Enhanced interfacial adhesion and osteogenesis for rapid "bone-like" biomineralization by PECVD-based silicon oxynitride overlays

SiONx Coating Regulates Mesenchymal Stem Cell Antioxidant Capacity via Nuclear Erythroid Factor 2 Activity under Toxic Oxidative Stress Conditions

Healing in compromised and complicated bone defects is often prolonged and delayed due to the lack of bioactivity of the fixation device, secondary infections, and associated oxidative stress. Here, we propose amorphous silicon oxynitride (SiONx) as a coating for the fixation devices to improve both bioactivity and bacteriostatic activity and reduce oxidative stress. We aimed to study the effect of increasing the N/O ratio in the SiONx to fine-tune the cellular activity and the antioxidant effect via the NRF2 pathway under oxidative stress conditions. The in vitro studies involved using human mesenchymal stem cells (MSCs) to examine the effect of SiONx coatings on osteogenesis with and without toxic oxidative stress. Additionally, bacterial growth on SiONx surfaces was studied using methicillin-resistant Staphylococcus aureus (MRSA) colonies. NRF2 siRNA transfection was performed on the hMSCs (NRF2-KD) to study the antioxidant response to silicon ions. The SiONx implant surfaces showed a >4-fold decrease in bacterial growth vs. bare titanium as a control. Increasing the N/O ratio in the SiONx implants increased the alkaline phosphatase activity >1.5 times, and the other osteogenic markers (osteocalcin, RUNX2, and Osterix) were increased >2-fold under normal conditions. Increasing the N/O ratio in SiONx enhanced the protective effects and improved cell viability against toxic oxidative stress conditions. There was a significant increase in osteocalcin activity compared to the uncoated group, along with increased antioxidant activity under oxidative stress conditions. In NRF2-KD cells, there was a stunted effect on the upregulation of antioxidant markers by silicon ions, indicating a role for NRF2. In conclusion, the SiONx coatings studied here displayed bacteriostatic properties. These materials promoted osteogenic markers under toxic oxidative stress conditions while also enhancing antioxidant NRF2 activity. These results indicate the potential of SiONx coatings to induce in vivo bone regeneration in a challenging oxidative stress environment.

Silicon Nitride Ceramics: Structure, Synthesis, Properties, and Biomedical Applications

Silicon nitride ceramics excel by superior mechanical, thermal, and chemical properties that render the material suitable for applications in several technologically challenging fields. In addition to high temperature, high stress applications have been implemented in aerospace gas turbines and internal combustion engines as well as in tools for metal manufacturing, forming, and machining. During the past few decades, extensive research has been performed to make silicon nitride suitable for use in a variety of biomedical applications. This contribution discusses the structure-property-application relations of silicon nitride. A comparison with traditional oxide-based ceramics confirms that the advantageous mechanical and biomedical properties of silicon nitride are based on a high proportion of covalent bonds. The present biomedical applications are reviewed here, which include intervertebral spacers, orthopedic and dental implants, antibacterial and antiviral applications, and photonic parts for medical diagnostics.

Revolutionizing bone regeneration: advanced biomaterials for healing compromised bone defects

In this review, we explore the application of novel biomaterial-based therapies specifically targeted towards craniofacial bone defects. The repair and regeneration of critical sized bone defects in the craniofacial region requires the use of bioactive materials to stabilize and expedite the healing process. However, the existing clinical approaches face challenges in effectively treating complex craniofacial bone defects, including issues such as oxidative stress, inflammation, and soft tissue loss. Given that a significant portion of individuals affected by traumatic bone defects in the craniofacial area belong to the aging population, there is an urgent need for innovative biomaterials to address the declining rate of new bone formation associated with age-related changes in the skeletal system. This article emphasizes the importance of semiconductor industry-derived materials as a potential solution to combat oxidative stress and address the challenges associated with aging bone. Furthermore, we discuss various material and autologous treatment approaches, as well as in vitro and in vivo models used to investigate new therapeutic strategies in the context of craniofacial bone repair. By focusing on these aspects, we aim to shed light on the potential of advanced biomaterials to overcome the limitations of current treatments and pave the way for more effective and efficient therapeutic interventions for craniofacial bone defects.

A facile way to construct Sr-doped apatite coating on the surface of 3D printed scaffolds to improve osteogenic effect

Bone-like apatite coating fabricated by biomineralization process is a facile way for surface modification of porous scaffolds to improve interfacial behaviors and thus facilitate cell attachment, proliferation, and differentiation for bone tissue engineering. In this study, a Sr-containing calcium phosphate solution was made and used to construct a thick layer of Sr-doped bone-like apatite on the surface of 3D printed scaffolds via biomineralization process. Importantly, Sr-doped bone-like apatite could form and fully cover the 3D printed scaffolds surface in hours. The characterization results indicated that Sr2+ ions successfully replaced Ca2+ ions in bone-like apatite and the molar ratio of Sr/(Ca+Sr) was up to 8.2%. Furthermore, the Sr-doped apatite coating increased the compressive strength and Young’s modulus of composite scaffolds. The compatibility and bioactivity of mineralized scaffolds were evaluated by cell attachment, proliferation, and differentiation of MC3T3-E1 cells. It was found that Sr-doped apatite coating could gradually release Sr2+ ions and further promote cell attachment, proliferation rate, and the expression of alkaline phosphatase activity and osteogenic related genes, such as collagen type I (Col I), Runt-related transcription factor 2 (Runx-2), osteopontin, and osterix. Therefore, the Sr-doped apatite coating fabricated by this facile and rapid biomineralization process offers a new strategy to modify 3D printed porous scaffolds with significantly improved mechanical and biological properties for bone tissue engineering applications.

Interfacial adhesion and surface bioactivity of anodized titanium modified with SiON and SiONP surface coatings

Titanium (Ti) surface modification via coating technologies (plasma spraying, electron-beam deposition) has been used to enhance bone-implant bonding by increasing the rate of hydroxyapatite (HA) formation, a property known as bioactivity. Regardless the enhancement in the surface activity, the high fabrication-temperature (> 600 °C) reduces coating-implant adhesion due to thermal expansion mismatch and reduces bioactivity due to increased crystallinity in the coating. Thus, amorphous surface coatings with strong Ti-substrate adhesion that can be fabricated at relatively low temperatures are crucially needed for enhanced osseointegration. Therefore, this study aimed to enhance the Ti surface bioactivity via strongly adherent bioactive thin film coatings deposited by low temperature (< 400 °C) plasma enhanced chemical vapor deposition technique on nanopore anodized-Ti (A-Ti) surface. Two groups of coating (silicon oxynitride (SiON) and silicon oxynitrophosphide (SiONP)) were deposited on anodized Ti and tested for interfacial adhesion and surface bioactivity. TEM and XPS were used to investigate the interfacial composition while interfacial adhesion was tested using nano-indentation tests which indicated a strong interfacial adhesion between the coatings and the A-Ti substrate. Surface bioactivity of the modified Ti was tested by comprehensive surface characterization (i.e., chemical composition, surface energy, morphology, and mechanical properties) and apatite formation on each surface. SiONP coating significantly enhanced the Ti surface bioactivity that presented the highest surface coverage of carbonated hydroxyapatite (HCA, ~ 40%) with a Ca/P ratio (~ 1.65) close to the stoichiometric hydroxyapatite (~ 1.67) found in bone biomineral. The HCA structure and morphology were confirmed by HR-TEM/SAED, XRD, FT-IR, and HR-SEM/EDX. MSCs in-vitro studies indicated preferable cells adhesion and proliferation on the modified surfaces without any cytotoxic effects. This study concluded that the improved surface bioactivity of Ti-SiON and Ti-SiONP coatings suggests their potential use as strongly adherent bioactive surface coatings for Ti implants.

Bioprinting of Stem Cells in Multimaterial Scaffolds and Their Applications in Bone Tissue Engineering

Bioprinting stem cells into three-dimensional (3D) scaffolds has emerged as a new avenue for regenerative medicine, bone tissue engineering, and biosensor manufacturing in recent years. Mesenchymal stem cells, such as adipose-derived and bone-marrow-derived stem cells, are capable of multipotent differentiation in a 3D culture. The use of different printing methods results in varying effects on the bioprinted stem cells with the appearance of no general adverse effects. Specifically, extrusion, inkjet, and laser-assisted bioprinting are three methods that impact stem cell viability, proliferation, and differentiation potential. Each printing method confers advantages and disadvantages that directly influence cellular behavior. Additionally, the acquisition of 3D bioprinters has become more prominent with innovative technology and affordability. With accessible technology, custom 3D bioprinters with capabilities to print high-performance bioinks are used for biosensor fabrication. Such 3D printed biosensors are used to control conductivity and electrical transmission in physiological environments. Once printed, the scaffolds containing the aforementioned stem cells have a significant impact on cellular behavior and differentiation. Natural polymer hydrogels and natural composites can impact osteogenic differentiation with some inducing chondrogenesis. Further studies have shown enhanced osteogenesis using cell-laden scaffolds in vivo. Furthermore, selective use of biomaterials can directly influence cell fate and the quantity of osteogenesis. This review evaluates the impact of extrusion, inkjet, and laser-assisted bioprinting on adipose-derived and bone-marrow-derived stem cells along with the effect of incorporating these stem cells into natural and composite biomaterials.

Silicon Oxynitrophosphide Nanoscale Coating Enhances Antioxidant Marker-Induced Angiogenesis During in vivo Cranial Bone-Defect Healing

Critical-sized bone defects are challenging to heal because of the sudden and large volume of lost bone. Fixative plates are often used to stabilize defects, yet oxidative stress and delayed angiogenesis are contributing factors to poor biocompatibility and delayed bone healing. This study tests the angiogenic and antioxidant properties of amorphous silicon oxynitrophosphide (SiONPx) nanoscale-coating material on endothelial cells to regenerate vascular tissue in vitro and in bone defects. in vitro studies evaluate the effect of silicon oxynitride (SiONx) and two different SiONPx compositions on human endothelial cells exposed to ROS (eg, hydrogen peroxide) that simulates oxidative stress conditions. in vivo studies using adult male Sprague Dawley rats (approximately 450 g) were performed to compare a bare plate, a SiONPx-coated implant plate, and a sham control group using a rat standard-sized calvarial defect. Results from this study showed that plates coated with SiONPx significantly reduced cell death, and enhanced vascular tubule formation and matrix deposition by upregulating angiogenic and antioxidant expression (eg, vascular endothelial growth factor A, angiopoetin-1, superoxide dismutase 1, nuclear factor erythroid 2-related factor 2, and catalase 1). Moreover, endothelial cell markers (CD31) showed a significant tubular structure in the SiONPx coating group compared with an empty and uncoated plate group. This reveals that atomic doping of phosphate into the nanoscale coating of SiONx produced markedly elevated levels of antioxidant and angiogenic markers that enhance vascular tissue regeneration. This study found that SiONPx or SiONx nanoscale-coated materials enhance antioxidant expression, angiogenic marker expression, and reduce ROS levels needed for accelerating vascular tissue regeneration. These results further suggest that SiONPx nanoscale coating could be a promising candidate for titanium plate for rapid and enhanced cranial bone-defect healing. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Human osteoblast-like SAOS-2 cells on submicron-scale fibers coated with nanocrystalline diamond films

A unique composite nanodiamond-based porous material with a hierarchically-organized submicron-nano-structure was constructed for potential bone tissue engineering. This material consisted of submicron fibers prepared by electrospinning of silicon oxide (SiO_x), which were oxygen-terminated (O-SiO_x) and were hermetically coated with nanocrystalline diamond (NCD) films. The NCD films were then terminated with hydrogen (H-NCD) or oxygen (O-NCD). The materials were tested as substrates for the adhesion, growth and osteogenic differentiation of human osteoblast-like Saos-2 cells. The number and the spreading area of the initially adhered cells, their growth rate during 7 days after seeding and the activity of alkaline phosphatase (ALP) were significantly higher on the NCD-coated samples than on the uncoated O-SiO_x samples. In addition, the concentration of type I collagen was significantly higher in the cells on the O-NCD-coated samples than on the bare O-SiO_x samples. The observed differences could be attributed to the tunable wettability of NCD and to the more appropriate surface morphology of the NCD-coated samples in contrast to the less stable, rapidly eroding bare SiO_x surface. The H-NCD coatings and the O-NCD coatings both promoted similar initial adhesion of Saos-2 cells, but the subsequent cell proliferation activity was higher on the O-NCD-coated samples. The concentration of beta-actin, vinculin, type I collagen and alkaline phosphatase (ALP), the ALP activity, and also the calcium deposition tended to be higher in the cells on the O-NCD-coated samples than on the H-NCD-coated samples, although these differences did not reach statistical significance. The improved cell performance on the O-NCD-coated samples could be attributed to higher wettability of these samples (water drop contact angle less than 10°), while the H-NCD-coated samples were hydrophobic (contact angle >70°). NCD-coated porous SiO_x meshes can therefore be considered as appropriate scaffolds for bone tissue engineering, particularly those with an O-terminated NCD coating.

A comparative study on silicon nitride, titanium and polyether ether ketone on mouse pre-osteoblast cells

The current study provides more insights about the surface bioactivity of the silicon nitride (Si₃N₄) as a potential candidate for bone regeneration in craniofacial and orthopaedic applications compared with conventional implantation materials. Current skeletal reconstructive materials such as titanium and polyether ether ketone (PEEK) are limited by poor long-term stability, biocompatibility and prolonged healing. Si₃N₄ is an FDA-approved material for an intervertebral spacer in spinal fusion applications. It is biocompatible and has antimicrobial properties. Here, we hypothesize that Si₃N₄ was found to be an osteoconductive material and conducts the growth, differentiation of MC3T3-E1 cells for extracellular matrix deposition, mineralization and eventual bone regeneration for craniofacial and orthopaedic applications. MC3T3-E1 cells were used to study the osteoblastic differentiation and mineralization on sterile samples of Si₃N₄, titanium alloy and PEEK. The samples were then analysed for extracellular matrix deposition and mineralization by FTIR, Raman spectroscopy, SEM, EDX, Alizarin Red, qRT-PCR and ELISA. The in vitro study indicates the formation of collagen fibres and mineral deposition on all three sample surfaces. There was more profound and faster ECM deposition and mineralization on Si₃N₄ surface as compared to titanium and PEEK. The FTIR and Raman spectroscopy show formation of collagen and mineral deposition at 30 days for Si₃N₄ and titanium and not PEEK. The peaks shown by Raman for Si₃N₄ resemble closely to natural bone. Results also indicate the upregulation of osteogenic transcription factors such as RUNX2, SP7, collagen type I and osteocalcin. The authors concluded that Si₃N₄ rapidly conducts mineralized tissue formation via extracellular matrix deposition and biomarker expression in mouse calvarial pre-osteoblast cells. Thus, this study confirms that the bioactive Si₃N₄ could be a potential material for craniofacial and orthopaedic applications leading to rapid bone regeneration that resemble the natural bone structure.

Ionic Silicon Protects Oxidative Damage and Promotes Skeletal Muscle Cell Regeneration

Volumetric muscle loss injuries overwhelm the endogenous regenerative capacity of skeletal muscle, and the associated oxidative damage can delay regeneration and prolong recovery. This study aimed to investigate the effect of silicon-ions on C2C12 skeletal muscle cells under normal and excessive oxidative stress conditions to gain insights into its role on myogenesis during the early stages of muscle regeneration. In vitro studies indicated that 0.1 mM Si-ions into cell culture media significantly increased cell viability, proliferation, migration, and myotube formation compared to control. Additionally, MyoG, MyoD, Neurturin, and GABA expression were significantly increased with addition of 0.1, 0.5, and 1.0 mM of Si-ion for 1 and 5 days of C2C12 myoblast differentiation. Furthermore, 0.1-2.0 mM Si-ions attenuated the toxic effects of H2O2 within 24 h resulting in increased cell viability and differentiation. Addition of 1.0 mM of Si-ions significantly aid cell recovery and protected from the toxic effect of 0.4 mM H2O2 on cell migration. These results suggest that ionic silicon may have a potential effect in unfavorable situations where reactive oxygen species is predominant affecting cell viability, proliferation, migration, and differentiation. Furthermore, this study provides a guide for designing Si-containing biomaterials with desirable Si-ion release for skeletal muscle regeneration.

Amorphous Silicon Oxynitrophosphide-Coated Implants Boost Angiogenic Activity of Endothelial Cells

Lack of osteointegration is a major cause of aseptic loosening and failure of implants used in bone replacement. Implants coated with angiogenic biomaterials can improve osteointegration and potentially reduce these complications. Silicon- and phosphorus-based materials have been shown to upregulate expression of angiogenic factors and improve endothelial cell functions. In the present study, we hypothesize that implants coated with amorphous silica-based coatings in the form of silicon oxynitrophosphide (SiONP) by using plasma-enhanced chemical vapor deposition (PECVD) technique could enhance human umbilical vein endothelial cell angiogenic properties in vitro. The tested groups were: glass coverslip (GCS), tissue culture plate, SiON, SiONP1 (O: 7.3 at %), and SiONP2 (O: 14.2 at %) implants. The SiONP2 composition demonstrated 3.5-fold more fibronectin deposition than the GCS (p < 0.001). The SiONP2 group also presented a significant improvement in the capillary tubule length and thickness compared with the other groups (p < 0.01). At 24 h, we observed at least a twofold upregulation of vascular endothelial growth factor A, hypoxia-inducible factor-1α, angiopoietin-1, and nesprin-2, more evident in the SiONP1 and SiONP2 groups. In conclusion, the studied amorphous silica-coated implants, especially the SiONP2 composition, could enhance the endothelial cell angiogenic properties in vitro and may induce faster osteointegration and healing. Impact Statement In this study, we report for the first time the significant enhancement of human umbilical vein endothelial cell angiogenic properties (in vitro) by the amorphous silica-based coatings in the form of silicon oxynitrophosphide (SiONP). The SiONP2 demonstrated 3.5-fold more fibronectin deposition than the glass coverslip and presented a significant improvement in the capillary tubule length and thickness. At 24 h, SiONP reported twofold upregulation of vascular endothelial growth factor A, hypoxia-inducible factor-1α, angiopoietin-1, and nesprin-2. The studied amorphous silica-coated implants enhance the endothelial cell angiogenic properties in vitro and may induce faster osteointegration and healing.

Rapid Regeneration of Vascularized Bone by Nanofabricated Amorphous Silicon Oxynitrophosphide (SiONP) Overlays

Fracture healing is a complex biological process. Severe bone loss and ischemia from traumatic fractures lead to inflammation and accumulation of damaging reactive oxygen species (ROS). Fixative devices that not only provide mechanical support but also stimulate antioxidants such as superoxide dismutase (SOD1) and influence signaling pathways for extracellular matrix (ECM) mineralization, are critical for normal healing of such fractures. In this study, we report a novel biomaterial, silicon oxynitrophosphide (SiONP) that provides sustained release of ionic silicon (Si⁺⁴) and phosphorous (P) over few weeks under physiological conditions. Anti-oxidant role of Si⁺⁴ and augmented ECM mineralization by P ions lead to enhanced osteogenesis coupled with quick revascularization for rapid bone regeneration. Plasma enhanced chemical vapor deposition (PECVD) provided a conformal, well adherent and highly reproducible surface chemistry overlaid onto nanofabricated bioinspired surfaces. The Nitrogen to P and O content ratio was observed to change the dissolution rate and the release kinetics of the overlaid film. The SiONP films with optimal release kinetics promoted anti-oxidant expression via enhanced SOD1, which downstream upregulated other osteogenic markers with MC3T3-E1 cells. These surfaces also promoted angiogenesis evident by formation of thicker tubules by Human umbilical vein endothelial cells (HUVEC). In-vivo evaluation using a rat critical-sized calvarial defect model showed rapid bone-regeneration for these nanofabricated biomaterials as compared to control groups, and opens new horizon for future clinical trials of new antioxidant materials on biomedical devices that can reduce healing time, lower medical care cost, and increase the quality of newly formed bone in critical size defects.

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.

Construction, characterization, and growth mechanism of high-density jellyfish-like GaN/SiOxNy nanomaterials on p-Si substrate by Au-assisted chemical vapor deposition approach

High-density GaN/SiO_xN_y jellyfish-like nanomaterials are synthesized on Au-coated p-type Si substrates by a chemical vapor deposition approach.

Ionic silicon improves endothelial cells' survival under toxic oxidative stress by overexpressing angiogenic markers and antioxidant enzymes

Oxidative stress, induced by harmful levels of reactive oxygen species, is a common occurrence that impairs proper bone defect vascular healing through the impairment of endothelial cell function. Ionic silicon released from silica-based biomaterials, can upregulate hypoxia-inducible factor-1α (HIF-1α). Yet it is unclear whether ionic Si can restore endothelial cell function under oxidative stress conditions. Therefore, we hypothesized that ionic silicon can help improve human umbilical vein endothelial cells' (HUVECs') survival under toxic oxidative stress. In this study, we evaluated the ionic jsilicon effect on HUVECs viability, proliferation, migration, gene expression, and capillary tube formation under normal conditions and under harmful hydrogen peroxide levels. We demonstrated that 0.5-mM Si4+ significantly enhanced angiogenesis in HUVECs under normal condition (p < 0.05). HUVECs exposed to 0.5-mM Si4+ presented a morphological change, even without the bed of Matrigel, and formed significantly more tube-like structures than the control (p < 0.001). In addition, 0.5-mM Si4+ enhanced cell viability in HUVECs under harmful H2 O2 levels. HIF-1α, vascular endothelial growth factor-A, and vascular endothelial growth factor receptor-2 were overexpressed more than twofold in silicon-treated HUVECs, under normal and toxic H2 O2 conditions. Moreover, the HUVECs were treated with 0.5-mM Si4+ overexpressed superoxide dismutase-1 (SOD-1), catalase-1 (Cat-1), and nitric oxide synthase-3 (NOS3) under normal and oxidative stress environment (p < 0.01). A computational model was used for explaining the antioxidant effect of Si4+ in endothelial cells and human periosteum cells by SOD-1 enhancement. In conclusion, we demonstrated that 0.5-mM Si4+ can recover the HUVECs' viability under oxidative stress conditions by reducing cell death and upregulating expression of angiogenic and antioxidant factors.

Role of Hydrogen and Nitrogen on the Surface Chemical Structure of Bioactive Amorphous Silicon Oxynitride Films

Silicon oxynitride (Si-O-N) is a new biomaterial in which its O/N ratio is tunable for variable Si release and its subsequent endocytotic incorporation into native hydroxyapatite for enhanced bone healing. However, the effect of nitrogen and hydrogen bonding on the formation and structure of hydroxyapatite is unclear. This study aims to uncover the roles of H and N in tuning Si-O-N surface bioactivity for hydroxyapatite formation. Conformal Si-O-N films were fabricated by plasma-enhanced chemical vapor deposition (PECVD) onto Ti/Si substrates. Fourier transform infrared spectroscopy (FTIR) and Rutherford backscattering spectrometry (RBS) analysis indicated increased Si-H and N-H bonding with increased N content. Surface energy decreased with increased N content. X-ray absorbance near edge structure (XANES) analysis showed tetrahedral coordination in O-rich films and trigonal coordination in N-rich films. O-rich films exhibited a 1:1 ratio of 2p3/2 to 2p1/2 electron absorbance, while this ratio was 1.73:1 for N-rich films. Both Si and N had a reduced partial charge for both O- and N-rich films, whereas O maintained its partial charge for either film. O-rich films were found to exhibit random bonding SizOxNy, while N-rich films exhibited random mixing: [Si-Si]-[Si-O]-[Si-N]. Thus, hydrogen bonding limits random nitrogen bonding in Si-O-N films via surface Si-H and N-H bonding. Moreover, increased nitrogen content reduces the partial charge of constituent elements and changes the bonding structure from random bonding to random mixing.

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.

SiO2/TiO2 Nanocomposite Films on Polystyrene for Light-Induced Cell Detachment Application

Light-induced cell detachment shows much potential in in vitro cell culture and calls for high-performance light-responsive films. In this study, a smooth and dense SiO₂/TiO₂ nanocomposite thin film with thickness of around 250 nm was first fabricated on H₂O₂ treated polystyrene (PS) substrate via a low-temperature sol-gel method. It was observed that the film could well-adhere on the PS surface and the bonding strength became increasingly high with the increase of SiO₂ content. The peeling strength and shear strength reached 3.05 and 30.02 MPa, respectively. It was observed the surface of the film could transform into superhydrophilic upon 20 min illumination of ultraviolet with a wavelength of 365 nm (UV365). In cell culture, cells, i.e., NIH3T3 and MC3T3-E1 cells, cultured on SiO₂/TiO₂ nanocomposite film were easily detached after 10 min of UV365 illumination; the detachment rates reached 90.8% and 88.6%, respectively. Correspondingly, continuous cell sheets with good viability were also easily obtained through the same way. The present work shows that SiO₂/TiO₂ nanocomposite thin film could be easily prepared on polymeric surface at low temperature. The corresponding film exhibits excellent biocompatibility, high bonding strength, and good light responses. It could be a good candidate for the surface of cell culture utensils with light-induced cell detachment property.

Tuning the fluorescence intensity and stability of porous silicon nanowires via mild thermal oxidation

Porous Si nanowires show anomalous luminescence quenching and improved sensing stability upon mild thermal oxidation.

Amorphous Silica: A New Antioxidant Role for Rapid Critical-Sized Bone Defect Healing

Traumatic fractures cause structurally unstable sites due to severe bone loss. Such fractures generate a high yield of reactive oxygen species (ROS) that can lead to oxidative stress. Excessive and prolonged ROS activity impedes osteoblast differentiation and instigates long healing times. Stimulation of antioxidants such as superoxide dismutase (SOD1), are crucial to reduce ROS, stimulate osteogenesis, and strengthen collagen and mineral formation. Yet, no current fixative devices have shown an ability to enhance collagen matrix formation through antioxidant expression. This study reports plasma-enhanced chemical vapor deposition based amorphous silicon oxynitride (Si(ON)x) as a potential new fracture healing biomaterial that adheres well to the implant surface, releases Si(+4) to enhance osteogenesis, and forms a surface hydroxyapatite for collagen mineral attachment. These materials provide a sustained release of Si(+4) in physiological environment for extended times. The dissolution rate partially depends on the film chemistry and can be controlled by varying O/N ratio. The presence of Si(+4) enhances SOD1, which stimulates other osteogenic markers downstream and leads to rapid mineral formation. In vivo testing using a rat critical-sized calvarial defect model shows a more rapid bone-regeneration for these biomaterials as compared to control groups, that implies the clinical significance of the presented biomaterial.

Plasma-Enhanced Chemical Vapor Deposition (PE-CVD) yields better Hydrolytical Stability of Biocompatible SiOx Thin Films on Implant Alumina Ceramics compared to Rapid Thermal Evaporation Physical Vapor Deposition (PVD)

Densely sintered aluminum oxide (α-Al2O3) is chemically and biologically inert. To improve the interaction with biomolecules and cells, its surface has to be modified prior to use in biomedical applications. In this study, we compared two deposition techniques for adhesion promoting SiOx films to facilitate the coupling of stable organosilane monolayers on monolithic α-alumina; physical vapor deposition (PVD) by thermal evaporation and plasma enhanced chemical vapor deposition (PE-CVD). We also investigated the influence of etching on the formation of silanol surface groups using hydrogen peroxide and sulfuric acid solutions. The film characteristics, that is, surface morphology and surface chemistry, as well as the film stability and its adhesion properties under accelerated aging conditions were characterized by means of X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and tensile strength tests. Differences in surface functionalization were investigated via two model organosilanes as well as the cell-cytotoxicity and viability on murine fibroblasts and human mesenchymal stromal cells (hMSC). We found that both SiOx interfaces did not affect the cell viability of both cell types. No significant differences between both films with regard to their interfacial tensile strength were detected, although failure mode analyses revealed a higher interfacial stability of the PE-CVD films compared to the PVD films. Twenty-eight day exposure to simulated body fluid (SBF) at 37 °C revealed a partial delamination of the thermally deposited PVD films whereas the PE-CVD films stayed largely intact. SiOx layers deposited by both PVD and PE-CVD may thus serve as viable adhesion-promoters for subsequent organosilane coupling agent binding to α-alumina. However, PE-CVD appears to be favorable for long-term direct film exposure to aqueous solutions.