Design and fabrication of cast orthopedic implants with freeform surface textures from 3-D printed ceramic shell

Three-dimensional printing is a solid freeform fabrication process, which c reates parts directly from a computer model. The parts are built by repetit ively spreading a layer of powder and selectively joining the powder in the layer by ink-jet printing of a binder material. 3D printing was applied to the fabrication of sub-millimeter surface textures with overhang and under cut geometries for use in orthopedic prostheses as bony ingrowth structures , 3D printing is used to fabricate ceramic molds of alumina powder and sili ca binder, and these molds are used to cast the bony ingrowth surfaces of C o-Cr (ASTM F75) alloy. Minimum positive feature sizes of the ceramic mold a nd, therefore, minimum negative feature sizes of castings were determined t o be approximately 200 x 200 x 175 mu m and were limited by the strength of ceramic needed to withstand handling. Minimum negative feature sizes in th e ceramic mold and, therefore, minimum positive features in the casting wer e found to be approximately 350 x 350 x 175 mu m and were determined by lim itations on removal of powder from the ceramic and the pressure required to fill these small features with molten metal during casting. Textures were designed with 5 layers of distinct geometric definition, allowing for the d esign of overhung geometry with overall porosity ranging from 30-70%. Featu res as small as 350 x 350 x 200 mu m were included in these designs and suc cessfully cast, (C) 2000 John Wiley & Sons, Inc.