A BIOMATERIAL COMPRISING A COMPOSITE MATERIAL OF CHITOSAN DERIVATIVE AND COLLAGEN AND A PROCESS FOR THE PRODUCTION OF THE SAME

Abstract: A biomaterial of excellent biocompatibility comprising a composite material of an N-acylchitosan and collagen. This biomaterial is suitable for use as a wound dressing material, vascular prosthesis, artificial skin or hemostatic agent.

Description: This invention relates to biomaterials of excellent biocompatibility comprising composite materials of N-succinylchitosans and collagens and a process for the production thereof. More particularly, it is concerned with biomaterials which can be applied as e.g., wound dressing materials, vascular prostheses, artificial skins and hemostatic agents, and a process for the production thereof. Chitosan is a composite polysaccharide consisting of N-acetyl-D-glucosamine and D-glucosamine, obtained by deacetylation of chitin with a concentrated alkali, in which the ratio of N-acetyl-D-glucosamine and D-glucosamine varies with the degree of the deacetylation as well known in the art. Collagen is a material that is of excellent biocompatibility, because it is a predominant component of the connective tissue and thus is most suitable as an extra-cellular matrix. Collagen has widely been used in cosmetics or biomaterials, since it has a relatively low antigenecity, although in implantation between different species, there arises a problem of antigenicity because of being a protein. A product of very low antigenicity is called atelocollagen, and is obtained by treating tropocollagen (collagen molecule) with a proteolytic enzyme (except collagenase) and removing the non-helix part (telopeptide) at the terminal of the molecule. This atelocollagen has significant features, i.e. best biocompatibility of the biomaterials which are commonly used at the present time, because of its low antigenecity, but the range of its use is limited since when applied to a living body, collagen is absorbed by the living body in due course and is more expensive than chitosan. A composite material of chitosan and collagen has been proposed so as to make the best use of the features of chitosan and collagen and to compensate for the disadvantages thereof (US Patent US-A-4,378,017). When chitosan is applied to a living body by itself, however, more foreign body reactions take place than with collagen and a number of giant cells are found around chitosan by an optical microscope, because chitosan is a polysaccharide not present in living bodies and apparently a foreign body to living bodies. Therefore, it is difficult to make use of chitosan alone as a biomaterial and the method of improving the biocompatibility of chitosan by adding collagen is still insufficient. Thus chitosan is not put to clinical and practical use. The present invention aims to provide a biomaterial containing a chemically modified chitosan derivative, whereby the disadvantages of the prior art can be overcome. The present invention also aims to provide a biomaterial which is excellent in biocompatibility. The present invention further aims to provide a chitosan derivative having excellent biocompatibility, which can be clinically put to practical use. The present invention still further aims to provide a process for the production of the biomaterial in effective manner. The present applicants, have made various studies on chitosan and collagen for a long time and consequently have found that a chitosan derivative, N-succinylchitosan which is obtained by chemically modifying chitosan, can suitably be used as a biomaterial and such a chitosan derivative can clinically be put to practical us in combination with collagen. The present invention is based on this finding. Accordingly, the present invention provides a biologically compatible material comprising from 50 to 90 % by weight of a composite material of an N-succinylchitosan and from 10 to 50 % by weight of a collagen, the N-succinylchitosan being obtained by succinylation of chitosan prepared by deacylation of chitin with a concentrated alkali to form a chitosan succinylated in a proportion of at least 55%. The biomaterial comprising a composite material of N-succinylchitosan and collagen according to the present invention can be prepared by subjecting the composite material in the form of a solution, dispersion or gel to freeze drying to form a spongy product, or by forming the composite material into a film or membrane. In the composite material of the present invention, the N-succinylchitosan can be obtained by modifying the amino group of chitosan. The collagen derivative can be succinylated, acetylated or methylated collagen. To the composite material of the present invention can preferably be added at least one member selected from the group consisting of chondroitin, chondroitin-4-sulfuric acid, dermatan sulfate, chondroitin-6-sulfuric acid, hyaluronic acid, fibronectin, fibrin, epidermal growth factors and fibroblast growth factors, thus giving a good wound curing effect. The thus obtained composite materials are suitable for use as artificial skins or wound dressing materials. Preferably, chondroitin, chondroitin-4 sulfuric acid, dermatan sulfate or chondroitin-6 sulfuric acid is incorporated at a proportion of 1 to 10 % by weight, hyaluronic acid incorporated at a proportion of 1 to 20 % by weight, fibronectin incorporated at a proportion of 0.001 to 0.01 % by weight, fibrin incorporated at a proportion of 0.01 to 0.1 % by weight and an epidermal growth factor or fibroblast growth factor incorporated at a proportion of 0.0001 to 0.001 % by weight. When heparin is incorporated in the composite material of an N-succinylchitosan and collagen, preferably in a proportion of 0.1 to 10 % by weight, the composite material has an excellent antithrombogenicity and is suitable for use as a coating material on the wall of blood vessels or as an artificial blood vessel. When protamine is incorporated in the composite material of an N-succinylchitosan and collagen, preferably in a proportion of 0.1 to 20 % by weight, the composite material has an excellent hemostatic effect and is suitable for use as a hemostatic agent. In the biomaterial of the present invention, the composite material of an N-succinylchitosan and collagen, which may be processed in the form of a sponge or coated onto a base material, can be subjected to bridge making by treating with a bifunctional bridging agent or by irradiation. The thus bridged product can further be subjected to sterilization. In the composite material comprising an N-succinylchitosan and collagen according to the present invention, the N-succinylchitosan is prepared by succinylation of chitosan. The chitosan used for the preparation of the N-succinylchitosan can be any acid-soluble one which can be obtained by deacetylation of chitin with a concentrated alkali. This deacetylation is carried out in such a manner such that chitosan is succinylated in a proportion of at least 55 %, preferably 70 to 100 %. The N-succinylchitosan is generally prepared by reacting such a chitosan with a carboxylic anhydride and thus effecting N-succinylation of the chitosan so as to give a chitosan succinylated in a proportion of at least 55 %, preferably 70 to 100 %, but the N-succinylation can also be carried out after collagen is added to the chitosan. For example, N-succinylchitosan is prepared by dissolving chitosan in an aqueous solution of acetic acid, diluting with methanol, mixing with carboxylic anhydride, diluting with water, subjecting to pH control with caustic soda and then subjecting to dialysis, concentration and freeze-drying in vacuum. In the composite material of an N-succinylchitosan and collagen according to the present invention, as the collagen, there can be used any simple substance of collagen or derivatives of collagen obtained by subjecting collagen to chemical treatment. In addition, atelocollagen with a raised biocompatibility and collagen derivatives obtained by chemically modifying collagen to raise the biocompatibility can also be used. For example, succinylated collagen obtained by treating collagen with succinic anhydride has an excellent antithrombogenicity and methylated collagen obtained by treating collagen with absolute methanol has an effect of increasing the reaction with thrombocyte. Depending upon these specific properties, therefore, various biomaterials suitable for intended uses can be obtained utilizing the chemical modification. Other reagents for the chemical modification include, for example, absolute ethanol, 2,4-dinitrofluorobenzene, 2,4,6-trinitrobenzenesulfonic acid, hypobromites, and 1,2-cyclohexanedione. The chemical modification of collagen is generally carried out by reacting collagen with a reactant or reagent, but it can of course be carried out after collagen is added to an N-succinylchitosan. When the reagent for the chemical modification of collagen is a carboxylic anhydride, collagen is added to chitosan to prepare a composite material which is then reacted with the carboxylic anhydride, whereby the N-succinylation of chitosan and the chemical modification of collagen can simultaneously be accomplished. The chemical modification of collagen may predominantly be carried out on the amino groups or carboxyl groups of collagen, preferably carried out in a proportion of 5 to 100 %, more preferably 30 to 100 % on the amino groups or carboxyl groups of collagen. The biomaterial of the present invention can be given a water holding property by adding chondroitin, chondroitin-4 sulfuric acid, dermatan sulfate, chondroitin-6 sulfuric acid or hyaluronic acid to the composite material comprising an N-succinylchitosan and collagen according to the present invention. Since these mucopolysaccharides are contained in the skin, and play an important role in holding water, application of the biomaterial of the present invention, for example, to medical treatment of a wound is effective for preventing the wound surface from drying. Moreover, addition of fibronectin or fibrin to the composite material of an N-succinylchitosan and collagen according to the present invention results in acceleration of repairing a wound part and addition of heparin or protamine thereto results in control of the reaction with blood. In order to improve the biocompatibility, it is required to make a biomaterial similar to the living body. The above described chemical modification and addition of the useful components occurring in the living body best answer this purpose. The biomaterial of the present invention can be prepared by drying a composite material or composition comprising an N-succinylchitosan and collagen in the form of a solution, dispersion or gel. When a solution or dispersion of the above described composite material is coated onto a surface of a base material such as glass plate and then dried, a biomaterial in the form of a film or membrane can be prepared. When the above described composite material is subjected to freeze drying, a spongy biomaterial can be prepared. Furthermore, the strength or water absorbing capacity of the biomaterial comprising the composite material of an N-succinylchitosan and collagen according to the present invention can be improved by treating the composite material with a bifunctional bridging agent or irradiating the same and thereby effecting bridge making. As the bifunctional bridging agent in bridging of the biomaterial, any materials having two or more functional groups can be used, but hexamethylene diisocyanate or glutaraldehyde is preferably used. The bridging reaction can be carried out by adding previously a bifunctional bridging agent to a solution or dispersion of the composite material of an N-succinylchitosan and collagen, forming it into a film, membrane or sponge and then subjecting it to bridging, or by forming the composite material of an N-succinylchitosan and collagen into a film, membrane or sponge, immersing it in a solution of a bridging agent or subjecting it to irradiation and thereby effecting bridging. As radiation, there can be used any of ultraviolet rays, gamma rays and corpuscular radiations such as alpha rays, but the use of ultraviolet rays or gamma rays is preferable. The biomaterial comprising the composite material of an N-succinylchitosan and collagen according to the present invention is generally used in the form of a film, membrane or sponge, but can also be used in combination with other biomaterials. The former case is exemplified by use as a wound dressing material, artificial skin, hemostatic agent or antiadhesive membrane, and the latter case, i.e. use in combination with other biomaterials is exemplified by the use as a coating on the inside or outside of a catheter or vascular prosthesis made up of a synthetic high molecular weight material. For the use as a coating on such a biomaterial of synthetic macromolecule, there is a method comprising immersing a biomaterial of synthetic macromolecule in a solution of the composite material of an N-succinylchitosan and collagen and then drying, a method comprising applying a viscous solution or dispersion of N-succinylchitosan and collagen to a biomaterial of synthetic macromolecule and then drying, and a method comprising in the above described method, carrying out drying after subjecting the coating to a chemical treatment by reacting the composite material with a carboxylic anhydride or another reactant. In such a combination of the composite material comprising an N-succinylchitosan and collagen according to the present invention with another biomaterial, the surface is coated with the composite material comprising an N-succinylchitosan and collagen according to the present invention and the surface of the biomaterial obtained by drying is in the form of a film or membrane, or the surface of the biomaterial obtained by freeze drying is in the form of a sponge, wherein the biocompatibility is improved. The biomaterial comprising the composite material of a chitosan derivative and collagen according to the present invention has an excellent biocompatibility and thus can be applied to a living body in safety without any problem of antigenecity. Since the chitosan derivative is prepared from a chitosan obtained by treating chitin with a concentrated alkali in a concentration of at least 40 %, in particular, the antigen-antibody reaction is greatly reduced and the safety is increased. When the composite material of the present invention is used as a wound dressing material or artificial skin in combination with other biomaterials, healing of a wound surface is accelerated, and the composite material of the present invention having been given a thrombogenicity or antithrombogenicity can be used as a hemostatic agent or vascular prosthesis with advantageous effects. The following examples are given in order to illustrate the present invention in detail without limiting the same. Example 1 Preparation of Chitosan 200 g of a crushed shell of chionoecetes was added to 2000 ml of 5 % hydrochloric acid, stirred at room temperature for 5 hours and then filtered. The residual solid product was washed with water, added to 2000 ml of a 5 % aqueous solution of sodium hydroxide, heated at 90 °C for 2.5 hours with agitation and then filtered. The residual solid product was washed with water. The thus obtained chitin was added to 2000 ml of a 50 % aqueous solution of sodium hydroxide, heated at 90 ° C for 2.5 hours with agitation and then filtered. The precipitated solid product was sufficiently washed with water and dried at 95 °C, thus obtaining 41 g of chitosan with a deacetylation degree of 99 %. Preparation of Atelocollagen A fresh calf dermis was finely crushed. 100 g of this fine powder was repeatedly washed with a 0.1 M aqueous solution of sodium acetate and washed with water. To 10 g of the thus obtained fine powder was added 4000 ml of 0.5 M aqueous solution of acetic acid, followed by agitation at 5 °C for 3 days, and precipitated insoluble collagen was then separated by filtration. 10 g of the insoluble collagen was added to 100 ml of 0.1 M acetic acid, to which 0.01 g of pepsin (manufactured by Sigma Co., 1 : 60,000) was added, and stirred at 20 °C for 3 days, thus obtaining a solution of atelocollagen (pepsin-solubilized collagen). The resulting solution of atelocollagen was filtered by a glass filter and an aqueous solution of sodium hydroxide was added to the resulting solution to adjust the pH to 7.5, thus forming a fibrous precipitate. The solution containing the precipitate was subjected to centrifugal separation at 7,000 G and 8,000 rpm and the thus separated precipitate was washed with distilled water 3 times, thus obtaining 7 g of atelocollagen. Example 2 Preparation of N-Succinylchitosan 2 g of the chitosan of Example 1 was dissolved in 40 ml of a 5 % aqueous solution of acetic acid and diluted with 160 ml of methanol. 2.1 g of succinic anhydride (corresponding to 1.5 mol per 1 mol of the amino group of chitosan) was dissolved in 50 ml of acetone and the whole quantity of the resulting acetone solution of succinic anhydride was added to the above described chitosan solution, and then allowed to stand for one night. The precipitate was separated by filtration and dried to obtain 2 g of a powder of N-succinyl-chitosan. The modification ratio of the amino groups of the chitosan amounted to 70 %. Preparation of Succinylated Collagen 2 g of collagen was dissolved in a mixed solution of 1.6 ml of concentrated hydrochloric acid and 100 ml of water, to which a 5 N aqueous solution of sodium hydroxide was gradually added to adjust the pH to 13 while stirring. 0.07 g of succinic anhydride (corresponding to 1 mol per 1 mol of the ε-amino group at the side chain of collagen) was dissolved in 10 ml of acetone and the whole quantity of the acetone solution was gradually added to the above described collagen solution, followed by stirring for one night while controlling constantly the pH to 13 with a 5 N aqueous solution of sodium hydroxide. The precipitate was separated by filtration, washed adequately with water and dried to obtain 2 g of succinylated collagen. The modification ratio of the ε-amino group of the collagen was 30 %. Preparation of Vascular Prosthesis 0.9 g of the thus resulting N-succinylchitosan and 0.1 g of the thus resulting succinylated collagen were dissolved in 100 ml of water, in which a vascular prosthesis (inner diameter 6 mm, length 5 cm) made of dacron whose surface had been subjected to a plasma treatment was immersed, and it was withdrawn and air-dried. After this procedure was repeated 20 times, the vascular prosthesis of dacron was immersed in a 1 % aqueous solution of glutar-aldehyde adjusted to pH 13 for 1 hour and thus bridged. This vascular prosthesis of dacron was adequately washed with water and air-dried, thus obtaining a vascular prosthesis whose surface was constructed of a film of a mixture of N-succinylchitosan and succinylated collagen. When the thus resulting vascular prosthesis was implanted in a living body, a good antithrombogenicity was obtained. Example 3 Preparation of Mixture of N-Succinyl-N-Octanoylchitosan and Succinylated Collagen 9 g of the N-succinylchitosan of Example 2 and 1 g of the succinylated collagen of Example 2 were dissolved in 500 ml of water and diluted with 2000 ml of methanol, to which 22 g of octanoic anhydride (caprylic anhydride) (corresponding to 2 molar equivalents to the hexosaminyl group of chitosan) was added, and the mixture was allowed to stand at room temperature for one night to obtain a solution of a mixture of N-succinyl-N-octanoylchitosan (acylation degree : 90 %) and succinylated collagen. Preparation of Film of Biomaterial The thus resulting solution of a mixture of N-succinyl-N-octanoylchitosan and succinylated collagen was coated onto a glass plate and then air-dried to form a film of 0.1 mm in thickness, consisting of the mixture of N-succinyl-N-octanoylchitosan and succinylated collagen, which was then bridged by irradiation of ultraviolet rays. When this film was applied to peritoneum as an antiadhesive membrane, a good result was given (no adhesion was found.) Example 4 Preparation of Methylated Collagen 2 g of the atelocollagen of Example 1 was immersed in 1000 ml of a HCL-acidic solution of absolute methanol to methylate the carboxyl groups at the side chains of collagen and 2 g of a methylated collagen was obtained. Example 5 The solution of a mixture of N-succinyl-N-octanoylchitosan and succinylated collagen obtained in Example 3 was dried in vacuum (0.1 torr) to obtain 10 g of a powder of the mixture of N-Succinyl-N-octanoylchitosan and succinylated collagen. 10 g of this powder was dissolved in 50 ml of water, to which 0.1 g of chondroitin-4 sulfuric acid, 0.1 g of dermatan sulfate, 0.05 g of hyaluronic acid, 0.0001 g of fibronectin and 0.001 g of fibrin were added, and the solution was stirred by means of a homogenizer. This solution was subjected to freeze drying in vacuum at 0.2 torr. The thus obtained spongy dried product was immersed in a 2 % methanol solution of hexamethylene diisocyanate, withdrawn therefrom, washed adequately with methanol, subjected again to drying in vacuum at 0.2 torr and then sliced in a thickness of 1 mm. Fibroblasts of a rat skin was implanted in this sponge (20 mm x 20 mm x 1 mm), incubated at 37 °C for 2 weeks and a blast-incorporated artificial skin was obtained. When the thus obtained artificial skin was grafted on a part of the back of a rat, from which the skin had been completely lost, and a piece of the epidermis was grafted on the artificial skin, the epidermis was generated, resulting in a complete healing. Example 6 Preparation of Vascular Prosthesis 0.9 g of the N-succinylchitosan obtained in Example 2, 0.1 g of the succinylated collagen obtained in Example 2 and 20 mg of heparin were dissolved in 100 ml of water and a vascular prosthesis having an excellent antithrombogenicity was prepared from the resulting solution in an analogous manner to Example 2.

Claims: A biologically compatible material comprising from 50 to 90 % by weight of a composite material of an N-succinylchitosan and from 10 to 50 % by weight of a collagen, the N-succinylchitosan being obtained by succinylation of chitosan prepared by deacylation of chitin with a concentrated alkali to form a chitosan succinylated in a proportion of at least 55%. A biologically compatible material as claimed in claim 1 wherein the collagen is collagen, an atelocollagen or a chemically modified collagen or a mixture thereof. A biologically compatible material as claimed in claim 2 wherein the chemically modified collagen is acetylated collagen, succinylated collagen, methylated collagen or a mixture thereof. A biologically compatible material as claimed in any one of claims 1 to 3 which further contains at least one of the following: chondroitin, chondroitin-4 sulfuric acid, dermatan sulfate, chondroitin-6 sulfuric acid, hyaluronic acid, fibronectin , fibrin, epidermal growth factors and fibroblast growth factors. A biologically compatible material as claimed in any one of claims 1 to 4 in the form of a film or a sponge. A process for the preparation of a biologically compatible material as claimed in any one of claims 1 to 5 which comprises preparing a solution, dispersion or gel of the composite material, and then subjecting the solution, dispersion or gel to drying. A process as claimed in claim 6 wherein the drying step consists of freeze drying or drying after coating a solution of the composite material onto a base material to form a film or membrane. A process as claimed in claim 6 or claim 7 wherein chemical modification of collagen is carried out after mixing N-succinylchitosan and collagen. A process as claimed in claim 8 wherein chemical modification is carried out on the amino groups or carboxyl groups of collagen in a proportion of 5 to 100% of the amino groups or carboxyl groups. A process as claimed in any one of claims 6 to 9 which further comprises treating the composite material with a bifunctional bridging agent or irradiating the same in order to effect bridging. A biologically compatible material as claimed in any one of claims 1 to 5, optionally in conjunction with another biologically compatible material, for use as an artificial skin, a wound dressing material, a vascular prothesis or a hemostatic agent.

Inventors: HIGASHIJIMA, HITOSHI, KIMURA, TAKASHI, KODAIRA, KAZUHIKO, MIYATA, TERUO, NOISHIKI, YASUHARU
Applicants: KATAKURA CHIKKARIN CO., LTD., KOKEN CO. LTD.
Application year: 1986
Main classification: A61L27
IPC codes: A61L27, A61L15, A61L31