Silicon Nitride Coatings and Biologic Applications

Silicon nitride coatings onto other biomaterials can provide a bioactive customized surface. Of the many techniques available, physical vapor deposition (PVD), chemical vapor deposition (CVD), and laser sintering are the most prevalent. These various methods are already used to deposit silicon nitride films onto microelectronics and related applications. Physical vapor deposition is the method of choice for coating medical implants due to its proven track record. Chemical vapor deposition can be modulated to allow silicon nitride film deposition onto heat-sensitive biomaterials like polyetheretherketone and cobalt-chromium-molybdenum alloys. Laser sintering allows the fabrication of intricate 3D structures from a powdered precursor and can deposit coatings directly onto a substrate. The end goal, in part, is to improve the wear performance of orthopedic bearings. Silicon nitride coatings have excellent wear resistance and can mitigate ion release from the underlying substrate. Notably, the solubility of silicon nitride thin films means that wear particles can dissolve in vivo, thereby mitigating the risk of adverse immune responses seen with metal or oxide-ceramic implant bearings. However, the solubility of the film itself, as well as adhesion to the substrate, can be a challenge to the application. Specific techniques to reduce the risk of coating delamination, while enhancing osteogenic and antipathogenic properties, are discussed in this chapter. Studies have confirmed that silicon nitride coatings are effective at promoting osteogenesis and discouraging pathogens, similar to silicon nitride itself. The combination of faster osteointegration of arthroplasty implants with a reduction in infection risk is highly desirable in orthopedic surgery. Encouraging data so far suggest that significant advancements will be forthcoming in the development of functional silicon nitride coatings for joint prostheses in the future. Beyond arthroplasty, dental implants, arthrodesis devices, intraocular pressure sensors, neurophotonic probes, and antithrombogenic applications in clinical medicine also stand to benefit from silicon nitride coatings.