Bioinspired Additive Manufacturing of Hierarchical Materials: From Biostructures to Functions

Throughout billions of years,biological systems have evolved sophisticated,multiscale hierarchical structures to adapt to changing environments.Biomaterials are synthesized under mild conditions through a bottom-up self-assembly process,utilizing substances from the surrounding environment,and meanwhile are regulated by genes and proteins.Additive manufacturing,which mimics this natural process,provides a promising approach to developing new materials with advantageous properties similar to natural biological materials.This review presents an overview of natural biomaterials,emphasizing their chemical and structural compositions at various scales,from the nanoscale to the macroscale,and the key mechanisms underlying their properties.Additionally,this review describes the designs,preparations,and applications of bioinspired multifunctional materials produced through additive manufacturing at different scales,including nano,micro,micro-macro,and macro levels.

Bioinspired cellulose-integrated MXene-based hydrogels for multifunctional sensing and electromagnetic interference shielding

Bioinspired hydrogels are complex materials with distinctive properties comparable to biological tissues.Their exceptional sensitivity to various external stimuli leads to substantial application potential in wearable smart devices.However,these multifaceted hydrogels are often challenging to be combined with pattern customization,stimulus responsiveness,self-healing,and biocompatibility.Herein,inspired by mussel secretions,a printable,self-healing,and biocompatible MXene-based composite hydrogel was designed and prepared by incorporating Ti3C2Tx MXene nanosheets into the hydrogel framework through the chelation of calcium ions(Ca2+)with polyacrylic acid and cellulose nanofibers at alkaline conditions.The biocompatible conductive hydrogel exhibited sensitivity(gauge factor of 2.16),self-healing(within 1 s),recognition,and adhesion,distinguishing it as an ideal candidate for wearable multifunctional sensors toward strain sensing,vocal sensing,signature detection,and Morse code transmission.Additionally,the multifunctional hydrogel manifested efficient electromagnetic interference shielding properties(reaching more than 30 dB at a thickness of 2.0 mm),protecting electronics and humans from electromagnetic radiation and pollution.Therefore,the presented work represents a versatile strategy for developing environmentally friendly conductive hydrogels,demonstrating the perspectives of intelligent hydrogels for multifunctional applications.

4D printing for future manufacturing

Additive manufacturing(AM),also called three-dimensional(3D)printing,offers disruptive design freedom and manufacturing flexibility due to the layer-wise incremental formation manner of components.Advancements in AM techniques provide unique advantages and feasibilities for overcoming challenges arising from fabricating parts with complexities in geometry,materials,and properties.

Integrating thin wall into block:A new scanning strategy for laser powder bed fusion of dense tungsten

Due to a combination of outstanding properties including high melting point,high density,low thermal expansion coefficient,low saturated vapor pressure and excellent thermal conductivity,tungsten(W)parts have been widely used as electrodes,heating elements,anti-scatter grids for Computed Tomography(CT)equipment,rocket nozzles and divertor materials for nuclear fusion[1].

Thermodynamics aided design of hBN-capsulated diboride powders from novel nitrate precursors for high entropy ceramics

Hexagonal BN-coated powders have been widely used in various engineering sectors,however,their pro-ductions are restricted by the complexity of gas-solid reactions.In this study,guided by thermodynamics,a novel approach to synthesize Layer-structured hexagonal BN(hBN)-coated high entropy diboride pow-ders in vacuum was developed,using metal salt Zr(NO_(3))4·5H_(2)O,HfCl_(4),NbC_(15),TaC_(15),C_(16)H_(36)O_(4)Ti,boric acid,and sucrose as raw materials.By adjusting the ratio of carbon to metal source(C/M),powders only consisting of two boride solid solutions and hBN were finally obtained,under an optimal process-ing condition of C/M=5.5 and synthesis temperature of 1400 ℃.Parts of hBN were found to coat on high-entropy metal diborides ceramic(HEB)particles,corresponding formation mechanism for core-shell structured powders was investigated,together with the liquid precursor assisted boro/carbothermal re-duction process.Starting from as-synthesized core-shell powders,(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))B2-11 vol%hBN ceramics were densified at 1900 ℃ under 50 MPa without holding,with a high relative density of 97.3%.

Self-supported high-entropy alloy electrocatalyst for highly efficient H_(2) evolution in acid condition

Developing non-precious catalysts as Pt substitutes for electrochemical hydrogen evolution reaction(HER)with superior stability in acidic electrolyte is of critical importance for large-scale,low-cost hydrogen production from water.Herein,we report a CoCrFeNiAl high-entropy alloy(HEA)electrocatalyst with self-supported structure synthesized by mechanical alloying and spark plasma sintering(SPS)consolidation.The HEA after HF treatment and in situ electrochemical activation for 4000 cycles of cyclic voltammetry(HF-HEAa2)presents favourable activity with overpotential of 73 mV to reach a current density of 10 mA cm^(2) and a Tafel slope of 39.7 mV dec1.The alloy effect of Al/Cr with Co/Fe/Ni at atomic level,high-temperature crystallization,as well as consolidation by SPS endow CoCrFeNiAl HEA with high stability in 0.5 M H2SO4 solution.The superior performance of HF-HEAa2 is related with the presence of metal hydroxides/oxides groups on HEA.

Hydroxylated high-entropy alloy as highly efficient catalyst for electrochemical oxygen evolution reaction

Oxygen evolution reaction(OER),a half reaction involved in electrochemical water splitting,CO2 reduction,and metal–air batteries,restricts the efficiency of these energy conversion systems due to sluggish reaction kinetics[1,2].To accelerate OER,highly efficient electrocatalysts are required.However,large-scale applications of the normally used OER catalysts(i.e.RuO2 and IrO2)are hampered by their instability and low abundance.It is highly desirable to develop earth-abundant catalysts with low cost,high activity and long-term stability.Co(Ni,Fe)(oxy)hydroxides(Co(Ni)-(O)OH)have emerged as promising OER catalysts in recent years[3].

In-situ synthesis and sintering of mullite glass composites by SPS

The main subject of this work is an investigation of the effects of heating rate and current on the crystallisation of amorphous precursors in spark plasma sintering(SPS).For this,dry gel of Al_(2)O_(3)-SiO_(2) with a molar ratio of 1:1,was synthesized and sintered in-situ by SPS,and also by hot pressing(HP)for comparison.Phase analysis showed that the only crystalline product in both cases was mullite,whose Al_(2)O_(3) content was lower in the SPS specimens.The microstructures showed a low volume fraction of large mullite fibers in the SPS specimens,whereas a high volume fraction of fine equiaxed grains was present in the HP specimen.The main difference in microstructure between HP and SPS specimens could be explained in terms of the higher heating rate of the SPS specimens.The size of the SPS die also affected the size and aspect ratio of the mullite fibers produced,which might have been due to either the different electrical current required or a difference in specimen temperature profile.

Grain-refining fabrication of nanocrystalline(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)high-entropy ceramics by ultra-high pressure sintering

As an important A_(2)B_(2)O_(7)-type ceramic,(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)high-entropy pyrochlore pos-sesses promising properties such as high melting point,high chemical durability,and low thermal conductivity.However,the low sintering ability limits its application in thermal barrier coating and radioactive waste immobilization.It usually needs long-term high-temperature soaking to achieve full density,but with inevitable grain growth.In this work,dense and grain-refined nanocrystalline(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)ceramics were prepared with ultra-high pressure sintering(UHPS)method under 10 GPa at a low temperature of 800℃.The densification behavior,microstructure evo-lution,and properties of the UHPS-ed samples were then investigated.The grain size of as-prepared(La_(0.2)Nd_(0.2)Sm_(0.2)Gd_(0.2)Eu_(0.2))_(2)Zr_(2)O_(7)ceramic was only 151 nm,which is 40%smaller than that of raw pow-der.In addition,it exhibited advantageous properties including both high hardness and aqueous durabil-ity.Plastic deformation under ultra-high pressure was believed as the dominant densification mechanism responsible for grain refinement and property improvement.

Bioprocess-inspired preparation of silica with varied morphologies and potential in lithium storage

As one of the most delicate bioprocesses in nature,biosilicification is closely related to biosilica with various morphologies,and has provided abundant inspiration to materials synthesis.In the present study,to explore the biosilica formation process and fabricate silica with an exquisite microstructure for lithiumion battery(LIB)electrodes,a bacterial phage(M13)is used as a biotemplate to synthesize silica with diverse morphologies:cylinders,hexagonal prisms,assemblies of smaller cylinders and nanowires.A facile ethanol bath method is conducted to coat the nanowires with nitrogen-containing carbon and carbon-coated SiO_(2) nanowires with mesochannels(C@msSiO_(2) NWs)are first used as anode materials for LIBs.Attributed to the uniform carbon coating and parallel mesochannel structure,the electronic conductivity and capacity to accommodate volume variations were significantly improved.In the electrochemical perfo rmance test,the composites calcined at 750℃(C@msSiO_(2) NWs-750)show an impressive capacity of 653 mA h g^(-1) at a current density of 500 mA g^(-1) and stability(1000 cycles).In view of the electrochemical test outcomes,the prepa ration of a sophisticated structure with an outstanding potential is easily achieved via a biomimetic strategy.

Reactive sintering of B4C-TaB2 ceramics via carbide boronizing:Reaction process, microstructure and mechanical properties

Carbide boronizing is a promising approach to obtain fine grained boron carbide based ceramics with improved mechanical properties. In this work, reaction process, microstructural characteristics and mechanical properties of BxC-TaB2(x = 3.7, 4.9, 7.1) ceramics were comprehensively investigated via this method. Dense BxC-TaB2 ceramics with refined microstructure were obtained from submicro tantalum carbide and boron powder mixtures at 1800℃/50 MPa/5 min by spark plasma sintering. The stoichiometry of boron carbide was determined from lattice parameters and Raman shift. It was found that uniformly distributed TaB2 grains in the BxC matrix is favor of the densification process and restricting grain growth.Besides, planar defects with high density were observed from the as-formed B7.1 C grains and transient stress was considered to contribute to the densification involved with plastic deformation. Microstructural observations indicate the dissolution of oxygen in the TaB2 lattice and most of the B7.1 C/TaB2 phase boundaries were clean. Owing to the highly faulted structure and finer grain size, as-obtained BxC-TaB2 ceramics exhibit high Vickers hardness(33.3–34.4 GPa at 9.8 N) and relatively high flexural strength ranging from 440 to 502 MPa.

Fabrication of laminated TiB2-B4C/Cu-Ni composites by electroplating and spark plasma sintering

We proposed a new method, electroplating followed by spark plasma sintering（SPS）, to fabricate laminated TiB2-B4 C/Cu-Ni composites with high strength and high toughness. It is found that a thin intermediate Cu layer can effectively enhance the strength of the interface between the ceramics and the metals, resulting in a high flexural strength and toughness of the laminated TiB2-B4 C composites simultaneously. A flexural strength and fracture toughness of 651 MPa and 11.6 MPam^（1/2） respectively,are achieved, an approximately 90% improvement over TiB2-B4 C bulk.

Bio-inspired high-efficiency photosystem by synergistic effects of core-shell structured Au@CdS nanoparticles and their engineered location on{001}facets of SrTiO_(3)nanocrystals

Natural photosynthesis,which provides a green and high-efficiency energy conversion path by spatial separation of photogenerated carriers through combined actions of molecules ingeniously arranged in an efficient solar nanospace,highlights the importance of rational nanostructure design to realize artificial high-efficiency photosystem.Inspired by these unique features,we constructed a high-efficiency ternary photosystem by selectively decorating the{001}facets of 18-facet SrTiO_(3)with Au@CdS photosensitizers via a green photo-assisted method.Benefiting from the dual-facilitated charge carriers transportation in core-shell structured Au@CdS heterojunction and well-faceted 18-facet SrTiO_(3)nanocrystal,such a photo-catalyst could realize the effective spatial separation of photogenerated electrons and holes.As expected,the 18-facet SrTiO_(3)/Au@CdS photocatalyst exhibits superior activity in visible-light-driven photocatalytic hydrogen evolution(4.61 mmol h^(−1)g^(−1)),166%improvement in comparison with randomly deposited Au@CdS(1.73 mmol h^(−1)g^(−1)).This work offers new insight into the development of green and high-efficiency photocatalytic systems based on the rational nanostructure design by crystal facet engineering.

Titanium nitrides as novel reactants for in-situ synthesis of TiB_(2)-based composites with improved properties

A novel in-situ reactive approach based on the reactions among TiN,aluminum and boron has been developed to synthesize TiB_(2)-based composites including TiB_(2)-h BN(TB)and TiB_(2)-h BN-AlN(TBA).Fully dense ceramics with fine-grained microstructure were successfully obtained via spark plasma sintering at 1850℃/60 MPa/5 min.Microstructure analysis suggests h BN flakes were homogenously distributed in the TiB_(2)matrix.For AlN,however,they were elongated into plate-like grains during sintering,in which lots of defects in terms of stacking faults and twinning structures were observed.The mechanical and thermophysical properties of as-sintered ceramics were comprehensively investigated and compared.In-corporating AlN significantly improved the flexure strength,hardness,fracture toughness and thermal conductivity of TiB_(2)-h BN ceramics.The electrical conductivity of TB(3.06×10^(6)S/m)is larger than that of TBA(2.35×10^(6)S/m)at room temperature,but the value(6×10^(5)S/m)was lower than that of TBA(6.9×10^(5)S/m)at 1173 K.Based on the measurement of electrical and thermal conductivity,electron and phonon contributions to thermal conductivities of TB and TBA were calculated and their temperature dependences were illustrated.

Highly efficient synthesis of boron nitride nanotubes by catalytic chemical vapor deposition of boron/nickel containing precursors

High-purity and high-yield boron nitride nanotubes with large aspect ratio were prepared by a facile two-step process,including the synthesis of boron/nickel containing precursors by precipitation reactions and subsequent thermally catalytic chemical vapor deposition reactions.The influence of catalyst content and annealing temperature on the phase composition and microstructure of the products were investigated.The results show that it is difficult to exert the catalytic effect of nickel-based catalyst at low temperatures(<1400℃).At appropriate temperatures(1400-1500℃),highly crystalline boron nitride nanotubes with a length of more than 50 mm and a diameter of 50 nm are formed.The content of catalyst in the precursor mainly affects the morphology of the boron nitride product.If the content is too low,it is easy to form boron nitride particles;while high catalyst content can easily lead to catalyst aggregation and form a submicron one-dimensional boron nitride with unregular structure.Based on microstructural evolutions,phase changes,and thermodynamic analysis,the vapor-liquid-solid(V-L-S)growth mechanism of the tip growth mode dominates the formation of boron nitride nanotubes has also been verified.

Novel synthesis approaches for new structures in confined space inspired by natural structure-forming processes

In living organisms,confined space with specific chemical composition and elaborate spatial distribution regulates the formation of natural structures.Learning from the natural structure-forming process,novel synthesis approaches in deliberated confined systems have been proposed for obtaining designed structures.Artificial confined systems can effectively regulate the synthesis of materials with defined structures according to the geometry of confinements.Collagen fibrils provide biological confinements for the formation of hierarchical structure with periodic arrangement.Genetically engineered living organisms with designed confinements can direct the synthesis of three-dimensional nanostructures.More novel structures will be rationally fabricated in the future with the aid of deeper understanding of biological processes.

Interdisciplinary Materials: Interdisciplinary and frontier researches between materials science and other disciplines

The integration of materials sciences with other dis-ciplines is not only a global development trend of mate-rials sciences and engineering but also a key scientific field advocated and valued by China.The importance of materials sciences is reflected in the establishment of the Department of Interdisciplinary Science by the National Natural Science Foundation of China,as well as dedi-cated research arrangements for the development of in-terdisciplinary subjects by the Ministry of Science and other departments.The integration of materials science with other disciplines has always been a feature and advantage of the Wuhan University of Technology.

Ultrastrong MXene film bridged by liquid metal

Two-dimensional(2D)titanium carbide(Ti3C2Tx)MXene nanosheets show promising mechanical and electrical properties,indicating great potential applications in aerospace and electronic devices,etc.[1,2].There are many assembling approaches including vacuum filtration,blade coating and layer-by-layer[3–5].However,it still remains a great challenge to realize the intrinsic performance of MXene nanosheets into macroscopic film due to low stress transfer efficiency,which usually is indued by the voids and misalignment during the assembling process[6].Thus,it remains a great challenge to assemble MXene nanosheets into high-performance macroscopic MXene films.