In situ polymerization into porous ceramics: a novel route to tough biomimetic materials

A hydroxyapatite-based biomimetic composite, which is henceforth referred to as a synthetic bony material with high toughness characteristics, was prepared. It was obtained from a hydroxyapatite (HAp) skeleton with a relative porosity fraction of approximately 32 vol %, prepared by cold-isostatic-press compaction, followed by a sintering process, leading to a hydroxyapatite structure containing percolated submicrometer porosity channels. The percolated pores were infiltrated with a liquid mixture of epsilon-caprolactam monomer and an initiator, before homogeneous in situ polymerization to 6-nylon within the fully percolated pore structure was induced thermally. The final composite consisted of a dense interpenetrated hydroxyapatite/6-nylon network in a fraction approximately 68/30 vol %. The work of fracture value of the hybrid composite was found to be comparable with those found in two natural materials (bovine femur and nacre), which were also investigated under the same testing conditions.