The incorporation of two-dimensional boron nitride, known as ‘white graphene’, into zirconia ceramics increases the strength of this material—used in hip, dental and knee prostheses—by 18%
A study led by the Institute of Materials Science of Seville (ICMS), a joint centre of the Spanish National Research Council (CSIC) and the University of Seville (US), together with the National Institute of Applied Sciences in Lyon (Claude Bernard Lyon University), has developed a new type of ceramic that is more resistant to deterioration caused by moisture and body temperature, which limits the lifespan of orthopaedic prostheses.
The results, published in Open Ceramics, demonstrate that the incorporation of ‘white graphene’ (two-dimensional boron nitride) nanosheets into advanced zirconia ceramics increases their resistance to microcracks by 18% and reduces their degradation to below 10% in aqueous environments, paving the way for more durable dental implants and hip and knee prostheses.
Advanced zirconia ceramics are a biocompatible and extremely hard material, used primarily in dental implants and crowns. However, this material is affected by hydrothermal ageing—caused by the combination of moisture and temperature—which promotes the formation of roughness and microcracks, thereby reducing the strength and lifespan of the component.
In this study, the team demonstrates that incorporating two-dimensional boron nitride nanosheets, known as ‘white graphene’, into zirconia ceramics results in a more resistant material. The nitride acts as a barrier against moisture by blocking the penetration of water into the ceramic, thereby delaying degradation. The resulting material complies fully with the ISO 13356 standard, which regulates zirconia surgical implants.
“In recent years, research has been conducted into composites and mixtures that improve the performance of these ceramics against moisture. Our work, although not yet of direct commercial application, is a further step in this direction,” explains Rosalía Poyato, a CSIC researcher at the ICMS and author of the study.
Greater resistance
To simulate the wear and tear caused by decades of being inside the human body, the samples were subjected to accelerated ageing tests in an autoclave, a device that exposes the material to saturated steam at high pressure and a constant temperature of 134 °C.
The study shows that, by adding white graphene, zirconia ceramics significantly improve their resistance to ageing, as after five hours in the autoclave (equivalent to almost 20 years inside the mouth), their degradation is less than 10%, well below the requirements of the ISO 13356 standard.
This is due to the waterproofing properties of white graphene, which takes its name from its structural similarity to graphene, although it is white in colour and has insulating properties. When this material is added in the form of nanosheets, it is distributed evenly among the grains that make up the ceramic, acting as a barrier that blocks the penetration of water and oxygen molecules into the interior.
Furthermore, the team found that the addition of two-dimensional boron nitride increases the material’s resistance to cracking in humid environments by 18%. To do this, they compared the ceramics’ resistance to crack propagation in samples exposed to air (with humidity between 40% and 60%) with those submerged in olive oil (a completely dry environment with no ambient humidity).
Biomedical innovation
To obtain the white graphene nanosheets, the researchers used a method known as shear exfoliation. This process involves applying mechanical forces to separate the microscopic layers of boron nitride powder until they become nanometre-thick sheets, just a few atoms thick. What is innovative about this work is that this process has been achieved using a domestic blender, a simple, sustainable and low-cost approach that minimises the use of chemicals and facilitates large-scale production of the material.
The work represents a further step in the team’s research, which specialises in the development of ceramics using two-dimensional materials and in gaining a deep understanding of how they function—a fundamental step towards developing effective solutions that improve the mechanical and functional properties of ceramic materials, thereby contributing to biomedical innovation.
The research is funded by the University of Seville’s Fourth Internal Plan, the European Ceramic Society, the European Regional Development Fund (ERDF), the Ministry of Science, Innovation and Universities, and the State Research Agency.