Nanopores exhibit a set of interesting transport properties that stem from interactions of the passing ions and molecules with the pore walls. Nanopores are used, for example, as ionic diodes and transistors, biosensors, and osmotic power generators. Using nanopores is however disadvantaged by their high resistance, small switching currents in nA range, low power generated, and signals that can be difficult to distinguish from the background. Here, we present a mesopore with ionic conductance reaching μS that rectifies ion current in salt concentrations as high as 1 M. The mesopore is conically shaped, and its region close to the narrow opening is filled with high molecular weight poly-l-lysine. To elucidate the underlying mechanism of ion current rectification (ICR), a continuum model based on a set of Poisson–Nernst–Planck and Stokes–Brinkman equations was adopted. The results revealed that embedding the polyelectrolyte in a conical pore leads to rectification of the effect of concentration polarization (CP) that is induced by the polyelectrolyte, and observed as voltage polarity-dependent modulations of ionic concentrations in the pore, and consequently ICR. Our work reveals the link between ICR and CP, significantly extending the knowledge of how charged polyelectrolytes modulate ion transport on nano- and mesoscales. The osmotic power application is also demonstrated with the developed polyelectrolyte-filled mesopores, which enable a power of up to ∼120 pW from one pore, which is much higher than the reported values using single nanoscale pores.

We previously established a simple method to immobilize the Arg-Gly-Asp (RGD) peptide on polycaprolactone (PCL) two-dimensional film surfaces that significantly improved bone marrow stromal cell (BMSC) adhesion to these films. The current work extends this modification strategy to three-dimensional (3D) PCL scaffolds to investigate BMSCs attachment, cellular distribution and cellularity, signal transduction and survival on the modified PCL scaffold compared to those on the untreated ones. The results demonstrated that treatment of 3D PCL scaffold surfaces with 1,6-hexanediamine introduced the amino functional groups onto the porous PCL scaffold homogenously as detected by a ninhydrin staining method. Followed by the cross-linking reaction, RGDC peptide was successfully immobilized on the surface of PCL scaffold. Although the static seeding method used in this study caused heterogeneous cell distribution, the RGD modified PCL scaffold still demonstrated the improved BMSC attachment and cellular distribution in the scaffold. More importantly, the integrin-mediated signal transduction FAK-PI3K-Akt pathway was significantly up-regulated by RGD modification and a subsequent increase in cell survival and growth was found in the modified scaffold. The present study introduces an easy method to immobilize RGD peptide on the 3D porous PCL scaffold and provides further evidence that modification of 3D PCL scaffolds with RGD peptides elicits specific cellular responses and improves the final cell-biomaterial interaction.

It is believed that ion current rectification (ICR), a property that assures preferential ionic transport in one direction, can only be observed in nanopores when the pore size is comparable to the thickness of the electric double layer (EDL). Rectifying nanopores became the basis of biological sensors and components of ionic circuits. Here we report that appreciable ICR can also occur in highly charged conical, polymer mesopores whose tip diameters are as large as 400 nm, thus over 100-fold larger than the EDL thickness. A rigorous model taking into account the surface equilibrium reaction of functional carboxyl groups on the pore wall and electroosmotic flow is employed to explain that unexpected phenomenon. Results show that the pore rectification results from the high density of surface charges as well as the presence of highly mobile hydroxide ions, whose concentration is enhanced for one voltage polarity. This work provides evidence that highly charged surfaces can extend the ICR of pores to the submicron scale, suggesting the potential use of highly charged large pores for energy and sensing applications. Our results also provide insight into how a mixture of ions with different mobilities can influence current-voltage curves and rectification.

Calcium ions play important roles in many physiological processes, yet their concentration is much lower than the concentrations of potassium and sodium ions. The selectivity of calcium channels is often probed in mixtures of calcium and a monovalent salt, e.g., KCl or NaCl, prepared such that the concentration of cations is kept constant with the mole fraction of calcium varying from 0 and 1. In biological channels, even sub-mM concentration of calcium can modulate the channels' transport characteristics; this effect is often explained via the existence of high affinity Ca 2+ binding sites on the channel walls. Inspired by properties of biological calcium-selective channels, we prepared a set of nanopores with tunable opening diameters that exhibited a similar response to the presence of calcium ions as biochannels. Nanopores in 15 nm thick silicon nitride films were drilled using focused ion beam and e-beam in a transmission electron microscope and subsequently rendered negatively charged through silanization. We found that nanopores with diameters smaller than 20 nm were blocked by calcium ions such that the ion currents in mixtures of KCl and CaCl 2 and in CaCl 2 were even ten times smaller than the ion currents in KCl solution. The ion current blockage was explained by the effect of local charge inversion where accumulated calcium ions switch the effective surface charge from negative to positive. The modulation of surface charge with calcium leads to concentration and voltage dependent local charge density and ion current. The combined experimental and modeling results provide a link between calcium ion-induced changes in surface charge properties and resulting ionic transport.

Drawing on the stressor-emotion model, we examine how customer mistreatment can evoke service workers' passive forms of deviant behaviors (i.e., work withdrawal behavior [WWB]) and negative impacts on their home life (i.e., work-family conflict [WFC]), and whether individuals' core self-evaluations and customer service training can buffer the negative effects of customer mistreatment. Using the experience sampling method, we collect daily data from 77 customer service employees for 10 consecutive working days, yielding 546 valid daily responses. The results show that daily customer mistreatment increases service workers' daily WWB and WFC through negative emotions. Furthermore, employees with high core self-evaluations and employees who received customer service training are less likely to experience negative emotions when faced with customer mistreatment, and thus are less likely to engage in WWB or provoke WFC. (PsycINFO Database Record

Accurately and rapidly analyzing the ionic current/conductance in a nanochannel, especially under the condition of overlapped electric double layers (EDLs), is of fundamental significance for the design and development of novel nanofluidic devices. To achieve this, an analytical model for the surface charge properties and ionic current/conductance in a pH-regulated nanochannel is developed for the first time. The developed model takes into account the effects of the EDL overlap, electroosmotic flow, Stern layer, multiple ionic species, and the site dissociation/association reactions on the channel walls. In addition to good agreement with the existing experimental data of nanochannel conductance available from the literature, our analytical model is also validated by the full model with the Poisson-Nernst-Planck and Navier-Stokes equations. The EDL overlap effect is significant at small nanochannel height, low salt concentration, and medium low pH. Neglecting the EDL overlap effect could result in a wrong estimation in the zeta potential and conductance of the nanochannel in a single measurement.

Ternary iron-boron-based bulk metallic glasses ͑BMGs͒ were explored exhibiting capability of thick amorphous casting at least 1 mm in rod diameter or 0.5 mm in plate thickness, excellent soft magnetic properties with saturation magnetization 1.56 T and coercivity smaller than 40 A / m, and electrical resistivity larger than 200 ⍀ cm. The BMG alloys represented by the formulas M a Fe b B c are based on two simple selection rules: ͑1͒ M is an element with an atomic radius at least 130% that of Fe; ͑2͒ M possesses eutectic points with both Fe and B, and the M-Fe eutectic is at the Fe-rich end. Among more than 30 candidate M elements, Sc, Y, Dy, Ho, and Er fulfill BMG capability at the composition range, in at %, 3 Ͻ a Ͻ 10, 18Ͻ c Ͻ 27, whereas a + b + c = 100. It is very remarkable that with a tiny addition of M, such as 4 at %, the critical cooling rate to form an amorphous state is abruptly lowered by more than four orders of magnitude as compared with Fe-B binary alloys, and a bulk amorphous state is achievable with only three elements ͑conventional ones 4-7 elements͒. These alloys are promising as core materials for transformers.

Due to its potential applications in biotechnology, ion current rectification (ICR) arising from the asymmetric nature of ion transport in a nanochannel has drawn the attention of researchers in various fields. Previous studies usually neglect the effects of osmotic and electroosmotic flows. In this study, a more general model taking account of these effects is adopted to describe the ICR behavior of a conical nanopore. The influences of the cone angle, surface charge density, and bulk salt concentration on this behavior are investigated, and mechanisms proposed to explain the results are obtained. We show that if the cone angle is enlarged by fixing the nanopore tip radius and raising its base radius, the ICR ratio has a local maximum. This behavior may not present if the cone angle is enlarged by fixing the nanopore base radius and raising its tip radius. The local maximum in the ICR ratio does not exist if the bulk salt concentration is sufficiently low or sufficiently high. This ratio also has a local maximum as the surface charge density varies, and the larger the cone angle, the higher the surface charge density at which the local maximum in the ICR ratio occurs.