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The long-ranged interactions induced by magnetic fields and capillary forces in multiphasic fluid–particle systems facilitate the assembly of a rich variety of colloidal structures and materials.

We investigate the role of the polymer network structure on the corrosion protection efficiency of thermoset epoxy coatings on metals as a prerequisite for the future design of safer alternatives to bisphenol A-based epoxy resins.

The antinoroviral effect of copper ions is well known, yet most of this work has previously been conducted in copper and copper alloy surfaces, not copper ions in solution. In this work, we characterized the effects that Cu ions have on human norovirus capsids' and surrogates' integrity to explain empirical data, indicating virus inactivation by copper alloy surfaces, and as means of developing novel metal ion-based virucides. Comparatively high concentrations of Cu(II) ions (10 mM) had little effect on the infectivity of human norovirus surrogates, so we used sodium ascorbate as a reducing agent to generate unstable Cu(I) ions from solutions of copper bromide. We found that significantly lower concentrations of monovalent copper ions (∼0.1 mM) compared to divalent copper ions cause capsid protein damage that prevents human norovirus capsids from binding to cell receptors

It is challenging to find a conventional nanofabrication technique that can consistently produce soft polymeric matter of high surface area and nanoscale morphology in a way that is scalable, versatile, and easily tunable. Here, the capabilities of a universal method for fabricating diverse nano- and micro-scale morphologies based on polymer precipitation templated by the fluid streamlines in multiphasic flow are explored. It is shown that while the procedure is operationally simple, various combinations of its intertwined mechanisms can controllably and reproducibly lead to the formation of an extraordinary wide range of colloidal morphologies. By systematically investigating the process conditions, 12 distinct classes of polymer micro- and nano-structures including particles, rods, ribbons, nanosheets, and soft dendritic colloids (dendricolloids) are identified. The outcomes are interpreted by delineating the physical processes into three stages: hydrodynamic shear, capillary and mechanical breakup, and polymer precipitation rate. The insights into the underlying fundamental mechanisms provide guidance toward developing a versatile and scalable nanofabrication platform. It is verified that the liquid shear-based technique is versatile and works well with many chemically diverse polymers and biopolymers, showing potential as a universal tool for simple and scalable nanofabrication of many morphologically distinct soft matter classes.

In this study, highly porous, ultrasoft polymeric mats mimicking human tissues were formed from novel polyurethane soft dendritic colloids (PU SDCs). PU SDCs have a unique fibrillar morphology controlled by antisolvent precipitation. When filtered from suspension, PU SDCs form mechanically robust nonwoven mats. The stiffness of the SDC mats can be tuned for physiological relevance. The unique physiochemical characteristics of the PU SDC particles dictate the mechanical properties resulting in tunable elastic moduli ranging from 200 to 800 kPa. The human lung A549 cells cultured on both stiff and soft PU SDC membranes were found to be viable, capable of supporting the air-liquid interface (ALI) cell culture, and maintained barrier integrity. Furthermore, A549 cellular viability and uptake efficiency of aerosolized tannic acid-coated gold nanoparticles (Ta-Au) was found to depend on elastic modulus and culture conditions. Ta-Au nanoparticle uptake was twofold and fourfold greater on soft PU SDCs, when cultured at submerged and ALI conditions, respectively. The significant increase in endocytosed Ta-Au resulted in a 20% decrease in viability, and a 4-fold increase in IL-8 cytokine secretion when cultured on soft PU SDCs at ALI. Common tissue culture materials exhibit super-physiological elastic moduli, a factor found to be critical in analyzing nanomaterial cellular interactions and biological responses.

Wearable and wireless monitoring of biomarkers such as lactate in sweat can provide a deeper understanding of a subject's metabolic stressors, cardiovascular health, and physiological response to exercise. However, the state-of-the-art wearable and wireless electrochemical systems rely on active sweat released either

In recent years, there have been many advances toward developing sustainable, micro- and nanoscale materials from biobased resources such as lignin aimed at strengthening the bioeconomy. It is critical to study the factors affecting nucleation and growth mechanisms, as well as the stability of lignin micro-and nanoparticles (LPs), to further enhance the development of such materials. However, there remains a gap in the literature examining the many interactions present during and after LP formation. These interactions vary with the chemical composition and molecular weight distribution of different kraft lignin (KL) fractions. To examine the composition of different lignin fractions, KL can be fractionated using water-miscible organic solvents of different polarities such as tetrahydrofuran (THF), acetone, and ethanol. Herein, we show that the micro- and nanoparticles formed from each lignin fraction exhibit significant differences in their size (50–300 nm), particle aggregation and fusion propensity, and spherical morphology in aqueous suspensions. These differences are proposed to be a result of the solvent–lignin–water interactions related to molecular weight and functional groups of the lignin fractions and solvent/water polarity. Another factor affecting the nucleation and growth of LPs is the lignin concentration. The LPs formed at low lignin concentrations exhibit a larger average particle size compared to the LPs formed at higher lignin concentrations due to the aggregation and fusion of the small particles. These results will allow for a stronger foundation in understanding the nucleation and growth of LPs when attempting to develop value-added applications for kraft lignin.

The interactions between biomembranes and particles are key to many applications, but the lack of controllable model systems to study them limits the progress in their research. Here, we describe how Janus polystyrene microparticles, half coated with iron, can be partially engulfed by artificial cells, namely giant vesicles, with the goals to control and investigate their adhesion and degree of encapsulation. The interaction between the Janus particles and these model cell membrane systems is mediated by electrostatic charge, offering a further mode of modulation in addition to the iron patches. The ferromagnetic particle coatings also enable the ability to manipulate and transport the vesicles by magnetic fields.

Miniaturized devices capable of active swimming at low Reynolds numbers are of fundamental importance and possess potential biomedical utility. The design of colloidal microswimmers requires not only miniaturizing reconfigurable structures but also understanding their interactions with media at low Reynolds numbers. We investigate the dynamics of "microscallops" made of asymmetric magnetic cubes, which are assembled and actuated using magnetic fields. One approach to achieving directional propulsion is to break the symmetry of the viscous forces by coupling the reciprocal motions of such microswimmers with the nonlinear rheology inherent in non-Newtonian fluids. When placed in shear-thinning fluids, the local viscosity gradient resulting from nonuniform shear stresses exerted by time-asymmetric strokes of the microscallops generates propulsive thrust through an effect we term "self-viscophoresis". Surprisingly, we found that the direction of propulsion changes with the size and structure of these assemblies. We analyze the origins of their directional propulsion and explain the variable propulsion direction in terms of multiple counterbalancing domains of shear dissipation around the microscale structures. The principles governing the locomotion of these microswimmers may be extended to other reconfigurable microbots assembled from colloidal-scale units.

Process control strategies based on the physiological status of cells have recently been used to enhance mammalian cell culture productivity and robustness. In this study, we investigated the feasibility of using full-spectrum dielectric spectroscopy for detecting shifts in cell physiology and as a feedback tool to increase process efficiency. Multi-frequency permittivity spectra were collected from cell culture processes in which apoptosis was induced by glucose depletion, nutrient depletion, or chemical treatment. Meanwhile, key parameters of critical frequency (fc) and Cole-Cole alpha (α) were calculated in real time from the β-dispersion curve and correlated to data from off-line viability measurements. Results show that physiological changes in apoptotic cells were reflected in the on-line parameters earlier than from off-line methods. Using information from the on-line parameters, we achieved partial or full recovery from early apoptosis by replenishing the depleted feed. We also demonstrate that by using trends in fc, we could detect a deviation in media preparation in a manufacturing process which could not be achieved using conventional measurements. The results demonstrate that full-spectrum dielectric spectroscopy can be used as a facile tool for early detection of physiological changes and process adjustment in real-time to enhance bioreactor process productivity and robustness.

Adoption of electric vehicles and increasing demands of consumer electronics require electrochemical energy storage devices with high capacity and rate capabilities. Supply-chain and material-cost concerns as well as charge-rate limitations associated with irreversible lattice changes motivates the replacement of mixed-metal oxide cathodes in lithium-ion batteries (LIBs). Electrochemically active polymeric materials have emerged as promising candidates to replace metal oxides due to their high tunability and increased capacity. However, many of these materials suffer from poor intrinsic electronic conductivity and may be soluble into the electrolyte, causing irreversible capacity fade. Nanostructuring and composite formation are two polymer processing methods that can be leveraged to combat these drawbacks. The introduction of new nanostructured and nanocomposite cell components can decrease diffusion length scales, increase mechanical stability, and allow for higher electronic conductivity in polymer electrodes. Herein, we utilize a new class of polymeric materials called soft dendritic colloids (SDCs) as a platform for creating such nanocomposites. These fibrillar polymeric particles, formed via turbulent solvent-nonsovent induced phase separation, have hierarchical morphology, large aspect ratios and demonstrate pronounced adhesion and network-forming behavior. SDC-based materials have shown impressive results as nonwoven polyvinylidene difluoride separators in Li-ion batteries. Herein, we propose and present their use as Li-ion battery electrodes with advanced structural properties, derived from electroactive polymeric materials.

The deposition of coatings with hierarchical morphology from hydrophobic and hydrophilic polymers is a common approach for making superhydrophobic and superhydrophilic coatings. The water-repellent, water-wicking, and anti-icing coatings reported here are made from a class of materials called soft dendritic colloids (SDCs). The branched, nanofibrous SDCs are produced in suspension through nonsolvent-induced phase separation in a turbulent medium. The properties of coatings formed by drying ethanol suspensions of SDCs made of polystyrene, polyvinyl alcohol, and polyester are compared. The highly branched SDC morphology creates entangled, porous coating layers with strong physical adhesion to the substrate due to the multitude of nanofiber sub-contacts analogous to the "gecko leg effect". Polystyrene SDC coatings show excellent superhydrophobicity but weaker adhesion due to low surface energy. Alternatively, polyvinyl alcohol SDC coatings show superhydrophilicity and strong adhesion from their high surface energy. Two strategies to improve the adhesivity and cohesivity of the SDCs layers are shown effective - use of intertwined networks and of silicone droplet microbinders. The water repulsion, together with the air trapped in the blended superhydrophobic coatings also makes them effective against ice nucleation and adhesion. Finally, these SDCs make thin, flexible, and durable nonwovens with similar properties.

Hypothesis Wetting characteristics of epoxy and phenolic resins on metals depend on the molecular interactions between resins’ functional groups and metal surface. Those interactions affect the practical adhesion strength of epoxy-phenolic coatings on metals. Estimation of the theoretical adhesion energies can reveal this system’s microscopic adhesion mechanisms. Experiments Adhesion is estimated theoretically based on resins’ wettability on metals, and experimentally through pull-off adhesion testing of cured coatings. The effect of various functional groups on adhesion is decoupled using epoxy and phenolic resins with different functionalities. To assess the impact of the metal passivation on adhesion, tinplated and tin-free steel substrates are used. Differences in their surface chemical composition and polarity are investigated using XPS. Findings Theoretical adhesion results reveal a superior adhesion of epoxy compared to phenolic resins. Moreover, epoxy resins having a higher content of epoxide-to-hydroxyl groups show improved theoretical and practical adhesion. The importance of epoxides in driving resins’ initial adhesion on metals is attributed to the formation of direct chemical bonds with active hydrogen on metal surfaces. The adhesion of coatings on tin-free steel is found to be higher than on tinplated steel. This is associated to the increased hydroxyl fraction on tin-free steel surface leading to more hydrogen bonds formation.

Magnetic fields offer untethered control over the assembly, dynamics, and reconfiguration of colloidal particles. However, synthesizing "soft" colloidal particles with switchable magnetic dipole moment remains a challenge, primarily due to strong coupling of the dipoles of the adjacent nanoparticles. In this article, we present a way to overcome this fundamental challenge based on a strategy to synthesize soft microbeads with tunable residual dipole moment. The microbeads are composed of a polydimethylsiloxane (PDMS) matrix with internally embedded magnetic nanoparticles (MNPs). The distribution and orientation of the MNPs within the PDMS bead matrix is controlled by an external magnetic field during the synthesis process, thus allowing for the preparation of anisotropic PDMS microbeads with internal magnetically aligned nanoparticle chains. We study and present the differences in magnetic interactions between microbeads containing magnetically aligned MNPs and microbeads with randomly distributed MNPs. The interparticle interactions in a suspension of microbeads with embedded aligned MNP chains result in the spontaneous formation of percolated networks due to residual magnetization. We proved the tunability of the structure by applying magnetization, demagnetization, and remagnetization cycles that evoke formation, breakup, and reformation of 2D percolated networks. The mechanical response of the microbead suspension was quantified by oscillatory rheology and correlated to the propensity for network formation by the magnetic microbeads. We also experimentally correlated the 2D alignment of the microbeads to the direction of earth's magnetic field. Overall, the results prove that the soft magnetic microbeads enable a rich variety of structures and can serve as an experimental toolbox for modeling interactions in dipolar systems leading to various percolated networks, novel magneto-rheological materials, and smart gels.

The preparation of fumed silica based anisometric supraparticles with well defined catalytically active patches suitable for self propulsion is presented here. These sub millimeter sized particles can self propel as they contain Pt covered magnetite Fe3O4 nanoparticles, where the Pt can decompose catalytically a fuel like H2O2 and thereby propel the supraparticles. By their magnetic properties, the catalytically active nanoparticles can be concentrated in patches on the supraparticle surface. The goal is to obtain robust supraparticles with well defined patchiness and long time stability during self propulsion through evaporation induced self assembly EISA on a superhydrophobic surface. The latter is a major issue as oxygen evolution can lead to the disintegration of the supraparticles. Therefore, enhanced mechanical stability is sought using a number of different additives, where the best results are obtained by incorporating polystyrene microspheres followed by heat treatment or reinforcement with microfibrillated cellulose MFC and sodium trisilicate Na2SiO3 . The detailed internal structure of the different types of particles is investigated by confocal micro X ray fluorescence spectroscopy CMXRF , which allows for precisely locating the catalytic Fe3O4 Pt nanoparticles within the supraparticles with a resolution in the m range. The insights on the supraparticle structure, together with their long time stability, allow fabricating optimized patchy supraparticles for potential applications in propulsion enhanced catalysis

Biomarkers in sweat are a largely untapped source of health information. Most of the currently available sweat harvesting and testing devices are incapable of operating under low-sweat rates such as those experienced by humans at rest. Here we analyze the in vitro and in vivo sampling of sweat through osmosis via the use of a hydrogel interfaced with the skin, without need for active perspiration. The hydrogel also interfaces with paper-based microfluidics to transport the fluid via capillary forces toward a testing zone and then evaporation pad. We show that the hydrogel solute content and area of the evaporation pad regulate the long-term extraction of sweat and its associated biomarkers. The results indicate that the platform can sample biomarkers from a model skin system continuously for approximately 12 h. On-skin testing of the platform on both resting and exercising human subjects confirms that it can sample sweat lactate directly from the surface of skin. The results highlight that lactate in sweat increases with exercise and as a direct result of muscle activity. Implementation of such new principles for sweat fluid harvesting and management via wearable patch devices can contribute toward the advancement of next generation wearables.

Lignin is the second most abundant biopolymer on Earth after cellulose. Since lignin breaks down in the environment naturally, lignin nanoparticles may serve as biodegradable carriers of biocidal actives with minimal environmental footprint compared to conventional antimicrobial formulations. Here, a lignin nanoparticle (LNP) coated with chitosan was engineered. Previous studies show both lignin and chitosan to exhibit antimicrobial properties. Another study showed that adding a chitosan coating can improve the adsorption of LNPs to biological samples by electrostatic adherence to oppositely charged surfaces. Our objective was to determine if these engineered particles would elicit toxicological responses, utilizing embryonic zebrafish toxicity assays. Zebrafish were exposed to nanoparticles with an intact chorionic membrane and with the chorion enzymatically removed to allow for direct contact of particles with the developing embryo. Both mortality and sublethal endpoints were analyzed. Mortality rates were significantly greater for chitosan-coated LNPs (Ch-LNPs) compared to plain LNPs and control groups. Significant sublethal endpoints were observed in groups exposed to Ch-LNPs with chorionic membranes intact. Our study indicated that engineered Ch-LNP formulations at high concentrations were more toxic than plain LNPs. Further study is warranted to fully understand the mechanisms of Ch-LNP toxicity.

The design of hydrogels where multiple interpenetrating networks enable enhanced mechanical properties can broaden their field of application in biomedical materials, 3D printing, and soft robotics. We report a class of self-reinforced homocomposite hydrogels (HHGs) comprised of interpenetrating networks of multiscale hierarchy. A molecular alginate gel is reinforced by a colloidal network of hierarchically branched alginate soft dendritic colloids (SDCs). The reinforcement of the molecular gel with the nanofibrillar SDC network of the same biopolymer results in a remarkable increase of the HHG’s mechanical properties. The viscoelastic HHGs show >3× larger storage modulus and >4× larger Young’s modulus than either constitutive network at the same concentration. Such synergistically enforced colloidal-molecular HHGs open up numerous opportunities for formulation of biocompatible gels with robust structure-property relationships. Balance of the ratio of their precursors facilitates precise control of the yield stress and rate of self-reinforcement, enabling efficient extrusion 3D printing of HHGs., Composites which are made up of a single polymer, and yet allow modulation of the mechanical properties of the matrix without stress concentration, are challenging to fabricate. Here, the authors design a selfreinforced homocomposite alginate hydrogel with enhanced mechanical properties incorporating soft dendritic alginate colloids in the matrix and demonstrate its application in extrusion printing.

We overview the ways in which electric fields can be used for on-chip manipulation and assembly of colloidal particles. Particles suspended in water readily respond to alternating (AC) or direct current (DC) electric fields. Charged particles in DC fields are moved towards oppositely charged electrodes by electrophoresis. Dielectrophoresis, particle mobility in AC fields, allows precise manipulation of particles through a range of parameters including field strength and frequency and electrode geometry. Simultaneously, DC or AC electrokinetics may drive liquid flows inside the experimental cells, which also leads to transport and redistribution of the suspended particles. Examples of dielectrophoretic manipulation and assembly of nanoparticles and microparticles by planar on-chip electrodes are presented. The structures assembled include conductive microwires from metallic nanoparticles and switchable two-dimensional crystals from polymer microspheres. We also discuss how dielectrophoresis and AC electrokinetics can be used in droplet-based microfluidic chips, biosensors, and devices for collection of particles from diluted suspensions.

Herein, we report a strategy for additive manufacturing of a mechanochemically active silicone ink primarily composed of PDMS microbeads. Extruded, stable structures of cured microbeads were held together with a “bridging material” comprising uncured PDMS and spiropyran in a water medium. The mechanochromic silicone ink was a shear-thinning gel that exhibited a yield stress, and thus, was suitable for direct-write 3D printing. The spiropyran was stable to mild conditions of the printing process, and after a thermal curing step, the printed silicone displayed reversible mechanochromic activity. The extruded composite displays chromophore activation at lower mechanical strains under uniaxial tension (60–70%) than in a film without the microbeads (130–140%). Multi-layered 3D printed constructs were fabricated and displayed mechanochromic activity in tension and compression. These experiments demonstrate the versatility of these silicone inks to produce 3D printed functional elastomers with mechanochemical activity.

We construct and investigate paper-based microfluidic devices, which model long-term fluid harvesting, transport, sensing, and analysis in new wearables for sweat analysis. Such devices can continuously wick fluid mimicking sweat and dispose of it on evaporation pads. We characterize and analyze how the action of capillarity and evaporation can cooperatively be used to transport and process sweat mimics containing dissolved salts and model analytes. The results point out that non-invasive osmotic extraction combined with paper microfluidics and evaporative disposal can enable sweat collection and monitoring for durations longer than 10 days. We model the fluid flow in the new capillary–evaporative devices and identify the parameters enabling their long-term operation. We show that the transport rates are sufficiently large to handle natural sweat rates, while we envision that such handling can be interfaced with osmotic harvesting of sweat, a concept that we demonstrated recently. Finally, we illustrate that the salt film deposited at the evaporation pad would eventually lead to cessation of the process but at the same time will preserve a record of analytes that may be used for long-term biomarker monitoring in sweat. These principles can be implemented in future platforms for wearable skin-interfacing assays or electronic biomarker monitors.

When a sessile droplet of a complex mixture evaporates, its nonvolatile components may deposit into various patterns. One such phenomena, the coffee ring effect, has been a topic of interest for several decades. Here, we identify what we believe to be a fascinating phenomenon of droplet pattern deposition for another well-known beverage-what we have termed a "whiskey web". Nanoscale agglomerates were generated in diluted American whiskeys (20-25% alcohol by volume), which later stratified as microwebs on the liquid-air interface during evaporation. The web's strandlike features result from monolayer collapse, and the resulting pattern is a function of the intrinsic molecular constituents of the whiskey. Data suggest that, for our conditions (diluted 1.0 μL drops evaporated on cleaned glass substrates), whiskey webs were unique to diluted American whiskey; however, similar structures were generated with other whiskeys under different conditions. Further, each product forms their own distinct pattern, demonstrating that this phenomenon could be used for sample analysis and counterfeit identification.

Emulsions stabilized by surface active particles are becoming an attractive alternative to conventional surfactant-stabilized emulsions. Biobased, environmentally friendly, and edible particles are particularly interesting for applications in foods, agriculture, and consumer products. Previously, water insoluble proteins such as prolamins have been only used as a platform for stabilization of water continuous emulsions. In this paper, we investigate the ability of zein particles to stabilize oil continuous emulsions. We synthesized and used zein particles in the form of (i) an aqueous, or (ii) an oil suspension. Aqueous suspensions of zein particles resulted in water-in-oil (w/o) emulsions that were generally stable for more than an hour, with up to 30 vol% water as the dispersed phase. Cryo-SEM images show that only a small fraction of zein particles are adsorbed at the oil-water interface as Pickering stabilizers. Adding an oil soluble surfactant (lecithin) prior to emulsification with zein particles in an aqueous suspension promoted the formation of oil-continuous emulsion with phase inversion point at 40 vol% of water. Zein particles suspended in oil produced less stable emulsions, which showed reversible phase inversion attributed to the electrostatic repulsion of hydrophilic protein loops above their isoelectric point. Our results show that zein particles act as a predominantly hydrophilic stabilizer that requires control prior to emulsification to form w/o emulsions. These emulsions, however, have only a limited stability.

Convective self-assembly, well known for producing highly ordered monolayer structures, has been used in this study to create novel surface patterns using the binary mixture of colloids. We demonstrate that different patterns form, based on the size ratio (Small/Large) of the particles, and particles volume ratio. Surprisingly, certain binary particle mixtures resulted in spontaneous size based segregation. In some cases, the particle separation occurred along the direction of the meniscus contact line, and by the mere design of the process, we created periodic stripe patterns with controlled width. The particle volume fraction, size differences, surface tension, and the curvature of the meniscus played a crucial factor in the segregation process as well as in determining the width of each of the stripes. Furthermore, based on both empirical and numerical analysis, a mechanism for size-based segregation of particles via directed self-assembly is proposed.

Soft and stretchable materials play an important role in the emerging fields of soft robotics, human-machine interfaces, and stretchable electronics. Hydrogels are compelling materials because they are soft, chemically tunable, biocompatible, and ionically conductive. Hydrogels have been used as components of skin mountable sensors, such as electrocardiogram (ECG) electrodes, and show promise in emerging devices as stretchable, transparent electrodes. Ultimately, these types of devices interface the hydrogel with rigid metallic electrodes to connect with electronic circuitry. Here, we show it is possible to interface hydrogel with liquid metal (eutectic gallium indium, EGaIn) electrodes to create completely soft and deformable electrodes that provide low resistance traces through the gel without altering its mechanical properties. As a case study, we created and tested electrodes for ECG monitoring. ECG electrodes require low impedance at biomedically relevant frequencies (1-50 Hz). Potentiostatic electrochemical impedance spectroscopy measurements show that capacitive effects at the hydrogel-EGaIn interface dominate the impedance at these low frequencies, yet can be reduced by interfacing the metal with acidic or basic hydrogels that remove the native oxide skin from the metal. Increasing the ionic strength of the hydrogel also helps in lowering the impedance of the metal-hydrogel electrodes. The resulting devices have signal-to-noise ratios that exceed commercial ECG electrodes. The softness of these hydrogels can be modified without compromising the electrical properties to create truly soft electrodes. Interfacing liquid metal conductors with hydrogels represents a potential strategy of creating soft electrodes for various bioelectronic applications, e-skins, and next-generation soft robotics.