Body absorbable sponge and method of making

Abstract

A conformable tissue absorbable surgical sponge is formed by dissolving a tissue absorbable polymer in hexafluoroisopropyl alcohol or hexafluoroacetone sesquihydrate, filtering, freezing and subliming off the solvent to give a tissue conformable flexible sponge which rapidly absorbs blood and other body fluids. The sponge may be used to absorb blood or other liquids during a surgical procedure or may be used as a hemostat and allowed to remain in a closed wound with the polymer being absorbed by living tissue.

Description

BACKGROUND OF THE INVENTION

Surgical sponges find many uses in which an absorbent sponge is desirable to soak up blood, serum, or other body fluids, which sponges are removed and discarded. Cotton gauze sponges are used in many instances. When used internally, there is a problem of part of the sponge coming off and leaving threads or larger portions of the sponge in the wound. Concern over leaving a sponge in a patient complicates operating room practice and involves extremely rigorous counting procedures to insure that no sponge is accidentally left in a closed wound.

In many surgical procedures requiring a hemostat to control bleeding, sutures and tieoffs can be used. In some instances it is highly desirable that additional methods of controlling bleeding be made available. More or less successful efforts have been made to secure conformable hemostats which can be used to control bleeding and then left in the wound. The problem is well recognized and more acceptable devices are in constant demand.

DESCRIPTION OF THE PRIOR ART

The use of polyglycolic acid is disclosed in a series of patents and applications to Schmitt, et al:

U.S. Pat. No. 3,297,033, Schmitt and Polistina, Jan. 10, 1967, SURGICAL SUTURES, discloses polyhydroxyacetic ester absorbable sutures. The material is also called polyglycolic acid, and is disclosed as permitting small quantities of comonomers to be present, such as dl-lactic acid, its optically active forms, homologs and analogs. A small quantity is recognized by the art as up to 15%, as shown by U.S. Pat. No. 2,668,162, Lowe, Feb. 2, 1954, PREPARATION OF HIGH MOLECULAR WEIGHT POLYHYDROXY-ACETIC ESTER.

U.S. Pat. No. 3,463,158, Schmitt and Polistina, Aug. 26, 1969, POLYGLYCOLIC ACID PROSTHETIC DEVICES, discloses surgical uses of polyglycolic acid, and incorporates definitions of some terms.

U.S. Pat. No. 3,620,218, Schmitt and Polistina, Nov. 16, 1971, CYLINDRICAL PROSTHETIC DEVICES OF POLYGLYCOLIC ACID, lists many uses of polyglycolic acid.

U.S. Pat. No. 3,736,646, Schmitt and Epstein, June 5, 1973, METHOD OF ATTACHING SURGICAL NEEDLES TO MULTIFILAMENT POLYGLYCOLIC ACID ABSORBABLE SUTURES, discloses surgical elements of a copolymer containing from 15 to 85 mol percent glycolic acid and 85 to 15 mol percent lactic acid.

U.S. Pat. No. 3,739,773, Schmitt and Polistina, June 19, 1973, POLYGLYCOLIC ACID PROSTHETIC DEVICES, claims particularly bone pins, plates, nails and screws of polyglycolic acid.

U.S. application Ser. No. 365,656, Schmitt and Polistina, May 31, 1973, SURGICAL DRESSINGS OF ABSORBABLE POLYMERS now U.S. Pat. No. 3,875,937, discloses additional subject matter on surgical dressings of polyglycolic acid.

U.S. Pat. No. 3,739,773, supra, lists a number of U.S. patents on methods for preparing polyglycolic acid and starting materials therefor.

In U.S. Pat. No. 3,620,218, supra, in Column 2 are listed a number of medical uses of polyglycolic acids, including in Column 2; line 52, knitted or woven fibrillar products, including velours, and mentioning specifically in line 53, burn dressings; line 57, felt or sponge for liver hemostasis; line 63, foam as absorbable prosthesis; and in lines 74 and 75, burn dressings (in combination with other polymeric films).

U.S. Pat. No. 3,737,440, Schmitt and Bailey, June 5, 1973, POLYGLYCOLIC ACID IN SOLUTIONS, discloses solutions of polyglycolic acid in hexafluoroisopropyl alcohol and hexafluoroacetone sesquihydrate, as well as wet and dry spinning of filaments and casting of films using these solutions.

U.S. Pat. No. 3,783,093, Gallacher, Jan. 1, 1974, FIBROUS POLYETHYLENE MATERIALS, discloses a fibrillated material, mentioning poly(glycolic acid) among others, in which one resin is mixed and fibrillated with another, and one resin leached out to give the product, a web of oriented, interconnected directional fiber-like strands, membranes, ribbons, branched ribbons and fibrils. These can be used as bandages and for other medical purposes. Example 15 shows 25 parts of poly(glycolic acid) and 75 parts of poly-(methyl methacrylate) leached with acetone.

U.S. Pat. No. 2,899,362, Sieger, Valentine, and Weidenheimer, Aug. 11, 1959, HEMOSTATIC SPONGES AND METHOD OF PREPARING SAME, discloses a whipped starch-gelatin mixture which is aerated and dried to form a sponge which may be used for hemostatic purposes.

U.S. Pat. No. 3,653,383, Wise, Apr. 4, 1972, ALGIN SPONGE AND PROCESS THEREFOR, discloses algin sponges made by freeze-drying aqueous alginate dispersions or gels which can be used for burn dressings, and other surgical purposes. The product after use is water-disintegrative.

Commercially, an oxidized regenerated cellulose is available, as in a gelatin foam distributed in sheet form. Both of these are absorbable in tissues. Under some conditions, the gelatin foam causes bile cysts. It is desirably wetted with saline at the time of use.

The complete disclosures of the above patents and articles are hereby herein incorporated by this reference thereto.

The use of gauzes, felts, and knitted fabrics as a wound dressing is quite conventional. The use of collagenous products as a sponge or pad has been diclosed. The requirements for surgical hemostats are varied and more satisfactory hemostats than presently available are constantly in demand.

SUMMARY OF THE INVENTION

It has now been found that a hemostat can be made by dissolving a tissue absorbable polymer in the very powerful solvents hexafluoroisopropyl alcohol or hexafluoroacetone sesquihydrate, preferably filtering the solution, freezing, and subliming off the solvent, yielding a sponge which is readily conformable to wound topography, highly absorbent and versatile. It may be used in procedures in which the foam sponge is to be left in the wound and absorbed by body tissues and also sees great acceptance in sponges which are used to absorb blood, serum or other liquids with the sponge being removed and discarded. Because there is the ever present risk of part of the sponge falling off and being left in the wound or through inadvertence being closed in the wound, it is desirable that tissue absorbable sponges be used for general surgical use, wherever tissue may grow into the sponge.

A sponge should have high absorptive capacity, should absorb fluids, particularly blood, rapidly, should be strong enough to be readily handled in surgical procedures, and conformable enough that it fits into whatever topography and space that is available, and be soft enough so that it does not injure sensitive tissues.

The absorbability of the present sponges by the body reduces the risks from the inadvertent enclosure of portions of a hemostatic sponge in living tissue--because such portions are absorbed and removed by the tissue itself.

Although freeze drying is a well-known technique, it is usually drying of water from frozen compositions in which water is to be removed by sublimation; and the product is usually rather brittle and friable so that it is not readily conformable, and is easily broken.

Here the solvent, which is removed by sublimation, is hexafluoroisopropyl alcohol or hexafluoroacetone sesquihydrate or a mixture of the two. The residual foam is softer and more conformable than products usually secured from aqueous systems. It is, of course, not possible to use an aqueous system with the tissue absorbable polymer of this invention. The polymers are not water soluble.

Because the solvent is volatile, and is sublimed to remove the major portion, and the resulting cake is dried to remove the small remaining portion, the absorbable sponge structure is more readily freed from other components than in a leach technique using a mixture of polymers in which one polymer is leached out, thus requiring elimination of not only the leached polymer, but also the leaching solvent.

Because the term "freeze-drying" sometimes implies an aqueous system, the term "sublimation-drying" is used in many places herein to accentuate that it is an organic solvent system which is being sublimed so that it could be called solvent-sublimation for sponge manufacture. Products prepared in an aqueous system are generally friable. Using hexafluoroisopropyl alcohol or hexafluoroacetone sesquihydrate as a solvent for polyglycolic acid, and other tissue absorbable compositions, yields a product which is readily flexible and tissue conformable.

Because homopolymeric polyglycolic acid is currently being used in sutures, has met with the approval of many government agencies in many countries, is commercially available, and is familiar to chemists, the present invention is primarily described in detail in relation to homopolymeric polyglycolic acid.

Polyglycolic acid containing up to 15% of other units, such as lactic acid units, is considered within the term polyglycolic acid as used hereien unless specified as homopolymeric. Other materials such as poly(N-acetyl-D-glucosamine) and polymers of 3-methyl-1,4-dioxane-2,5-dione may be used. Poly(N-acetyl-D-glycosamine) is described in U.S. Ser. No. 441,717, filed on or about Feb. 11, 1974, Richard Carl Capozza, POLY(N-ACETYL-D-GLUCOSAMINE) PRODUCTS.

The present invention is particularly useful with tissue absorbable polymers which are insoluble in common organic solvents.

The foam should conform to the surface of the tissue. Conformation comprises an assessment of the suppleness, resiliency, and foam's ability to mimic the topography of the wound in such a fashion that there is a minimum gap between the tissue and the foam which minimizes air gaps and pools of liquid. If pools of liquid build up, whether of serum or blood, such pools may become sites for the growth of undesirable microorganisms, particularly for external dressings. If the foam conforms adequately to the surface of the wound, the body's own defense mechanisms are effective up to the zone of contact with the foam, and bacterial contamination is minimized.

DRAWINGS

FIG. 1 shows a scanning electron microscope photomicrograph at 50 diameters magnification of the surface of a frozen and dried sample produced in accordance with Example 1.

FIG. 2 is a portion of the same structure at 300 diameters magnification.

FIG. 3 is a photomicrograph similar to FIG. 1 at 50 diameters magnification of the reverse side of the same structure.

FIG. 4 is the same surface as FIG. 3, but at 300 diameters magnification.

FIG. 5 is a razor cut cross section of the same sample as FIG. 1 at 50 diameters magnification.

FIG. 6 is the same razor cut cross section as FIG. 5 at 300 diameters magnification.

A scale on each photomicrograph shows relative sizes.

As exemplified by the drawing, the polyglycolic acid forms ribbons and shows a fibrillar structure with the ribbons, sheets and fibers interconnected with many of the ribbons having considerable greater width than thickness. The thickness in general is within the range of from about 1 to 5 microns. The dried structure is spongy in character but resilient so as to be conformable to a wound surface and is not friable and brittle as are most frozen-dried solids in which the solids are dried from an aqueous system.

EXAMPLE 1

Polyglycolic Acid in Hexafluoroisopropyl Alcohol

10.3 Grams of low crystallinity homopolymeric polyglycolic acid was dissolved in 150 milliliters of hexafluoroisopropyl alcohol by stirring at 36.degree. to 37.degree.C. until solution resulted (about 3 hours). The resulting solution was freed from dust and inadvertent trace contaminants by filtration through a sintered glass filter, and transferred to a flat bottom dish. An additional 100 milliliters of hexafluoroisopropyl alcohol was used to dilute the solution to about 4% concentration (wt./vol.). The dish was surrounded by a solid carbon dioxide-acetone mixture until the solution was solidly frozen. The dish in its frozen condition was placed in a resin kettle which was sealed and connected to a high vacuum system. Vacuum was maintained using a solid carbon dioxide acetone cooled trap to protect the vacuum pump for 16 hours during which time the kettle was allowed to warm up with the hexafluoroisopropyl alcohol being maintained in its solid state by evaporative cooling, and with no meltbacks. After the thus formed foam had only a few percent residual hexafluoroisopropyl alcohol therein, the foam cake was removed, cut into 1/8 inch thick slices and further subjected to vacuum and heat at about 55.degree.C. until substantially all of the hexafluoroisopropyl alcohol was removed.

The solvent free foam was placed in strippable packages, sterilized with 12% ethylene oxide in dichlorodifluoromethane and thus kept dry and sterile until time of use.

As a hemostatic sponge, the foam conforms well to a wound and arrests the flow of blood immediately. The initial arresting of bleeding is largely mechanical. Blood then coagulates in the sponge, which both arrests the further flow of blood, and tends to hold the sponge in position. The slices can be cut or broken into a size and shape adapted to cover a particular wound. The foam is usable in a wound which is to be closed, such as, for example, on the surface of the liver with the foam being closed into the abdominal cavity, or it may be used on the surface of the body as protection, and allowed to remain until the wound is healed. The foam may be used as an absorbent to absorb blood and other fluids at the site of a wound to dry the wound for subsequent suturing or closing as required by a particular surgical procedure.

In test animals on sacrifice, the foam is found to be essentially absorbed within 90 days.

EXAMPLE 2

Polyglycolic Acid in Hexafluoroacetone Sesquihydrate

1.9 Grams of homopolymeric polyglycolic acid was dissolved in 45 ml. of hexafluoroacetone sesquihydrate by heating the mixture of 50.degree.C. with stirring for three hours, yielding a solution having a concentration of approximately 4.2% (wt./vol.). The solution was filtered through a sintered glass filter and transferred to a flat dish and the clear amber solution was set in a solid carbon dioxide-acetone mixture for about an hour until frozen completely solid.

The dish was then placed in a vacuum chamber and the hexafluoroacetone sesquihydrate was sublimed off at a reduced pressure of about 1 torr. After about 24 hours, the spongelike foam obtained was removed, sliced into 1/8 inch thick slices, and again placed in a closed chamber evacuated at 1 torr. with heating to about 80.degree.C. for several days. The product was then essentially free from solvent. The slices were sealed in strippable packages, sterilized with ethylene oxide and kept dry until time for use, using techniques routinely employed for polyglycolic acid sutures.

The sponge was an effective absorbent for blood and served as an effective hemostat on wound surfaces.

In accordance with conventional usage in the polymer field, the polymers herein described are named from the monomer or monomers from which the polymers can be considered as formed. For instance, the key polymer, polyglycolic acid, is so named whether made from glycolic acid or glycolide, even though the units in the chain could properly be described as glycolyl linkages. Particularly, when considered with the incorporated cited prior art, and commercial usage in the field, such nomenclature is regarded as historically the most significant and the least ambiguous.

Claims

I claim:

1. A method of making a hemostat comprising dissolving a tissue-absorbable polymer in hexafluoroisopropyl alcohol or hexafluoroacetone sesquihydrate, filtering to remove any insoluble contaminants, freezing the solution and subliming off the solvent, whereby an absorbable sponge structure is formed, which is essentially non-directional and is readily conformable to tissue surfaces.

2. The method of claim 1 in which the tissue absorbable polymer comprises glycolic acid, having such a high glycolic acid content that it is insoluble in common organic solvents.

3. The method of claim 2 in which the tissue absorbable polymer is homopolymeric polyglycolic acid.

4. A hemostatic surgical sponge of a tissue absorbable polymer comprising glycolic acid, having at least 85% of the monomer units of glycolic acid, whereby it is insoluble in common organic solvents, in the form of a sheet having interconnected ribbons and ligaments of a single polymer which is essentially non-directional having a network of connecting elements, and which is sufficiently flexible to be readily conformable to a wound surface.

5. The sponge of claim 4 in which the tissue absorbable polymer is homopolymeric polyglycolic acid.

6. A hemostatic surgical sponge of a tissue absorbable polymer in the form of a sheet having interconnected ribbons and ligaments of a single polymer which is essentially non-directional having a network of connecting elements, and which is sufficiently flexible to be readily conformable to a wound surface; made by the process of dissolving a tissue-absorbable polymer in hexafluoroisopropyl alcohol or hexafluoroacetone sesquihydrate, filtering to remove any insoluble contaminants, freezing the solution and subliming off the solvent, whereby an absorbable sponge structure is formed, which is essentially non-directional and is readily conformable to tissue surfaces.