从低维到高维的仿生材料制备及其应用进展

经过数十亿年的进化,自然界中的生物材料表现出许多卓越的性质和独特的功能。这些生物材料通常是由生物体内的有限组分在温和条件下组装而成,其优异的性能在很大程度上来源于复杂的多级结构,例如含邻苯二酚单元的贻贝粘附蛋白具有普适的强粘附力,珠-线结构的蜘蛛丝具有优异机械性能和集水能力,空心结构的北极熊毛发具有隔热保温作用,规则微纳结构的蝴蝶翅膀显示多彩的颜色,梯度多孔结构的柚子皮具有优异的阻尼减震效果等。以自然界的设计原理为灵感制造人工材料在材料科学和工程领域受到了极大关注,过去数10年,这方面的研究成果不胜枚举。总结了仿生材料在结构仿生方面的研究进展,选取了几个从低维到高维尺度上的典型例子概述了仿生材料的结构和功能之间的关系。     

25th Anniversary Article: Artificial Carbonate Nanocrystals and Layered Structural Nanocomposites Inspired by Nacre: Synthesis,Fabrication and Applications

Rigid biological systems are increasingly becoming a source of inspiration for the fabrication of next generation advanced functional materials due to their diverse hierarchical structures and remarkable engineering properties. Among these rigid biomaterials, nacre, as the main constituent of the armor system of seashells, exhibiting a well‐defined ‘brick‐and‐mortar’ architecture, excellent mechanical properties, and interesting iridescence, has become one of the most attractive models for novel artificial materials design. In this review, recent advances in nacre‐inspired artificial carbonate nanocrystals and layered structural nanocomposites are presented. To clearly illustrate the inspiration of nacre, the basic principles relating to plate‐like aragonite single‐crystal growth and the contribution of hierarchical structure to outstanding properties in nacre are discussed. The inspiration of nacre for the synthesis of carbonate nanocrystals and the fabrication of layered structural nanocomposites is also discussed. Furthermore, the broad applications of these nacre inspired materials are emphasized. Finally, a brief summary of present nacre‐inspired materials and challenges for the next generation of nacre‐inspired materials is given.     

Immobilization of biomaterials to nano-assembled films (self-assembled monolayers, Langmuir-Blodgett films, and layer-by-layer assemblies) and their related functions

For utilization of highly sophisticated functions of biomaterials in nano-scale functional systems, immobilization of biomaterials on artificial devices such as electrodes via thin film technology is one of the most powerful strategies. In this review, we focus on three major organic ultrathin films, self-assembled monolayers (SAM), Langmuir-Blodgett (LB) films, and layer-by-layer (LBL) assemblies, and from the viewpoints of biomaterial immobilization, typical examples and recent progresses in these film technologies are described. The SAM method allows facile contact between biomaterials and man-made devices, and well used for bio-related sensors. In addition, recent micro-fabrication techniques such as micro-contact printing and dip-pen nanolithography were successfully applied to preparation of biomaterial patterning. A monolayer at the air-water interface, which is a unit structure of LB films, provides a unique environment for recognition of aqueous biomaterials. Recognition and immobilization of various biomaterials including nucleotides, nucleic acid bases, amino acids, sugars, and peptides were widely investigated. The LB film can be also used for immobilization of enzymes in an ultrathin film on an electrode, resulting in sensor application. The LBL assembling method is available for wide range of biomaterials and provides great freedom in designs of layered structures. These advantages are reflected in preparation of thin-film bio-reactors where multiple kinds of enzymes sequentially operate. LBL assemblies were also utilized for sensors and drug delivery systems. This kind of assembling structures can be prepared on micro-size particle and very useful for preparation of hollow capsules with biological functions.     

3D Printing of Ultralight Biomimetic Hierarchical Graphene Materials with Exceptional Stiffness and Resilience

Biological materials with hierarchical architectures (e.g., a macroscopic hollow structure and a microscopic cellular structure) offer unique inspiration for designing and manufacturing advanced biomimetic materials with outstanding mechanical performance and low density. Most conventional biomimetic materials only benefit from bioinspired architecture at a single length scale (e.g., microscopic material structure), which largely limits the mechanical performance of the resulting materials. There exists great potential to maxime the mechanical performance of biomimetic materials by leveraging a bioinspired hierarchical structure. An ink‐based three‐dimensional (3D) printing strategy to manufacture an ultralight biomimetic hierarchical graphene material (BHGMs) with exceptionally high stiffness and resilience is demonstrated. By simultaneously engineering 3D‐printed macroscopic hollow structures and constructing an ice‐crystal‐induced cellular microstructure, BHGMs can achieve ultrahigh elasticity and stability at compressive strains up to 95%. Multiscale finite element analyses indicate that the hierarchical structures of BHGMs effectively reduce the macroscopic strain and transform the microscopic compressive deformation into the rotation and bending of the interconnected graphene flakes. This 3D printing strategy demonstrates the great potential that exists for the assembly of other functional materials into hierarchical cellular structures for various applications where high stiffness and resilience at low density are simultaneously required.     

25th Anniversary Article: Rational Design and Applications of Hydrogels in Regenerative Medicine

Hydrogels are hydrophilic polymer‐based materials with high water content and physical characteristics that resemble the native extracellular matrix. Because of their remarkable properties, hydrogel systems are used for a wide range of biomedical applications, such as three‐dimensional (3D) matrices for tissue engineering, drug‐delivery vehicles, composite biomaterials, and as injectable fillers in minimally invasive surgeries. In addition, the rational design of hydrogels with controlled physical and biological properties can be used to modulate cellular functionality and tissue morphogenesis. Here, the development of advanced hydrogels with tunable physiochemical properties is highlighted, with particular emphasis on elastomeric, light‐sensitive, composite, and shape‐memory hydrogels. Emerging technologies developed over the past decade to control hydrogel architecture are also discussed and a number of potential applications and challenges in the utilization of hydrogels in regenerative medicine are reviewed. It is anticipated that the continued development of sophisticated hydrogels will result in clinical applications that will improve patient care and quality of life.     

Biomaterial‐Based “Structured Opals” with Programmable Combination of Diffractive Optical Elements and Photonic Bandgap Effects

Naturally occurring iridescent systems produce brilliant color displays through multiscale, hierarchical assembly of structures that combine reflective, diffractive, diffusive, or absorbing domains. The fabrication of biopolymer‐based, hierarchical 3D photonic crystals through the use of a topographical templating strategy that allows combined optical effects derived from the interplay of predesigned 2D and 3D geometries is reported here. This biomaterials‐based approach generates 2D diffractive optics composed of 3D nanophotonic lattices that allow simultaneous control over the reflection (through the 3D photonic bandgap) and the transmission (through 2D diffractive structuring) of light with the additional utility of being constituted by a biocompatible, implantable, edible commodity textile material. The use of biopolymers allows additional degrees of freedom in photonic bandgap design through directed protein conformation modulation. Demonstrator structures are presented to illustrate the lattice multifunctionality, including tunable diffractive properties, increased angle of view of photonic crystals, color‐mixing, and sensing applications.     

自组装制备有机/无机层状复合材料

自然界中形成的生物材料在结构和性能上具有优异的配备性。模仿生物矿化的形成机制,利用自组装原理能够仿生合成出性能优良和具有多级结构特点的有机/无机界面层状复合材料。本文在总结近年来最新研究的成果上,简要介绍了自组装和生物矿化的机理,重点阐述了基于无机相层的自组装和以有机大分子为模板自组装制备有机／无机层状复合材料两种合成连径,并对未来的发展趋势做了展望。     

Histidine as a key modulator of molecular self-assembly: Peptide-based supramolecular materials inspired by biological systems

Histidine, a versatile proteinogenic amino acid, plays a broad range of roles in all living organisms and behaves as a key mediator of the interactions of biomolecules with inorganic constituents. The self-assembly of histidine-rich peptides and proteins is critical in biology, as the histidine unit is both a multifunctional regulator and an ideal motif for the construction of complex biological structures. In particular, non-covalent interactions between the imidazole ring and other molecular building blocks and metal ions are routinely employed to generate these complexes. Therefore, this strategy can be duplicated in an artificial context to create sophisticated bioactive materials. In this review, we first highlight a clear perspective of the bio-inspired design strategies which can replicate the hierarchical structure of biological systems allowing the engineering of the supramolecular self-assembly of histidine-functionalized peptides. We further summarize advancements in the field of peptide supramolecular structures incorporating histidine residues in the peptide backbone to generate organized functional supramolecular biomaterials with customizable features. We also discuss significant advances and future prospects in supramolecular self-assembly of histidine-functionalized peptides, as well as provide an overview of advanced techniques for the fabrication of histidine-based biomaterials for bio-nanotechnology, optoelectronic engineering, and biomedicine. Overall, artificial supramolecular materials based on histidine functionalized peptides, motivated by the intriguing properties discovered in natural proteins, bear the potential to boost the creation of sustainable bio-inspired materials.     

Chemically Modified Silk Proteins

Silks are of central importance as smart natural biomaterials and are attracting increasing attention for their biomimetic potential due to their sophisticated molecular structure, self‐assembly mechanism, impressive mechanical properties, biocompatibility, and biodegradability. The versatility of silk proteins (SP) allows the chemical modification of silk‐based materials with diverse morphologies under harsh conditions. The chemical modification of amino acids within SP enables the expanded generation of new biomaterials and the extension of their potential functional applications. The authors review the current chemical modification strategies and routes for the functionalization of SP.

     

Inkjet Printing of Patterned,Multispectral, and Biocompatible Photonic Crystals

Patterning of photonic crystals to generate rationally designed color‐responsive materials has drawn considerable interest because of promising applications in optical storage, encryption, display, and sensing. Here, an inkjet‐printing based strategy is presented for noncontact, rapid, and direct approaches to generate arbitrarily patterned photonic crystals. The strategy is based on the use of water‐soluble biopolymer‐based opal structures that can be reformed with high resolution through precise deposition of fluids on the photonic crystal lattice. The resulting digitally designed photonic lattice formats simultaneously exploit structural color and material transience opening avenues for information encoding and combining functions of optics, biomaterials, and environmental interfaces in a single device.     

Recent Progress in Biomimetic Additive Manufacturing Technology: From Materials to Functional Structures

Nature has developed high‐performance materials and structures over millions of years of evolution and provides valuable sources of inspiration for the design of next‐generation structural materials, given the variety of excellent mechanical, hydrodynamic, optical, and electrical properties. Biomimicry, by learning from nature's concepts and design principles, is driving a paradigm shift in modern materials science and technology. However, the complicated structural architectures in nature far exceed the capability of traditional design and fabrication technologies, which hinders the progress of biomimetic study and its usage in engineering systems. Additive manufacturing (three‐dimensional (3D) printing) has created new opportunities for manipulating and mimicking the intrinsically multiscale, multimaterial, and multifunctional structures in nature. Here, an overview of recent developments in 3D printing of biomimetic reinforced mechanics, shape changing, and hydrodynamic structures, as well as optical and electrical devices is provided. The inspirations are from various creatures such as nacre, lobster claw, pine cone, flowers, octopus, butterfly wing, fly eye, etc., and various 3D‐printing technologies are discussed. Future opportunities for the development of biomimetic 3D‐printing technology to fabricate next‐generation functional materials and structures in mechanical, electrical, optical, and biomedical engineering are also outlined.     

Modulation of Multiscale 3D Lattices through Conformational Control: Painting Silk Inverse Opals with Water and Light

Structural proteins from naturally occurring materials are an inspiring template for material design and synthesis at multiple scales. The ability to control the assembly and conformation of such materials offers the opportunity to define fabrication approaches that recapitulate the dimensional hierarchy and structure–function relationships found in nature. A simple and versatile directed assembly method of silk fibroin, which allows the design of structures across multiple dimensional scales by generating and tuning structural color in large‐scale, macro defect‐free colloidally assembled 3D nanostructures in the form of silk inverse opals (SIOs) is reported. This approach effectively combines bottom‐up and top‐down techniques to obtain control on the nanoscale (through silk conformational changes), microscale (through patterning), and macroscale (through colloidal assembly), ultimately resulting in a controllable photonic lattice with predefined spectral behavior, with a resulting palette spanning almost the entire visible range. As a demonstration of the approach, examples of “multispectral” SIOs, paired with theoretical calculations and analysis of their response as a function of changes of lattice constants and refractive index contrast are illustrated.     

Patterning Porous Oxides within Microchannel Networks

A continuing challenge for materials chemists and engineers is the ability to create multifunctional composite structures with well‐defined superimposed structural order from nanometer to micrometer length scales. Materials with three‐dimensional structures ordered over multiple length scales can be prepared by carrying out colloidal crystallization and inorganic/organic cooperative self‐assembly within microchannel networks. The resulting materials show hierarchical ordering over several discrete and tunable length scales ranging from several nanometers to micrometers. These patterned porous materials hold promise for use as advanced catalysts, sensors, low‐k dielectrics, optoelectronic and integrated photonic crystal devices.     

Tuning Surface Properties of Low Dimensional Materials via Strain Engineering

The promising and versatile applications of low dimensional materials are largely due to their surface properties, which along with their underlying electronic structures have been well studied. However, these materials may not be directly useful for applications requiring properties other than their natal ones. In recent years, strain has been shown to be an additionally useful handle to tune the physical and chemical properties of materials by changing their geometric and electronic structures. The strategies for producing strain are summarized. Then, the electronic structure of quasi‐two dimensional layered non‐metallic materials (e.g., graphene, MX2, BP, Ge nanosheets) under strain are discussed. Later, the strain effects on catalytic properties of metal‐catalyst loaded with strain are focused on. Both experimental and computational perspectives for dealing with strained systems are covered. Finally, an outlook on engineering surface properties utilizing strain is provided.     

Weak formulation of Biot's equations in cylindrical coordinates with harmonic expansion in the circumferential direction

A weak symmetric form of Biot's equation in cylindrical coordinates with a spatial Fourier expansion in the circumferential direction is presented. The solid phase displacement and the pore pressure are used as the dependent variables. The original three‐dimensional boundary value problem is here, due to the orthogonality of the harmonic functions and the rotationally symmetric geometry, decomposed into independent two‐dimensional problems, one for each harmonic function. This formulation provides a computationally efficient procedure for vibroacoustic finite element modelling of rotationally symmetric three‐dimensional multilayered structures including porous elastic materials. By numerical simulations, this method is compared with, and verified against, full three‐dimensional Cartesian coordinate system finite element models. Copyright © 2009 John Wiley & Sons, Ltd.     

Polymeric Graphene Bulk Materials with a 3D Cross‐Linked Monolithic Graphene Network

Although many great potential applications are proposed for graphene, till now none are yet realized as a stellar application. The most challenging issue for such practical applications is to figure out how to prepare graphene bulk materials while maintaining the unique two‐dimensional (2D) structure and the many excellent properties of graphene sheets. Herein, such polymeric graphene bulk materials containing three‐dimensional (3D) cross‐linked networks with graphene sheets as the building unit are reviewed. The theoretical research on various proposed structures of graphene bulk materials is summarized first. Then, the synthesis or fabrication of these graphene materials is described, which comprises mainly two approaches: chemical vapor deposition and cross‐linking using graphene oxide directly. Finally, some exotic and exciting potential applications of these graphene bulk materials are presented.     

Assemblies of biomaterials in mesoporous media

Assemblies of biomaterials onto mechanically stable inorganic structure are advantageous for the practical applications because of the potential to improve the stability and performance of biomaterials in the biocatalytic processes. Among many kinds of inorganic materials, mesoporous materials such as mesoporous silica and mesoporous carbon have attracted special attention owing to their well-defined structures and perfectly controlled pore geometries, which would lead to unique functions such as size selective adsorption of biomaterials. In the first part of this review, adsorption behaviors of proteins, enzymes, vitamins, and amino acids in aqueous solutions onto mesoporous media are systematically explained. Pore geometries (pore diameter and volume) of mesoporous materials are the crucial factors for the size selective adsorption of biomaterials, especially proteins, which often have a size comparable to pore dimension. The studies on the adsorption of biomaterials on the mesoporous carbon reveal that hydrophobic interaction between guest molecules and surface of the mesoporous materials is an important parameter which controls the amount of biomaterials adsorption. Enhanced adsorption of biomaterials was commonly observed at their isoelectric point, where electrostatic repulsion is minimized between the biomaterials. In addition, several functions such as biomolecular separation, reactor function, controlled drug release, and photochemical properties are discussed in the latter sections. Studies on assemblies of biomaterials in mesoporous media are still in initial stage, but the development of appropriately designed mesoporous materials would powerfully promote researches in these fascinating unexplored fields.     

An X‐FEM and level set computational approach for image‐based modelling: Application to homogenization

The advances in material characterization by means of imaging techniques require powerful computational methods for numerical analysis. The present contribution focuses on highlighting the advantages of coupling the extended finite elements method and the level sets method, applied to solve microstructures with complex geometries. The process of obtaining the level set data starting from a digital image of a material structure and its input into an extended finite element framework is presented. The coupled method is validated using reference examples and applied to obtain homogenized properties for heterogeneous structures. Although the computational applications presented here are mainly two‐dimensional, the method is equally applicable for three‐dimensional problems. Copyright © 2010 John Wiley & Sons, Ltd.     

Nanoimprint Lithography for Functional Three‐Dimensional Patterns

Nanoimprint lithography (NIL) is viewed as an alternative nanopatterning technique to traditional photolithography, allowing micrometer‐scale and sub‐hundred‐nanometer resolution as well as three‐dimensional structure fabrication. In this Research News article we highlight current activities towards the use of NIL in patterning active or functional materials, and the application of NIL in patterning materials that present both chemistry and structure/topo­graphy in the patterned structures, which provide scaffolds for subsequent manipulation. We discuss and give examples of the various materials and chemistries that have been used to create functional patterns and their implication in various fields as electronic and magnetic devices, optically relevant structures, biologically important surfaces, and 3D particles.     

Nanomechanical and Charge Transport Properties of Two‐Dimensional Atomic Sheets

The materials properties of graphene and other two‐dimensional atomic sheets are influenced by atomic‐scale defects, mechanical deformation, and microstructures. Thus, for graphene‐based applications, it is essential to uncover the roles of atomic‐scale defects and domain structures of two‐dimensional layers in charge transport properties. This review highlights recent studies of nanomechanical and charge transport properties of two‐dimensional atomic sheets, including graphene, MoS₂, and boron nitrides. Because of intrinsic structural differences, two‐dimensional atomic sheets give rise to unique nanomechanical properties, including a dependence on layer thickness and chemical modification that is in contrast to three‐dimensional continuum media. Mapping of local conductance and nanomechanical properties on a graphene layer can be used to image the domain and microstructures of two‐dimensional atomic layers. This paper also reviews recent experimental and theoretical findings on the role of bending, defects, and microstructures on nanomechanical and transport properties of graphene‐derived materials.