Synthesis,Properties,and Biological Application of Perfect Crystal Gold Nanowires:A Review

In the last decade,numerous kinds of nanoscale materials have been created.Their characteristics are critically influenced by their synthetic or fabrication methods.In this review article,we introduce perfect crystal gold nanowires(Au NWs) synthesized by vapor transport method and summarize their material properties and biological applications.Single-crystalline Au NWs having no defects or twins show unique mechanical,electrical,and electrochemical characteristics.Notably,they are exceptionally competent in penetrating cells or tissues with minimum biological damage and in the electrical analysis and manipulation of biological activities in the cells and/or tissues.It is expected that the Au NWs would give us technological breakthrough in diverse applications such as nanoscale functional components as well as new insights in fundamental material science.     

Inspiration from butterfly and moth wing scales: Characterization,modeling, and fabrication

Through billions of years of evolution, nature has created biological materials with remarkable properties. Studying these biological materials can guide the design and fabrication of bio-inspired materials. Many of the complex natural architectures, such as shells, bones, and honeycombs, have been studied to imitate the design and fabrication of materials with improved hardness and stiffness. Recently, an increasing number of researchers have investigated the wings of lepidopterans (butterflies and moths) because these structures may exhibit dazzling colors. Based on previous studies, these iridescent colors are attributable to periodic structures on the scales that constitute the wing surfaces. These complex and diverse structures have recently become a focus of multidisciplinary research due to their promising applications in the display of structural colors, advanced sensors, and solar cells. This review provides a broad overview of the research into these wings, particularly the microstructures in the wing scales. This review investigates the following three fields: structural characterization and optical property analysis of lepidopteran wings, modeling and simulation of the optical properties and microstructure, and the fabrication of artificial structures inspired by these wings.     

Tissue-Mimetic Supramolecular Polymer Networks for Bioelectronics

Addressing the mechanical mismatch between biological tissue and traditional electronic materials remains a major challenge in bioelectronics. While rigidity of such materials limits biocompatibility, supramolecular polymer networks can harmoniously interface with biological tissues as they are soft, wet, and stretchable. Here, an electrically conductive supramolecular polymer network that simultaneously exhibits both electronic and ionic conductivity while maintaining tissue-mimetic mechanical properties, providing an ideal electronic interface with the human body, is introduced. Rational design of an ultrahigh affinity host–guest ternary complex led to binding affinities (>10¹³ M^-2) of over an order of magnitude greater than previous reports. Embedding these complexes as dynamic cross-links, coupled with in situ synthesis of a conducting polymer, resulted in electrically conductive supramolecular polymer networks with tissue-mimetic Young's moduli (<5 kPa), high stretchability (>500%), rapid self-recovery and high water content (>84%). Achieving such properties enabled fabrication of intrinsically-stretchable stand-alone bioelectrodes, capable of accurately monitoring electromyography signals, free from any rigid materials.     

A novel approach via combination of electrospinning and FDM for tri-leaflet heart valve scaffold fabrication

In this paper, a novel combination method of electrospinning and rapid prototyping (RP) fused deposition modeling (FDM) is proposed for the fabrication of a tissue engineering heart valve (TEHV) scaffold. The scaffold preparation consisted of two steps: tri-leaflet scaffold fabrication and heart valve ring fabrication. With the purpose of mimicking the anisotropic mechanical properties of the natural heart valve leaflet, electrospun thermoplastic polyurethane (ES-TPU) was introduced as the tri-leaflet scaffold material. ES-TPU scaffolds can be fabricated to have a well-aligned fiber network, which is important for applications involving mechanically anisotropic soft tissues. We developed ES-TPU scaffolds as heart valve leaflet materials under variable speed conditions and measured fiber alignment by fast Fourier transform (FFT). By using FFT to assign relative alignment values to an electrospun matrix, it is possible to systematically evaluate how different processing variables affect the structure and material properties of a scaffold. TPU was suspended at certain concentrations and electrospun from 1,1,1,3,3,3-hexafluoro-2-propanol onto rotating mandrels (200–3000 rpm). The scaffold morphological property and mechanical anisotropic property are discussed in the paper as a function of fiber diameter and mandrel RPM. The induction of varying degrees of anisotropy imparted distinctive material properties to the electrospun scaffolds. A dynamic optimum design of the heart valve ring graft was constructed by FDM. Fabrication of a 3D heart valve ring was constructed using pro-engineer based on optimum hemodynamic analysis and was converted to an STL file format. The model was then created from PCL which was sewed and glued with electrospun nanofibrous leaflets. This proposed method was proven as a promising fabrication process in fabricating a specially designed graft with the correct physical and mechanical properties.     

Covalent Bonding of Thermoplastics to Rubbers for Printable,Reel‐to‐Reel Processing in Soft Robotics and Microfluidics

The lamination of mechanically stiff structures to elastic materials is prevalent in biological systems and popular in many emerging synthetic systems, such as soft robotics, microfluidics, stretchable electronics, and pop‐up assemblies. The disparate mechanical and chemical properties of these materials have made it challenging to develop universal synthetic procedures capable of reliably adhering to these classes of materials together. Herein, a simple and scalable procedure is described that is capable of covalently laminating a variety of commodity (“off‐the‐shelf”) thermoplastic sheets to silicone rubber films. When combined with laser printing, the nonbonding sites can be “printed” onto the thermoplastic sheets, enabling the direct fabrication of microfluidic systems for actuation and liquid handling applications. The versatility of this approach in generating thin, multifunctional laminates is demonstrated through the fabrication of milliscale soft actuators and grippers with hinged articulation and microfluidic channels with built‐in optical filtering and pressure‐dependent geometries. This method of fabrication offers several advantages, including technical simplicity, process scalability, design versatility, and material diversity. The concepts and strategies presented herein are broadly applicable to the soft robotics, microfluidics, and advanced and additive manufacturing communities where hybrid rubber/plastic structures are prevalent.     

Stimuli–Responsive Mechanoadaptive Elastomeric Composite Materials: Challenges,Opportunities, and New Approaches

Stimuli–responsive mechanoadaptive materials, capable of reversibly changing their mechanical properties when exposed to an external stimulus, are the next generation of smart materials with immense transformative potential for various technological applications. Although the concept of adaptive mechanical properties has been proven for some materials, it remains very challenging for soft elastomeric materials. The aim of this review is to provide new ideas and strategies for the development of mechanoadaptive elastomeric composites using commercial rubber as the matrix polymer. The fundamental question addressed here is as follows: How do the phase-responsive functional fillers alter the mechanical properties? For a given physical network environment, what is the mechanism that gives rise to the stimuli–responsive properties of the resulting composites? Herein, the preparation, structure, and properties of recently developed mechanoadaptive elastomeric materials are summarized. Furthermore, based on their structure–property relationships, plausible applications of these smart materials in various technology-specific applications such as soft robotics, actuators, sensors, smart tires, automotive design, aerospace, etc. are demonstrated with representative examples. Finally, the article critically discusses the existing challenges in the field of mechanoadaptive elastomers in order to provide valuable insights in this area.     

Nanolattices: An Emerging Class of Mechanical Metamaterials

In 1903, Alexander Graham Bell developed a design principle to generate lightweight, mechanically robust lattice structures based on triangular cells; this has since found broad application in lightweight design. Over one hundred years later, the same principle is being used in the fabrication of nanolattice materials, namely lattice structures composed of nanoscale constituents. Taking advantage of the size‐dependent properties typical of nanoparticles, nanowires, and thin films, nanolattices redefine the limits of the accessible material‐property space throughout different disciplines. Herein, the exceptional mechanical performance of nanolattices, including their ultrahigh strength, damage tolerance, and stiffness, are reviewed, and their potential for multifunctional applications beyond mechanics is examined. The efficient integration of architecture and size‐affected properties is key to further develop nanolattices. The introduction of a hierarchical architecture is an effective tool in enhancing mechanical properties, and the eventual goal of nanolattice design may be to replicate the intricate hierarchies and functionalities observed in biological materials. Additive manufacturing and self‐assembly techniques enable lattice design at the nanoscale; the scaling‐up of nanolattice fabrication is currently the major challenge to their widespread use in technological applications.     

Nanoreinforced Hydrogels for Tissue Engineering: Biomaterials that are Compatible with Load‐Bearing and Electroactive Tissues

Given their highly porous nature and excellent water retention, hydrogel‐based biomaterials can mimic critical properties of the native cellular environment. However, their potential to emulate the electromechanical milieu of native tissues or conform well with the curved topology of human organs needs to be further explored to address a broad range of physiological demands of the body. In this regard, the incorporation of nanomaterials within hydrogels has shown great promise, as a simple one‐step approach, to generate multifunctional scaffolds with previously unattainable biological, mechanical, and electrical properties. Here, recent advances in the fabrication and application of nanocomposite hydrogels in tissue engineering applications are described, with specific attention toward skeletal and electroactive tissues, such as cardiac, nerve, bone, cartilage, and skeletal muscle. Additionally, some potential uses of nanoreinforced hydrogels within the emerging disciplines of cyborganics, bionics, and soft biorobotics are highlighted.     

High-frequency micromechanical resonators from aluminium-carbon nanotube nanolaminates

At micro- and nanoscales, materials with high Young's moduli and low densities are of great interest for high-frequency micromechanical resonator devices. Incorporating carbon nanotubes (CNTs), with their unmatched properties, has added functionality to many man-made composites. We report on the fabrication of < or = 100-nm-thick laminates by sputter-deposition of aluminium onto a two-dimensional single-walled CNT network. These nanolaminates--composed of Al, its native oxide Al(2)O(3) and CNTs--are fashioned, in a scalable manner, into suspended doubly clamped micromechanical beams. Dynamic flexural measurements show marked increases in resonant frequencies for nanolaminates with Al-CNT laminae. Such increases, further supported by quasi-static flexural measurements, are partly attributable to enhancements in elastic properties arising from the addition of CNTs. As a consequence, these nanolaminate micromechanical resonators show significant suppression of mechanical nonlinearity and enhanced strength, both of which are advantageous for practical applications and analogous to biological nanocomposites, similarly composed of high-aspect-ratio, mechanically superior mineral platelets in a soft protein matrix.     

A novel approach via combination of electrospinning and FDM for tri-leaflet heart valve scaffold fabrication

In this paper, a novel combination method of electrospinning and rapid prototyping (RP) fused deposition modeling (FDM) is proposed for the fabrication of a tissue engineering heart valve (TEHV) scaffold. The scaffold preparation consisted of two steps: tri-leaflet scaffold fabrication and heart valve ring fabrication. With the purpose of mimicking the anisotropic mechanical properties of the natural heart valve leaflet, electrospun thermoplastic polyurethane (ES-TPU) was introduced as the tri-leaflet scaffold material. ES-TPU scaffolds can be fabricated to have a well-aligned fiber network, which is important for applications involving mechanically anisotropic soft tissues. We developed ES-TPU scaffolds as heart valve leaflet materials under variable speed conditions and measured fiber alignment by fast Fourier transform (FFT). By using FFT to assign relative alignment values to an electrospun matrix, it is possible to systematically evaluate how different processing variables affect the structure and material properties of a scaffold. TPU was suspended at certain concentrations and electrospun from 1,1,1,3,3,3-hexafluoro-2-propanol onto rotating mandrels (200―3000 rpm). The scaffold morphological property and mechanical anisotropic property are discussed in the paper as a function of fiber diameter and mandrel RPM. The induction of varying degrees of anisotropy imparted distinctive material properties to the electrospun scaffolds. A dynamic optimum design of the heart valve ring graft was constructed by FDM. Fabrication of a 3D heart valve ring was constructed using pro-engineer based on optimum hemodynamic analysis and was converted to an STL file format. The model was then created from PCL which was sewed and glued with electrospun nanofibrous leaflets. This proposed method was proven as a promising fabrication process in fabricating a specially designed graft with the correct physical and mechanical properties.     

Nanobiomaterials and Nanoanalysis: Opportunities for Improving the Science to Benefit Biomedical Technologies

Nanomaterials advocated for biomedical applications must exhibit well‐controlled surface properties to achieve optimum performance in complex biological or physiological fluids. Dispersed materials with extremely high specific surface areas require as extensive characterization as their macroscale biomaterials analogues. However, current literature is replete with many examples of nanophase materials, most notably nanoparticles, with little emphasis placed on reporting rigorous surface analysis or characterization, or in formal implementation of surface property standards needed to validate structure‐property relationships for biomedical applications. Correlations of nanophase surface properties with their stability, toxicity and biodistributions are essential for in vivo applications. Surface contamination is likely, given their processing conditions and interfacial energies. Leaching adventitious adsorbates from high surface area nanomaterials is a possible toxicity mechanism. Polydimethylsiloxane (PDMS), long known as a ubiquitous contaminant in clean room conditions, chemical synthesis and microfabrication, remains a likely culprit in nanosystems fabrication, especially in synthesis, soft lithography and contact molding methods. New standards and expectations for analyzing the interfacial properties of nanoparticles and nano‐fabricated technologies are required. Surface science analytical rigor similar to that applied to biomedical devices, nanophases in microelectronics and heterogeneous catalysts should serve as a model for nanomaterials characterization in biomedical technologies.     

Extreme Specific Stiffness Through Interactive Cellular Networks in Bi-Level Micro-Topology Architected Metamaterials

Architected lattice materials, realized through artificial micro-structuring, have drawn tremendous attention lately due to their enhanced mechanical performances in multifunctional applications. However, the research area on the design of artificial microstructures for the modulation of mechanical properties is increasingly becoming saturated due to extensive investigations considering different possibilities of lattice geometry and beam-like network design. Thus, there exists a strong rationale for innovative design at a more elementary level. It can enhance and grow the microstructural space laterally for exploiting the potential of geometries and patterns in multiple length scales, and the mutual interactions thereof. A bi-level design is proposed, where besides having the architected cellular networks at an upper scale, the constituting beam-like members at a lower scale are further topology-engineered for most optimum material utilization. The coupled interaction of beam-level and lattice-level architectures can enhance the specific elastic properties to an extreme extent (up to ≈25 and 20 times, depending on normal and shear modes, respectively), leading to ultra-lightweight multifunctional materials for critical applications under static and dynamic environments.     

Nucleation and Crystallization Phenomena in Glass‐Ceramics

Glass‐ceramics are modern multiphase materials. Different types of glass‐ceramics can be fabricated and their properties tailored to meet specific requirements. It is possible, therefore, to produce glasses that combine desirable optical properties such as transparency and mechanical properties such as strength. Furthermore, this controlled development of glass‐ceramics also enables the fabrication of materials exhibiting properties that are unknown in conventional glasses and ceramics. In this article, the authors discuss nucleation and crystallization phenomena in the controlled development of various glass‐ceramics on the basis of their own work. The reaction mechanisms in the formation of glass‐ceramics and their microstructures are illustrated. In addition, the resulting properties of the glass‐ceramics and their particular applications are presented.     

The quest for stiff,strong and tough hybrid materials: an exhaustive exploration

How to arrange soft materials with strong but brittle reinforcements to achieve attractive combinations of stiffness, strength and toughness is an ongoing and fascinating question in engineering and biological materials science. Recent advances in topology optimization and bioinspiration have brought interesting answers to this question, but they provide only small windows into the vast design space associated with this problem. Here, we take a more global approach in which we assess the mechanical performance of thousands of possible microstructures. This exhaustive exploration gives a global picture of structure–property relationships and guarantees that global optima can be found. Landscapes of optimum solutions for different combinations of desired properties can also be created, revealing the robustness of each of the solutions. Interestingly, while some of the major hybrid designs used in engineering are absent from the set of solutions, the microstructures emerging from this process are reminiscent of materials, such as bone, nacre or spider silk.     

TiO2空心球制备及在染料敏化太阳能电池和锂离子电池中应用的研究进展

空心球结构的半导体氧化物具有密度低、比表面积大、机械和热稳定性好等优点。空心球结构对TiO_2纳米材料的电化学性能有着显著的优化作用,TiO_2空心球作为一种重要的半导体氧化物具有良好的物理和化学性质,在多种领域均表现出潜在的应用价值,制备大小和壳层数均可控的半导体TiO_2空心球已引起了研究者的广泛关注。主要综述了在硬模板、软模板和无模板条件下TiO_2空心球的制备方法;同时还介绍了其在染料敏化太阳能电池和锂离子电池方面的最新研究进展;最后,对TiO_2空心球的可控合成前景进行了展望。     

Self-assembled microdevices driven by muscle

Current procedures for manual extraction of mature muscle tissue in micromechanical structures are time consuming and can damage the living components. To overcome these limitations, we have devised a new system for assembling muscle-powered microdevices based on judicious manipulations of materials phases and interfaces. In this system, individual cells grow and self-assemble into muscle bundles that are integrated with micromechanical structures and can be controllably released to enable free movement. Having realized such an assembly with cardiomyocytes we demonstrate two potential applications: a force transducer able to characterize in situ the mechanical properties of muscle and a self-assembled hybrid (biotic/abiotic) microdevice that moves as a consequence of collective cooperative contraction of muscle bundles. Because the fabrication of silicon microdevices is independent of the subsequent assembly of muscle cells, this system is highly versatile and may lead to the integration of cells and tissues with a variety of other microstructures.     

Al2O3-and ZrO2-modified dental glass ceramics

Castable machinable glass-ceramics have been widely considered as aesthetic materials for dental restoration. In order to extend their applications to bridge-work fabrication, it is necessary to increase their fracture strength and fracture toughness. The effects of ziconia and alumina additions on the properties of glass-ceramics, especially on the mechanical properties were studied. It was found that appropriate addition of alumina increases the bending strength due to aluminium strengthening the glass-ceramic by means of incorporation into the glass network. However, additions of ziconia fail to show promising results on the mechanical property. The evolution of recrystallization and the associated microstructure were also studied and are discussed.     

Merger of structure and material in nacre and bone – Perspectives on de novo biomimetic materials

In contrast to synthetic materials, evolutionary developments in biology have resulted in materials with remarkable structural properties, made out of relatively weak constituents, arranged in complex hierarchical patterns. For instance, nacre from seashells is primarily made of a fragile ceramic, yet it exhibits superior levels of strength and toughness. Structural features leading to this performance consist of a microstructure organized in a hierarchical fashion, and the addition of a small volume fraction of biopolymers. A key to this mechanical performance is the cohesion and sliding of wavy ceramic tablets. Another example is bone, a structural biological material made of a collagen protein phase and nanoscopic mineral platelets, reaching high levels of toughness and strength per weight. The design and fabrication of de novo synthetic materials that aim to utilize the deformation and hardening mechanism of biological materials such as bone or nacre is an active area of research in mechanics of materials. In this review, our current knowledge on microstructure and mechanics of nacre and bone are described, and a review of the fabrication of nacre-inspired artificial and related materials is presented. Both experimental and simulation approaches are discussed, along with specific examples that illustrate the various approaches. We conclude with a broader discussion of the interplay of size effects and hierarchies in defining mechanical properties of biological materials.     

Heterofunctional nanomaterials: fabrication, properties and applications in nanobiotechnology

Nanotechnology and nanoengineering includes a novel class of materials that are gaining significant recognition to pursuit technological/biological advances in diverse fields including, biology, medicine, electronics, engineering etc. due to their unique size- and shape-dependent intrinsic physicochemical, optoelectronic and biological properties. Characteristics such as high surface to volume ratios and quantum confinement results in materials that are qualitatively different from their bulk counterparts. These properties not only make them suitable for numerous applications in existing and emerging technologies, but also have outstanding role in many fields that provide inspiration for their fabrication. In Today's trend nanotechnology is spreading vigorously where researchers all over the world are focusing towards their synthesis and applications. Therefore, this review is helpful for the researchers in the field of nanobiotechnology/nanomedicine, providing a brief overview of nanotechnology, covering nanomaterial synthesis methods (with emphasis on environmentally benign greener approaches), their properties, and applications; such as drug delivery, bio-labeling, nanotoxicity etc. The influence of synthesis methods and surface coatings/stabilizing agents and their subsequent applications is discussed, and a broad outline on the biomedical applications into which they have been implemented is also presented.     

液体弹珠的微流体操作及工程应用

微流体技术是一种精确操控和检测微量流体的新兴技术,广泛应用于生物、化学、材料等领域的实验及工程中.液体弹珠作为一种新兴的数字微流体平台在近几年快速发展.它是一种将疏水的微纳米级颗粒包裹在液滴表面形成的软物质,体积通常在几微升到几百微升之间.区别于构建特殊表面微结构或化学改性制备的超疏水表面,液体弹珠是通过颗粒层阻隔内部液体与载体的微观接触,构建类似于莱顿弗罗斯特液滴的结构来实现微量液体在固体或液体表面不润湿且稳定存在的目的.目前的研究已经证明液体弹珠拥有独特优越的物理性能,如液体弹珠表面的颗粒层将固-液接触转化为固-固和固-气接触,因此具有不粘的特性,与载体表面的摩擦很小,在很小的外力作用下就可以实现灵活移动且不污染弹珠内的液体和载体.当表面颗粒呈多层且致密分布时也并非完全阻隔外界环境,在很大程度上能够减缓内部液体的蒸发且具有良好的气体渗透性,而且液体弹珠具有较好的稳固性,往往能够承受30％的可逆线性弹性形变,这些性能使液体弹珠可以作为理想的数字微流体平台.液体弹珠的原材料十分丰富,从而决定了其性状具有灵活的可调控性,所用颗粒的疏水性和形状会直接影响液体弹珠的力学性能,例如棒状颗粒包裹的液体弹珠具有更大的刚度,链状颗粒包裹的液体弹珠具有优越的弹性性能.颗粒的化学性质可以按需赋予液体弹珠不同的响应特性,从而衍生出多种操控手段,主要方式包括静电力、磁力、自推进、光辐射、温度、超声等,完成液体弹珠的精确移动、定位、颗粒层开启和关闭以及释放内部液体的操作.以上特性使液体弹珠能够应用于各种工程中,在细胞组织和微生物的培养以及微型化学反应器方面具有很好的应用前景,同时还被广泛应用于传感器、制药和精密仪器等领域,例如光电传感、污水检测、微型胶囊制备、构建纳米复合透镜以及精准电化学沉积等.同时液体弹珠制备方法较简单,无需复杂仪器设备,具有很高的经济效益.本文结合近年来液体弹珠相关研究的发展现状介绍了液体弹珠的制备方法、结构特点、材料和不同于纯液滴的性质主要包括有效表面张力、力学稳定性和蒸发速率,归纳了几种主流操作控制液体弹珠移动和释放的手段并分析优势与不足,总结了目前液体弹珠在工程上的主要应用并对其未来的发展趋势和应用前景进行展望.