Load-bearing and ductile hydroxylapatite/polyethylene composites for bone replacement

This work reports the application of non-conventional processing techniques to produce hydroxylapatite/polyethylene (HA/PE) composites. HA/PE composites were prepared with different amounts (10 to 50% by weight) of the reinforcement under two preparation procedures: bi-axial rotating drum and twin screw extrusion (TSE). These compounds were processed by conventional injection moulding and by Scorim (shear controlled orientation in injection moulding) under a wide range of processing windows. Results of tensile tests are discussed in terms of the morphology of the mouldings evaluated by polarised light microscopy and scanning electron microscopy. By optimising the processing routes and parameters it was possible to develop composites with a stiffness and strength in the bounds of human cortical bone, but exhibiting a very high ductility. For composites, compounded by TSE and then Scorim processed, a maximum modulus of 7.5 GPa and a strain at break as high as 19% could be obtained, for a HA weight fraction of 30%. The obtained mechanical properties (matching those of bone) combined with the bioactive behaviour of the HA phase, widen the field of application of these type of composites to orthopaedic load-bearing implants.