Bioceramics: Bioinert, Bioactive, and Coatings, Volume II

Dear Colleagues,

Bioceramics can be classed into three main types: bioinert, bioactive, and coatings. Two bioinert bioceramics (alumina and ZTA—zirconia-toughened alumina), three bioactive bioceramics (bioglass, hydroxyapatite, and tricalcium phosphate), and two bioceramic coatings (DLC—diamond-like-carbon; Oxinium®—oxidized zirconium), have all been ground-breaking bioceramics in the medical device and tissue-engineering realm, having had a revolutionary impact on 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 for an alumina dental implant. The year 1970 was filled with extraordinary breakthroughs for alumina in biomedical engineering, both in bionics and orthopaedics; David Cowdery invented the alumina-feedthrough, resulting in the world’s first hermetic implantable bionic implant (pacemaker) still used as the industry standard today, with the bionic implant industry being worth USD 25 billion. The alumina feedthrough has evolved enormously, from Cowdery’s 1970 single-channel alumina pacemaker to this decade’s Suaning 1145-channel alumina bionic eye feedthrough. 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 today is 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 using 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 through doping with powdered bioglass. It also sees significant use in bone grafts. Early experimentation with synthetic hydroxyapatite (HA) predates the 1970-era of bioglass and alumina innovations. HA has proved to be a versatile bioactive bioceramic, capable of direct hard-tissue 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 USD 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 were discussed above. DLC has outstanding antithrombogenic 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 commercially significant bioceramics, including alumina, ZTA, bioglass, HA/TCP, DLC, and Oxinium®.

Prof. Dr. Andrew Ruys
Guest Editor

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• bioceramics
• alumina
• zirconia-toughened alumina—ZTA
• bioglass—bioactive glass
• hydroxyapatite—HA
• tricalcium phosphate—TCP
• diamond-like carbon—DLC
• oxidised zirconium—Oxinium®
• titanium nitride—TiN
• hip replacement
• orthopaedics
• bionic feedthrough
• dental implant
• tissue scaffold
• tissue engineering