Porous PEEK structures with approximately 85% open porosity have been made using PEEK-OPTIMA® powder and a particulate leaching technique using porous, near-spherical, sodium chloride beads. A novel manufacturing approach is presented and compared with a traditional dry mixing method. Irrespective of the method used, the use of near-spherical beads with a fairly narrow size range results in uniform pore structures. However the integration, by tapping, of fine PEEK into a pre-existing network salt beads, followed by compaction and "sintering", produces porous structures with excellent repeatability and homogeneity of density; more uniform pore and strut sizes; an improved and predictable level of connectivity via the formation of "windows" between the cells; faster salt removal rates and lower levels of residual salt. Although tapped samples show a compressive yield stress > 1 MPa and stiffness > 30 MPa for samples with 84% porosity, the presence of windows in the cell walls means that tapped structures show lower strengths and lower stiffnesses than equivalent structures made by mixing.
A simple and adaptable process for the production of porous PEEK has been demonstrated herein, which uses compression moulding to infiltrate molten PEEK into of a packed bed of salt beads. The process has the capacity to vary the pore size and porosity within the range suitable for materials to replace bone, but compressive testing showed the stiffness to be well below the target to match trabecular bone. This issue was addressed by creating a hybrid structure, integrating "pillars" of solid PEEK into the porous structure, by the injection overmoulding of compression moulded PEEK-salt inserts that contained drilled holes. Good bonding between the moulding and the insert was demonstrated and it was found that as little as 35 mm 2 of support, in the form of PEEK "pillars" was required to achieve the target performance.
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AbstractPorous Ti with open porosity in the range of 70-80% has been made using Ti powder and a particulate leaching technique using porous, spherical, NaCl beads. By incorporating the Ti powder into a pre-existing network of salt beads, by tapping followed by compaction, salt dissolution and "sintering", porous structures with uniform density, pore and strut sizes and a predictable level of connectivity have been produced, showing a significant improvement on the structures made by conventional powder mixing processes. Parts made using beads with sizes in the range of 0.5-1.0 mm show excellent promise as porous metals for medical devices, showing structures and porosities similar to those of commercial porous metals used in this sector, with inter-pore connections that are similar to trabecular bone. The elastic modulus (0.86 GPa) is lower than those for commercial porous metals and more closely matches that of trabecular bone and good compressive yield strength is retained (21 MPa). The ability to further tailor the structure, in terms of the density and the size of the pores and interconnections has also been demonstrated by immersion of the porous components in acid.
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