Nanostructures have attracted huge interest as a rapidly growing class of materials for many applications. Several techniques have been used to characterize the size, crystal structure, elemental composition and a variety of other physical properties of nanoparticles. In several cases, there are physical properties that can be evaluated by more than one technique. Different strengths and limitations of each technique complicate the choice of the most suitable method, while often a combinatorial characterization approach is needed. In addition, given that the significance of nanoparticles in basic research and applications is constantly increasing, it is necessary that researchers from separate fields overcome the challenges in the reproducible and reliable characterization of nanomaterials, after their synthesis and further process (e.g. annealing) stages. The principal objective of this review is to summarize the present knowledge on the use, advances, advantages and weaknesses of a large number of experimental techniques that are available for the characterization of nanoparticles. Different characterization techniques are classified according to the concept/group of the technique used, the information they can provide, or the materials that they are destined for. We describe the main characteristics of the techniques and their operation principles and we give various examples of their use, presenting them in a comparative mode, when possible, in relation to the property studied in each case.

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Characterization techniques for nanoparticles: comparison and complementarity upon studying nanoparticle properties

Lanthanide Nanoparticles: From Design toward Bioimaging and Therapy

MnFe2O4 nanoparticles have been synthesized on a large scale by a simple hydrothermal process in a wild condition, and the RGO/MnFe2O4 nanocomposites were also prepared under ultrasonic treatment based on the synthesized nanoparticles. The absorption properties of MnFe2O4/wax, RGO/MnFe2O4/wax and the RGO/MnFe2O4/PVDF (polyvinylidene fluoride) composites were studied; the results indicated that the RGO/MnFe2O4/PVDF composites show the most excellent wave absorption properties. The minimum reflection loss of RGO/MnFe2O4/PVDF composites with filler content of 5 wt % can reach −29.0 dB at 9.2 GHz, and the bandwidth of frequency less than −10 dB is from 8.00 to 12.88 GHz. The wave absorbing mechanism can be attributed to the dielectric loss, magnetic loss and the synergetic effect between RGO+MnFe2O4, RGO+PVDF and MnFe2O4+PVDF.

Enhanced microwave absorption property of reduced graphene oxide (RGO)-MnFe2O4 nanocomposites and polyvinylidene fluoride.

Successful materials design for bone-tissue engineering requires an understanding of the composition and structure of native bone tissue, as well as appropriate selection of biomimetic natural or tunable synthetic materials (biomaterials), such as polymers, bioceramics, metals and composites. Scalable fabrication technologies that enable control over construct architecture at multiple length scales, including three-dimensional printing and electric-field-assisted techniques, can then be employed to process these biomaterials into suitable forms for bone-tissue engineering. In this Review, we provide an overview of materials-design considerations for bone-tissue-engineering applications in both disease modelling and treatment of injuries and disease in humans. We outline the materials-design pathway from implementation strategy through selection of materials and fabrication methods to evaluation. Finally, we discuss unmet needs and current challenges in the development of ideal materials for bone-tissue regeneration and highlight emerging strategies in the field. Design of bone-tissue-engineering materials involves consideration of multiple, often conflicting, requirements. This Review discusses these considerations and highlights scalable technologies that can fabricate natural and synthetic biomaterials (polymers, bioceramics, metals and composites) into forms suitable for bone-tissue-engineering applications in human therapies and disease models.

Materials design for bone-tissue engineering

Graphene is composed of single-atom thick sheets of sp2 bonded carbon atoms that are arranged in a perfect two-dimensional (2D) honeycomb lattice. Because of this structure, graphene is characterized by a number of unique and exceptional structural, optical, and electronic properties.1 Specifically, these extraordinary properties include, but are not limited to, a high planar surface area that is calculated to be 2630 m2 g−1,2 superior mechanical strength with a Young’s modulus of 1100 GPa,3 unparalleled thermal conductivity (5000 W m−1 K−1),4 remarkable electronic properties (e.g., high carrier mobility [10 000 cm2 V−1 s−1] and capacity),5 and alluring optical characteristics (e.g., high opacity [~97.7%] and the ability to quench fluorescence).6 As such, it should come as no surprise that graphene is currently, without any doubt, the most intensively studied material for a wide range of applications that include electronic, energy, and sensing outlets.1c Moreover, because of these unique chemical and physical properties, graphene and graphene-based nanomaterials have attracted increasing interest, and, arguably, hold the greatest promise for implementation into a wide array of bioapplications.7

In the last several years, numerous studies have utilized graphene in bioapplications ranging from the delivery of chemotherapeutics for the treatment of cancer8 to biosensing applications for a host of medical conditions9 and even for the differentiation and imaging of stem cells.10 While promising and exciting, recent reports have demonstrated that the combination of graphene with nanomaterials such as nanoparticles, thereby forming graphene–nanoparticle hybrid structures, offers a number of additional unique physicochemical properties and functions that are both highly desirable and markedly advantageous for bioapplications when compared to the use of either material alone (Figure 1).11 These graphene–nanoparticle hybrid structures are especially alluring because not only do they display the individual properties of the nanoparticles, which can already possess beneficial optical, electronic, magnetic, and structural properties that are unavailable in bulk materials, and of graphene, but they also exhibit additional advantageous and often synergistic properties that greatly augment their potential for bioapplications.




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Figure 1


Graphene nanoparticle hybrids exist in two forms, as graphene–nanoparticle composites and graphene-encapsulated nanoparticles, and can be used for various bioapplications including biosensors, photothermal therapies, stem cell/tissue engineering, drug/gene delivery, and bioimaging. Panel (A) reprinted with permission from ref 110. Copyright 2012 Wiley. Panel (B) reprinted with permission from ref 211. Copyright 2013 Elsevier. Panel (C) reprinted with permission from ref 244. Copyright 2013 Wiley.

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Design, Synthesis, and Characterization of Graphene–Nanoparticle Hybrid Materials for Bioapplications

Additive manufacturing (AM) of ceramic materials has attracted tremendous attention in recent years, due to its potential to fabricate suitable advanced ceramic structures for various engineering applications. Robocasting, a subset of ceramic AM, is an ideal technique for constructing fine and dense ceramic structures with geometrically complex morphology. With the freedom and convenience to deposit various materials within any 3D spatial position, ceramic robocasting opens up unlimited opportunities, which are otherwise hardly attainable from other AM techniques. Here, a summary of the recent progress on the fabrication of single and multi-ceramic structures by robocasting is provided, as well as the prospects of achieving shapeable ceramic structures. The current challenges in ceramic robocasting and an outlook on its development, especially toward the fabrication of self-shaping ceramic structures, are also discussed.

Ceramic Robocasting: Recent Achievements, Potential, and Future Developments.

In this study, MnFe(2)O(4) nanoparticle (MFNP)-decorated graphene oxide nanocomposites (MGONCs) are prepared through a simple mini-emulsion and solvent evaporation process. It is demonstrated that the loading of magnetic nanocrystals can be tuned by varying the ratio of graphene oxide/magnetic nanoparticles. On top of that, the hydrodynamic size range of the obtained nanocomposites can be optimized by varying the sonication time during the emulsion process. By fine-tuning the sonication time, MGONCs as small as 56.8 ± 1.1 nm, 55.0 ± 0.6 nm and 56.2 ± 0.4 nm loaded with 6 nm, 11 nm, and 14 nm MFNPs, respectively, are successfully fabricated. In order to improve the colloidal stability of MGONCs in physiological solutions (e.g., phosphate buffered saline or PBS solution), MGONCs are further conjugated with polyethylene glycol (PEG). Heating by exposing MGONCs samples to an alternating magnetic field (AMF) show that the obtained nanocomposites are efficient hyperthermia agents. At concentrations as low as 0.1 mg Fe mL(-1) and under an 59.99 kA m(-1) field, the highest specific absorption rate (SAR) recorded is 1588.83 W g(-1) for MGONCs loaded with 14 nm MFNPs. It is also demonstrated that MGONCs are promising as magnetic resonance imaging (MRI) T(2) contrast agents. A T(2) relaxivity value (r(2) ) as high as 256.2 (mM Fe)(-1) s(-1) could be achieved with MGONCs loaded with 14 nm MFNPs. The cytotoxicity results show that PEGylated MGONCs exhibit an excellent biocompatibility that is suitable for biomedical applications.

Synthesis of Manganese Ferrite/Graphene Oxide Nanocomposites for Biomedical Applications

Magnetic resonance imaging (MRI) has become an integral part of modern clinical imaging due to its non-invasiveness and versatility in providing tissue and organ images with high spatial resolution. With the current MRI advancement, MRI imaging probes with suitable biocompatibility, good colloidal stability, enhanced relaxometric properties and advanced functionalities are highly demanded. As such, MRI contrast agents (CAs) have been an extensive research and development area. In the recent years, different inorganic-based nanoprobes comprising inorganic magnetic nanoparticles (MNPs) with an organic functional coating have been engineered to obtain a suitable contrast enhancement effect. For biomedical applications, the organic functional coating is critical to improve colloidal stability and biocompatibility. Simultaneously, it also provides a building block for generating a higher dimensional secondary structure. In this review, the combinatorial design approach by a self-assembling pre-formed hydrophobic inorganic MNPs core (from non-polar thermolysis synthesis) into various functional organic coatings (e.g. ligands, amphiphilic polymers and graphene oxide) to form water soluble nanocomposites will be discussed. The resultant magnetic ensembles were classified based on their dimensionality, namely, 0-D, 1-D, 2-D and 3-D structures. This classification provides further insight into their subsequent potential use as MRI CAs. Special attention will be dedicated towards the correlation between the spatial distribution and the associated MRI applications, which include (i) coating optimization-induced MR relaxivity enhancement, (ii) aggregation-induced MR relaxivity enhancement, (iii) off-resonance saturation imaging (ORS), (iv) magnetically-induced off-resonance imaging (ORI), (v) dual-modalities MR imaging and (vi) multifunctional nanoprobes.

Nanostructured magnetic nanocomposites as MRI contrast agents

Carbon based 2-D material graphene oxide (GO) is a promising platform for preparing composites for biomedical applications because of its superior water solubility and low toxicity. Herein, we reported a convenient route to prepare fluorescent nanocomposites incorporating water-soluble GO sheets and Zn doped AgInS2 nanoparticles. According to the study, the photoluminescence of the Zn doped AgInS2 nanoparticles was well maintained after the hybridization using GO. No obvious emission shift was observed and the PL intensity was stable for over three months with negligible quenching. The PEGylated AIZS–GO nanocomposites could be readily up-taken by NIH/3T3 cells (mouse embryonic fibroblast cell line) while no distinct cytotoxicity was observed. The subsequent in vitro cellular imaging of NIH/3T3 cells proved that the as-prepared AIZS–GO–PEG nanocomposites were potential fluorescent probes for biomedical targeting and imaging.

Graphene oxide based fluorescent nanocomposites for cellular imaging

Advanced ceramic materials with complex design have become inseparable from the current engineering applications. Due to the limitation of traditional ceramic processing, ceramic additive manufacturing (AM) which allows high degree of fabrication freedom has gained significant research interest. Among these AM techniques, low-cost robocasting technique is often considered to fabricate complex ceramic components. In this work, aqueous ceramic suspension comprising of commercial nano-sized yttria-stabilized zirconia (YSZ) powder has been developed for robocasting purpose. Both fully and partially stabilized YSZ green bodies with complex morphologies were successfully printed in ambient conditions using relatively low-solid-content ceramic suspensions ( 94% of the theoretical density despite its high linear shrinkage (up to 33%). The microstructure analysis indicated that dense fully and partially stabilized YSZ with grain size as small as 1.40 ± 0.53 and 0.38 ± 0.10 μm can be obtained, respectively. The sintered partially stabilized YSZ solid and porous mesh samples (porosity of macro-pores >45%) exhibited hardness up to 13.29 GPa and flexural strengths up to 242.8 ± 11.4 and 57.3 ± 5.2 MPa, respectively. The aqueous-based ceramic suspension was also demonstrated to be suitable for the fabrication of large YSZ parts with good repeatability.

Erwin Peng

Papers

Ceramic Robocasting: Recent Achievements, Potential, and Future Developments.

Synthesis of Manganese Ferrite/Graphene Oxide Nanocomposites for Biomedical Applications

Nanostructured magnetic nanocomposites as MRI contrast agents

Graphene oxide based fluorescent nanocomposites for cellular imaging

Robocasting of dense yttria-stabilized zirconia structures