MEDICAL IMPLANT

Abstract: A medical implant coated with a polymeric material having hydrophilicity and osteoconductivity. When the implant is embedded in depth in a living body, the polymeric material absorbs moisture to swell up, bringing about an effect of dispersing the external stress applied to the implant. This volumetric increase also brings the implant into close contact with the bone of the implantation site, thus remarkably improving the stability in the early stage of the implantation and more strengthening the osseointegration of the implant in the bone as time passes.

Description: MEDICAL IMPLANT BACKGROUND OF THE INVENTION Field of the Invention The present invention relates, in general, to a medical implant and, more particularly, to an implant coated with a polymeric material of hydrophilicity and osteoconductivity which enables the implant to secure stability in an early stage of the implantation and to be more strongly integrated in a bone tissue with the lapse of time. Description of the Prior Art In medicine, an implant is a device intended to be embedded in a tissue for therapeutic purpose or its desired aim. Generally, after an implant is embedded in a predetermined tissue site of a living body, e.g. nasal bone, dental root or other type bones, the integration of the implant is accomplished either through a medium of soft tissue between the implant and the tissue or by filling this site with a bone only without any intermediate. The latter case is called complete osseointegration. After implantation in a bone tissue, the therapeutic purpose of the implant can be achieved with a higher possibility as the interface between the implant and its surrounding bone is filled with a larger amount of bony material. In conventional techniques, the osseointegration between an implant and a bone was found to be only about 60% and thus, there is a limit in the therapy with implant. SUMMARY OF THE INVENTION It is an object of the present invention to overcome the above problems encountered in prior arts and to provide a medical implant which is greatly improved in osseointegration as well as in stability in the early stage of the implantation. In accordance with the present invention, there is provided a medical implant which is coated with a polymeric material having hydrophilicity and osteoconductivity both. DETAILED DESCRIPTION OF THE INVENTION Chitosan, a natural polymer which can be relatively easily obtained from the nature, shows both hydrophilicity and osteoconductivity. These properties enable chitosan to be used as a medical implant . When chitosan is placed in depth of a body, the polymeric compound absorbs moisture from the body, swelling up. This volumetric increase of the polymeric compound brings about an effect of dispersing the external stress applied to the implant. In addition, while being volumetrically increased, the polymeric compound placed in depth in a living body allows the implant to come into close contact with the bone, thus exceptionally augmenting the stability of the implant in the early stage of the implantation. Further, because the polymeric compound embedded together with an implant in a living body displays superior osteoconductivity, the osseointegration of the implant into neighboring bones is further strengthened with the lapse of time . A better understanding of the present invention may be obtained in light of following examples which are set forth to illustrate, but are not to be construed to limit, the present invention. In the following examples, prevailing Branemar implants in current use were coated with or without chitosan and implanted in living bodies. In either case, the implants were tested for their stability in the early stage of the implantation. EXAMPLES I THROUGH XVIII A set of test samples were prepared by coating chitosan on the surfaces of implants . Another set of test samples were un-coated implants. The test samples each were embedded in a knee bone of a pig. 3-4 days after this implantation, each of the test samples was laterally applied with a force of 20 N and then, the displacement of the implants was measured. From this, the stiffness of the implants anchored in the bones was evaluated and is given as shown in Table I below. TABLE 1 Unit : Kg/mm 2 Sample Uncoated Coated 1 32.519 63.087 2 54.218 30.895 3 24.035 58.201 4 52.697 46.919 5 30.404 33.772 6 35.403 69.154 7 44.800 39.016 8 30.020 26.009 9 21.980 71.826 10 21.500 42.172 11 35.960 44.695 12 38.560 50.578 13 19.252 39.016 14 35.549 26.009 15 52.939 71.826 16 25.321 42.172 17 47.925 44.695 18 22.022 50.578 Average 34.728 47.108 Std.Deviat 'n 11.668 14.956 Shear Stress Test 0.011 In the table, higher values for the implants mean that the implants are laterally moved in shorter distances when the same force is applied. It is apparent from the table that the displacement of the implants is smaller upon the lateral application of a force of 20 N to the implants as they are of larger stiffness. Therefore, since the coated implants with chitosan have larger stiffness than do the uncoated ones in each samples, the coating with chitosan endows the implants with great stability in the early stage of the implantation. In detail, the coated implants are more improved in the initial stability than the uncoated ones by about 36%. Besides chitosan, examples of the naturally occurring compounds which can be as a coat for a medical implant include cellulose polymers, such as cellulose, cellulose acetate, cellulose nitrate and ethyl cellulose, protein polymers, such as gelatin and collagen, guar gum, and cellulose acetate butyrate . Examples of the synthetic polymers useful as such a coat include poly- -lactide, poly- D- -lactide, polyglycolide-lactide, polyacrylonitrile, polyvinylacetate, polyvinylalcohol, poly γ-benzyl-L- glutamate, polyphosphazene , polyalkyleneoxalate , polydimethylsiloxane, polyurethane, polyetherurethane amide, polyesterurethane and the mixtures thereof. As described hereinbefore, when the implant coated with a polymeric material of hydrophilicity and osteoconductivity is embedded in depth in a living body, the polymeric material absorbs moisture to swell up, bringing about an effect of dispersing the external stress applied to the implant. In addition, the implant are brought into close contact with the bone of the graft site by virtue of the volumetric increase and thus, obtains remarkably improved stability in the early stage of the implantation. Furthermore, the polymer of hydrophilicity and osteoconductivity more strengthens the osseointegration of the implant in the bone as time passes. The present invention has been described in an illustrative manner, and it is to be understood the terminology used is intended to be in the nature of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, it is to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Claims: WHAT IS CLAIMED IS; 1. A medical implant embedded in the depth of a bone, wherein said medical implant is coated with a polymeric material which is of hydrophilicity and osteoconductivity. 2. A medical implant as set forth in claim 1, wherein said medical implant is swelled when said implant is embedded in the depth of a bone, thereby dispersing the external stress applied to said medical implant . 3. A medical implant as set forth in claim 1, wherein said polymeric material is selected from the group consisting of chitosan, cellulose, cellulose acetate, cellulose nitrate, ethyl cellulose, gelatin, collagen, guar gum, cellulose acetate butyrate . 4. A medical implant as set forth in claim 1, wherein said polymeric material is selected from the group consisting of poly-L-lactide, poly-D-L-lactide, polyglycolide-lactide, polyacrylonitrile, polyvinylacetate, polyvinylalcohol, poly γ-benzyl-L-glutamate, polyphosphazene, polyalkyleneoxalate, polydimethylsiloxane, polyurethane, polyetherurethane amide, polyesterurethane . 5. A medical implant as set forth in claim 1, wherein said polymeric material is selected from the group consisting of chitosan, cellulose, cellulose acetate, cellulose nitrate, ethyl cellulose, gelatin, collagen, guar gum, cellulose acetate butyrate and selected from the group consisting of poly-L-lactide, poly-D-L-lactide, polyglycolide-lactide, polyacrylonitrile, polyvinylacetate, polyvinylalcohol, poly γ-benzyl-L-glutamate, polyphosphazene, polyalkyleneoxalate, polydimethylsiloxane, polyurethane, polyetherurethane amide, polyesterurethane . 6. A medical implant as set forth in any one of claims 1 to 5, wherein said implant is an artificial tooth to be embedded in a dental root .

Inventors: LEE YONG CHAN, LEE, YONG, CHAN
Applicants: LEE YONG CHAN, LEE, YONG, CHAN
Application year: 1997
Main classification: A61L27
IPC codes: A61C8, A61C13, A61F2, A61L27