Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1998-11-12
2001-08-28
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C523S113000, C523S115000, C523S128000, C525S450000, C604S530000, C623S022290, C623S926000, C264S230000
Reexamination Certificate
active
06281262
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to shape-memory biodegradable and absorbable materials which can be recovered to the original shape by reheating and degraded and absorbed in vivo.
BACKGROUND OF THE INVENTION
Materials to be embedded in living bodies (i.e., implant materials) include metals, bioceramics, polymers, those with biological origins and hybrid materials.
These materials may be classified into so-called absorbable ones which are gradually absorbed and discharged from the body after exerting the functions in vivo and non-absorbable ones which cannot be degraded but substantially remain as such in vivo.
When these non-absorbable materials (synthetic materials) are kept in vivo over a long time, it is feared that these foreign matters undergoes some undesirable reactions due to the differences in physical or chemical (physiological) properties from biological constituents or the expression of toxicity caused by corrosion. Therefore, these materials are sometimes taken out from the body, if possible, by reoperative surgery. In such a case, a patient should be burdened with repeated pains and an additional fee. To relieve this situation, it has been required to develop biological materials which can be used as substitutes for the existing ones without resorting to any reoperative surgery.
Although biodegradable and absorbable materials are expected as useful in satisfying the above requirement, there are not such a great variety of absorbable materials as being usable as substitutes for all of nonabsorbable implant materials made of metals, ceramics, polymers, etc. Thus, research and development have been made to obtain a substitute for each of these existing materials.
Operative suture yarns and metallic materials (stainless steel, titanium, silver, platinum) employed for ligating missing or amputated parts are biomaterials which remain in the body after the completion of the operation. Suture yarns should be selected by considering tissue disorder, tissue tension, the occurrence of suture complication, effects of bodily fluids on the threads, infection, etc.
In general, silk yarns are employed in ligating fasciae and peritonea, nylon yarns are employed in ligating skin and nerves, polyester yarns are employed in fixing heart and tendons, while polypropylene yarns are employed in anastomosing nerves and blood vessels. Synthetic absorbable suture yarns (polyglycolic acid-based type) are used not only in the above sites but also in digestive tracts, etc.
In sites where a high strength is needed, on the other hand, use is made of metal wires made of stainless steel, titanium, etc. However, use of these metallic materials brings about troubles in image diagnosis. That is to say, light reflected thereby causes halation in magnetic resonance images (MRI) or computer tomography (CT) which have been rapidly spread in recent years as means for monitoring the conditions of patients under operation or postoperative healing state. Thus, it has been required to develop novel materials for suture, anastomosis or ligation which are usable as substitutes for metal wires.
As described above, various suture yarns are selected in operations to suit the occasion. In many cases, these yarns are employed in stanching, suturing or anastomosing various sites other than the main incised part. However, it sometimes takes the greater part of time to perform these treatments. Under these circumstances, it has been required to develop materials for suturing, anastomosing and ligating with which these treatments can be carried out more easily.
For example,. an incised tendon is fixed by suturing with a yarn. However, the procedure therefor has been becoming more and more complicated and it is therefore needed to develop fixation materials and convenient methods therefor. In operations in the thoracic or abdominal cavity, it is frequently observed that more than 50 blood vessels are incised. In such a case, it is necessary to perform suture and ligation at least 100 times for stanching and postoperative fixation. Therefore, it has been required to develop methods and materials by which these procedures can be carried out more easily. In addition, it is a practice to leave the conventional nonabsorbable materials as such in the body, since bypasses can be spontaneously formed after ligating blood vessels. Further, it is troublesome and risky to open-out the body again to take out metal clips, staples or various suture yarns therefrom, and there arises a dilemma that the body once opened-out should be sutured again. Accordingly, it is ideal that the materials to be used for the above purposes are biomaterials which can be degraded and absorbed in vivo and then discharged from the body, since the above-mentioned problems can be avoided by using these materials.
To achieve the above object, attempts have been made to produce staples and clips made of biodegradable and absorbable polymers (polyglycolic acid, polylactic acid, glycolic acid/lactic acid copolymer, polydioxanone, etc.) which have been molded into particular shapes designed by taking the physical strength of the polymers into consideration and can be physically caulked by using particular instruments. These products are used in operations in practice. However, these products still suffer from some disadvantages. Namely, they are troublesome in handling. In addition, they should be considerably larger in size than metallic ones because of the poor physical strength thereof. Moreover, they cannot be fastened tightly, since they are inferior in ductility to metals.
SUMMARY OF THE INVENTTON
The present invention, which has been completed in order to satisfy the above requirements, aims at developing shape-memory biodegradable and absorbable implant materials made of novel biodegradable and absorbable materials which are hydrolyzed and absorbed in vivo when allowed to stand therein. These biodegradable and absorbable materials are usable as medical prosthetic appliances, fillers or scaffolds. Moreover, they make it possible to easily and surely perform anastomosis, ligation, suture, fixation, fixation, etc., for example, ligating or anastomosing incised blood vessels (stanching), suturing incised sites, fixing incised tendons and fixing and fixing fractured bones. When employed in MRI or CT, they cause no halation. They are further useful as base materials in controlled drug-release or tissue engineering.
As shape-memory materials, there have been developed synthetic polymers (norbornane-based one, trans-polyisoprene, styrene/butadiene copolymer, polyolefin, polyester, polyurethane, polyacryl, etc.) and natural polymers (cellulose fiber, protein fiber, etc.). However, none of them is biodegradable and absorbable in vivo. That is to say, it has never been reported hitherto that a biodegradable and absorbable material recognized as a biocompatible material is processed into a shape-memory material and embedded in vivo in practice, as done in the present invention.
The fundamental shape-memory biodegradable and absorbable material of the present invention, by which the above-mentioned objects have been achieved, is made of amolded article of a lactic acid-based polymer wherein said material can be recovered to the original shape without applying any external force thereto but by heating to a definite temperature or above. Namely, a molded article made of a lactic acid-based polymer in a definite shape is deformed into another molded article at a temperature (Tf) higher than the glass transition temperature (Tg) thereof but lower than the crystallization temperature (Tc) thereof (or 100° C. when the molded article has no crystallization temperature) and then fixing said molded article to the thus deformed shape by cooling it as such to a temperature lower than the glass transition temperature (Tg), wherein said molded article can be recovered to the former molded article of the original shape by heating it again to said deformation temperature (Tf) or above.
REFERENCES:
patent: 4916207 (1990-04-01), Boyle, Jr. et al.
patent: 4950258 (199
Sughrue Mion Zinn Macpeak & Seas, PLLC
Szekely Peter
Takiron Co., Ltd.
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