In vitro degradation of Polyactive 1000PEOT70PBT30 devices.

Polyactive 1000PEOT70PBT30 (a segmented block copolymer of poly(ethylene oxide terephtalate)/poly(butylene terephtalate) with 70/30 PEOT/PBT ratio) was processed into three different types of samples: injection molded to rods, hot-pressed to films and to composite membranes made by hot-pressing a tubular mesh of poly-L,D-lactide 96/4 between two films of Polyactive. The molecular weight of Polyactive was not influenced by processing, but gamma-sterilization seemed to increase the weight average molecular weight (Mw). Mechanical properties of the rods and films decreased rapidly in hydrolytic conditions due to the hydrogel nature of the polymer, swelling and degradation. Mesh reinforcement increased the mechanical properties, but the components separated during soaking. In vitro the molecular weight of the rods and films started to decrease immediately, but the PEOT (or PEO) proportion remained relatively constant for 26 weeks. Macroscopically, all the wet devices remained intact, but fragmented on drying. Microscopically, topographical formations of polymer were found on the surfaces and small sodium-rich spots were precipitated onto and inside the polymer. Thermal measurements showed that polymer consisted of amorphous PEOT segments and both amorphous and crystalline PBT segments.

Comparison of strength properties of poly-L/D-lactide (PLDLA) 96/4 and polyglyconate (Maxon) sutures: in vitro, in the subcutis, and in the achilles tendon of rabbits.

Achilles tendon rupture is a common injury. Absorbable sutures are not commonly used because of their limited strength properties. Recently, sutures with prolonged strength retention properties have been developed. The aim of the study is to test the mechanical properties of recently developed poly-L/D-lactide (PLDLA) sutures in comparison with polyglyconate (Maxon) sutures. PLDLA (0.2 mm thick) and Maxon (4.0) sutures were studied in vitro by immersion in a buffered saline solution (pH 7.4). Tensile strength tests were done on sutures retrieved after 1-26 weeks. In vivo, they were implanted in the subcutis of 32 rabbits. Tensile strength tests were done on sutures retrieved after 1-6 weeks. The sutures were also used to repair the Achilles tendon in rabbits. Maximum force before breaking and percentage elongation of tendons were determined. Although PLDLA had a lower initial tensile strength than Maxon, PLDLA showed more prolonged tensile strength retention than Maxon. Tendons repaired with PLDLA, however, had a lower strength than Maxon-repaired tendons at six weeks (insignificant difference). PLDLA has more prolonged tensile strength properties compared with Maxon. Thus, PLDLA offers an alternative to Maxon in repair of the Achilles tendon.

Pliable polylactide plates for guided bone regeneration: manufacturing and in vitro.

Three different types of pliable and bioabsorbable plates, 0.4 mm thick, were developed for guided bone regeneration to cover cranial defects. The processing (extrusion, melt-spinning, knitting and heat pressing) and in vitro degradation of the materials were studied. Materials used were poly-L,DL-lactide with an L/DL ratio of 70/30 (PLA70) and poly-L,D-lactide with an L/D ratio of 96/4 (PLA96). The initial tensile strengths of gamma-sterilized PLA96, PLA70 and the PLA70-PLA96 composite plates were 45.7 +/- 3.8, 51.2 +/- 3.6 and 24.7 +/- 5.1 MPa respectively. The composite plates were the stiffest and lasted for more than 24 weeks. The glass transition temperature (Tg) of both polymers decreased in vitro. The crystallinity of PLA96 increased tenfold within 18 weeks. For initially amorphous PLA70 the highest melting enthalpy was 89 J/g at 60 weeks. PLA70 became partially crystalline and the plates changed from transparent to white and swollen. Extrusion and sterilization decreased the initially different molecular weight (Mw) values to the same level. After 18 weeks of hydrolysis, Mw was 15,000 Da for PLA96 and 12,000 Da for PLA70. For the components of the composite plate Mw was 15,000 Da for the PLA70 plate and 27,000 Da for the PLA96 mesh. Morphologically, all the hydrolysed plates retained, for a long period, a solid surface layer under which a porous structure formed. Crystalline branches and some single crystals were seen. The composite plates had the slowest degradation rate and they remained intact the longest.

Tissue biocompatibility of a new caprolactone-coated self-reinforced self-expandable poly-L-lactic acid bioabsorbable urethral stent.

BACKGROUND AND PURPOSE: The bioabsorption time as well as other properties of bioabsorbable polymers can be affected by the choice of the basic molecule, by the degree of its polymerization, and by the coating material used in the device. The aim of our present study was to evaluate the biocompatibility of a new caprolactone copolymer-coated, self-reinforced poly-L-lactic acid (SR-PLLA) urethral stent by means of a rabbit muscle implantation test. This new material has previously been tested for cytotoxicity using the thymidine incorporation method (DNA synthesis inhibition test), no toxicity being evidenced. MATERIALS AND METHODS: Fifteen male rabbits were used as experimental animals. Rods made from pure lactic acid, pure caprolactone copolymer, and caprolactone-coated lactic acid were placed on both sides of the dorsal muscles, eight implants per rabbit. Rods made from latex and silicone were used as positive and negative controls, respectively. The animals were sacrificed after 1 week, 1 month, or 6 months. Tissue reactions around the implants were analyzed and scored semiquantitatively. RESULTS: Acute tissue reactions attributable to operative trauma were seen in all specimens at 1 week. After 6 months, chronic inflammatory changes and foreign-body reactions were seen only in the positive controls. CONCLUSION: The new caprolactone copolymer material is highly biocompatible.

Cytotoxicity testing of a new caprolactone-coated self-expanding bioabsorbable self-reinforced poly-L-lactic acid urethral stent.

Forty to 75% of strictures recur within 2 years of urethrotomy and the essential problem remains how to prevent the edges of the cut stricture from adhering to each other and the scar from shrinking. To solve this problem different kinds of urethral stents have been used. Recently a new bioabsorbable self-expanding urethral stent was developed by our group. The core consists of self-reinforced (SR) poly-L-lactic acid (PLLA) and the coating is made of an amorphous copolymer of caprolactone and D,L-lactic acid [P(epsilon-CL/ D,L-LA)]. The aim of our present study was to test the cytotoxicity of the new material used to coat the SR-PLLA urethral stent utilizing the thymidine incorporation method (DNA synthesis inhibition test). The new materials showed no acute toxicity and can be regarded as biocompatible in medical devices.