Chemical Concentration Gradients Research Articles

Continuous polyamorphic transition in high-entropy metallic glass

Polyamorphic transition (PT) is a compelling and pivotal physical phenomenon in the field of glass and materials science. Understanding this transition is of scientific and technological significance, as it offers an important pathway for effectively tuning the structure and property of glasses. In contrast to the PT observed in conventional metallic glasses (MGs), which typically exhibit a pronounced first-order nature, herein we report a continuous PT (CPT) without first-order characteristics in high-entropy MGs (HEMGs) upon heating. This CPT behavior is featured by the continuous structural evolution at the atomic level and an increasing chemical concentration gradient with temperature, but no abrupt reduction in volume and energy. The continuous transformation is associated with the absence of local favorable structures and chemical heterogeneity caused by the high configurational entropy, which limits the distance and frequency of atomic diffusion. As a result of the CPT, numerous glass states can be generated, which provides an opportunity to understand the nature, atomic packing, formability, and properties of MGs. Moreover, this discovery highlights the implication of configurational entropy in exploring polyamorphic glasses with an identical composition but highly tunable structures and properties.

Droplet array with microfluidic concentration gradient (DA-MCG) for 2-dimensional reaction condition screening

Droplet microfluidic technology can use each microdroplet as a microreactor, which has the advantages of low reagent dosage, less cross contamination, and fast reaction time. Combining concentration gradient generation with droplet formation and capture to form a two-dimensional reaction condition screening platform (including reactant concentration and reaction time) is expected to broaden the application range of microfluidic screening. In this work, a microfluidic chip that can dynamically generate and capture microdroplets and form static microdroplet array was designed and fabricated. An optimized Christmas tree structure by adjusting the horizontal channel length ratio was used to generate a chemical concentration gradient while obtaining a uniform outlet flow rate, forming a droplet array with different concentrations. The performance of droplet array with microfluidic concentration gradient (DA-MCG) was verified using sodium fluorescein as a model reagent. The chromogenic reaction of NaOH and phenolphthalein, and luminol chemiluminescence reaction were used to verify the two-dimensional screening ability of DA-MCG. The results indicated that the DA-MCG has the potential to be applied in the field of multi-dimensional drug screening.

Nanoscopic Imaging of Self-Propelled Ultrasmall Catalytic Nanomotors.

Ultrasmall nanomotors (<100 nm) are highly desirable nanomachines for their size-specific advantages over their larger counterparts in applications spanning nanomedicine, directed assembly, active sensing, and environmental remediation. While there are extensive studies on motors larger than 100 nm, the design and understanding of ultrasmall nanomotors have been scant due to the lack of high-resolution imaging of their propelled motions with orientation and shape details resolved. Here, we report the imaging of the propelled motions of catalytically powered ultrasmall nanomotors─hundreds of them─at the nanometer resolution using liquid-phase transmission electron microscopy. These nanomotors are Pt nanoparticles of asymmetric shapes ("tadpoles" and "boomerangs"), which are colloidally synthesized and observed to be fueled by the catalyzed decomposition of NaBH4 in solution. Statistical analysis of the orientation and position trajectories of fueled and unfueled motors, coupled with finite element simulation, reveals that the shape asymmetry alone is sufficient to induce local chemical concentration gradient and self-diffusiophoresis to act against random Brownian motion. Our work elucidates the colloidal design and fundamental forces involved in the motions of ultrasmall nanomotors, which hold promise as active nanomachines to perform tasks in confined environments such as drug delivery and chemical sensing.

Synthesis and Assembly of Photoresponsive Colloidal Tubes.

Inspired by the sophisticated multicomponent and multistage assembly of proteins and their mixtures in living cells, this study rationally designs and fabricates photoresponsive colloidal tubes that can self-assemble and hybrid-assemble when mixed with colloidal spheres and rods. Time-resolved observation and computer simulation reveal that the assembly is driven by phoretic attraction originating from osmotic pressures. These pressures are induced by the chemical concentration gradients generated by the photochemical reaction caused by colloidal tubes in a H2O2 solution under ultraviolet (UV) irradiation. The assembled structure is dictated by the size and shape of the constituent colloids as well as the intensity of the UV irradiation. Additionally, the resulting assembly can undergo self-propelled motion originating from the broken symmetry of the surrounding concentration gradients. This motion can be steered by a magnetic field and used for microscale cargo delivery. The study demonstrates a facile synthesis method for colloidal tubes and highlights their unique potential for controlled, hierarchical self-assembly and hybrid-assembly.

A Control-Theoretic Spatio-Temporal Model for Wildfire Smoke Propagation Using UAV-Based Air Pollutant Measurements

Wildfires have the potential to cause severe damage to vegetation, property and most importantly, human life. In order to minimize these negative impacts, it is crucial that wildfires are detected at the earliest possible stages. A potential solution for early wildfire detection is to utilize unmanned aerial vehicles (UAVs) that are capable of tracking the chemical concentration gradient of smoke emitted by wildfires. A spatiotemporal model of wildfire smoke plume dynamics can allow for efficient tracking of the chemicals by utilizing both real-time information from sensors as well as future information from the model predictions. This study investigates a spatiotemporal modeling approach based on subspace identification (SID) to develop a data-driven smoke plume dynamics model for the purposes of early wildfire detection. The model was learned using CO2 concentration data which were collected using an air quality sensor package onboard a UAV during two prescribed burn experiments. Our model was evaluated by comparing the predicted values to the measured values at random locations and showed mean errors of 6.782 ppm and 30.01 ppm from the two experiments. Additionally, our model was shown to outperform the commonly used Gaussian puff model (GPM) which showed mean errors of 25.799 ppm and 104.492 ppm, respectively.

Гомеостаз концентрацій кальцію, калію, натрію сперми бугаїв і матково-вагінального слизу корів

The difference in concentration indicators (mM) of alkali metal ions (Са2+, К+, Na+) and the calculated ratio indices (RI:1) of their pairs (Nа+:Са2+, К+:Са2+, Nа+:К+) in bull semen samples and uterine-vaginal mucus (UVM) of the Ukrainian black-spotted breed cows was determined and suggests that the ability of sperm to passively and/or actively move through the channels and ducts of the genital organs can be associated with the physicochemical processes of passive diffusion and active transport of substances that occur in the "sperm – UVM " system. The power of the energy of chemical and electrochemical concentration gradients and the power of ion pumps of the osmotic pressure of inorganic and oncotic – organic substances promotes the movement of spermatozoa to the place of their contact with the egg cell. In favor of the proposed hypothesis indicate the obtained probable (Р ˂ 0.001) results of the stoichiometry parameters of the concentrations of Ca2+ (10 vs. 6) and Na+ (62 vs. 1066 mM) of sperm and UVM, respectively. The determined difference is also illustrated by the unequal indices of ion pair concentration ratios. If their value in sperm samples is directed from the pair Na+:К+ to the pair Na+:Са2+ (1.4:1 → 5:1 →6:1), then in the samples of UVM – from К+:Са2+ to Na+: Ca2+ (8:1 → 23:1 → 193:1). The difference in indices of a number of pairs (К+:Са2+ → Nа+:К+ → Nа+:Са2+) of sperm and UVM is directed from a smaller to a larger value (3:1 ˂ 22:1 ˂ 187:1). If the calculated changes are expressed as percentages, then the difference in indicators in the samples of the UVM, respectively, is 41; 94 and 97 %, which is in 2; 16 and 30 times more than sperm samples. This may mean that the determined significant difference in the physical and chemical state of organic and inorganic substances in the environment of the channels and ducts of the genital organs of cows creates conditions that contribute to the active and passive movement of sperm through the channels and ducts of their genital organs

Typhoon eye-shaped global convective flow field-induced colloidal motor swarm

In nature, living individuals such as fish, gather as much as possible in the wild to carry out life activities to improve their survival rate and environmental adaptability. Colloidal motors are often used as models to form various swarms and reveal their intrinsic mechanisms. Here, we rely on a global convective flow field to prompt the formation of a colloidal motor swarm that can absorb all motors in the range of light radiation without assembly limits. The peanut-shaped colloidal motor photocatalytically decomposes hydrogen peroxide and generates the chemical concentration gradient, which triggers convective flows at its waist in the x-z plane and attracts nearby motors. When motors converge towards the center of the light gradient field due to their positive phototaxis, the chemical gradient fluid resulting from motors’ non-uniform distribution in the entire domain induces a typhoon eye-shaped global convective flow field that flows from the edge of the light to the center. Compared with individuals, the global convective flow has a wider attraction range and gathers motors into a swarm. Moreover, with the number of collected motors increasing, the convective flow integrated in the x-z plane is stronger and ceaselessly accumulates more motors toward the z-axis. The formed swarm can also move to other areas under light control to collect more motors. Such collective phenomena provide a chance for understanding the emergence mechanism of biological swarms and applying artificial swarms to environmental governance, information collection, and drug release.

A Systematic Review on Organ-on-a-Chip in PDMS or Hydrogel in Dentistry: An Update of the Literature.

Organs-on-a-chip (OoCs) are microfluidic devices constituted by PDMS or hydrogel in which different layers of cells are separated by a semipermeable membrane. This technology can set many parameters, like fluid shear stress, chemical concentration gradient, tissue-organ interface, and cell interaction. The use of these devices in medical research permits the investigation of cell patterning, tissue-material interface, and organ-organ interaction, mimicking the complex structures and microenvironment of human and animal bodies. This technology allows us to reconstitute in vitro complex conditions that recapitulate in vivo environments. One of the main advantages of these systems is that they represent a very realistic model that, in many cases, can replace animal experimentation, eliminating costs and related ethical issues. Organ-on-a-chip can also contain bacteria or cancer cells. This technology could be beneficial in dentistry for testing novel antibacterial substances and biomaterials, performing studies on inflammatory disease, or planning preclinical studies. A significant number of publications and reviews have been published on this topic. Still, to our knowledge, they mainly focus on the materials used for fabrication and the different patterns of the chip applied to the experimentations. This review presents the most recent applications of organ-on-a-chip models in dentistry, starting from the reconstituted dental tissues to their clinical applications and future perspectives.

Hydrochemical mixing‐zones trigger dolomite formation in an alkaline lake

AbstractDolomite is globally present in past geological records, but rare in modern environments. The mechanisms favouring its precipitation under ambient conditions remain highly debated. This study investigates sediments, containing high concentrations of early diagenetic calcian dolomite, from alkaline Lake Van (Republic of Türkiye, formally Turkey) dating back to 252 ka bp. Powder X‐ray diffraction and scanning electron microscopy evidence suggests that dolomite formation is associated with prior dissolution of aragonite and low‐Mg calcite and a subsequent co‐precipitation with, and/or partial transformation of, high‐Mg calcite into dolomite. The infrequent presence of diatom frustules encapsulated by dolomite suggests, for Lake Van, unusually low pore‐water pH at the time of dolomite formation. Conditions facilitating the preservation of silica, as well as dissolution and subsequent reprecipitation of carbonate phases, could result from periodic reventilations of Lake Van's deep water and an advection of pore fluids with contrasting redox potential and chemical concentration gradients. This continental analogue of the coastal ‘mixing‐zone’ dolomitization model argues that not overcoming a single specific hydrochemical threshold, but highly dynamic and fluctuating conditions trigger dolomite formation in Lake Van.

Directional and Reconfigurable Assembly of Active Colloidal Motors Triggered by Chemical Communications

AbstractAnisotropic colloidal particles can directionally self‐assemble, but the resulting assemblies cannot reconfigure unless the surface properties of colloidal particles change. Although external fields with adjustable inputs can guide the reconstruction of active structures after stimulating the dynamic assembly of active colloidal motors, the interaction between colloidal motors is unclear. Here, the study reports a bioinspired communication and directed assembly of peanut‐shaped colloidal motors with the emergence of ordered ribbon structures triggered by self‐generated chemical fields. The colloidal motors photocatalytically decompose the fuel to create the chemical concentration gradient fields and exert long‐range attractions on the colloidal scale, which enable colloidal motors to communicate by sensing each other, synchronizing orientation, and assembling side‐by‐side after the collision between their local flow fields. The inter‐individual communication occurs at a critical distance of ≈4.4 µm, resulting from the interplay between hydrodynamic effects, long‐ranged phoretic attraction, and short‐ranged magnetic interaction. The linear ribbons are still active owing to the symmetry breaking of the local fluid field and can be switched between rigid and flexible states according to light conditions to simulate the polymer conformation. The complexity of colloidal motors can be combined with external manipulations to manufacture active soft materials with precise and adaptive functions.

A PDMS-Agar Hybrid Microfluidic Device for the Investigation of Chemical-Mechanical Associative Learning Behavior of C. elegans.

Associative learning is a critical survival trait that promotes behavioral plasticity in response to changing environments. Chemosensation and mechanosensation are important sensory modalities that enable animals to gather information about their internal state and external environment. However, there is a limited amount of research on these two modalities. In this paper, a novel PDMS-agar hybrid microfluidic device is proposed for training and analyzing chemical-mechanical associative learning behavior in the nematode Caenorhabditis elegans. The microfluidic device consisted of a bottom agar gel layer and an upper PDMS layer. A chemical concentration gradient was generated on the agar gel layer, and the PDMS layer served to mimic mechanical stimuli. Based on this platform, C. elegans can perform chemical-mechanical associative learning behavior after training. Our findings indicated that the aversive component of training is the primary driver of the observed associative learning behavior. In addition, the results indicated that the neurotransmitter octopamine is involved in regulating this associative learning behavior via the SER-6 receptor. Thus, the microfluidic device provides a highly efficient platform for studying the associative learning behavior of C. elegans, and it may be applied in mutant screening and drug testing.

Acoustofluidic control of chemical concentration within picoliter droplets in a disposable microfluidic chip

We propose an acoustofluidic method to dynamically control the chemical concentration (CC) within picoliter-scale droplets at high-throughput production exceeding 2000 drops per second. Co-flowing laminar streams of two fluids were rapidly mixed via acoustic streaming flow-induced micro-vortices, and the mixing index was precisely controlled by modulating the wave amplitude. The mixed aqueous sample was fed into a T-junction as a dispersed phase with a continuous phase oil to produce droplets. We conducted numerical and experimental analysis on the flow mixing in terms of the flow rate and wave amplitude. We produced the droplets with tunable CCs with higher than 100-fold enhancement and the droplet libraries with varying inter-droplet chemical concentration (CCD) gradients. The temporal stability and dynamic controllability of the CCD were also verified by the experiments. We demonstrated the applicability of the proposed method by generating doxorubicin-loaded droplets with tunable CCs. The proposed device includes a disposable microfluidic chip to enable the reusable transducer on the piezoelectric substrate, leading to improved flexibility and functionality. We expect that the proposed method to produce droplet libraries with desired CCs is promising for various droplet microfluidic applications including high-through drug screening and discovery, combinatorial biochemistry, and synthesis of functionalized hydrogels.

Ti2Ni and TiNi3 intermetallic compounds to prepare dense TiNi alloy with enhanced recovery property

TiNi alloys fabricated through powder metallurgy suffer from low density and unsatisfactory recovery strain. In this paper, Ti2Ni/TiNi3 intermetallic compounds instead of Ti/Ni elements powders were chosen to improve both the relative density and recovery strain of TiNi alloy. The Kirkendall pores can be avoided due to the decreasing of the Ni atomic chemical concentration gradient in Ti2Ni/TiNi3, and the cracks and pores can be filled by liquid Ti2Ni, which improves the density of TiNi alloy up to 96.8%. Benefiting from the nano-crystalline/ amorphous matrix, the recoverable strain of TiNi alloy increased up to 7.46%. This novelty method shows great potential in developing low-cost and high-performance TiNi shape memory alloy.

Shape-Dictated Self-Assembly of Photoresponsive Hybrid Colloids.

The shape-dictated self-assembly of hybrid colloids induced by chemical concentration gradients generated by photocatalytic reactions of the colloids is studied. Different shapes enable the formation of assemblies with distinct lattice structures including hexagons, distorted hexagons, and squares, which are corroborated by computer simulations. Furthermore, assemblies change from lattices to chains when increasing the attraction between the colloids. The results show that photoresponsive hybrid colloids possess a unique capability for shape-dependent self-assembly, offering a practical and versatile approach to manipulate self-assembly at the microscale.

Bioinspired Jellyfish-like Carbon/Manganese nanomotors with H2O2 and NIR light Dual-propulsion for enhanced tumor penetration and chemodynamic therapy

Chemodynamic therapy (CDT), which catalyzes the production of highly toxic reactive oxygen species (ROS), has been widely used in tumor therapy in the past five years. However, most of the current nanomaterials for CDT are difficult to penetrate into the tumor effectively due to the lack of motility, resulting in an unsatisfactory CDT effect. Herein, bioinspired jellyfish-like carbon/manganese nanomotors (JCMNs) are designed to achieve hydrogen peroxide (H2O2) and NIR light dual-propulsion for the enhanced CDT therapy. Based on the jellyfish-like asymmetric structure, the manganese component can catalyze H2O2 to generate chemical concentration gradient, propelling JCMNs to dynamically generate ROS in cells by self-diffusiophoresis. In addition, the carbon component of JCMNs can absorb near-infrared (NIR) light to produce a temperature gradient, driving JCMNs to enhance tumor penetration by self-thermophoresis. The combination of chemical and NIR light propulsions significantly improves the efficiency of tumor CDT, revealing that it should be a reasonable strategy to promote the development of nanobiomedicine by endowing nanosystems with propulsion capacity.

Cryopreservable Through-Hole Arrays for the High-Throughput Three-Dimensional Smartphone-Based Cell Colorimetric Assay.

In vitro assays are an important platform for cancer research as they allow high-throughput experimentation that is not possible using in vivo animals. Although various in vitro assays are developed to study cell viability or migration, many of these assays are often limited to two dimensions, involving complex procedures or relying specialized equipment, etc. Here, we designed a simple colorimetric assay that accommodates automatic liquid samples loading, high-throughput generation of chemical concentration gradient, three-dimensional (3D) cell culture establishment, and smartphone-based colorimetric readouts. This assay is based on through-hole arrays in the poly(methyl methacrylate) (PMMA) layers. Liquid samples can be automatically loaded into through-hole arrays in PMMA layers by capillary force. Different drug concentrations can be generated by aligning and stacking to mix the contents of the corresponding through-holes with different volumes. 3D culture of cancer cells can be established by the rapid absorption of cell suspensions into the macroporous gels. After exposing the 3D cultured cells to different drug concentrations, the number of viable cells and migrated cells was reflected by the color change of Alamar blue, which enable on-site readout by a smartphone. This assay can study cell viability as well as cell migration, the two main characteristics of cancer cells, using one device. Interestingly, HeLa cells remained with high viability after cryopreservation at -80 °C, which allows for storage and distribution using dry ice. The simple protocol, along with the cryopreservability at -80 °C facilitates its ease of use to study cell viability together with cell migration in common laboratories or clinical settings.

Design of Christmas-Tree-like Microfluidic Gradient Generators for Cell-Based Studies

Microfluidic gradient generators (MGGs) provide a platform for investigating how cells respond to a concentration gradient or different concentrations of a specific chemical. Among these MGGs, those based on Christmas-tree-like structures possess advantages of precise control over the concentration gradient profile. However, in designing these devices, the lengths of channels are often not well considered so that flow rates across downstream outlets may not be uniform. If these outlets are used to culture cells, such non-uniformity will lead to different fluidic shear stresses in these culture chambers. As a result, cells subject to various fluidic stresses may respond differently in aspects of morphology, attachment, alignment and so on. This study reports the rationale for designing Christmas-tree-like MGGs to attain uniform flow rates across all outlets. The simulation results suggest that, to achieve uniform flow rates, the lengths of vertical channels should be as long as possible compared to those of horizontal channels, and modifying the partition of horizontal channels is more effective than elongating the lengths of vertical channels. In addition, PMMA-based microfluidic chips are fabricated to experimentally verify these results. In terms of chemical concentrations, perfect linear gradients are observed in devices with modified horizontal channels. This design rationale will definitely help in constructing optimal MGGs for cell-based applications including chemotherapy, drug resistance and drug screening.

Composite Norland Optical Adhesive (NOA)/silicon flow focusing devices for colloidal particle manipulation and synthesis

Microfluidic flow focusing devices are widely used to generate steep chemical concentration gradients at the interface between miscible or partially miscible streams. In this study, first we present an optimised protocol for the manufacturing of composite flow focusing devices, consisting of a micropatterned layer of Norland Optical Adhesive (NOA) glue bound to flat or microgrooved silicon substrates. Then, three different applications of these devices are demonstrated, namely (i) particle spreading and focusing in continuous flows past flat substrates, (ii) particle accumulation within the dead-end cavities of microgrooved substrates and (iii) synthesis of nano-sized liposomes. Colloidal particle spreading, focusing and accumulation were achieved through diffusiophoresis transport induced by salt concentration gradients at the interface between electrolyte streams. Epi-fluorescence microscopy was adopted to characterise the spatio-temporal distribution of silica and polystyrene nanoparticles in the devices with flat or microgrooved surfaces. The effects of particle zeta potential and groove thickness on particle dynamics were investigated. 1,2-di-(9Z-octadecenoyl)-sn-glycero-3-phosphocholine (DOPC) liposomes were generated by hydrodynamic focusing and characterised via dynamic light scattering. Liposome populations with controlled narrow size distributions could be achieved by adjusting the flow rate conditions in the devices. This work demonstrates that composite NOA/silicon flow junction devices offer a competitive alternative to conventional PDMS chips and can support a wide range of microfluidic applications, including nanoparticle synthesis, characterisation and filtration, drug encapsulation and biochemical analysis.

Design, simulation and application of multichannel microfluidic chip for cell migration

Cell migration is defined as the directional movement of cells toward a specific chemical concentration gradient, which plays a crucial role in embryo development, wound healing and tumor metastasis. However, current research methods showed low flux and are only suitable for single-factor assessment, and it was difficult to comprehensively consider the effects of other parameters such as different concentration gradients on cell migration behavior. In this paper, a four-channel microfluidic chip was designed. Its characteristics were as follows: it relied on laminar flow and diffusion mechanisms to establish and maintain a concentration gradient; it was suitable for observation of cell migration in different concentration gradient environment under a single microscope field; four cell isolation zones (20 μm width) were integrated into the microfluidic device to calibrate the initial cell position, which ensured the accuracy of the experimental results. In particular, we used COMSOL Multiphysics software to simulate the structure of the chip, which demonstrated the necessity of designing S-shaped microchannel and horizontal pressure balance channel to maintain concentration gradient. Finally, neutrophils were incubated with advanced glycation end products (AGEs, 0, 0.2, 0.5, 1.0 μmol·L -1), which were closely related to diabetes mellitus and its complications. The migration behavior of incubated neutrophils was studied in the 100 nmol·L -1 of chemokine (N-formylmethionyl-leucyl-phenyl-alanine) concentration gradient. The results prove the reliability and practicability of the microfluidic chip.

The role of predicted chemotactic and hydrocarbon degrading taxa in natural source zone depletion at a legacy petroleum hydrocarbon site

Petroleum hydrocarbon contamination is a global problem which can cause long-term environmental damage and impacts water security. Natural source zone depletion (NSZD) is the natural degradation of such contaminants. Chemotaxis is an aspect of NSZD which is not fully understood, but one that grants microorganisms the ability to alter their motion in response to a chemical concentration gradient potentially enhancing petroleum NSZD mass removal rates. This study investigates the distribution of potentially chemotactic and hydrocarbon degrading microbes (CD) across the water table of a legacy petroleum hydrocarbon site near Perth, Western Australia in areas impacted by crude oil, diesel and jet fuel. Core samples were recovered and analysed for hydrocarbon contamination using gas chromatography. Predictive metagenomic profiling was undertaken to infer functionality using a combination of 16 S rRNA sequencing and PICRUSt2 analysis. Naphthalene contamination was found to significantly increase the occurrence of potential CD microbes, including members of the Comamonadaceae and Geobacteraceae families, which may enhance NSZD. Further work to explore and define this link is important for reliable estimation of biodegradation of petroleum hydrocarbon fuels. Furthermore, the outcomes suggest that the chemotactic parameter within existing NSZD models should be reviewed to accommodate CD accumulation in areas of naphthalene contamination, thereby providing a more accurate quantification of risk from petroleum impacts in subsurface environments, and the scale of risk mitigation due to NSZD.