Title

Solid freeform fabrication of biological materials

Date of Completion

January 2006

Keywords

Engineering, Biomedical|Engineering, Materials Science

Degree

Ph.D.

Abstract

This thesis investigates solid freeform fabrication of biological materials for dental restoration and orthopedic implant applications. The basic approach in this study for solid freeform fabrication of biological materials is micro-extrusion of single or multiple slurries for 3D components and inkjet color printing of multiple suspensions for functionally graded materials (FGMs). Common issues associated with micro-extrusion and inkjet color printing are investigated. These common issues include (i) formulation of stable slurries with a pseudoplastic property, (ii) cross-sectional geometry of the extrudate as a function of the extrusion parameters, (iii) fabrication path optimization for extrusion process, (iv) extrusion optimization for multi-layer components, (v) composition control in functionally graded materials, and (vi) sintering optimization to convert the freeform fabricated powder compact to a dense body for biological applications. ^ The present study clearly shows that the rheological and extrusion behavior of dental porcelain slurries depend strongly on the pH value of the slurry and extrusion conditions. A slurry with pseudoplastic properties is a basic requirement for obtaining extruded lines with rectangular cross-sections. The cross-sectional geometry of the extrudate is also strongly affected by extrusion parameters including the extrusion nozzle height, nozzle moving speed, extrusion rate, and critical nozzle height. Proper combinations of these extrusion parameters are necessary in order to obtain single line extrudates with near rectangular cross-sections and 3D objects with dimensional accuracy, uniform wall thickness, good wall uprightness, and no wall slumping. Based on these understandings, single-wall, multi-wall, and solid teeth have been fabricated via micro-extrusion of the dental slurry directly from a CAD digital model in 30 min. ^ Inkjet color printing using stable Al2O3 and ZrO 2 aqueous suspensions has been developed to fabricate functionally graded materials. The volume and composition of the suspensions printed in droplets at a small area are controlled by the inkjet Cyan-Magenta-Yellow-Black color printing principle. The potential of this newly-developed method for fabricating FGMs with arbitrarily designed three-dimensional composition profiles is demonstrated. ^ Sintering investigation focuses on dental porcelain and hydroxyapatite (HA) bodies. Proper sintering conditions have been established for dental porcelain bodies to maintain dimensional accuracy and to prevent slumping. For sintering of HA bodies, a novel approach for sintering of HA bodies at temperatures as low as 900°C has been developed. Low temperature sintering of HA bodies is critical for the success of fabricating functionally graded HA/Ti-6Al-4V materials for orthopedic implant applications because co-sintering of HA and Ti-4Al-4V at temperatures above 950°C can result in the formation of soluble tricalcium phosphate and severe oxidation of Ti-6Al4V. The low temperature sintering of nanocrystalline HA developed in this study, based on the morphology driven anisotropic crystal coarsening mechanism, opens up the opportunity to fabricate functionally graded HA/Ti-6Al-4V materials with no decomposition of HA and oxidation of Ti-6Al-4V and to improve the quality of HA coatings on Ti alloys. ^