In Situ Spectroscopic Screening of Osteosarcoma Living Cells on Stoichiometry-Modulated Silicon Nitride Bioceramic Surfaces

Recent advances in the application and biological mechanism of silicon nitride osteogenic properties: a review

Silicon nitride, an emerging bioceramic material, is highly sought after in the biomedical industry due to its osteogenesis-promoting properties, which are a result of its unique surface chemistry and excellent mechanical properties. Currently, it is used in clinics as an orthopedic implant material. The osteogenesis-promoting properties of silicon nitride are manifested in its contribution to the formation of a local osteogenic microenvironment, wherein silicon nitride and its hydrolysis products influence osteogenesis by modulating the biological behaviors of the constituents of the osteogenic microenvironment. In particular, silicon nitride regulates redox signaling, cellular autophagy, glycolysis, and bone mineralization in cells involved in bone formation via several mechanisms. Moreover, it may also promote osteogenesis by influencing immune regulation and angiogenesis. In addition, the wettability, surface morphology, and charge of silicon nitride play crucial roles in regulating its osteogenesis-promoting properties. However, as a bioceramic material, the molding process of silicon nitride needs to be optimized, and its osteogenic mechanism must be further investigated. Herein, we summarize the impact of the molding process of silicon nitride on its osteogenic properties and clinical applications. In addition, the mechanisms of silicon nitride in promoting osteogenesis are discussed, followed by a summary of the current gaps in silicon nitride mechanism research. This review, therefore, aims to provide novel ideas for the future development and applications of silicon nitride.

In Situ Raman Study of Neurodegenerated Human Neuroblastoma Cells Exposed to Outer-Membrane Vesicles Isolated from Porphyromonas gingivalis

The aim of this study was to elucidate the chemistry of cellular degeneration in human neuroblastoma cells upon exposure to outer-membrane vesicles (OMVs) produced by Porphyromonas gingivalis (Pg) oral bacteria by monitoring their metabolomic evolution using in situ Raman spectroscopy. Pg-OMVs are a key factor in Alzheimer's disease (AD) pathogenesis, as they act as efficient vectors for the delivery of toxins promoting neuronal damage. However, the chemical mechanisms underlying the direct impact of Pg-OMVs on cell metabolites at the molecular scale still remain conspicuously unclear. A widely used in vitro model employing neuroblastoma SH-SY5Y cells (a sub-line of the SK-N-SH cell line) was spectroscopically analyzed in situ before and 6 h after Pg-OMV contamination. Concurrently, Raman characterizations were also performed on isolated Pg-OMVs, which included phosphorylated dihydroceramide (PDHC) lipids and lipopolysaccharide (LPS), the latter in turn being contaminated with a highly pathogenic class of cysteine proteases, a key factor in neuronal cell degradation. Raman characterizations located lipopolysaccharide fingerprints in the vesicle structure and unveiled so far unproved aspects of the chemistry behind protein degradation induced by Pg-OMV contamination of SH-SY5Y cells. The observed alterations of cells' Raman profiles were then discussed in view of key factors including the formation of amyloid β (Aβ) plaques and hyperphosphorylated Tau neurofibrillary tangles, and the formation of cholesterol agglomerates that exacerbate AD pathologies.

Silicon Oxynitride Thin Film Coating to Lossy Mode Resonance Fiber-Optic Refractometer

A fiber-optic refractometer for various liquids with refractive indices in the range from 1.33 to 1.43 has been manufactured and tested. The sensor is based on a thin silicon oxynitride (Si₃N_4-xO_x) film coated thinned optic fiber section (taper) obtained in a multimode all-silica optical fiber by chemical etching of the reflective cladding. The film was deposited on the cylindrical surface of the thinned fiber by the surface plasma chemical vapor deposition method (SPCVD). Lossy mode resonance (LMR) was observed in the transmission spectrum of the coated taper at a wavelength dependent on the refractive index of the liquid in which the taper was immersed. We tested the obtained sensors in distilled water, isopropyl alcohol, dimethylformamide, and their aqueous solutions. It was found that with the help of the SPCVD, one can obtain a set of sensors in a single deposition run with the dispersion of sensitivity and spectral position of LMR no more than 5%. Maximum sensitivity of the manufactured sensors to surrounding media refractive index (SMRI) variation exceeds 1090 nm/RIU, which is the highest value recorded to date for a sensor with a non-oxide coating.

Silicon Nitride, a Bioceramic for Bone Tissue Engineering: A Reinforced Cryogel System With Antibiofilm and Osteogenic Effects

Silicon nitride (SiN [Si3N4]) is a promising bioceramic for use in a wide variety of orthopedic applications. Over the past decades, it has been mainly used in industrial applications, such as space shuttle engines, but not in the medical field due to scarce data on the biological effects of SiN. More recently, it has been increasingly identified as an emerging material for dental and orthopedic implant applications. Although a few reports about the antibacterial properties and osteoconductivity of SiN have been published to date, there have been limited studies of SiN-based scaffolds for bone tissue engineering. Here, we developed a silicon nitride reinforced gelatin/chitosan cryogel system (SiN-GC) by loading silicon nitride microparticles into a gelatin/chitosan cryogel (GC), with the aim of producing a biomimetic scaffold with antibiofilm and osteogenic properties. In this scaffold system, the GC component provides a hydrophilic and macroporous environment for cells, while the SiN component not only provides antibacterial properties and osteoconductivity but also increases the mechanical stiffness of the scaffold. This provides enhanced mechanical support for the defect area and a better osteogenic environment. First, we analyzed the scaffold characteristics of SiN-GC with different SiN concentrations, followed by evaluation of its apatite-forming capacity in simulated body fluid and protein adsorption capacity. We further confirmed an antibiofilm effect of SiN-GC against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) as well as enhanced cell proliferation, mineralization, and osteogenic gene upregulation for MC3T3-E1 pre-osteoblast cells. Finally, we developed a bioreactor to culture cell-laden scaffolds under cyclic compressive loading to mimic physiological conditions and were able to demonstrate improved mineralization and osteogenesis from SiN-GC. Overall, we confirmed the antibiofilm and osteogenic effect of a silicon nitride reinforced cryogel system, and the results indicate that silicon nitride as a biomaterial system component has a promising potential to be developed further for bone tissue engineering applications.

Tailoring Silicon Nitride Surface Chemistry for Facilitating Odontogenic Differentiation of Rat Dental Pulp Cells

Silicon nitride (Si3N4) can facilitate bone formation; hence, it is used as a biomaterial in orthopedics. Nevertheless, its usability for dentistry is unexplored. The aim of the present study was to investigate the effect of Si3N4 granules for the proliferation and odontogenic differentiation of rat dental pulp cells (rDPCs). Four different types of Si3N4 granules were prepared, which underwent different treatments to form pristine as-synthesized Si3N4, chemically treated Si3N4, thermally treated Si3N4, and Si3N4 sintered with 3 wt.% yttrium oxide (Y2O3). rDPCs were cultured on or around the Si3N4 granular beds. Compared with the other three types of Si3N4 granules, the sintered Si3N4 granules significantly promoted cellular attachment, upregulated the expression of odontogenic marker genes (Dentin Matrix Acidic Phosphoprotein 1 and Dentin Sialophosphoprotein) in the early phase, and enhanced the formation of mineralization nodules. Furthermore, the water contact angle of sintered Si3N4 was also greatly increased to 40°. These results suggest that the sintering process for Si3N4 with Y2O3 positively altered the surface properties of pristine as-synthesized Si3N4 granules, thereby facilitating the odontogenic differentiation of rDPCs. Thus, the introduction of a sintering treatment for Si3N4 granules is likely to facilitate their use in the clinical application of dentistry.

Activity and Mechanism of Action of the Bioceramic Silicon Nitride as an Environmentally Friendly Alternative for the Control of the Grapevine Downy Mildew Pathogen Plasmopara viticola

Downy mildew of grapevine, caused by Plasmopara viticola (Berk. and Curt.) Berl. and de Toni, is one of the most devastating diseases of grapevine, severely affecting grape and wine production and quality worldwide. Infections are usually controlled by the intensive application of synthetic fungicides or by copper-based products in organic farming, rising problems for soil contamination and adverse impacts on environment and human health. While strict regulations attempt to minimize their harmful consequences, the situation calls for the development of alternative fungicidal strategies. This study presents the unprecedented case of a bioceramic, silicon nitride, with antimicrobial properties against P. viticola, but without adverse effects on human cells and environment, opening the way to the possible extension of silicon nitride applications in agriculture. Raman spectroscopic assessments of treated sporangia in conjunction with microscopic observations mechanistically showed that the nitrogen-chemistry of the bioceramic surface affects pathogen's biochemical components and cell viability, thus presenting a high potential for host protection from P. viticola infections.

Surface functionalization of PEEK with silicon nitride

Surface roughness, bioactivity, and antibacterial properties are desirable in skeletal implants. We hot-pressed a mix of particulate sodium chloride (NaCl) salt and silicon nitride (β-Si3N4) onto the surface of bulk PEEK. NaCl grains were removed by leaching in water, resulting in a porous PEEK surface embedded with ~15 vol.% β-Si3N4 particles. This functionalized surface showed the osteogenic and antibacterial properties previously reported in bulk silicon nitride implants. Surface enhancement of PEEK with β-Si3N4 could improve the performance of spinal fusion cages, by facilitating arthrodesis and resisting bacteria.

Raman Probes for In Situ Molecular Analyses of Peripheral Nerve Myelination

The myelinating activity of living Schwann cells in coculture with neuronal cells was examined in situ in a Raman microprobe spectroscope. The Raman label-free approach revealed vibrational fingerprints directly related to the activity of Schwann cells' metabolites and identified molecular species peculiar to myelinating cells. The identified chemical species included antioxidants, such as hypotaurine and glutathione, and compartmentalized water, in addition to sphingolipids, phospholipids, and nucleoside triphosphates also present in neuronal and nonmyelinating Schwann cells. Raman maps at specific frequencies could be collected, which clearly visualized the myelinating action of Schwann cells and located the demyelinated ones. An important finding was the spectroscopic visualization of confined water in the myelin structure, which exhibited a quite pronounced Raman signal at ∼3470 cm^-1. This peculiar signal, whose spatial location precisely corresponded to a low-frequency fingerprint of hypotaurine, was absent in unmyelinating cells and in bulk water. Raman enhancement was attributed to frustration in the hydrogen-bond network as induced by interactions with lipids in the myelin sheaths. According to a generally accepted morphological model of myelin, an explanation was offered of the peculiar Raman scattering of water confined in intraperiod lines, according to an ordered hydrogen bonding structure. The possibility of concurrently mapping antioxidant molecules and compartmentalized water structure with high spectral accuracy and microscopic spatial resolution enables probing myelinating activity and might play a key-role in future studies of neuronal pathologies. Compatible with life, Raman microprobe spectroscopy with the newly discovered probes could be suitable for developing advanced strategies in the reconstruction of injured nerves and nerve terminals at neuromuscular junctions.

Effects of a Coating of Nano Silicon Nitride on Porous Polyetheretherketone on Behaviors of MC3T3-E1 Cells in Vitro and Vascularization and Osteogenesis in Vivo

To improve the bioperformances of porous polyetheretherketone (PPK) for bone repair, silicon nitride-coated PPK (CSNPPK) was prepared by a method of suspension coating and melt binding. The results revealed that, as compared with PPK, the surface roughness, compressive strength, and water absorption of CSNPPK increased, while the pore size and porosity of CSNPPK exhibited no obvious changes. In addition, the cellular responses (including attachment, proliferation, and differentiation as well as osteogenically related gene expressions) of the MC3T3-E1 cells to CSNPPK were remarkably promoted compared with PPK and dense polyetheretherketone in vitro. Moreover, in the model of rabbit femoral condyle defects, the results of micro computed tomography and histological and mechanical evaluation revealed that the ingrowth of new vessels and bone tissues into CSNPPK was significantly greater than that into PPK in vivo. Furthermore, the load-displacement and push-out loads for CSNPPK with bone tissues were higher than for PPK, indicating good osseointegration. In short, CSNPPK not only promoted vascularization but also enhanced osteogenesis as well as osseointegration in vivo. Therefore, it can be suggested that CSNPPK with good biocompatibility, osteogenic activity, and vascularization might be a promising candidate as an implant for bone substitute and repair.

In situ molecular vibration insights into the antibacterial behavior of silicon nitride bioceramic versus gram-negative Escherichia coli

Gram-negative bacteria represent a substantial fraction of pathogens responsible for periprosthetic infections. Given the increasing resistance of such bacteria to antibiotics, significant efforts are nowadays paid in developing new biomaterial surfaces, which offer resistance against bacterial adhesion and/or possess inherent antibacterial effects. Non-oxide silicon nitride (Si₃N₄) bioceramic in its polycrystalline form is a biomaterial with inherent antibacterial properties. Building upon previous phenomenological findings, the present study focuses on vibrational analyses of the metabolic response of Escherichia coli at the molecular level. A time-lapse study is conducted upon exposing the bacteria in vitro to Si₃N₄ bioceramic surfaces. A comparison is carried out with the as-cultured bacterial strain and with bacteria exposed to other commercially available biomaterials, namely, Ti-alloy (Ti6Al4V-ELI) and zirconia-toughened alumina (ZTA) oxide bioceramic tested under exactly the same experimental conditions. The metabolic pathways before and after exposure to different substrates were monitored by means of Raman and FTIR spectroscopies. Results indicated the development of significant osmotic stress in the bacterial strain and constant concentration decreases of its cellular compounds markers over time upon exposure to Si₃N₄. This ultimately led to bacterial lysis (also confirmed by conventional fluorescence microscopy assays). The main antibacterial effect was of chemical origin and driven by the elution of nitrogen ions from the Si₃N₄ surface, successively converted into ammonia (NH₃) or ammonium (NH₄)⁺ in aqueous solution, depending on environmental pH. The presence of these nitrogen species created osmotic stress in the cytoplasmic space. In answer to the osmotic stress, metabolic rates changed rapidly, the bacterial membrane was damaged, and lysis occurred almost completely within 48 h exposure. The antibacterial behavior exerted by the Si₃N₄ substrate on E. coli was more effective than that observed on the biomedical Ti6Al4V alloy. Conversely, no lysis but bacterial proliferation was recorded for E. coli exposed to ZTA bioceramic oxide substrates.

3D-additive deposition of an antibacterial and osteogenic silicon nitride coating on orthopaedic titanium substrate

A 3D-additive manufacturing approach produced a dense Si₃N₄ ceramic coating on a biomedical grade commercially pure titanium (cp-Ti) substrate by an automatic laser-sintering procedure. Si₃N₄ coatings could be prepared with thicknesses from the single to the tens of microns. A coating thickness, t = 15 ± 5 μm, was selected for this study, based on projections of homogeneity and scratching resistance. The Si₃N₄ coating met the 20 N threshold required for biomaterial applications, according to the standard scratch testing (ASTM C1624-05). The Si₃N₄ coating imparted both the antibacterial and osteogenic properties of bulk Si₃N₄ to the cp-Ti substrate. Both properties were comparable to those previously described for bulk Si₃N₄ biomedical implants. The newly developed Si₃N₄-coating was applied to commercially available Ti-alloy acetabular shells for total hip arthroplasty. A "glowing" test based on luciferase gene transformation was applied to visualize the colonization of gram-negative Escherichia coli on Si₃N₄-coated and uncoated Ti-alloy acetabular shells. The results showed that the coating technology conferred resistance to Staphylococcus epidermidis and Escherichia coli adhesion onto the bulk acetabular sockets.

Enhanced bioactivity of Si3N4 through trench-patterning and back-filling with Bioglass®

Using a simple and innovative sandblasting process, disks of monolithic biomedical silicon nitride (β-Si₃N₄) were texturized with a matrix of regular, discrete square trenches with a total depth in the range of hundreds of microns. The process consisted of sandblasting Si₃N₄ substrates through a stainless-steel wire-mesh (150 or 200 μm) using abrasive silicon carbide powders (α-SiC, ∼40 μm) under 1,034 kPa (150 psi) of gas pressure. The depth of the porosities could be controlled varying both the treatment time and the distance from the surface. Part of the samples were then filled with 45S5 Bioglass® powders to improve the osteointegration and stimulate the production of bone tissue. Due to the increased macroscopic and microscopic roughness, biological testing using human osteosarcoma cells (SaOS-2) showed improved cell proliferation and greater production of both mineral (hydroxyapatite) and organic (collagen) phases on the patterned surfaces compared to untreated β-Si₃N₄ or to the biomedical titanium control samples. Both of these effects were further enhanced when the porosities were filled with Bioglass®.

Silicon Nitride: A Bioceramic with a Gift

In the closing decades of the 20th century, silicon nitride (Si₃N₄) 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-NH₄⁺ and NH₃-both of which are leached from the wet Si₃N₄ surface.

Silicon nitride enhances osteoprogenitor cell growth and differentiation via increased surface energy and formation of amide and nanocrystalline HA for craniofacial reconstruction

The bioactive silicon nitride (Si₃N₄) has been FDA cleared for use as spinal intervertebral arthrodesis devices. Because its surface properties promote bone ongrowth and ingrowth, it also has the potential to benefit craniofacial reconstruction. Thus, the aim of this work was to determine whether the surface properties of Si₃N₄ could enhance the osteoblast cell growth, differentiation and nucleation of hydroxyapatite (HA) crystals compared to conventional implant materials such as titanium (Ti) and polyether ether ketone (PEEK). X-ray absorbance near-edge structure analysis (XANES) indicated the presence of Si-Si, Si-O and Si-N bonding. Surface wettability studies confirmed that Si₃N₄ exhibits the lowest contact angle and highest surface energy. Cell culture studies showed that osteoblast growth was enhanced on Si₃N₄ after 1 day and up to 7 days. Si₃N₄ surface induced highest surface coverage and thickness of nanocrystalline HA (211) and (203) in cell-free in vitro studies after 7 days of culture. Raman spectroscopy analysis confirmed the presence of surface functional groups consisting of phosphate and carbonate species. Interestingly, Si₃N₄ surface showed amide and hydroxyproline groups, the precursors to collagen, which were not observed on Ti and PEEK surfaces. Furthermore, Si₃N₄ surface indicated high expression of RUNX2, enhanced cell differentiation and dense collagenous ECM after 30 days of the in vitro study. The present study concluded that Si₃N₄ surface enhances osteoprogenitor cell adhesion, growth, RUNX2 expression and ECM formation via the coupled effects of higher surface energy and the presence of amide and nanocrystalline HA functional groups.

Bioglass functionalization of laser-patterned bioceramic surfaces and their enhanced bioactivity

The surfaces of silicon nitride (β-Si3N4) and zirconia toughened alumina (ZTA) were patterned using a high-energy laser source, which operated at a wavelength of 1064 nm. The patterning procedure yielded a series regular, cylindrical cavities 500 and 300 μm in diameter and depth, respectively. These cavities were subsequently filled with bioglass mixed with different fractions of Si3N4 powder (0, 5, and 10 mol.%) to obtain bioactive functionalized bioceramic surfaces. The laser-patterned samples were first characterized using several spectroscopic techniques before and after functionalization, and then tested in vitro with respect to their osteoconductivity using a human osteosarcoma cell line (SaOS-2). After in vitro testing, fluorescence microscopy was used to address the biological response and to estimate osteopontin and osteocalcin protein contents and distributions. The presence of bioglass greatly enhanced the biological response of both ceramic surfaces, but mainly induced production of inorganic apatite. On the other hand, the addition of minor fraction of Si3N4 into the bioglass-filled holes greatly enhanced bio-mineralization and stimulated the SaOS-2 cells to produce higher amounts of bone extracellular matrix (collagen and proteins), thus enhancing the osteopontin to osteocalcin ratio. It was also observed that the presence of a fraction of Si3N4 in the powder mixture filling the holes bestowed more uniform cell colonization on the otherwise bioinert ZTA surface.

Comparison of polyetheretherketone versus silicon nitride intervertebral spinal spacers in a caprine model

Polyetheretherketone (PEEK) is commonly used as a spinal spacer for intervertebral fusion surgery. Unfortunately, PEEK is bioinert and does not effectively osseointegrate into living bone. In contrast, comparable spacers made of silicon nitride (Si₃ N₄ ) possess a surface nanostructure and chemistry that encourage appositional bone healing. This observational study was designed to compare the outcomes of these two biomaterials when implanted as spacers in an adult caprine model. Lumbar interbody fusion surgeries were performed at two adjacent levels in eight adult goats using implants of PEEK and Si₃ N₄ . At six-months after surgery, the operative and adjacent spinal segments were extracted and measured for bone fusion, bone volume, bone-implant contact (BIC) and soft-tissue implant contact (SIC) ratios, and biodynamic stability. The null hypothesis was that no differences in these parameters would be apparent between the two groups. Fusion was observed in seven of eight implants in each group with greater bone formation in the Si₃ N₄ group (52.6%) versus PEEK (27.9%; p = 0.2). There were no significant differences in BIC ratios between PEEK and Si₃ N₄ , and the biodynamic stability of the two groups was also comparable. The results suggest that Si₃ N₄ spacers are not inferior to PEEK and they may be more effective in promoting arthrodesis. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 00B: 000-000, 2018. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 688-699, 2019.

A single center retrospective clinical evaluation of anterior cervical discectomy and fusion comparing allograft spacers to silicon nitride cages

BACKGROUND

Iliac crest autograft or allograft spacers have been traditionally utilized in anterior cervical discectomy and fusion (ACDF) to provide vertebral stabilization and enhanced osteogenesis. However, abiotic cages have largely replaced these allogenic sources due to host-site morbidities and disease transmission risks, respectively. Although devices made of polyetheretherketone (PEEK) or titanium-alloys (Ti) have gained wide popularity, they lack osteoinductive or conductive capabilities. In contrast, silicon nitride (Si3N4) is a relatively new implant material that also provides structural stability and yet purportedly offers osteopromotive and antimicrobial behavior. This study compared radiographic outcomes at ≥12 months of follow-up for osseous integration, fusion rate, time to fusion, and subsidence in ACDF patients with differing intervertebral spacers.

METHODS

Fifty-eight ACDF patients (108 segments) implanted with Si3N4 cages were compared to thirty-four similar ACDF patients (61 segments) implanted with fibular allograft spacers. Lateral radiographs (normal, flexion, and extension) were obtained at 3, 6, 12, and 24 months to assess osseous integration, the presence of bridging bone, the absence of peri-implant radiolucencies, subsidence, and fusion using both interspinous distance (ISD) and Cobb angle methods.

RESULTS

In patients with ≥12 months of follow-up, fusion for the allograft spacers and Si3N4 cages was 86.84% and 96.83%, respectively (ISD method, P=0.10), and 67.65% and 84.13%, respectively (Cobb angle method P=0.07), while osseointegration was 76.32% and 93.65%, respectively (P=0.02). The time to fusion significantly favored the Si3N4 cages (4.08 vs. 8.64 months (ISD method, P=0.01), and 6.76 vs. 11.74 months (Cobb angle method, P=0.04). The assessed time for full osseointegration was 7.83 and 19.24 months for Si3N4 and allograft, respectively (P=0.00). Average subsidence at 1-year follow-up was 0.51 and 2.71 mm for the Si3N4 and allograft cohorts, respectively (P=0.00).

CONCLUSIONS

In comparison to fibular allograft spacers, Si3N4 cages showed earlier osseointegration and fusion, higher fusion rates, and less subsidence.

In vitroantibacterial activity of oxide and non-oxide bioceramics for arthroplastic devices: II. Fourier transform infrared spectroscopy

The metabolic response of Gram-positiveStaphylococcus epidermidisbacteria to bioceramic substrates was probed by Fourier transform infrared spectroscopy.

Human osteoblasts grow transitional Si/N apatite in quickly osteointegrated Si3N4 cervical insert

Silicon nitride (Si₃N₄) ceramics possesses surface chemistry that accelerates bone repair, as previously established by in vitro experiments using both osteosarcoma and mesenchymal cells. The release of silicic acid and nitrogen compounds from the surface Si₃N₄ enhanced in vitro cellular activity. The results of this study demonstrate for the first time that the osseointegration behavior previously observed is operative with a peculiar chemistry within the human milieu. Si and N elements stimulated progenitor cell differentiation and osteoblastic activity, which ultimately resulted in accelerated bone ingrowth. At the molecular scale, insight into the effect of silicon and nitrogen ions released from the Si₃N₄ surface was obtained through combined histomorphometric analyses, Raman, Fourier-transform-infrared, and X-ray photoelectron spectroscopies. Identical analyses conducted on a polyetheretherketone (PEEK) spinal explant showed no chemical changes and a lower propensity for osteogenic activity. Silicon and nitrogen are key elements in stimulating cells to generate bony apatite with crystallographic imperfections, leading to enhanced bioactivity of Si₃N₄ biomedical devices.

STATEMENT OF SIGNIFICANCE

This research studies osseointegration processes comparing results from explanted PEEK and Si₃N₄ spinal spacers. Data show that the formation of hydroxyapatite on silicon nitride bio-ceramic surfaces happens with a peculiar mechanism inside the human body. Silicon and nitrogen were incorporated inside the bony tissue structure allowing the developing of off-stoichiometric bony apatite and stimulating progenitor cell differentiation/osteoblastic activity. Silicon and nitrogen ions released from the Si₃N₄ surface were detected through combined histologic analyses, Raman microspectroscopy, Fourier-transform-infrared, and X-ray photoelectron spectroscopies.

Development of a SiYAlON glaze for improved osteoconductivity of implantable medical devices

The application of bioactive coatings onto orthopaedic appliances is commonly performed to compensate for the otherwise bioinert nature of medical devices and to improve their osseointegration. Calcium phosphates, hydroxyapatite (HAp), and bioglasses are commercially available for this purpose. Until recently, few other inorganic compounds have been identified with similar biofunctionality. However, silicon nitride (Si₃ N₄ ) has emerged as a new orthopaedic material whose unique surface chemistry also enhances osteoconductivity. Recent research has confirmed that its minority intergranular phase, consisting of silicon yttrium aluminum oxynitride (SiYAlON), is principally responsible for this improvement. As a result, it was hypothesized that SiYAlON itself might serve as an effective osteoconductive coating or glaze for medical devices. To test this hypothesis, a process inspired by traditional ceramic whiteware glazing was developed. A slurry containing ingredients similar to the intergranular SiYAlON composition was applied to a Si₃ N₄ surface, which was then subjected to a heat treatment to form a glaze. Various analytical tools were employed to assess its chemistry and morphology. It was found that the glaze was comprised predominately of Y₅ Si₃ O₁₂ N, a compound commonly referred to as N-apatite, which is isostructural to native HAp. Subsequent exposure of the glazed surface to acellular simulated body fluid led to increased deposition of biomimetic HAp-like crystals, while exposure to Saos-2 osteosarcoma cells in vitro resulted in greater HAp deposition relative to control samples. The observation that SiYAlON exhibits enhanced osteoconductivity portends its potential as a therapeutic aid in bone and tissue repair. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1084-1096, 2018.

Bioactive silicon nitride: A new therapeutic material for osteoarthropathy

While the reciprocity between bioceramics and living cells is complex, it is principally governed by the implant's surface chemistry. Consequently, a deeper understanding of the chemical interactions of bioceramics with living tissue could ultimately lead to new therapeutic strategies. However, the physical and chemical principles that govern these interactions remain unclear. The intricacies of this biological synergy are explored within this paper by examining the peculiar surface chemistry of a relatively new bioceramic, silicon nitride (Si3N4). Building upon prior research, this paper aims at obtaining new insights into the biological interactions between Si3N4 and living cells, as a consequence of the off-stoichiometric chemical nature of its surface at the nanometer scale. We show here yet unveiled details of surface chemistry and, based on these new data, formulate a model on how, ultimately, Si3N4 influences cellular signal transduction functions and differentiation mechanisms. In other words, we interpret its reciprocity with living cells in chemical terms. These new findings suggest that Si3N4 might provide unique new medicinal therapies and effective remedies for various bone or joint maladies and diseases.