A novel ceramic coating for reduced metal ion release in metal‐on‐metal hip surgery

Human joints are considered one of the best performing bearings known to man.  However, longer life spans and more active lifestyles result in a high probability of failure within an average lifetime.  Although joint replacement is one of the most successful procedures in modern surgery, and a range of metal alloys are commonly used, they result in an increase of local and circulating metal products causing high short-term failure rates.  Thin ceramic coatings can be an excellent means of preserving the toughness of the metal alloy whilst improving its biocompatibility with the human body.

The National HIPIMS Technology Centre has successfully exploited a synergy between smart material combination, unique coating structure and advanced High Power Impulse Magnetron Sputtering (HIPIMS) deposition method to produce a novel high-quality application-tailored CrN/NbN coating, which is a promising candidate representing the next generation of coatings for medical implants. The mechanical properties of the coating are far superior to those of conventional PVD coatings, offering improved adhesion and wear performance. The biological performance and improvement in corrosion resistance and, as a result, negligible (below the detection limit) metal ion release, makes this a promising solution for patients with metal ion sensitivity.

Another important feature of this coating is the improvement in fatigue strength that it imparts on the substrate. This improvement in fatigue life may provide an additional benefit by allowing the development of thinner-sectioned more bone-conserving designs of orthopaedic components.

In vitro biological testing has been performed in line with the requirements of ISO 10993 in order to assess the safety of the coating in biological environments; cytotoxicity, genotoxicity and sensitisation testing have been performed, all showing no adverse effects.  The safety of the coating in biological environments was confirmed in vivo using a repeatable and reproducible total hip replacement ram model.

The coating technology and material developed at the National HIPIMS Technology Centre at Sheffield Hallam University have been taken towards industrial implementation in collaboration with Zimmer Biomet, the world’s largest manufacturer of orthopaedic implants and Ionbond, one of the largest global suppliers of coatings.

Since 2012, Zimmer Biomet has dedicated a team of up to 10 and created jobs at its facilities in the UK and USA to enable testing and qualifying the new coating to the international standards applicable to the orthopaedic industry for mechanical device testing, rotating beam fatigue, cytotoxicity, genotoxicity, sensitisation and metal ion release. The multi-million-pound investment ranked these projects amongst the highest priority within the company. 

Dr. I. Khan, Chief Technology Officer at Zimmer Biomet UK said:

"Zimmer Biomet have enjoyed a fruitful collaboration with Sheffield Hallam University for more than a decade that has culminated in the development of several next generation coatings for orthopaedic implants and instruments. These novel coatings provide vast improvements over contemporary coatings used in orthopaedics, offering superior implant performance and longevity. Their addition to our products promises to enhance the lives of tens of thousands of patients with huge savings to the UK and other healthcare systems around the world.  The addition to our portfolio of products utilising these advanced coatings should additionally help Zimmer Biomet realise millions of dollars of additional revenue."

In 2005 Ionbond UK acquired a license from SHU for plasma pretreatment by HIPIMS.  Ionbond dedicated a team of 5 and invested £235,000 in equipment to enable the implementation of HIPIMS technology.

Dr. C. Constable, CEO of Ionbond UK Ltd. Said:

“Our collaborative work with Sheffield Hallam University established the first industrial facility for High Impulse Magnetron Sputtering (HIPIMS) in the UK. 
A few years later the industrial scale equipment armed with new HIPIMS technology and the continued support from SHU has given Ionbond the unique capability to develop the next generation of PVD coatings.  These new coatings with vastly enhanced properties are able to solve the pressing problems and challenges of modern high technology industry and provide solutions that current PVD methods could not.  Our product development focus thus far has concentrated on enhancing the function of orthopaedic implants and valves related to nuclear energy production.  The versatility of the HIPIMS technology allows Ionbond to be at the forefront of industrial product development for many years to come unlocking the potential to generate millions of additional sales.”

Prof. Ehiasarian's work on this project earned him the IONBOND IHI Group Industrial Award of Recognition for his leadership in 2015, an indication of the new facility’s importance to the group.