Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346

Gold nanoparticles: assembly, supramolecular chemistry, quantum-size-related properties, and applications toward biology, catalysis, and nanotechnology.

Nanomaterials are engineered structures with at least one dimension of 100 nanometers or less. These materials are increasingly being used for commercial purposes such as fillers, opacifiers, catalysts, semiconductors, cosmetics, microelectronics, and drug carriers. Materials in this size range may approach the length scale at which some specific physical or chemical interactions with their environment can occur. As a result, their properties differ substantially from those bulk materials of the same composition, allowing them to perform exceptional feats of conductivity, reactivity, and optical sensitivity. Possible undesirable results of these capabilities are harmful interactions with biological systems and the environment, with the potential to generate toxicity. The establishment of principles and test procedures to ensure safe manufacture and use of nanomaterials in the marketplace is urgently required and achievable.

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Toxic Potential of Materials at the Nanolevel

Synthesis and surface engineering of iron oxide nanoparticles for biomedical applications

Rapid growth in nanotechnology is increasing the likelihood of engineered nanomaterials coming into contact with humans and the environment. Nanoparticles interacting with proteins, membranes, cells, DNA and organelles establish a series of nanoparticle/biological interfaces that depend on colloidal forces as well as dynamic biophysicochemical interactions. These interactions lead to the formation of protein coronas, particle wrapping, intracellular uptake and biocatalytic processes that could have biocompatible or bioadverse outcomes. For their part, the biomolecules may induce phase transformations, free energy releases, restructuring and dissolution at the nanomaterial surface. Probing these various interfaces allows the development of predictive relationships between structure and activity that are determined by nanomaterial properties such as size, shape, surface chemistry, roughness and surface coatings. This knowledge is important from the perspective of safe use of nanomaterials.

Understanding biophysicochemical interactions at the nano–bio interface

http://sistemas.eel.usp.br/docentes/arquivos/2166002/1234Nb/Geetha-review2009.pdf

Ti based biomaterials, the ultimate choice for orthopaedic implants – A review

Nanoceramic surface roughness enhances osteoblast and osteoclast functions for improved orthopaedic/dental implant efficacy

In an attempt to simulate the microstructure and mechanical properties of natural bone, novel nanoceramic/polymer composite formulations were fabricated and characterized with respect to their cytocompatibility and mechanical properties. The bending moduli of nanocomposite samples of either poly(L-lactic acid) (PLA) or poly(methyl methacrylate) (PMMA) with 30, 40, and 50 wt % of nanophase (<100 nm) alumina, hydroxyapatite, or titania loadings were significantly (p < 0.05) greater than those of pertinent composite formulations with conventional, coarser grained ceramics. The nanocomposite bending moduli were 1–2 orders of magnitude larger than those of the homogeneous, respective polymer. For example, compared with 0.06 GPa for the 100% PLA, the bending modulus of 50/50 nanophase alumina/PLA composites was 3.5 GPa. Osteoblast adhesion on the surfaces of the nanophase alumina/PLA composites increased as a function of the nanophase ceramic content. Most importantly, osteoblast adhesion on the 50/50 nanophase alumina/PLA substrates was similar to that observed on the 100% nanophase ceramic substrates. Similar trends of osteoblast adhesion were observed on the surfaces of the nanophase titania/polymer and nanophase hydroxyapaptite/polymer composites that were tested. In contrast, fibroblast adhesion on the nanophase composites was either similar or lower than that observed on the conventional composites with either PLA or PMMA and minimum on all tested neat nanophase substrates. The calcium content in the extracellular matrix of cultured osteoblasts was also enhanced on the nanoceramic/PLA composite substrates tested as a function of the nanophase ceramic loading and duration of cell culture. The results of the present in vitro study provide evidence that nanoceramic/polymer composite formulations are promising alternatives to conventional materials because they can potentially be designed to match the chemical, structural, and mechanical properties of bone tissue in order to overcome the limitations of the biomaterials currently used as bone prostheses. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 72A: 98–106, 2005

Evaluation of cytocompatibility and bending modulus of nanoceramic/polymer composites.

The synthesis of nanometer-sized atomic clusters of metals and ceramics by means of the gas-condensation method, followed by their in situ consolidation under high-vacuum conditions, has resulted in a new class of ultrafine-grained interface materials. These nanophase materials, with average grain sizes presently ranging from about 5 to 25 nm, exhibit properties that are often rather different and improved relative to those of conventional materials. In addition, their processing characteristics appear in some cases to be greatly improved over their conventional coarser grained counterparts. The synthesis of nanophase materials by means of cluster assembly under controlled conditions should enable the design of materials, heretofore unavailable, with improved or unique properties. As such, it is likely that the combination of new capabilities to synthesize, characterize, anc) engineer the properties of materials based on the assembly of atomic clusters will significantly impact materials science and engineering in the coming years. The assembly of matter by the consolidation of gas-condensed atomic clusters is probably as old as the universe itself, since this is thought to be the way condensed matter formed during the cooling period that followed the “big bang,” as evidenced by the structure of the earliest meteorites. The modern synthesis of ultrafine-grained materials by the in situ consolidation of nanometer-sized gas-condensed ultrafine particles or atomic clusters, however, was first suggested by Gleiter.

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Nanophase Materials Assembled from Atomic Clusters

Nanocrystalline, single-phase undoped ZnO was sintered to 95%–98% of theoretical density at 650°–700°C, using pressureless isothermal sintering. The density increased very rapidly at 500°–600°C, remained constant with sintering temperature until ∼900°C, and then decreased slightly. The estimated activation energy for densification at 600°–700°C (275 kJ/mol) was comparable to grain-growth activation energies previously reported for microcrystalline ZnO but much greater than the grain-growth activation energy measured in the present work. A bimodal microstructure, consisting of nanocrystalline grains within larger ensembles (“supergrains”), was observed, and both modes grew as the sintering temperature increased. The grain-growth activation energy for the nanocrystalline grains was extremely low, ∼20 kJ/mol. The activation energy for the growth of the supergrains depended strongly on temperature but was ∼54 kJ/mol at >500°C. The important mechanisms probably are rearrangement of the nanoparticle grains, with simultaneous surface and boundary diffusion, and vapor transport above 900°C.

Sintering and Characterization of Nanophase Zinc Oxide

The promise of nanobiomaterials for diagnostic and therapeutic biomedical applications has been widely reported throughout the scientific community, and great strides have been made in those directions. And yet, the translation of nanomaterial-based therapeutics to clinical applications remains an elusive target. Many challenges have blocked the usage of nanomaterials in biomedicine, including potential toxicity, immunogenicity, and decreased efficacy. In order to overcome some of these issues, detailed studies have been undertaken to understand fundamental interactions between nanomaterials and the biological environment. In particular, recent developments in nanoparticle synthesis, a better understanding and control over nanoparticle surface chemistry, as well as the organization of that chemistry on the nanoparticle surface, has allowed researchers to begin to understand how spatial arrangement of atomic and molecular species at an interface can affect protein adsorption, structure, and subsequent biol...

Richard W. Siegel

Papers

Nanoceramic surface roughness enhances osteoblast and osteoclast functions for improved orthopaedic/dental implant efficacy

Evaluation of cytocompatibility and bending modulus of nanoceramic/polymer composites.

Nanophase Materials Assembled from Atomic Clusters

Sintering and Characterization of Nanophase Zinc Oxide

Engineering Nanomaterials for Biomedical Applications Requires Understanding the Nano-Bio Interface: A Perspective.