A load-bearing, bioabsorbable surgical repair device manufactured from a copolymer having a plurality of first linkages of lactide or lactide/glycolide, and a plurality of second linkages of a polymer having a glass transition temperature below ambient temperature. The second linkages preferably are selected from: 1,3-dioxan-2-one; 1,4-dioxan-2-one; and e-caprolactone.

Absorbable surgical repair devices

A standard protocol is proposed which has been used to study comparatively the degradation mechanism of bioresorbable poly(α-hydroxy acids) with respect to macromolecular structural characteristics and solid-state morphologies. As a first approach, the hydrolytic degradation of poly(dl-lactic acid) (PLA50) parallelepipedic specimens (15 mm×10 mm×2 mm), processed by compression moulding and machining, was investigated in two aqueous media: iso-osmolar saline and pH 7.4 phosphate buffer. Various techniques (namely weighing, size-exclusion chromatography (SEC), potentiometry, cryometry and enzymatic assay) have been applied to these specimens in order to monitor the degradation. Data show conclusively that the degradation of massive PLA50 specimens proceeds more rapidly in the centre than at the surface. This feature has been related to the formation of an outer layer of slowly degrading polymer, which is caused by surface phenomena and entraps degrading macromolecules. Only oligomers can diffuse and dissolve in the surrounding media. Accordingly, the number of carboxylic groups present in the inner part of the degrading specimens becomes larger than at the surface and accelerates ester bond cleavage. The resultant autocatalytic mechanism explains well the fact that partially degraded PLA50 exhibits bimodal SEC chromatograms although this polymer is amorphous.

Structure-property relationships in the case of the degradation of massive poly(α-hydroxy acids) in aqueous media

The field of biodegradable polymers is a fast growing area of polymer science because of the interest of such compounds for temporary surgical and pharmacological applications. Aliphatic polyesters constitute the most attractive family among which poly(α-hydroxy acids) have been extensively studied. In the past two decades, several excellent reviews have been published to present the general properties of aliphatic polyesters. The aim of this paper is to complete the information collected so far with a special attention to the complex phenomena of biodegradability and biocompatibility. Indeed, the degradation of a polymer leads to the delivery of low molecular weight degradation by-products whose effects on the host body have to be considered. The consequences of the absence of standard terminology are first discussed with respect to words such as biodegradable and bioresorbable. Poly(α-hydroxy acids) derived from lactic and glycolic acids are then introduced in order to make easier the critical discussions of the following problems from literature data: biocompatibility, biodegradability, bioresorbability, mechanism of hydrolysis (enzymaticvs simple chemistry), polymodality of molecular weight distributions during degradation and the effects of the presence of oligomers. Finally, some specific comments are made on other aliphatic polyesters such as poly(hydroxy butyrate) and poly(β-malic acid).

Bioresorbability and biocompatibility of aliphatic polyesters

A completely bioabsorbable reinforced composite material for use in medical implants and a method for making same. The composite material comprises a hybrid yarn of intimately co-mingled reinforcement fibers of a crystalline polymer and matrix fibers of a polymer having a glass transition temperature below the melting point of the crystalline polymer. The hybrid yarn is heated under pressure to a processing temperature between the glass transition temperature of the matrix fibers and the melting point of the crystalline polymer to form a continuous matrix with reinforcing fibers of crystalline polymer. The composite material may be formed by a two step consolidation process.

Bioabsorbable medical implants

Six polylactides, polymerized with Salen−Al−OCH3 initiator and having optical purities between 43% and 100%, were analyzed by differential scanning calorimetry, X-ray diffraction, and optical microscopy, following various crystallization conditions. It was found that each of those polylactides can crystallize, even those with low optical purities; their crystallization rate is, however, slower than those for high optical purity polyesters. Moreover, the low optical purity polymers tend to form stereocomplexes between the l and d sequences of the same polylactide, which behavior is ascribed to their multiblock microstructure. A correlation was found between the measured melting temperature of optically active polylactides and their average sequence length.

Crystallization and Melting Behavior of Polylactides

The feasability of using poly(α-hydroxy-acid)s (poly-(glycolic acid), poly(L-lactic acid), L and D-lactic acid stereocopolymers and copolymers of glycolic and L- and D-lactic acids) for processing bioresorbable bone plates, screws, nails etc..., is questioned in regard to the requirements for effective applications and to the data reported in the open literature. Experiments carried out on home-made samples confirm the biocompatibility of these polyesters and the fast resorption of the amorphous compounds. In contrast, our results concerning crystalline poly(L-lactic acid) disagree with those of the literature. The discrepancies might result from differences in the basic material, differences in crystallinity and/or degradation of macromolecules which has been shown to occur sometimes during the elaboration of ready-for-implantation samples. Indeed, quasi-biostable bone plates based on isotactic poly(L-lactic acid) have been obtained according to an elaboration process which preserves the integrity of the synthesized macromolecules. The effects of enantiomeric purity and of implantation time on the tensile strength are reported for a series of welldefined stereocopolymers. Current studies show that highly isotactic poly(lactic acid)s (L/L+D > 92%) are polymers of particular interest for effective applications in bone surgery, especially for the construction of completely resorbable composite devices whose reinforcement consists of poly(glycolic acid) fibers.

Stereoregular bioresorbable polyesters for orthopaedic surgery

Osteosynthesis parts are made of an absorbable polymer composition consisting of a matrix of lactic acid homopolymer, or a copolymer very high in lactic acid units, having discrete reinforcement elements embedded therein. The reinforcement elements are made of glycolic acid homopolymer or copolymers predominant in glycolic acid units. Such a composition may be shaped with a minimum of polymer degradation into osteosynthesis parts exhibiting good resilience, shock resistance, and tensile strength.

New prosthesis parts, their preparation and their application

Pieces d'osteosynthese, ayant la forme d'un solide tridimensionnel, a base de polymere biocompatible resorbable. osteosynthesis pieces, having the shape of a three-dimensional solid, based resorbable biocompatible polymer. Elles se presentent sous la forme de pieces composites constituees par une matrice en poly-acide lactique ou en un copolymere de celui-ci, ladite matrice contenant des elements de renfort, noyes dans la matrice, a base d'acide polyglycolique ou d'un copolymere de celui-ci, et contenant eventuellement une charge capable de stimuler la resorption du polymere au profit d'un tissu neoforme. They are in the form of composite bodies formed by a polylactic acid matrix or a copolymer thereof, said matrix containing reinforcement elements embedded in the matrix, based on polyglycolic acid or a copolymer thereof, and optionally containing a filler capable of stimulating the absorption of the polymer to the benefit of newly formed tissue. Application a la reparation et a la consolidation de fractures osseuses. Application repair and consolidation of bone fractures.

Osteosynthesis elements and their preparation

Nouveau materiau de prothese. Ce materiau est constitue par un polymere biocompatible et resorbable contenant une charge capable de stimuler la resorption du polymere au profit d'un tissu osseux neoforme. Application a la realisation de protheses osseuses.

Jean Leray

Papers

Stereoregular bioresorbable polyesters for orthopaedic surgery

New prosthesis parts, their preparation and their application

Osteosynthesis elements and their preparation

Nouveau materiau de prothese osseuse et son application

Knochenersatzmaterial und dessen verwendung