Tapping the Role of Microbial Biosurfactants in Pesticide Remediation: An Eco-Friendly Approach for Environmental Sustainability

Pesticides are used indiscriminately all over the world to protect crops from pests and pathogens. If they are used in excess, they contaminate the soil and water bodies and negatively affect human health and the environment. However, bioremediation is the most viable option to deal with these pollutants, but it has certain limitations. Therefore, harnessing the role of microbial biosurfactants in pesticide remediation is a promising approach. Biosurfactants are the amphiphilic compounds that can help to increase the bioavailability of pesticides, and speeds up the bioremediation process. Biosurfactants lower the surface area and interfacial tension of immiscible fluids and boost the solubility and sorption of hydrophobic pesticide contaminants. They have the property of biodegradability, low toxicity, high selectivity, and broad action spectrum under extreme pH, temperature, and salinity conditions, as well as a low critical micelle concentration (CMC). All these factors can augment the process of pesticide remediation. Application of metagenomic and in-silico tools would help by rapidly characterizing pesticide degrading microorganisms at a taxonomic and functional level. A comprehensive review of the literature shows that the role of biosurfactants in the biological remediation of pesticides has received limited attention. Therefore, this article is intended to provide a detailed overview of the role of various biosurfactants in improving pesticide remediation as well as different methods used for the detection of microbial biosurfactants. Additionally, this article covers the role of advanced metagenomics tools in characterizing the biosurfactant producing pesticide degrading microbes from different environments.

Low Fouling Polysulfobetaines with Variable Hydrophobic Content

Amphiphilic polymer coatings combining hydrophilic elements, in particular zwitterionic groups, and hydrophobic elements comprise a promising strategy to decrease biofouling. However, the influence of the content of the hydrophobic component in zwitterionic coatings on the interfacial molecular reorganization dynamics and the anti-fouling performance is not well understood. Therefore, coatings of amphiphilic copolymers of sulfobetaine methacrylate 3-[N-2'-(methacryloyloxy)ethyl-N,N-dimethyl]-ammonio propane-1-sulfonate (SPE) are prepared which contain increasing amounts of hydrophobic n-butyl methacrylate (BMA). Their fouling resistance is compared to that of their homopolymers PSPE and PBMA. The photo-crosslinked coatings form hydrogel films with a hydrophilic surface. Fouling by the proteins fibrinogen and lysozyme as well as by the diatom Navicula perminuta and the green algae Ulva linza is assessed in laboratory assays. While biofouling is strongly reduced by all zwitterionic coatings, the best fouling resistance is obtained for the amphiphilic copolymers. Also in preliminary field tests, the anti-fouling performance of the amphiphilic copolymer films is superior to that of both homopolymers. When the coatings are exposed to a marine environment, the reduced susceptibility to silt incorporation, in particular compared to the most hydrophilic polyzwitterion PSPE, likely contributes to the improved fouling resistance.

Water-soluble polycarbodiimides and their cytotoxic and antifungal properties

We have successfully synthesized water-soluble neutral and polyelectrolyte helical polycarbodiimides and studied their biological properties. These polymers were prepared by decorating carbodiimide backbones with nonionic, hydrophilic functional groups such as dimethylamine, piperazine, and morpholine. Additionally, the 3° amines present in these functional groups were quaternized using methyl iodide as the alkylating agent to produce their ionic analogs. Polycarbodiimides were chosen as the base polymer used because of their facile chemical modification, pH tolerance in terms of both their helical conformations and degradation behaviors, and tunable helical inversion barriers. Hydrophilic side groups, such as morpholine, dimethylamine, and piperazine, can be used to balance the amphiphilic architecture of the polycarbodiimides along with lipophilic groups, such as alkyl side chains. A chiral R or S BINOL Ti(IV) isopropoxide catalyst was used to control the handedness of the polycarbodiimide helices in these studies. These ionic and neutral polycarbodiimides were subsequently studied for potential antimicrobial and cytotoxic properties. Poly[N-methyl-N'-2-morpholinoethylcarbodiimide], as an example, exhibited significant antifungal properties against Candida albicans. Also, Poly[N-methyl-N'-2-morpholinoethylcarbodiimide] showed significant inhibition of biofilm formation. This suggests that the polymer is a promising candidate for antifungal biomedical applications. Measuring cytotoxicity against urinary bladder cancer cells, poly[N-[3-(dimethylamino)propyl)]-N'-[3-(morpholino)propyl]carbodiimide] (S-cat) and poly[N-[3-(dimethylamino)propyl)]-N'-[3-(morpholino)propyl]carbodiimide]-MeI (S-cat) showed significantly low IC₅₀ values. The IC₅₀ values of poly[N-[3-(dimethylamino)propyl)]-N'-[3-(morpholino)propyl]carbodiimide] (S-cat) and Poly[N-[3-(dimethylamino)propyl)]-N'-[3-(morpholino)propyl]carbodiimide]-MeI (S-cat) are 3.50 μM and 1.27 μM, respectively. The significantly low cancer cell growth inhibition concentration implies the highest cytotoxicity of the polymers, suggesting potential applications as cancer therapeutics. These results also showed that the functionalization and chirality of polycarbodiimides modulate their anticancer and antifungal activity.

Self-assembly of Amphiphilic Porphyrins To Construct Nanoparticles for Highly Efficient Photodynamic Therapy

Hydrophobic photosensitizers greatly affect cell permeability and enrichment in tumors, but they cannot be used directly for clinical applications because they always aggregate in water, preventing their circulation in the blood and accumulation in tumor cells. As a result, amphiphilic photosensitizers are highly desirable. Although nanomaterial-based photosensitizers can solve water solubility, they have the disadvantages of complicated operation, poor reproducibility, low drug loading, and poor stability. In this work, an efficient synthesis strategy is proposed that converts small molecules into nanoparticles in 100 % aqueous solution by molecular assembly without the addition of any foreign species. Three photosensitizers with triphenylphosphine units and ethylene glycol chains of different lengths, TPP-PPh₃ , TPP-PPh₃ -2PEG and TPP-PPh₃ -4PEG, were synthesized to improve amphiphilicity. Of the three photosensitizers, TPP-PPh₃ -4PEG is the most efficient (singlet oxygen yield: 0.89) for tumor photodynamic therapy not only because of its definite constituent, but also because its amphiphilic structure allows it to self-assemble in water.

Hydrophobically-Modified PEG Hydrogels with Controllable Hydrophilic/Hydrophobic Balance

This work reports on a novel method to synthesize hydrophobically-modified hydrogels by curing epoxy monomers with amines. The resulting networks contain hydrophilic poly(ethylene glycol) (PEG) segments, poly(propylene glycol) (PPG) segments, and C₁₈ alkyl segments. By varying the content of C₁₈ segments, networks with different hydrophilic-lipophilic balance (HLB) are obtained. All networks show an amphiphilic behavior, swelling considerably both in organic solvents and in aqueous media. In the latter they display a thermosensitive behavior, which is highly affected by the network HLB and the pH of the solution. A decrease in HLB results in an increment of the polymer weight content (w_p) due to hydrophobic association. Furthermore, a reduction in HLB induces a remarkable increase in initial modulus, elongation at break and tensile strength, especially when w_p becomes greater than about 10%. Low field nuclear magnetic resonance (LF-NMR) experiments evidence that, when HLB decreases, a sudden and considerable increase in hydrogel heterogeneity takes place due to occurrence of extensive physical crosslinking. Available data suggest that in systems with w_p ≳ 10% a continuous physical network superimposes to the pre-existing chemical network and leads to a sort of double network capable of considerably improving hydrogel toughness.

Tuning the Surface Properties of Poly(Allylamine Hydrochloride)-Based Multilayer Films

The layer-by-layer (LbL) method of polyelectrolyte multilayer (PEM) fabrication is extremely versatile. It allows using a pair of any oppositely charged polyelectrolytes. Nevertheless, it may be difficult to ascribe a particular physicochemical property of the resulting PEM to a structural or chemical feature of a single component. A solution to this problem is based on the application of a polycation and a polyanion obtained by proper modification of the same parent polymer. Polyelectrolyte multilayers (PEMs) were prepared using the LbL technique from hydrophilic and amphiphilic derivatives of poly(allylamine hydrochloride) (PAH). PAH derivatives were obtained by the substitution of amine groups in PAH with sulfonate, ammonium, and hydrophobic groups. The PEMs were stable in 1 M NaCl and showed three different modes of thickness growth: exponential, mixed exponential-linear, and linear. Their surfaces ranged from very hydrophilic to hydrophobic. Root mean square (RMS) roughness was very variable and depended on the PEM composition, sample environment (dry, wet), and the polymer constituting the topmost layer. Atomic force microscopy (AFM) imaging of the surfaces showed very different morphologies of PEMs, including very smooth, porous, and structured PEMs with micellar aggregates. Thus, by proper choice of PAH derivatives, surfaces with different physicochemical features (growth type, thickness, charge, wettability, roughness, surface morphology) were obtained.

Insights into Regional Wetting Behaviors of Amphiphilic Collagen for Dual Separation of Emulsions

Industrial manufacture generates a huge quantity of emulsion wastewater, which causes serious threats to the aquatic ecosystems. Water-in-oil (W/O) and oil-in-water (O/W) emulsions are two major types of emulsions discharged by industries. However, dual separation of W/O and O/W emulsions remains a challenging issue due to the contradictory permselectivity for separating the two emulsions. In the present investigation, the amphiphilicity-derived regional wetting mechanism of water and oil on the amphiphilic collagen fibers was revealed based on the combination of numerous experiments and molecular dynamics (MD) simulations. Electrostatic interactions and van der Waals force were manifested to be the driving forces of regional wetting in the hydrophilic and hydrophobic regions, respectively. The regional wetting endowed amphiphilic collagen fibers with underwater oleophobicity and underoil hydrophilicity, which enabled dual separation of emulsions by selectively retaining the dispersed water phase of W/O emulsions in the hydrophilic regions while the dispersed oil phase of O/W emulsions in the hydrophobic regions. The achieved separation efficiency was higher than 99.98%, and the flux reached 3337.6 L m^-2 h^-1. Initial wetting status significantly affects the regional wetting-enabled dual separation. Based on the MD simulations, amphiphilic intramolecular conformations of tropocollagen were suggested to be the origins of regional wetting on collagen fibers. Our findings may pave the way for developing high-performance dual separation materials that are promising to be utilized for the practical treatment of emulsion wastewater.

An Amphiphilic PEGylated Peptide Dendron-Gemcitabine Prodrug-Based Nanoagent for Cancer Therapy

An amphiphilic peptide dendrimer conjugated with gemcitabine (GEM), PEGylated dendron-Gly-Phe-Leu-Gly-GEM (PEGylated dendron-GFLG-GEM), is developed as a nano-prodrug for breast cancer therapy. The self-assembled behavior is observed under a transmission electron microscopy and dynamic light scattering. The negatively charged surface and hydrodynamic size of the amphiphilic nanosized prodrug supported that the prodrug can maintain the stability of GEM during circulation and accumulate in the tumor tissue. Drug release assays are conducted to monitor the release of GEM from this nanodrug delivery system in response to the tumor microenvironment, and these assays confirm that GEM released from the nanocarrier is identical to free GEM. The GEM prodrug can prevent proliferation of tumor cells. The therapeutic effect against breast cancer is systematically investigated using an in vivo animal model. Immunohistochemical results are aligned with the significantly enhanced anticancer efficacy of GEM released from the prodrug. This self-assembled amphiphilic drug delivery nanocarrier may broaden the application for GEM and other anticancer agents for breast cancer chemotherapy.

Robust and High-Temperature-Resistant Nanofiber Membrane Separators for Li-Metal, Li-Sulfur, and Aqueous Li-Ion Batteries

Mechanically strong separators with good electrolyte wettability and low-shrinkage properties are desirable for highly efficient and safe lithium batteries. In this study, multifunctional nanofiber membranes are fabricated by electrospinning a homogeneous solution containing amphiphilic poly(ethylene glycol)diacrylate-grafted siloxane and polyacrylonitrile. After the chemical cross-linking of siloxane, the prepared nanofiber membranes are found to exhibit good mechanical properties, high thermostability, and superior electrolyte-philicity with aqueous and nonaqueous electrolytes. Li-metal cells with the fabricated membrane separator exhibit high cycling stability (Coulombic efficiency of 99.8% after 1000 cycles). Moreover, improved cycling stability of Li-sulfur batteries can be achieved using these membrane separators. These membrane separators can be further used in flexible aqueous lithium-ion batteries and exhibit steady electrochemistry performance. This work opens up a potential route for designing multifunctional universal separators for rechargeable batteries.

Nanomedical Applications of Amphiphilic Dendrimeric Micelles

In recent years, polymeric materials with the ability to self-assemble into micelles have been increasingly investigated for application in various fields, but mainly in biomedicine. Micellar morphology is interesting in the field of drug transport and delivery, since micelles can encapsulate hydrophobic molecules in their nucleus, have active molecules in their outer layer, and due to their nanometric size, can take advantage of the enhanced permeability and retention (EPR) effect, prolong the time in circulation and avoid renal clearance. In addition, nanobioactive molecules (joined in covalent form or by host-host interaction), such as drugs, bioimaging molecules, targeting ligands, "cross-linkable" molecules or bonds, sensitive to internal or external stimuli, can be incorporated into them and showed better activity as anticancer agents, siRNA delivery agents as well as antiviral and antiparasitic compounds. The present work is a review of the information published, which is the most important about the synthesis and biological importance of the confined multivalent cooperation and the ability to modify the dendritic structure, provide the versatility to create and improve the amphiphiles used in the micellar supramolecular field. The most studied structures are the hybrid copolymers formed by the combination of linear polymers and dendrons. However, small dendritic molecules that do not involve linear polymers have also been developed, such as Janus dendrimers, facial dendrons, and dendritic amphiphiles with only one dendron. Amphiphilic dendrimer micelles have achieved efficient and promising results, both in in vitro and in vivo tests, which encourage their research for future application in nanotherapies.

Comparative analysis of two isocyanate-free urethane-based gels for antifouling applications

Amphiphilic gels consisting of acrylamide (AAM)/2-hydroxyethyl methacrylate (HEMA), hexafluorobutyl methacrylate (HFBMA) and non-isocyanate urethane dimethacrylate (NIUDMA) of varying molecular weights were compared. A three-level Taguchi analysis was performed using the amount of AAM/HEMA, HFBMA, NIUDMA and reaction time as dependent variables to determine the optimal formulation of the gels with maximized toughness and elastic modulus. The results were compared with commercial AF/FR Intersleek® coatings (IS 700, IS 900 and IS 1100SR) for their antifouling performance against a marine microalga (Navicula incerta), a marine bacterium (Cellulophaga lytica) and adult barnacles (Amphibalanus amphitrite). The toughness, elastic modulus and strain at break of the optimized AAM gels ranged from 3 to7 MPa, 25 to 72 MPa and 80% to 170%, respectively, whereas those of the optimized HEMA gels ranged from 1 to 3 MPa, 13 to 23 MPa and 76% to 160%, respectively. The gels, particularly AHN(E9) and HHN(E12), showed reductions of attachment compared with IS700 of up to 93% and 58%, respectively.

Tough amphiphilic antifouling coating based on acrylamide, fluoromethacrylate and non-isocyanate urethane dimethacrylate crosslinker

This study is focused on the development of tougher gels using combinations of acrylamide, fluoromethacrylate and a non-isocyanate urethane dimethacrylate (NIUDMA) crosslinker. The NIUDMA was tailored with 2, 3-epoxypropoxy propyl-polydimethylsiloxane segments E9 (MW = 0.36 kg mol^-1), E11 (MW = 0.5-0.6 kg mol^-1) and E12 (MW = 1-1.4 kg mol^-1). A 3 level Taguchi design was used to evaluate the role of each component of the ternary copolymer gel on the elastic modulus and toughness. The toughness ranged from 2.5-7 MJ m^-3 whereas the modulus ranged from 27-70 MPa. The formulations with the highest toughness and modulus were screened for their antifouling potential in biological assays against the microalga Navicula incerta and the bacterium Cellulophaga lytica. The E9 gels showed the best performance, achieving a 73% reduction in N. incerta cells and a 92% reduction in C. lytica biofilm remaining after water jetting treatments, when compared with the commercial Intersleek product IS700.

Anti-biofouling properties of poly(dimethyl siloxane) with RAFT photopolymerized acrylate/methacrylate surface grafts against model marine organisms

Biofouling of man-made surfaces by marine organisms is a global problem with both financial and environmental consequences. However, the development of non-toxic anti-biofouling coatings is challenged by the diversity of fouling organisms. One possible solution leverages coatings composed of diverse chemical constituents. Reversible addition-fragmentation chain-transfer (RAFT) photopolymerization was used to modify poly(dimethylsiloxane) (PDMSe) surfaces with polymeric grafts composed of three successive combinations of acrylamide, acrylic acid, and hydroxyethyl methacrylate. RAFT limited conflicting variables and allowed for the effect of graft chemistry to be isolated. While all compositions enhanced the anti-biofouling performance compared with the PDMSe control, the ternary, amphiphilic copolymer was the most effective with 98% inhibition of the attachment of zoospores of the green alga Ulva linza, 94% removal of cells of the diatom Navicula incerta, and 62% removal of cells of the bacterium Cellulophaga lytica. However, none of the graft compositions tested were able to mitigate reattachment of adult barnacles, Amphibalanus amphitrite.

Novel Temperature/Reduction Dual-Stimulus Responsive Triblock Copolymer [P(MEO2MA-co- OEGMA)-b-PLLA-SS-PLLA-b-P(MEO2MA-co-OEGMA)] via a Combination of ROP and ATRP: Synthesis, Characterization and Application of Self-Assembled Micelles

Novel temperature/reduction dual stimulus-responsive triblock copolymers, poly [2-(2-methoxyethoxy) ethyl methacrylate-co-oligo (ethylene glycol) methacrylate]-b-(L-polylactic acid)-SS-b-(L-polylactic acid)-b-poly[2-(2-methoxyethoxy) ethyl methacrylate-co-oligo(ethylene glycol)methacrylate] [P(MEO₂MA-co-OEGMA)-b-PLLA-SS-PLLA-b-P(MEO₂MA-co-OEGMA)] (SPMO), were synthesized by ring opening polymerization (ROP) of L-lactide and 2,2’-dithio diethanol (SS-DOH), and random copolymerization of MEO₂MA and OEGMA monomers via atom transfer radical polymerization (ATRP) technology. The chemical structures and compositions of the novel copolymers were demonstrated by proton nuclear magnetic resonance (¹H NMR) and Fourier transform infrared spectroscopy (FTIR). The molecular weights of the novel copolymers were measured by size exclusive chromatography (SEC) and proved to have a relatively narrow molecular weight distribution coefficient (ÐM ≤ 1.50). The water solubility and transmittance of the novel copolymers were tested via visual observation and UV–Vis spectroscopy, which proved the SPMO had a good hydrophilicity and suitable low critical solution temperature (LCST). The critical micelle concentration (CMC) of the novel polymeric micelles were determined using surface tension method and fluorescent probe technology. The particle size and morphology of the novel polymeric micelles were characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The sol–gel transition behavior of the novel copolymers was studied via vial flip experiments. Finally, the hydrophobic anticancer drug doxorubicin (DOX) was used to study the in vitro release behavior of the novel drug-loaded micelles. The results show that the novel polymeric micelles are expected to become a favorable drug carrier. In addition, they exhibit reductive responsiveness to the small molecule reducing agent dithiothreitol (DTT) and temperature responsiveness with temperature changes.

Preparation of amphiphilic magnetic polyvinyl alcohol targeted drug carrier and drug delivery research

Currently, magnetic applications have great potential for development in the field of drug carriers. In this paper, Fe₃O₄-PVA@SH, an amphiphilic magnetically targeting drug carrier, was prepared by using Fe₃O₄ and PVA with thiohydrazide-iminopropyltriethoxysilane(TIPTS). The loading capacity of Fe₃O₄-PVA@SH on Aspirin and the drug release kinetics of loaded drugs were studied. The obtained Fe₃O₄-PVA@SH exhibits excellent drug release properties in simulating the human body fluid environment (pH 7.2). Since magnetically targeting drug carriers are readily available and have excellent biocompatibility and the characteristics of drug release. This work’s development, preparing amphiphilic magnetically targeting drug carriers in drug delivery and other fields, has great significance.

Amphiphilic Aminoglycosides as Medicinal Agents

The conjugation of hydrophobic group(s) to the polycationic hydrophilic core of the antibiotic drugs aminoglycosides (AGs), targeting ribosomal RNA, has led to the development of amphiphilic aminoglycosides (AAGs). These drugs exhibit numerous biological effects, including good antibacterial effects against susceptible and multidrug-resistant bacteria due to the targeting of bacterial membranes. In the first part of this review, we summarize our work in identifying and developing broad-spectrum antibacterial AAGs that constitute a new class of antibiotic agents acting on bacterial membranes. The target-shift strongly improves antibiotic activity against bacterial strains that are resistant to the parent AG drugs and to antibiotic drugs of other classes, and renders the emergence of resistant Pseudomonas aeruginosa strains highly difficult. Structure–activity and structure–eukaryotic cytotoxicity relationships, specificity and barriers that need to be crossed in their development as antibacterial agents are delineated, with a focus on their targets in membranes, lipopolysaccharides (LPS) and cardiolipin (CL), and the corresponding mode of action against Gram-negative bacteria. At the end of the first part, we summarize the other recent advances in the field of antibacterial AAGs, mainly published since 2016, with an emphasis on the emerging AAGs which are made of an AG core conjugated to an adjuvant or an antibiotic drug of another class (antibiotic hybrids). In the second part, we briefly illustrate other biological and biochemical effects of AAGs, i.e., their antifungal activity, their use as delivery vehicles of nucleic acids, of short peptide (polyamide) nucleic acids (PNAs) and of drugs, as well as their ability to cleave DNA at abasic sites and to inhibit the functioning of connexin hemichannels. Finally, we discuss some aspects of structure–activity relationships in order to explain and improve the target selectivity of AAGs.

Suppressing the Shuttle Effect and Dendrite Growth in Lithium-Sulfur Batteries

Practical applications of lithium-sulfur batteries are simultaneously hindered by two serious problems occurring separately in both electrodes, namely, the shuttle effects of lithium polysulfides and the uncontrollable growth of lithium dendrites. Herein, to explore a facile integrated approach to tackle both problems as well as guarantee the efficient charge transfer, we used two-dimension hexagonal VS₂ flakes as the building blocks to assemble nanotowers on the separators, forming a symmetrical double-side-modified polypropylene separator without blocking the membrane pores. Benefiting from the "sulfiphilic" and "lithiophilic" properties, high interfacial electronic conductivity, and the unique hexagonal tower-form nanostructure, the D-HVS@PP separator not only guarantees the effective suppression of the lithium polysulfide shuttle and the rapid ion/electron transfer but also realizes uniform and stable lithium nucleation and growth during cycling. Hence, just at the expense of an 11% increase in the separator weight (0.14 mg cm^-2), the D-HVS@PP separator delivers an over 16 times higher initial areal capacity (8.3 mAh cm^-2) than a conventional PP separator (0.5 mAh cm^-2) under high sulfur-loading conditions (9.24 mg cm^-2). Even when used under a low electrolyte/sulfur ratio of 4 mL g^-1 and a practically relevant N/P ratio of 1.7, the D-HVS@PP separator still enabled stable cycling with a high cell-level gravimetric energy density. The potentials in broader applications (Li-S pouch battery and Li-LiFePO₄ battery) and the promising commercial prospect (large-scale production and recyclability) of the developed separator are also demonstrated.

Accelerated Reaction Rates within Self-Assembled Polymer Nanoreactors with Tunable Hydrophobic Microenvironments

Performing reactions in the presence of self-assembled hierarchical structures of amphiphilic macromolecules can accelerate reactions while using water as the bulk solvent due to the hydrophobic effect. We leveraged non-covalent interactions to self-assemble filled-polymer micelle nanoreactors (NR) incorporating gold nanoparticle catalysts into various amphiphilic polymer nanostructures with comparable hydrodynamic nanoreactor size and gold concentration in the nanoreactor dispersion. We systematically studied the effect of the hydrophobic co-precipitant on self-assembly and catalytic performance. We observed that co-precipitants that interact with gold are beneficial for improving incorporation efficiency of the gold nanoparticles into the nanocomposite nanoreactor during self-assembly but decrease catalytic performance. Hierarchical assemblies with co-precipitants that leverage noncovalent interactions could enhance catalytic performance. For the co-precipitants that do not interact strongly with gold, the catalytic performance was strongly affected by the hydrophobic microenvironment of the co-precipitant. Specifically, the apparent reaction rate per surface area using castor oil (CO) was over 8-fold greater than polystyrene (750 g/mol, PS 750); the turnover frequency was higher than previously reported self-assembled polymer systems. The increase in apparent catalytic performance could be attributed to differences in reactant solubility rather than differences in mass transfer or intrinsic kinetics; higher reactant solubility enhances apparent reaction rates. Full conversion of 4-nitrophenol was achieved within three minutes for at least 10 sequential reactions demonstrating that the nanoreactors could be used for multiple reactions.

Absorbent-Adsorbates: Large Amphiphilic Janus Microgels as Droplet Stabilizers

Microgel particles are cross-linked polymer networks that absorb certain liquids causing network expansion. The type of swelling fluid and extent of volume change depends on the polymer-liquid interaction and the network's cross-link density. These colloidal gels can be used to stabilize emulsion drops by adsorbing to the interface of two immiscible fluids. However, to enhance the adsorption abilities of these predominantly hydrophilic gel particles, some degree of hydrophobicity is needed. An amphiphilic Janus microgel with spatially distinct lipophilic and hydrophilic sides is desired. Here, we report the fabrication of poly(ethylene glycol) diacrylate/poly(propylene glycol) diacrylate Janus microgels (JM) using microfluidic drop making. The flow streams of the two separate and immiscible monomer solutions are brought into contact and intersected by a third immiscible fluid in a flow-focusing junction to form Janus droplets. The individual droplets are cross-linked via UV irradiation to form monodispersed microgel particles with opposing hydrophilic and hydrophobic 3D-networked polymer matrices. By combining two chemically different polymer gel networks, an amphiphilic emulsion stabilizer is formed that adsorbs to the oil-water interface while its faces absorb their respective water or hydrocarbon solvents. The resulting water-in-oil emulsions are stabilized and destabilized via a thermal-responsive hydrogel. Stimuli-responsive droplets are demonstrated by adding a short-chain oligo ethylene glycol acrylate molecule to the hydrogel formulation on the Janus microgel particle. Droplets stabilized by these particles experience a sudden increase in droplet diameter around 60 °C. This work with absorbent particles may prove useful for applications in bio catalysis, fuel production, and oil transportation.

Amphipathic Substrates Based on Crosslinker-Free Poly(ε-Caprolactone):Poly(2-Hydroxyethyl Methacrylate) Semi-Interpenetrated Networks Promote Serum Protein Adsorption

A simple procedure has been developed to synthesize uncrosslinked soluble poly(hydroxyethyl methacrylate) (PHEMA) gels, ready for use in a subsequent fabrication stage. The presence of 75 wt % methanol (MetOH) or dimethylformamide (DMF) impedes lateral hydroxyl–hydroxyl hydrogen bonds between PHEMA macromers to form during their solution polymerization at 60 °C, up to 24 h. These gels remain soluble when properly stored in closed containers under cold conditions and, when needed, yield by solvent evaporation spontaneous physically-crosslinked PHEMA adapted to the mould used. Moreover, this two-step procedure allows obtaining multicomponent systems where a stable and water-affine PHEMA network would be of interest. In particular, amphiphilic polycaprolactone (PCL):PHEMA semi-interpenetrated (sIPN) substrates have been developed, from quaternary metastable solutions in chloroform (CHCl₃):MetOH 3:1 wt. and PCL ranging from 50 to 90 wt % in the polymer fraction (thus determining the composition of the solution). The coexistence of these countered molecules, uniformly distributed at the nanoscale, has proven to enhance the number and interactions of serum protein adsorbed from the acellular medium as compared to the homopolymers, the sIPN containing 80 wt % PCL showing an outstanding development. In accordance to the quaternary diagram presented, this protocol can be adapted for the development of polymer substrates, coatings or scaffolds for biomedical applications, not relying upon phase separation, such as the electrospun mats here proposed herein (12 wt % polymer solutions were used for this purpose, with PCL ranging from 50% to 100% in the polymer fraction).

Synthesis and Self-Assembly of Poly(N-Vinylcaprolactam)-b-Poly(ε-Caprolactone) Block Copolymers via the Combination of RAFT/MADIX and Ring-Opening Polymerizations

Well-defined amphiphilic, biocompatible and partially biodegradable, thermo-responsive poly(N-vinylcaprolactam)-b-poly(ε-caprolactone) (PNVCL-b-PCL) block copolymers were synthesized by combining reversible addition-fragmentation chain transfer (RAFT) and ring-opening polymerizations (ROP). Poly(N-vinylcaprolactam) containing xanthate and hydroxyl end groups (X–PNVCL–OH) was first synthesized by RAFT/macromolecular design by the interchange of xanthates (RAFT/MADIX) polymerization of NVCL mediated by a chain transfer agent containing a hydroxyl function. The xanthate-end group was then removed from PNVCL by a radical-induced process. Finally, the hydroxyl end-capped PNVCL homopolymer was used as a macroinitiator in the ROP of ε-caprolactone (ε-CL) to obtain PNVCL-b-PCL block copolymers. These (co)polymers were characterized by Size Exclusion Chromatography (SEC), Fourier-Transform Infrared spectroscopy (FTIR), Proton Nuclear Magnetic Resonance spectroscopy (¹H NMR), UV–vis and Differential Scanning Calorimetry (DSC) measurements. The critical micelle concentration (CMC) of the block copolymers in aqueous solution measured by the fluorescence probe technique decreased with increasing the length of the hydrophobic block. However, dynamic light scattering (DLS) demonstrated that the size of the micelles increased with increasing the proportion of hydrophobic segments. The morphology observed by cryo-TEM demonstrated that the micelles have a pointed-oval-shape. UV–vis and DLS analyses showed that these block copolymers have a temperature-responsive behavior with a lower critical solution temperature (LCST) that could be tuned by varying the block copolymer composition.

Comparison between novel star-like redox-sensitive amphiphilic block copolymer and its linear counterpart copolymer as nanocarriers for doxorubicin

Linear and star-like redox-sensitive amphiphilic block copolymers have been studied as anticancer drug delivery systems. However, few reports directly compared the properties of those two structures especially when they are used as nanocarriers for antitumor drugs. To address this, a novel star-like copolymer and its linear counterpart were synthesized with a hydrophobic/redox-responsive/hydrophilic structure. The overall molecular weight of the star-shaped copolymer was nearly equal to that of the linear counterpart. The star-like micelles exhibit size of 90 nm, which was smaller than that of linear copolymers (151.6 nm) and critical micelle concentration of 1 mg/L, which was lower than that of the linear micelles (8.9 mg/L). The disassembly behaviors and the redox-sensitivity of the nanoparticles to reductive stimuli of glutathione was evaluated from the changes of the micellar size and morphology. Furthermore, doxorubicin was physically loaded into the hydrophobic part of the copolymers. The drug-loading capacities in the star-like and linear micelles were 15.94 and 7.53 wt%, respectively. Drug release studies carried out at two different glutathione concentrations. A cytotoxicity study of the micelles was performed by MTT assay. The prepared star copolymer showed no significant toxicity against HDF cells while enhanced cytotoxicity of the DOX-loaded micelles against MCF-7 cells was observed. Therefore, developing sucrose-PCL-SS-PEG copolymer reported in this paper as an effective reduction-responsive carrier with excellent properties and cell biocompatibility is promising for the efficient intracellular delivery of hydrophobic chemotherapeutic drugs. This work also indicates that modification of the nanocarrier structure is a potential strategy for optimizing drug delivery.

Membrane Environment Enables Ultrafast Isomerization of Amphiphilic Azobenzene

The non-covalent affinity of photoresponsive molecules to biotargets represents an attractive tool for achieving effective cell photo-stimulation. Here, an amphiphilic azobenzene that preferentially dwells within the plasma membrane is studied. In particular, its isomerization dynamics in different media is investigated. It is found that in molecular aggregates formed in water, the isomerization reaction is hindered, while radiative deactivation is favored. However, once protected by a lipid shell, the photochromic molecule reacquires its ultrafast photoisomerization capacity. This behavior is explained considering collective excited states that may form in aggregates, locking the conformational dynamics and redistributing the oscillator strength. By applying the pump probe technique in different media, an isomerization time in the order of 10 ps is identified and the deactivation in the aggregate in water is also characterized. Finally, it is demonstrated that the reversible modulation of membrane potential of HEK293 cells via illumination with visible light can be indeed related to the recovered trans→cis photoreaction in lipid membrane. These data fully account for the recently reported experiments in neurons, showing that the amphiphilic azobenzenes, once partitioned in the cell membrane, are effective light actuators for the modification of the electrical state of the membrane.

Amphiphilic additives in silicone oil tamponade and emulsification: an eye-on-a-chip study

AIMS

Recently, chemically modified silicone oil has been demonstrated as a reservoir for sustained release of intraocular drugs, many of which might be amphiphilic in nature. In this work, we study the effect of amphiphilic additives in silicone oil on emulsification under eye-like movements.

METHODS

Three silicone-oil-soluble surfactants, namely DC749, MQ1640 and FZ2233, were used as model amphiphilic additives. The change of viscosity was measured by a rheometer in the cone-and-plate geometry. The interfacial tension (IFT) between silicone oil and model aqueous phase was measured by pendant drop tensiometry. Emulsification of silicone oil was induced by simulated saccadic eye movements on a cell-coated eye-on-a-chip platform for 4 days. The number of emulsified silicone oil droplets observed in the aqueous phase was assessed daily by optical microscopy.

RESULTS

Significantly more emulsified droplets were formed in silicone oil with DC749 or MQ1640 (P < 0.05). However, such increase was not directly related to the change in IFT nor viscosity. Moreover, water droplets were also found in the silicone oil, but not in the control silicone oil without additive.

CONCLUSIONS

The amphiphilic substances in silicone oil promoted emulsification. Besides typical oil-in-water drops that normally affect the eye, water-in-oil drops were also formed. Before silicone oil could be considered as a vehicle for drug delivery, the nature of the drug and its possible effect on emulsification and therefore on the pharmacokinetics needs to be investigated. An additional concern is that water-in-oil droplets in the eye would affect the optical clarity of silicone oil and might cause visual symptoms.

Dewetting from Amphiphilic Minichannel Surfaces during Condensation

Condensation heat transfer can be altered significantly by changing the texture and material of a surface to promote droplet removal and therefore lower thermal resistance. These designs are often expensive and fragile, however, and are fabricated using micro- or nanoscale features that are not easily implemented in real-world systems. Here, we present a novel macromachined amphiphilic surface that promotes droplet removal and resists permanent flooding via a spontaneous dewetting transition. While much of the research in condensation involves condensing on surfaces that are fully or mostly hydrophobic, droplets on the surface presented here nucleate and grow inside the structure on a hydrophilic material. The absence of any coating between the liquid and the conductive surface has the benefits of both decreasing thermal resistance and enhancing nucleation density. When the liquid grows to a critical size inside the channel, its elongated shape becomes unstable and spontaneously dewets to form rounded droplets on the hydrophobic fin peaks. The removal of liquid from the channels promotes new growth on the bare hydrophilic material, while the emerged rounded droplets can more easily shed from the hydrophobic fins. The dewetting phenomenon is shown experimentally and characterized analytically such that a desired critical water slug length could be designed by changing geometric parameters of the surface structure. The macroscale machined surface is also more durable than typical nanofabricated surfaces and easier to manufacture, making the surface more applicable to use in real-world systems. Spontaneous condensate dewetting on the amphiphilic structure is expected to enhance the study of inhibiting flooding on condensing surfaces and provide new pathways for droplet shedding techniques without a requirement for nanothin hydrophobic coatings.