Capturing Carriers and Driving Depolarization by Defect Engineering for Dielectric Energy Storage

The inevitable defect carriers in dielectric capacitors are generally considered to depress the polarization and breakdown strength, which decreases energy storage performances. Distinctive from the traditional aims of reducing defects as much as possible, this work designs (Fe_Ti^' - V_o^••)^• and (Fe_Ti^″ - V_o^••) defect dipoles by oxygen vacancy defect engineering in acceptor doped Sr₂Bi₄Ti_(5-x)Fe_xO₁₈ layered perovskite films with n-type leakage conductance. It is shown that oxygen vacancies effectively capture electrons (carriers) in n-type dielectrics to enhance the breakdown strength. Meanwhile, defect dipoles provide a driving field for depolarization to engineer the generation energy of domains and the domain wall energy, which effectively lowers the residual polarization P_r but not at the expense of the maximum polarization P_max as relaxor ferroelectric regulations. Such defect engineering effectively breaks through the limitation, in which the energy storage density suffers from the trade-off relationship between polarization and breakdown strength. The Sr₂Bi₄Ti_4.92Fe_0.08O₁₈ film with the proper oxygen vacancy content achieves a high energy density of 110.5 J/cm³ and efficiency of 70.0% at a high breakdown strength of 3915 kV/cm. This work explores an alternative way for breakthroughs possible in the intrinsic trade-off relationship to regulate dielectric energy storage by defect engineering.

Capturing Magnesium Ions via Microfluidic Hydrogel Microspheres for Promoting Cancellous Bone Regeneration

Metal ions are important trace elements in the human body, which directly affect the human metabolism and the regeneration of damaged tissues. For instance, the advanced combination of magnesium ions (Mg²⁺) and bone repair materials make the composite materials have the function of promoting vascular repair and enhancing the adhesion of osteoblasts. Herein, inspired by magnets to attract metals, we utilized the coordination reaction of metal ion ligand to construct a bisphosphonate-functionalized injectable hydrogel microsphere (GelMA-BP-Mg) which could promote cancellous bone reconstruction of osteoporotic bone defect via capturing Mg²⁺. By grafting bisphosphonate (BP) on GelMA microspheres, GelMA-BP microspheres could produce powerful Mg²⁺ capture ability and sustained release performance through coordination reaction, while sustained release BP has bone-targeting properties. In the injectable GelMA-BP-Mg microsphere system, the atomic percentage of captured Mg²⁺ was 0.6%, and the captured Mg²⁺ could be effectively released for 18 days. These proved that the composite microspheres could effectively capture Mg²⁺ and provided the basis for the composite microspheres to activate osteoblasts and endothelial cells and inhibit osteoclasts. Both in vivo and in vitro experimental results revealed that the magnet-inspired Mg²⁺-capturing composite microspheres are beneficial to osteogenesis and angiogenesis by stimulating osteoblasts and endothelial cells while restraining osteoclasts, and ultimately effectively promote cancellous bone regeneration. This study could provide some meaningful conceptions for the treatment of osteoporotic bone defects on the basis of metal ions.

Freeze the Moment: High Speed Capturing of Weakly Bonded Dynamic Nanoparticle Assemblies in Solution by Ag Ion Soldering

Despite the versatile forms of colloidal aggregates, these spontaneously formed structures are often hard to find a suitable application in nanotechnology and materials science. A determinate reason is the lack of a suitable method to capture the transiently formed and quickly evolving colloidal structures in solution. To address this challenge, a simple but highly efficient strategy is herein reported to capture the dynamic and metastable colloidal assemblies formed in an aqueous or nonaqueous solution. This process takes advantage of a recently developed Ag ion soldering reaction to realize a rapid fixation of as-formed metastable assemblies. This method works efficiently for both solid (3D) nanoparticle aggregates and weakly bonded fractal nanoparticle chains (1D). In both cases, very high capturing speed and close to 100% efficiency are achieved to fully retain a quickly growing structure. The soldered nanochains further enable a fabrication of discrete, uniform, and functionalizable nanoparticle clusters with enriched linear conformation by mechanical shearing, which would otherwise be difficult to make. The captured products are water dispersible and mechanically robust, favoring an exploration of their properties toward possible applications. The work paves a way to previously untouched aspects of colloidal science and thus would create new chances in nanotechnology.