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Silicon nitride (Si3N4) is a promising biomaterial, currently used in spinal fusion implants. Such implants should result in high vertebral union rates without major complications. However, pseudarthrosis remains an important complication that could lead to a need for implant replacement. Making silicon nitride implants more bioactive could lead to higher fusion rates, and reduce the incidence of pseudarthrosis. In this study, it was hypothesized that creating a highly negatively charged Si3N4 surface would enhance its bioactivity without affecting the antibacterial nature of the material. To this end, samples were thermally, chemically, and thermochemically treated. Apatite formation was examined for a 21-day immersion period as an in-vitro estimate of bioactivity. Staphylococcus aureus bacteria were inoculated on the surface of the samples, and their viability was investigated. It was found that the thermochemically and chemically treated samples exhibited enhanced bioactivity, as demonstrated by the increased spontaneous formation of apatite on their surface. All modified samples showed a reduction in the bacterial population; however, no statistically significant differences were noticed between groups. This study successfully demonstrated a simple method to improve the in vitro bioactivity of Si3N4 implants while maintaining the bacteriostatic properties.

Injectable poly (methyl methacrylate) (PMMA) bone cements are widely used in orthopaedics to stabilize fractures and for implant fixation. However, bacterial attachment to bone cements leads to significant complications that can create a need for implant revision. Common attempts at reducing bacterial attachment are through the addition of antibiotics or antibacterial nanometals to the bone cements. However, clinical data is inconclusive on the effectiveness of antibiotic-loaded bone cements and a negative osteoblastic response has been reported for certain additive concentrations. There is therefore a need for an additive that can positively affect osteoblastic behaviour while inhibiting bacterial attachment. Silicon nitride (Si3N4) could be such an additive, with initial studies showing promise in achieving antipathogenic properties. The aim of this study was hence to investigate the possibility of creating a bone cement that can support osteoblast growth while reducing bacterial attachment by introducing silicon nitride powders into an injectable PMMA cement. To this end, commercially available bone cements were doped with 5%, 10% and 20% weight/weight (w/w) of Si3N4. Their mechanical properties were examined through compression testing and their radiopacity was evaluated through fluoroscopy imaging. The samples that fulfilled compressive strength requirements had their biological properties tested using Staphylococcus epidermidis bacteria for antibacterial properties and MC3T3-E1 preosteoblasts for the examination of cytotoxicity. Bone cements that were doped with up to 20% w/w Si3N4 were radiopaque (only 13% reduction in optical density compared to radiopaque controls) and retained their compressive strength (85.35 ± 2.1 MPa compared to 83.4 ± 1.9 MPa for the commercial cements), while significantly reducing bacterial attachment by more than 90% compared to commercial cements and achieving a similar level of preosteoblast metabolic activity. This study supports further evaluation of Si3N4 as an additive to injectable bone cements as a way to create mechanically stable, radiopaque, bacteriostatic bone cements that could improve osteointegration.

Containing the spread of pathogens and treating the diseases they cause have become topics of high importance and urgency for researchers. Recent epidemics and pandemics, key amongst them being the pandemic caused by the coronavirus disease (COVID-19), have highlighted the devastating results virus infections can have on our society. Uncovering and utilising materials for the protection from and treatment of virus-induced diseases can considerably alleviate the load imposed on healthcare systems worldwide. Silicon nitride is a biocompatible ceramic material used in orthopedic implants that is effective in the inactivation of single-stranded RNA viruses. However, the effect of the material on the more resilient DNA viruses remains unknown. This study aimed to investigate the antiviral behaviour of the material, in powder and bulk form, against DNA viruses, and more specifically the human adenovirus. The results of the study indicated that silicon nitride dramatically reduces adenoviral infectivity in powder (>98% reduction in infective virus compared to untreated samples) and bulk form (>73% reduction in infective virus compared to negative control). In both cases, inactivation was achieved rapidly, in one minute for powders and 10 minutes for bulk surfaces. The findings of this study strengthen the potential of silicon nitride to be used as an antiviral agent, aiding the fight against the spread of both DNA and RNA virus diseases.

The spread of SARS-CoV-2 led to a global pandemic that caused several million deaths. The severity of this pandemic created challenges for scientists worldwide regarding the prevention of the spread of COVID-19, the disease the virus causes. While the use of personal protective equipment and social distancing limited the spread of the virus, high transmission rates were noted. A solution to the issue of viral spread can be partially given by the utilization of antiviral materials for long-term protection against pathogens on environmental surfaces. To this end, nitrides are materials of high interest due to their proven efficiency in inactivating bacteria and viruses. Silicon nitride (Si3N4) is a ceramic material that possesses an inactivation mechanism termed ‘catch and kill’. In this study we hypothesized that a surface-modified Si3N4 material whose hydrophilicity has been increased through a heat treatment could lead to high attachment and inactivation of SARS-CoV-2 virions. Si3N4 powders were oxidized, characterized and the inactivation of SARS-CoV-2 by them was tested. The results showed that oxidized Si3N4 was highly effective in binding and inactivating SARS-CoV-2 after as little as one minute of contact and can be used to inhibit the spread of COVID-19 under certain circumstances.