Construction of Triboelectric Series and Chirality Detection of Amino Acids Using Triboelectric Nanogenerator.

Triboelectrification necessitates a frictional interaction between two materials, and their contact electrification is characteristically based on the polarity variance in the triboelectric series. Utilizing this fundamental advantage of the triboelectric phenomenon, different materials can be identified according to their contact electrification capability. Herein, an in-depth analysis of the amino acids present in the stratum corneum of human skin is performed and these are quantified regarding triboelectric polarization. The principal focus of this study lies in analyzing and identifying the amino acids present in copious amounts in the stratum corneum to explain their positive behavior during the contact electrification process. Thus, an augmented triboelectric series of amino acids with quantified triboelectric charging polarity by scrutinizing the transfer charge, work function, and atomic percentage is presented. Furthermore, the chirality of aspartic acid as it is most susceptible to racemization with clear consequences on the human skin is detected. The study is expected to accelerate research exploiting triboelectrification and provide valuable information on the surface properties and biological activities of these important biomolecules.

Mechanochemical Reactivity of a 1,2,4-Triazoline-3,5-dione-Anthracene Diels-Alder Adduct.

Force-responsive molecules that produce fluorescent moieties under stress provide a means for stress-sensing and material damage assessment. In this work, we report a mechanophore based on Diels-Alder adduct TAD-An of 4,4'-(4,4'-diphenylmethylene)-bis-(1,2,4-triazoline-3,5-dione) and initiator-substituted anthracene that can undergo retro-Diels-Alder (rDA) reaction by pulsed ultrasonication and compressive activation in bulk materials. The influence of having C-N versus C-C bonds at the sites of bond scission is elucidated by comparing the relative mechanical strength of TAD-An to another Diels-Alder adduct MAL-An obtained from maleimide and anthracene. The susceptibility to undergo rDa reaction correlates well with bond energy, such that C-N bond containing TAD-An degrades faster C-C bond containing MAL-An because C-N bond is weaker than C-C bond. Specifically, the results from polymer degradation kinetics under pulsed ultrasonication shows that polymer containing TAD-An has a rate constant of 1.59×10-5  min-1 , while MAL-An (C-C bond) has a rate constant of 1.40×10-5  min-1 . Incorporation of TAD-An in a crosslinked polymer network demonstrates the feasibility to utilize TAD-An as an alternative force-responsive probe to visualize mechanical damage where fluorescence can be "turned-on" due to force-accelerated retro-Diels-Alder reaction.

Guanidinium-Functionalized Polymer Dielectrics for Triboelectric Bacterial Detection.

Development of rapid detection strategies that target potentially pathogenic bacteria has gained increasing attention due to the increasing awareness for better health and safety. In this study, we evaluate an intrinsically antimicrobial polymer, 2Gdm, which is a poly(norbornene)-based functional polymer featuring guanidinium groups as side chains, for bacterial detection by the means of triboelectric nanogenerators (TENGs) and triboelectric nanosensors (TENSs). Attachment of bacteria to the sensing layer is anticipated to alter the overall triboelectric properties of the underlying polymer layer. The positively charged guanidinium functional groups can interact with the negatively charged phospholipid bilayer of bacteria and lead to bacterial death, which can then be detected by optical microscopy, X-ray photoelectron microscopy, and more advanced self-powered sensing techniques such as TENGs and TENSs. The double bonds present along the poly(norbornene) backbone allow for thermally induced cross-linking to obtain X-2Gdm and thus rendering materials remain stable in water. By monitoring the change in voltage output after immersion in various concentrations of Gram-negative Escherichia coli (E. coli) and Gram-positive Streptococcus pneumoniae (S. pneumoniae), we have demonstrated the utility of X-2Gdm as a new polymer dielectric for autonomous bacterial detection. As the bacterial concentration increases, the amount of adsorbed bacteria also increases, resulting in a decrease in the surface potential of the X-2Gdm thin film; this reduction in surface potential can cause a decrease in the triboelectric output for both TENGs and TENSs, which serves as a key working mechanism for facile bacterial detection. TENG and TENS systems are capable of detecting E. coli and S. pneumoniae within a range of 4 × 105 to 4 × 108 CFU/mL with a limit of detection of 106 CFU/mL. This report highlights the promising prospects of employing TENGs and TENSs as innovative sensing technologies for rapid bacterial detection by leveraging the electrostatic interactions between bacterial cell membranes and cationic groups present on polymer surfaces.

Antifouling Properties of Amine-Oxide-Containing Zwitterionic Polymers.

Biofouling due to nonspecific proteins or cells on the material surfaces is a major challenge in a range of applications such as biosensors, medical devices, and implants. Even though poly(ethylene glycol) (PEG) has become the most widely used stealth material in medical and pharmaceutical products, the number of reported cases of PEG-triggered rare allergic responses continues to increase in the past decades. Herein, a new type of antifouling material poly(amine oxide) (PAO) has been evaluated as an alternative to overcome nonspecific foulant adsorption and impart comparable biocompatibility. Alkyl-substituted PAO containing diethyl, dibutyl, and dihexyl substituents are prepared, and their solution properties are studied. Photoreactive copolymers containing benzophenone as the photo-cross-linker are prepared by reversible addition-fragmentation chain-transfer polymerization and fully characterized by gel permeation chromatography and dynamic light scattering. Then, these water-soluble polymers are anchored onto a silicon wafer with the aid of UV irradiation. By evaluating the fouling resistance properties of these modified surfaces against various types of foulants, protein adsorption and bacterial attachment assays show that the cross-linked PAO-modified surface can efficiently inhibit biofouling. Furthermore, human blood cell adhesion experiments demonstrate that our PAO polymer could be used as a novel surface modifier for biomedical devices.

High-Performance Inverted Organic Solar Cells via the Incorporation of Thickness-Insensitive and Low-Temperature-Annealed Nonconjugated Polymers as Electron Transport Materials.

Developing new electron transport layers has been an effective way to fabricate high-performance bulk-heterojunction organic solar cells (OSCs). Resolving the longstanding problems associated with commonly used zinc oxide (ZnO), such as electron traps and light-induced device deterioration, however, is still a great challenge. In this study, glycerol diglycidyl ether (GDE) and 1,4-butanesultone (BS) are blended with polyethyleneimine (PEI) to produce cross-linkable PEI-based materials, PEI-GDE and PEI-GDE-BS, which can function as alternative electron transport layers to replace conventional ZnO cathode-modifying layers in inverted OSCs. PEI-GDE and PEI-GDE-BS are amendable to low-temperature annealing processes to produce cross-linked films. The inverted device structure of ITO/ETL/PM6:BTP-BO-4F:PC71BM/MoO3/Ag was used to evaluate the effects of incorporating PEI-GDE and PEI-GDE-BS as electron transport materials. Compared with ZnO-based devices, the PEI-GDE- and PEI-GDE-BS-based devices exhibit significant improvements in photovoltaic performances due to smoother surface roughness, higher charge collection and exciton dissociation efficiencies, higher electron mobilities, and stronger π-π interactions. In particular, a PEI-GDE-BS-based device shows an outstanding power conversion efficiency (PCE) of 17.55% with a VOC of 0.83 V, a JSC of 27.88 mA/cm2, and an FF of 75.96%, which offers great possibilities in the applications of flexible solar cells.

Surface Modification of Ultrafiltration Membranes with 1,4-Benzoquinone and Polyetheramines to Improve Fouling Resistance.

Membrane fouling remains a key challenge for membrane separations. Hydrophilic membrane surface modification can mitigate irreversible foulant deposition, thereby improving fouling resistance. We report new hydrophilic membrane coatings based on 1,4-benzoquinone and various commercially available polyetheramines. These coatings, prepared from 1,4-benzoquinone and Jeffamine EDR 148, poly(benzoquinone-Jeffamine EDR 148) (p(BQ-EDR 148)), were used to modify polysulfone (PS) ultrafiltration membranes. In fouling experiments using an oil/water emulsion, membranes exhibited comparable fouling resistance to that of polydopamine (pDA)-modified membranes. Based on contact angle measurements, p(BQ-EDR 148) and pDA-modified membranes have similar levels of hydrophilicity, and both exhibited higher threshold flux values than those of their unmodified analogues. Based on their similar threshold flux values, p(BQ-EDR 148)-modified (76 LMH) and pDA-modified membranes (74 LMH) should have similar fouling resistance. Moreover, the mean pore size of p(BQ-EDR 148)-modified membranes can be tuned, while keeping the pure water permeance constant, by changing the deposition time and molar ratio of benzoquinone to EDR 148 in the modification solution.

DoA Estimation for FMCW Radar by 3D-CNN.

A method of direction-of-arrival (DoA) estimation for FMCW (Frequency Modulated Continuous Wave) radar is presented. In addition to MUSIC, which is the popular high-resolution DoA estimation algorithm, deep learning has recently emerged as a very promising alternative. It is proposed in this paper to use a 3D convolutional neural network (CNN) for DoA estimation. The 3D-CNN extracts from the radar data cube spectrum features of the region of interest (RoI) centered on the potential positions of the targets, thereby capturing the spectrum phase shift information, which corresponds to DoA, along the antenna axis. Finally, the results of simulations and experiments are provided to demonstrate the superior performance, as well as the limitations, of the proposed 3D-CNN.

Enhanced polymer mechanical degradation through mechanochemically unveiled lactonization.

The mechanical degradation of polymers is typically limited to a single chain scission per triggering chain stretching event, and the loss of stress transfer that results from the scission limits the extent of degradation that can be achieved. Here, we report that the mechanically triggered ring-opening of a [4.2.0]bicyclooctene (BCOE) mechanophore sets up a delayed, force-free cascade lactonization that results in chain scission. Delayed chain scission allows many eventual scission events to be initiated within a single polymer chain. Ultrasonication of a 120 kDa BCOE copolymer mechanically remodels the polymer backbone, and subsequent lactonization slowly (~days) degrades the molecular weight to 4.4 kDa, > 10× smaller than control polymers in which lactonization is blocked. The force-coupled kinetics of ring-opening are probed by single molecule force spectroscopy, and mechanical degradation in the bulk is demonstrated. Delayed scission offers a strategy to enhanced mechanical degradation and programmed obsolescence in structural polymeric materials.

Rapid Prototyping of an Open-Surface Microfluidic Platform Using Wettability-Patterned Surfaces Prepared by an Atmospheric-Pressure Plasma Jet.

Open-surface microfluidics is promising in terms of enabling economical and rapid biochemical analysis for addressing challenges associated with medical diagnosis and food safety. To this end, we present a simple and economical approach to develop an open-surface microfluidic platform suitable for facile liquid transport and mixing. Customizable patterns with tailored wettability are deposited using a plasma-assisted deposition technique under atmospheric pressure. The flow of the dispensed liquid is driven by gravity, and the tilting angle of the device determines the extent of mixing. First, a hexamethyldisiloxane film was deposited to create hydrophobic patterns on glass, and then, hydrophilic acrylic acid was deposited by a patterned cardboard mask to construct a channel suitable for forming channels to transport aqueous liquids without the need of an external energy input; the liquid can be confined to designated pathways. Several designs including Y-junctions, serpentine-shaped patterns, splitting channels, and concentration gradient generation patterns are presented. The proposed method can spatially pattern a surface with a hydrophobic/hydrophilic area, which can function as a microfluidic channel, and the surface can be applied in microfluidic devices with other types of substrates.

Single-Junction Organic Solar Cell Containing a Fluorinated Heptacyclic Carbazole-Based Ladder-Type Acceptor Affords over 13% Efficiency with Solution-Processed Cross-Linkable Fullerene as an Interfacial Layer.

In this article, a fluorinated heptacyclic dithienocyclopentacarbazole (DTC)-based non-fullerene acceptor (NFA), DTC(4Ph)-4FIC, is synthesized and blended with J71, PBDB-T, and PBDB-TF, featuring complementary absorption and well-matched energy levels. The DTC(4Ph)-4FIC neat film exhibits face-on preference, whereas the nonfluorinated counterpart, DTC(4Ph)-IC, exhibits edge-on preference; this unique feature owing to fluorination in DTC-based NFAs is observed for the first time. More importantly, DTC(4Ph)-4FIC exhibits improved power conversion efficiencies (PCEs) of 10.92 and 10.41% in J71- and PBDB-T-containing devices, while the devices that employed DTC(4Ph)-IC afford PCEs of 7.76 and 9.48%, respectively. Because PBDB-TF is known to exhibit lower energy levels than J71 and PBDB-T, the corresponding device affords a VOC of 0.95 V, a JSC of 18.29 mA cm-2, a FF of 75.70%, and a PCE of 13.15%, which is 20 and 26% higher than J71- and PBDB-T-containing devices. Furthermore, the inverted device containing the PBDB-TF:DTC(4Ph)-4FIC blend is fabricated using cross-linkable fullerene (C-PCBSD) as the cathode interlayer, affording a decent PCE of 13.36%, with a VOC of 0.94 V, a JSC of 20.20 mA cm-2, and a FF of 70.42%.

Porphyrin-Containing Polymer as a Superior Blue Light-Absorbing Additive To Afford High- Jsc Ternary Solar Cells.

Integrating an additional component featuring complementary light absorption into binary polymer solar cells is a superior tactic to ameliorate solar cell efficiency and stability. An appropriate additive not only extends the absorption range but may also facilitate charge separation and transport processes. In this work, we elucidate the effects of incorporating a porphyrin-containing conjugated polymer (PPor-1), which displays absorption in 350-500 nm, into binary PTB7-Th:4TIC and PTB7-Th:ITIC blends, affording devices with an average power conversion efficiency approaching 9%. We successfully demonstrate that PPor-1 can be incorporated as an additive to impart improved Jsc (up to 19.1 mA cm-2).

Regiochemical Effects on Mechanophore Activation in Bulk Materials.

Mechanochromic force probes, including spiropyran derivatives, have proven to be useful in visualizing the stress/strain distribution and fracture behavior in polymeric materials. Here, we report the macroscopic response of silicone elastomers including cross-links made up of three spiropyran (SP) regioisomers. The SP derivatives SP( o), SP( m), and SP( p) are connected to the network through an identical attachment point on the indoline fragment and regioisomeric attachments ortho, meta, and para to the spirocyclic C-O bond on the benzaldehyde fragment, respectively. The relative colorimetric response of these regioisomers under quasi-static uniaxial tensile load is SP( o) > SP( m) > SP( p), consistent with the expected mechanical sensitivity of the regioisomers obtained from molecular modeling. The extrapolated strain onset for detectable activation of all three regioisomers, however, is indistinguishable and occurs at ∼90% uniaxial strain. Finally, the ratiometric response of the three isomers is constant across the strains investigated (90-135% uniaxial strain), in contrast to expectations based on simulations of strained intact polymer networks.

Cross-linked Triarylamine-Based Hole-Transporting Layer for Solution-Processed PEDOT:PSS-Free Inverted Perovskite Solar Cells.

The device performance of inverted organic metallohalide perovskite solar cells (OMPSCs) is optimized via tailoring the electrode surfaces with electron- and hole-transporting materials. This work demonstrates the fabrication of PEDOT:PSS-free OMPSCs using a hole-transporting composite material consisting of bilayered vanadium oxide (VO x) and a thermally cross-linked triarylamine-based material X-DVTPD, which contributes to higher Voc and Jsc values. The hydrophobicity of X-DVTPD resulted in the formation of large perovskite crystals and enhanced the stability of OMPSCs. Integration of ionic fullerene derivative, fulleropyrrolidinium iodide, in OMPSCs as a hole-blocking interfacial layer at the interface with Ag proves effective to further boost the device efficiency to 18.08%.

Functional droplets that recognize, collect, and transport debris on surfaces.

We describe polymer-stabilized droplets capable of recognizing and picking up nanoparticles from substrates in experiments designed for transporting hydroxyapatite nanoparticles that represent the principal elemental composition of bone. Our experiments, which are inspired by cells that carry out materials transport in vivo, used oil-in-water droplets that traverse a nanoparticle-coated substrate driven by an imposed fluid flow. Nanoparticle capture is realized by interaction of the particles with chemical functionality embedded within the polymeric stabilizing layer on the droplets. Nanoparticle uptake efficiency is controlled by solution conditions and the extent of functionality available for contact with the nanoparticles. Moreover, in an elementary demonstration of nanoparticle transportation, particles retrieved initially from the substrate were later deposited "downstream," illustrating a pickup and drop-off technique that represents a first step toward mimicking point-to-point transportation events conducted in living systems.

Underwater Superoleophobic Surfaces Prepared from Polymer Zwitterion/Dopamine Composite Coatings.

Hydration is central to mitigating surface fouling by oil and microorganisms. Immobilization of hydrophilic polymers on surfaces promotes retention of water and a reduction of direct interactions with potential foulants. While conventional surface modification techniques are surface-specific, mussel-inspired adhesives based on dopamine effectively coat many types of surfaces and thus hold potential as a universal solution to surface modification. Here, we describe a facile, one-step surface modification strategy that affords hydrophilic, and underwater superoleophobic, coatings by the simultaneous deposition of polydopamine (PDA) with poly(methacryloyloxyethyl phosphorylcholine) (polyMPC). The resultant composite coating features enhanced hydrophilicity (i.e., water contact angle of ~10° in air) and antifouling performance relative to PDA coatings. PolyMPC affords control over coating thickness and surface roughness, and results in a nearly 10 fold reduction in Escherichia coli adhesion relative to unmodified glass. The substrate-independent nature of PDA coatings further promotes facile surface modification without tedious surface pretreatment, and offers a robust template for codepositing polyMPC to enhance biocompatibility, hydrophilicity and fouling resistance.

Antifouling Electrospun Nanofiber Mats Functionalized with Polymer Zwitterions.

In this study, we exploit the excellent fouling resistance of polymer zwitterions and present electrospun nanofiber mats surface functionalized with poly(2-methacryloyloxyethyl phosphorylcholine) (polyMPC). This zwitterionic polymer coating maximizes the accessibility of the zwitterion to effectively limit biofouling on nanofiber membranes. Two facile, scalable methods yielded a coating on cellulose nanofibers: (i) a two-step sequential deposition featuring dopamine polymerization followed by the physioadsorption of polyMPC, and (ii) a one-step codeposition of polydopamine (PDA) with polyMPC. While the sequential and codeposited nanofiber mat assemblies have an equivalent average fiber diameter, hydrophilic contact angle, surface chemistry, and stability, the topography of nanofibers prepared by codeposition were smoother. Protein and microbial antifouling performance of the zwitterion modified nanofiber mats along with two controls, cellulose (unmodified) and PDA coated nanofiber mats were evaluated by dynamic protein fouling and prolonged bacterial exposure. Following 21 days of exposure to bovine serum albumin, the sequential nanofiber mats significantly resisted protein fouling, as indicated by their 95% flux recovery ratio in a water flux experiment, a 300% improvement over the cellulose nanofiber mats. When challenged with two model microbes Escherichia coli and Staphylococcus aureus for 24 h, both zwitterion modifications demonstrated superior fouling resistance by statistically reducing microbial attachment over the two controls. This study demonstrates that, by decorating the surfaces of chemically and mechanically robust cellulose nanofiber mats with polyMPC, we can generate high performance, free-standing nanofiber mats that hold potential in applications where antifouling materials are imperative, such as tissue engineering scaffolds and water purification technologies.

Recombinant OmpA protein fragments mediate interleukin-17 regulation to prevent Escherichia coli meningitis.

BACKGROUND: Neonates are at a higher risk for bacterial meningitis than children of other age groups. Although the mortality rates have decreased over the past few decades, neonatal meningitis is still a severe disease with high morbidity. For bacterial meningitis, antibiotic therapy is the primary choice for management. However, neurologic complications often cannot be averted; ∼40% of survivors exhibit neurological sequelae. Escherichia coli infection is the common cause of neonatal meningitis. Previously, we have demonstrated that the recombinant loop 1-3, loop 2-3, and loop 2-4 fragments of OmpA protein can protect mice from death after intracerebral E. coli infection. In this study, the protective effects of the recombinant OmpA protein fragments in E. coli intracerebral infections were investigated. METHODS: The effects of E. coli intracerebral infection on cytokine and chemokine expression were determined. We also used various recombinant fragments of the OmpA protein to investigate the effects of these recombinant OmpA protein fragments on cytokine and chemokine expression. RESULTS: In this study, we demonstrated that the expression of interleukin-17 and other cytokines, chemokines, inducible nitric oxide synthase, and cyclooxygenase-2 are involved in the inflammatory processes of intracerebral E. coli infection. We also demonstrated that specific recombinant OmpA protein fragments (L1-3, L2-3, L2-4, and L3) can regulate cytokine, chemokine, nitric oxide synthase, and cyclooxygenase-2 expression and, subsequently, protect mice from death caused by intracerebral infection of E. coli. CONCLUSION: This finding indicates the potential for developing a new therapeutic approach to improve the prognosis of bacterial meningitis.

Photopatternable Biodegradable Aliphatic Polyester with Pendent Benzophenone Groups.

Highly efficient photo-cross-linking reactions enable numerous applications in biomaterials. Here, a photopatternable biodegradable aliphatic polyester with benzophenone pendent groups was synthesized by copper-catalyzed alkyne-azide cycloaddition, affording polyesters that undergo UV-induced cross-linking to yield photopatterned films. Using this material, a self-folding multilayer structure containing polyester/hydrogel bilayer hinges was fabricated. Upon swelling of the hydrogel layer, the construct folds into a triangular tube, which subsequently unfolds due to lipase-catalyzed degradation of the polyester layer. The ability to precisely design such degradation-induced structural changes offers potential for biomaterials and medical applications, such as evolving and responsive 2D and 3D tissue engineering scaffolds.

Synthesis, characterization and catalytic activity of magnesium and zinc aminophenoxide complexes: catalysts for ring-opening polymerization of L-lactide.

A series of novel magnesium and zinc aminophenoxide complexes were successfully synthesized and one zinc complex was characterized by X-ray crystallography. They were also investigated as initiators for the ring opening polymerization of L-lactide. The complexes are effective in forming polylactides with good conversions. The nature and steric bulk of the ligands coordinated to the central metal ions enormously influenced the polymer properties. Among all the complexes, the zinc aminophenoxide complexes as initiators produced polymers with good molecular weight control and relatively narrow PDIs.

Tuning the magnetic resonance imaging properties of positive contrast agent nanoparticles by surface modification with RAFT polymers.

A novel surface modification technique was employed to produce a polymer modified positive contrast agent nanoparticle through attachment of well-defined homopolymers synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. A range of RAFT homopolymers including poly[N-(2-hydroxypropyl)methacrylamide], poly(N-isopropylacrylamide), polystyrene, poly(2-(dimethylamino)ethyl acrylate), poly(((poly)ethylene glycol) methyl ether acrylate), and poly(acrylic acid) were synthesized and subsequently used to modify the surface of gadolinium (Gd) metal-organic framework (MOF) nanoparticles. Employment of a trithiocarbonate RAFT agent allowed for reduction of the polymer end groups under basic conditions to thiolates, providing a means of homopolymer attachment through vacant orbitals on the Gd3+ ions at the surface of the Gd MOF nanoparticles. Magnetic resonance imaging (MRI) confirmed the relaxivity rates of these novel polymer modified structures were easily tuned by changes in the molecular weight and chemical structures of the polymers. When a hydrophilic polymer was used for modification of the Gd MOF nanoparticles, an increase in molecular weight of the polymer provided a respective increase in the longitudinal relaxivity. These relaxivity values were significantly higher than both the unmodified Gd MOF nanoparticles and the clinically employed contrast agents, Magnevist and Multihance, which confirmed the construct's ability to be utilized as a positive contrast nanoparticle agent in MRI. Further characterization confirmed that increased hydrophobicity of the polymer coating on the Gd MOF nanoparticles yielded minimal changes in the longitudinal relaxivity properties but large increases in the transverse relaxivity properties in the MRI.