Hydroxyapatite–tricalcium phosphate mixtures of various compositions were extruded by a solid freeforming process to form lattice structures to serve as hard tissue scaffolds. The unwelded filaments, sintered at temperatures from 1100 to 1300°C, had radii from 115 to 135 μm and were tested in three point flexural loading using a purpose-built fixture. Flexural strength ranged from 20 to 100 MPa depending on composition and sintering temperature. Weibull moduli up to 13 were obtained. Compositions with 50% or more tri-calcium phosphate did not develop strengths much above 40 MPa and the strength of most compositions fell when the sintering temperature exceeded 1250°C. Multiple layer lattice structures were created and tested in compression.

Four different alumina pastes with various solvent volume fractions were processed by extrusion free forming and the pressures generated in the extrusion process were recorded and analyzed. The extrusion pressure increased as the solvent volume fraction decreased. Air bubbles and particle agglomeration influenced the final properties of the product and caused pressure to fluctuate. An aging process for the paste was introduced to obtain more even solvent distribution and hence deliver highly regular ceramic lattice structures.

The dissolution behaviour of calcium phosphate filaments made by extrusion freeforming for hard tissue scaffolds was measured. The solubility of filaments with different HA/β-TCP ratios sintered at temperatures from 1,100 to 1,300°C was measured under simulated physiological conditions (tris buffer solution: tris(hydroxyl) methyl–aminomethane–HCl), pH 7.4, 37°C). Calcium and phosphate concentrations were measured separately by inductively coupled plasma (ICP) atomic emission spectroscopy. Surface morphologies and composition before and after immersion were analyzed by SEM and EDS. The results clearly show that as the β-TCP content increased, the dissolution increased. Higher sintering temperatures, with consequent closure of surface pores, resulted in lower dissolution. Examination of the surface suggested dissolution on preferred sites by pitting.

Lattices consisting of hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) mixtures were prepared by extrusion freeforming to serve as bone substitute structures in which both shape and structural hierarchy are determined by computer control. Fine ceramic filaments were prepared from a non-aqueous, solvent-based, ceramic–polymer paste and sintered at temperatures from 1100 to 1300°C. The characteristics of the sintered filaments were investigated because this determines the resulting microporosity and phase content while the higher levels of porosity are computer controlled. The effects of HA/β-TCP ratio and sintering temperature on the microstructure, density, shrinkage and final phase content were studied. These results provide a design reference for hard tissue engineering scaffolds built from these materials.