5 - Metal microfiber-reinforced hydroxyapatite

Abstract

This chapter is the most detailed treatise that the author is aware of on the topic of manufacturing of short-metal-microfiber-reinforced ceramics by powder metallurgy techniques. The author has worked in the field since the early 1990s. This chapter is specifically about metal microfiber-reinforced hydroxyapatite: both stainless steel and FeCralloy® short metal microfibers were investigated. Hydroxyapatite (HA) is the mineral component of bone. It has the chemical formula Ca10(PO4)6(OH)2. Synthetic hydroxyapatite is a widely used calcium phosphate bioceramic, but in the presence of inorganic additives, such as reinforcement fibers, HA decomposes during sintering to a soluble calcium phosphate phase that resorbs in the body. Hot-isostatic pressing overcame that problem. The FeCralloy® microfibers gave outstanding toughening at 15vol% with ~200-fold improvement in Ƴf (work of fracture) compared to the pure HA control, and toughness comparable to bovine cortical bone. The stainless steel fibers produced a less substantial toughening effect. In vitro testing proved that 316L stainless steel microfibers did not cause cytotoxicity in the HA composites. In vivo sheep testing demonstrated that 316L stainless steel microfibers did not compromise the excellent bonding osteogenesis of HA.