Silicon nitride bioceramics in healthcare

Silicon nitride (Si3N4) is biocompatible and stable invivo, and these properties, when combined with its superior mechanical properties, make Si3N4 an attractive ceramic implant material in some healthcare applications, particularly in orthopedic surgery. Si3N4 is used in spinal fusion surgery, is under development for use as bearings in joint replacement, and is being considered for use as dental implants. While Si3N4 implants are currently created using conventional ceramic processing techniques, additive manufacturing provides the capacity to create custom implants with the required anatomical shape, precise dimensions, and well-controlled microstructure. Si3N4 can be created with a smooth or microrough surface topography, and its surface chemistry can be varied from a silica-rich to a predominantly silicon-amine composition, which can influence the response of cells, tissues, and bacteria invivo. Si3N4 implants have shown attractive osseointegration and antimicrobial activity invivo, while Si3N4 bearings have shown low wear rates when articulating against itself or against polyethylene. The objective of this article is to review recent developments in the design, processing, and evaluation of Si3N4 implants for healthcare applications.