Oxygen Inhibition Research Articles

Denitrification effect and strengthening mechanism of SAD/A system at low temperature by gel-immobilization technology

Sulfur autotrophic denitrification coupled anaerobic ammonia oxidation (SAD/A) has several advantages over other denitrification processes; for example, it does not consume the organic carbon source, has low operation costs, and produces less excess sludge; however, it has certain disadvantages as well, such as a long start-up time, easy loss of bacteria, and low microbial activity at low temperature. The use of microbial immobilization technology to embed functional bacteria provides a feasible method of resolving the above problems. In this study polyvinyl alcohol‑sodium alginate was used to prepare a composite carrier for fixing anaerobic ammonia oxidizing bacteria (AAOB) and sulfur oxidizing bacteria (SOB), and the structure and morphology of the encapsulated bodies were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. Subsequently, the nitrogen removal performance of the immobilized microbial carriers in the gradient cooling process (30 °C to 10 °C) was determined, and the corresponding mechanism was discussed. The results showed that the nitrate-removal efficiencies observed with granular sludge and gel embedding were at 10 °C 21.44 % and 14.31 % lower, than those at 30 °C, respectively, whereas the ammonia-removal efficiency decreased by up to approximately three-fold. The main mechanism was the ‘insulation’ provided by the external gel composed of PVA and SA for the internal sludge and subsequent improvement of its low temperature resistance, while protecting AAOB and SOB from oxygen inhibition, which is conducive to enriching denitrifying bacteria. In addition, the gel does not change the internal sludge species, it can shift the dominance of specific microorganisms and improve the removal efficiency of nitrogen. In summary, the immobilization of AAOB and SOB by the gel can achieve effectively mitigate nitrogen pollution in low temperature environments, thus indicating that the SAD/A process has broad engineering application prospects.

Eliminating the oxygen inhibition in the redox free radical polymerization of alicyclic polyurethane acrylate coatings: A study of the beneficial effect of paraffin wax

Elimination of oxygen inhibition is still a challenge in the preparation of copolymers for steel bridge deck coatings industry by redox free radical polymerization (RFRP) technique in air and at room temperature. Herein, solvent-free paraffin wax composite alicyclic polyurethane acrylate (PW/APUA) coatings cured in air and at room temperature were developed by RFRP technique, and the efficacy and mechanism of oxygen inhibition elimination by paraffin wax during curing was investigated. The results of tensile, contact angle (CA) and water absorption (WA) tests showed that compared with pure APUA coating, the PW/APUA coatings exhibited superior mechanical properties and water resistance at room temperature, with tensile strength, elongation at break and CA up to 25.1 MPa, 204.23 % and 112.5°, respectively, and WA down to 0.008 %. Thermogravimetric analysis (TGA) suggested that the thermal initial decomposition of the coating increased from 180 °C to 200 °C after incorporation of paraffin wax. Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) indicated that two glass transition temperatures of PW/APUA coating with 0.3 % paraffin wax were −88.4 °C and 92.6 °C, respectively. Moreover, microstructural characterization of PW/APUA coatings revealed that paraffin wax eliminated oxygen inhibition by forming a dense barrier layer on the air contact surface of the APUA coating. Furthermore, the paraffin wax molecules co-crystallized with the non-polar groups of acrylates, but did not form new chemical bonds. This study provides a distinct and general strategy for eliminating oxygen inhibition of RFRP technology in air.

Synthesis of UV rapid curing silicone coatings via photoinitiated thiol-ene click polymerization for pressure-sensitive adhesive

UV-curable silicone pressure-sensitive adhesive (SPSA) is composed of silicone rubber and silicone resin. Generally, the CC double bond in acryloyloxy group provides a photocurable group for SPSA. However, oxygen inhibition of acryloyloxy group block the degree of cure and CC double bond conversion of SPSA during the photopolymerization. Therefore, efficient photocurable groups for UV curing SPSA is particularly important to be developed. Thiol-ene click polymerizations have been widely used in photocrosslinked polymers due to the rapid efficiency of reactions. In this study, sulfhydryl functionalized silicone resin (SFSR) and methacrylate functionalized amino silicone rubber (MFASR) were synthesized to prepare a SPSA via photoinitiated thiol-ene click polymerization. The double bond in MSASR and sulfhydryl in SFSR were characterized by FT-IR spectroscopy and 1H NMR spectroscopy. The double bond conversion of SPSA was calculated after polymerization. The cohesion of SPSA was improved by SFSR, while the crosslinking degree was improved by thiol-ene. The loop tack of SPSA with 50 wt% SFSR was 9.01 N, and the 180° peel strength was 11.37 N/25 mm. The SPSA maintained good bonding adhesion to steel at various temperature.

Relationship between oxygen partial pressure and inhibition of cell aggregation of human adipose tissue-derived mesenchymal stem cells stored in cell preservation solutions

IntroductionThis study investigated the storage conditions under which cell aggregation occurs and the conditions that inhibit cell aggregation when human adipose tissue-derived mesenchymal stem cells (hADSCs) are stored in lactated Ringer’s solution (LR) supplemented with 3% trehalose and 5% dextran 40 (LR-3T-5D). MethodsWe first examined the effects of storage temperature and time on the aggregation and viability of hADSCs stored in LR and LR-3T-5D. The cells were stored at 5 °C or 25 °C for various times up to 24 h. We then evaluated the effects of storage volume (250-2,000 μL), cell density (2.5-20 × 105 cells/mL), and nitrogen gas replacement on aggregation, oxygen partial pressure (pO2), and viability of hADSCs stored for 24 h at 25 °C in LR-3T-5D. ResultsWhen stored in LR-3T-5D, viability did not change under either condition compared with pre-storage, but the cell aggregation rate increased significantly with storage at 25 °C for 24 h (p<0.001). In LR, the aggregation rate did not change under either condition, but cell viability decreased significantly after 24 h at both 5 °C and 25 °C (p < 0.05). The cell aggregation rates and pO2 tended to decrease with increasing solution volume and cell density. Nitrogen gas replacement significantly decreased the cell aggregation rate and pO2 (p < 0.05). However, there were no differences in viability among cells stored under conditions of different storage volumes, densities, and nitrogen gas replacement. ConclusionsAggregation of cells after storage at 25 °C in LR-3T-5D may be suppressed by increasing the storage volume and cell density as well as by incorporating nitrogen replacement, which lowers the pO2 in the solution.

Correlation between Critical Energy, Penetration Depth, and Photopolymerization Kinetics in Aluminum–Phosphate–Silicate Hybrid Materials for Vat Photopolymerization

The photopolymerization of aluminum–phosphate–silicate resins obtained from the hybrid sol–gel route for Vat photopolymerization (VPP) process was investigated. The printing parameters derived from Jacob’s work curve model, critical energy (Ec) and penetration depth (Dp), were determined as a function of laser power and MPTMS (silicate) concentration for materials with stoichiometry Si(x)-(Al + P)(1–x), 0 ≤ x ≤ 0.7. The kinetics of photopolymerization was further explored using steady- and unsteady-state photo-DSC experiments. The oxygen inhibition and primary termination had similar contributions to the polymerization process for all compositions, while the propagation and bimolecular termination constants increased with MPTMS concentration. These experimental results were used to test the validity of the Ec ∝ kt1/2/kp and Dp ∝ ϵ relationship derived from a photochemical model for VPP assuming steady-state kinetics. Both Ec ∝ (kt1/2/kp) and Dp ∝ ϵ may be used to predict critical energy and penetration values for an arbitrary resin without calculating its work curve function, according to our study.

Oxygen tolerance and detoxification mechanisms of highly enriched planktonic anaerobic ammonium-oxidizing (anammox) bacteria

Oxygen is a key regulatory factor of anaerobic ammonium oxidation (anammox). Although the inhibitory effect of oxygen is evident, a wide range of oxygen sensitivities of anammox bacteria have been reported so far, which makes it difficult to model the marine nitrogen loss and design anammox-based technologies. Here, oxygen tolerance and detoxification mechanisms of four genera of anammox bacteria; one marine species (“Ca. Scalindua sp.”) and four freshwater anammox species (“Ca. Brocadia sinica”, “Ca. Brocadia sapporoensis”, “Ca. Jettenia caeni”, and “Ca. Kuenenia stuttgartiensis”) were determined and then related to the activities of anti-oxidative enzymes. Highly enriched planktonic anammox cells were exposed to various levels of oxygen, and oxygen inhibition kinetics (50% inhibitory concentration (IC50) and upper O2 limits (DOmax) of anammox activity) were quantitatively determined. A marine anammox species, “Ca. Scalindua sp.”, exhibited much higher oxygen tolerance capability (IC50 = 18.0 µM and DOmax = 51.6 µM) than freshwater species (IC50 = 2.7–4.2 µM and DOmax = 10.9–26.6 µM). The upper DO limit of “Ca. Scalindua sp.” was much higher than the values reported so far (~20 µM). Furthermore, the oxygen inhibition was reversible even after exposed to ambient air for 12–24 h. The comparative genome analysis confirmed that all anammox species commonly possess the genes considered to function for reduction of O2, superoxide anion (O2•-), and H2O2. However, the superoxide reductase (Sor)-peroxidase dependent detoxification system alone may not be sufficient for cell survival under microaerobic conditions. Despite the fact that anaerobes normally possess no or little superoxide dismutase (Sod) or catalase (Cat), only Scalindua exhibited high Sod activity of 22.6 ± 1.9 U/mg-protein with moderate Cat activity of 1.6 ± 0.7 U/mg-protein, which was consistent with the genome sequence analysis. This Sod-Cat dependent detoxification system could be responsible for the higher O2 tolerance of Scalindua than other freshwater anammox species lacking the Sod activity.

Preparation and properties of UV cation-initiated self-crosslinking acrylate pressure-sensitive adhesive without reactive diluent

The aim of this paper is to synthesize a UV-initiated self-crosslinking epoxy acrylate pressure-sensitive adhesive (PSA) without reactive diluents. The monomers butyl acrylate, 2-ethylhexyl acrylate, and glycidyl methacrylate (GMA) and functional monomers acrylic acid (AA) and hydroxyethyl methacrylate were used as raw materials. Dodecyl mercaptan was used as a chain-transfer agent, and benzoyl peroxide (BPO) was used as an initiator for free radical polymerization in the synthesis of an acrylate prepolymer containing epoxy groups. When a cationic UV initiator was added, the system showed the characteristics of a nonreactive diluent and emitted a faint odor. A self-crosslinking epoxy acrylate PSA was obtained by coating at room temperature and UV light initiation. The effects of AA and GMA dosages, photoinitiator dosage, and curing time on the product's properties were investigated. Viscosity was characterized with a rotary viscometer, whereas the structure, glass transition temperature, and thermal decomposition were characterized through Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis, respectively. Results showed that the PSAs containing 3.5 % AA, 12.5 % GMA, and 2 % photoinitiator 6976 and subjected to 40 s of curing time had the best overall performance, with a loop tack of 11.1 N/25 mm, 180° peel adhesion of 14.5 N/25 mm, dynamic shear strength of 9.2 N/12 mm × 12 mm, and good heat resistance at 80 °C for 4 h without adhesive loss after peeling. A novel self-crosslinking PSA glue was successfully prepared by introducing epoxy groups into the molecular chains of prepolymers and controlling the viscosity of the prepolymers with a chain transfer agent. These procedures effectively remediate the shortcomings of current acrylate PSA glue, which contain active diluents, produce irritating odor, and undergo oxygen inhibition polymerization, offering great prospects for industrial applications.

THE EFFECT OF GLYCERIN APPLICATION ON ROUGHNESS OF NANOHYBRID COMPOSITE RESIN IMMERSED IN ISOTONIC DRINK

ABSTRACTBackground: Composite resin is the most commonly used restorative material. One type of composite resin based on the filler material is a nanohybrid composite resin which has the advantage of good strength and smooth surface to produce good improvements in terms of durability and aesthetics. The roughness of the resin can be affected by drinks with low pHs, such as isotonic drink. Glycerin can reduce the roughness of the composite resin by acting as a barrier so that an oxygen inhibition layer (OIL) is not formed. Purpose: This study is to determine the effect of glycerin application on the roughness of nanohybrid composite resin immersed in an isotonic drink. Method: A total of 32 samples of nanohybrid composite resin used in this study were made with a diameter of 5 mm and a thickness of 2 mm. The nanohybrid composite resin samples were divided into group I without glycerin application and group II with glycerin application before the light curing process. Both groups were then immersed in an isotonic drink for 18 hours in an incubator. The research continued with roughness testing using a surface roughness tester. Result: There was a significant difference in the roughness of the nanohybrid composite resin immersed in an isotonic drink with and without glycerin application. This is indicated by the p-value &lt; 0.05 in the unpaired bivariate t-test, which means that there is a significant difference in the two sample groups. Conclusion: The application of glycerin can reduce the roughness of the nanohybrid composite resin immersed in isotonic drink. Keywords: Glycerin application, Nanohybrid composite resin, Roughness.

Mechanical Consequences of Oxygen Inhibition in Vat Polymerization

AbstractVat polymerization is a type of additive manufacturing that is used extensively to produce micro‐architected structures for mechanical applications, which brings the mechanical properties of photopolymerized resins into sharp focus. However, it is known that photopolymerization is sensitive to a number of factors, perhaps the most notorious of which is oxygen inhibition. Herein, the degree to which oxygen inhibition influences the macroscopic and microscopic properties of structures made using vat polymerization is explored. This work is motivated by an observation of lattices being &gt;4 times softer in the experiment than predicted by simulation, which is hypothesized to be due to the material at the surface being incompletely cured. This hypothesis is supported by four‐point bending tests in which flexural modulus is found to increase with beam thickness. Nanoindentation and bulk compression studies show that this surface softening is present for three distinct resins. Importantly, it is observed that structures post‐print cured in nitrogen are stiffer than those post‐print cured in air, however, regardless of the post‐print curing environment, printing samples in the presence of oxygen makes them softer than samples photocured in nitrogen. Collectively, these results show the outsized influence of oxygen inhibition on micro‐architected structures realized using vat polymerization.

Magnetically Actuable Complex‐Shaped Microgels for Spatio‐Temporal Flow Control

AbstractComplex‐shaped microgels are promising building blocks for soft metamaterials. Their active and remote orientational control provides significant potential in architecting them in time and space. This work describes the use of magnetically actuable microgels of complex shape for spatio‐temporal flow control and showcases the concept for microfluidic impellers. First, the fabrication of complex‐shaped magnetically actuable poly(ethylene glycol) diacrylate based microgels via stop‐flow lithography is presented. The microgels comprise a pre‐programmed magnetic moment set by pre‐aligned maghemite nanospindles during the fabrication step. This feature allows the microgels to be positioned in a static magnetic field and rotate under application of a rotating external field. The dependence of the magnetic field rotation rate and strength, maghemite content, and microgel shape on the magnetic response of the microgels is comprehensively quantified. Finally, the magnetic complex‐shaped microgels are integrated as actuable impellers in a microfluidic chip. The microgels are positioned in space by polymerizing them around fixed poly(dimethylsiloxane) (PDMS) pillars. Free rotation around the PDMS pillar is achieved due to the oxygen inhibition layer at the chip and pillar surface. The versatility of the fabrication methodology is showcased by the investigation of in‐chip mixing in a microfluidic device consisting of soft responsive impellers.

Thiol-Acrylate polyHIPEs via Facile Layer-by-Layer Photopolymerization.

A highly reactive thiol-ene high internal phase emulsion based on the monomers 1,6-hexanediol diacrylate and tris 2-(3-mercaptopropionyloxy)ethyl isocyanurate was developed for the purpose of light-driven additive manufacturing, resulting in highly porous customizable poly(high internal phase emulsion) materials. The formulation was specifically designed to facilitate short irradiation times and low amounts of photoinitiator. Furthermore, the developed emulsion does not rely on employing harmful solvents to make scale-up and industrial applications feasible. The selected thiol was added to the printing formulation as a chain-transfer agent, decreasing the brittleness of the acrylate-based system and potential of oxygen inhibition. The thickness of the printed layers lay <50 μm, and the average pore size of all samples was <5 μm.

The future of visible light photoinitiators of polymerization for photocrosslinking applications

Photopolymerization under visible light is an active research field whose intense research activity is supported by the recent advances in 3D and 4D printing. Within this perspective article, emerging trends in visible light photopolymerization for photocrosslinking applications will be presented. Notably, the performant multicomponent photoinitiating systems extensively used in the past are now progressively discarded in favor of mono-component systems easier to handle. The reduction of side-products formed during polymerization, the reduction of oxygen inhibition, the formation of dyes by intermolecular charge transfer interactions or the development of more ecological polymerization processes using sunlight as the irradiation source have recently been the focus of intense research efforts. Furthermore, emerging trends in processes favoring the elongation of the polymer lifetime such as self-healing will be presented and this perspective article aims at presenting the most recent breakthroughs in these attempts. To end, the future vision of visible light photopolymerization for photocrosslinking applications will be discussed.

Study on Press Formability and Properties of UV-Curable Polyurethane Acrylate Coatings with Different Reactive Diluents.

UV-curable coatings have numerous advantages, including environmental sustainability due to 100% solid content, economic feasibility attributable to relatively fast curing time, decent appearance, mechanical properties, chemical resistance, and abrasion resistance. However, UV-curable polyurethane acrylate coatings on metals apparently restrict their engineering applications owing to low mechanical properties and poor thermal stability, giving UV-curable coatings less flexibility and formability. In this study, we evaluated the property change of films according to the type of reactive diluents that lowers the viscosity of UV-curing coatings for pre-coated metal and has a substantial effect on the curing rate, viscoelastic properties, adhesive properties, and flexibility of the film. Moreover, there are many changes in the properties of coatings according to varied curing conditions in order to evaluate the oxygen inhibition phenomenon during the curing process in the atmosphere. In particular, to evaluate the effect of reactive diluents on forming formability, which is the most crucial property for the pre-coated metal, this study used conventional formability tests, such as t-bending or the Erichsen test. Moreover, a cross-die cup drawing mold with a similar form as failure and Safety Zone was utilized in order to obtain clearer information on its actual formability. The analysis on the effect of failure and safety zone on the material used in press forming was conducted by assessing limit punch height and forming a limit diagram of the manufactured film according to varied reactive diluents.

Effects of reducing, stabilizing, and antibiotic agents on “Candidatus Kuenenia stuttgartiensis”

Anaerobic ammon ium oxidizing (anammox) bacteria oxidize ammonium and reduce nitrite, producing N2, and could play a major role in energy-optimized wastewater treatment. However, sensitivity to various environmental conditions and slow growth currently hinder their wide application. Here, we attempted to determine online the effect of environmental stresses on anammox bacteria by using an overnight batch activity test with whole cells, in which anammox activity was calculated by quantifying N2 production via headspace-pressure monitoring. A planktonic mixed culture dominated by “Candidatus Kuenenia stuttgartiensis” strain CSTR1 was cultivated in a 30-L semi-continuous stirring tank reactor. In overnight resting-cell anammox activity tests, oxygen caused strong inhibition of anammox activity, which was reversed by sodium sulfite (30 µM). The tested antibiotics sulfamethoxazole, kanamycin, and ciprofloxacin elicited their effect on a dose-dependent manner; however, strain CSTR1 was highly resistant to sulfamethoxazole. Anammox activity was improved by activated carbon and Fe2O3. Protein expression analysis from resting cells after anammox activity stimulation revealed that NapC/NirT family cytochrome c (KsCSTR_12840), hydrazine synthase, hydrazine dehydrogenase, hydroxylamine oxidase, and nitrate:nitrite oxidoreductase were upregulated, while a putative hydroxylamine oxidoreductase HAO (KsCSTR_49490) was downregulated. These findings contribute to the growing knowledge on anammox bacteria physiology, eventually leading to the control of anammox bacteria growth and activity in real-world application.Key Points• Sulfite additions can reverse oxygen inhibition of the anammox process• Anammox activity was improved by activated carbon and ferric oxide• Sulfamethoxazole marginally affected anammox activityGraphical abstract

Microfluidic-templated cell-laden microgels fabricated using phototriggered imine-crosslinking as injectable and adaptable granular gels for bone regeneration.

Injectable granular gels consisting of densely packed microgels serving as scaffolding biomaterial have recently shown great potential for applications in tissue regeneration, which allow administration via minimally invasive surgery, on-target cargo delivery, and high efficiency in nutrient/waste exchange. However, limitations such as insufficient mechanical strength, structural integrity, and uncontrollable differentiation of the encapsulated cells in the scaffolds hamper their further applications in the biomedical field. Herein, we developed a new class of granular gels via bottom-up assembly of cell-laden microgels via photo-triggered imine-crosslinking (PIC) chemistry based on the microfluidic technique. The particulate nature of the granular gels rendered them with shear-thinning and self-healing behavior, thereby functioning as an injectable and adaptable cellularized scaffold for bone tissue regeneration. Specifically, single cell-laden, monodisperse microgels composed of methacrylate- and o-nitrobenzene-functionalized hyaluronic acid and gelatin were prepared using a high-throughput microfluidic technique with a production rate up to 3.7×108 microgels/hr, wherein the PIC chemistry alleviated the oxygen inhibition on free-radical polymerization and facilitated enhanced fabrication accuracy, accelerated gelation rate, and improved network strength. Further in vitro and in vivo studies demonstrated that the microgels can serve as carriers to support the activity of the encapsulated mesenchymal stem cells; these cell-laden microgels can also be used as cellularized bone fillers to induce the regeneration of bone tissues as evidenced by the in vivo experiment using the rat femoral condyle defect model. In general, these results represent a significant step toward the precise fabrication of engineered tissue mimics with single-cell resolution and high cell-density and can potentially offer a powerful tool for the design and applications of a next generation of tissue engineering strategy. STATEMENT OF SIGNIFICANCE: Using microfluidic droplet-based technology, we hereby developed a new class of injectable and moldable granular gels via bottom-up assembly of cell-laden microgels as a versatile platform for tissue regeneration. Phototriggered imine-crosslinking chemistry was introduced for microgel cross-linkage, which allowed for the fabrication of microgels with improved matrix homogeneity, accelerated gelation process, and enhanced mechanical strength. We demonstrated that the microgel building blocks within the granular gels facilitated the proliferation and differentiation of the encapsulated mesenchymal stem cells, which can further serve as a cellularized scaffold for the treatment of bone defects.

Chemical Optimization Strategy of Rapid Additive Manufacturing via Up‐Conversion Assisted Photopolymerization Based Direct Ink Writing

AbstractLight‐driven 3D printing can empower the liberty of creation and concretize the original creation in versatile conditions with plenty of choices in resolution or properties. However, photopolymerization‐based 3D printing inks are facing a trade‐off between requiring processing rate and satisfying performance, and a chemical optimization strategy is proposed to achieve the ink demands of rapid direct ink writing utilizing up‐conversion assisted photopolymerization. Since acylphosphonate can generate two reactive radicals and tertiary amine can reinitiate polymerization in oxygen inhibition, the yielded active species in limited irradiation of 3D printing are maximized to accelerate the polymerization by theoretically and experimentally interpreting the roles of up‐conversion particle, photoinitiators, and co‐initiator played in printing. High print speed in depositing and in situ curing (3.56 × 104 mm3 h−1) are realized, and the manufacturing time is shortened by multi‐resolution printing which is impressive compared to current 3D printing methods. The strategy is simultaneously compatible with rigid and elastomeric materials, and will surely contribute to other light‐driven 3D printing technologies for extensive applications.

Nano-TiO2 aggravates bioaccumulation and developmental neurotoxicity of difenoconazole in zebrafish larvae via oxidative stress and apoptosis: Protective role of vitamin C

Titanium dioxide nanoparticles (n-TiO2) could enhance the bioavailability and toxicity of coexisting organic contaminants in the aquatic environment. This study attempted to investigate the combined effects of n-TiO2 and difenoconazole (DIF) on the neurodevelopment of zebrafish and the underlying mechanisms. In this study, zebrafish embryos were exposed to n-TiO2 (100 μg/L), DIF (0, 0.1 and 0.5 mg/L) and their mixtures from 4 to 96 h post fertilization (hpf) and neurotoxicity was evaluated. Our results indicated that n-TiO2 adsorbed DIF into the brain of zebrafish and significantly enhanced the bioaccumulation of DIF and n-TiO2 in the 0.5 mg/L co-exposure group. 100 μg/L n-TiO2 was not developmentally toxic to the zebrafish larvae, but it exacerbated DIF-induced neurobehavioral alterations in the zebrafish larvae. n-TiO2 also aggravated DIF-induced suppression of central nervous system (CNS) neurogenesis in Tg (HuC:egfp) zebrafish, motor neuron axon length in Tg (hb9:egfp) zebrafish, and downregulation of neurodevelopmental genes (elavl3, ngn1, gap43, gfap and mbp). In addition, DIF elevated oxidative stress by accumulation of reactive oxygen species (ROS) and inhibition of antioxidant enzymes, and triggered apoptosis by upregulation of p53, bax, bcl-2 and caspase-3, which were markedly intensified in the presence of n-TiO2. Moreover, vitamin C (VC) ameliorated n-TiO2/DIF-induced abnormal locomotor behaviors and neurotoxicity by inhibiting oxidative stress and apoptosis, indicating that oxidative stress and apoptosis are involved in n-TiO2/DIF-induced neurotoxicity. Taken together, our data indicated that n-TiO2 enhanced the accumulation of DIF and heightened oxidative stress and apoptosis, thereby inducing neurotoxicity. This study exemplifies the importance of the toxicity assessment of chemical mixtures and novel insights to mitigate their combined toxicity.

Free-radical photoring-opening polymerization of cyclic allylic sulfide: From photocleavable photoinitiators to three components photoredox systems

Photopolymers form a family of materials that have been developed to meet specific demands in fields such as coatings, varnishes, semiconductors, optical fibers, printing plates, holographic recording, etc. However, the multifunctional acrylate monomers currently used present an important volume contraction. A drawback for applications where little shrinkage during polymerization is mandatory to keep shapes and properties of the material. To overcome this problem, monomers reacting by ring opening polymerization can be used. Among possible monomers, cyclic allylic sulfides are very interesting candidates: they are highly reactive and their polymerization mechanism is almost not affected by the presence of oxygen. In this work the effects of the photoinitiating systems on the free radical ring opening photopolymerization kinetics of an eight-member cyclic allylic sulfide is studied. It is shown that cleavable type I, bimolecular type II and three components redox photoinitiating systems allow the formation of linear photopolymers with high polymerization rates and final conversions. The photopolymerization kinetics obtained show that the photopolymerization is not sensitive to oxygen which leads to reduced exposure time and higher sensitivity. This remarkable property should also extend the usage of such monomers in the coating applications where oxygen inhibition is a drawback. Finally, the benefit of ring opening polymerization process is demonstrated trough the volume contraction measurement which was found to be lower than 1.5%.

Formation mechanism and regulation of silicon vacancy centers in polycrystalline diamond films

Diamond silicon vacancy centers (SiV centers) have important application prospects in quantum information technology and biomarkers. In this work, the formation mechanism and regulation method of SiV center during the growth of polycrystalline diamond on silicon substrate are studied. By changing the ratio of nitrogen content to oxygen content in the growing atmosphere of diamond, the photoluminescence intensity of SiV center can be controlled effectively, and polycrystalline diamond samples with the ratios of SiV center photoluminescence peak to diamond intrinsic peak as high as 334.46 and as low as 1.48 are prepared. It is found that nitrogen promotes the formation of SiV center in the growth process, and the inhibition of oxygen. The surface morphology and photoluminescence spectrum for each of these samples show that the photoluminescence peak intensity of SiV center is positively correlated with the grain size of diamond, and the SiV center’s photoluminescence peak in the diamond film with obvious preferred orientation of crystal plane is higher. The distribution of Si centers and SiV centers on the surface of polycrystalline diamond are further characterized and analyzed by photoluminescence, Raman surface scanning and depth scanning spectroscopy. It is found that during the growth of polycrystalline diamond, the substrate silicon diffuses first into the diamond grain and then into the crystal structure to form the SiV center. This paper provides a theoretical basis for the development and application of SiV centers in diamond.

The anti-breast cancer stem cell properties of gold(i)-non-steroidal anti-inflammatory drug complexes.

The anti-breast cancer stem cell (CSC) properties of a series of gold(i) complexes comprising various non-steroidal anti-inflammatory drugs (NSAIDs) and triphenylphosphine 1-8 are reported. The most effective gold(i)-NSAID complex 1, containing indomethacin, exhibits greater potency for breast CSCs than bulk breast cancer cells (up to 80-fold). Furthermore, 1 reduces mammosphere viability to a better extent than a panel of clinically used breast cancer drugs and salinomycin, an established anti-breast CSC agent. Mechanistic studies suggest 1-induced breast CSC death results from breast CSC entry, cytoplasm localisation, an increase in intracellular reactive oxygen species levels, cyclooxygenase-2 downregulation and inhibition, and apoptosis. Remarkably, 1 also significantly inhibits tumour growth in a murine metastatic triple-negative breast cancer model. To the best of our knowledge, 1 is the first gold complex of any geometry or oxidation state to demonstrate anti-breast CSC properties.