Internal fixation devices (IFD) for bone fracture repair may be fabricated from metals or from resorbable (biodegradable) polymers. The advantages of polymeric devices are: (1) they do not corrode; (2) moduli may be matched more closely to that of bone, thus avoiding stress shielding; (3) resorbability obviates the necessity of surgical removal. Mechanical properties of polymeric IFD's over its in situ lifetime (dimensional stability, stiffness, strength) may be improved by internal reinforcement with a resorbable element. The approach described herein uses a poly (lactide-c-glycolide) (PLGA) as the major structural element in which is molecularly dispersed, as a solid solution, the unsaturated polyester poly (propylene fumarate) (PPF). Mechanical properties improvement are achieved by crosslinking the PPF with a vinyl monomer such as vinyl pyrrolidone (VP). This should result in slower decrease of strength and longer maintenance of dimensional stability on exposure to conditions facilitating hydrolytic degradation. Because the crosslinked PPF is also subject to hydrolysis at the fumarate ester bonds, it also is degradable. Phase I experimental work includes: (1) elucidation of the crosslink density and average crosslink length; (2) sample preparation of model fixtures and in vitro testing of mechanical properties over time (compressive tensile and bending strengths and moduli and dimensional stability); and (3) measurement of PLGA and PPF degradation over in vitro exposure time.
Of the more than 1.1 million fractures in the U.S. each year, greater than 470,000 require internal fixation devices to stabilize the fracture during the healing process. While there is significant clinical demand for resorbable devices, available products have not been widely adopted because of problems with dimensional stability. A molecularly reinforced, but still resorbable fixation device, which can ameliorate these responses of bowing and deforming, i.e. maintain dimensional stability, would address the clinical demand for resorbable orthopedic fixtures.
| Lewandrowski, K U; Gresser, J D; Wise, D L et al. (2000) Tissue responses to molecularly reinforced polylactide-co-glycolide implants. J Biomater Sci Polym Ed 11:401-14 |
