Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
1998-08-26
2003-01-07
Nguyen, Dinh X. (Department: 3626)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S011110, C623S023510, C623S023580, C623S023750
Reexamination Certificate
active
06503278
ABSTRACT:
The invention relates to under tissue conditions degradable material.
In surgery, it is known to employ implants manufactured of biodegradable (under tissue conditions absorbable) polymers for connecting tissues together, for separating tissues from each other, for temporarily replacing tissues partially or entirely and for guiding the healing or growth of the tissues. It is known to manufacture of partly crystallized thermoplastic, biodegradable polymers strong implant materials by stretching elongated blanks, such as fibres or bars in a manner that the crystalline structure of the materials is modified and directed (oriented) increasing the strength and the stiffness of the material in the orientation direction. Publication U.S. Pat. No. 4,968,317 presents partly crystalline, biodegradable biomaterials, oriented by the drawing technique which can be used when manufacturing e.g. various equipments for fixation of bone fractures. Publication EP-03211761 presents a method for manufacturing oriented, partially crystalline, biodegradable material by cooling the thermoplastic polymer to a temperature lower than its glass-transition temperature, in which the nucleation of the crystals takes place, and by reheating the material to a temperature which is higher than the glass-transition temperature of the material but lower than its melting temperature, and by stretching the material under these conditions to gain orientation.
Publication WPI ACC No: 89-220470/30 presents a surgical biomaterial consisting of molecularly oriented lactic acid polymers or its copolymer with glycol acid, having a crystal content of 10 to 60% in the material and a compression bending strength of 160 to 250 MPa.
Partially crystalline biodegradable polymer materials can be used for manufacturing e.g. various rods, screws, plates etc. to be employed e.g. when repairing bone fractures or damages in connective tissue. The following publications disclose results of applying these types of materials in surgical use: P. Rokkanen et al.: “Utilisation des implants biodegradables dans le traitement chirurgical des fractures et au cours des ostéotomies”, Orthop. Traumato 12, (1992), pp. 107-11; E. K. Partio et al.: “Immobilisierung und Frühmobilisierung von Malleolarfrak-turen nach Osteosynthese mit resorbierbaren Schrauben”, Unfall-chirurgie 18(5), (1992), pp. 304-310; H. Pihlaiamäki et al.: “Absorbable pins of self-reinforced poly-l-lactic acid for fixation of fractures and osteotomies”, J Bone Joint Surg 74-B(6), (1992), pp. 853-857; T. Yamamuro et al.: “Bioabsorbable osteosynthetic implants of ultra high strength poly-L-lactide. A clinical study”, Int. Orthop. 18, (1994), pp. 332-340.
Crystalline configuration as such gives the non-oriented biodegradable materials strength and toughness in a manner that they can be employed e.g. in bone surgery, in selected surgical embodiments, such as in healing of non-loaded bone fractures (cf. e.g. S. Vainionpää, P. Rok-kanen and P. Törmälä: “Surgical applications of biodegradable polymers in human tissues”, Prog. Polym. Sci. 14, (1989), pp. 679-716).
Although the partially crystalline biodegradable materials have good, in case of oriented materials even excellent, strength properties, and the strength retention time in vivo can be controlled to a typical term of 1 to 12 months, the disadvantage is very slow degrading of the crystal phase of the material. Numerous researches have found out that partially crystalline, biodegradable materials first degrade at their amorphous (noncrystalline) parts, since degrading starts and is easiest in the amorphous areas of the material, which are situated between the crystalline areas (cf. e.g. E. W. Fischer, H. J. Sterzel, G. Wegner G.: “Investigation of the structure of solution grown crystals of lactide copolymers by means of chemical reactions”. Kolloid-Z. Polym. 251, (1973), pp. 980-990). As a result of the said heterogeneous degradation, in the last phase of the polymer absorbing, mainly crystalline, very slowly degradable particles are created. In some tissues, these particles can cause harmful side effects, such as swelling in the tissue and pain (cf. e.g. E. J. Bergsma et al.: “Foreign Body Reactions to Resorbable Poly (L-lactide) Bone Plates and Screws Used for the Fixation of Unstable Zygomatic Fractures”, J. Oral Maxillofac. Surg. 51, (1993) pp. 666-670).
However, since the non-crystalline (amorphous) biodegradable polymer material has no slowly degradable crystal structures, degradation of amorphous polymer is under tissue conditions faster than degradation of partially crystalline polymer, and due to the lack of crystalline structure, no such harmful tissue reactions can occur when the amorphous polymers are degrading, as described e.g. in the above mentioned publication E. J. Bergsma et al. However, a drawback with amorphous biodegradable polymers is their poor mechanical strength properties. As for the mechanical properties, the amorphous biodegradable materials are either very ductile (“rubber-like”), if their glass-transition temperature is under the body temperature, or, on the other hand, they are hard and glass-like it their glass-transition temperature is over the body temperature. In every case, the amorphous polymers have relatively weak strength properties.
Insufficient strength of the amorphous, biodegradable polymer implants is found in clinical research as high frequency of breaking of fracture fixations. E.g. the publication K. E. Rehm, H.-J Helling, L. Claes: “Bericht der Arbeitsgruppe Biodegradable Implante”, Akt. Traumatol. 24 (1994), pp. 70-74 presents clinical results from 57 patients. In the research, various fractures in the cancellous bone area were fixated with biodegradable rods manufactured of amorphous poly-L/DL-lactide (with L/DL ratio of 70/30). In the post-surgical follow-up of the patients, a dislocation of bone fragment was noticed in tour patients, which signifies fies that this complication was found in 7% of the patients. Further, with two patients (3.5 % of the patients) dislocation of the rod head was found. Thus, the total proportion of complications was high: 10.5%. Dislocation of bone fragment and dislocation of rod head show that the strength of the amorphous lactide copolymer, particularly the shear strength, was not sufficient for providing safe healing. This result differs clearly e.g. from the clinical research of H. Pihlajamäki et al.: “Absorbable pins of self-reinforced poly-L-lactic acid for fixation of fractures and osteotomies”, J. Bone Joint Surg. (Br) Vol. 74-B, (1992), pp. 853-357, using rods of a corresponding type for the fixation of fractures and osteotomies in cancellous bone area, which rods were manufactured of partly crystalline, oriented (self-reinforced) poly-L-lactide. The research comprised 27 fixation-operated patients, in whom no bone fragment dislocations or rod dislocations were found in the post-operation follow-up (8 to 37 months); i.e. the degree of complications was 0%. Since the shear strength of partially crystalline, oriented polylactide rods is more than double compared to that of amorphous, non-oriented polylactide rods (the shear strength of rods used by Pihla-jamäki et al. was 100 to 180 MPa and the shear strength of rods used by Rehm et al. was measured 46 to 54 MPa, cf. Example 1), it is obvious that the high proportion of complications in the research of Rehm et al. was due to insufficient strength properties of the material used in their study. On the other hand, since no slow-absorbtion, crystalline phase is present in the amorphous polymer, absorbing of the amorphous polymer takes place, after loosing the strength, faster than absorbtion of partly crystalline polymer. For example according to the publication of Rehm et al., rods manufactured of amorphous poly-L/DL-lactide were absorbed almost entirely in two years under tissue conditions, whereas according to Bergsma et al., there was a significant quantity of crystalline poly-L-lactide present at the operation site in the patient even after three years and eight months after the implantatio
Pohjonen Timo
Törmälä Pertti
Bionx Implants Oy
Kenyon & Kenyon
Nguyen Dinh X.
LandOfFree
Under tissue conditions degradable material and a method for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Under tissue conditions degradable material and a method for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Under tissue conditions degradable material and a method for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3001378