Liquid-laid, Non-woven, Fibrous Collagen Derived Surgical Web Having Hemostatic And Wound Sealing Properties

Abstract

Liquid-laid, non-woven, fibrous web having hemostatic and adhesive properties sufficient to seal a wound formed of fibers of ionizable, water-insoluble, partial acid salts of collagen, the web having certain specified absorbency and porosity characteristics. In order to prevent excessive swelling of the fibers with resulting excessive hornification or densification upon drying, it is essential that mixtures of water-miscible organic liquids such as ethanol with specified minor porportions of water be utilized as the slurrying media.

Description

This invention relates to liquid-laid, non-woven sheets or webs particularly suited for medical and surgical purposes consisting essentially of finely-divided fibers derived from collagen.

It has been known that collagen in various treated and prepared forms is useful in medical and surgical procedures and in the treatment of wounds. Collagen in certain forms has hemostatic properties when used as a wound dressing and has a low level of anti-genicity. In the copending application of Orlando A. Battista, Mamerto M. Cruz, Jr., and Merritt R. Hait, Ser. No. 76,638, filed Sept. 29, 1970 and now U.S. Pat. No. 3,742,955 there is described a fluffy, finely-divided fibrous collagen product derived from natural collagen which when wet with blood has hemostatic properties and a unique adhesive property which is sufficient to join together severed biological surfaces. This form of collagen demonstrates an unexpected and entirely unique adhesive property when wet with blood in live warm blooded animals and in many instances can actually be used to adhere severed tissues without the use of sutures. The disclosure of this above identified application is herein incorporated and made a part of the present disclosure.

As indicated in the above entitled application, the hemostat-adhesive material is in a fluffy, finely-divided fibrous form and the form for use in this invention consists essentially of a water-insoluble, ionizable, partial salt of collagen, the fibrous mass having a density of not more than about 8 pounds per cubic foot, preferably the bulk density is between 1.5 and 6.0 pounds per cubic foot. The mass when combined with blood in a wound forms a mass that is self-adherent to the tissue surfaces and will seal the wound without the use of sutures. The partial salt of collagen consists essentially of an ionizable, water-insoluble, partial acid salt of collagen consisting from about 50 percent to about 90 percent of the theoretical stoichiometric amount of the ionizable acid. The fluffy, finely-divided fibers for use in the present invention may be prepared as described in the aforementioned application.

Because of the low density and fluffiness of the product of the aforementioned application, it is necessary to transfer the product to the wound by the use of forceps or manually with rubber gloves. In such handling procedures fibers become dislodged from the bulk being handled and portions will adhere to the forceps or rubber gloves.

In copending application Ser. No. 76,638, it is stated that the fluffy, finely divided fibrous collagen product may be converted into non-woven webs by a wet method such as commonly employed in forming papers. It is also stated that in such method the fibrous collagen is slurried in a water-miscible organic liquid of the type used in producing the fibrous collagen.

In the conventional production of water-laid fibrous sheets or webs such as papers, naturally occurring cellulose fibers such as wood pulp and cotton linters are mechanically hydrated as by beating and mixing in a paper mill beater in the presence of a large excess of water. In forming a pulp slurry by a beating operation, the fibers become hydrated and exhibit a microscopic and submicroscopic peeling of individual fibrils along the surface of the fibers and at the end of the fiber bundles. The slurry is then passed to a suitable screen to lay down the fibers as a sheet or mat. The physical properties of the sheet, such as strength, tear and burst are dependent to a large extent on the hydration of the fibers and an interlocking of the hydrated fibers and of the fibrillae on the fibers and the fiber-to-fiber bonding which develops upon drying.

Because of the greater sensitivity to water of the fibers of the fluffy, finely divided partial salt of collagen having the hemostatic and unique adhesive characteristics as described in the afore-mentioned application, water-laid fibrous sheets or webs formed from such fibers are harsh and boardy and parchment-like in structure with complete loss of hemostatic and adhesive properties thereby rendering such sheets unsatisfactory for surgical purposes.

The principal purpose of the present invention is to provide a liquid-laid, non-woven web which retains the hemostatic-adhesive properties of the fluffy, fibrous partial salt of collagen.

A further purpose of the invention is to provide a method of forming the liquid-laid, non-woven sheet or web of the fluffy, finely-divided fibrous collagen derived product which is flexible, non-flaking, and has sufficient strength to permit its application to a wound without separation into individual fibers.

A further purpose of the present invention is to provide a method of forming a liquid-laid, non-woven fibrous web of the finely-divided fibrous collagen derived product which retains the hemostatic and unique adhesive properties of a finely-divided fibrous mass as described in the aforementioned application.

Further objects and advantages of the present invention will become apparent to those skilled in the art from the following description of the method and product.

The present invention is based upon the discovery that non-woven webs or sheets which retain the hemostatic and unique adhesive properties of the fluffy, finely-divided fibers of the partial salt of collagen can be formed by slurrying the fibers in a mixture of a water-miscible organic liquid and water in certain relative proportions and depositing the fibers from such slurry.

In the drawings:

FIG. 1 is a graph illustrating the freeness of the fibers when slurried in ethanol and ethanol-water mixtures of varying composition; and,

FIGS. 2 through 7 are graphs illustrating the variations in the physical properties of the liquid-laid, non-woven sheets or webs prepared from slurries of the fibers in ethanol and ethanol-water mixtures of varying composition.

In order to avoid the production of products having a parchment-like structure and to provide the web or sheet with requisite characteristics, it is essential that the slurrying liquid consists of a mixture having a composition, by volume, in the range of from 95 percent organic liquid and 5 percent water to about 85 percent organic liquid and 15 percent water. Where the amount of water is less than about 5 volumes of water to 95 volumes of the organic liquid, the finished product is unsatisfactory in that it has no dry web strength and is extremely flaky; that is, upon handling, fibers readily separate from the sheet. At least this minimum amount of water must be present so as to provide a sufficient degree of bonding between the fibers to form a coherent and handleable sheet. In those instances where the sheet is vacuum dried the amount of water preferably should not exceed about 15 volumes of water to 85 volumes of organic liquid, preferably 95 volumes of organic liquid and 5 volumes of water. If the amount of water exceeds this ratio, the fibers become so firmly bonded together that there is a loss in absorbency and flexibility and a marked loss of the hemostatic and adhesive properties of the sheet. Where the sheet is to be freeze dried the liquid may consist of up to about 20 volumes of water to 80 volumes of organic liquid, preferably 90 volumes of organic liquid and 10 volumes of water. Here again, where the amount of water exceeds this value there is a loss in the desired properties.

The water-miscible organic liquid consists of low molecular weight alcohols, ketones and the like such as, for example, methanol, ethanol, isopropanol, amyl alcohol, methylethyl ketone, acetone, and mixtures of these organic liquids. It is possible to increase the amount of water providing that a salt which hydrates is present such as sodium sulfate and calcium chloride. The use of the organic liquids other than ethanol is feasible, however, where the product is intended for surgical uses it is essential that the product be freed of such solvent.

After depositing or sheeting the fibers upon a suitable collecting screen excess liquid may be separated as by pressing and the application of vacuum. The product is then freeze dried or vacuum dried to preserve the absorbency, flexibility and hemostatic-adhesive properties. Freeze drying is preferred because it provides softer, more absorbent and more flexible products that exhibit no noticeable decrease in the hemostatic-adhesive properties of the fibrous material. One of the unique characteristics of these liquid-laid non-woven sheets or webs is that upon heat sterilization as by heating at 120.degree.C. for from 20 to 30 hours there is an improvement in the tear strength of the sheet as well as in the hemostatic properties.

The fibrous collagen product can be prepared from any undenatured collagen in the natural state or delimed edible forms of collagen including, for example, hide, gut, tendon, cartilage or other high fibrous collagen source material preferably chopped up for easier handling. The collagen is preferably in a wet and never-dried state or, if dried, drying has been effected under conditions which minimize denaturation. Satisfactory raw materials for the collagen include, for example, fresh cowhides and calfhides, salted down cowhides, wet moosehide, pigskins, sheepskins and goatskins as conventionally used for making leather. Special technical hide collagen prepared from hide splits and possessing a minimal reduced bacteria count is also satisfactory. The preferred raw material, because of availability is corium derived from never-dried cowhide or technical grades of collagen prepared from cowhide and other animal hides.

The wet collagen source material such as hide is diced or chopped into small fragments of from one-fourth to one-half inch sizes in a cutting or grinding mill, such as, for example, an Urschel Mill. Alternatively, these fragments may be mixed with crushed ice and then passed through the Urschel Mill with cutting heads of smaller dimension to fiberize the collagen into a coarse fibrous product.

If swelling or hydration of the collagen fibers is not controlled during the subsequent treatment wherein the collagen is subject to mechanical shredding or opening in a liquid medium, excessive hornification or densification will occur when the material is dried down thereby effectively preventing the satisfactory deaggregation of the collagen fibrils during the final mechanical treatment. The initial swelling of the collagen fibers in the wet state affords many more sites for hornification that is desirable thus resulting in a dense, non-absorbent material. When hornification and densification occurs, the product will not have the required hemostatic and adhesive characteristics.

The wet or moist collagen source material is mechanically dispersed or slurried in an aqueous liquid which controls the swelling of the fibers. The aqueous liquid comprises water and a water-miscible organic liquid such as low molecular weight alcohols, ketones, and the like, such as, for example, methanol, ethanol, isopropanol, methylethyl ketone, acetone and the like in a weight range of between about 90 percent of the organic liquid and 10 percent water and about 50 percent organic liquid and 50 percent water. Where the proportion of water is too high, the collagen fibers swell to such a great extent that they lose their fiber identity with an attendant densification during the subsequent drying step. When this occurs, it becomes commercially unfeasible to subsequently deaggregate or fluff the fibrous product and attain the bulk density requirements necessary for the present invention. Although such product will possess some hemostatic properties, it does not possess the desired adhesion to severed biological surfaces and will not provide the required mechanical properties of the collagen-blood matrix between the severed surfaces to seal the wound.

The bulk of the liquid is drained from the mass and the fibrous collagen slurried and washed with a water-miscible organic liquid such as the alcohol and again the bulk of the liquid is separated from the partially swollen wet collagen material. Preferably, the collagen material is slurried in the organic liquid to reduce the water content to a minimum. In general, the use of three slurrying steps with the organic liquid will reduce the amount of water present to about 1 percent. The organic liquid is removed as by centrifugation and final drying. Drying may be effected either by oven drying or vacuum drying as at, for example, 40.degree.C. under a 29 inch vacuum for about 16 hours. In general, this vacuum drying will reduce the volatile content to under 1 percent.

The partial acid salt of collagen is formed by incorporating the required amount of an ionizable acid in the aqueous liquid wherein the collagen is dispersed or slurried. The amount of acid incorporated in the aqueous liquid is such as to provide the product with a bound acid content of from about 50 percent to 90 percent preferably about 60 percent to 85 percent of the theoretical stoichiometric bound acid content. After the acid has reacted with the dispersed collagen, the reaction mass is subjected to slurrying and washing with the water-miscible organic liquid and the collagen salt processed as above described.

Before the final deaggregation into constituent fibers or fluffing operation to produce the product having the required bulk density, the fibrous material is preferably conditioned to contain about 8 percent to 15 percent volatiles. This conditioning may be readily effected by allowing the product to remain at normal atmospheric temperatures and humidities (for example, 70.degree. - 75.degree.F., 40% - 60% R.H.) for from about 8 to 24 hours. The final fiber deaggregation or fluffing operation is necessary to provide the requisite bulk density. This operation is an "opening" operation whereby the diced material is converted into bundles of individual fibers. In forming the product of the present invention, the final fiber deaggregation or fluffing operation does not separate all of the dried bundles into ultimate individual fibrils but the product does contain finer fiber bundles (smaller in diameter) as compared to the coarser fiber bundles obtained at the end of the drying and conditioning operations. This deaggregation or fluffing may be effected by apparatus such as a hammer mill type comminution mill such as a Fitz Mill.

Alternatively, the wet collagen source material is merely diced or chopped into small fragments as described hereinbefore and then introduced into and mixed in a water-miscible organic liquid such as ethanol or isopropanol. Mixing is continued for about 1 hour so as to permit thorough penetration of the organic liquid into the small fragments. The bulk of the liquid is then separated as by draining or centrifuging and the recovered fragments again introduced into and mixed in the organic liquid for about 1 hour. Again, the bulk of the liquid is separated and the procedure repeated. At the end of this period, the liquid is centrifuged from the mixture and the wet fragments dried as by oven drying or vacuum drying. The resulting product, after conditioning as described above, is then subjected to a fiberizing and deaggregation or fluffing operation. To produce a partial ionizable salt of collagen, the desired amount of acid may be mixed with the organic liquid in any one of the above described steps, preferably in the second step. In such instances, the time of treatment with the organic liquid containing the acid should be prolonged to permit the required reaction between the acid and the collagen. Obviously, the time periods may be reduced by operating under pressure.

In order for the fibrous product to exhibit the desired hemostatic-adhesive properties and required physical properties the starting fibers of the partial salt of collagen should possess effective lengths within certain ranges. The effective fiber lengths may be determined in accordance with TAPPI Standard Method T233 su-64 utilizing a McNett Classifier having four tanks provided with a 20 mesh screen (openings 840 microns), a 35 mesh screen (openings 500 microns), a 65 mesh screen (openings 230 microns) and a 150 mesh screen (openings 100 microns), respectively.

Because of the excessive swelling of the fibers in water of the partial salts of collagen, these fibers are unsatisfactory for use in a fiber classifier. Accordingly, the partial salt fibers are converted to collagen fibers while preventing excessive swelling of the partial salt fibers. Such conversion may be effected as by slurrying the partial salt fibers at a solids concentration of about 1 percent for about 30 minutes in a mixture of 90 volumes ethanol and 10 volumes water adjusted to and maintained at a pH of 10.5 by addition of ammonium hydroxide solution. The fibers are recovered by the use of a nylon filter fabric in a Buchner funnel and using a water asperator. The recovered fibers are slurried at a 1 percent solids concentration in a mixture of 90 volumes ethanol and 10 volumes water for about 30 minutes to wash out soluble salt and the fibers recovered by the same type filtration. The recovered fibers are then given two additional washes using 100 percent ethanol. The finally recovered alcohol-wet fibers should not be allowed to dry but are slurried in the required volume of water at the recommended solids content for the specific classifier.

When ten gram samples of partial salt fibers satisfactory for the purposes of the present invention are subjected to testing by the use of the McNett Classifier the samples exhibit a fiber length distribution of about

45 to 55 percent retained on a 20 mesh screen (840 microns)

20 to 25 percent retained on a 35 mesh screen (500 microns)

3 to 6 percent retained on a 65 mesh screen (230 microns)

0.5 to 1.5 percent retained on a 150 mesh screen (100 microns)

30 percent maximum passing a 150 mesh screen.

Where the proportion of long fibers is too high the partial salt fibers upon slurrying in the ethanol-water mixture, the fibers floculate and agglomerate into ropey masses. Where the proportion of short fibers is too high, there is a loss in the adhesive properties of the liquid-laid sheets.

A measure of the fluffiness and a rough indication of a satisfactory fiber length distribution of the fibers is bulk density.

The bulk density is measured by adding the fibrous collagen products as initially fluffed to a 100 ml. graduate cylinder without any compression step and determining the weight of the added 100 mls. of the product.

In forming the partial salt of collagen, hydrochloric acid is the preferred acid and is used in the examples which follow merely because it is relatively inexpensive and allows ready flexibility and ease of control. Other ionizable acids, both inorganic and ionizable organic acids, such as, for example, sulfuric acid, hydrobromic acid, phosphoric acid, cyanoacetic acid, acetic acid, citric acid and lactic acid are satisfactory. Sulfuric acid, for example, is satisfactory, but control of the action is difficult. Citric acid may be substituted for hydrochloric acid with about equal results. "Ease of control" has reference to the ability to arrest the swelling and hydrolysis of the collagen fibers so as to prevent the rapid degradation of the material to a water-soluble product.

In the examples which follow, the fluffy, finely-divided fibrous collagen product was derived from wet or green bovine corium. The collagen product was a water-insoluble, ionizable, partial hydrogen chloride salt of collagen containing approximately 84% of the theoretical stoichiometric bound acid content. The product was deaggregated or fluffed by passing it through a Fitz Mill (Model DA50-6-5634) operated at 6,250 rpm. equipped with a No. 4 screen having openings of 0.243 inch. It was then subjected to a second pass using a special slotted sceen having openings 0.062 inch .times. 0.5 inch with the slots at an angle of 30.degree. to the sides of the screen.

The fiber length distribution of the fibrous partial salt of collagen determined by the use of a McNett Classifier was about

48 percent retained on a 20 mesh screen

22 percent retained on a 35 mesh screen

3.6 percent retained on a 65 mesh screen

0.7 percent retained on a 150 mesh screen

25.7 percent passing a 150 mesh screen.

The bulk density of the fluffed, fibrous partial salt of collagen was 2.0 - 2.5 pounds per cubic foot.

Upon disintegrating a sample of the fluffy, finely-divided fibrous material in water at a solids concentration of 0.5 percent by weight by subjecting the mixture to the action of a Waring Blendor at high speed for 30 minutes, a stable dispersion was formed having a pH of 3.20.

In the production of the liquid-laid, non-woven webs of the present invention, conventional apparatus such as used in the papermaking industry and in the production of non-woven webs may be used. The finely-divided, fibrous collagen product is slurried in the water-miscible organic liquid-water mixture by the use of a suitable mixing device such as a beater wherein the beater is used solely as a mixing device since the fibrous product does not require hydration or fibrillation. The slurry or furnish may contain from about 0.1 percent to about 3 percent of the fibrous product, preferably about 0.5 percent. The slurry or furnish is then passed to a suitable collecting screen where the fibrous product is sheeted or deposited. Fourdrinier, cylinder vat, Rotoformer and other sheet forming devices are satisfactory. After removing the wet-laid sheet or web from the collecting screen, excess liquid may be removed by passing the sheet between press rolls and then drying the sheet.

The degree of swelling or hydration of the fibers in ethanol and ethanol-water mixtures is illustrated by a freeness test using a Canadian Standard Freeness Tester. The method of testing was in accord with TAPPI Standard Test Method T227 m-58. In this series of tests, slurries containing 0.3% fibers were formed in ethanol and ethanol-water mixtures, as set forth in Table 1, by adding the fibers to the liquid and manually agitating with a wide blade spatula for 5 minutes. 1,000 mls of the slurry were then poured into the cylinder of the Freeness Tester and measuring the volume of liquid discharged from the side discharge tube. This volume in mls. is reported in Table 1 as CSF No. and the data illustrated in FIG. 1. This test illustrates that as the proportion of water in the slurrying liquid increases, the swelling of the fibers increases and, accordingly, the freeness decreases.

The variations in absorbency, tear strength, burst factor, tensile strength, stiffness as well as other properties of the hemostatic-adhesive non-woven webs of the present invention may be illustrated by reference to the preparation of handsheets utilizing liquids varying in relative proportions of ethanol and water. In the preparation of these handsheets a modified 8 inch .times. 8 inch Williams handsheet mold was utilized. The normal wire mesh screen at the bottom of the handsheet mold was covered with a polypropylene filter fabric consisting of a 2/2 twill weave structure, the fabric having a porosity of 85-90 CFM (Chicopee Polypropylene 6016800 fabric) the edges of the fabric being sealed to the wire mesh.

In each instance the ball valve located at the bottom of the hand-sheet mold's water leg was closed and the specified liquid, about 4,000 mls., poured through the polypropylene filter cloth to bring the level of the liquid to just cover the polypropylene filter cloth. For the preparation of hand-sheets of approximately 1 mm. thick (approximately 175.5 lbs. per 3,000 sq.ft.), 9.0 gms. of the fluffy, fibrous material was added to 3,000 mls. of the liquid, forming a slurry of about 0.37% by weight of the fibers, and the slurry gently agitated for approximately 5 minutes. The slurry was then poured into the handsheet mold and the slurry agitated by lowering and raising a perforated plunger 3 times. The ball valve was then opened to allow most of the liquid to drain by hydrostatic pressure usually requiring from about 20 to 30 seconds. About 1 to 2 inches of liquid was allowed to remain over the polypropylene filter fabric and thin areas or voids in the sheet on the filter fabric were filled in with suspended fibers by gently agitating the slurry with a spatula and moving fibers to the thin areas or voids. When the sheet appeared to be quite uniform, the ball valve was opened completely and all liquid allowed to drain.

The mold was then opened and the formed wet non-woven web covered with a plain weave polypropylene filter fabric having a porosity of about 90 CFM (Chicopee Polypropylene 6970500 fabric). Dry blotting paper was sandwiched between very fine Dacron cloths and then placed over the polypropylene fabric and gently pressed to absorb some of the liquid. This procedure with the sandwiched blotting paper was repeated a second time. A similar sandwich of dry blotting paper and Dacron cloth was then placed over the polypropylene fabric and the forming plate with the sandwiched wet laid web removed from the mold and gently placed upside down with the sandwiched blotting paper being placed on a sheet of polyester film. The forming plate was then lifted and the wet laid web gently peeled from the polypropylene filter fabric covering the forming plate wire mesh. The exposed side of the removed wet laid web was then covered with a polypropylene filter fabric (Chicopee Polypropylene 697050 fabric) and a sandwiched blotting paper between Dacron cloth placed over the fabric. The assembly was then gently rolled with a printer's rubber roller to remove additional liquid and this procedure repeated by rolling at 90.degree. to the direction of the first rolling. A dry sheet of sandwiched blotting paper was then applied after removal of the wetted sandwiched blotting paper and the assembly turned over and a dry sheet of sandwiched blotting paper placed on the upper side and the rolling procedure was repeated. The sandwiched blotting paper and polypropylene filter fabrics were then removed and the wet laid web placed between polyester films and both sides gently rolled with a printer's roller. The wet-laid webs between polyester films were then stored in polyethylene bags until sufficient numbers of the sheets were prepared to subject them to a drying step using either a photographic dryer, freeze dryer, Noble and Wood hot plate or vacuum oven.

Freeze drying was effected in a Repp Freeze Drier, Model 40, with an initial shelf temperature of about -40.degree.C., a vacuum of 50 microns, heating cycle to 38.degree. C. over a period of 2 hours and a condenser temperature of about -60.degree. C. Vacuum drying was effected in a conventional vacuum oven at a vacuum of about 30 inches of mercury and a temperature of 35.degree. to 40.degree.C. overnight.

Handsheets prepared as above described and dried by freeze drying and vacuum drying were subjected to various physical testing after heat sterilization by heating in an air oven at 120.degree. C. for 28 hours. Samples of the hand-sheets when dispersed at 0.5 % solids in water in a Waring Blendor at high speed for 30 minutes formed dispersions having a pH of 3.22 which was substantially identical to the pH of dispersions formed from the original fibers.

The absorbency of freeze dried and vacuum dried products formed from the slurries in different compositions was determined by the use of a mixture of 90 volumes of ethanol and 10 volumes of water. The central portions (1 1/2 inch in diameter) of plastic screw tops of 4 oz. jars were removed leaving a sufficient annular flange to cover the top edge of the jars. Samples of the various non-woven sheets in the form of circular discs 2 inches in diameter were placed on the top edges of the jars and the cut screw tops placed on the jars to secure the circular discs on the jar tops. The liquid was allowed to drip through a distance of one-half inch on to the center of the sheet drop by drop allowing each drop to be absorbed by the sheet before the succeeding drop was added. This was allowed to continue until a drop of liquid dripped from the bottom of the sheet into the jar. The flow of liquid was then arrested. The percentage of absorbence was calculated from the weight of the original dry sample and the weight of the wetted sample, the data, the average for two samples, being presented in Table 1. The data are plotted in FIG. 2.

The tensile strength of the various sheets was measured by the use of a Thwing-Albert electrohydraulic tensile tester Model No. 37-4 at a 5.5 Kg and 31.8 Kg loading. In accordance with TAPPI Standard Test Method T220 m-60, the test was applied to six strips of each of the sheets cut 15 mm. wide and the results reported in Table 1 are the average breaking load in Kg for the 15 mm strips. The data are plotted in FIG. 3.

Samples of the sheets were subjected to a tear test in accordance with TAPPI Standard Test Method T220 m-60 using an Elmendorf Tear Tester. The Tear Factor (average of two sheets) was calculated from the average force in grams to tear a single sheet. The Tear Factor as reported in Table 1 is equivalent to the number of square decimeters of the sheet, the weight of which, if applied to a single sheet would cause a tear in the sheet to progress. The Tear Factor is plotted in FIG. 4.

Samples of the sheets were also subjected to a bursting test in accordance with TAPPI Standard Test Method T403 ts- 63 using a Mullen Burst Tester. The Burst Factor was calculated from the pressure in psi required to burst the samples. The values reported in Table 1 and plotted in FIG. 5 are the average values for two samples.

The stiffness of the sheets was measured by maintaining samples wrapped on a glass cylinder for 24 hours at room temperature (73.degree.F) and a relative humidity of about 50 percent and then releasing the samples and allowing them to flatten under their own weight. The samples were cut into 3 in. .times. 7 in. strips, wrapped around a glass tube 2.25 in. in diameter and held in place by scotch tape. At the end of the 24 hour-period the tube was placed on a horizontal surface with the mid portion of the sample sheet in contact with the horizontal surface. The tape was then cut and the free ends of the samples allowed to separate from the glass tube and unfold or uncurl under their own weight. The amount of uncurling was determined by measuring the angle between the horizontal surface and the uncurled ends of the samples. The angle in degrees is termed the Stiffness Factor, which is the average for four sheets, both ends, and is reported in Table 1 and plotted in FIG. 6.

The porosities of the sheets were determined by the use of a Gurley Densometer (Closed-Top Model) in accordance with TAPPI Standard Test Method T460 os-68. This test measures the air resistance of the sheets and is reported in Table 1 as the average time in seconds required to displace 100 ml. of air through an area of 6.45 sq.cm. of the paper. The reported values are averages for two to six tests. These data are plotted in FIG. 7 and reported in Table 1. ##SPC1##

The data in Table 1 and FIGS. 2 through 7 illustrate that more than about 15% water by volume in the ethanol-water mixtures used in forming the slurries or furnishes for the preparation of the liquid-laid, vacuum dried sheets causes excessive swelling of the fibers and the sheets begin to exhibit hornification or densification. Similarly, in the case of the freeze dried sheets, where the ethanol-water mixtures contain more than about 20 percent water by volume the sheets begin to exhibit hornification or densification. This is particularly evidenced by the leveling off of the absorbency (FIG. 2). Tear Factor (FIG. 4) and Stiffness Factor (FIG. 6) and by the rapid rise in the tensile break load (FIG. 3), Burst Factor (FIG. 5) and porosity (FIG. 7) of the sheets.

Similar properties result when the other water-miscible organic liquids are substituted for the ethanol. As indicated hereinbefore, where the product is intended for surgical procedures it is essential that such organic liquid and/or salt used in the slurrying liquid must be removed.

The fibrous collagen products prepared in the above examples were employed in surgical test procedures designed to provide the efficacy of the material both as a hemostat and adhesive for severed biological surfaces in a warm blooded animal when wet with blood. "Severed" biological surfaces for the purposes of this invention includes cut, sliced, ripped, abraded, torn, punctured, burned, and tissue severed by any means or method whereby a fresh biological surface is present. Biological surfaces will include tissue, cartrilage, vessels, bone or other normal organic parts of the warm blooded animal which may require mending or joining.

The in vivo surgical procedure was carried out on anaesthetized mongrel dogs. The liver of the dog was exposed and a centimeter square lesion was created by sharp excision of 1 mm. thick cortical tissue to yield a uniformly bleeding surface. Swatches were cut from samples of the various hand-sheets prepared as described hereinbefore. The investigators were provided with swatches without knowledge of the history of the samples so that all testing was "blind." Each swatch was placed over the uniformly bleeding lesion and pressure applied for 60 seconds, after which pressure was removed. In the case of satisfactory samples, hemostasis was effected within this time period. After 5 to 10 minutes, removal of the excess outer marginal portions of the swatch was attempted by pulling off such portions. Subsequent to rating the swatch, it was forcibly removed and a uniformly bleeding lesion reestablished and another swatch placed over the lesion as described and the swatch rated.

The investigators evaluated the samples and rated them upon their hemostatic efficacy, degree of adhesiveness to the bleeding surface and delamination property. The rating was on an arbitrary scale of 0 to 5, 0 indicating that the sample exhibited no hemostatic property, no adhesiveness to the wound surface and that the sample could not be delaminated; that is, excess marginal portions could not be removed without overcoming the adhesiveness and thereby permitting resumption of bleeding. The delamination is highly desirable so that in an internal surgical procedure, no more of the material be allowed to remain than is necessary to effect hemostasis and seal the wound and excess material be removed. A surgical cotton gauze pad used as control was ineffective in producing hemostasis, was not adhesive to the wound and, of course, the entire pad could be lifted from the wound. Upon this basis it received a 0 rating and was unsatisfactory. A rating of 1 indicating poor and unsatisfactory properties. A rating of 2 indicating a fair functioning but unsatisfactory. A rating of 3 indicating a good functional action and the acceptability of the material is questionable. A rating of 4 indicating a very good functional action and satisfactory. A rating of 5 indicating an excellent functional action and satisfactory.

The investigators' ratings of the samples based upon the evaluations and based upon the foregoing considerations are set forth in Table 2. In addition, the investigators also observed the handling characteristics of the samples. These characteristics included a consideration of the physical properties such as cohesiveness and flakiness of the sheet, the friability, the stiffness and the ability to cut swatches of the required size from the sheet with scissors to form a clean cut. The investigators comments with respect to these characteristics are set forth in the Table 2. ##SPC2##

Although the sheets prepared from the 100% ethanol slurries received high in vivo ratings, based upon hemostatic efficacy, adhesiveness and delamination, the sheets are not deemed satisfactory from a handling viewpoint. Because of the loose, crumbly and friable characteristics of these sheets, the products may be said to be delicate and can not withstand normal shipping and handling. Upon handling, the sheets exhibit excessive flaking and loss of fibers. Such sheets can not withstand slight abrasion.

Where the sheets are too stiff and are too harsh and boardy, they have a low hemostatic efficacy, low adhesive quality and cannot be delaminated without opening the wound. Furthermore, such sheets do not readily conform to irregular surfaces encountered in a wound and, hence, are unsatisfactory.

From the foregoing discussion and the in vivo evaluation, it is clear that severed biological surfaces may be joined and a wound sealed without the use of sutures by the application of the sheets or webs of this invention. In sealing the wound, the web when wetted with blood combines with the blood to form a mass that is self-adherent to the wound tissue to seal the wound. It is only necessary to apply pressure to the web for a short period sufficient only until hemostasis has occured after which pressure may be removed.

Based upon the evaluations of the various handsheets, products satisfactory for the purposes of the present invention have physical properties within the following ranges:

Absorbency of a mixture of 90 volumes of ethanol and 10 volumes of water from about 100 % to about 300 % by weight;

Tensile strength in Kg. per 15 mm. strip from about 1 to about 4;

Tear Factor from about 5 to about 50;

Burst Factor from about 1.2 to about 6;

Stiffness Factor from about 15.degree. to about 100.degree.; and,

Porosity in seconds to pass 100 ml. of air per 6.45 sq.in. from about 4 to about 15.

The absorbency and porosity values and Stiffness Factor are probably the simplest and most readily determinable properties. These properties considered together for sheets or webs of a basis weight of approximately 175.5 pounds per 3,000 square feet are not only a fair indication of the ability of the sheet to withstand normal and ordinary shipping and handling without flaking, but also a fair indication of the hemostatic-adhesive efficacy.

Freeze dried products prepared from slurries of the fibers in 90 volumes of ethanol and 10 volumes of water and vacuum dried products prepared from slurries of the fibers in 95 volumes of ethanol and 5 volumes of water have closely similar physical properties and from the in vivo evaluations are about equivalents and the preferred products.

Claims

What is claimed is:

1. A hemostatic adhesive dressing for severed biological surfaces comprising a liquid-laid, non-woven web having hemostatic-adhesive properties comprising hemostatic-adhesive fibers of ionizable, water-insoluble, partial acid salts of collagen, the web having an absorbency of a mixture of 90 volumes of ethanol and 10 volumes of water of between about 100 percent and about 300 percent by weight and a porosity of from about 4 to about 15 seconds per 6.45 sq. cm. based upon a web having a basis weight of about 175.5 lbs. per 3,000 sq.ft., the fibers of the partial acid salt of collagen containing from about 50% to about 90% of the theoretical stoichiometric amount of ionizable acid.

2. A dressing as defined in claim 1 wherein the web has a Stiffness Factor of from about 15.degree. to about 100.degree. based upon a web having a basis weight of about 175.5 lbs. per 3,000 sq.ft.

3. A dressing as defined in claim 1 wherein the fibers are partial hydrogen chloride salts of collagen.

4. A dressing as defined in claim 2 wherein the fibers are partial hydrogen chloride salts of collagen containing from 60 percent to 85 percent of the theoretical stoichiometric amount of hydrogen chloride.

5. A dressing as defined in claim 1 wherein the fibers have a fiber length distribution by the McNett Classifier such that about

45 to 55% are retained on a 20 mesh screen,

20 to 25% are retained on a 35 mesh screen,

3 to 6% are retained on a 65 mesh screen,

0.5 to 1.5% are retained on a 150 mesh screen, and not more than 30% pass a 150 mesh screen.

6. A dressing as defined in claim 2 wherein the fibers are partial hydrogen chloride salts of collagen containing from 60% to 85% of the theoretical stoichiometric amount of hydrogen chloride and the fibers have a fiber length distribution by the McNett Classifier such that about 48% are retained on a 20 mesh screen, about 22% are retained on a 35 mesh screen, about 3.6% are retained on a 65 mesh screen, about 0.7% are retained on a 150 mesh screen and the balance passes a 150 mesh screen.

7. The method of forming a hemostatic adhesive liquid-laid, non-woven web dressing for severed biological surfaces from hemostatic-adhesive fibers of ionizable, water-insoluble, partial acid salts of collagen including the steps of slurrying the fibers in a mixture of a water-miscible organic liquid and water, sheeting the fibers to form a web and drying the web, the fibers of the partial acid salt of collagen containing from about 50% to about 90% of the theoretical stoichiometric amount of ionizable acid, the mixture of organic liquid and water consisting of from about 95 volumes of organic liquid and about 5 volumes of water to about 80 volumes of organic liquid and 20 volumes of water.

8. The method as defined in claim 7 wherein the fibers have a fiber length distribution by the McNett Classifier such that about

45 to 55% are retained on a 20 mesh screen,

20 to 25% are retained on a 35 mesh screen,

3 to 6% are retained on a 65 mesh screen,

0.5 to 1.5% are retained on a 150 mesh screen, and

not more than 30% pass a 150 mesh screen.

9. The method as defined in claim 7 wherein the organic liquid is ethanol.

10. The method as defined in claim 7 wherein the mixture consists of from about 95 volumes of ethanol and about 5 volumes of water to about 80 volumes of ethanol and about 20 volumes of water and the web is freeze dried.

11. The method as defined in claim 7 wherein the mixture consists of from about 95 volumes of ethanol and about 5 volumes of water to about 85 volumes of ethanol and about 15 volumes of water and the web is vacuum dried.

12. The method as defined in claim 7 wherein the fibers of the partial acid salt of collagen contain from 60% to 85% of the theoretical stoichiometric amount of hydrogen chloride, the mixture consists of 90 volumes of ethanol and 10 volumes of water, the fibers have a fiber length distribution by the McNett Classifier such that about 48% are retained on a 20 mesh screen, about 22% are retained on a 35 mesh screen, about 3.6% are retained on a 65 mesh screen, about 0.7% are retained on a 150 mesh screen and the balance passes a 150 mesh screen and the web is freeze dried.

13. The method of joining severed biological surfaces in a living warm blooded animal which comprises placing between and in contact with the severed surfaces a liquid-laid, non-woven fibrous web of hemostatic-adhesive fibers of ionizable, water-insoluble, partial acid salts of collagen, allowing the web to become wetted with blood, pressing the web into contact with the severed surfaces until hemostasis has been effected and then releasing the pressure, the web having the property of combining with blood to effect hemostasis and to form a mass with the blood that is self-adherent to the severed surfaces and thereby seal the wound, the web having an absorbency of a mixture of 90 volumes of ethanol and 10 volumes of water of between about 100% and 300% by weight and having a porosity of from about 4 to about 15 seconds per 6.45 sq.cm. based upon a web having a basis weight of about 175.5 lbs. per 3,000 sq.ft., the fibers of the partial acid salt of collagen containing from about 50% to about 90% of the theoretical stoichiometric amount of ionizable acid.