Processing and characterization of absorbable polylactide polymers for use in surgical implants

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Abstract
Absorbable fibers of linear poly‐α‐hydroxy acids have been used successfully in providing temporary scaffolds for tissue regeneration. In some surgical applications, degradation rates for poly(glycolide) (PGA) are too high, but implants of poly(L‐lactide) (PLLA) fibers may degrade too slowly for optimal function. Polymers produced by copolymerization of L‐lactide with varying amounts of D‐lactide may offer an alternative choice for absorbable fiber based implants. Poly(L/D‐lactide) stereocopolymers with L/D lactide molar ratios of 95/5, 90/10, and 85/15 were considered. Melt‐spun/hot‐drawn fibers with L/D molar ratios of 90/10 and 85/15 and draw ratios ranging from 3.0 to 8.9 were further evaluated by mechanical testing, differential scanning calorimetry, birefringence, x‐ray diffraction, and in vitro exposure to pH 7.4 phosphate buffered saline at 37°C. Fabrication was reproducible and results indicated that tensile strength, modulus, and birefringence all increased with increasing draw ratio up to a draw ratio of 6.7 and declined thereafter; elongation to failure decreased for the entire range studied. For fibers with a draw ratio of 6.7, there was a 10% relative difference in crystallinity between the 90/10 and 85/15 lactide fibers (90/10 was higher). Wet strength retention after 12 weeks in vitro exposure was approximately 10% for the 90/10 fibers and 30% for the 85/15 fibers. The intermediate wet strength retention of lactide stereocopolymer fibers when compared to reported values for PGA and PLLA fibers, suggests these materials may be useful in absorbable surgical implants for tissue repair and regeneration. © 1994 John Wiley & Sons, Inc.