Biological and bioinspired materials: Structure leading to functional and mechanical performance

Nature has achieved materials with properties and mechanisms that go far beyond the current know-how of the engineering-materials industry.The remarkable efficiency of biological materials,such as their exceptional properties that rely on weak constituents,high performance per unit mass,and diverse functionalities in addition to mechanical properties,has been mostly attributed to their hierarchical structure.Key strategies for bioinspired materials include formulating the fundamental understanding of biological materials that act as inspiration,correlating this fundamental understanding to engineering needs/problems,and fabricating hierarchically structured materials with enhanced properties accordingly.The vast,existing literature on biological and bioinspired materials can be discussed in terms of functional and mechanical aspects.Through essential representative properties and materials,the development of bioinspired materials utilizes the design strategies from biological systems to innovatively augment material performance for various practical applications,such as marine,aerospace,medical,and civil engineering.Despite the current challenges,bioinspired materials have become an important part in promoting innovations and breakthroughs in the modern materials industry.

Bioinspired fish-scale-like magnesium composites strengthened by contextures of continuous titanium fibers:Lessons from nature

Natural fish scales demonstrate outstanding mechanical efficiency owing to their elaborate architectures and thereby may serve as ideal prototypes for the architectural design of man-made materials.Here bioinspired magnesium composites with fish-scale-like orthogonal plywood and double-Bouligand architectures were developed by pressureless infiltration of a magnesium melt into the woven contextures of continuous titanium fibers.The composites exhibit enhanced strength and work-hardening ability compared to those estimated from a simple mixture of their constituents at ambient to elevated temperatures.In particular,the double-Bouligand architecture can effectively deflect cracking paths,alleviate strain localization,and adaptively reorient titanium fibers within the magnesium matrix during the deformation of the composite,representing a successful implementation of the property-optimizing mechanisms in fish scales.The strength of the composites,specifically the effect of their bioinspired architectures,was interpreted based on the adaptation of classical laminate theory.This study may offer a feasible approach for developing new bioinspired metal-matrix composites with improved performance and provide theoretical guidance for their architectural designs.

Nature-inspired materials and designs for flexible lithium-ion batteries

Flexible lithium-ion batteries(FLBs)are of critical importance to the seamless power supply of flexible and wearable electronic devices.However,the simultaneous acquirements of mechanical deformability and high energy density remain a major challenge for FLBs.Through billions of years of evolutions,many plants and animals have developed unique compositional and structural characteristics,which enable them to have both high mechanical deformability and robustness to cope with the complex and stressful environment.Inspired by nature,many new materials and designs emerge recently to achieve mechanically flexible and high storage capacity of lithiumion batteries at the same time.Here,we summarize these novel FLBs inspired by natural and biological materials and designs.We first give a brief introduction to the fundamentals and challenges of FLBs.Then,we highlight the latest achievements based on nature inspiration,including fiber-shaped FLBs,origami and kirigami-derived FLBs,and the nature-inspired structural designs in FLBs.Finally,we discuss the current status,remaining challenges,and future opportunities for the development of FLBs.This concise yet focused review highlights current inspirations in FLBs and wishes to broaden our view of FLB materials and designs,which can be directly“borrowed”from nature.

Inorganic ionic polymerization:A bioinspired strategy for material preparation

Bioinspired materials with excellent properties have attracted intense interests of scientists,and the methodology for rationally design of these materials is crucially important.This review briefly introduces our recent achievements on inorganic ionic polymerization for bioinspired material preparation.The inorganic ionic polymerization realized the assembly of inorganic ions in a way similar to the polymerization in polymer chemistry,overcoming the limitation by classical nucleation pathway.It enabled the moldable construction of inorganic minerals and even the reconstruction of enamel tissue,which commonly only achieved by biomineralization.In the presence of organic molecules,the inorganic ionic polymerization could participate in the organic polymerization,resulting in hybrids with molecular-scaled organic-inorganic homogeneity.And furthermore,under the regulation of bio-inspired molecules,the condensed state of the assembled inorganic ions could show unusual behaviors:such as adding the flexibility to commonly fractal inorganic minerals,and flowability to solid mineral particles.It enabled the production of flexible mineral materials as plastic substitute,and the extrusion forming of moldable minerals under room temperature.The inorganic ionic polymerization demonstrated a promising way to synthesize inorganics in a more rational way,which may shed light on more advanced bio-inspired and biomimetic material.

Smart dielectric materials for next-generation electrical insulation

Smart dielectric materials with bioinspired and autonomous functions are expected to be designed and fabricated for nextgeneration electrical insulation.Similar to organisms,such dielectrics with selfadaptive,selfreporting,and selfhealing capabilities can be employed to avoid,diagnose,and repair electrical damage to prevent catastrophic failure and even a blackout.Compared with traditional dielectrics,the utilization of smart materials not only increases the stability and durability of power apparatus but also reduces the costs of production and manufacturing.In this review,researches on selfadaptive,selfreporting,and selfhealing dielectrics in the field of electrical insulation,and illuminating studies on smart polymers with autonomous functions in other fields are both introduced.The principles,methods,mechanisms,applications,and challenges of these materials are also briefly presented.

Daytime Radiative Cooling:Artificial and Bioinspired Strategies

Traditional cooling systems have been posing a significant challenge to the global energy crisis and climate change due to the high energy consumption of the cooling process.In recent years,the emerging daytime radiative cooling provides a promising solution to address the bottleneck of traditional cooling technology by passively dissipating heat radiation to outer space without any energy consumption through the atmospheric transparency window(8~13μm).Whereas its stringent optical criteria require sophisticated and high cost fabrication producers,which hinders the applicability of radiative cooling technology.Many efforts have been devoted to develop high-efficiency and low-cost daytime radiative cooling technologies for practical application,including the nanophotonics based artificial strategy and bioinspired strategy.In order to systematically summarize the development and latest advance of daytime radiative cooling to help developing the most promising approach,here in this paper we will review and compare the two typical strategies on exploring the prospect approach for applicable radiative cooling technology.We will firstly sketch the fundamental of radiative cooling and summarize the common methods for construction radiative cooling devices.Then we will put an emphasis on the summarization and comparison of the two strategies for designing the radiative cooling device,and outlook the prospect and extending application of the daytime radiative cooling technology.

Energy-absorbing porous materials:Bioinspired architecture and fabrication

Energy-absorbing materials are widely used in transportations,sports,and the military applications.Particularly,porous materials,including natural and artificial materials,have attracted tremendous attentions due to their light weight and excellent energy absorption capability.This review summarizes the recent progresses in the natural and artificial energy-absorbing porous materials.First,we review the typical natural porous materials including cuttlebone,bighorn sheep horn,pomelo peel,and sunflower stem pith.The architectures,energy absorption abilities,and mechanisms of these typical natural materials and their bioinspired materials are summarized.Then,we provide a review on the fabrication methods of artificial energy-absorbing porous materials,such as conventional foaming and three-dimensional(3D)printing.Finally,we address the challenges and prospects for the future development of energy-absorbing porous materials.More importantly,our review provides a direct guidance for the design and fabrication of energy-absorbing porous materials required for various engineering applications.

Bioinspired Adaptive Gel Materials with Synergistic Heterostructures

In nature, many biological soft tissues with synergistic heterostructures, such as sea cucumbers, skeletal muscles and cartilages, exhibit high functionality to adapt to complex environments. In artificial soft materials, hydrogels are similar to biological soft tissues due to the unique integration of ＂soft and wet＂ properties and elastic characteristics. However, currently hydrogel materials lack their necessary adaptability, including narrow working temperature windows and uncontrollable mechanics, thus restrict their engineering application in complex environments. Inspired by abovementionedbiological soft tissues, researchers have increasingly developed heterostructural gel materials as functional soft materials with high adaptability to various mechanical and environmental conditions. This article summarizes our recent work on high-performance adaptive gel materials with synergistic heterostructures, including the critical design criteria and the state-of-the-art fabrication strategies of our gel materials. The functional adaptation properties of these heterostructural gel materials are also presented in details, including temperature, wettability, mechanical and shape adaption.

Bioinspired nanocomposites with self-adaptive mechanical properties

Conventional synthetic materials have fixed mechanical properties and suffer defects,damage,and degradation over time.This makes them unable to adapt to changing environments and leads to limited lifecycles.Recently,self-adaptive materials inspired by natural materials have emerged as a solution to address these problems.With the ability to change their mechanical properties based on changing mechanical environments,repairing defects,and maintaining their mechanical properties,these materials can lead to improved performance while decreasing waste.In this review,we explore self-adaptive phenomena found in nature that have inspired the development of synthetic self-adaptive materials,and the mechanisms that have been employed to create the next generation of materials.The potential applications of these materials,the challenges that existing approaches face,and future research opportunities are also discussed.

Bioinspired designs in active metal-based batteries

Active metal-based batteries are drawing increased attention because of their inherent high energy density and specific capacity.Some grand challenges,such as dendrite growth,electrode degradation,rapid performance fading,etc.,have limited their practical application.Bioinspiration,which involves taking cues from the structures and functions of the natural world,can lead to a wealth of conceptually fresh approaches to regulator the metal ion transportation to achieve a dendrite-free metal plating,thwart the side-reaction reactions,and retard the structural distortions,for a more reliable and secure operation of active metal-based batteries.In this review,we concentrate on the fabrication and application of bioinspired designs in active metal-based batteries with enhanced performance,along with discussion on the challenges and opportunities associated with this promising topic.We anticipate that this review can offer some insights into the development of functional materials by learning from nature and provide some approaches for the innovations of either the battery structures or the energy materials for metal-based batteries.

Scoping biology-inspired chemical engineering

Biology is a rich source of great ideas that can inspire us to find successful ways to solve the challenging problems in engineering practices including those in the chemical industry. Bio-inspired chemical engineering(Bio Ch E)may be recognized as a significant branch of chemical engineering. It may consist of, but not limited to, the following three aspects: 1) Chemical engineering principles and unit operations in biological systems; 2) Process engineering principles for producing existing or developing new chemical products through living ‘devices';and 3) Chemical engineering processes and equipment that are designed and constructed through mimicking(does not have to reproduce one hundred percent) the biological systems including their physical–chemical and mechanical structures to deliver uniquely beneficial performances. This may also include the bio-inspired sensors for process monitoring. In this paper, the above aspects are defined and discussed which establishes the scope of BioChE.

Bioinspired directional liquid transport induced by the corner effect

Many natural creatures have demonstrated unique abilities in directional liquid transport(DLT)for better adapting to the local environment,which,for a long time,have inspired the material fabrication for applications in microfluidics,self-cleaning,water collection,etc.Recently,DLTs aroused by the corner effect have been witnessed in various natural organisms,where liquid transports/spreads spontaneously along the corner structures in microgrooves,wedges or conical structures driven by micro-/nano-scaled capillary forces without external energy input.Particularly,these DLTs show advantages of ultrahigh speed,continuous proceeding,and/or external controllability.Here,we reviewed recent research advances on the bioinspired DLTs induced by the corner effect,as well as the involved mechanisms and the artificial counterpart materials with various applications.We also introduced some bioinspired materials that are capable of stimulus-responsive DLT under external fields.Finally,we suggested perspectives of the bioinspired DLTs in liquid manipulations.

Friction and wear behavior of bioinspired composites with nacre-like lamellar and brick-and-mortar architectures against human enamel

Friction and wear performance is critical for dental materials which are inevitably subject to reciprocating friction against opposing teeth in applications.Here in-vitro friction and wear behavior of bioinspired ceramic-polymer composites,which possess nacre-like lamellar and brick-and-mortar architectures and resemble human teeth in their stiffness and hardness,against human tooth enamel were quantitatively investigated to imitate actual service conditions in line with standardized testing configuration.The composites were revealed to exhibit different wear mechanisms and lead to differing extents of wear to the opposing tooth enamel depending on their specific architectural types and orientations.In particular,the brick-and-mortar architecture displayed much less wear than the lamellar one,without obviously roughening the contact surfaces with enamel owing to its high ceramic content,and as such did not accelerate the wear of enamel as compared to smooth ceramics.Such characteristics,combined with its unique stiffness and hardness matching those of human enamel as well as the good fracture toughness and machinability,endow the composite with a promising potential for dental applications.This work may provide an experimental basis to this end and may also give insights towards designing new bioinspired wear-resistant materials for reducing friction and wear.

Engineering Mechanical Strong Biomaterials Inspired by Structural Building Blocks in Nature

The intricate multiscale architectures in natural structural building blocks provide many sources of inspiration for the designs of artificial biomaterials.In nature,the assembly of highly ordered molecular crystals and amorphous aggregates often derives from inter-and intra-molecular interactions of biomacromolecules,e.g.,proteinaceous materials.The structural biomaterials derived from the protein self-assembly behave with remarkable mechanical performance.However,there is still a grand challenge to mimic the mechanical properties of natural protein-based biomaterials in a rational design fashion to yield comparable man-made synthetic ensembles.In this review,a brief perspective on current challenges and advances in terms of bioinspired structural materials is presented.We outline a framework for mimicking protein self-assembly of natural building blocks across multiscale and highlight the critical role of synthetic biology and chemical modifications in material biosynthesis.Particularly,we focus on the design and promising applications of protein-based fibers,adhesives,dynamic hydrogels and engineered living materials,in which natural mechanical functions are effectively reproduced.

Ice-templated porous tungsten and tungsten carbide inspired by natural wood

The structures of tungsten and tungsten carbide scaffolds play a key role in determining the properties of their infiltrated composites for multifunctional applications.However,it is challenging to construct and control the architectures by means of self-assembly in W/WC systems because of their large densities.Here we present the development of unidirectionally porous architectures,with high porosities exceeding 65 vol.%,for W and WC scaffolds which in many respects reproduce the design motif of natural wood using a direct ice-templating technique.This was achieved by adjusting the viscosities of suspensions to retard sedimentation during freezing.The processing,structural characteristics and mechanical properties of the resulting scaffolds were investigated with the correlations between them explored.Quantitative relationships were established to describe their strengths based on the mechanics of cellular solids by taking into account both inter-and intra-lamellar pores.The fracture mechanisms were also identified,especially in light of the porosity.This study extends the effectiveness of the ice-templating technique for systems with large densities or particle sizes.It further provides preforms for developing new natureinspired multifunctional materials,as represented by W/WC-Cu composites.

Amphiphilic Pd@micro-organohydrogels with controlled wettability for enhancing gas-liquid-solid triphasic catalytic performance

The wettability of catalyst plays an important role in regulating catalytic performance in heterogenous catalysis because the microenvironment around the catalytic sites directly determines the mass transfer process of reactants.Inspired by gas trapped on the surface of subaquatic spiders,amphiphilic micro-organohydrogels with tunable surface wettabilities were developed by anchoring various alkane chains onto a poly(2-(dimethylamino)ethyl methacrylate)(p(DMAEMA))hydrophilic microgel network.Palladium nanoparticles(Pd NPs)were encapsulated in amphiphilic microgels(amphiphilic Pd@M)to catalyze hydrogenation reaction,achieving higher activities than pristine monohydrophilic Pd@M composite.The underwater oleophilicity and aerophilicity of Pd@M composites were quantified by oil/gas adhesion measurements and computational simulations.The higher amphiphilic catalytic activities are attributed to the formation of a gas-oil-solid reaction interface on the catalyst surfaces,allowing rapid transport of H2 and organic substrates through water to the Pd catalytic sites.Additionally,amphiphilic Pd@M composites also exhibit more superior catalytic performance in multi-substrates reaction.

Nanofibril Organization in Silk Fiber as Inspiration for Ductile and Damage-Tolerant Fiber Design

Ductile and damage-tolerant fibers(DDTFs)are desired in aerospace engineering,mechanical engineering,and biomedical engineering because of their ability to prevent the catastrophic sudden structural/mechanical failure.However,in practice,design and fabrication of DDTFs remain a major challenge due to finite fiber size and limited processing techniques.In this regard,animal silks can provide inspirations.They are hierarchically structured protein fibers with an elegant trade-off of mechanical strength,extensibility and damage tolerance,making them one of the toughest materials known.In this article,we confirmed that nanofibril organization could improve the ductility and damage-tolerance of silk fibers through restricted fibril shearing,controlled slippage and cleavage.Inspired by these strategies,we further established a rational strategy to produce polyamide DDTFs by combining electrospinning and yarn-spinning techniques.The resultant polymeric DDTFs show a silk-like fracture resistance behavior,indicating potential applications in smart textile,biomedicine,and mechanical engineering.