Open-pored metal foams have been partly used for orthopedic or dental applications because of their good bone ingrowth behavior and low elastic modulus. In this paper, we report a method that can produce open-pored Ti foams using a technique that combines the powder injection molding process and feedstocks containing expandable polystyrene beads as a space holder. The expandable beads in the feedstocks undergo swelling during the foaming process, which causes the spaces occupied by the expandable beads to directly contact each other and become interconnected. This behavior results in the formation of open-pored Ti foams with high porosity (equivalently, low Young's modulus) and large faces (greater than 140 µm). Compared to metallic foams prepared by conventional methods, Ti foams produced in this study have significantly larger face sizes (140-170 µm) and lower Young's modulus (~17 GPa). These characteristics of the developed foam materials can promote fast bone growth into open-pored porous structures and permit improved fixture installation stability. This paper discusses the mechanism for the formation of the openpored porous structure, and analyzes the effect of various processing conditions on the face size, porosity, and Young's modulus of Ti foams.
Methods to evaluate powder injection molding feedstock without performing the complete processing were developed to reduce the development-to-commercialization cycle time for feedstock. The mixing homogeneity of the powder and binder, rheological properties, mechanical property and shape retainability during debinding were characterized to evaluate the feedstock. The validity of using these parameters was investigated through comparison with various feedstocks. Based on these results, the evaluation methods developed in this work have potential to aid in the selection of proper feedstock without undergoing the subsequent processing.
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