Surgery – Instruments – Suture or ligature
Reexamination Certificate
2000-03-20
2002-10-01
McDermott, Corrine (Department: 3738)
Surgery
Instruments
Suture or ligature
C623S023580, C623S013180
Reexamination Certificate
active
06458148
ABSTRACT:
DESCRIPTION
The present invention relates to a strand-like implant of resorbable polymer material, a process for its production and its use in surgery.
Implants are frequently used in surgery for fixing and supporting, as well as for temporary or permanent replacement of damaged body parts. Examples are surgical suture threads, vascular prostheses, as well as artificial ligaments and fascicles.
Implants in the form of cords or bands have been developed, particularly for use in orthopedic surgery on humans and animals. They are e.g. used in the reconstruction or prosthetics in the area of the locomotor system, such as a cruciate knee ligament rupture.
However, when using non-resorbable materials, such as e.g. polytetrafluoro-ethylene, there are often persistent foreign body reactions and delayed infections caused by the implant.
Developments have therefore been directed towards partly or completely body-resorbable implant materials. Reference is made in this connection to the implant cord made from polydioxanone disclosed in the Ethicon German patent DE-C2 4012602. EP-B1-0 241 252 describes a lactide/glycolide polymer, which is end-masked with dodecanol.
The cords or bands known from the prior art suffer from a number of disadvantages. Thus, some resorbable materials have an accelerated resorption and therefore lead to an excessively rapid strength reduction, which impedes the result of the healing. High stiffness levels of the cords leads to a poor knotting behaviour and risks of an imprecise positioning in the operating field. In addition, the rough surfaces of the cords are prejudicial to the pull-through behaviour and can damage surrounding body tissue. The problem of the invention is to provide a strand-like implant of a resorbable polymer, which has good mechanical characteristics combined with a good decomposition and resorption behaviour in vivo, which is easy and inexpensive to manufacture and which can also be easily and reliably used for surgical implantations.
This problem is solved by a strand-like implant of resorbable polymer material, which is essentially formed as a random copolymer of L-lactide and glycolide, in which the L-lactide and glycolide are present in a composition in the range of more than 80 mole % lactide and less than 20 mole % glycolide to 95 mole % lactide and 5 mole % glycolide, particularly in a ratio of 90:10, which has in the textile structure a tensile strength of more than 200 N/mm
2
. Preference is given to a tensile strength of more than 250 N/mm
2
based on the total cross-section of the implant. As the structure generally only contains approximately 50 to 70% polymer material in the cross-section, the tensile strength based on the polymer of the structure is correspondingly higher. The tensile strength can be in the range 400 to 500 N/mm
2
.
Advantageously the implant according to the invention is characterized by an elongation at break of less than 30%, particularly less than 20%. Preferably an implant strand according to the invention has an elongation at break of 15 to 20%. Preference is given according to the invention to implants having a limited extension combined with a high breaking force. The implant is also preferably characterized in that the polymer material is not end-masked in its molecular structure. As a result of the correlation of the structure and polymer characteristics particularly advantageous physical and chemical properties are obtained for the implant according to the invention. It in particular exclusively comprises lactide and glycolide components, an end-masking being unnecessary.
Advantageously for an application of the invention the average molecular weight of the resorbable polymer material is at least 50,000 Dalton. According to the invention the average molecular weight can be 100,000 to 500,000 and in particular 200,000 Dalton. Such an average molecular weight value can also be obtained by mixing polymer fractions having different molecular weights.
The setting of the desired molecular weight can take place during the polymerization process according to procedures known to the experts. With a long-lasting polymerization reaction the viscosity of the polymer product obtained can decrease again through the formation of a balanced reaction. A checking of the degree of polymerization and the molecular weight obtained can take place by sampling and measuring the viscosity. Viscosity measurements take place in chloroform at 25° C. in a 0.1% solution.
Advantageously the polymer material in the finished implant has a residual monomer content of less than 1 and in particular less than 0.5 wt. %, based on the total polymer. The monomer present can be a lactide monomer, glycolide monomer or a mixture of both. The low content of unreacted monomer can influence the decomposition behaviour of the resorbable polymer in a manner advantageous for the invention. By controlling the unpolymerized monomer content it is possible to influence the decomposition profile. The setting of the residual monomer content can take place during the polymerization process using procedures known to the experts.
According to the invention, the inherent viscosity of the polymer material in the finished implant can be in the range 0.7 to 1.3 dl/g. For example, preferably the inherent viscosity of a raw fibre spun from the polymer material according to the invention can be 0.9 to 1.2 dl/g. Preferably the inherent viscosity of a textile strand produced from the polymer material according to the invention can be 0.9 to 1.1 dl/g.
The chemical composition and molecular structure of the copolymers according to the invention, combined with the structure of the implant, have an advantageous action on the characteristics of products produced therefrom. Examples thereof are favourable mechanical characteristics such as good flexibility, e.g. low flexural rigidity, good modulus behaviour and good knotting characteristics, such as are desired in particular for medical applications, e.g. in surgical implants.
The decomposition of the implant according to the invention takes place in the body of an animal or a human in which it was implanted during surgery as a result of hydrolysis processes. Under physiological conditions tissue and body fluids participate in the reaction. The decomposition process can take place hydrolytically and/or enzymatically, the polymer chain being split into smaller and more readily soluble fragments. The decomposition products are conveyed away by the metabolic system and are discharged from the organism in the same way as other metabolic waste materials. For a good compatibility of the resorbable implant material in the patient, it is important that during the decomposition process no harmful metabolites form or are enriched. The unmasked lactide-glycolide polymers according to the invention are in particular characterized in that no toxic decomposition products are formed during their decomposition in vivo. Experimental investigations on resorbable polymer strand-like implants according to the invention have revealed that decomposition in vitro takes place in roughly the same way as decomposition in vivo.
The implant according to the invention can be advantageously characterized in that the half-life period of its strength in vitro and in vivo is 8 to 16 and in particular 10 to 14 weeks. This means that at the end of 10 to 14 weeks the remaining strength still has half the original strength value. Within this time period the natural endogenous tissue can re-form to such an extent that it can take over the strength functions again. Thus, there is gradually a sliding taking over of the function fulfilled by the implant by the natural body tissue until finally the implant material is completely resorbed and removed from the body. The implant according to the invention is preferably characterized in that its in vivo resorption time is 6 to 18 months. Advantageously the resorption time of the implant is in particular 9 to 12 months.
The copolymer of L-lactide and glycolide to be used for the implant strand according to the inven
Dauner Martin
Goldmann Helmut
Hierlemann Helmut
Planck Heinrich
Aesculag AG & Co. KG
Jackson Suzette J.
McDermott Corrine
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