Huai-Ling Gao

Synthetic nacre by predesigned matrix-directed mineralization

Making nacre shine in the lab Many of the materials that animals use to make shells and skeletons are built with brittle or soft molecules. They owe their amazing mechanical properties to their layered construction, which is a challenge for synthetic fabrication. Pearly nacre, for example, has proved challenging to make owing to its complex structure of aragonite crystals in an organic matrix. Using an assembly-and-mineralization approach, Mao et al. have managed to fabricate nacre in the laboratory (see the Perspective by Barthelat). First, a layered, three-dimensional chitosan matrix is made, within which aragonite nanocrystals are precipitated from a solution containing calcium bicarbonate. Science, this issue p. 107; see also p. 32 A consecutive assembly-and-mineralization process leads to synthetic nacre, which strongly resembles natural nacre. [Also see Perspective by Barthelat] Although biomimetic designs are expected to play a key role in exploring future structural materials, facile fabrication of bulk biomimetic materials under ambient conditions remains a major challenge. Here, we describe a mesoscale “assembly-and-mineralization” approach inspired by the natural process in mollusks to fabricate bulk synthetic nacre that highly resembles both the chemical composition and the hierarchical structure of natural nacre. The millimeter-thick synthetic nacre consists of alternating organic layers and aragonite platelet layers (91 weight percent) and exhibits good ultimate strength and fracture toughness. This predesigned matrix-directed mineralization method represents a rational strategy for the preparation of robust composite materials with hierarchically ordered structures, where various constituents are adaptable, including brittle and heat-labile materials.

Macroscopic free-standing hierarchical 3D architectures assembled from silver nanowires by ice templating.

As macroscopic three dimensional (3D) architectures show increasing significance, much effort has been devoted to the hierarchical organization of 1D nanomaterials into serviceable macroscopic 3D assemblies. How to assemble 1D nanoscale building blocks into 3D hierarchical architectures is still a challenge. Herein we report a general strategy based on the use of ice as a template for assembling 1D nanostructures with high efficiency and good controllability. Free-standing macroscopic 3D Ag nanowire (AgNW) assemblies with hierarchical binary-network architectures are then fabricated from a 1D AgNW suspension for the first time. The microstructure of this 3D AgNW network endows it with electrical conductivity and allows it to be made into stretchable and foldable conductors with high electromechanical stability. These properties should make this kind of macroscopic 3D AgNW architecture and it composites suitable for electronic applications.

Super-elastic and fatigue resistant carbon material with lamellar multi-arch microstructure.

Low-density compressible materials enable various applications but are often hindered by structure-derived fatigue failure, weak elasticity with slow recovery speed and large energy dissipation. Here we demonstrate a carbon material with microstructure-derived super-elasticity and high fatigue resistance achieved by designing a hierarchical lamellar architecture composed of thousands of microscale arches that serve as elastic units. The obtained monolithic carbon material can rebound a steel ball in spring-like fashion with fast recovery speed (∼580 mm s−1), and demonstrates complete recovery and small energy dissipation (∼0.2) in each compress-release cycle, even under 90% strain. Particularly, the material can maintain structural integrity after more than 106 cycles at 20% strain and 2.5 × 105 cycles at 50% strain. This structural material, although constructed using an intrinsically brittle carbon constituent, is simultaneously super-elastic, highly compressible and fatigue resistant to a degree even greater than that of previously reported compressible foams mainly made from more robust constituents.

PEGylated Upconverting Luminescent Hollow Nanospheres for Drug Delivery and In Vivo Imaging

Upconversion luminescent hollow Y2 O3 :Yb(3+) /Er(3+) nanospheres can be synthesized by an etching-free process, which hold promising potential for applications such as drug delivery, angiography, and high-contrast cellular as well as tissue imaging, with no damage from radiation or toxicity.

Bioinspired greigite magnetic nanocrystals: chemical synthesis and biomedicine applications

Large scale greigite with uniform dimensions has stimulated significant demands for applications such as hyperthermia, photovoltaics, medicine and cell separation, etc. However, the inhomogeneity and hydrophobicity for most of the as prepared greigite crystals has limited their applications in biomedicine. Herein, we report a green chemical method utilizing β-cyclodextrin (β-CD) and polyethylene glycol (PEG) to synthesize bioinspired greigite (Fe3S4) magnetic nanocrystals (GMNCs) with similar structure and magnetic property of magnetosome in a large scale. β-CD and PEG is responsible to control the crystal phase and morphology, as well as to bound onto the surface of nanocrystals and form polymer layers. The GMNCs exhibit a transverse relaxivity of 94.8 mM−1s−1 which is as high as iron oxide nanocrystals, and an entrapment efficiency of 58.7% for magnetic guided delivery of chemotherapeutic drug doxorubicin. Moreover, enhanced chemotherapeutic treatment of mice tumor was obtained via intravenous injection of doxorubicin loaded GMNCs.

Mass production of bulk artificial nacre with excellent mechanical properties

Various methods have been exploited to replicate nacre features into artificial structural materials with impressive structural and mechanical similarity. However, it is still very challenging to produce nacre-mimetics in three-dimensional bulk form, especially for further scale-up. Herein, we demonstrate that large-sized, three-dimensional bulk artificial nacre with comprehensive mimicry of the hierarchical structures and the toughening mechanisms of natural nacre can be facilely fabricated via a bottom-up assembly process based on laminating pre-fabricated two-dimensional nacre-mimetic films. By optimizing the hierarchical architecture from molecular level to macroscopic level, the mechanical performance of the artificial nacre is superior to that of natural nacre and many engineering materials. This bottom-up strategy has no size restriction or fundamental barrier for further scale-up, and can be easily extended to other material systems, opening an avenue for mass production of high-performance bulk nacre-mimetic structural materials in an efficient and cost-effective way for practical applications.Artificial materials that replicate the mechanical properties of nacre represent important structural materials, but are difficult to produce in bulk. Here, the authors exploit the bottom-up assembly of 2D nacre-mimetic films to fabricate 3D bulk artificial nacre with an optimized architecture and excellent mechanical properties.

A shape-memory scaffold for macroscale assembly of functional nanoscale building blocks

A shape-memory chitosan scaffold (CSS) fabricated by an ice-templated method can be used as a versatile host matrix for self-assembly of a wide range of functional nanoscale building blocks, and thus it can produce a family of functional three-dimensional (3D) macroscale assemblies, which show promising practical application potential in various fields.

Synthesis of Tunable Theranostic Fe3O4@Mesoporous Silica Nanospheres for Biomedical Applications

Abstract Tunable theranostic Fe(3) O(4) @mesoporous silica nanospheres: Tunable theranostic Fe(3) O(4) @mesoporous silica nanospheres for diagnosis and gene therapy have been designed. The tunable delivery doses of imaging probe and gene by Fe(3) O(4) @mesoporous silica nanospheres can be realized by the tunable magnetic cores and modification of surface charges. These Fe(3) O(4) @mesoporous silica nanospheres may act as a theranostic nanosystem due to good biocompatibility, effective MRI diagnosis and gene delivery capabilities.

An investigation of zirconium(IV)–glycine(CP-2) hybrid complex in bovine serum albumin protein matrix under varying conditions

The morphological and structural transformation process of the water soluble zirconium–glycine hybrid cluster [Zr6(O)4(OH)4(H2O)8(Gly)8]12+ (CP-2) in a bovine serum albumin (BSA) protein matrix was comprehensively investigated. Based on the zeta-potential analysis, positive CP-2 clusters tend to adsorb onto the surface of the backbone of BSA, forming BSA–CP-2 hybrids through direct mixing. After aging the solution at 37 °C for several weeks, white floccules appeared in solution indicating the phase transformation of BSA–CP-2 bio–inorganic hybrid. A series of characterizations (zeta-potential measurements, dynamic light scattering measurements, transmission and scanning electron microscopy, X-ray diffraction, and so on) were carried out to analyze the interaction between CP-2 and BSA under varying pH value and salt concentrations in order to demonstrate the transformation of the CP-2 to amorphous ziconium hydroxide. The coagulant action of CP-2 with BSA indicates that the zirconium(IV)–glycine complex may be efficacious as an antiperspirant and in water treatment.

Strong and stiff Ag nanowire-chitosan composite films reinforced by Ag–S covalent bonds

High-performance composites containing various kinds of nanofibers as reinforcing building blocks have recently received considerable attention, owing to their superior mechanical properties. One of the effective strategies to reinforce these composites involves strengthening interfacial interactions via covalent bonds. However, in contrast to nanosheets, covalent bonds have been rarely used in nanofiber-reinforced composites. Herein, we report the macroscale fabrication of a series of Ag nanowire (NW)-thiolated chitosan (TCS) composite films via spray induced self-assembly. The obtained films were significantly strengthened by Ag–S covalent bonds formed between the Ag NWs and the thiol groups of TCS. The tensile strength of the optimized Ag NW-TCS film was up to 3.9 and 1.5 times higher compared with that of pure TCS and Ag NW-chitosan (CS) films, respectively.