Characterization and Design of Novel Bioabsorbable Metals for Orthopaedic Applications
The longevity and mechanical properties of biomaterials in the high load-bearing applications of orthopaedic fixation devices are of paramount concern to medical and engineering professionals. Even devices manufactured using the current “gold standard” metals usually require removal or replacement after a certain period of time, often due to biocompatibility or failure issues. In the case of pins, screws, fusion cages, and other such devices, mechanical support is only needed temporarily, until the body fully recovers. As long as a material meets the temporary mechanical and biological needs during healing, it would be very convenient if the device slowly degraded away leaving only healthy, organic tissue. To address this novel challenge, a bioabsorbable metal was investigated to determine whether a device made from such a biomaterial could be a viable future competitor in the orthopaedic fixation market. The cytocompatibility of one such metal was characterized in vitro over the course of 28-day degradation experiments, and the mechanics of an idealized, time-dependent bone-metal composite material were studied over multiple continuums. The presence of a bioabsorbable metal, tested over multiple length scales and using multiple shape factors, was found to inhibit neither the proliferation nor the mineralization of bone progenitor cells. Through the use of theoretical cellular solid models, certain porous metal foam microstructures were found to produce advantageous macroscale stiffness and permeability values. Further experimental studies and model refinement are necessary to elucidate more precisely the optimal material parameters for a given application; however, initial results indicate a promising future for bioabsorbable metals within the orthopaedics realm.
Nauman, Purdue University.
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