Hai-Dong Yu

Bioinspired fabrication of 3D hierarchical porous nanomicrostructures of calcium carbonate for bone regeneration

Hierarchical calcium carbonate structures with multi-scale organization have been successfully fabricated covering the full range of pore sizes from nano-, to micro- to macrofeatures. The resulting 3D scaffolds, with a close resemblance to bone structures, have been evaluated in vitro and in vivo and showed great potential for bone regeneration.

Noncontact orientation of objects in three-dimensional space using magnetic levitation.

Significance We describe several noncontact methods of orienting objects in three-dimensional (3D) space using Magnetic Levitation (MagLev), and report the discovery of a sharp geometry-dependent transition of the orientation of levitating objects. An analytical theory of the orientation of arbitrary objects in MagLev explains this transition. MagLev is capable of manipulating and orienting hard and soft objects, and objects of irregular shape. Because controlling the orientation of objects in space is a prerequisite for assembling complex structures from simpler components, this paper extends MagLev into 3D self-assembly, robotic assembly, and noncontact (stiction-free) orientation of hard and soft objects for applications in biomimetics, soft robotics, and stimulus-responsive materials, among others. This paper describes several noncontact methods of orienting objects in 3D space using Magnetic Levitation (MagLev). The methods use two permanent magnets arranged coaxially with like poles facing and a container containing a paramagnetic liquid in which the objects are suspended. Absent external forcing, objects levitating in the device adopt predictable static orientations; the orientation depends on the shape and distribution of mass within the objects. The orientation of objects of uniform density in the MagLev device shows a sharp geometry-dependent transition: an analytical theory rationalizes this transition and predicts the orientation of objects in the MagLev device. Manipulation of the orientation of the levitating objects in space is achieved in two ways: (i) by rotating and/or translating the MagLev device while the objects are suspended in the paramagnetic solution between the magnets; (ii) by moving a small external magnet close to the levitating objects while keeping the device stationary. Unlike mechanical agitation or robotic selection, orienting using MagLev is possible for objects having a range of different physical characteristics (e.g., different shapes, sizes, and mechanical properties from hard polymers to gels and fluids). MagLev thus has the potential to be useful for sorting and positioning components in 3D space, orienting objects for assembly, constructing noncontact devices, and assembling objects composed of soft materials such as hydrogels, elastomers, and jammed granular media.

Aggregation-driven growth of well-oriented ZnO nanorod arrays

Here we report an aggregation-driven growth of highly oriented and densely packed ZnO nanorod arrays through a simple natural oxidation process of pure metal zinc in formamide/water solution at low temperature. Very intense orange emission was observed in the resulting nanoparticle-built ZnO nanorods with numerous interfacial defects among their primary nanoparticles.

High-Sensitivity Measurement of Density by Magnetic Levitation

This paper presents methods that use Magnetic Levitation (MagLev) to measure very small differences in density of solid diamagnetic objects suspended in a paramagnetic medium. Previous work in this field has shown that, while it is a convenient method, standard MagLev (i.e., where the direction of magnetization and gravitational force are parallel) cannot resolve differences in density <10(-4) g/cm(3) for macroscopic objects (>mm) because (i) objects close in density prevent each other from reaching an equilibrium height due to hard contact and excluded volume, and (ii) using weaker magnets or reducing the magnetic susceptibility of the medium destabilizes the magnetic trap. The present work investigates the use of weak magnetic gradients parallel to the faces of the magnets as a means of increasing the sensitivity of MagLev without destabilization. Configuring the MagLev device in a rotated state (i.e., where the direction of magnetization and gravitational force are perpendicular) relative to the standard configuration enables simple measurements along the axes with the highest sensitivity to changes in density. Manipulating the distance of separation between the magnets or the lengths of the magnets (along the axis of measurement) enables the sensitivity to be tuned. These modifications enable an improvement in the resolution up to 100-fold over the standard configuration, and measurements with resolution down to 10(-6) g/cm(3). Three examples of characterizing the small differences in density among samples of materials having ostensibly indistinguishable densities-Nylon spheres, PMMA spheres, and drug spheres-demonstrate the applicability of rotated Maglev to measuring the density of small (0.1-1 mm) objects with high sensitivity. This capability will be useful in materials science, separations, and quality control of manufactured objects.

Top-down fabrication of calcite nanoshoot arrays by crystal dissolution.

Nucleation Growth The last few decades have witnessed the successful exploration and great achievement for developing solution phase syntheses of monodisperse colloidal nanocrystals in the quantum-confi ned size regime, which enable systematic characterization of the structural, electronic, and optical properties of materials as they evolve from molecular to bulk in the nanometer size range. [ 1 , 2 ]

High-Level Incorporation of Silver in Gold Nanoclusters: Fluorescence Redshift upon Interaction with Hydrogen Peroxide and Fluorescence Enhancement with Herbicide.

High-level incorporation of Ag in Au nanoclusters (NCs) is conveniently achieved by controlling the concentration of Ag(+) in the synthesis of bovine serum albumin (BSA)-protected Au NCs, and the resulting structure is determined to be bimetallic Ag28 Au10-BSA NCs through a series of characterizations including energy-dispersive X-ray spectroscopy, mass spectroscopy, and X-ray photoelectron spectroscopy, together with density functional theory simulations. Interestingly, the Ag28 Au10 NCs exhibit a significant fluorescence redshift rather than quenching upon interaction with hydrogen peroxide, providing a new approach to the detection of hydrogen peroxide through direct comparison of their fluorescence peaks. Furthermore, the Ag28 Au10 NCs are also used for the sensitive and selective detection of herbicide through fluorescence enhancement. The detection limit for herbicide (0.1 nm) is far below the health value established by the U.S. Environmental Protection Agency; such sensitive detection was not achieved by using AuAg NCs with low-level incorporation of Ag or by using the individual metal NCs.

Fabrication and osteoregenerative application of composition-tunable CaCO3/HA composites†‡

A series of porous CaCO3/HA composites have been produced with an increased molar percentage of HA from 0, 10, 25, 50, 75 to 100%. The compression strength of the CaCO3/HA composites increases proportionally before reaching 50% and gradually levels off with a further increase up to 100%. The 50% CaCO3/HA composite, with a similar compression strength to natural bone, has been evaluated in vitro and in vivo, showing great potential for osteoregenerative applications. A three-step chemical process for preparing the CaCO3/HA composites has been revealed by time-dependent XRD analysis: (i) CaCO3 → CaO + CO2↑, (ii) 10CaO + 6(NH4)2HPO4 → Ca10(PO4)6(OH)2 + 12NH3↑ + 8H2O↑, and (iii) CaO + CO2 → CaCO3/Ca(OH)2 + CO2 → CaCO3 + H2O. The initial formation of porous CaO by a fast release of CO2 at high temperature leads to the production of the porous CaCO3/HA composites. Such understanding may allow us to extend this solid-phase fabrication approach to various other porous composites with controlled compositions for promising applications.