Evidence of ratchet effect in nanowires of a conducting polymer

Ratchet effect, observed in many systems starting from living organism to artificially designed device, is a manifestation of motion in asymmetric potential. Here we report results of a conductivity study of Polypyrrole nanowires, which have been prepared by a simple method to generate a variation of doping concentration along the length. This variation gives rise to an asymmetric potential profile that hinders the symmetry of the hopping process of charges and hence the value of measured resistance of these nanowires become sensitive to the direction of current flow. The asymmetry in resistance was found to increase with decreasing nanowire diameter and increasing temperature. The observed phenomena could be explained with the assumption that the spatial extension of localized state involved in hopping process reduces as the doping concentration reduces along the length of the nanowires.Comment: Revtex, two column, 4 pages, 10 figure

Mucin-Inspired Thermoresponsive Synthetic Hydrogels Induce Stasis in Human Pluripotent Stem Cells and Human Embryos.

Human pluripotent stem cells (hPSCs; both embryonic and induced pluripotent) rapidly proliferate in adherent culture to maintain their undifferentiated state. However, for mammals exhibiting delayed gestation (diapause), mucin-coated embryos can remain dormant for days or months in utero, with their constituent PSCs remaining pluripotent under these conditions. Here we report cellular stasis for both hPSC colonies and preimplantation embryos immersed in a wholly synthetic thermoresponsive gel comprising poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) [PGMA55-PHPMA135] diblock copolymer worms. This hydroxyl-rich mucin-mimicking nonadherent 3D gel maintained PSC viability and pluripotency in the quiescent G0 state without passaging for at least 14 days. Similarly, gel-coated human embryos remain in a state of suspended animation (diapause) for up to 8 days. The discovery of a cryptic cell arrest mechanism for both hPSCs and embryos suggests an important connection between the cellular mechanisms that evoke embryonic diapause and pluripotency. Moreover, such synthetic worm gels offer considerable utility for the short-term (weeks) storage of either pluripotent stem cells or human embryos without cryopreservation

Tetrastichus howardi (Olliff) (Hymenoptera: Eulophidae), a hyperparasitoid of tachinid natural enemies of elicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) in India

Tetrastichus howardi was identified as a hyperparasitoid of the tachinids Goniophthalmus halli and Senometopia illota, both parasitoids of Helicoverpa armigera pupae, in pigeon pea fields in southern India. Fifty-nine percent of G. halli and S. illota pupae were parasitized by T. howardi, resulting in a hyperparasitism rate of 1.9%. Unlike previous studies, T. howardi was not recorded as a primary parasitoid of H. armigera pupae. Rather than behaving as a pupal guild parasitoid, the data suggest that T. howardi oviposit in the larval stage of tachinid parasitoids while they are developing inside H. armigera pupae. The fact that T. howardi was not a primary parasitoid of H. armigera pupae suggests that this species is able to distinguish between parasitised and unparasitized H. armigera pupae

A survey of insecticide resistance in Helicoverpa armigera in the Indian subcontinent

Helicoverpa armigera (Hübner) larvae were collected from field crops and wild hosts in India, Nepal and Pakistan from 1991 to 1995, and ninety eight laboratory cultures established. Cypermethrin, fenvalerate, endosulfan, quinalphos, monocrotophos and methomyl insecticides were topically applied to 30–40 mg, first laboratory generation larvae and resistance determined from log dose probit bioassays. Significant levels of cypermethrin and fenvalerate resistance were found in all field strains, demonstrating that resistance to at least some pyrethroids is now ubiquitous in H. armigera populations in the Indian subcontinent; cypermethrin and fenvalerate resistance levels ranged from 5– to 6500–fold and 16– to 3200–fold respectively. Pyrethroid resistance levels were highest in the intensive cotton and pulse growing regions of central and southern India where excessive application of insecticide is common. In all field strains assayed, pre-treatment with the metabolic synergist piperonyl butoxide (pbo), resulted in significant suppression of pyrethroid resistance. However, in nearly all cases, full suppression of resistance was not achieved. This residual non-pbo-suppressible resistance was most likely due to a nerve-insensitivity resistance mechanism. Pbo-insensitive resistance was highest in regions of India where insecticides were frequently applied to cotton and legume crops. In some regions where insecticides were heavily overused, a second high order nerve-insensitivity mechanism (possibly a Super -Kdr type mechanism), may have been present. Incipient endosulfan resistance (1–28-fold), was present throughout India, Nepal and Pakistan. Low to moderate levels of resistance (2–59–fold), were reported to the phosphorothionate group organophosphate, quinalphos, in India and Pakistan, but there was no evidence of significant resistance (0.4–3–fold), to the phosphate group organophosphate, monocrotophos, under our bioassay conditions between 1993 and 1994. H. armigera strains collected in Nepal in 1993 and 1994 were susceptible to quinalphos, but by 1995, 4–5–fold resistance was detected. It is probable that much of the resistance to pyrethroid, organophosphate and carbamate insecticides in the Indian subcontinent can be attributed to an inherited or inducible mixed function oxidase complex. Non-pbo-suppressible resistance becomes significant in regions and periods in the season when insecticide selection pressure on resistant H. armigera larvae on cotton and legume crops is very high

Spin-echo small-angle neutron scattering (SESANS) studies of diblock copolymer nanoparticles

Poly(glycerol monomethacrylate)–poly(benzyl methacrylate) (PGMA–PBzMA) diblock copolymer nanoparticles were synthesized via polymerization-induced self-assembly (PISA) using reversible addition–fragmentation chain-transfer (RAFT) aqueous emulsion polymerization in D2O. Such PISA syntheses produce sterically-stabilized nanoparticles in situ and can be performed at relatively high copolymer concentrations (up to 50 wt%). This PGMA–PBzMA formulation is known to form only spherical nanoparticles in water using aqueous emulsion polymerization (Macromolecules, 2014, 47, 5613–5623), which makes it an ideal model system for exploring new characterization methods. The polymer micelles were characterized using small-angle X-ray scattering (SAXS) and a recently developed form of neutron scattering, spin-echo small-angle neutron scattering (SESANS). As far as we are aware, this is the first report of a study of polymer micelles by SESANS, and the data agree well with reciprocal-space scattering. Using this technique enables characterization of the concentrated, as synthesized dispersions directly without dilution, and this will provide a method to study self-assembled polymer systems that have concentration dependent morphologies, while still maintaining the advantages of scattering techniques

Ptychographic X-ray tomography reveals additive zoning in nanocomposite single crystals

Single crystals containing nanoparticles represent a unique class of nanocomposites whose properties are defined by both their compositions and the structural organization of the dispersed phase in the crystalline host. Yet, there is still a poor understanding of the relationship between the synthesis conditions and the structures of these materials. Here ptychographic X-ray computed tomography is used to visualize the three-dimensional structures of two nanocomposite crystals – single crystals of calcite occluding diblock copolymer worms and vesicles. This provides unique information about the distribution of the copolymer nano-objects within entire, micron-sized crystals with nanometer spatial resolution and reveals how occlusion is governed by factors including the supersaturation and calcium concentration. Both nanocomposite crystals are seen to exhibit zoning effects that are governed by the solution composition and interactions of the additives with specific steps on the crystal surface. Additionally, the size and shape of the occluded vesicles varies according to their location within the crystal, and therefore the solution composition at the time of occlusion. This work contributes to our understanding of the factors that govern nanoparticle occlusion within crystalline materials, where this will ultimately inform the design of next generation nanocomposite materials with specific structure/property relationships

Impact of Sorghum on Natural Parasitism of helicoverpa armigera (hubner) by Trichogramma Chilonis IIhii in Cotton in Southern India,

Field trials were condu cted on three cotton hybrids (MECH 1, MECH 12, and RCH 2) grown alone, and with a sorghum hybrid (CSH as a neighbouring crop at two 1) villages, RavulapaJly and Sankeypally, in Ranga Reddy district. Cotton hybrids grown neighbouring to sorghum had significantly higher levels of egg parasitism by TricllOgraJrlma chilonis than in a monocrop. The enhanced level of parasitis m was due to a temporal shift in the T. chilonis population from sorghum to cotton during the cropping season. Paras it ism on sorghum increased slowly in relation to host egg density at both the'village sites and reached a peak of 70% and 60% by mid-September at Ravulapally and S a nkey pally respectively. The mean clutch size on sorghum was 2.06, w i th a maximum of 5 parasitoids emerged per egg. Parasitism of Helicoverpa eggs on cotton by T. chilollis r eac hed a maximum of 68% in mid-October annigera as a neighbouring crop to sorghum and 45% as a 1110nocrop. The mean when grown clutch size on cotton was 2.24, with a maximum of 5 parasitoids emerged per egg. Among the three cotton hybrids tested, parasiti9m was significantly higher on MECH 12 e i t h er grown alone or neighbouring to sorghum.The results are discllssed in terms of the dyn a mi c s of T. chi/ollis buildup on sorghum ancl its subsequent migration to cotton management strategy to suppress the population carryover of H. annigera on as a cotlon

Aqueous one-pot synthesis of epoxy-functional diblock copolymer worms from a single monomer: new anisotropic scaffolds for potential charge storage applications

Nitroxide-functional polymers have garnered considerable interest in recent years and appear to hold promise for energy storage applications. However, their synthesis can be both expensive and time-consuming. Here, we propose a highly convenient method for the preparation of TEMPO-functional diblock copolymer nanoparticles directly in water. Epoxy-functional diblock copolymer worms are synthesized from a single monomer, glycidyl methacrylate (GlyMA), using a three-step, one-pot protocol in aqueous solution via polymerization-induced self-assembly (PISA). First, an initial aqueous emulsion of GlyMA was heated at 85 °C for 9 h to afford an aqueous solution of glycerol monomethacrylate (GMA). Then reversible addition-fragmentation chain transfer (RAFT) polymerization of GMA was conducted in aqueous solution using a dicarboxylic acid-based RAFT agent to produce a water-soluble PGMA homopolymer. Finally, chain extension of this pre-cursor block via RAFT aqueous emulsion polymerization of GlyMA at 50 °C produced amphiphilic diblock copolymer chains that self-assembled in situ to form a 15% w/w aqueous dispersion of diblock copolymer worms. These worms can be derivatized directly using 4-amino-TEMPO in aqueous solution, affording novel crosslinked anisotropic nanoparticles that contain a relatively high density of stable nitroxide radicals for potential charge storage applications</p

ABC Triblock Copolymer Worms: Synthesis, Characterization, and Evaluation as Pickering Emulsifiers for Millimeter-Sized Droplets

Polymerization-induced self-assembly (PISA) is used to prepare linear poly(glycerol monomethacrylate)–poly(2-hydroxypropyl methacrylate)–poly(benzyl methacrylate) [PGMA–PHPMA–PBzMA] triblock copolymer nano-objects in the form of a concentrated aqueous dispersion via a three-step synthesis based on reversible addition–fragmentation chain transfer (RAFT) polymerization. First, GMA is polymerized via RAFT solution polymerization in ethanol, then HPMA is polymerized via RAFT aqueous solution polymerization, and finally BzMA is polymerized via “seeded” RAFT aqueous emulsion polymerization. For certain block compositions, highly anisotropic worm-like particles are obtained, which are characterized by small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The design rules for accessing higher order morphologies (i.e., worms or vesicles) are briefly explored. Surprisingly, vesicular morphologies cannot be accessed by targeting longer PBzMA blocks—instead, only spherical nanoparticles are formed. SAXS is used to rationalize these counterintuitive observations, which are best explained by considering subtle changes in the relative enthalpic incompatibilities between the three blocks during the growth of the PBzMA block. Finally, the PGMA–PHPMA–PBzMA worms are evaluated as Pickering emulsifiers for the stabilization of oil-in-water emulsions. Millimeter-sized oil droplets can be obtained using low-shear homogenization (hand-shaking) in the presence of 20 vol % n-dodecane. In contrast, control experiments performed using PGMA–PHPMA diblock copolymer worms indicate that these more delicate nanostructures do not survive even these mild conditions

Controlling Surface Topology and Functionality of Electrospun Fibers using Amphiphilic Block Copolymers to Direct Mesenchymal Progenitor Cell Adhesion

Surface patterning in three dimensions is of great importance in biomaterials design for controlling cell behavior. A facile one-step functionalization of biodegradable PDLLA fibers using amphiphilic diblock copolymers is demonstrated here, to systematically vary the fiber surface composition. The copolymers comprise a hydrophilic poly[oligo(ethylene glycol) methacrylate] (POEGMA), poly[(2-methacryloyloxy)ethyl phosphorylcholine] (PMPC) or poly[2-(dimethylamino)ethyl methacrylate)] (PDMAEMA) block and a hydrophobic poly(L-lactide) (PLA) block. The block copolymer modified fibers have increased surface hydrophilicity compared to PDLLA fibers. Mixtures of PLA-PMPC and PLA-POEGMA copolymers are utilized to exploit micro-phase separation of the incompatible hydrophilic PMPC and POEGMA blocks at the fiber surface. Conjugation of an RGD cell-adhesive peptide to one hydrophilic block (POEGMA) using thiol-ene chemistry produces fibers with domains of cell-adhesive (POEGMA) and cell-inert (PMPC) sites, mimicking the adhesive properties of the extracellular matrix (ECM). Human mesenchymal progenitor cells (hES-MPs) showed much better adhesion to the fibers with surface adhesive heterogeneity, compared to fibers with only adhesive or only inert surface chemistries