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The phospholipid lecithin (L) and the nonionic surfactant Tween 80 (T) are used together in various contexts, including in drug delivery and oil spill remediation. There is hence a need to elucidate the nanostructures in LT mixtures, which is the focus of this paper. We study these mixtures using cryogenic transmission electron microscopy (cryo-TEM), coupled with dynamic light scattering and small-angle neutron scattering. As the concentration of Tween 80 is increased, the vesicles formed by lecithin are transformed into spherical micelles. We identify bicelles (i.e., disc-like micelles) as well as cylindrical micelles as the key stable nanostructures formed at intermediate L/T ratios. The bicelles have diameters ∼13-26 nm, and the bicelle size decreases as the Tween 80 content increases. We propose that the lecithin lipids form the body of the discs, while the Tween 80 surfactants occupy the rims. This hypothesis is consistent with geometric arguments because lecithin is double-tailed and favors minimal curvature, whereas the single-tailed Tween 80 molecules prefer curved interfaces. In the case of cylindrical micelles, cryo-TEM reveals that the micelles are short (length22 nm) and flexible. We are able to directly visualize the microstructure of the aggregates formed by lecithin-Tween 80 mixtures, thereby enhancing the understanding of morphological changes in the lecithin-Tween 80 system.

In nature, various structures such as fruits and vegetables have a water-rich core that is covered by a hydrophobic layer, i.e., their skin. The skin creates a barrier that prevents chemicals in the external environment from entering the core; at the same time, the skin also ensures that the water in the core is preserved and not lost by evaporation. Currently, for many applications involving hydrogels, especially in areas such as soft robotics or bioelectronic interfaces, it would be advantageous if the gel could be encased in a skin-like material. However, forming such a skin around a gel has proved challenging because the skin would need to be a hydrophobic material with a distinct chemistry from the hydrophilic gel core. Here, we present a simple solution to this problem, which allows any hydrogel of arbitrary composition and geometry to be encased by a thin, transparent "skin." Our synthesis technique involves an inside-out polymerization, where one component of the polymerization (the initiator) is present only in the gel core, while other components (the monomers) are present only in the external medium. Accordingly, a thin polymeric layer (∼10-100 µm in thickness) grows outward from the core, and the entire process can be completed in a few minutes. We show that the presence of the skin prevents the gel from swelling in water and also from drying in air. Likewise, hydrophilic solutes in the gel core are completely prevented by the skin from leaking out into the external solution, while harsh chemicals (e.g., acids, bases, and chelators) or harmful microbes are prevented from entering the gels. The properties of the skin are all tunable, including its thickness and its mechanical properties. When the monomer used is urethane diacrylate, the resulting polyurethane skin is elastomeric, transparent, and peelable from the core gel. Conversely, when polyethylene glycol dimethacrylate is used as the monomer, the skin is hard and brittle (glass-like). The ability to grow a skin readily around any given hydrogel is likely to prove useful in numerous applications, such as in maintaining the electrical functionality of gel-based wires or circuit elements.

Marine oil dispersants typically contain blends of surfactants dissolved in solvents. When introduced to the crude oil-seawater interface, dispersants facilitate the breakup of crude oil into droplets that can disperse in the water column. Recently, questions about the environmental persistence and toxicity of commercial dispersants have led to the development of "greener" dispersants consisting solely of food-grade surfactants such as l-α-phosphatidylcholine (lecithin, L) and polyoxyethylenated sorbitan monooleate (Tween 80, T). Individually, neither L nor T is effective at dispersing crude oil, but mixtures of the two (LT blends) work synergistically to ensure effective dispersion. The reasons for this synergy remain unexplained. More broadly, an unresolved challenge is to be able to predict whether a given surfactant (or a blend) can serve as an effective dispersant. Herein, we investigate whether the LT dispersant effectiveness can be correlated with thermodynamic phase behavior in model systems. Specifically, we study ternary "DOW" systems comprising LT dispersant (D) + a model oil (hexadecane, O) + synthetic seawater (W), with the D formulation being systematically varied (across 0:100, 20:80, 40:60, 60:40, 80:20, and 100:0 L:T weight ratios). We find that the most effective LT dispersants (60:40 and 80:20 L:T) induce broad Winsor III microemulsion regions in the DOW phase diagrams (Winsor III implies that the microemulsion coexists with aqueous and oil phases). This correlation is generally consistent with expectations from hydrophilic-lipophilic deviation (HLD) calculations, but specific exceptions are seen. This study then outlines a protocol that allows the phase behavior to be observed on short time scales (ca. hours) and provides a set of guidelines to interpret the results. The complementary use of HLD calculations and the outlined fast protocol are expected to be used as a predictive model for effective dispersant blends, providing a tool to guide the efficient formulation of future marine oil dispersants.

Recently, we have created ‘artificial cells’ with an architecture mimicking that of typical eukaryotic cells. Our design uses common biopolymers like alginate and chitosan to create multi-compartment capsules (MCCs) via oil-free microfluidics. MCCs (~ 500 μm in diameter) can be engineered with multiple inner compartments, each with a distinct payload. This mimics the distinct organelles in eukaryotic cells, each of which has unique properties. In this study, we encapsulate microbial cells from two distinct kingdoms — Pseudomonas aeruginosa (bacteria) and Candida albicans (fungi) — in the inner compartments of MCCs. The two microbes are commonly found in biofilms at sites of infection in humans. We first demonstrate that the MCC can serve as a simple platform to observe the comparative growth of the cells in real time. Unlike typical co-culture in solution or on agar plates, the cells can grow in their own compartments without direct physical contact. Moreover, the hydrogel matrix in the compartments mimics the three-dimensional (3-D) environment that cells naturally encounter during their growth. Small molecules added to the solution are shown to permeate through the capsule walls and affect cell growth: for example, cationic surfactants inhibit the fungi but not the bacteria. Conversely, low pH and kanamycin inhibit the bacteria but not the fungi. Also, when the bacteria are present in adjacent compartments, the fungal cells mostly stay in a yeast morphology, meaning as spheroidal cells. In contrast, in the absence of the bacteria, the fungi transition into hyphae, i.e., long multicellular filaments. The inhibition of this morphological switch in fungal cells is shown to be induced by signaling molecules (specifically, the quorum sensing autoinducer-1 or AI-1) secreted by the bacteria. Thus, the MCC platform can also be used to detect cross-kingdom signaling between the compartmentalized microbes.

Glycosaminoglycans (GAGs) are molecules that govern the load-bearing and frictional properties of cartilage and the lubricating properties of synovial fluid of joints. Most GAGs in the body form pr...

“Smart” fluids displaying large changes in their rheological properties in response to external stimuli have been of great interest in recent years. For example, “smart” wormlike micelles (WLMs) that respond to pH can be readily formulated by combining a cationic surfactant such as cetyltrimethylammonium bromide (CTAB) with an aromatic compound such as 1,2-dihydroxybenzene (DHB). Here, we show that a pH-responsive aqueous formulation as mentioned above can be simultaneously made responsive to ultraviolet (UV) light by incorporating a photoacid generator (PAG) into the system. A commercially available PAG, diphenyliodonium-2-carboxylate, is used here. Upon exposure to UV light, this PAG irreversibly photolyzes into iodobenzene (IB) and benzoic acid (BA), with the formation of BA, leading to a drop in pH. WLMs formed by mixtures of CTAB, DHB, and the PAG are systematically characterized before and after UV irradiation. As the PAG photolyzes, an increase in the viscosity of WLMs occurs by a factor of 1000. We show that the ratio of the zero-shear viscosity η0 (after UV/before UV) depends on the initial pH of the sample. The UV-induced increase in η0 can be attributed to the growth of WLMs in solution, which in turn is influenced by both the ionization state of DHB and the presence of IB and BA.

Hydrogels of biopolymers such as agar and gelatin are widely used in many applications, and in many cases, the gels are loaded with nanoparticles. The polymer chains in these gels are cross-linked by physical bonds into three-dimensional networks, with the mesh size of these networks typically being 10-100 nm. One class of "soft" nanoparticles are liposomes, which have an aqueous core surrounded by a lipid bilayer. Solutes encapsulated in the liposomal core can be delivered externally over time. In this paper, we create liposomes with diameters ∼150 nm from an unsaturated phospholipid (lecithin) and embed them in agar gels (the aqueous phase also contains 0-50% of glycerol, which is an active ingredient in cosmetic products). Upon placing this gel in quiescent water, we find that the liposomes release out of the gel into the water over a period of 1-3 days, even though the gel remains intact.

Wormlike micelles (WLMs) are polymer-like chains formed by surfactant self-assembly in water. Recently, we have shown that WLMs can also be self-assembled in polar organic liquids like glycerol using a cationic surfactant and an aromatic salt. In this work, we focus on the dynamic rheology of the WLMs in glycerol and demonstrate that their rheology is very different from that of WLMs in water. Aqueous WLMs that are entangled into transient networks exhibit the rheology of a perfect Maxwell fluid having a single relaxation time tR-thereby, their elastic modulus G' and viscous modulus G″ intersect at a crossover frequency ωc = 1/tR. WLMs in glycerol also form entangled networks, but they are not Maxwell fluids; instead, they exhibit a double-crossover of G' and G″ (at ωc1 and ωc2) within the ω-window accessible by rheometry (10-2 to 102 rad/s). The first crossover at ωc1 (∼1 rad/s) corresponds to the terminal relaxation time (i.e., the timescale for chains to disentangle from the transient network and relax by reptation). At the other extreme, at frequencies above ωc2 (which is ∼10 rad/s), the rheology is dominated by the segmental motion of the chains. This "breathing regime" has rarely been accessed via experiments for aqueous WLMs because it falls around 105 rad/s. We believe that glycerol, a solvent that is much more viscous than water, exerts a crucial influence in pushing ωc2 to 1000-fold lower frequencies. On the basis of the rheology, we also hypothesize that WLMs in glycerol are shorter and weakly entangled compared to WLMs in water. Moreover, we suggest that WLMs in glycerol are "unbreakable" chains-i.e., the chains remain mostly intact instead of breaking and re-forming frequently-and this polymer-like behavior explains why the samples are quite unlike Maxwell fluids.

Recent success in extending the electrochemical stability window of aqueous electrolytes to 3.0 V by using 21 mol kg-1 “water-in-salt” (WiS) has raised a high expectation for developing safe aqueous Li-ion batteries. However, the most compatible Li4Ti5O12 anodes still cannot use WiS electrolyte due to the cathodic limit (1.9 V vs. Li/Li+). Herein, a UV-curable hydrophilic polymer is introduced to further extend the cathodic limit of WiS electrolytes and replace the separator. In addition, a localized strongly basic solid polymer electrolyte (SPE) layer is coated on the anode to promote the formation of an LiF-rich SEI. The synthetic impacts of UV-crosslinking and local alkaline SPE on the anodes extend the electrochemical stability window of the solid-state aqueous polymer electrolyte to ∼3.86 V even at a reduced salt concentration of 12 mol kg−1. It enables a separator-free LiMn2O4//Li4Ti5O12 aqueous full cell with a practical capacity ratio (P/N = 1.14) of the cathode and anode to deliver a steady energy density of 151 W h kg−1 at 0.5C with an initial Coulombic efficiency of 90.50% and cycled for over 600 cycles with an average Coulombic efficiency of 99.97%, which has never been reported before for an aqueous LiMn2O4//Li4Ti5O12 full cell. This flexible and long-duration aqueous Li-ion battery with hydrogel WiSE can be widely used as a power source in wearable devices and electrical transportations where both energy density and battery safety are of high priority. An ultra-thick LTO electrode with UV-curable polymer electrolyte as the binder is demonstrated as a solid state battery electrode. And a high-voltage (7.4 V) solid-state bipolar cell is assembled with a solid-state UV-curable polymer as the electrolyte.

The self-assembly of lipids into nanoscale vesicles (liposomes) is routinely accomplished in water. However, reports of similar vesicles in polar organic solvents like glycerol, formamide, and ethylene glycol (EG) are scarce. Here, we demonstrate the formation of nanoscale vesicles in glycerol, formamide, and EG using the common phospholipid lecithin (derived from soy). The samples we study are simple binary mixtures of lecithin and the solvent, with no additional cosurfactants or salt. Lecithin dissolves readily in the solvents and spontaneously gives rise to viscous fluids at low lipid concentrations (∼2-4%), with structures ∼200 nm detected by dynamic light scattering. At higher concentrations (>10%), lecithin forms clear gels that are strongly birefringent at rest. Dynamic rheology confirms the elastic response of gels, with their elastic modulus being ∼20 Pa at ∼10% lipid. Images from cryo-scanning electron microscopy (cryo-SEM) indicate that concentrated samples are "vesicle gels," where multilamellar vesicles (MLVs, also called "onions"), with diameters between 50 and 600 nm, are close-packed across the sample volume. This structure can explain both the elastic rheology as well as the static birefringence of the samples. The discovery of vesicles and vesicle gels in polar solvents widens the scope of systems that can be created by self-assembly. Interestingly, it is much easier to form vesicles in polar solvents than in water, and the former are stable indefinitely, whereas the latter tend to aggregate or coalesce over time. The stability is attributed to refractive index-matching between lipid bilayers and the solvents, i.e., these vesicles are relatively "invisible" and thus experience only weak attractions. The ability to use lipids (which are "green" or eco-friendly molecules derived from renewable natural sources) to thicken and form gels in polar solvents could also prove useful in a variety of areas, including cosmetics, pharmaceuticals, and lubricants.

Biodegradation of oil by marine bacteria is a significant pathway to oil spill remediation. Marine hydrocarbon degrading bacteria are known to form biofilms consisting of exopolymer and interconnected bacterial cells. This work indicates that microbial biofilm aids in the stabilization of dispersed oil droplets through the formation of biofilm at the oil–water interface and is therefore an environmentally benign and sustainable method to aid dispersion of spilled oil. Using a model hydrocarbon degrading organism Alcanivorax borkumensis, we show, through a combination of optical and high-resolution cryogenic scanning electron microscopy, that these microbes sequester into biofilm at the oil–water interface. We show that the bacterial culture incubated for 3 days and containing biofilm can disperse oil slicks moderately well (40–50%) as estimated by the baffled flask test and can thus be used as an environmentally benign response to oil spills. The dispersion occurs through bacterial adsorption at the oil–w...

Aqueous capsules made from polymers typically allow their encapsulated cargo (e.g., drugs, dyes, proteins) to slowly diffuse out into the solvent through the capsule shell. In many applications, there is a need for a ‘hermetic’ seal to protect the cargo from the solvent over extended periods of time. Ideally, this hermetic seal should also be capable of being broken on-demand to enable cargo release. We demonstrate a new design for capsules having the above combination of properties. The key is to create the capsule shell from wax materials (alkanes and fatty acids) with a defined melting temperature Tm. Capsules can be loaded with any desired material, including strong acids or bases, reactive or unstable reagents (such as H2O2), and biopolymer gels. When sealed capsules are placed in water, no leakage is observed for over six weeks. The capsules can also encapsulate volatile liquids and remain air-tight over at least three weeks. On the other hand, under mild heat (above Tm, e.g., to 45 °C), the shell melts, releasing the core contents into the surrounding solvent. This provides a convenient thermal on–off “switch” for delivering contents from the capsules. The utility of these capsules is shown by implementing a nitrate-detection assay using hazardous chemicals (including H2SO4) sealed in the capsules. These “smart” capsules thus constitute a modular, mass-producible platform that could be useful in diverse applications.

Microgels of biopolymers such as alginate are widely used to encapsulate cells and other biological payloads. Alginate is an attractive material for cell encapsulation because it is nontoxic and convenient: spherical alginate gels are easily created by contacting aqueous droplets of sodium alginate with divalent cations such as Ca2+. Alginate chains in the gel become cross-linked by Ca2+ cations into a 3-D network. When alginate gels are placed in a buffer, however, the Ca2+ cross-links are eliminated by exchange with Na+, thereby weakening and degrading the gels. With time, encapsulated cells are released into the external solution. Here, we describe a simple solution to the above problem, which involves forming alginate gels enveloped by a thin shell of a covalently cross-linked gel. The shell is formed via free-radical polymerization using conventional monomers such as acrylamide (AAm) or acrylate derivatives, including polyethylene glycol diacrylate (PEGDA). The entire process is performed in a single step at room temperature (or 37 °C) under mild, aqueous conditions. It involves combining the alginate solution with a radical initiator, which is then introduced as droplets into a reservoir containing Ca2+ and monomers. Within minutes of either simple incubation or exposure to ultraviolet (UV) light, the droplets are converted into alginate-polymer microcapsules with a core of alginate and a shell of the polymer (AAm or PEGDA). The microcapsules are mechanically more robust than conventional alginate/Ca2+ microgels, and while the latter swell and degrade when placed in buffers or in chelators like sodium citrate, the former remain stable under all conditions. We encapsulate both bacteria and mammalian cells in these microcapsules and find that the cells remain viable and functional over time. Lastly, a variation of the synthesis technique is shown to generate multilayered microcapsules with a liquid core surrounded by concentric layers of alginate and AAm gels. We anticipate that the approaches presented here will find application in a variety of areas including cell therapies, artificial cells, drug delivery, and tissue engineering.

Bleeding from injuries to the torso region is a leading cause of fatalities in the military and in young adults. Such bleeding cannot be stopped by applying direct pressure (compression) of a bandage. An alternative is to introduce a foam at the injury site, with the expansion of the foam counteracting the bleeding. Foams with an active hemostatic agent have been tested for this purpose, but the barrier created by these foams is generally not strong enough to resist blood flow. In this paper, we introduce a new class of foams with enhanced rheological properties that enable them to form a more effective barrier to blood loss. These aqueous foams are delivered out of a double-barrelled syringe by combining precursors that produce bubbles of gas (CO2) in situ. In addition, one barrel contains a cationic polymer (hydrophobically modified chitosan, hmC) and the other an anionic polymer (hydrophobically modified alginate, hmA). Both these polymers function as hemostatic agents due to their ability to connect blood cells into networks. The amphiphilic nature of these polymers also enables them to stabilize gas bubbles without the need for additional surfactants. hmC-hmA foams have a mousse-like texture and exhibit a high modulus and yield stress. Their properties are attributed to the binding of hmC and hmA chains (via electrostatic and hydrophobic interactions) to form a coacervate around the gas bubbles. Rheological studies are used to contrast the improved rheology of hmC-hmA foams (where a coacervate arises) with those formed by hmC alone (where there is no such coacervate). Studies with animal wound models also confirm that the hmC-hmA foams are more effective at curtailing bleeding than the hmC foams due to their greater mechanical integrity.

The two-tailed anionic surfactant, AOT is well-known to form spherical reverse micelles in organic solvents such as cyclohexane and n-alkanes. Here, we report that trace amounts (e.g., around 1 mM) of the dihydroxy bile salt, sodium deoxycholate (SDC) can transform these dilute micellar solutions into self-supporting, transparent organogels. Gels can be obtained at a total AOT + SDC concentration as low as 6 mM or about 2 mg mL−1. Among all the bile salts studied, SDC is the only one that is capable of inducing organogels. The structure and rheology of these organogels is reminiscent of the self-assembled networks formed by proteins such as actin in water. In particular, both classes of gels exhibit the remarkable property of strain-stiffening, where the gel stiffness (modulus) increases with strain amplitude. Structurally, both gels are based on entangled networks of long, cylindrical filaments. We propose that SDC forms hydrogen bonds with AOT headgroups, transforming some of the spherical AOT micelles into semiflexible filaments. The average diameter of these filaments has been measured by small-angle neutron scattering (SANS), and suggests that SDC molecules are stacked together in the filament core.

Amphiphilic biopolymers such as hydrophobically modified chitosan (hmC) have been shown to convert liquid blood into elastic gels. This interesting property could make hmC useful as a hemostatic agent in treating severe bleeding. The mechanism for blood gelling by hmC is believed to involve polymer-cell self-assembly, i.e., insertion of hydrophobic side chains from the polymer into the lipid bilayers of blood cells, thereby creating a network of cells bridged by hmC. Here, we probe the above mechanism by studying dilute mixtures of blood cells and hmC in situ using optical microscopy. Our results show that the presence of hydrophobic side chains on hmC induces significant clustering of blood cells. The extent of clustering is quantified from the images in terms of the area occupied by the 10 largest clusters. Clustering increases as the fraction of hydrophobic side chains increases; conversely, clustering is negligible in the case of the parent chitosan that lacks hydrophobes. Moreover, the longer the hydrophobic side chains, the greater the clustering (i.e., C12 > C10 > C8 > C6). Clustering is negligible at low hmC concentrations but becomes substantial above a certain threshold. Finally, clustering due to hmC can be reversed by adding the supramolecule α-cyclodextrin, which is known to capture hydrophobes in its binding pocket. Overall, the results from this work are broadly consistent with the earlier mechanism, albeit with a few modifications.

Nanoerythrosomes (NERs), vesicle-like nanoparticles derived from red blood cells, represent a new and interesting vector for therapeutic molecules and imaging probes, mainly thanks to their high stability and excellent biocompatibility. Aiming to present a proof-of-concept of the use of NERs as diagnostic tools for in vitro/in vivo imaging purposes, we report here several functionalization routes to decorate the surfaces of NERs derived from bovine blood with two different fluorophores: 7-amino-4-methylcumarin and dibenzocyclooctinecyanine5.5. Notably, the fluorophores were cross-linked to the NERs surface with glutaraldehyde and, in the case of dibenzocyclooctinecyanine5.5, also using a click-chemistry route, termed strain-promoted azide-alkyne cycloaddition. The physicochemical characterization highlighted the high stability of the NERs derivatives in physiological conditions. Furthermore, the loading efficiency of the fluorophores on the NERs surface was evaluated using both UV–Vis spectroscopy and fluorescence microscopy.

We describe batch generation of uniform multifunctional chitosan microparticles for isolation of rare cells, such as circulating tumor cells (CTCs), from a sample of whole blood. The chitosan microparticles were produced in large numbers using a simple and inexpensive microtubing arrangement. The particles were functionalized through encapsulation of carbon black, to control autofluorescence, and surface attachment of streptavidin, to enable interactions with biotinylated antibodies. These large custom modified microparticles (≈164 μm diameter) were then packed into a microfluidic channel to demonstrate their utility in rare cell capture. Blood spiked with breast cancer (MCF-7) cells was first treated with a biotinylated antibody (anti-EpCAM, which is selective for cancer cells like MCF-7) and then pumped through the device. In the process, the cancer cells were selectively bound to the microparticles through non-covalent streptavidin–biotin interactions. The number density of captured cells was determined by fluorescence microscopy at physiologically relevant levels. Selective capture of the MCF-7 cells was characterized, and compared favorably with previous approaches. The overall approach using custom synthesized microparticles is versatile, and can allow researchers more flexibility for rare cell capture through simpler and cheaper methods than are currently employed.

We report a simple and reliable approach to fabricate composite hydrogel sheets with spatially patterned regions of plasmonic gold nanoparticles using a combination of contact printing and diffusion-controlled galvanic replacement reaction. In response to near-infrared laser irradiation, the localized increase in temperature induced the controlled shape deformation of the composite hydrogels, due to the combined effect of photothermal heating of the loaded gold nanoparticles and the thermal responsiveness of the hydrogel matrix. The same hydrogel can be designed to exhibit different modes of shape deformation depending on the direction of light irradiation, which has rarely been reported previously. The composite hydrogels may find applications in biomedicine and soft robots.

Many biological materials, such as the squid beak and the spinal disc, have a combination of stiff and soft parts with very different mechanical properties, for example, the elastic modulus (stiffness) of the stiffest part of the squid beak is about 100 times that of the softest part. Researchers have attempted to mimic such structures using hydrogels but have not succeeded in synthesizing bulk gels with such large variations in moduli. Here, we present a general approach that can be used to form hydrogels with two or more zones having appreciably different mechanical characters. For this purpose, we use a technique developed in our lab for creating hybrid hydrogels with distinct zones. For the soft zone of the gel, we form a polymer network using a conventional acrylic monomer [ N, N'-dimethylacrylamide (DMAA)] and with laponite (LAP) nanoparticles as the cross-linkers. For the stiff zone, we combine DMAA, LAP, and a methacrylated silica precursor ([3-(methacryloyloxy)-propyl]trimethoxy-silane). When this mixture is polymerized, nanoscale silica particles (∼300 nm in diameter) are formed, and these serve as additional cross-links between the polymer chains, making this network very stiff. The unique character of each zone is preserved in the hybrid gel, and different zones are covalently linked to each other, thereby ensuring robust interfaces. Rheological measurements show that the elastic modulus of the stiff zone can be more than 100 times that of the soft zone. This ratio of moduli is the highest reported to date in a single, continuous gel and is comparable to the ratio in the squid beak. We present different variations of our soft-stiff hybrid gels, including multizone cylinders and core-shell discs. Such soft-stiff gels could have utility in bioengineering, such as in interfacing stiff medical implants with soft tissues.

Dispersants, used in the mitigation of oil spills, are mixtures of amphiphilic molecules (surfactants) dissolved in a solvent. The recent large-scale use of dispersants has raised environmental concerns regarding the safety of these materials. In response to these concerns, our lab has developed a class of eco-friendly dispersants based on blends of the food-grade surfactants, soy lecithin (L) and Tween 80 (T), in a solvent. We have shown that these "L/T dispersants" are very efficient at dispersing crude oil into seawater. The solvent for dispersants is usually selected based on factors like toxicity, volatility, or viscosity of the overall mixture. However, with regard to the dispersion efficiency of crude oil, the solvent is considered to play a negligible role. In this paper, we re-examine the role of solvent in the L/T system and show that it can actually have a significant impact on the dispersion efficiency. That is, the dispersion efficiency can be altered from poor to excellent simply by varying the solvent while keeping the same blend of surfactants. We devise a systematic procedure for selecting the optimal solvents by utilizing Hansen solubility parameters. The optimal solvents are shown to have a high affinity for crude oil and limited hydrophilicity. Our analysis further enables us to identify solvents that combine high dispersion efficiency, good solubility of the L/T surfactants, a low toxicity profile, and a high flash point.

Li-S batteries have been considered promising candidates for the next-generation energy storage devices because of their extremely high energy densities and low cost. However, Li dendrite formation/dissolution and shuttle of high-order polysulfides prevent their practical applications. Herein, we demonstrate a highly concentrated electrolyte, 12 M lithium bis(fluorosulfonyl)imide (LiFSI) salt in DME solvent (12 M LiFSI/DME), that can effectively suppress both the Li dendritic growth on the anode and the polysulfide shuttle reactions on the cathode side. The highly concentrated electrolyte along with the robust solid electrolyte interphase (SEI) formed therein play the key role in achieving high coulombic efficiencies for both Li stripping/plating (> 99.2%) and S cathode (> 99.7%). Based on the in-depth understanding of the interactions between electrodes and highly concentrated electrolyte, we designed a novel dilute electrolyte (1 M LiFSI/HFE + DME), which achieves similar electrochemical performances in Li-S batteries as the concentrated electrolytes. These Li-S batteries with the highest CE for Li anode and sulfur cathode maintains a high reversible capacity of 786 mA h/g at 0.1 A/g after 300 cycles, or 644 mA h/g at 300th cycle even at 1 A/g without any detectable shuttle reactions.

Background Currently, the standard of care for treating severe hemorrhage in a military setting is Combat Gauze (CG). Previous work has shown that hydrophobically modified chitosan (hm-C) has significant hemostatic capability relative to its native chitosan counterpart. This work aims to evaluate gauze coated in hm-C relative to CG as well as ChitoGauze (ChG) in a lethal in vivo hemorrhage model. Methods Twelve Yorkshire swine were randomized to receive either hm-C gauze ( n = 4), ChG ( n = 4), or CG ( n = 4). A standard hemorrhage model was used in which animals underwent a splenectomy before a 6-mm punch arterial puncture of the femoral artery. Thirty seconds of free bleeding was allowed before dressings were applied and compressed for 3 min. Baseline mean arterial pressure was preserved via fluid resuscitation. Experiments were conducted for 3 h after which any surviving animal was euthanized. Results hm-C gauze was found to be at least equivalent to both CG and ChG in terms of overall survival (100% versus 75%), number of dressing used (6 versus 7), and duration of hemostasis (3 h versus 2.25 h). Total post-treatment blood loss was lower in the hm-C gauze treatment group (4.7 mL/kg) when compared to CG (13.4 mL/kg) and ChG (12.1 mL/kg) groups. Conclusions hm-C gauze outperformed both CG and ChG in a lethal hemorrhage model but without statistical significance for key endpoints. Future comparison of hm-C gauze to CG and ChG will be performed on a hypothermic, coagulopathic model that should allow for outcome significance to be differentiated under small treatment groups.

Eukaryotic cells have an architecture consisting of multiple inner compartments (organelles) such as the nucleus, mitochondria, and lysosomes. Each organelle is surrounded by a distinct membrane and has unique internal contents; consequently, each organelle has a distinct function within the cell. In this study, we create biopolymer microcapsules having a compartmentalized architecture as in eukaryotic cells. To make these capsules, we present a biocompatible method that solely uses aqueous media (i.e., avoids the use of oil phases), requires no sacrificial templates, and employs a minimal number of steps. Our approach exploits the electrostatic complexation of oppositely charged polymers dissolved in aqueous media. Specifically, droplets of an anionic biopolymer are generated using a simple microcapillary device, with the droplets being sheared off the capillary tip by pulses of gas (air or nitrogen). The liquid droplets are then introduced into a reservoir whereupon they encounter multivalent cations as well as a cationic biopolymer; thereby, a solid shell is formed around each droplet by electrostatic interactions between the polymers while the core is ionically cross-linked into a gel. In the next step, a discrete number of these capsules are encapsulated within a larger outer capsule by repeating the same process with a wider capillary. Our approach allows us to control the overall diameter of these multicompartment capsules (MCCs) (∼300-500 μm), the diameters of the inner compartments (∼100-300 μm), and the number of inner compartments in an MCC (1 to >5). More importantly, we can encapsulate different payloads in each of the inner compartments, including colloidal particles, enzymes, and microbial cells, in all cases preserving their native functions. A hallmark of biological cells is the existence of cascade processes, where products created in one organelle are transported and used in another. As an initial demonstration of the capabilities afforded by our MCCs, we study a simple cascade process involving two strains of bacteria (E. coli), which communicate through small molecules known as autoinducers. In one compartment of the MCC, we cultivate E. coli that produces autoinducer 2 (AI-2) in the presence of growth media. The AI-2 then diffuses into an adjacent compartment within the MCC wherein a reporter strain of E. coli is cultivated. The reporter E. coli imbibes the AI-2 and in turn, produces a fluorescence response. Thus, the action (AI-2 production) and response (fluorescence signal) are localized within different compartments in the same MCC. We believe this study is an important advance in the path towards an artificial cell.

Wormlike micelles (WLMs) formed from surfactants have attracted much attention for their ability to thicken water in a manner similar to water-soluble polymers. It is known that WLMs are cylindrical filaments that can attain very long contour lengths (∼few μm), akin to chains of polymers with ultra-high molecular weights (UHMWs). In this study, we aim to make a direct comparison between the thickening capabilities of WLMs and UHMW polymers. The chosen surfactant is erucyl dimethyl amidopropyl betaine (EDAB), a C22-tailed zwitterionic surfactant known to form particularly long WLMs independent of salt. The chosen polymer is nonionic polyacrylamide (PAM) having an UHMW of 12 MDa. Both EDAB WLMs and the PAM show strong thickening capability in saline water at 25 °C, but the WLMs are more efficient. For example, a 1.0 wt% EDAB WLM sample has a similar zero-shear viscosity η0 (∼40 000 mPa s) to a 2.5 wt% PAM solution. When temperature is increased, both samples show an exponential reduction in viscosity, but the WLMs are more sensitive to temperature. Microstructural differences between the two systems are confirmed by data from small-angle neutron scattering (SANS) and cryo-transmission electron microscopy (cryo-TEM). As expected, the key differences are that the WLM chains have a larger core radius (Rcore) and in turn, a longer persistence length (lp) than the PAM chains.

Hydrogels with shapes that can be adapted to their environment have attracted great attention from both academia and industry. We report herein a new and robust strategy to reprogram the light-induced shape transformation of a thermoresponsive composite hydrogel sheet with erasable and rewritable patterns of iron oxide nanoparticles as photothermal agents. Numerous distinct and reversible shape transformations are achieved from a single hydrogel sheet by repeatably writing in the sheet with different nanoparticle patterns. The shape transformations were verified by finite element modeling. The present strategy is simple, fast, and efficient in reprogramming the shape change of the thermoresponsive hydrogel material. The composite hydrogel sheet may find applications in soft robotics, tissue engineering, and controlled release.

We demonstrate the use of electric fields to rapidly form gels of the biopolymer alginate (Alg) in specific three-dimensional (3-D) shapes and patterns. In our approach, we start with a gel of the biopolymer agarose, which is thermoresponsive and hence can be molded into a specific shape. The agarose mold is then loaded with Ca2+ cations and placed in a beaker containing an Alg solution. The inner surface of the beaker is surrounded by aluminum foil (cathode), and a copper wire (anode) is stuck in the agarose mold. These are connected to a direct current (DC) power source, and when a potential of ∼10 V is applied, an Alg gel is formed in a shape that replicates the mold. Gelation occurs because the Ca2+ ions electrophoretically migrate away from the mold, whereupon they cross-link the Alg chains adjacent to the mold. At low Ca2+ (0.01 wt %), the Alg gel layer grows outward from the mold surface at a steady rate of about 0.8 mm/min, and the gel stops growing when the field is switched off. After a gel of d...

Wormlike micelles (WLMs) are long, flexible cylindrical chains formed by the self-assembly of surfactants in semidilute solutions. Scientists have been fascinated by WLMs because of their similarities to polymers, while at the same time, the viscoelastic properties of WLM solutions have made them useful in a variety of industrial applications. To date, most studies on WLMs have been performed in water (i.e., a highly polar liquid), while there are a few examples of "reverse" WLMs in oils (i.e., highly nonpolar liquids). However, in organic solvents with lower polarity than water such as glycerol, formamide, and ethylene glycol, there have been no reports of WLMs thus far. Here, we show that it is indeed possible to induce a long-tailed cationic surfactant to assemble into WLMs in several of these solvents. To form WLMs, the surfactant is combined with a "binding" salt, i.e., one with a large organic counterion that is capable of binding to the micelles. Examples of such salts include sodium salicylate and sodium tosylate, and we find self-assembly to be maximized when the surfactant and salt concentrations are near-equimolar. Interestingly, the addition of a simple, inorganic salt such as sodium chloride (NaCl) to the same surfactant does not induce WLMs in polar solvents (although it does so in water). Thus, the design rules for WLM formation in polar solvents are distinct from those in water. Aqueous WLMs have been characterized at temperatures from 25 °C and above, but few studies have examined WLMs at much lower (e.g., subzero) temperatures. Here, we have selected a surfactant with a very low Krafft point (i.e., the surfactant does not crystallize out of solution upon cooling due to a cis-unsaturation in its tail) and a low-freezing solvent, viz. a 90/10 mixture of glycerol and ethylene glycol. In these mixtures, we find evidence for WLMs that persist down to temperatures as low as -20 °C. Rheological techniques as well as small-angle neutron scattering (SANS) have been used to characterize the WLMs under these conditions. Much like their aqueous counterparts, WLMs in polar solvents show viscoelastic properties, and accordingly, these fluids could find applications as synthetic lubricants or as improved antifreezing fluids.

A simple amphiphile, N-cardanyltaurine amide (NCT) with different degrees of cis-unsaturation in its tail resulted in the formation of strong organogels. Interestingly, this is in contrast to the commonly accepted notion that introducing unsaturation in alkyl chains enhances fluidity in lipid assemblies. The physico-chemical and first-principles DFT calculations confirmed the pegging of ‘kinked’ unsaturated side chains, where the hydrophobic interlocking as in Velcro fasteners leads to a network of cylindrical micelles, resulting in self-standing organogels. Textural profile analysis and spectroscopic details substantiated the dynamic assembly to resemble a 3D network of gelators rather than being a cross-linked or polymerized matrix of monomers.

We have developed microscale polymer capsules that are able to chemically degrade a certain type of polymeric microbead in their immediate vicinity. The inspiration here is from the body’s immune system, where killer T cells selectively destroy cancerous cells or cells infected by pathogens while leaving healthy cells alone. The “killer” capsules are made from the cationic biopolymer chitosan by a combination of ionic cross-linking (using multivalent tripolyposphate anions) and subsequent covalent cross-linking (using glutaraldehyde). During capsule formation, the enzyme glucose oxidase (GOx) is encapsulated in these capsules. The target beads are made by ionic cross-linking of the biopolymer alginate using copper (Cu2+) cations. The killer capsules harvest glucose from their surroundings, which is then enzymatically converted by GOx into gluconate ions. These ions are known for their ability to chelate Cu2+ cations. Thus, when a killer capsule is next to a target alginate bead, the gluconate ions diffuse...

External triggers such as pH or temperature can induce hydrogels to swell or shrink rapidly. Recently, these triggers have also been used to alter the three-dimensional (3-D) shapes of gels: for example, a flat gel sheet can be induced to fold into a tube. Self-folding gels are reminiscent of natural structures such as the Venus flytrap, which folds its leaves to entrap its prey. They are also of interest for applications in sensing or microrobotics. However, to advance the utility of self-folding gels, the range of triggers needs to be expanded beyond the conventional ones. Toward this end, we have designed a class of gels that change shape in response to very low concentrations of specific biomolecules. The gels are hybrids of three different constituents: (A) polyethylene glycol diacrylate (PEGDA); (B) gelatin methacrylate-co-polyethylene glycol dimethacrylate (GelMA-co-PEGDMA); and (C) N-isopropylacrylamide (NIPA). The thin-film hybrid is constructed as a bilayer or sandwich of two layers, with an A/B layer (alternating strips of A and B) sandwiched above a layer of gel C. Initially, when this hybrid gel is placed in water, the C layer is much more swollen than the A/B layer. Despite the swelling mismatch, the sheet remains flat because the A/B layer is very stiff. When collagenase enzyme is added to the water, it cleaves the gelatin chains in B, thus reducing the stiffness of the A/B layer. As a result, the swollen C layer is able to fold over the A/B layer, causing the sheet to transform into a specific shape. The typical transition is from flat sheet to closed hollow tube, and the time scale for this transition decreases with increasing enzyme concentration. Shape transitions are induced by enzyme levels as low as 0.75 U/mL. Interestingly, a shape transition is also induced by adding the lysate of murine fibroblast cells, which contains enzymes from the matrix metalloproteinase (MMP) family at levels around 0.1 U/mL (MMPs are similar to collagenase in their ability to cleave gelatin). We further show that transitions from flat sheets to other shapes such as helices and pancakes can be engineered by altering the design pattern of the gel. Additionally, we have made a rudimentary analog of the Venus flytrap, with two flat gels ("leaves") flanking a central folding gel ("hinge"). When enzyme is added, the hinge bends and brings the leaves together, trapping objects in the middle.

We report the design of hydrogels that can act as "smart" valves or membranes. Each hydrogel is engineered with a pore (about 1 cm long and1 mm thick) that remains closed under ambient conditions but opens under specific conditions. Our design is inspired by the stomatal valves in plant leaves, which regulate the movement of water and gases in and out of the leaves. The design features two different gels, active and passive, which are attached concentrically to form a disc-shaped hybrid film. The pore is created in the central active gel, and the conditions for opening the pore can be tuned based on the chemistry of this gel. For example, if the active gel is made from N-isopropylacrylamide (NIPA), the actuation of the pore depends on the temperature of water relative to 32 °C, which is the lower-critical solution temperature (LCST) of NIPA. The concentric design of our hybrid provides directionality to the volumetric transition of the active gel, i.e., it ensures that the pore opens as the active gel shrinks. In turn, contact with hot water (T32 °C) opens the pore and allows the water to pass through the gel. Conversely, the pore remains closed when the water is cold (T32 °C). The gel thereby acts as a "smart" valve that is able to regulate the flow of solvent depending on its properties. We have extended the concept to other stimuli that can cause gel-swelling transitions including solvent composition, pH, and light. Additionally, when two different gel-based valves are arranged in series, the assembly acts as a logical "AND" gate, i.e., water flows through the valve-combination only if it simultaneously satisfies two distinct conditions (such as its pH being below a critical value and its temperature being above a critical value).

When administered intravenously, active targeting of drug nanocarriers (NCs) improves biodistribution and endocytosis. Targeting may also improve oral delivery of NCs to treat gastrointestinal (GI) pathologies or for systemic absoption. However, GI instability of targeting moieties compromises this strategy. We explored whether encapsulation of antibody-coated NCs in microcapsules would protect against gastric degradation, providing NCs release and targeting in intestinal conditions. We used nanoparticles coated with antibodies against intercellular adhesion molecule-1 (anti-ICAM) or non-specific IgG. NCs (~160-nm) were encapsulated in ~180-μm microcapsules with an alginate core, in the absence or presence of a chitosan shell. We found >95% NC encapsulation within microcapsules and

Liposomes are nanoscale containers that are typically synthesized from lipids using a high-shear process such as extrusion or sonication. While liposomes are extensively used in drug delivery, they do suffer from certain problems including limited colloidal stability and short circulation times in the body. As an alternative to liposomes, we explore a class of container structures derived from erythrocytes (red blood cells). The procedure involves emptying the inner contents of these cells (specifically hemoglobin) and resuspending the empty structures in buffer, followed by sonication. The resulting structures are termed nanoerythrosomes (NERs), i.e., they are membrane-covered nanoscale containers, much like liposomes. Cryo-transmission electron microscopy (cryo-TEM) and small-angle neutron scattering (SANS) are employed for the first time to study these NERs. The results reveal that the NERs are discrete spheres (∼110 nm diameter) with a unilamellar membrane of thickness ∼4.5 nm. Remarkably, the biconcave disc-like shape of erythrocytes is also exhibited by the NERs under hypertonic conditions. Moreover, unlike typical liposomes, NERs show excellent colloidal stability in both buffer as well as in serum at room temperature, and are also able to withstand freeze-thaw cycling. We have explored the potential for using NERs as colloidal vehicles for targeted delivery. Much like conventional liposomes, NER membranes can be decorated with fluorescent or other markers, solutes can be encapsulated in the cores of the NERs, and NERs can be targeted to specifically bind to mammalian cells. Our study shows that NERs are a promising and versatile class of nanostructures. NERs that are harvested from a patient's own blood and reconfigured for nanomedicine can potentially offer several benefits including biocompatibility, minimization of immune response, and extended circulation time in the body.

Effectiveness of oil spill dispersants containing lecithin/Tween 80 (L/T) blends in ethanol was measured as a function of L:T ratio, surfactant:solvent ratio, solvent composition, and dispersant:oil ratio (DOR) using baffled flask dispersion effectiveness tests. Optimal L:T ratios are between 60:40 and 80:20 (w/w); at higher L:T ratios, effectiveness is limited by high interfacial tension, while at lower L:T ratios, insufficient lecithin is present to form a well-packed monolayer at an oil-water interface. These optimal L:T ratios retain high effectiveness at low DOR: 80:20 (w/w) L:T dispersant is 89% effective at 1:25 DOR (v/v) and 77% effective at 1:100 DOR (v/v). Increasing surfactant:solvent ratio increases dispersant effectiveness even when DOR is proportionally reduced to keep total surfactant concentration dosed into the oil constant. Replacing some of the ethanol with octane or octanol also increases dispersant effectiveness, suggesting that ethanol's hydrophilicity lowers dispersant-oil miscibility, and that more hydrophobic solvents would increase effectiveness.

Background A novel injectable expanding foam based on hydrophobically modified chitosan (HM-CS) was developed to improve hemostasis during surgeries. HM-CS is an amphiphilic derivative of the natural biopolymer chitosan (CS); HM-CS has been shown to improve the natural hemostatic characteristics of CS, but its internal safety has not been systematically evaluated. The goal of this study was to compare the long-term in vivo safety of HM-CS relative to a commonly used fibrin sealant (FS), TISSEEL (Baxter). Methods Sixty-four Sprague–Dawley rats (275-325 g obtained from Charles River Laboratories) were randomly assigned to control (n = 16) or experimental (n = 48) groups. Samples of the test materials (HM-CS [n = 16], CS [n = 16], and FS [n = 16]) applied to a nonlethal liver excision (0.4 ± 0.3 g of the medial lobe) in rats were left inside the abdomen to degrade. Animals were observed daily for signs of morbidity and mortality. Surviving animals were sacrificed at 1 and 6 wk; the explanted injury sites were microscopically assessed. Results All animals (64/64) survived both the 1- and 6-wk time points without signs of morbidity. Histological examination showed a comparable pattern of degradation for the various test materials. FS remnants and significant adhesions to neighboring tissues were observed at 6 wk. Residual CS and HM-CS were observed at the 6 wk with fatty deposits at the site of injury. Minimal adhesions were observed for CS and HM-CS. Conclusions The internal safety observed in the HM-CS test group after abdominal implantation indicates that injectable HM-CS expanding foam may be an appropriate internal use hemostatic candidate.

The spontaneous folding of flat gel films into tubes is an interesting example of self-assembly. Typically, a rectangular film folds along its short axis when forming a tube; folding along the long axis has been seen only in rare instances when the film is constrained. Here, we report a case where the same free-swelling gel film folds along either its long or short axis depending on the concentration of a solute. Our gels are sandwiches (bilayers) of two layers: a passive layer of cross-linked N,N'-dimethylyacrylamide (DMAA) and an active layer of cross-linked DMAA that also contains chains of the biopolymer alginate. Multivalent cations like Ca2+ and Cu2+ induce these bilayer gels to fold into tubes. The folding occurs instantly when a flat film of the gel is introduced into a solution of these cations. The likely cause for folding is that the active layer stiffens and shrinks (because the alginate chains in it get cross-linked by the cations) whereas the passive layer is unaffected. The resulting mismatch in swelling degree between the two layers creates internal stresses that drive folding. Cations that are incapable of cross-linking alginate, such as Na+ and Mg2+, do not induce gel folding. Moreover, the striking aspect is the direction of folding. When the Ca2+ concentration is high (100 mM or higher), the gels fold along their long axis, whereas when the Ca2+ concentration is low (40 to 80 mM), the gels fold along their short axis. We hypothesize that the folding axis is dictated by the inhomogeneous nature of alginate-cation cross-linking, i.e., that the edges get cross-linked before the faces of the gel. At high Ca2+ concentration, the stiffer edges constrain the folding; in turn, the gel folds such that the longer edges are deformed less, which explains the folding along the long axis. At low Ca2+ concentration, the edges and the faces of the gel are more similar in their degree of cross-linking; therefore, the gel folds along its short axis. An analogy can be made to natural structures (such as leaves and seed pods) where stiff elements provide the directionality for folding.