed and washed with a dilute mineral acid, such as dilute hydrochloric acid or a mixture of dilute hydrochloric acid and an aliphatic alcohol, to destroy the borohydride and to remove any metal salts which may be present in the treated oxidized cellulosic material. Thereafter, the treated oxidized cellulosic material is preferably washed again with an alcohol to remove any acid remaining. The treated cellulose may then be dried and sterilized in a conventional manner, such as by the treatment of the oxidized cellulosic material with formaldehyde.

The following examples will serve to illustrate the principal concepts of the present invention.

EXAMPLE 1

A piece of cotton gauze is oxidized by contacting it with gaseous nitrogen dioxide for a period of 25 hours at 20.degree. C. After the oxidation reaction is completed, the gauze of oxidized cellulose is washed with a mixture of equal parts by weight of water and ethanol to remove remaining nitrogen oxides and to prevent shrinkage.

Thereafter, the gauze of oxidized cellulose is immersed in a mixture of 70 percent by weight methanol and 30 percent by weight water, and a sufficient quantity of a solution of 0.5 N sodium hydroxide is added to raise the pH of the solution to about 10.5. Next, sodium borohydride is added to the solution to provide a ratio of 0.1 parts by weight sodium borohydride per 1 part oxidized cellulose. The oxidized cellulose is allowed to remain in contact with the borohydride solution for 1 hour at room temperature, and then the treated oxidized cellulose is removed from the solution, washed with dilute hydrochloric acid, and washed with ethanol.

The resulting product is dried and sterilized, and is found to have excellent stability at room temperatures.

It will be understood that the step of washing the oxidized cellulosic material with an aliphatic alcohol, such as methanol, ethanol, isopropanol, or water, or mixtures thereof prior to the borohydride treatment(the use of an ethanol-water mixture as exemplified in Example 1 is an optional step. It is frequently preferred to wash the oxidized cellulosic material in this manner subsequent to oxidation in order to insure the dimensional stability and thereby avoid shrinkage.

EXAMPLE 2

A gauze pad formed of rayon is wetted with liquid nitrogen dioxide at ambient temperature and atmospheric pressure, and allowed to dry until it has a dry appearance. Thereafter, the pad is exposed to gaseous nitrogen dioxide at atmospheric pressure at a temperature of 70.degree. C. An oxidation level corresponding to oxidation of about 25 percent of methylol groups present is obtained.

Repetition of the foregoing cycle of wetting with nitrogen dioxide, drying and contacting with gaseous nitrogen dioxide is repeated until the oxidation level reaches at least 90 percent.

Thereafter, the pad is immersed in a methanol-water mixture containing 65 percent by weight methanol, and the pH of the solution is raised by adding sufficient 0.5 N KOH until the pH is about 10. Then, sodium borohydride is added to the solution in an amount to provide a ratio of about 0.2 parts by weight borohydride per 1 part of oxidized cellulose, and the oxidized cellulose is allowed to remain in contact with the solution for a period of 50 minutes.

The treated oxidized cellulose is then removed from the solution, washed with a dilute HCl-methanol mixture and washed again with ethanol. After drying and sterilization, the pad is found to have excellent stability at room temperatures.

EXAMPLE 3

A pad of cotton fibers is wetted with liquid nitrogen dioxide containing 2 percent water, and is then exposed, while still wet with liquid nitrogen dioxide, to hot gaseous nitrogen dioxide at 70.degree. C. and atmospheric pressure. The cellulose is found to be 45 percent oxidized based upon the methylol groups in the cellulose.

The foregoing procedure is repeated until the cellulose is at least 90 percent oxidized, and then the pad is washed with aqueous methanol. Thereafter, the pad is immersed in an ethanol-water mixture containing 75 percent by weight methanol, and the pH of the solution is raised to about 10 by adding 0.6 N NaOH.

Potassium borohydride is added, and the mixture is allowed to stand for 1.5 hours at ambient temperatures. The treated oxidized cellulose is removed from the solution, washed in the manner shown in Example 1, dried and sterilized.

The hemostatic materials of oxidized cellulose treated in accordance with the practice of the invention are susceptible to a wide variety of uses. Oxidized cellulose treated in accordance with the present invention is a natural hemostat, and forms, when contacted with human blood, a dark gellatinous mass which in effect serves as an artificial clot within the area of the bleeding within a few minutes from the time the oxidized cellulose is applied.

One of the principal advantages of the use of an oxidized cellulose treated in accordance with the concepts of the present invention is that it gradually dissolves and/or absorbed by body fluid which makes it possible to utilize hemostatic materials formed of the material in closed wounds without the concommitant occurrence of an adverse tissue reaction.

The hemostatic materials of the present invention in the form of knitted fabrics, carded fiber pads, sutures and like articles have broad application in any type of surgery,and in other situations where the control of bleeding is required. The material is placed in contact with the bleeding vessel whereby a clot forms within a few minutes. The wound may be, if conditions dictate, closed with the hemostatic material in place, and the hemostat will be dissolved by body fluids. Alternatively, the material may be removed after a clot has formed without sticking of the material to the wound or renewed bleeding since the portion of the material directly in contact with the wound has dissolved.

It will be apparent from the foregoing that the present invention provides a new and improved oxidized cellulosic material which may be used as a hemostatic material having heretofore unattainable stability, and which may be prepared by a simple and economic process without the need to employ expensive reagents.

It will be understood that various changes and modifications may be made in the details of formulation and procedure and use which provide the characteristics of the invention without departing from the spirit thereof, particularly as defined in the following claims.

Claims

We claim:

1. In the method of stabilizing a hemostatic material consisting of an oxycellulose pad, the improvement comprising immersing said oxycellulose pad in an aqueous alcoholic solution containing a borohydride for a period of from 0.1 to 5 hours at a temperature of from 0.degree. to 70.degree. C. and a pH of 9-12.

2. A process as defined in claim 1 wherein said borohydride is sodium borohydride.

3. A process as defined in claim 1 wherein said solution contains at least 20 percent by weight of alcohol.

4. In the method of stabilizing a hemostatic material consisting of a cellulosic pad, the improvement comprising first oxidizing said cellulosic gauze pad with nitrogen dioxide and thereafter immersing said cellulosic pad in an aqueous alcoholic solution at a pH of from 9-12 wherein said solution contains an alkali borohydride.

5. A process as defined in claim 4 wherein said nitrogen dioxide is in the liquid phase.

6. A process as defined in claim 4 wherein said nitrogen dioxide is in the gaseous phase.