ABSTRACT
The discovery of bioactive glasses in the late 1960s opened an entirely new area of using glasses as materials that promote tissue growth in medicine (Hench et al. 1972). The development of bioactive glasses was a result of the purposeful development of a novel material that would satisfy several critical requirements of a prosthetic material. One of the most important requirements was to Œnd a material that would not form interfacial scar tissue around the implant but instead bond to the living tissue (Hench 2006). The approach was to tailor the new prosthetic material of components that are naturally found in bones in the human body. The Œrst bioactive glasses were tailored of large amounts of calcium oxide and phosphorus pentoxide (P2O5) in a sodium oxide (Na2O)–silicon dioxide (SiO2) matrix (Hench 2006). From the point of view of glass technology, the choice of the composition was simple but genius-the oxide compositions chosen are not chemically durable; instead, they will dissolve gradually, Œrst by releasing ions of sodium, calcium, and phosphate from the glass surface. Sodium ions are abundant in the human body, whereas the ions of calcium and phosphate that are released from the glass precipitate as hydroxyapatite as the interfacial solution becomes supersaturated. Some glasses within the Na2O-CaOP2O5-SiO2 system formed a strong adherent bond to bone. This bone-bonding capability distinguishes bioactive glasses from bioinert materials that form a nonadherent Œbrous capsule at the interface of the host tissue. One of the glasses, 45S5 Bioglass, formed a strong bond with the bone within a few days. It was found that 45S5 also bonded to the soft tissue (Wilson et al. 1981). Later, materials showing this kind of tissue-bonding ability have been deŒned as bioactive materials (Williams 1999).
