Tailoring Macromolecular Expression at Polymersome Surfaces

A series of amphiphilic ABC triblock copolymers are synthesized by atom transfer radical polymerization, wherein the ‘A’ and ‘C’ blocks are hydrophilic and the pH‐sensitive ‘B’ block can be switched from hydrophilic in acidic solution to hydrophobic at pH 7. Careful addition of base to the molecularly dissolved copolymer in acidic solution readily induces the self‐assembly of such triblock copolymers at around neutral pH to form pH‐sensitive polymersomes (a.k.a. vesicles) with asymmetric membranes. By systematic variation of the relative volume fractions of the ‘A’ and ‘C’ blocks, the chemical nature of the polymer chains expressed at the interior or exterior corona of the polymersomes can be selected. Treatment of primary human dermal fibroblast cells with these asymmetric polymersomes demonstrates the biological consequences of such spatial segregation, with both polymersome cytotoxicity and endocytosis rates being dictated by the nature of the polymersome surface chemistry. The pH‐sensitive nature of the polymersomes readily facilitates their dissociation after endocytosis due to the relatively low endosomal pH, which results in the rapid release of an encapsulated dye. Selective binding of anionic substrates such as DNA within the inner cationic polymersome volume, coupled with a biocompatible exterior, leads to potential gene delivery applications for these pH‐sensitive asymmetric nanovectors.     

Proton Transport from Dendritic Helical‐Pore‐Incorporated Polymersomes

The ability to add synthetic channels to polymersome (polymer vesicle) membranes could lead to novel membrane composites with unique selectivity and permeability. Proton transport through two different synthetic pores, self‐assembled from either a dendritic dipeptide, (6Nf‐3,4‐3,5)12G2‐CH₂‐Boc‐L‐Tyr‐L‐Ala‐OMe, or a dendritic ester, (R)‐4Bp‐3,4‐dm8G1‐COOMe, incorporated into polymersome membranes are studied. Polymersomes provide an excellent platform for studying such transport processes due to their robustness and mechanical and chemical stability compared to liposomes. It is found that the incorporated dendritic dipeptide and dendritic ester assemble into stable helical pores in the poly(ethylene oxide)‐polybutadiene (PEO‐PBD) polymersomes but not in the poly(2‐methyloxazoline)‐poly(dimethylsiloxane)‐poly(2‐methyl oxazoline) (PMOX‐PDMS‐PMOX) polymersomes. The incorporation is confirmed by circular dichroism (CD), changes in purely synthetic mechanical strength (e.g., areal expansion modulus) as assessed by micropipette aspiration, and cryo‐TEM. In addition to the structural analyses, a transport measurement shows the incorporated dendritic helical pores allow facile transport of protons across the polymersome membranes after up to one month of storage. This integration of synthetic porous channels with polymersome substrates could provide a valuable tool for studying active transport processes in a composite membrane. These composites will ultimately expand the family of biologically inspired porous‐membrane mimics.     

Siliceous Unilamellar Vesicles and Foams by Using Block‐Copolymer Cooperative Vesicle Templating

By employing commercial poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) block copolymers as templates in near‐neutral aqueous solutions in the absence of organic cosolvents, unilamellar siliceous vesicles and nanofoams with ultrahigh pore volumes (> 3 cm³ g^–1) are successfully synthesized. At controlled pH, a tubular micelle → unilamellar vesicle → nanofoam structural transformation is observed by increasing the reaction temperature. It is proposed that the siliceous vesicles are synthesized via a co‐operative block‐copolymer vesicle templating approach, while the siliceous nanofoams are obtained by the fusion of vesicles at increased ionic strength. Compared to literature methods to synthesize siliceous vesicles and foams, our method is convenient, cheap, and produces a high yield. Siliceous nanofoams synthesized by using our approach show superior bioimmobilization capacity over other porous materials for biomolecules with large molecular weight.     

Giant Chromatic Lipid/Polydiacetylene Vesicles for Detection and Visualization of Membrane Interactions

We present the construction of microscopic vesicular particles comprising phospholipids and polydiacetylene (PDA), a polymer with unique color and fluorescence properties. We show that the vesicle‐embedded PDA domains function as chromatic reporters of membrane events, undergoing dramatic colorimetric and fluorescence transformations induced by interactions with membrane‐active species. In particular, the micrometer sizes of the giant vesicles facilitate their utilization for visual inspection of membrane events by conventional microscopy techniques. The morphology, size, and chromatic properties of the vesicular aggregates depend upon the type of phospholipids and the molecular ratio between the phospholipids and diacetylene, indicating that the lipids and polymer form interdependent domains within the vesicles. The giant chromatic aggregates have been employed for detection and microscopic visualization of varied membrane processes, including lipid interactions of lipophilic drugs, binding of antimicrobial peptides, and membrane attachment by virus particles.     

Ultracytochemical demonstration of Ca2(+)-ATPase activity in the rat saphenous artery and its innervated nerve terminal

The localization of Ca2(+)-ATPase activity was ultracytochemically investigated in the rat saphenous artery and nerve terminals innervating the saphenous artery using a lead citrate method devised by Ando et al. (1981). Intense reaction products in the saphenous arterial endothelial cells were observed inside the caveolae and vesicles along the luminal and abluminal sides. In addition, Ca2(+)-ATPase activity was observed on the external side of the luminal, abluminal and lateral plasma membrane, and the outer membrane of mitochondria. In the smooth muscle cells, intense Ca2(+)-ATPase activity on the inside of caveolae and vesicles was observed, comparing in intensity with that on the plasma membrane of smooth muscle cells. In the nerve terminals innervating the saphenous artery, Ca2(+)-ATPase activity was demonstrated on the plasma membrane of the nerve terminal-Schwann cell interface, the axolemma of unmyelinated axons and the plasma membrane of Schwann cells. It is suggested from the above ultracytochemical results that Ca2(+)-ATPase activity plays an important role in the contraction and relaxation of the saphenous artery, and in the neurotransmitter release.     

In Situ Generated Gold Nanoparticle Hybrid Polymersomes for Water‐Soluble Chemotherapeutics: Inhibited Leakage and pH‐Responsive Intracellular Release

Drug leakage in blood circulation is generally a serious concern to polymersomes when loading water‐soluble chemotherapeutics. If packing density of polymersome membrane is strengthened, premature drug release will be inhibited. Therefore, synthesis of a series of amphiphilic polyphosphazenes (PNPs) with 2‐diethylaminoethyl 4‐aminobenzoate (DEAB) as hydrophobic side groups and amino‐terminal poly(ethylene glycol) (NH₂‐PEG₂₀₀₀) as hydrophilic chains is presented. By controlling the ratio of DEAB to NH₂‐PEG₂₀₀₀, the optimal PNP‐3 is screened to ensure polymersome formation and high loading of doxorubicin hydrochloride (DOX·HCl). In situ generation method is initially employed to introduce gold nanoparticles (AuNPs) into vesicles' lamella, which can homogeneously distribute among DEAB sides via coordination interaction and act as inorganic cross‐linkers to aggregate polymer chains. Drug leakage of resultant AuNP hybrid PNP‐3 polymersome (IAuPNP‐3) at pH 7.4 is effectively alleviated and the systemic circulation time of DOX·HCl in mice is obviously prolonged. Besides, pH‐responsive drug release, due to the protonation of tertiary amine in DEAB, contributes to fast intracellular action. Based on the cooperation of these functions, DOX·HCl‐loaded IAuPNP‐3 finally achieves the highest in vivo antitumor efficacy compared with free DOX·HCl, drug‐loaded PNP, or EAuPNP prepared by prepreparation AuNPs method.     

Nanowrinkled and Nanoporous Polyethylene Membranes Via Entanglement Arrangement Control

Crystalline homopolymers, including polyethylene (PE), which has the simplest architecture, form a nanometer‐sized combination of crystalline and amorphous components, but their arrangement control, similar to self‐assembled phase‐separation of block‐copolymers, is usually difficult. However, molecular entanglements trapped between crystalline and amorphous components of homopolymers coincide with the segmental linking points on the interfaces of the microphase separation for block copolymers. Nanowrinkled PE membranes are prepared with a network of 30 nm‐thick homogeneous lamellae using a novel entanglement control technique composed of biaxial melt‐drawing and melt‐shrinking procedures, which are limited for highly entangled ultrahigh molecular weight materials. Such a network arrangement of nanowrinkling lamellae spreading on membrane surface and also across the membrane thickness improves the mechanical properties of both tensile strength and tearing strength. Subsequent cold‐drawing causes delamination of the lamellar interfaces, leading to the resultant nanoporous morphology composed of passing‐through channels that are several tens of nanometers in diameter, without any solvent processing.     

Azobenzene Functionalized Organic Covalent Frameworks: Controlled Morphologies and Photo-Regulated Adsorption

Covalent organic frameworks (COFs) containing azobenzene building blocks carry great potential for use in intelligent storage, separation, chemical sensing, and catalysis due to their intriguing photo-responsiveness. However, azobenzene units are often exploited as the linkers to form the framework of COFs, thereby restricting their molecular motion and photoisomerization. Herein, a simple yet robust template-free solvothermal strategy is reported to yield azobenzene-dangled COFs (Azo-COFs) with their azobenzene moieties suspending within the pores. The crystallinity, specific surface area, and morphology of Azo-COFs can be conveniently tailored by changing the ratio of amine to aldehyde monomers. Notably, the Azo-COFs provide sufficient free space for the reversible trans-to-cis isomerization of the dangled azobenzene units inside the pores, thus reversibly regulating surface wettability of Azo-COFs. The adsorption capacity of Azo-COFs toward organic dye molecules is increased by 3.7-fold when irradiated with ultraviolet light, which can be ascribed to the intelligent closing/opening of molecular gates rendered by photoisomerization of azobenzene moieties. As such, the ability to photoregulate the adsorption of Azo-COFs highlights their significance in functioning as smart porous nanomaterials for applications in cargo release, molecular sieves, ion transport, energy conversion systems, and environmental remediation.     

Polymeric Giant Unilamellar Vesicles with Integrated DNA-Origami Nanopores: An Efficient Platform for Tuning Bioreaction Dynamics Through Controlled Molecular Diffusion

Giant unilamellar vesicles (GUVs) are microcompartments serving to confine reactions, allow signaling pathways, or design synthetic cells. Polymer GUVs are composed of copolymer membranes mimicking cell membranes, and present advantages over lipid-based GUVs, such as higher mechanical stability and chemical versatility. Such microcompartments are essential for understanding reactions/signaling occurring in cells, which are difficult to study by in vivo approaches due to the cell's complexity. However, the lack of control over their production, stability, and membrane diffusion properties is still limiting their use for bio-related applications. Here, polymer GUVs produced by microfluidics and permeabilized with DNA-origami nanopores (DoNs) that present a high level of control over these essential properties are introduced. After systematic optimization of conditions, DoN-GUVs reveal a narrow size distribution, allow for high encapsulation efficiencies, and are stable for weeks, protecting encapsulated biomolecules. The kinetics of diffusion of molecules through the GUV's membrane is tuned by insertion of DoNs with a controlled 3D- structure. DNA polymerase I, encapsulated as model for bioreactions, successfully produced DNA duplex strands with spatiotemporal control. DoN-GUVs loaded with active molecules open new avenues in bioreactions, from the detection of biomolecules, over the tuning of molecular transport rates, to the investigation of cellular processes/signaling.     

Stepwise Drug‐Release Behavior of Onion‐Like Vesicles Generated from Emulsification‐Induced Assembly of Semicrystalline Polymer Amphiphiles

Tailoring unique nanostructures of biocompatible and degradable polymers and the consequent elucidation of shape effects in drug delivery open tremendous opportunities not only to broaden their biomedical applications but also to identify new directions for the design of nanomedicine. Cellular organelles provide the basic structural and functional motif for the development of novel artificial nanoplatforms. Herein, aqueous onion‐like vesicles structurally mimicking multicompartmentalized cellular organelles by exhibiting exquisite control over the molecular assembly of poly(ethylene oxide)‐block‐poly(ε‐caprolactone) (PEO‐b‐PCL) semicrystalline amphiphiles are reported. Compared to in situ self‐assembly, emulsification‐induced assembly endows the resulting nanoaggregates of PEO‐b‐PCL with structural diversity such as helical ribbons and onion‐like vesicles through the molecular packing modification in the hydrophobic core with a reduction of inherent crystalline character of PCL. In particular, onion‐like vesicles composed of alternating walls and water channels are interpreted by nanometer‐scale 3D visualization via cryogenic‐electron tomo­graphy (cryo‐ET). Interestingly, the nature of the multi‐walled vesicles results in high drug‐loading capacity and stepwise drug release through hydrolytic cleavage of the PCL block. The crystalline arrangement of PCL at the molecular scale and the spatial organization of assembled structure at the nanoscale significantly affect the drug‐release behavior of PEO‐b‐PCL nanovehicles.     

Microscopic Morphology of Polyfluorene–Poly(ethylene oxide) Block Copolymers: Influence of the Block Ratio

In this paper, we describe the synthesis and characterization of poly(9,9′‐dioctylfluorene)–poly(ethylene oxide) (PF‐PEO) block copolymers with different block ratio and molecular architectures (diblock or triblock copolymers). Tapping‐mode atomic force microscopy is used to investigate the relationship between the molecular structure and the microscopic morphology of thin deposits. Copolymers with a low average volume ratio of PEO (f_EO from 0.1 to 0.3) exhibit a well‐defined organization into nanoribbons. A model of chain packing is proposed; these structures arise from the interplay of π–π interactions between conjugated PF segments and the interactions of PEO with the mica substrate surface. For copolymers with higher average volume ratio of PEO (f_EO > 0.4), the organized structures disappear and lead to untextured aggregates, probably because long‐range, regular π–π stacking of the segments can no longer take place. We also observe that the nature of the solvent from which deposits are grown and the substrate polarity have a strong impact on the microscopic morphology.     

Catanionic Surfactant Vesicles as a New Platform for Probing Glycan–Protein Interactions

Glycomics lags substantially behind proteomics and genomics in its ability to decipher and synthesize complex glycans. The slow progress in deciphering glycan interactions at a molecular level is in large part due to the absence of a functional system to express, on a large scale, carbohydrates of known structure, in the context of a biologically relevant assay system. Here, the characterization of glycan‐functionalized catanionic surfactant vesicles (CVs) as a platform for glycan synthesis is described, and it is demonstrated that the resulting glycan‐functionalized CVs can serve as a scaffold for the interrogation of protein‐glycan interactions. It is demonstrated that Neisseria gonorrhoeae lipooligosaccharide (LOS) glycosyltransferase LgtE, an enzyme that catalyzes the addition of galactose onto a terminal glucose found on LOS, can be used to biochemically modify LOS or glucose functionalized CVs. CVs are characterized by differential lectin binding using flow cytometry. LgtE activity is measured on whole cells and LOS functionalized vesicles and found to have approximately the same biochemical properties. It is further demonstrated that CVs can be inkjet printed. This paper presents proof‐of‐concept that glycan‐functionalized catanionic vesicles can be used to create a high‐specificity and high‐throughput glycan array that will allow for the investigation of a variety of protein–glycan interactions.     

Asymptotically Gaussian weight distribution and performance of multicomponent turbo block codes and product codes

It was suggested by Battail that a good long linear code should have a weight distribution close to that of random coding, rather than a large minimum distance, and a turbo code should be also designed using a random-like criterion. In this paper, we first show that the weight distribution of a high-rate linear block code is approximately Gaussian if the code rate is close enough to one, and then proceed to construct a low-rate linear block code with approximately Gaussian weight distribution by using the turbo-coding technique. We give a sufficient condition under which the weight distribution of multicomponent turbo block (MCTB) codes (multicomponent product (MCP) codes, respectively) can approach asymptotically that of random codes, and further develop two classes of MCTB codes (MCP codes) satisfying this condition. Simulation results show that MCTB codes (MCP codes) having asymptotically Gaussian weight distribution can asymptotically approach Shannon's capacity limit. MCTB codes based on single parity-check (SPC) codes have a far poorer minimum distance than MCP codes based on SPC codes, but we show by simulation that when the bit-error rate is in the important range of 10/sup -1/-10/sup -5/, these codes can still offer similar performance for the additive white Gaussian noise channel, as long as the code length of the SPC codes is not very short. These facts confirm in a more precise way Battail's inference about the "nonimportance" of the minimum distance for a long code.     

A Thermoresponsive Antimicrobial Wound Dressing Hydrogel Based on a Cationic Betaine Ester

This work reports a thermoresponsive multifunctional wound dressing hydrogel based on ABA triblock copolymers synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization. The inner B block consists of a positively‐charged hydrolysable betaine ester loaded with an antimicrobial drug as its counter ion and the B block is flanked by two outer A blocks of thermoresponsive poly (N‐isopropylacrylamide) (PNIPAM). A solution containing the triblock copolymers can be applied to wound sites and immediately turns into a physical gel at the body temperature. This wound dressing can reduce the risk of wound infection by releasing small‐molecular‐weight antimicrobial drug and facilitate the attachment of mammalian cells during tissue regeneration through its positive surface charge. The cationic betaine ester can then hydrolyze at the wound site to its zwitterionic form, which is known to be biocompatible and nonsticky. The thermoresponsive in situ gelation feature along with controlled drug release, enhanced tissue–hydrogel interactions as well as long‐term biocompatibility make this hydrogel a very promising material for antimicrobial wound dressing applications.     

Diffusion-based analysis of molecular interactions in microfluidic devices

The study of molecular interactions in biological fluids is important as a research tool to elucidate molecular and biological function, for discovering or designing molecules that have a desirable function, and for measuring or detecting analytes for clinical diagnostic purposes. Microfluidics is an emerging technology that has proven useful for studying and controlling molecular interactions with the potential advantages of reduced sample and reagent volumes, short reaction times, portable instrumentation, and high throughput. At microscale dimensions, diffusive transport of many biologically relevant molecules can cover large fractions of a fluid channel in a short time (seconds to minutes). We have exploited this feature to analyze molecular interactions based on changes in the diffusive transport of one of the reacting components. Here, we present a new assay configuration for studying molecular binding interactions and report new developments in the fabrication and use of hydrogels for diffusion-based analysis. We also overview system configurations and analysis techniques that have proven useful for studying molecular interactions of biological analytes and discuss their ability to operate using complex fluids such as blood.     

Fabrication of Microbeads with a Controllable Hollow Interior and Porous Wall Using a Capillary Fluidic Device

Poly(D ,L ‐lactide‐co‐glycolide) (PLGA) microbeads with a hollow interior and porous wall are prepared using a simple fluidic device fabricated with PVC tubes, glass capillaries, and a needle. Using the fluidic device with three flow channels, uniform water‐in‐oil‐in‐water (W‐O‐W) emulsions with a single inner water droplet can be achieved with controllable dimensions by varying the flow rate of each phase. The resultant W‐O‐W emulsions evolve into PLGA microbeads with a hollow interior and porous wall after the organic solvent in the middle oil phase evaporates. Two approaches are employed for developing a porous structure in the wall: emulsion templating and fast solvent evaporation. For emulsion templating, a homogenized, water‐in‐oil (W/O) emulsion is introduced as the middle phase instead of the pure oil phase. Low‐molecular‐weight fluorescein isothiocyanate (FITC) and high‐molecular‐weight fluorescein isothiocyanate–dextran conjugate (FITC–DEX) is added to the inner water phase to elucidate both the pore size and their interconnectivity in the wall of the microbeads. From optical fluorescence microscopy and scanning electron microscopy images, it is confirmed that the emulsion‐templated microbeads (W‐W/O‐W) have larger and better interconnected pores than the W‐O‐W microbeads. These microstructured microbeads can potentially be employed for cell encapsulation and tissue engineering, as well as protection of active agents.     

A Microfluidic Tool for Fine‐Tuning Motion of Soft Micromotors

Microfluidics is an ideal tool for the design of self‐assembled micromotors. It allows for easy change of solutions, catalysts, and flow rates, which affect shape, structure, and motion of the resulting micromotors. A microfluidic tool generating aqueous‐two‐phase‐separating droplets of UV‐polymerizable poly(ethylene glycol)diacrylate (PEGDA) and an inert phase, salt, or polysaccharide, is utilized to fabricate asymmetric microbeads. Different molecular weights and branching of polysaccharides are used to study the effect on shape, surface roughness, and motion of the particles. The molecular weight of the polysaccharide determines the roughness of the motors inner surface. Smooth openings are obtained by low molecular weight dextran, while high surface roughness is obtained with a high molecular weight branched polysaccharide. Since roughness plays an important role in bubble pinning, it influences both speed and trajectory. Increasing speeds are obtained with increasing roughness and trajectories ranging from linear, circular to tumble‐and‐run depending on the nature of bubble pinning. This microfluidic tool allows for fine‐tuning shape, structure, and motion by easy change of solutions, catalysts, and flow rates.     

Self-Assembled Facilitated Transport Membranes with Tunable Carrier Distribution for Ethylene/Ethane Separation

Facilitated transport membranes (FTMs) are a forward-looking technology and have triggered revolutions in many energy-intensive gas separations. However, the precise manipulation of carrier distribution within FTMs, as well as the visualization of membrane structure at the nanoscale, has never been reported. Herein, FTMs are constructed with tunable carrier distribution by a facile ion/molecule self-assembly of protic ionic liquid crystal salts (PILSs), polyol, and ethylene-transport carrier for highly efficient sub-angstrom scale ethylene/ethane (0.416nm/0.443nm) separation. The elaborate regulation of non-covalent interactions by optimizing the ion/molecule compositions within membrane confers the bi-continuous nanostructure of FTMs, resulting in the formation of successive carrier wires and enormous 3D interconnected ethylene transport pathways, which is verified and visualized by molecular dynamics simulations and synchronous small- and wide-angle X-ray scattering (SWAXS). The as-designed FTMs manifest simultaneously super-high selectivity, excellent ethylene permeance, and robust long-term stability, which exceeds previously reported ethylene/ethane separation membranes. This study clearly draws the first picture of carrier distribution within FTMs, and deep insight into membrane structure will shed light on the design of high-performance separation membranes for energy-intensive gas separations.     

Slowing DNA Transport Using Graphene–DNA Interactions

Slowing down DNA translocation speed in a nanopore is essential to ensuring reliable resolution of individual bases. Thin membrane materials enhance spatial resolution but simultaneously reduce the temporal resolution as the molecules translocate far too quickly. In this study, the effect of exposed graphene layers on the transport dynamics of both single (ssDNA) and double‐stranded DNA (dsDNA) through nanopores is examined. Nanopore devices with various combinations of graphene and Al₂O₃ dielectric layers in stacked membrane structures are fabricated. Slow translocations of ssDNA in nanopores drilled in membranes with layers of graphene are reported. The increased hydrophobic interactions between the ssDNA and the graphene layers could explain this phenomenon. Further confirmation of the hydrophobic origins of these interactions is obtained through reporting significantly faster translocations of dsDNA through these graphene layered membranes. Molecular dynamics simulations confirm the preferential interactions of DNA with the graphene layers as compared to the dielectric layer verifying the experimental findings. Based on our findings, we propose that the integration of multiple stacked graphene layers could slow down DNA enough to enable the identification of nucleobases.     

骨骼肌兴奋收缩偶联时肌膜下小泡的超微结构变化

目的：从毫秒级功能变化水平实时观察骨骼肌肌膜下小泡在收缩潜伏期内的时相-形态变化。方法：采用双红外线探测器-计算机控制的电刺激-超低温快速冷冻固定同步技术,对电刺激后的蟾蜍骨骼肌组织作快速冷冻固定,冷冻置换,微波浸透包埋和超薄切片,在透射电镜下观察该骨骼肌细胞在电刺激后0．0ms,4．6ms,24ms的超微结构变化。结果：未加刺激的骨骼肌细胞的肌膜下仅见少量小泡分布;施加刺激4．6ms后肌膜下出现大量小泡,并由3～8个小泡融合成聚合体;24ms后小泡急剧减少,仅残留少量小泡紧靠肌膜下。结论：骨骼肌兴奋．收缩偶联发生时,肌膜下出现大量小泡。