Surgery: splint – brace – or bandage – Bandage structure – Skin laceration or wound cover
Reexamination Certificate
1999-02-17
2001-01-16
Brown, Michael A. (Department: 3764)
Surgery: splint, brace, or bandage
Bandage structure
Skin laceration or wound cover
C602S041000, C602S044000, C602S045000, C602S046000, C602S047000
Reexamination Certificate
active
06175053
ABSTRACT:
TECHNICAL FIELD
This invention relates to a wound dressing material for dressing skin defect regions caused by a wound or burn and accelerating a cure of these regions and a method for preparing the same.
BACKGROUND TECHNOLOGY
In general, wound dressing materials used for healing skin defect regions are required to have the following properties and functions:
1) improved skin compatibility without irritating the skin,
2) flexibility sufficient to expand as the skin moves, and
3) infection controllability.
In order to provide these properties and functions, there have been developed wound dressing materials comprising bio-originated substances such as a pig skin, chitin and collagen or other porous substances.
When a skin defect is caused by a wound, burn, etc., the defect regions are treated by being covered with a conventional wound dressing material as a first aid and then grafting skin from buttocks or other parts to the defect region after the condition thereof is recovered to a level to be further treated.
When a conventional wound dressing material is used, however, the dressing material should be stripped off wherever the defect region is treated.
On all such occasions, new skin, which is regenerating under the dressing material is unfavorably destroyed.
Further, the flexibility of conventional dressing materials comes into question because these materials do not flexibly deform enough following the movement of the skin, which sometimes causes pain.
In the case of porous dressing materials, the infection controllability thereof is also called in question in addition to the flexibility.
As a medical material originating from a protein fiber, silk has been used for a long time as an excellent biocompatible suture.
A permeable membrane which comprises a crystalline substance containing- and water insoluble-fibroin is known as a membrane comprising a protein fiber-originated component (see, Japanese Patent Laid-Open Publication Nos. 63-246,169 and 1-118,545).
A water insoluble fibroin membrane described in Japanese Patent Laid-Open Publication No. 1-118,545 has various uses such as artificial skins, wigs, sweat clothes and the like because of excellent vapor permeability, improved transparency and mechanical strength, and desirable affinity to the human body.
On the other hand, Japanese Patent Laid-Open Publication No. 2-233,128 describes that a crystalline substance containing- and water insoluble-membrane prepared from fibroin and sericin exhibits excellent oxygen permeability, improved transparency and mechanical strength, desirable biocompatiblity and high stability to the human body, and is accordingly useful as contact lenses, artificial skins, blood bags and the like.
Furthermore, Japanese Patent Laid-Open Publication No. 56-40,156 describes that a porous membrane is prepared by blending a water soluble compound such as ethylene glycol, polyalkylene glycol and glycerine to sericin, which exhibits appropriate water absorption properties and vapor permeability required for a skin protecting material, and improved flexibility.
In these crystalline substance containing membranes which comprise water insoluble fibroin, the crystallinity thereof is necessarily at least more than 10%, and preferably more than 15% so as to keep the mechanical strength, while the water content is about 10 to 60% by weight. The crystallinity should be more than 20%, particularly in the case of the above mentioned porous membrane in which the above-mentioned water soluble compound is blended to fibroin.
Fibroin containing permeable membranes of the conventional type, in which the crystallinity is more than 10% to adequately keep the mechanical strength, may be used as artificial skins.
However, these conventional membranes exhibit insufficient flexibility and water absorption properties to use as a wound dressing material for healing a skin defect region, while in the case of porous membranes, the infection controllability is also in question, and accordingly, it is not intended in essence to use such permeable membranes themselves as a wound dressing material.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a novel wound dressing material which has biocompatibility and infection controllability as essential properties required for such a material, as well as excellent flexibility and water absorption properties, thereby accelerating smooth regeneration of a skin defect without stripping off the regenerating skin while removing the material from the skin, and a method for preparing the same.
The inventor has found that an amorphous film comprising fibroin as a main component is an excellent wound dressing material.
As a result of our eager investigation continued after our previous patent application (Japanese Patent Application No. 8-28,559), it has been also found that a highly flexible and water-absorbing amorphous film of a crystallinity below 10% exhibits particularly excellent properties as a wound dressing material when fibroin is combined with sericin, which has a binder-like function to fibroin.
The present invention has thus completed on the basis of the above mentioned information.
According to the present invention, there are provided a wound dressing material which comprises (a) an amorphous film of crystallinity below 10% containing fibroin and sericin as a main component, and a powder type wound dressing material which comprises (b) fibroin and sericin as a main component, and a method for preparing these wound dressing materials.
In order to further improve the healing effect to a wounded region, various healing agents or remedies may be added to these wound dressing materials as set forth in the following.
There may be added disinfectants (additives used for microorganism elimination or ablution) such as iodine, potassium iodide, povidon iodine, acrinol, hydrogen peroxide, isopropyl methylphenol, benzalkonium chloride, cetyl chloride pyridinium, chlorohexidine and the like.
There may also be added at least one or more than two kinds of cure accelerating agents (additives for accelerating a wound treatment) selected from a group consisting of, for example, allantoin, dibucaine hydrochloride, chlorophenylamine malate and the like.
Further, a vasoconstrictor such as naphazoline hydrochloride may be added.
An astringent such as zinc oxide may also be added.
Furthermore, a crust regenerating agent such as boric acid may be added.
All of these additives may be added in a selectively combined use of two or more.
The amount of the above mentioned disinfectants to be added to the wound dressing material is preferably less than 30% by weight, more preferably 0.5 to 20% by weight and most preferably 1 to 15% by weight so as not to lose the essential properties of the material. If the amount increases over 30% by weight, the wound dressing material becomes hard and fragile.
The wound dressing material of an amorphous film (a) comprises a dense and non-porous film of a crystallinity below 10% which contains 0 to 99% by weight of fibroin and 1 to 100% by weight of sericin and has a density of 1.1 to 1.4 g/cm
3
determined by the density-gradient tube method using toluene and tetrachlorocarbon, a thickness of 10 to 130 &mgr;m, water absorption of 100% or more after one hour-immersion in water at room temperature and a water soluble portion in an amount of 10% or more. The powder type wound dressing material (b) is obtained by milling and pulverizing the amorphous film (a).
The density is preferably 1.36 to 1.38 g/cm
3
. The film tends to be porous because of foams when the density is less than 1.1 g/cm
3
, while the crystallinity increases excessively when the density is more than 1.4 g/cm
3
.
Similarly, a film of 10 &mgr;m or less in thickness is easily torn, while the crystallinity increases undesirably when the thickness is more than 130 &mgr;m.
The wound dressing material of the present invention is basically prepared from a raw material, which contains protein fiber-originated fibroin and sericin obtained from silkworms, by dissolving the raw material in
Brown Michael A.
Flynn ,Thiel, Boutell & Tanis, P.C.
Hamilton Lalita M.
Japan as represented by Director General of National Institute o
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