Replamineform Inspired Bone Structures (RIBS) using multi-piece molds and advanced ceramic gelcasting technology

Abstract

A new technology was developed for quickly, simply, and affordably creating Replamineform Inspired Bone Structures (RIBS) that combines multi-piece mold manufacturing for creating complex macroscale geometries with advanced ceramic gelcasting technology for controlling microporosity. A conventional gelcast alumina formulation was modified by adding 0-10 wt. % of fugitive carbon particles (graphitic and activated) to obtain porous microstructures during sintering. The carbon-filled gelcast alumina formulation was used to create replicas of bone structures by filling a multi-piece mold automatically generated from a 3-D image of a real bone. Both types of carbon produced total porosity levels of up to 35% that increased with carbon content in a manner that indicated residual porosity from the burned out carbon was not being consumed during sintering. However, activated carbon specimens exhibited linearly increasing percentage of closed porosity with increasing carbon content, while graphitic samples exhibited more interconnected porosity with pore channels in the range of 200 µm. The influence of porosity on mechanical properties was studied by compression tests. The tests indicated that 35% total porosity in bone replicas can decrease strength 88%, decrease stiffness 80%, and reduce total deformation 40% in comparison to bone replicas with 13% total porosity fabricated without carbon. The reduction in stiffness was consistent with a model developed from microscale finite element analysis of overlapping solid spheres that produce microstructures similar to those observed in these specimens. Furthermore, the increased porosity of the material permits axial cracks to grow and bifurcate more easily at substantially reduced deformation and load levels.

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