Silicon Nitride Bioceramics Induce Chemically Driven Lysis inPorphyromonas gingivalis

Abstract

Organisms of Gram-negative phylum bacteroidetes, Porphyromonas gingivalis, underwent lysis on polished surfaces of silicon nitride (Si3N4) bioceramics. The antibacterial activity of Si3N4 was mainly the result of chemically driven principles. The lytic activity, although not osmotic in nature, was related to the peculiar pH-dependent surface chemistry of Si3N4. A buffering effect via the formation of ammonium ions (NH4(+)) (and their modifications) was experimentally observed by pH microscopy. Lysis was confirmed by conventional fluorescence spectroscopy, and the bacteria's metabolism was traced with the aid of in situ Raman microprobe spectroscopy. This latter technique revealed the formation of peroxynitrite within the bacterium itself. Degradation of the bacteria's nucleic acid, drastic reduction in phenilalanine, and reduction of lipid concentration were observed due to short-term exposure (6 days) to Si3N4. Altering the surface chemistry of Si3N4 by either chemical etching or thermal oxidation influenced peroxynitrite formation and affected bacteria metabolism in different ways. Exploiting the peculiar surface chemistry of Si3N4 bioceramics could be helpful in counteracting Porphyromonas gingivalis in an alkaline pH environment.

Bacteriostatic behavior of surface modulated silicon nitride in comparison to polyetheretherketone and titanium

“…In addition to surface charge and wetting considerations, it has also been recently demonstrated that surface dissolution of Si 3 N 4 also impacts bacterial adhesion and biofilm formation . In the presence of moisture, there is a diffusion‐limited thermodynamic driving force to convert silicon nitride to silicic acid (Si(OH) 4 ) and ammonia (NH 3 ) as indicated in Equation below: …”

“…The release of NH 3 from the Si 3 N 4 surface not only increases the local pH to ≈8.5, which deleteriously affects bacteria adhesion, but it also affects their metabolism in a manner similar to the elution of nitric oxide (NO) from xerogel polymers . Charville et al demonstrated this in a study which examined the effect of NO release from fibrinogen‐mediated xerogel coated glass slides on the adhesion of S. aureus , S. epidermidis , and E. coli .…”

Bioactive silicon nitride: A new therapeutic material for osteoarthropathy

“…It is speculated that nitrogen scavenging occurred through NH 4 + uptake driven by the membrane potential. Previously, pH microscopy experiments demonstrated that ammonia formation and pH buffering readily occurs at the surface of Si 3 N 4 when exposed to a biological environment20. Surface alkalization might also play a role in enhancing the metabolic uptake of nitrogen50.…”

“…Cells metabolically assimilate and transform water, carbon dioxide (CO 2 ), and three inorganic nitrogen compounds – ammonium (NH 4 + ), nitrate (NO 3 − ), and di-nitrogen (N 2 ) – into complex biomolecules19. One of the more obvious and yet intriguing aspects involving the use of silicon nitride as a biomaterial is that H 4 SiO 4 , NH 4 + , NO 3 − , and N 2 are all promptly and copiously available during biological interactions20. The peculiar chemistry of Si 3 N 4 , which can be chemically-modulated21, facilitates a range of favorable metabolic interactions between both eukaryotic and prokaryotic cells at its inorganic surface820.…”

“…It should be noted that Si 3 N 4 spinal implants are nowadays successfully employed and show excellent osteogenesis55. Moreover, pH microscopy data collected during a bacterial study on the surface of Si 3 N 4 revealed pH buffering effects due to surface reactions involving charged nitrogen compounds20. These properties could be exploited in local treatments of osteoporotic bone segments (i.e., vertebral body) through a local implantation.…”