Mobilization of Colloid- and Nanoparticle-Bound Arsenic in Contaminated Paddy Soils during Reduction and Reoxidation.

The association of arsenic (As) with colloidal particles could facilitate its transport to adjacent water systems or alter its availability in soil-rice systems. However, little is known about the size distribution and composition of particle-bound As in paddy soils, particularly under changing redox conditions. Here, we incubated four As-contaminated paddy soils with distinctive geochemical properties to study the mobilization of particle-bound As during soil reduction and subsequent reoxidation. Using transmission electron microscopy-energy dispersive spectroscopy and asymmetric flow field-flow fractionation, we identified organic matter (OM)-stabilized colloidal Fe, most likely in the form of (oxy)hydroxide-clay composite, as the main arsenic carriers. Specifically, colloidal As was mainly associated with two size fractions of 0.3-40 and >130 kDa. Soil reduction facilitated the release of As from both fractions, whereas reoxidation caused their rapid sedimentation, coinciding with solution Fe variations. Further quantitative analysis demonstrated that As concentrations positively correlated with both Fe and OM concentrations at nanometric scales (0.3-40 kDa) in all studied soils during reduction and reoxidation, yet the correlations are pH-dependent. This study provides a quantitative and size-resolved understanding of particle-bound As in paddy soils, highlighting the importance of nanometric Fe-OM-As interactions in paddy As geochemical cycling.

Novel oral microscope gives mechanistic insights into colloidal drivers of friction in oral biofilms.

Texture and mouthfeel are central to the sensory enjoyment of food and beverages. Yet our incomplete understanding of how food boluses are transformed in the mouth limits our texture prediction ability. As well as thin film tribology, the interaction of food colloids with the oral tissue and salivary biofilms plays a key role in texture perception via mechanoreceptors in the papillae. In this study we describe the development of an oral microscope capable of quantitative characterization of the inactions of food colloids with papillae and their concurrent saliva biofilm. We also highlight how the oral microscope revealed key microstructural drivers of several topical phenomena (oral residue formation, coalescence in-mouth, grittiness of protein aggregates and finally microstructural origin of polyphenol astringency) in the domain of texture creation. The coupling of a fluorescent food grade dye with image analysis enabled specific and quantitative determination of the microstructural changes in mouth. Emulsions either underwent no aggregation, small aggregation, or extensive aggregation depending on whether their surface charge facilitated complexation with the saliva biofilm. Quite surprisingly cationic gelatin emulsions that were already aggregated with saliva in mouth underwent coalescence if subsequently exposed to tea polyphenols (EGCG). Large protein aggregates were found to aggregate with the saliva coated papillae, increasing their size tenfold and possibly explaining why there are perceived as gritty. An exciting observation was the oral microstructural changes that occurred upon exposure to tea polyphenols (EGCG). Filiform papillae shrunk, and the saliva biofilm was seen to precipitate/collapse, exposing a very rough tissue surface. These tentative early steps are the first in vivo microstructural insights into the different food oral transformations that are drivers of key texture sensation.

Biological colloids: Unique properties of membraneless organelles in the cell.

Biomolecular condensates are membraneless, intracellular organelles that form via liquid-liquid phase separation (LLPS) and have the ability to concentrate a wide range of molecules in the cellular milieu. These organelles are highly dynamic and play pivotal roles in cellular organization and physiology. Many studies also link the formation and misregulation of condensates to diseases such as neurodegenerative disorders and cancer. Biomolecular condensates represent a special type of colloids that actively interact with their environment to sustain physiological functions, due to which their misregulation may upset cell signaling, resulting in pathological states. In this review, we discuss the mechanisms underlying the formation, dynamics, and evolution of these biological colloids, with a special focus on their surface properties that are critical in their interaction with other components of the cell. We also summarize experimental approaches that enable the detailed characterization of the formation, interactions, and functions of these cellular colloidal organelles.

Torque-Driven Orientation Motion of Chemotactic Colloidal Motors.

We report a direct experimental observation of the torque-driven active reorientation of glucose-fueled flasklike colloidal motors to a glucose gradient exhibiting a positive chemotaxis. These streamlined flasklike colloidal motors are prepared by combining a hydrothermal synthesis and a vacuum infusion and can be propelled by an enzymatic cascade reaction in the glucose fuel. Their flasklike architecture can be used to recognize their moving posture, and thus the dynamic glucose-gradient-induced alignment and orientation-dependent motility during positive chemotaxis can be examined experimentally. The chemotactic mechanism is that the enzymatic reactions inside lead to the glucose acid gradient and the glucose gradient which generate two phoretic torques at the bottom and the opening respectively, and thus continuously steer it to the glucose gradient. Such glucose-fueled flasklike colloidal motors resembling the chemotactic capability of living organisms hold considerable potential for engineering active delivery vehicles in response to specific chemical signals.

Reversible and spatiotemporal control of colloidal structure formation.

Tuning colloidal structure formation is a powerful approach to building functional materials, as a wide range of optical and viscoelastic properties can be accessed by the choice of individual building blocks and their interactions. Precise control is achieved by DNA specificity, depletion forces, or geometric constraints and results in a variety of complex structures. Due to the lack of control and reversibility of the interactions, an autonomous oscillating system on a mesoscale without external driving was not feasible until now. Here, we show that tunable DNA reaction circuits controlling linker strand concentrations can drive the dynamic and fully reversible assembly of DNA-functionalized micron-sized particles. The versatility of this approach is demonstrated by programming colloidal interactions in sequential and spatial order to obtain an oscillatory structure formation process on a mesoscopic scale. The experimental results represent an approach for the development of active materials by using DNA reaction networks to scale up the dynamic control of colloidal self-organization.

Deposition of Polymer Particles with Fibrinogen Corona at Abiotic Surfaces under Flow Conditions.

The deposition kinetics of polymer particles with fibrinogen molecule coronas at bare and poly-L-lysine (PLL) modified mica was studied using the microfluid impinging-jet cell. Basic physicochemical characteristics of fibrinogen and the particles were acquired using dynamic light scattering and the electrophoretic mobility methods, whereas the zeta potential of the substrates was determined using streaming potential measurements. Subsequently, an efficient method for the preparation of the particles with coronas, characterized by a controlled fibrinogen coverage, was developed. This enabled us to carry out measurements, which confirmed that the deposition kinetics of the particles at mica vanished at pH above 5. In contrast, the particle deposition of PLL modified mica was at maximum for pH above 5. It was shown that the deposition kinetics could be adequately analyzed in terms of the mean-field approach, analogously to the ordinary colloid particle behavior. This contrasts the fibrinogen molecule behavior, which efficiently adsorbs at negatively charged substrates for the entire range pHs up to 9.7. These results have practical significance for conducting label-free immunoassays governed by the specific antigen/antibody interactions.

Transmembrane transport in inorganic colloidal cell-mimics.

A key aspect of living cells is their ability to harvest energy from the environment and use it to pump specific atomic and molecular species in and out of their system-typically against an unfavourable concentration gradient1. Active transport allows cells to store metabolic energy, extract waste and supply organelles with basic building blocks at the submicrometre scale. Unlike living cells, abiotic systems do not have the delicate biochemical machinery that can be specifically activated to precisely control biological matter2-5. Here we report the creation of microcapsules that can be brought out of equilibrium by simple global variables (illumination and pH), to capture, concentrate, store and deliver generic microscopic payloads. Borrowing no materials from biology, our design uses hollow colloids serving as spherical cell-membrane mimics, with a well-defined single micropore. Precisely tunable monodisperse capsules are the result of a synthetic self-inflation mechanism and can be produced in bulk quantities. Inside the hollow unit, a photoswitchable catalyst6 produces a chemical gradient that propagates to the exterior through the membrane's micropore and pumps target objects into the cell, acting as a phoretic tractor beam7. An entropic energy barrier8,9 brought about by the micropore's geometry retains the cargo even when the catalyst is switched off. Delivery is accomplished on demand by reversing the sign of the phoretic interaction. Our findings provide a blueprint for developing the next generation of smart materials, autonomous micromachinery and artificial cell-mimics.

Do Macrocyclic Peptide Drugs Interact with Bile Salts under Simulated Gastrointestinal Conditions?

Peptide drugs face several barriers to oral delivery, including enzymatic degradation in the gastrointestinal tract and low membrane permeability. Importantly, the direct interaction between various biorelevant colloids (i.e., bile salt micelles and bile salt-phospholipid mixed micelles) present in the aqueous gastrointestinal environment and peptide drug molecules has not been studied. In this work, we systematically characterized interactions between a water-soluble model peptide drug, octreotide, and a range of physiologically relevant bile salts in solution. Octreotide membrane flux in pure bile salt solutions and commercially available biorelevant media, i.e., fasted state simulated intestinal fluid (FaSSIF) and fed state simulated intestinal fluid (FeSSIF), was evaluated using a side-by-side diffusion cell equipped with a cellulose dialysis membrane. All seven micellar bile salt solutions as well as FaSSIF and FeSSIF decreased octreotide membrane flux, and dihydroxy bile salts were found to have a much larger effect than trihydroxy bile salts. An inverse relationship between octreotide membrane flux and pancreatic enzymatic stability was also observed; bile salt micelles and bile salt-phospholipid mixed micelles provided a protective effect toward enzymatic degradation and prolonged octreotide half-life in vitro. Diffusion ordered nuclear magnetic resonance (DOSY NMR) spectroscopy and dynamic light scattering (DLS) were used as complementary experimental techniques to confirm peptide-micelle interactions in solution. Experiments were also performed using desmopressin as a second model peptide drug; desmopressin interacted with bile salts in solution, albeit to a lower extent relative to octreotide. The findings described herein demonstrate that amphiphilic, water-soluble peptide drugs do interact with bile salts and phospholipids in solution, with an effect on peptide membrane flux and enzymatic stability. Correspondingly, oral peptide drug absorption and bioavailability may be impacted.

Effect of starch-hydrocolloid complexes with heat-moisture treatment on in vivo digestibility.

The purpose of this study was to investigate the effect of starch-hydrocolloid (gum arabic, xanthan gum, and guar gum) complexes with heat-moisture treatment (HMT) on in vivo digestibility. In vivo digestibility experiments revealed that the body weight, liver weight, and fat index of mice in the intervention group were significantly reduced compared with those in the high-fat group. Glucose tolerance improved, and blood lipid levels, liver and adipose tissue morphology returned to normal. The results of mRNA expression levels showed that the intervention of corn starch-hydrocolloid complexes after HMT down-regulated the expression level of genes related to fat synthesis compared with the high-fat group, which could decrease lipid deposition and stabilize blood lipid levels. Results revealed that starch-xanthan gum complex (1 : 40 ratio) with HMT could markedly reduce the digestibility of starch. Overall, this study provides new ideas for the application of low-glycemic-index and functional foods.

Lipids, membranes, colloids and cells: A long view.

This paper revisits long-standing ideas about biological membranes in the context of an equally long-standing, but hitherto largely unappreciated, perspective of the cell based on concepts derived from the physics and chemistry of colloids. Specifically, we discuss important biophysical aspects of lipid supramolecular structure to understand how the intracellular milieu may constrain lipid self-assembly. To this end we will develop four lines of thought: first, we will look at the historical development of the current view of cellular structure and physiology, considering also the plurality of approaches that influenced its formative period. Second, we will review recent basic research on the structural and dynamical properties of lipid aggregates as well as the role of phase transitions in biophysical chemistry and cell biology. Third, we will present a general overview of contemporary studies into cellular compartmentalization in the context of a very rich and mostly forgotten general theory of cell physiology called the Association-Induction Hypothesis, which was developed around the time that the current view of cells congealed into its present form. Fourth, we will examine some recent developments in cellular studies, mostly from our laboratory, that raise interesting issues about the dynamical aspects of cell structure and compartmentalization. We will conclude by suggesting what we consider are relevant questions about the nature of cellular processes as emergent phenomena.

Nanoemulgel for Improved Topical Delivery of Desonide: Formulation Design and Characterization.

This research aimed to develop a novel drug delivery system to improve treatment of skin disorders. The system is comprised of a Carbopol 980-based nanoemulgel (NE-gel) containing a desonide (DES; 0.05%, w/w) nanoemulsion (NE), which has a small particle size, high encapsulation efficiency, good thermodynamic stability, good permeation ability, and high skin retention. DES-loaded NE (DES-NE) was prepared by high-pressure homogenization. The developed formulation was characterized by differential scanning calorimetry (DSC), X-ray diffraction, drug release, skin permeation, and drug retention. DES in vitro release and skin permeation studies with different formulations of artificial membrane and rat abdominal skin were performed with the Franz diffusion cell system. Confocal laser scanning microscopy (CLSM) was used to detect the localization and permeation pathways of drugs in the skin. Compared with commercially available gel (CA-gel) and NE, the NE-gel release process conformed to the Higuchi release model (R2 = 0.9813). NE-gel prolonged the drug release time and allowed for reduced administration dose and frequency. The unit cumulative permeation of NE and NE-gel through the skin for 12 h was 63.13 ± 2.78 and 42.53 ± 2.06 µg/cm2, respectively, values significantly higher (p < 0.01) than that of the CA-gel (30.65 ± 1.25 µg/cm2) and CA-cream (15.21 ± 0.97 µg/cm2). The DES-NE and DES NE-gel skin drug retention was significantly higher than commercially available formulations (p < 0.01). Hence, the prepared NE-gel is a potential vehicle for improved topical DES delivery for better treatment of skin disorders.

PLA-coated Imwitor® 900 K-based herbal colloidal carriers as novel candidates for the intra-articular treatment of arthritis.

Although there are several treatments for rheumatoid arthritis (RA), outcomes are unsatisfactory and often associated with many side effects. We attempted to improve RA therapeutic outcomes by intra-articular administration of dual drug-loaded poly(lactic) acid (PLA)-coated herbal colloidal carriers (HCCs). Curcumin (CU) and resveratrol (RES) were loaded into HCCs because of their safety and significant anti-inflammatory activity. HCCs were prepared using a high-pressure, hot homogenization technique and evaluated in vitro and in vivo using a complete Freund's adjuvant-induced arthritis model. Transmission electron microscope (TEM) evaluated coating selected formulations with PLA, which increased particle sizes from 52 to 89.14 nm. The entrapment efficiency of both formulations was approximately 76%. HCCs significantly increased the amount of RES and CU released compared with the drug suspensions alone. The in vivo treated groups showed a significant improvement in joint healing. PLA-coated HCCs, followed by uncoated HCCs, yielded the highest reductions in knee diameter, myeloperoxidase (MPO) levels, and tumor necrosis factor-alpha (TNFα) levels. Histological examination of the dissected joints revealed that PLA-coated HCCs followed by uncoated HCCs exhibited the most significant joint healing effects. Our results demonstrate the superiority of intra-articularly administered HCCs to suppress RA progression compared with RES or CU suspensions alone.

A Crowding Barrier to Protein Inhibition in Colloidal Aggregates.

Small molecule colloidal aggregates adsorb and partially denature proteins, inhibiting them artifactually. Oddly, this inhibition is typically time-dependent. Two mechanisms might explain this: low concentrations of the colloid and enzyme might mean low encounter rates, or colloid-based protein denaturation might impose a kinetic barrier. These two mechanisms should have different concentration dependencies. Perplexingly, when enzyme concentration was increased, incubation times actually lengthened, inconsistent with both models and with classical chemical kinetics of solution species. We therefore considered molecular crowding, where colloids with lower protein surface density demand a shorter incubation time than more crowded colloids. To test this, we grew and shrank colloid surface area. As the surface area shrank, the incubation time lengthened, while as it increased, the converse was true. These observations support a crowding effect on protein binding to colloidal aggregates. Implications for drug delivery and for detecting aggregation-based inhibition will be discussed.

Pattern formation and polarity sorting of driven actin filaments on lipid membranes.

Collective motion of active matter is ubiquitously observed, ranging from propelled colloids to flocks of bird, and often features the formation of complex structures composed of agents moving coherently. However, it remains extremely challenging to predict emergent patterns from the binary interaction between agents, especially as only a limited number of interaction regimes have been experimentally observed so far. Here, we introduce an actin gliding assay coupled to a supported lipid bilayer, whose fluidity forces the interaction between self-propelled filaments to be dominated by steric repulsion. This results in filaments stopping upon binary collisions and eventually aligning nematically. Such a binary interaction rule results at high densities in the emergence of dynamic collectively moving structures including clusters, vortices, and streams of filaments. Despite the microscopic interaction having a nematic symmetry, the emergent structures are found to be polar, with filaments collectively moving in the same direction. This is due to polar biases introduced by the stopping upon collision, both on the individual filaments scale as well as on the scale of collective structures. In this context, positive half-charged topological defects turn out to be a most efficient trapping and polarity sorting conformation.

Functionalization of colloidal nanoparticles with a discrete number of ligands based on a "HALO-bioclick" reaction.

A recombinant HALO-GFP fusion protein was designed and isolated to demonstrate the feasibility of controlling the number and orientation of protein ligands to be conjugated on colloidal gold nanoparticles. AuNPs functionalized with exactly one or exactly two GFP molecules exhibited fully preserved functionality of the protein. The method is very straightforward and generally provides highly bioactive nanoparticle-protein conjugates.

Viscosity decay of hydrocolloids under oral conditions.

The aim of this study was to understand the contribution of hydrocolloids to oral structure breakdown of starch-based systems in relation to mouthfeel sensations. For this, carrot purees were prepared using corn starch and a different second thickener (λ-carrageenan, carboxymethylcellulose (CMC), xanthan gum, or an extra amount of starch). The viscosity decay of purees under in vitro oral conditions was measured (starch pasting cell adapted to a rheometer) when shearing at a constant shear rate in the presence of artificial saliva. Sensory properties of purees were described using the Flash Profile technique by a group of 13 panellists. Oral viscosity decay of systems was modelled using a second order structural kinetic equation that included three parameters: initial viscosity, rate of breakdown, and viscosity at equilibrium. Although they had the same initial viscosity, the structural breakdown of the purees in oral conditions varied, depending on the second thickener used. The structure of purees containing xanthan and λ-carrageenan were more resistant under oral conditions exhibiting a slow and smaller breakdown. In contrast, purees containing only starch showed a rapid and large decay because of the complete structure breakdown by amylase. For puree containing CMC, there was also a rapid decrease, but smaller than starch, indicating that part of the structure remained after digestion. Texture sensations freely described by assessors varied according to two main sensory dimensions, that were clearly related to the structural breakdown parameters. As expected, the dimension of thickness (from watery and liquid to thick and viscous) separated base purees from thickened purees and was related to the initial viscosity. The smoothness dimension (from rough and lumpy to the smooth and creamy) was related to the viscosity at equilibrium indicating that after the oral digestion, the characteristics of the remaining structure can explain differences in complex attributes of semisolid systems such as smoothness and creaminess.

Microbial Transglutaminase as a Tool to Improve the Features of Hydrocolloid-Based Bioplastics.

Several proteins from animal and plant origin act as microbial transglutaminase substrate, a crosslinking enzyme capable of introducing isopeptide bonds into proteins between the aminoacids glutamines and lysines. This feature has been widely exploited to modify the biological properties of many proteins, such as emulsifying, gelling, viscosity, and foaming. Besides, microbial transglutaminase has been used to prepare bioplastics that, because made of renewable molecules, are able to replace the high polluting plastics of petrochemical origin. In fact, most of the time, it has been shown that the microbial enzyme strengthens the matrix of protein-based bioplastics, thus, influencing the technological characteristics of the derived materials. In this review, an overview of the ability of many proteins to behave as good substrates of the enzyme and their ability to give rise to bioplastics with improved properties is presented. Different applications of this enzyme confirm its important role as an additive to recover high value-added protein containing by-products with a double aim (i) to produce environmentally friendly materials and (ii) to find alternative uses of wastes as renewable, cheap, and non-polluting sources. Both principles are in line with the bio-economy paradigm.

Colloidal graphene oxide enhances the activity of a lipase and protects it from oxidative damage: Insights from physicochemical and molecular dynamics investigations.

Physical adsorption of lipase from Thermomyces lanuginosus onto single-layer sheets of graphene oxide (GO) was studied using the response surface methodology to evaluate the physicochemical factors - temperature, pH, ionic strength, and concentration - affecting the enzymatic activity and the immobilization efficiency. The immobilization efficiency and the activity of the enzyme were inversely proportional to each other. Specifically, higher pH values increased the immobilization efficacy, but produced changes in the aggregation state and secondary structure of the enzyme, thus decreasing its activity. Lower pH values, in turn, reduced the immobilization efficacy, but increased the activity of the adsorbed lipase. The adsorbed and the free lipase were followed during 600 ns and 3.5 µs, respectively, in molecular dynamics (MD) simulations. MD trajectories showed that irreversible adsorption freezes the enzyme in a state with a correctly opened catalytic cavity, while the active site remains without a direct interaction with the GO adsorbent. In contrast to the interfacial activation of lipases in a hydrophobic environment, where the catalytic pocket attaches to the hydrophobic surface, the adsorption onto GO made the active site of the lipase accessible by altering the tertiary structure of the enzyme, leading to a higher catalytic efficiency. Experimental investigations confirmed that the physical adsorption onto GO induces tertiary structure changes in the lipase and protects it from H2O2 by accepting the oxidative damage upon itself. In summary, the physical adsorption of the lipase onto GO is mainly affected by pH and could possibly provide a spreadable and robust catalytic interface for biotechnological applications.

Colloidal Transformations in MS2 Virus Particles: Driven by pH, Influenced by Natural Organic Matter.

Enteric viruses, such as enterovirus, norovirus, and rotavirus, are among the leading causes of disease outbreaks due to contaminated drinking and recreational water. Viruses are difficult to remove from water through filtration based on physical size exclusion-for example by gravity-driven filters-due to their nanoscale size. To understand virus removal in drinking water treatment systems, the colloidal nanostructure of a model virus, the MS2 bacteriophage, has been investigated in relation to the effect of pH and natural organic matter in water. Dynamic light scattering, small-angle X-ray scattering, and cryogenic transmission electron microscopy demonstrated that the water pH has a major influence on the colloidal structure of the virus: The bacteriophage MS2's structure in water in the range pH = 7.0 to 9.0 was found to be spherical with core-shell-type structure with a total diameter of 27 nm and a core radius of around 8 nm. Reversible transformations from 27 nm particles at pH = 7.0 to micrometer-sized aggregates at pH = 3.0 were observed. In addition, the presence of natural organic matter that simulates the organic components present in surface water was found to enhance repulsion between virus particles, reduce the size of aggregates, and promote disaggregation upon pH increase. These findings allow a better understanding of virus interactions in water and have implications for water treatment using filtration processes and coagulation. The results will further guide the comprehensive design of advanced virus filter materials.

Glucose and Maltose Surface-Functionalized Thermoresponsive Poly(N-Vinylcaprolactam) Nanogels.

Soft nanoparticles are interesting materials due to their size, deformability, and ability to host guest molecules. Surface properties play an essential role in determining the fate of the particles in biological medium, and coating of the nanoparticles (and polymers) with carbohydrates has been found to be an efficient strategy for increasing their biocompatibility and fine-tuning other important properties such as aqueous solubility. In this work, soft nanogels of poly(N-vinylcaprolactam), PNVCL, were surface-functionalized with different glucose and maltose ligands, and the colloidal properties of the gels were analyzed. The PNVCL nanogels were first prepared via semibatch precipitation polymerization, where a comonomer, propargyl acrylate (PA), was added after preparticle formation. The aim was to synthesize "clickable" nanogels with alkyne groups on their surfaces. The nanogels were then functionalized with two separate azido-glucosides and azido-maltosides (containing different linkers) through a copper-catalyzed azide-alkyne cycloaddition (CuAAc) click reaction. The glucose and maltose bearing nanogels were thermoresponsive and shrank upon heating. Compared to the PNVCL-PA nanogel, the carbohydrate bearing ones were larger, more hydrophilic, had volume phase transitions at higher temperatures, and were more stable against salt-induced precipitation. In addition to investigating the colloidal properties of the nanogels, the carbohydrate recognition was addressed by studying the interactions with a model lectin, concanavalin A (Con A). The binding efficiency was not affected by the temperature, which indicates that the carbohydrate moieties are located on the gel surfaces, and are capable of interacting with other biomolecules independent of temperature. Thus, the synthesis produces nanogels, which have surface functions capable of biorelevant interactions and a thermoresponsive structure. These types of particles can be used for drug delivery.