Multiscale Approach for Tuning Communication among Chemical Oscillators Confined in Biomimetic Microcompartments.

ConspectusInspired by the biological world, new cross-border disciplines and technologies have emerged. Relevant examples include systems chemistry, which offers a bottom-up approach toward chemical complexity, and bio/chemical information and communication technology (bio/chemical ICT), which explores the conditions for propagating signals among individual microreactors separated by selectively permeable membranes. To fabricate specific arrays of microreactors, microfluidics has been demonstrated as an excellent method. In particular, droplet-based microfluidics is a powerful tool for encapsulating biological entities and chemical reagents in artificial microenvironments, mostly water-in-oil microdroplets. In these systems, the interfaces are liquid-liquid, and their physicochemical properties are key factors for tuning the coupling between molecular diffusion. Simple and double emulsions, where aqueous domains are in equilibrium with oil domains through boundary layers of amphiphilic molecules, are organized assemblies with high interfacial-area-to-volume ratios. These membranes can be engineered to obtain different surface charges, single- or multilayer stacking, and a variable degree of defects in molecular packing. Emulsions find application in many fields, including the food industry, pharmaceutics, and cosmetics. Furthermore, micro- and nanoemulsions can be used to model the propagation of chemical species through long distances, which is not only vital for cell signaling but also significant in molecular computing. Here we present in-depth research on the faceted world of solutions confined in restricted environments. In particular, we focused on the multiscale aspects of structure and dynamics from molecular to micro and macro levels. The Belousov-Zhabotinsky chemical reaction, known for its robustness and well-documented oscillatory behavior, was selected to represent a generic signal emitter/receiver confined within microenvironments separated by liquid-liquid interfaces. In this pulse generator, the temporal and spatial progressions are governed by periodic fluctuations in the concentration of chemical species, which act as activatory or inhibitory messengers over long distances. When organized into "colonies" or arrays, these micro-oscillators exhibit emergent dynamical behaviors at the population level. These behaviors can be finely tuned by manipulating the geometrical distribution of the oscillators and the properties of the interfaces at the nanoscale. By carefully selecting the membrane composition, it is possible to drive the system toward either in-phase, antiphase, or mixed synchronization regimes among individual oscillators, depending on messenger molecules. This relatively simple lab-scale model replicates some of the communication strategies commonly found in biological systems, particularly those based on the passive diffusion of chemical and electrical signals. It can help shed light on fundamental life processes and inspire new implementations in molecular computing and smart materials.

Biosynthesis of magnetic nanoparticles from nano-degradation products revealed in human stem cells.

While magnetic nanoparticles offer exciting possibilities for stem cell imaging or tissue bioengineering, their long-term intracellular fate remains to be fully documented. Besides, it appears that magnetic nanoparticles can occur naturally in human cells, but their origin and potentially endogenous synthesis still need further understanding. In an effort to explore the life cycle of magnetic nanoparticles, we investigated their transformations upon internalization in mesenchymal stem cells and as a function of the cells' differentiation status (undifferentiated, or undergoing adipogenesis, osteogenesis, and chondrogenesis). Using magnetism as a fingerprint of the transformation process, we evidenced an important degradation of the nanoparticles during chondrogenesis. For the other pathways, stem cells were remarkably "remagnetized" after degradation of nanoparticles. This remagnetization phenomenon is the direct demonstration of a possible neosynthesis of magnetic nanoparticles in cellulo and could lay some foundation to understand the presence of magnetic crystals in human cells. The neosynthesis was shown to take place within the endosomes and to involve the H-subunit of ferritin. Moreover, it appeared to be the key process to avoid long-term cytotoxicity (impact on differentiation) related to high doses of magnetic nanoparticles within stem cells.

Tip Streaming of a Lipid-Stabilized Double Emulsion Generated in a Microfluidic Channel.

Water/oil/water (w/o/w) double emulsions (DEs) are multicompartment structures which can be used in many technological applications and in fundamental studies as models of cell like microreactors or templates for other materials. Herein, we study the flow dynamics of water/oil/water double emulsions generated in a microfluidic device and stabilized with the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). We show that by varying the concentration of lipids in the oil phase (chloroform) or by modulating the viscosity of the aqueous continuous phase, the double emulsions under flow exhibit a rich dynamic behavior. An initial deformation of the double emulsions is followed by tube extraction at the rear end, relative to the flow direction, resulting in pinch off at the tube extremity by which small aqueous compartments are released. These compartments are phospholipid vesicles as deduced from fluorescence experiments. The overall process can thus be of help to shed light on the mechanical aspects of phenomena such as the budding and fusion in cell membranes.

Synchronization scenarios induced by delayed communication in arrays of diffusively coupled autonomous chemical oscillators.

We study the impact of delayed feedbacks in the collective synchronization of ensembles of identical and autonomous micro-oscillators. To this aim, we consider linear arrays of Belousov-Zhabotinsky (BZ) oscillators confined in micro-compartmentalised systems, where the delayed feedback mimics natural lags that can arise due to the confinement properties and mechanisms driving the inter-oscillator communication. The micro-oscillator array is modeled as a set of Oregonator-like kinetics coupled via mass exchange of the chemical messengers. Changes in the synchronization patterns are explored by varying the delayed feedback introduced in the messenger species Br2. A direct transition from anti-phase to in-phase synchronization and back to the initial anti-phase scheme is observed by progressively increasing the time delay from zero to the value T0, which is the oscillation period characterising the system without any delayed coupling. The route from anti- to in-phase oscillations (and back) consists of regimes where windows of in-phase oscillations are periodically broken by anti-phase beats. Similarities between these phase transition dynamics and synchronization scenarios characterising the coordination of oscillatory limb movements are finally discussed.

Transient cell stiffening triggered by magnetic nanoparticle exposure.

BACKGROUND: The interactions between nanoparticles and the biological environment have long been studied, with toxicological assays being the most common experimental route. In parallel, recent growing evidence has brought into light the important role that cell mechanics play in numerous cell biological processes. However, despite the prevalence of nanotechnology applications in biology, and in particular the increased use of magnetic nanoparticles for cell therapy and imaging, the impact of nanoparticles on the cells' mechanical properties remains poorly understood. RESULTS: Here, we used a parallel plate rheometer to measure the impact of magnetic nanoparticles on the viscoelastic modulus G*(f) of individual cells. We show how the active uptake of nanoparticles translates into cell stiffening in a short time scale (< 30 min), at the single cell level. The cell stiffening effect is however less marked at the cell population level, when the cells are pre-labeled under a longer incubation time (2 h) with nanoparticles. 24 h later, the stiffening effect is no more present. Imaging of the nanoparticle uptake reveals almost immediate (within minutes) nanoparticle aggregation at the cell membrane, triggering early endocytosis, whereas nanoparticles are almost all confined in late or lysosomal endosomes after 2 h of uptake. Remarkably, this correlates well with the imaging of the actin cytoskeleton, with actin bundling being highly prevalent at early time points into the exposure to the nanoparticles, an effect that renormalizes after longer periods. CONCLUSIONS: Overall, this work evidences that magnetic nanoparticle internalization, coupled to cytoskeleton remodeling, contributes to a change in the cell mechanical properties within minutes of their initial contact, leading to an increase in cell rigidity. This effect appears to be transient, reduced after hours and disappearing 24 h after the internalization has taken place.

Insight into the Ferrier Rearrangement by Combining Flash Chemistry and Superacids.

The transformation of glycals into 2,3-unsaturated glycosyl derivatives, reported by Ferrier in 1962, is supposed to involve an α,ß unsaturated glycosyl cation, an elusive ionic species that has still to be observed experimentally. Herein, while combination of TfOH and flow conditions failed to observe this ionic species, its extended lifetime in superacid solutions allowed its characterization by NMR-based structural analysis supported by DFT calculations. This allyloxycarbenium ion was further exploited in the Ferrier rearrangement to afford unsaturated nitrogen-containing C-aryl glycosides and C-alkyl glycosides under superacid and flow conditions, respectively.

Division of Ferrofluid Drops Induced by a Magnetic Field.

We report a comprehensive study of the division of ferrofluid drops caused by their interaction with a permanent magnet. As the magnet gradually approaches the sessile drop, the drop deforms into a spiked cone and then divides into two daughter droplets. This process is the result of a complex interplay between the polarizing effect caused by the magnetic field and the magnetic attraction due to the field gradient. As a first attempt to describe it, during each scan we identify two characteristic distances between the magnet and the drop: zmax, corresponding to the drop reaching its maximum height, and zsaddle, corresponding to the formation of a saddle point on the drop peak identifying the beginning of the drop breakup. We have investigated the location of these two points using sessile drops of ferrofluid water solutions at various concentrations and volumes, deposited on four surfaces of different wettability. An empirical scaling law based on dimensionless variables is found to accurately describe these experimental observations. We have also measured the maximum diameter of the drops right before the division and found that it is very close to a critical size, which depends on the magnetic attraction.

Lipid-Stabilized Water-Oil Interfaces Studied by Microfocusing Small-Angle X-ray Scattering.

Water-in-oil (w/o) simple emulsions are dispersed microconfined systems that find applications in many areas of advanced materials and biotechnology, such as the food industry, drug delivery, and cosmetics, to name but a few. In these systems, the structural and chemical properties of the boundary layer at the w/o interface are of paramount importance in determining functionality and stability. Recently, microfluidic methods have emerged as a valuable tool for fabricating monodisperse emulsion droplets. Because of the intrinsic flexibility of microfluidics, different interfaces can be obtained, and general principles governing their stability are needed to guide the experimental approach. Herein, we investigate the structural characteristics of the region encompassing the liquid/liquid (L/L) interface of w/o emulsions generated by a microfluidic device in the presence of phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and other intercalating amphiphiles (dopants) using microfocused small-angle X-rays scattering (µ-SAXS). We show that phospholipids provide a stable and versatile boundary film of ∼100 µm whose basic units are swollen and uncorrelated DMPC bilayers. The internal arrangement of this interfacial film can be tuned by adding molecules with a different packing parameter, such as cholesterol, which is able to increase the stiffness of the lipid membranes and trigger interbilayer correlation.

Sprouting Droplets Driven by Physical Effects Alone.

Combining a partially miscible three-liquid system with interfacially trapped silica colloids, we show that small droplets can exhibit dramatic growth phenomena driven by physical effects alone. The mass dense droplets sprout tubes which grow vertically upward in a gravitational field and respond to the presence of other droplets in their path. Two of the liquids in our system are water and toluene. By varying the third liquid, we are able to relate the growth behavior to the details of the underlying three-fluid phase diagram and the changes to the interfacial tension. Additionally, we introduce a pendant drop in the path of our growing drop. We use this to confirm that growth is driven by the partitioning of solvents, that exchange of solvents between droplets is chemically selective, and that the exchange behavior can itself generate further growth phenomena.

Static Magnetowetting of Ferrofluid Drops.

We report results of a comprehensive study of the wetting properties of sessile drops of ferrofluid water solutions at various concentrations deposited on flat substrates and subjected to the action of permanent magnets of different sizes and strengths. The amplitude and the gradient of the magnetic field experienced by the ferrofluid are changed by varying the magnets and their distance to the surface. Magnetic forces up to 100 times the gravitational one and magnetic gradients up to 1 T/cm are achieved. A rich phenomenology is observed, ranging from flattened drops caused by the magnetic attraction to drops extended normally to the substrate because of the normal traction of the magnetic field. We find that the former effect can be conveniently described in terms of an effective Bond number that compares the effective drop attraction with the capillary force, whereas the drop's vertical elongation is effectively expressed by a dimensionless number S, which compares the pressure jump at the ferrofluid interface because of the magnetization with the capillary pressure.

Scanning electrochemical microscopy of Belousov-Zhabotinsky reaction: how confined oscillations reveal short lived radicals and auto-catalytic species.

Oscillating chemical reactions, encapsulated within artificial vesicles have been demonstrated as a powerful analogy of living cells for the investigation of chemical communication and morphogenesis. However, little is understood with regards to the influence of confinement on the reactivity of such systems. Herein, the effect of confinement on the Belousov-Zhabotinsky (BZ) oscillating reaction in bulk solution, (employing ferroin as a catalyst and malonic acid as the organic substrate) is investigated using scanning electrochemical microscopy (SECM) toward different insulating surfaces such as glass, silanized glass, or PTFE. An unexpected increase in the amplitude of the BZ reaction at a tip-substrate distance of ∼12-15 µm is observed. By simulating different reaction mechanisms, from simple EC' catalysis to more sophisticated Oregonator or even an 11-reaction scheme, it is shown that such behavior reveals the intervention of redox catalysis processes and particularly the short-lived highly reactive radical intermediate BrO2(•) indirectly detected at micromolar concentrations. The reinspection of the EC' mechanism shows that the homogeneous catalysis route is confirmed and kinetically characterized from SECM toward an insulating substrate, with promising potentiality in many systems. More specifically to the complex chemical case of BZ reactions, the mechanism is understood from the envelope curves of the oscillations, which are assessed in the absence of the oscillation (absence of organic substrate).

Biodegradation by Cancer Cells of Magnetite Nanoflowers with and without Encapsulation in PS-b-PAA Block Copolymer Micelles.

Magnetomicelles were produced by the self-assembly of magnetite iron oxide nanoflowers and the amphiphilic poly(styrene)-b-poly(acrylic acid) block copolymer to deliver a multifunctional theranostic agent. Their bioprocessing by cancer cells was investigated in a three-dimensional spheroid model over a 13-day period and compared with nonencapsulated magnetic nanoflowers. A degradation process was identified and monitored at various scales, exploiting different physicochemical fingerprints. At a collective level, measurements were conducted using magnetic, photothermal, and magnetic resonance imaging techniques. At the nanoscale, transmission electron microscopy was employed to identify the morphological integrity of the structures, and X-ray absorption spectroscopy was used to analyze the degradation at the crystalline phase and chemical levels. All of these measurements converge to demonstrate that the encapsulation of magnetic nanoparticles in micelles effectively mitigates their degradation compared to individual nonencapsulated magnetic nanoflowers. This protective effect consequently resulted in better maintenance of their therapeutic photothermal potential. The structural degradation of magnetomicelles occurred through the formation of an oxidized iron phase in ferritin from the magnetic nanoparticles, leaving behind empty spherical polymeric ghost shells. These results underscore the significance of encapsulation of iron oxides in micelles in preserving nanomaterial integrity and regulating degradation, even under challenging physicochemical conditions within cancer cells.

Confining calcium oxalate crystal growth in a carbonated apatite-coated microfluidic channel to better understand the role of Randall's plaque in kidney stone formation.

Effective prevention of recurrent kidney stone disease requires the understanding of the mechanisms of its formation. Numerous in vivo observations have demonstrated that a large number of pathological calcium oxalate kidney stones develop on an apatitic calcium phosphate deposit, known as Randall's plaque. In an attempt to understand the role of the inorganic hydroxyapatite phase in the formation and habits of calcium oxalates, we confined their growth under dynamic physicochemical and flow conditions in a reversible microfluidic channel coated with hydroxyapatite. Using multi-scale characterization techniques including scanning electron and Raman microscopy, we showed the successful formation of carbonated hydroxyapatite as found in Randall's plaque. This was possible due to a new two-step flow seed-mediated growth strategy which allowed us to coat the channel with carbonated hydroxyapatite. Precipitation of calcium oxalates under laminar flow from supersaturated solutions of oxalate and calcium ions showed that the formation of crystals is a substrate and time dependent complex process where diffusion of oxalate ions to the surface of carbonated hydroxyapatite and the solubility of the latter are among the most important steps for the formation of calcium oxalate crystals. Indeed when an oxalate solution was flushed for 24 h, dissolution of the apatite layer and formation of calcium carbonate calcite crystals occurred which seems to promote calcium oxalate crystal formation. Such a growth route has never been observed in vivo in the context of kidney stones. Under our experimental conditions, our results do not show any direct promoting role of carbonated hydroxyapatite in the formation of calcium oxalate crystals, consolidating therefore the important role that macromolecules can play in the process of nucleation and growth of calcium oxalate crystals on Randall's plaque.

Impact of airborne iron oxide nanoparticles on Tillandsia usneoides as a model plant to assess pollution in heavy traffic areas.

Due to the increasing evidence of widespread sub-micron pollutants in the atmosphere, the impact of airborne nanoparticles is a subject of great relevance. In particular, the smallest particles are considered the most active and dangerous, having a higher surface/volume ratio. Here we tested the effect of iron oxide (Fe3O4) nanoparticles (IONPs) with different mean diameter and size distribution on the model plant Tillandsia usneoides. Strands were placed in home-built closed boxes and exposed to levels of airborne IONPs reported for the roadside air, i.e. in the order of 107 - 108 items m-2. Plant growth and other morpho-physiological parameters were monitored for two weeks, showing that exposure to IONPs significantly reduced the length increment of the treated strands with respect to controls. A dose-dependence of this impairing effect was found only for particles with mean size of a few tens of nanometers. These were also proved to be the most toxic at the highest concentration tested. The IONP-induced hamper in growth was correlated with altered concentration of macro- and micronutrients in the plant, while no significant variation in photosynthetic activity was detected in treated samples. Microscopy investigation showed that IONPs could adhere to the plant surface and were preferentially located on the trichome wings. Our results report, for the first time, evidence of the negative effects of airborne IONP pollution on plant health, thus raising concerns about related environmental risks. Future research should be devoted to other plant species and pollutants to assess the impact of airborne pollution on plants and devise suitable attenuation practices.

Emergence of magnetic nanoparticles in photothermal and ferroptotic therapies.

With their distinctive physicochemical features, nanoparticles have gained recognition as effective multifunctional tools for biomedical applications, with designs and compositions tailored for specific uses. Notably, magnetic nanoparticles stand out as first-in-class examples of multiple modalities provided by the iron-based composition. They have long been exploited as contrast agents for magnetic resonance imaging (MRI) or as anti-cancer agents generating therapeutic hyperthermia through high-frequency magnetic field application, known as magnetic hyperthermia (MHT). This review focuses on two more recent applications in oncology using iron-based nanomaterials: photothermal therapy (PTT) and ferroptosis. In PTT, the iron oxide core responds to a near-infrared (NIR) excitation and generates heat in its surrounding area, rivaling the efficiency of plasmonic gold-standard nanoparticles. This opens up the possibility of a dual MHT + PTT approach using a single nanomaterial. Moreover, the iron composition of magnetic nanoparticles can be harnessed as a chemotherapeutic asset. Degradation in the intracellular environment triggers the release of iron ions, which can stimulate the production of reactive oxygen species (ROS) and induce cancer cell death through ferroptosis. Consequently, this review emphasizes these emerging physical and chemical approaches for anti-cancer therapy facilitated by magnetic nanoparticles, combining all-in-one functionalities.

High-throughput large scale microfluidic assembly of iron oxide nanoflowers@PS-b-PAA polymeric micelles as multimodal nanoplatforms for photothermia and magnetic imaging.

Magnetic nanoparticles have been extensively explored as theranostic agents both in academic and clinical settings. Their self-assembly into nanohybrids using block copolymers can lead to new nanostructures with high functionalities and performances. Herein, we demonstrate a high-throughput and scalable method to elaborate magnetic micelles by the assembly of iron oxide magnetite nanoflowers, an efficient nanoheater, and the block copolymer Poly(styrene)-block-poly(acrylic acid) via a microfluidic-assisted nanoprecipitation method. We show that the size and shape of the magnetomicelles can be easily tuned by modulating the residence time in the microfluidic channel. In addition to their biocompatibility, we demonstrate the potential of these magnetic nanohybrids as multimodal theranostic platforms capable of generating heat by photothermia and functioning as negative contrast agents in magnetic resonance imaging and as imaging tracers in magnetic particle imaging. Notably, they outperform currently commercially available particles in terms of imaging functionalities.

In Vivo Assimilation of CuS, Iron Oxide and Iron Oxide@CuS Nanoparticles in Mice: A 6-Month Follow-Up Study.

Nanoparticles (NPs) are at the leading edge of nanomedicine, and determining their biosafety remains a mandatory precondition for biomedical applications. Herein, we explore the bioassimilation of copper sulfide NPs reported as powerful photo-responsive anticancer therapeutic agents. The nanoparticles investigated present a hollow shell morphology, that can be left empty (CuS NPs) or be filled with an iron oxide flower-like core (iron oxide@CuS NPs), and are compared with the iron oxide nanoparticles only (iron oxide NPs). CuS, iron oxide@CuS and iron oxide NPs were injected in 6-week-old mice, at doses coherent with an antitumoral treatment. Cu and Fe were quantified in the liver, spleen, kidneys, and lungs over 6 months, including the control animals, thus providing endogenous Cu and Fe levels in the first months after animal birth. After intravenous NPs administration, 77.0 ± 3.9% of the mass of Cu injected, and 78.6 ± 3.8% of the mass of Fe, were detected in the liver. In the spleen, we found 3.3 ± 0.6% of the injected Cu and 3.8 ± 0.6% for the Fe. No negative impact was observed on organ weight, nor on Cu or Fe homeostasis in the long term. The mass of the two metals returned to the control values within three months, a result that was confirmed by transmission electron microscopy and histology images. This bioassimilation with no negative impact comforts the possible translation of these nanomaterials into clinical practice.

Angular orientation between the cores of iron oxide nanoclusters controls their magneto-optical properties and magnetic heating functions.

Oriented attachment of nanobricks into hierarchical multi-scale structures such as inorganic nanoclusters is one of the crystallization mechanisms that has revolutionized the field of nano and materials science. Herein, we show that the mosaicity, which measures the misalignment of crystal plane orientation between the nanobricks, governs their magneto-optical properties as well as the magnetic heating functions of iron oxide nanoclusters. Thanks to high-temperature and time-resolved millifluidic, we were able to isolate and characterize (structure, properties, function) the different intermediates involved in the diverse steps of the nanocluster's formation, to propose a detailed dynamical mechanism of their formation and establish a clear correlation between changes in mosaicity at the nanoscale and their resulting physical properties. Finally, we demonstrate that their magneto-optical properties can be described using simple molecular theories.

Structure-Property-Function Relationships of Iron Oxide Multicore Nanoflowers in Magnetic Hyperthermia and Photothermia.

Magnetite and maghemite multicore nanoflowers (NFs) synthesized using the modified polyol-mediated routes are to date among the most effective nanoheaters in magnetic hyperthermia (MHT). Recently, magnetite NFs have also shown high photothermal (PT) performances in the most desired second near-infrared (NIR-II) biological window, making them attractive in the field of nanoparticle-activated thermal therapies. However, what makes magnetic NFs efficient heating agents in both modalities still remains an open question. In this work, we investigate the role of many parameters of the polyol synthesis on the final NFs' size, shape, chemical composition, number of cores, and crystallinity. These nanofeatures are later correlated to the magnetic, optical, and electronic properties of the NFs as well as their collective macroscopic thermal properties in MHT and PT to find relationships between their structure, properties, and function. We evidence the critical role of iron(III) and heating ramps on the elaboration of well-defined NFs with a high number of multicores. While MHT efficiency is found to be proportional to the average number of magnetic cores within the assemblies, the optical responses of the NFs and their collective photothermal properties depend directly on the mean volume of the NFs (as supported by optical cross sections numerical simulations) and strongly on the structural disorder in the NFs, rather than the stoichiometry. The concentration of defects in the nanostructures, evaluated by photoluminescence and Urbach energy (EU), evidence a switch in the optical behavior for a limit value of EU = 0.4 eV where a discontinuous transition from high to poor PT efficiency is also observed.

High Temperature Continuous Flow Syntheses of Iron Oxide Nanoflowers Using the Polyol Route in a Multi-Parametric Millifluidic Device.

One of the most versatile routes for the elaboration of nanomaterials in materials science, including the synthesis of magnetic iron oxide nanoclusters, is the high-temperature polyol process. However, despite its versatility, this process still lacks reproducibility and scale-up, in addition to the low yield obtained in final materials. In this work, we demonstrate a home-made multiparametric continuous flow millifluidic system that can operate at high temperatures (up to 400 °C). After optimization, we validate its potential for the production of nanomaterials using the polyol route at 220 °C by elaborating ferrite iron oxide nanoclusters called nanoflowers (CoFe2O4, Fe3O4, MnFe2O4) with well-controlled nanostructure and composition, which are highly demanded due to their physical properties. Moreover, we demonstrate that by using such a continuous process, the chemical yield and reproducibility of the nanoflower synthesis are strongly improved as well as the possibility to produce these nanomaterials on a large scale with quantities up to 45 g per day.