The remarkable stoichiometric flexibility of hydroxyapatite (HAp) enables the formation of a variety of charged structural sites at the material's surface which facilitates bone remodeling due to binding of biomolecule moieties in zwitterionic fashion. In this paper, we report for the first time that an optimized biomedical grade silicon nitride (Si3N4) demonstrated cell adhesion and improved osteoconductivity comparable to highly defective, non-stoichiometric natural hydroxyapatite. Si3N4's zwitterionic-like behavior is a function of the dualism between positive and negative charged off-stoichiometric sites (i.e., N-vacancies versus silanols groups, respectively). Lattice defects at the biomaterial's surface greatly promote interaction with positively- and negatively-charged functional groups in biomolecules, and result in the biologically effective characteristics of silicon nitride. These findings are anticipated to be a starting point for further discoveries of therapeutic bone-graft substitute materials.
The issue of spine-related disorders is a global healthcare concern that requires effective solutions to restore normal spine functioning. Spinal fusion implants have become a standard approach for this purpose, making it crucial to develop biomaterials and structures that possess high osteogenic capacities and exhibit mechanical properties and dynamic responses similar to those of the host bone. This study focused on the fabrication of 3D-printed polyether ether ketone/silicon nitride (PEEK/SiN) scaffolds with a triply periodic minimal surface (TPMS) structure, which offers several advantages, such as a large surface area and uniform stress distribution under load. The mechanical properties and dynamic response of PEEK/SiN scaffolds with varying porosities were evaluated through mechanical testing and finite element analysis. The scaffold with 30% porosity exhibited a compressive strength (34.56 ± 1.91 MPa) and elastic modulus (734 ± 64 MPa) similar to those of trabecular bone. In addition, the scaffold demonstrated favorable damping properties. The biological data revealed that incorporating silicon nitride into the PEEK scaffold stimulated osteogenic differentiation. In light of these findings, it can be inferred that PEEK/SiN TPMS scaffolds exhibit significant potential for use in bone tissue engineering and represent a promising option as candidates for spinal fusion implants.
The metabolic response of Gram-positive Staphylococcus epidermidis (S. epidermidis) bacteria to bioceramic substrates was probed by means of Fourier transform infrared spectroscopy (FTIR). Oxide zirconia-toughened alumina (ZTA) and non-oxide silicon nitride (Si3N4) substrates were tested. Bacteria exposed to silica glass substrates were used as a control. S. epidermidis, a major cause of periprosthetic infections, was screened to obtain a precise time-lapse knowledge of its molecular composition and to mechanistically understand its interaction with different substrates. At the molecular level, the structure of proteins, lipids, nucleic acid, and aromatic amino acids evolved with time in response to different substrates. In combination with statistical validation and local pH measurements, a chemical lysis mechanism was spectroscopically observed in situ on the Si3N4 substrates. Utilization of FTIR in this study avoided fluorescence noise which occurred while probing the ZTA samples with Raman spectroscopy in a companion paper. The substrate-driven dynamics of polysaccharide and peptide variations in the bacterial cell wall, peculiar to Si3N4 bioceramics, are elucidated.
IntroductionPeriprosthetic infections are leading causes of revision surgery resulting in significant increased patient comorbidities and costs. Considerable research has targeted development of biomaterials that may eliminate implant-related infections.1 This in vitro study was developed to compare biofilm formation on three materials used in spinal fusion surgery – silicon nitride, PEEK, and titanium – using one gram-positive and one gram-negative bacterial species.Materials and MethodsSeveral surface treated silicon nitride (Si3N4, MC2®, Amedica Corporation, Salt Lake City, UT), poly-ether-ether-ketone (PEEK, ASTM D6262), and medical grade titanium (Ti6Al4V, ASTM F136) discs O12.7 × 1mm were prepared or acquired for use in this well-plate study. Each group of discs (n=3) were ultrasonically cleaned, UV-sterilized, inoculated with 105 Staphylococcus epidermidis (ATCC® 25922™) or Escherichia coli (ATCC® 14990™) and placed in a culture medium of phosphate buffered saline (PBS) containing 7% glucose and 10...
Back Cover: Silicon nitride (Si3N4) is a bioceramic with unique surface chemistry, friendly to cells and adverse to bacteria. A 15vol.% Si3N4 particulate dispersion into polyetheretherketone (PEEK) proved capable to translate such a unique biochemical behavior to a polymer-matrix composite, which also became X-ray translucent and retained a modulus of elasticity comparable to bone. This is reported by Giuseppe Pezzotti, Elia Marin, Tetsuya Adachi, Federica Lerussi, Alfredo Rondinella, Francesco Boschetto, Wenliang Zhu, Takashi Kitajima, Kosuke Inada, Bryan J. McEntire, Ryan M. Bock, B. Sonny Bal, Osam Mazda in article number 1800033.
Abstract Medical-grade masks and N95 respirators containing non-woven fibers are designed to prevent the spread of airborne diseases. While they effectively trap respiratory droplets and aerosols, they cannot lyse entrapped pathogens. Embedded antimicrobial agents such as silver, copper, zinc, iodine, peptides, quaternary ammonium salts, or nanoparticles have been used to overcome this limitation. However, their effectiveness remains debatable because these materials can be toxins, allergens, irritants, and environmental hazards. Recently, silicon nitride (Si 3 N 4 ) was found to be a potent antipathogenic compound, and it may be an ideal agent for masks. In powder or solid form, it is highly effective in inactivating bacteria, fungi, and viruses while leaving mammalian tissue unaffected. The purpose of this study was to serially assess the antiviral efficacy of Si 3 N 4 against SARS-CoV-2 using powders, solids, and embedded nonwoven fabrics. Si 3 N 4 powders and solids were prepared using conventional ceramic processing. The “pad-dry-cure” method was used to embed Si 3 N 4 particles into polypropylene fibers. Fabric testing was subsequently conducted using industrial standards—ISO 18184 for antiviral effectiveness, ASTM F2299 and EN 13274-7 for filtration efficiency, EN 14683 for differential pressure drop, and ISO 18562-2 for particle shedding. A modification of ISO 18562-3 was also employed to detect ammonia release from the fabric. Antiviral effectiveness for Si 3 N 4 powders, solids, and embedded fabrics were 99.99% at ≤ 5 min, ~ 93% in 24 h, and 87% to 92% in 120 min, respectively. Results of the standard mask tests were generally within prescribed safety limits. Further process optimization may lead to commercial Si 3 N 4 -based masks that not only “catch” but also “kill” pathogenic microbes.
Alumina particles have successfully been alkylated via a condensation reaction between surface hydroxide sites and different, long chain alcohol molecules, specifically decanol, dodecanol, and octadecanol. These hydrophobic particles have been successfully dispersed in water using different C n TAB surfactant molecules, where n =10, 12, 14, 16. The effect of the length of the surfactant molecule and its concentration was quantified with rheological experiments. Rheology and conductivity measurements were used to determine the minimum amount of the surfactant needed to disperse the alkylated powder. Slurries formulated with the alkylated powder and the proper amount of C n TAB exhibited Newtonian rheology for n ≥10. ξ potential measurements showed that the surface charge on the particles was always positive confirming that the C n TAB molecules, with a positive head group, surrounded the alkylated particles. Such powder did not have an isoelectric point. In addition, the Newtonian behavior of the alkylated‐alumina/C n TAB slurry systems were independent of pH.
