Journal
MACROMOLECULAR SYMPOSIA
Volume 197, Issue -, Pages 355-368Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/masy.200350731
Keywords
bone fixation; hydrostatic extrusion; poly(L-lactide) rods; ultra high modulus; ultra high strength
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The hydrostatic molecular orientation technique was used to explore the highest mechanical improvements achievable for poly-L-lactide (PLLA). The mechanical attributes of these materials designed for bone fracture fixation devices, i.e. bending strength and modulus were measured and compared with those prepared by stretching method. The starting samples were prepared by conventional melt extrusion at 200 degreesC followed by hydrostatic extrusion at 140 degreesC using glycerin filled extruder. Uniaxially stretched rods were prepared by drawing in silicon oil at 120 degreesC. The physical properties of these rods are inadequate as mechanical supports in the dynamic healing process of the bone. Moreover, they underwent a marked strength deterioration when immersed in aqueous buffered solution for 90 days. On the other hand, the hydrostatic extrusion technique produced rods with progressively higher bending strength that showed only a small drop after 90 days hydrolytic degradation. Micrographs suggested a superior molecular orientation and packing, which could be associated with the improved performance. The hydrostatic extrusion technique proved to be a safe and effective approach for strengthening biodegradable polymeric materials for dynamic mechanical support in orthopedic medical devices.
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