Silicon Nitride: A Bioceramic with a Gift

Abstract

In the closing decades of the 20th century, silicon nitride (Si 3 N 4 ) was extensively developed for high-temperature gas turbine applications. Technologists attempted to take advantage of its superior thermal and mechanical properties to improve engine reliability and fuel economy. Yet, this promise was never realized in spite of the worldwide research, which was conducted at that time. Notwithstanding this disappointment, its use in medical applications in the early 21st century has been an unexpected gift. While retaining all of its engineered mechanical properties, it is now recognized for its peculiar surface chemistry. When immersed in an aqueous environment, the slow elution of silicon and nitrogen from its surface enhances healing of soft and osseous tissue, inhibits bacterial proliferation, and eradicates viruses. These benefits permit it to be used in a wide array of different disciplines inside and outside of the human body including orthopedics, dentistry, virology, agronomy, and environmental remediation. Given the global public health threat posed by mutating viruses and bacteria, silicon nitride offers a valid and straightforward alternative approach to fighting these pathogens. However, there is a conundrum behind these recent discoveries: How can this unique bioceramic be both friendly to mammalian cells while concurrently lysing invasive pathogens? This unparalleled characteristic can be explained by the pH-dependent kinetics of two ammonia speciesNH 4 + and NH 3 both of which are leached from the wet Si 3 N 4 surface.

Off-Stoichiometric Reactions at the Cell–Substrate Biomolecular Interface of Biomaterials: In Situ and Ex Situ Monitoring of Cell Proliferation, Differentiation, and Bone Tissue Formation

“…Eleven Raman bands were located in the monitored spectral window, the precise frequencies of which as well as their physical origins have been reported in a previous paper [10]. In the case of cells cultured on Si 3 N 4 substrates, no significant variations in relative intensity when compared with the positive control sample could be observed after 48 h for RNA/DNA-related Bands 5 (at 783 cm −1 ), 6 (at 794 cm −1 ), and 7 (at 813 cm −1 ).…”

“…After an initial proposal of osteoinductivity for calcium phosphate containing biomaterials [4,5], only one study has proposed osteoinductivity for alumina ceramics [6]; however, several studies have favored titanium as an osteoinductive substrate [7,8]. Recent in vivo and in vitro studies [9,10] have indicated that silicon nitride, a non-oxide bioceramic previously considered to be fully bioinert [1], is instead a formidable stimulator of osteoblastogenesis and osteoinductivity. The mechanisms of osteoinduction by the above biomaterials have been phenomenologically covered by the above publications, but the fundamental chemistry driving osteoblastogenesis and the successive bone formation needs additional elucidation.…”

Instantaneous “catch‐and‐kill” inactivation of SARS‐CoV‐2 by nitride ceramics

“…It possesses a unique surface biochemistry that inhibits bacterial infections by longterm elution of nitrogen (promptly converted into ammonia) in minute concentrations that, unlike bacteria and viruses, mammalian cells can easily metabolize. 4 Within 1 minute, influenza A and enterovirus were completely inactivated by Si 3 N 4 bioceramic particles suspended in water. 5 In this study, we exposed SARS-CoV-2 virions to the above bioceramic as well as to aluminum nitride (AlN) micrometric powders suspended in water.…”

Rapid Inactivation of SARS-CoV-2 by Silicon Nitride, Copper, and Aluminum Nitride

“…A curious finding is that Si3N4 implants have a lower incidence of bacterial infection (i.e., less than 0.006%) when compared to other implant materials (2.7% to 18%) [14]. This property reflects the complex surface biochemistry of Si3N4 that elutes minute amounts of nitrogen, which is converted to ammonia, ammonium, and other reactive nitrogen species (RNS) that inhibit bacteria [15]. A recent investigation also found that viral exposure to sintered Si3N4 powders in aqueous suspension inactivated H1N1 (Influenza A/Puerto Rico/8/1934), Feline calicivirus, and Enterovirus (EV-A71) [16].…”