Bioceramics: Bioinert, Bioactive, and Coatings

Dear Colleagues,

Bioceramics can be classed as three main types: Bioinert, bioactive, and coatings. Two bioinert bioceramics (Alumina and ZTA—zirconia toughened alumina), three bioactive bioceramics (bioglass, hydroxyapatite, and tri-calcium phosphate), and two bioceramic coatings (DLC—diamond-like-carbon and Oxinium®—oxidized zirconium), have all been ground-breaking bioceramics in the medical device and tissue-engineering realm. Each has had a revolutionary impact in the medical field in recent decades. Other niche bioceramics are also significant, such as zirconia and pyrolytic carbon.

Bioinert: The first documented reference to the idea of alumina as a biomaterial is in a 1933 German patent by Rock, but it was to be three decades before alumina again appeared in the literature in a biomedical context, with the 1965 patent of Sami Sandhaus on an alumina dental implant. 1970 was an extraordinary breakthrough year for alumina in biomedical engineering in both bionics and orthopaedics. In 1970, David Cowdery invented the alumina-feedthrough, resulting in the world’s first hermetic implantable bionic implant (pacemaker). Today, the bionic implant industry is a $25 billion industry, and the alumina feedthrough remains the industry standard. The alumina feedthrough has evolved enormously from the single-channel alumina pacemaker feedthrough of Cowdery in 1970 to the 1145-channel alumina bionic eye feedthrough of Suaning this decade. In 1970, Pierre Boutin implanted the world’s first “ceramic hip” utilizing an alumina-on-alumina bearing. The alumina hip bearing subsequently evolved in Germany as CeramTec Biolox to an extraordinary level of sophistication, particularly since 2003 when ZTA (zirconia toughened alumina) was introduced. Today, more than 50% of the 1.3 million hip replacements implanted annually use alumina or ZTA bearings.

Bioactive: At almost the same time, in the late 1960s, Larry Hench invented Bioglass (bioactive glass), which is today revolutionizing the field of regenerative medicine. Bioglass is capable of stimulating, not just hard tissue regeneration, but also soft tissue regeneration, giving it a unique niche in the realm of bioceramics. Moreover, the biodegradability and bioactivity of bioglass can be engineered by compositional variation, making it a very versatile bioactive bioceramic. One of the most important uses of bioglass is in polymer implants and scaffolds, rendered bioactive by doping with powdered bioglass. It also sees significant use in bone grafts. Early experimentation with synthetic hydroxyapatite (HA) predates the 1970-era bioglass, and alumina innovations. HA has proved to be a versatile bioactive bioceramic capable of hard-tissue direct bonding osteogenesis, and able to be engineered to be either biodegradable or non-biodegradable in vivo. In its non-biodegradable form, HA has been widely used since the 1990s in plasma-sprayed bioactive coatings on metal implants. As a biodegradable bioactive bioceramic, silicon-doped hydroxyapatite was first reported in a 1988 paper by Andrew Ruys. It was patented in 1996 by Serena Best, commercialized as Apatech, and sold to Baxter International for $330 Million in 2010. Silicon-doped HA scaffolds are now a leading global tissue scaffold technology. Tricalcium phosphate (TCP), the anhydrous biodegradable form of HA, is also widely used in synthetic bone graft applications.

Bioceramic coatings have also had a significant impact on the realm of biomaterials and medical devices in recent decades. Plasma sprayed HA coatings are discussed above. DLC has outstanding anti-thrombogenic properties and has seen significant use in blood-contacting implants. Oxidised zirconium (Oxinium®) is widely used in hip and knee implants for its superior wear resistance and similar biocompatibility compared to Cobalt-Chrome bearings.

This Special Issue is dedicated to all of the important innovations in bioceramics, with a particular focus on the commercially significant bioceramics: Alumina, ZTA, bioglass, HA/TCP, DLC, and Oxinium®

Prof. Andrew Ruys
Guest Editor

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