Oxygen Inhibition Research Articles

Tailoring Common Hydrogels into 3D Cell Culture Templates.

Physiologically relevant cell-based models require engineered microenvironments which recapitulate the topographical, biochemical, and mechanical properties encountered in vivo. In this context, hydrogels are the materials of choice. Here a light-based toolbox is able to craft such microniches out of common place materials. Extensive use of benzophenone photoinitiators and their interaction with oxygen achieves this. First, the oxygen inhibition of radicals is harnessed to photoprint hydrogel topographies. Then the chemical properties of benzophenone are exploited to crosslink and functionalize native hydrogels lacking photosensitive moieties. At last, photoscission is introduced: an oxygen-driven, benzophenone-enabled reaction that photoliquefies Matrigel and other common gels. Using these tools, soft hydrogel templates are tailored for cells to grow or self-organize into standardized structures. The described workflow emerges as an effective microniche manufacturing toolset for 3D cell culture.

Constrained Window Design in Projection Stereolithography for Continuous Three-Dimensional Printing.

Although continuous projection Stereolithography (SL) printing is one of the next-generation ultra-fast additive manufacturing (AM) processes, its current constrained window design of the resin vat is suffering from many challenges, such as the complex control mechanism and limited hardware lifetime. In this article, we investigate a novel constrained window design, namely Island Window (IW), for the continuous three-dimensional (3D) printing by using the projection SL process. The proposed IW window has a highly oxygen-permeable polydimethylsiloxane membrane onto the laser-machined acrylic vat frame, which allows the formation of an effective liquid interface (>200 μm oxygen inhibition layer) to enable the continuous projection SL process. Experimental results verified the feasibility of the window design for extending the maximum printing time (increased by up to 73%) due to the enhanced oxygen concentration. It was also found that the maximum printing speed for producing parts with a smooth surface (Rz <30 μm) can be as high as 90 mm/h, which is comparable to the speeds in recently reported continuous SL processes. In addition, a variety of parts were successfully fabricated through continuous 3D printing by using the proposed IW design, implying tremendous promise for future low-cost, high-resolution, easy-controlled, and ultra-fast AM processes.

Oxygen inhibition induced hydrophilic-hydrophobic surface for self-assembled droplet microarrays

Hydrophilic-hydrophobic surface is vital for the study of the wettability behavior of microdroplets. In this paper, a method for preparation of hydrophilic-hydrophobic patterned surface is proposed based on the oxygen inhibition effect. Oxygen inhibition is very common in photo-cured process, and usually should be avoided for its adverse effect on curing quality. However, it also results in numerous nanostructures naturally formed on the cured layer surface, and the density and sizes of the nanostructures can be modulated conveniently by adjusting the exposure time. Based on this phenomenon, the cured layer surface having hydrophobicity can be processed. The contact angle system is used to measure the contact angle of the cured layer surface, and the morphology of the cured layer surface is measured in detail by atomic force microscopy and scanning electron microscope.The hydrophobic layer is only 1.5 $$\upmu $$ m thick. By combining maskless lithography, patterned surface with nanostructures can be easily formed in just one step without any special treatment. This helps us to generate highly controllable hydrophilic-hydrophobic surface effectively in a very simple and low-cost way. With this method self-assembled droplet microarrays are successfully achieved. The results offer a new idea for the control of surface wettability and may find wide potential applications in microfluidics.

Cashew (Anacardium occidentale L.) Nuts Counteract Oxidative Stress and Inflammation in an Acute Experimental Model of Carrageenan-Induced Paw Edema.

Background: Anacardium occidentale L. is a medicinal plant with powerful anti-oxidative and anti-inflammatory properties. Acute inflammatory events cause tissue alterations, decrease of anti-oxidative endogenous enzymes such as superoxide dismutase, catalase and glutathione, neutrophils infiltration, increase in the activities of myeloperoxidase, malondialdehyde, and pro-inflammatory release. Methods: Paw edema was induced by subplantar injection of carrageenan into the right hind paw in rats, but 30 min before a group of animals were orally treated with 100 mg/kg of cashew nuts to evaluate the anti-inflammatory and anti-oxidative response. Results: In the present work, we found that (1) cashew nuts reduced the development of carrageenan-induced paw edema limiting the formation of edema and pain; (2) cashew nuts ameliorated the diminutions of the anti-oxidative enzymes caused by carrageenan injection; (3) cashew nuts decreased myeloperoxidase malondialdehyde activity induced by carrageenan; and (4) cashew nuts acted by blocking pro-inflammatory cytokines response and nitrate/nitrite formation stimulated by carrageenan injection. Conclusions: The mechanisms of anti-inflammatory and analgesic effects exerted by cashew nuts were relevant to oxygen free radical scavenging, anti-lipid peroxidation, and inhibition of the formation of inflammatory cytokines.

Comparative study of the impact of additives against oxygen inhibition on pendulum hardness and abrasion resistance for UV-curable wood finishes

The multiple advantages of UV-curable coatings, such as high curing speeds and cross-linking densities, low VOC and energy consumption led to a widespread interest for a wide range of applications. Free-radical photopolymerization constitutes one of the most used methods of polymerization. However, oxygen present in the atmosphere is able to inhibit radical formation and propagation, which is considered a major drawback. Among all the strategies developed for reducing the oxygen inhibition, the addition of reactive additives is often preferred. This method does not require major changes in the production lines of the industries or in the formulations compositions. The efficiency of reactive additives against oxygen inhibition has been investigated in multiple studies, but in different experimental conditions. The addition of the reactive additives can also influence coatings hardness and abrasion resistance which are considered important mechanical properties. The aim of this study is to evaluate additives overall performances. Eleven of the chosen additives were previously described in the literature. The four remaining are commercial products never used for that application, like a polyhedral oligomeric silsesquioxane bearing a thiol function, which later showed the best results. Reduction of oxygen inhibition was analyzed by photo differential scanning calorimetry (Photo-DSC) and Confocal Raman Micro-spectroscopy (CRM). Pendulum hardness and abrasion resistance measurements were used to determine the influence of the additives on the mechanical properties of the coatings. The results obtained show that most of the additives tested had reducing effect on the pendulum hardness, but helped in improving the abrasion resistance.

Modeling the oxygen inhibition in microalgae: An experimental approach based on photorespirometry

Microalgae cultivation has been the object of relevant interest for many industrial applications. Where high purity of the biomass/product is required, closed photobioreactors (PBRs) appear to be the best technological solution. However, as well as cost, the major drawback of closed systems is oxygen accumulation, which is well known to be responsible for growth inhibition. Only a few quantitative approaches have attempted to describe and model oxygen inhibition, which is the result of different biological mechanisms. Here, we have applied a photorespirometric protocol to assess and quantify the effect of high oxygen concentration on photosynthetic production rate. In particular, the effects of light intensity and biomass concentration were assessed, resulting in different maximum inhibitory oxygen concentrations. Literature models available were found not to fully represent experimental data as a function of concentration and light. Accordingly, a new formulation was proposed and validated to describe the photosynthetic rate as a function of external oxygen concentration.

Epoxide-based PDMS membranes with an ultrashort and controllable membrane-forming process for 1-butanol/water pervaporation

The ultrashort and controllable membrane-forming process is highly required in large-scale production of PDMS membrane. To shorten the cross-linking time, an UV-induced ring-opening polymerization of the epoxide groups was introduced to the preparation of PDMS membranes. PDMS was firstly functionalized with epoxide groups, providing the possibility of being cross-linked under UV irradiation. With this strategy, the membrane curing was finished within 200 s, hence shortened by two orders of magnitude in comparison with the conventional thermal-driven method. Meanwhile, the cationic photoinitiation of epoxide groups can be achieved without oxygen inhibition in an open-air environment. Moreover, the viscosity of the coating solution in the groove is kept constant when protected from light, thus meeting the requirement of the coatability. When applied to the pervaporation of a 1.5 wt% 1-butanol/water solution at 55 °C, the measured 1-butanol separation factor was 45 and the total flux was 1119 g m−2 h−1. This novel strategy shows a great prospect in the continuous preparation of membrane.

Suppressed Oxygen Inhibition in UV Curable Formulations Using a Diene as an Additive

Suppressed Oxygen Inhibition in UV Curable Formulations Using a Diene as an Additive

3D printing preview for stereo-lithography based on photopolymerization kinetic models

The diversity of biomedical applications makes stereolithographic (SL) three-dimensional (3D) printing process complex. A strategy was developed to simulate the layer-by-layer fabrication of 3D printed products combining polymerization kinetic with reaction conditions to realize print preview. As a representative example, the typical UV-curable dental materials based on epoxy acrylate and photoinitiator with different molar ratios was exposed under varying intensity of UV light to verify the simulation results. A theoretical kinetics model containing oxygen inhibition was established. In-situ FTIR was employed to measure propagation and termination constants while coupled UV/vis was performed to examine the law of light attenuation during cure reaction, even with various colours and additives. Simulation results showed that the correlation coefficient square between the experiments and simulations of epoxy acrylate with 1%, 2% and 3% initiator upon 20 mW/cm2 UV light are 0.8959, 0.9324 and 0.9337, respectively. Consequently, our simulation of photopolymerization for SL 3D printing successfully realized visualization of printing quality before practically printing the targeted biomedical objects with complex topology structures.

Effective nitrogen removal from ammonium-depleted wastewater by partial nitritation and anammox immobilized in granular and thin layer gel carriers

This study investigates the effect of physicochemical conditions on the partial nitritation and anammox treatment by immobilized ammonia oxidizers under ammonium-deplete conditions. The impact of oxygen and temperature was studied by measuring the activity of immobilized aerobic and anaerobic ammonia-oxidizing organisms (Ammonia-oxidizing bacteria (AOB) and archaea (AOA), and Anammox bacteria) embedded in polyvinyl alcohol – sodium alginate (PVA-SA) beads and in thin layer poly-ethylene glycol hydrogels. Beads and flat hydrogels were incubated in a fluidized bed reactor (FBR) and in two flow cells, respectively. Both systems were fed with synthetic wastewater (15 mg N–NH4+/L) at different temperatures (20 °C and/or 30 °C) and different dissolved oxygen (DO) concentrations (0.1, 0.3, 0.5 and/or 1 mg/L) over 152 and 207 days, respectively. The FBR system had a maximum removal rate of 1.7 g-N/m3/d at 0.1 mg O2/L, corresponding to 80% removal efficiency, while a high aerobic ammonia-oxidizing activity but a partial oxygen inhibition of Anammox bacteria were observed at higher DO concentrations. In both flow cells, nitrogen removal efficiency was highest (80%) at 30 °C and 1 mg O2/L while removal was less favorable at lower DO and lower temperature. Our results indicate a potential use of hydrogel beads for an energy efficient technology with reduced aeration demand for treating low ammonia wastewater, while layered hydrogels are a possible first step for biological treatments of wastewater using tangential flow. In addition, we provide blueprint drawings of the flow cells, which may be used to 3D-print the apparatus for other applications.

Activation of Nrf2/AREs-mediated antioxidant signalling, and suppression of profibrotic TGF-β1/Smad3 pathway: a promising therapeutic strategy for hepatic fibrosis — A review

Hepatic fibrosis (HF) is a wound-healing response that occurs during chronic liver injury and features by an excessive accumulation of extracellular matrix (ECM) components. Activation of hepatic stellate cell (HSC), the leading effector in HF, is responsible for overproduction of ECM. It has been documented that transforming growth factor-β1 (TGF-β1) stimulates superfluous accumulation of ECM and triggers HSCs activation mainly via canonical Smad-dependent pathway. Also, the pro-fibrogenic TGF-β1 is correlated with generation of reactive oxygen species (ROS) and inhibition of antioxidant mechanisms. Moreover, involvement of oxidative stress (OS) can be clearly elucidated as a fundamental event in liver fibrogenesis. Nuclear factor erythroid 2-related factor 2-antioxidant response elements (Nrf2-AREs) pathway, a group of OS-mediated transcription factors with diverse downstream targets, is associated with the induction of diverse detoxifying enzymes and the most pivotal endogenous antioxidative system. More specifically, Nrf2-AREs pathway has recently assigned as a new therapeutic target for cure of HF. The overall goal of this review will focus on recent findings about activation of Nrf2-AREs-mediated antioxidant and suppression of profibrotic TGF-β1/Smad3 pathway in the liver, providing an overview of recent advances in transcriptional repressors that dislocated during HF formation, and highlighting possible novel therapeutic targets for liver fibrosis.

Activation and Deactivation of Chain-transfer Agent in Controlled Radical Polymerization by Oxygen Initiation and Regulation

The activation and deactivation of the chain-transfer agent were achieved by oxygen initiation and regulation with triethylborane under ambient temperature and atmosphere. The autoxidation of triethylborane overcame the oxygen inhibition and produced initiating radicals that selectively activate the chain-transfer agent for the chain growth or deactivate the active chain-end of polymer in controlled radical polymerization. Both activation and deactivation were highly efficient with broad scope for various polymers with different chain-transfer agents in both organic and aqueous systems. Oxygen molecule was particularly used as an external regulator to initiate and achieve the temporal control of both activation and deactivation by simply feeding the air.

A Novel Nanoimprint Lithography Thiol-ene Resist for Sub-70 nm Nanostructures

In this paper, we propose a novel kind of UV click-polymerization thiol-ene copolymers as nanoimprint lithography resists for sub-70 nm resolution patterns. High-precision mold imprint and release are two of the most critical steps of nanoimprint lithography, which requires the resists with properties of excellent conformal replication and low surface energy. Conventional UV-curable resists used in nanoimprint lithography, such as acrylate, epoxy resin, and vinyl ether, cannot satisfy all these properties requirements because they exhibit surface oxygen inhibition during polymerization, or materials fracture and delamination during mold releasing. A novel kind of thiol-ene copolymers have been investigated in this study, which have many properties favorable for use as nanoimprint lithography resists to imprint sub-70 nm and high-aspect-ratio nanostructures. These properties include sufficiently low viscosity and high Young's modulus, low surface energy for easy demolding, polymerization in benign ambient, and in particular, high chemical-etch resistance. These excellent properties give improve nanoimprinting results.

Critical design factors for polyvinyl alcohol hydrogel entrapping ammonia-oxidizing bacteria: biomass loading, distribution of dissolved oxygen, and bacterial liability

The single-stage configuration of the partial nitritation (PN)–anaerobic ammonium oxidation (AMX) process is preferred due to low pH fluctuation and the low concentration of inhibitory NO2-. The novel core-shell structure integrates ammonia-oxidizing reaction in the outer layer to protect AMX bacteria in the core gel bead from oxygen inhibition and provide NO2-. Here, the initial activity of ammonia-oxidizing bacteria (AOB) in the outer layer was assessed by the specific oxygen uptake rate (OUR). AOB activity was positively correlated with biomass loading in the outer layer. A maximum OUR of 10.5 mg-DO/L∙h was achieved with AOB loading of 0.23 mg-VSS per bead. During AOB enrichment, the NO2- production rate was linearly increased up to 0.65 kg-N/m3-d for 17 days (PVA hydrogel packing ratio=17%). The maximum oxygen penetration depth (OPD) was reduced from 966.7±52.3 μm before enrichment to 333.3±36.4 μm after the AOB enrichment. The liable bacteria were observed within a range of 165 μm of the outer layer using the live and dead cell staining. Based on the OPD and liable cell distribution results, a minimal outer layer thickness of approximately 350 μm was suggested to facilitate a successful PN–AMX process.

Use of floating acylphosphine oxide-based photoinitiators to reduce surface oxygen inhibition of UV-LED photopolymerization

a series of acylphosphine oxide-based self-floating photoinitiators (PIs) of (TPO-F/Si/C12/C22) for improving the surface oxygen inhibition resistance are synthesized by following the modification of the traditional PI of ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate (TPO-L). The four self-floating PIs bear low surface free energy units of fluorine, polysiloxane, C12 and C22 long chain aliphatic alkane, respectively. The self-floating ability are assessed by UV absorption spectra and further confirmed by the X-ray photoelectron spectroscopy (XPS) and the water contact angle tests. The self-floating ability of the PIs can enable the UV-LED photopolymerization of the acrylic monomers to conquer the surface oxygen inhibition by increasing the local PI concentration, which is evidenced by ATR-IR, confocal Raman microscopy (CRM) and Photo-DSC. The self-floating ability enriches the PIs in the upper layers to consume the surface oxygen as well as to enable the fast cure of the resin surface to stop the further penetration of the oxygen into deeper sites.

Role of mutant KRAS as a biomarker in FL118-induced apoptosis, reactive oxygen species (ROS) production and inhibition of survivin, Mcl-1 and XIAP in human bladder cancer.

e15651 Background: Effective treatment of bladder cancer patients has not been realized over the past two decades due to heterogeneity with key oncogenic and tumor suppressor gene mutations, which is a major hurdle for effective treatment of the disease. Methods: Cancer cell growth/viability was determined using MTT assays; protein gene expression profiles were determined by both Western blots and proteomics technologies; PARP cleavage were determined by Western blots; genetic modulation of protein gene expression was realized by shRNA silencing or forced expression of the gene; reactive oxygen species (ROS) production was measured using a ROS assay kit; and human bladder xenograft tumor growth was determined using animal models. Results: Our study indicated that FL118, an innovative small molecule, exhibits differential anticancer efficacy in high-grade bladder cancer cell lines (HT1376, T24, UMUC-3). FL118 is highly effective at inhibiting the viability of T24 and UMUC-3 bladder cancer cells, which have Hras and Kras mutations, respectively. In contrast, HT1376 with wild-type Ras exhibits insensitivity to FL118-mediated inhibition of cell viability. Consistently, FL118 strongly induced PARP cleavage (hallmark of apoptosis) and inhibited the expression of survivin, XIAP and/or Mcl-1 in both T24 and UMUC-3 cells but not in the HT1376 cells. Our studies further indicated that the constitutive AKT and ERK1/2 signaling does not play a major role in these FL118-mediated effects. Instead, mutant Kras appeared to be involved in FL118 efficacy and played a positive role in mediating FL118 effects. Silencing of mutant Kras via shRNA reduced both FL118-induced PARP cleavage and downregulation of survivin, XIAP and Mcl-1 in UMUC-3 cells, suggesting mutant Kras is required for FL118 to exhibit high efficacy. FL118 increases ROS production in T24 and UMUC-3 cells but not in HT1376 cells. Silencing of mutant Kras with shRNA in UMUC-3 cells significantly reduced FL118-mediated ROS generation. Additionally, proteomics analyses of UMUC3 and HT1376 cell protein profiles after FL118 treatment support the obtained results described above. Consistent with these in vitro results, in vivo studies indicated that UMUC3 is highly sensitive and HT1376 is highly resistant to FL118 treatment. Conclusions: Our studies suggest that mutant Kras is a favorable biomarker for FL118 targeted treatment in human bladder cancer.

Surface Chemical Functionalization of Wrinkled Thiol-ene Elastomers for Promoting Cellular Alignment.

Wrinkled polymer surfaces find broad applicability; however, the polymer substrates are often limited to poly(dimethylsiloxane) (PDMS), which limits spatial control over wrinkle features and surface chemistry. An approach to surface functionalization of wrinkled elastomer substrates is demonstrated through versatile, multistep thiol-ene click chemistry. The elastomer is formed using a thiol-Michael reaction of tetrathiol with excess diacrylates while wrinkle formation is induced through a second free radical UV polymerization of the acrylates on the surface of the elastomer. Due to oxygen inhibition of the free radical polymerization, pendant acrylates at the surface remain unreacted and are subsequently functionalized with a multi-functional thiol, which can be further reacted through a number of thiol-X 'click' reactions. As a demonstration, these thiol surfaces are further modified to either promote cell adhesion of human mesenchymal stem cells (hMSCs) through coupling with RGDS-containing peptides or surface passivation through reaction with hydrophilic hydroxyl ethyl acrylate moieties. Through engineering a combination of surface chemistry and surface topography, hMSCs exhibited increased spreading and cell density on RGDS-functionalized surfaces and a two-fold increase in cell alignment when cultured on wrinkled substrates. Gradient functionalized surfaces created by tuning the wrinkle wavelength with UV irradiation enabled rapid screening of the effect of topography on the hMSCs. Further, this novel application of click chemistry enables simultaneous tuning of wrinkle topology and surface chemistry towards targeted material applications.

High Productivity Ethanol from Solid-State Fermentation of Steam-Exploded Corn Stover Using Zymomonas mobilis by N2 Periodic Pulsation Process Intensification.

Solid-state fermentation, featured by water-saving, eco-friendly and high concentration product, is a promising technology in lignocellulosic ethanol industry. However, in solid-state fermentation system, large gas content inside the substrate directly leads to high oxygen partial pressure and inhibits ethanol fermentation. Z. mobilis can produce ethanol from glucose near the theoretical maximum value, but this ethanol yield would be greatly decreased by high oxygen partial pressure during solid-state fermentation. In this study, we applied N2 periodic pulsation process intensification (NPPPI) to ethanol solid-state fermentation, which displaced air with N2 and provided a proper anaerobic environment for Z. mobilis. Based on the water state distribution, the promotion effects of NPPPI on low solid loading and solid-state fermentation were analyzed to confirm the different degrees of oxygen inhibition in ethanol solid-state fermentation. During the simultaneous saccharification solid-state fermentation, the NPPPI group achieved 45.29% ethanol yield improvement and 30.38% concentration improvement compared with the control group. NPPPI also effectively decreased 58.47% of glycerol and 84.24% of acetic acid production and increased the biomass of Z. mobilis. By coupling the peristaltic enzymatic hydrolysis and fed-batch culture, NPPPI made the ethanol yield and concentration reach 80.11% and 55.06g/L, respectively, in solid-state fermentation.

Radiation crosslinking of pigmented coating material by UV LEDs enabling depth curing and preventing oxygen inhibition

LED light sources emit in a small wavelength region, e.g. in the blue light and UV-A. These LEDs can be applied for the radiation curing via radical polymerization, which is a growing sector in the coating industry. LEDs will in prospect substitute mercury arc lamps as the light sources, but development of higher intense LEDs and also in the UV-B or UV-C range is still in progress. In this report the efficiency of initiator systems was analyzed for the photopolymerization of UDMA. The chosen systems are usually used in the coating industry and others were invented in the dentistry and holography. The aim is the depth curing of urethane dimethacrylate (UDMA) with the help of UV LEDs at 365 nm, 395 nm, and 405 nm. The overlap of the absorbance of the initiator systems and the emission of the LED is discussed regarding the reactivity in the top layer and a thickness up to 20 mm hereby giving insights in the influence of the light source and the reactivity or spectral properties of the initiator system on the photopolymerization process. Surprisingly, the initiator systems like Ivocerin, and HABI-mercapto, which are unusual as initiators for the curing of coatings, show a high efficiency. Even pigmented and filled systems are curable up to a depth of 4–20 mm, respectively. Furthermore, applying a UV-C LED at 278 nm and using these initiators also decrease the tackiness on the surface caused by oxygen inhibition.

KIF15 promotes the evolution of gastric cancer cells through inhibition of reactive oxygen species-mediated apoptosis.

Kinesin family member 15 (KIF15) is a member of the kinesin superfamily of proteins, which promotes cell mitosis, participates in the transport of intracellular materials, and helps structural assembly and cell signaling pathways transduction. However, its biological role and molecular mechanisms of action in the development of gastric cancer (GC) remain unclear. In the present study, an integrated analysis of The Cancer Genome Atlas (TCGA), Gene Expression Omnibus database, and Kaplan-Meier plotter database was performed to predict the expression and prognostic value of KIF15 in GC patients. Detection of KIF15 expression in GC cells and tissues was performed by a quantitative polymerase chain reaction. In vitro cell proliferation, viability, colony formation ability and flow cytometry assays, and in vivo tumorigenicity assay, were performed to evaluate the effects of KIF15 knockdown on GC cell phenotype. It was demonstrated that the expression of KIF15 messenger RNA in GC tissues was significantly higher compared with that in adjacent tissues, and was closely associated with larger tumor size and poor patient prognosis. In addition, functional studies demonstrated that, due to the increase in reactive oxygen species (ROS) generation, the interference with the expression of KIF15 not only decreased cell proliferation but also increased cell apoptosis and induced cell cycle arrest. ROS-mediated activation of c-Jun N-terminal kinase/c-Jun signaling reduced cell proliferation by regulating the GC cell cycle and increasing apoptosis. Taken together, the results of the present study indicate that KIF15 is an oncoprotein contributing to GC progression, and is expected to help identify novel biomarkers and treatment targets in GC.