Artificial bone that beats the real thing

Researchers from the Institute of Chemistry at the Russian Academy of Sciences have developed a method for synthesizing high-quality composite artificial bone for medical applications¹ by adapting an industrial spark plasma method for fabricating ceramics from powders. The approach, reported in the Russian Journal of Inorganic Chemistry, promises to greatly reduce fabrication cost and time, and increase bone implant biocompatibility.

The structural component of natural bone is composed of the calcium- and phosphorous-bearing mineral hydroxyapatite, which is pervaded by a microstructured network of pores, blood vessels and other tissues. When a fracture occurs, the body initiates a cascade of processes, starting with the formation of softer porous bone mineralisation, which is then vascularised, hardened and remodelled over time. When natural bone regeneration fails, compatible artificial bone implants are needed which can eventually be incorporated and remodelled in the same way as natural bone.

As lead researcher, Evgeniy Papynov, explains, however, this not always easy to achieve in practice.

“Synthetic hydroxyapatite has a full range of biocompatible and bioactive properties, but due to the porous framework, it has low mechanical strength as an implant, which can be a problem for complex volumetric structures,” says Papynov. “A promising approach is to incorporate synthetic wollastonite, a calcium silicate which has a much higher strength and is still biocompatible. However, existing methods for synthesizing bone-ceramic composites do not preserve the desired porous structure and can destroy bioactive components.”

The research team turned to a ceramic fabrication method called spark plasma sintering, in which an electrical spark is used to quickly spot-heat a ceramic powder. This allows for highly controlled heating, enough to form a solid ceramic, without overheating, which can destroy microstructures and organic molecules.

“In our method we used a powder in the form of a reaction mixture, which, during heating, undergoes a chemical transformation to form a new bioceramic compound,” says Papynov. “To make the powder, we used a sol-gel method with a polymer template to prepare a composite of calcium silicate and hydroxyapatite with submicron-sized pores.”

On sintering, the powder turns into crystalline wollastonite with hydroxyapatite in a polymer template, which is removed by heating to give a structured porous hybrid bone-ceramic composite.

“The composition, structure and properties of the resulting bioceramic make it functionally similar to natural bone and suitable for implantation for the reconstruction and regeneration of bone defects,” says Papynov. “We are also looking at incorporating functional biomolecules, such as chemotherapy drugs, which could be useful for treating bone cancers.”