Core@Double-Shell Engineering of Zn Particles toward Elevated Dielectric Properties: Multiple Polarization Mechanisms in Zn@Znch@PS/PVDF Composites.

Flexible dielectrics with large dielectric constant (ε') coupled with low loss are highly pursued in many applications. To bolster the ε' of raw Zn (zinc)/poly(vinylidene fluoride, PVDF) while maintaining pimping dielectric loss, in this study, the core@double-shell structured Zn@zinc carbonate (ZnCH)@polystyrene (PS) particles are first synthesized through a suspension polymerization of styrene, and then composited with PVDF to elevate the ε' and keep low loss of the composites. By optimizing the PS shells' thickness and tailoring the electrical resistivity of Zn@ZnCH@PS particles, both the slow inter-particle polarization and fast intra-particle polarization in the composites can be decoupled and synergistically tuned, thus, the Zn@ZnCH@PS/PVDF achieves a much higher ε' and lower dielectric loss, simultaneously, which far exceed the unmodified Zn/PVDF. Both experiment and theoretic calculation reveal that the double-shell ZnCH@PS not only induces and promotes multiple polarizations enhancing the composites' ε', especially at the optimized PS's thickness, but also maintains suppressed loss and conductivity thanks to their obvious barrier effect on long-range charge migration. The core@double-shell filler design strategy facilitates the development of polymer composites with desirable dielectric properties for applications in electronic and electrical power systems.

Carbon Nanotube Template-Assisted Synthesis of Conjugated Microporous Polytriphenylamine with High Porosity for Efficient Supercapacitive Energy Storage.

Engineering of conjugated microporous polymers (CMPs) with high porosity, redox activity, and electronic conductivity is of significant importance for their practical applications in electrochemical energy storage. Aminated-multiwall carbon nanotubes (NH2 -MWNT) are utilized to modulate the porosity and electronic conductivity of polytriphenylamine (PTPA), which is synthesized via Buchwald-Hartwig coupling reaction of tri(4-bromophenyl)amine and phenylenediamine as constitutional units in a one-step in situ polymerization process. Compared to PTPA, the specific surface area of core-shell PTPA@MWNTs has been greatly improved from 32 to 484 m2  g-1 . The PTPA@MWNTs exhibites an improved specific capacitance, with the highest value 410 F g-1 in 0.5 M H2 SO4 at a current of 10 A g-1 achieve for PTPA@MWNT-4 due to the hierarchical meso-micro pores, high redox-activity and electronic conductivity. Symmetric supercapacitor assemble by PTPA@MWNT-4 has a capacitance of 216 F g-1 of total electrode materials and retains 71% of initial capacitance after 6000 cycles. This study gives new insights into the role of CNT templates in the adjustment of molecular structure, porosity, and electronic property of CMPs for the high-performance electrochemical energy storage.

Epitaxial seeded growth of rare-earth nanocrystals with efficient 800 nm near-infrared to 1525 nm short-wavelength infrared downconversion photoluminescence for in†vivo bioimaging.

Novel ß-NaGdF4/Na(Gd,Yb)F4:Er/NaYF4:Yb/NaNdF4:Yb core/shell 1/shell 2/shell 3 (C/S1/S2/S3) multi-shell nanocrystals (NCs) have been synthesized and used as probes for in vivo imaging. They can be excited by near-infrared (800 nm) radiation and emit short-wavelength infrared (SWIR, 1525 nm) radiation. Excitation at 800 nm falls into the "biological transparency window", which features low absorption by water and low heat generation and is considered to be the ideal excitation wavelength with the least impact on biological tissues. After coating with phospholipids, the water-soluble NCs showed good biocompatibility and low toxicity. With efficient SWIR emission at 1525 nm, the probe is detectable in tissues at depths of up to 18 mm with a low detection threshold concentration (5 nM for the stomach of nude mice and 100 nM for the stomach of SD rats). These results highlight the potential of the probe for the in vivo monitoring of areas that are otherwise difficult to analyze.

Tailoring the properties of composite scaffolds with a 3D-Printed lattice core and a bioactive hydrogel shell for tissue engineering.

The optimal performance of scaffolds for tissue engineering relies on a proper combination of their constituent biomaterials and on the design of their structure. In this work, composite scaffolds with a core-shell architecture are realized by grafting a gelatin-chitosan hydrogel onto a 3D-printed polylactic acid (PLA) core, aiming in particular at bone regeneration. This hydrogel was recently found to sustain osteogenic differentiation of mesenchymal stromal cells, leading to new bone tissue formation. Here, the integration with rigid PLA lattice structures provides improved mechanical support and finer control of strength and stiffness. The core is prepared by fused deposition modeling with the specific aim to study several lattice structures and thereby better tune the scaffold mechanical properties. In fact, the core architecture dictates the scaffold strength and stiffness, which are seen to match those of different types of bone tissue. For all lattice types, the hydrogel is found to penetrate throughout the entire core and to present highly interconnected pores for cell colonization. By varying the void volume fraction in the core it is possible to significantly change the bioactive shell content, as well as the mechanical properties, over a wide range of values. Looking for design guidelines, relationships between stiffness/strength and density are here outlined for scaffolds featuring different lattice parameters. Moreover, by acting on the core strut arrangement, scaffolds are reinforced along specific directions, as evaluated under compressive and bending loading conditions.

Single-Step Synthesis of Alginate Microgels Enveloped with a Covalent Polymeric Shell: A Simple Way to Protect Encapsulated Cells.

Microgels of biopolymers such as alginate are widely used to encapsulate cells and other biological payloads. Alginate is an attractive material for cell encapsulation because it is nontoxic and convenient: spherical alginate gels are easily created by contacting aqueous droplets of sodium alginate with divalent cations such as Ca2+. Alginate chains in the gel become cross-linked by Ca2+ cations into a 3-D network. When alginate gels are placed in a buffer, however, the Ca2+ cross-links are eliminated by exchange with Na+, thereby weakening and degrading the gels. With time, encapsulated cells are released into the external solution. Here, we describe a simple solution to the above problem, which involves forming alginate gels enveloped by a thin shell of a covalently cross-linked gel. The shell is formed via free-radical polymerization using conventional monomers such as acrylamide (AAm) or acrylate derivatives, including polyethylene glycol diacrylate (PEGDA). The entire process is performed in a single step at room temperature (or 37 °C) under mild, aqueous conditions. It involves combining the alginate solution with a radical initiator, which is then introduced as droplets into a reservoir containing Ca2+ and monomers. Within minutes of either simple incubation or exposure to ultraviolet (UV) light, the droplets are converted into alginate-polymer microcapsules with a core of alginate and a shell of the polymer (AAm or PEGDA). The microcapsules are mechanically more robust than conventional alginate/Ca2+ microgels, and while the latter swell and degrade when placed in buffers or in chelators like sodium citrate, the former remain stable under all conditions. We encapsulate both bacteria and mammalian cells in these microcapsules and find that the cells remain viable and functional over time. Lastly, a variation of the synthesis technique is shown to generate multilayered microcapsules with a liquid core surrounded by concentric layers of alginate and AAm gels. We anticipate that the approaches presented here will find application in a variety of areas including cell therapies, artificial cells, drug delivery, and tissue engineering.

Spatiotemporally programmable surface engineered nanoparticles for effective anticancer drug delivery.

Surface engineered nanoparticles (NPs) are fabricated from polycaprolactone-polyethylenimine-folic acid (PCL-PEI-FA) and polycaprolactone-S-S-polyethylene glycol (PCL-S-S-PEG) copolymers. FESEM reveals the core-shell structure of these NPs of about 230 nm size. It is assumed that the inner cores of these NPs are composed of PCL, while the outer shells are adorned with PEG and folic acid, introducing a stealthy nature and specific targeting capability. Moreover, the disulfide bonds in the PCL-S-S-PEG copolymers provide a reduction-induced degradation characteristic in these NPs. Cell line experiments demonstrate the enhanced endocytosis and cytotoxicity of these NPs. Thus PCL-PEI-FA/PCL-S-S-PEG NPs could be a better candidate for the tumor specific delivery of hydrophobic drugs.