Advanced Materials

Orchestrated control of matrix property and geometry is reported by Rashid Bashir, Hyunjoon Kong, and co-workers on page 58. The “living” microvascular stamp releases multiple angiogenic factors and subsequently creates functional neo-vessels with the same pattern as that engraved in the stamp. The stamp consists of live cells that secrete angiogenic factors, an engineered hydrogel matrix that promotes cellular expression of angiogenic factors, and a three-dimensional geometry that localizes the angiogenic factors within the pattern.

The cover image shows a biofunctionalized hydrogel that is bonded directly onto myocardial tissue, delivering regenerative cells and therapeutics. On page 64, Andrés García and co-workers describe how maleimide-based cross-linking improves polyethylene glycol hydrogel engineering, leading to rapid gelation, high cytocom-patibility, and facile in situ delivery.

Semiconductor alloy nanowires with spatially graded compositions (and bandgaps) provide a new material platform for many new multifunctional optoelectronic devices, such as broadly tunable lasers, multispectral photodetectors, broad-band light emitting diodes (LEDs) and high-efficiency solar cells. Here, recent studies on composition or bandgap-graded semiconductor alloy nanowires based on a single substrate or along single nanowires are reviewed.

Organic thin-film transistors, including organic field-effect transistors and organic electrochemical transistors, can be used in various types of chemical and biological sensors, such as pH, humidity, ion, glucose, DNA, enzyme, antibody-antigen, cell and dopamine sensors. The organic transistors are expected to have more important sensing applications with the development of organic electronics.

Polycrystalline graphene sensors are presented by Richard I. Masel and co-workers on page 53. The image shows polycrystalline graphene ribbon chemiresistors with gold contacts visualizing linear defects or wrinkles in the graphene. Floating or attached toluene molecules act as electron donors. Such defective graphene devices exhibit a higher chemical sensitivity than pristine graphene or carbon nanotube chemire-sistors. (Image by Alex Jerez, Beckman Institute, University of Illinois at Urbana-Champaign.)

Polycrystalline graphene sensors easily obtained through chemical vapor deposition (CVD) have been developed for chemical sensing. We show that linear defects or continuous lines of point defects on these sensors result in significantly higher sensitivity than that of pristine graphene and carbon nanotube film sensors. Further sensitivity enhancement is obtained by cutting the graphene into ribbons of width comparable to the linear defect dimensions (micrometers).

This study presents a “living” microvascular stamp that releases multiple angiogenic factors and subsequently creates functional neovessels with the same pattern as that engraved in the stamp. The stamp consists of live cells that secrete angiogenic factors, an engineered hydrogel matrix that promotes cellular expression of angiogenic factors, and a three-dimensional geometry that localizes the angiogenic factors within the pattern.

Engineered polyethylene glycol-maleimide matrices for regenerative medicine exhibit improved reaction efficiency and a wider range of Young's moduli by utilizing maleimide cross-linking chemistry. This hydrogel chemistry is advantageous for cell delivery due to the mild reaction that occurs rapidly enough for in situ delivery, while easily lending itself to “plug-and-play” design variations such as incorporation of enzyme-cleavable cross-links and cell-adhesion peptides.

Utilizing a non-resonant graded material consisting of an array of artificially patterned superconducting and soft ferromagnetic elements, we construct a dc magnetic cloak. When an external dc magnetic field is applied, we find that the interior of the cloak is completely shielded while the exterior field remains unperturbed, as if the cloak and the cloaked region are just an empty space.

An entirely new class of membranes with superior polarization is presented by Xian Ning Xie and co-workers, on page 76. The polarization of such a membrane is up to a million times that of conventional polarizable materials and, in practice, the membrane is immediately applicable for energy storage and associated technologies, such as hybrid/electric vehicles, solar panels, power grids, and consumer electronics.

A new class of super polarization membrane is described. In terms of fundamental properties, the membrane exhibits the largest polarization, reasonable polarization retention, and high ionic conductivity. In practice, the membrane is immediately applicable in energy storage, and the associated technology is not only inexpensive, but also massive scalable and environment-friendly. The energy-storage membrane has wide applications in the energy efficiency and management of solar panels, wind turbines, and hybrid/electric vehicles.

An entirely bottom-up approach for the preparation of liquid crystalline suspensions of core-shell nanowires for ordered bulk heterojunction photovoltaics is demonstrated. Side-on attachment of polythiophene derivatives to ZnO nanowires promotes a co-axial polymer backbone-nanowire arrangement which favors high hole mobility. This strategy offers structural control over multiple length scales and a viable means of fabricating ordered films over large areas.

A relaxor ferroelectric polymer poly(vinylidene fluoride-trifluoroethylene-chlorofloroethylene) exhibits a high relative dielectric constant (k) (∼60). The high-k polymer is used successfully in solution processable low-voltage OTFTs as the gate insulator for the first time. Both n-channel and p-channel OTFTs based on conjugated polymers are fabricated and show carrier mobilities higher than 0.1 cm² V⁻¹ s⁻¹ at an operating voltage of 3 V.

Gold nanocrystals are dispersed uniformly in poly(dimethylsiloxane) to produce a plasmonic composite. The composite can be readily used to fabricate microfluidic channels. An efficient optical heating approach on the microfluidic chips made of the composite is realized on the basis of plasmon-enabled photothermal conversion. A fluid flow switch based on the plasmonic heating is also demonstrated.

Ag₂S nanocrystals (NCs) are embedded into a GeS₂ matrix while controlling the size, shape, and interparticle spacing of the Ag₂S NCs. We demonstrate that the ionic and electronic properties of these inorganic nanocomposites can be systematically controlled by varying the diameter of the Ag₂S NCs. We also observe an ionic conductivity enhancement relative to pure Ag₂S and (GeS₂)_0.5(Ag₂S)_0.5 glass.

The image shows a sketch of a Chinese silkworm spinning a silk fiber. Using shear-induced polarization light imaging, Oleksandr O. Mykhaylyk and co-workers at Sheffield and Oxford Universities demonstrate on page 105 that the work required to produce natural silk fibers is at least ten times less than that required for a typical synthetic polymer. They also (re)define the concept of polymer crys-tallization and class silks as a new nanocomposite state of biological matter: “aquamelts”.

It is shown that the work required to produce natural silk fibers is at least ten times less than a classic synthetic polymer, yet still nature produces a fiber with superior mechanical properties. The concept of polymer crystallization is (re)defined and silks are classed as a new nanocomposite state of biological matter called aquamelts.

Replacing batteries by nanogenerators (NGs) in small consumer electronics is one of the goals in the emerging field of self-powered nanotechnology. We show that the maximum measured output voltage of an NG optimized with pretreatments on the as-grown ZnO nanowire films reaches 20 V and the output current exceeds 6 μA, which corresponds to a power density of 0.2 W cm⁻³. The NG is also demonstrated to replace a battery for driving a electronic watch.

A novel multifunctional polymeric micelle bearing a pH-tunable on-off module for programmed drug release, folate for tumor targeting, and quantum dots for fluorescent imaging is described. The micelle can turn drug release off at neutral pH whereas on inside lysosomes. QD functionalization allows a clear elucidation of pH-tunable drug release and facile visualization of in vivo delivery event.

A novel solid electrolyte with a three-dimensional ionic channel is used in a solid-state dye-sensitized solar cell, which produces a power conversion efficiency of 6.63% with a fill factor of 0.73. The findings presented will pave a new way for the design of new solid electrolytes towards high-efficiency solid state dye-sensitized solar cells.

Using a porphyrin-functionalized graphene-modified electrode, an electrochemical impedance peptide sensor for label-free detection of cyclin A₂ has been constructed. This electrochemical sensor can not only detect protein in cancer cells but also differentiate cancer cells from normal ones. Furthermore, the assay provides the potential of using a simple electrochemical technique to estimate the efficiency of anticancer drugs in cancer therapy.

A reproducible and steady magnetoresistance switch effect of Sn-doped Bi₂Te₃ topological insulator films with a Pt/Sn-doped Bi₂Te₃/Pt structure is observed when a parallel magnetic field is applied.