Multi-material 3D nanoprinting for structures to functional micro/nanosystems

Multi-material 3D fabrication at the nanoscale has been a long-sought goal in additive manufacturing,with great potential for the direct construction of functional micro/nanosystems rather than just arbitrary 3D structures.To achieve this goal,researchers have introduced several nanoscale 3D printing principles,explored various multi-material switching and combination strategies,and demonstrated their potential applications in 3D integrated circuits,optoelectronics,biological devices,micro/nanorobots,etc.Although some progress has been made,it is still at the primary stage,and a serious breakthrough is needed to directly construct functional micro/nano systems.In this perspective,the development,current status and prospects of multi-material 3D nanoprinting are presented.We envision that this 3D printing will unlock innovative solutions and make significant contributions to various technologies and industries in the near future.

3D Printing of Tough Hydrogel Scaffolds with Functional Surface Structures for Tissue Regeneration

Hydrogel scaffolds have numerous potential applications in the tissue engineering field.However,tough hydrogel scaffolds implanted in vivo are seldom reported because it is difficult to balance biocompatibility and high mechanical properties.Inspired by Chinese ramen,we propose a universal fabricating method(printing-P,training-T,cross-linking-C,PTC&PCT)for tough hydrogel scaffolds to fill this gap.First,3D printing fabricates a hydrogel scaffold with desired structures(P).Then,the scaffold could have extraordinarily high mechanical properties and functional surface structure by cycle mechanical training with salting-out assistance(T).Finally,the training results are fixed by photo-cross-linking processing(C).The tough gelatin hydrogel scaffolds exhibit excellent tensile strength of 6.66 MPa(622-fold untreated)and have excellent biocompatibility.Furthermore,this scaffold possesses functional surface structures from nanometer to micron to millimeter,which can efficiently induce directional cell growth.Interestingly,this strategy can produce bionic human tissue with mechanical properties of 10 kPa-10 MPa by changing the type of salt,and many hydrogels,such as gelatin and silk,could be improved with PTC or PCT strategies.Animal experiments show that this scaffold can effectively promote the new generation of muscle fibers,blood vessels,and nerves within 4 weeks,prompting the rapid regeneration of large-volume muscle loss injuries.

Development and application prospect of stem cell combined with 3D printing technology for oral disease

With organ transplantation facing many dilemmas,tissue and organ regeneration as an alternative has bright prospects.In regenerative medicine,Three-dimensional(3D)printing technology and stem cells has been widely applied to the treatment of diseases related to tissue or organ replacement in dentistry,respectively.However,there are very few studies on the combination of the two,and even fewer clinical studies have been reported in dentistry.In this review,the current oral tissue engineering in vivo and in vitro based on 3D printing and stem cell technology will be summarized,and the discussion on the development prospects of this research direction will be given.Besides,the working principles and advantages&disadvantages of several types of 3D printers,as well as the mechanism of stem cells in tissue engineering will be elucidated.This review provides clinicians and researchers with the current state of research and trends in the combination of stem cells and 3D printing technology to treat oral-related diseases.In the future,3D bioprinters are poised for ongoing innovation with the advancement of relevant technologies,catalyzing an increase in clinical studies focused on treating oral diseases using stem cells and 3D scaffolds.Consequently,these developments will further advance the field of oral tissue engineering.

Critical quality indicators of high-performance polyetherimide(ULTEM)over the MEX 3D printing key generic control parameters:Prospects for personalized equipment in the defense industry

Additive Manufacturing(AM)can provide customized parts that conventional techniques fail to deliver.One important parameter in AM is the quality of the parts,as a result of the material extrusion 3D printing(3D-P)procedure.This can be very important in defense-related applications,where optimum performance needs to be guaranteed.The quality of the Polyetherimide 3D-P specimens was examined by considering six control parameters,namely,infill percentage,layer height,deposition angle,travel speed,nozzle,and bed temperature.The quality indicators were the root mean square(Rq)and average(Ra)roughness,porosity,and the actual to nominal dimensional deviation.The examination was performed with optical profilometry,optical microscopy,and micro-computed tomography scanning.The Taguchi design of experiments was applied,with twenty-five runs,five levels for each control parameter,on five replicas.Two additional confirmation runs were conducted,to ensure reliability.Prediction equations were constructed to express the quality indicators in terms of the control parameters.Three modeling approaches were applied to the experimental data,to compare their efficiency,i.e.,Linear Regression Model(LRM),Reduced Quadratic Regression Model,and Quadratic Regression Model(QRM).QRM was the most accurate one,still the differences were not high even considering the simpler LRM model.

Progress in Organ Bioprinting for Regenerative Medicine

Organ damage or failure arising from injury,disease,and aging poses challenges due to the body’s limited regenerative capabilities.Organ transplantation presents the issues of donor shortages and immune rejection risks,necessitating innovative solutions.The three-dimensional(3D)bioprinting of organs on demand offers promise in tissue engineering and regenerative medicine.In this review,we explore the state-of-the-art bioprinting technologies,with a focus on bioink and cell type selections.We follow with discussions on advances in the bioprinting of solid organs,such as the heart,liver,kidney,and pancreas,highlighting the importance of vascularization and cell integration.Finally,we provide insights into key challenges and future directions in the context of the clinical translation of bioprinted organs and their large-scale production.

Recent advances in 3D-printing-based organ-on-a-chip

Organ-on-a-chip(OOC)facilitates precise manipulation of fluids in microfluidic chips and simulation of the physiological,chemical,and mechanical characteristics of tissues,thus providing a promising tool for in vitro drug screening and physiological modeling.In recent decades,this technology has advanced rapidly because of the development of various three-dimensional(3D)printing techniques.3D printing can not only fabricate microfluidic chips using materials such as resins and polydimethylsiloxane but also construct biomimetic tissues using bioinks such as cell-loaded hydrogels.In this review,recent advances in 3D-printing-based OOC are systematically summarized based on materials used for direct or indirect 3D printing of OOC,3D printing techniques for the construction of OOC,and applications of 3D-printing-based OOC in models of the heart,blood vessels,intestines,liver,and kidney.Moreover,the paper outlines prospective vistas and hurdles within the field,intended to catalyze innovative use of 3D printing methodologies to propel OOC advancements.

Two-photon polymerization-based 4D printing and its applications

Two-photon polymerization(TPP)is a cutting-edge micro/nanoscale three-dimensional(3D)printing technology based on the principle of two-photon absorption.TPP surpasses the diffraction limit in achieving feature sizes and excels in fabricating intricate 3D micro/nanostructures with exceptional resolution.The concept of 4D entails the fabrication of structures utilizing smart materials capable of undergoing shape,property,or functional changes in response to external stimuli over time.The integration of TPP and 4D printing introduces the possibility of producing responsive structures with micro/nanoscale accuracy,thereby enhancing the capabilities and potential applications of both technologies.This paper comprehensively reviews TPP-based 4D printing technology and its diverse applications.First,the working principles of TPP and its recent advancements are introduced.Second,the optional4D printing materials suitable for fabrication with TPP are discussed.Finally,this review paper highlights several noteworthy applications of TPP-based 4D printing,including domains such as biomedical microrobots,bioinspired microactuators,autonomous mobile microrobots,transformable devices and robots,as well as anti-counterfeiting microdevices.In conclusion,this paper provides valuable insights into the current status and future prospects of TPP-based4D printing technology,thereby serving as a guide for researchers and practitioners.

Droplet morphology analysis of drop-on-demand inkjet printing

As an accurate 2D/3D fabrication tool,inkjet printing technology has great potential in preparation of micro electronic devices.The morphology of droplets produced by the inkjet printer has a great impact on the accuracy of deposition.In this study,the drop-on-demand(DoD)inkjet simulation model was established,and the accuracy of the simulation model was verified by corresponding experiments.The simulation result shows that the velocity of the droplet front and tail,as well as the time to disconnect from the nozzle is mainly affected by density(ρ),viscosity(μ)and surface tension(σ)of droplets.When the liquid filament is about to disconnect from the nozzle,the filament length and filament front velocity are found to have a linear correlation withσ/ρμand ln(ρ/(μσ1/2)).

3D bioprinting： an emerging technology full of opportunities and challenges

Three-dimensional （3D） printing is a novel promising technology based on 3D imaging and layer-by-layer additive fabrication. It has a profound influence on all aspects of our lives and is playing an increasing important role in many areas including engineering, manufacturing, art, education and medicine. ＂3D bioprinting＂ has been put forward with the technical progress in 3D printing and might be a possible way to solve the serious problem of human organ shortage in tissue engineering and regenerative medicine. Many research groups flung them into this area and have already made some gratifying achievements. However, it is a long way to fabricate a live organ. Many elements lead to the limitation of 3D bioprinting. This review introduces the background and development history of 3D bioprinting, compares different approaches of 3D bioprinting and illustrates the key factors of the printing process. Meanwhile, this review also points out existing challenges of 3D bioprinting and has a great prospect. Some points proposed in this review might be served as reference for the research of this field.

Pioneering the direct large-scale laser printing of flexible“graphenic silicon”self-standing thin films as ultrahigh-performance lithium-ion battery anodes

Recent technological advancements,such as portable electronics and electric vehicles,have created a pressing need for more efficient energy storage solutions.Lithium-ion batteries(LIBs)have been the preferred choice for these applications,with graphite being the standard anode material due to its stability.However,graphite falls short of meeting the growing demand for higher energy density,possessing a theoretical capacity that lags behind.To address this,researchers are actively seeking alternative materials to replace graphite in commercial batteries.One promising avenue involves lithiumalloying materials like silicon and phosphorus,which offer high theoretical capacities.Carbon-silicon composites have emerged as a viable option,showing improved capacity and performance over traditional graphite or pure silicon anodes.Yet,the existing methods for synthesizing these composites remain complex,energy-intensive,and costly,preventing widespread adoption.A groundbreaking approach is presented here:the use of a laser writing strategy to rapidly transform common organic carbon precursors and silicon blends into efficient“graphenic silicon”composite thin films.These films exhibit exceptional structural and energy storage properties.The resulting three-dimensional porous composite anodes showcase impressive attributes,including ultrahigh silicon content,remarkable cyclic stability(over 4500 cycles with∼40%retention),rapid charging rates(up to 10 A g^(-1)),substantial areal capacity(>5.1 mAh cm^(-2)),and excellent gravimetric capacity(>2400 mAh g^(-1) at 0.2 A g^(-1)).This strategy marks a significant step toward the scalable production of high-performance LIB materials.Leveraging widely available,cost-effective precursors,the laser-printed“graphenic silicon”composites demonstrate unparalleled performance,potentially streamlining anode production while maintaining exceptional capabilities.This innovation not only paves the way for advanced LIBs but also sets a precedent for transforming various materials into high-performing electrodes,promising reduced complexity and cost in battery production.

Polar-coordinate line-projection light-curing continuous 3D printing for tubular structures

3D printing techniques offer an effective method in fabricating complex radially multi-material structures.However,it is challenging for complex and delicate radially multi-material model geometries without supporting structures,such as tissue vessels and tubular graft,among others.In this work,we tackle these challenges by developing a polar digital light processing technique which uses a rod as the printing platform.The 3D model fabrication is accomplished through line projection.The rotation and translation of the rod are synchronized to project and illuminate the photosensitive material volume.By controlling the distance between the rod and the printing window,we achieved the printing of tubular structures with a minimum wall thickness as thin as 50 micrometers.By controlling the width of fine slits at the printing window,we achieved the printing of structures with a minimum feature size of 10 micrometers.Our process accomplished the fabrication of thin-walled tubular graft structure with a thickness of only 100 micrometers and lengths of several centimeters within a timeframe of just 100 s.Additionally,it enables the printing of axial multi-material structures,thereby achieving adjustable mechanical strength.This method is conducive to rapid customization of tubular grafts and the manufacturing of tubular components in fields such as dentistry,aerospace,and more.

3D printing encouraging desired in-situ polypyrrole seed-polymerization for ultra-high energy density supercapacitors

The tireless pursuit of supercapacitors with high energy density entails the parallel advancement of wellsuited electrode materials and elaborately engineered architectures.Polypyrrole(PPy)emerges as an exceedingly conductive polymer and a prospective pseudocapacitive materials for supercapacitors,yet the inferior cyclic stability and unpredictable polymerization patterns severely impede its real-world applicability.Here,for the first time,an innovative seed-induced in-situ polymerization assisted 3D printing strategy is proposed to fabricate PPy-reduced graphene oxide/poly(vinylidene difluoride-cohexafluoropropylene)(PVDF-HFP)(PPy-rGO/PH)electrodes with controllable polymerization behavior and exceptional areal mass loading.The preferred active sites uniformly pre-planted on the 3D-printed graphene substrates serve as reliable seeds to induce efficient polypyrrole deposition,achieving an impressive mass loading of 185.6 mg cm^(-2)(particularly 79.2 mg cm^(-2)for polypyrrole)and a superior areal capacitance of 25.2 F cm^(-2)at 2 mA cm^(-2)for a 12-layer electrode.In agreement with theses appealing features,an unprecedented areal energy density of 1.47 mW h cm^(-2)for a symmetrical device is registered,a rarely achieved value for other PPy/rGO-based supercapacitors.This work highlights a promising route to preparing high energy density energy storage modules for real-world applications.

Coaxial electrohydrodynamic printing of core–shell microfibrous scaffolds with layer-specific growth factors release for enthesis regeneration

The rotator cuff tear has emerged as a significant global health concern.However,existing therapies fail to fully restore the intricate bone-to-tendon gradients,resulting in compromised biomechanical functionalities of the reconstructed enthesis tissues.Herein,a tri-layered core–shell microfibrous scaffold with layer-specific growth factors(GFs)release is developed using coaxial electrohydrodynamic(EHD)printing for in situ cell recruitment and differentiation to facilitate gradient enthesis tissue repair.Stromal cell-derived factor-1(SDF-1)is loaded in the shell,while basic fibroblast GF,transforming GF-beta,and bone morphogenetic protein-2 are loaded in the core of the EHD-printed microfibrous scaffolds in a layer-specific manner.Correspondingly,the tri-layered microfibrous scaffolds have a core–shell fiber size of(25.7±5.1)μm,with a pore size sequentially increasing from(81.5±4.6)μm to(173.3±6.9)μm,and to(388.9±6.9μm)for the tenogenic,chondrogenic,and osteogenic instructive layers.A rapid release of embedded GFs is observed within the first 2 d,followed by a faster release of SDF-1 and a slightly slower release of differentiation GFs for approximately four weeks.The coaxial EHD-printed microfibrous scaffolds significantly promote stem cell recruitment and direct their differentiation toward tenocyte,chondrocyte,and osteocyte phenotypes in vitro.When implanted in vivo,the tri-layered core–shell microfibrous scaffolds rapidly restored the biomechanical functions and promoted enthesis tissue regeneration with native-like bone-to-tendon gradients.Our findings suggest that the microfibrous scaffolds with layer-specific GFs release may offer a promising clinical solution for enthesis regeneration.

Investigation on mechanical properties regulation of rock-like specimens based on 3D printing and similarity quantification

3D printing is widely adopted to quickly produce rock mass models with complex structures in batches,improving the consistency and repeatability of physical modeling.It is necessary to regulate the mechanical properties of 3D-printed specimens to make them proportionally similar to natural rocks.This study investigates mechanical properties of 3D-printed rock analogues prepared by furan resin-bonded silica sand particles.The mechanical property regulation of 3D-printed specimens is realized through quantifying its similarity to sandstone,so that analogous deformation characteristics and failure mode are acquired.Considering similarity conversion,uniaxial compressive strength,cohesion and stress–strain relationship curve of 3D-printed specimen are similar to those of sandstone.In the study ranges,the strength of 3D-printed specimen is positively correlated with the additive content,negatively correlated with the sand particle size,and first increases then decreases with the increase of curing temperature.The regulation scheme with optimal similarity quantification index,that is the sand type of 70/140,additive content of 2.5‰and curing temperature of 81.6℃,is determined for preparing 3D-printed sandstone analogues and models.The effectiveness of mechanical property regulation is proved through uniaxial compression contrast tests.This study provides a reference for preparing rock-like specimens and engineering models using 3D printing technology.

Near-zero-adhesion-enabled intact wafer-scale resist-transfer printing for high-fidelity nanofabrication on arbitrary substrates

There is an urgent need for novel processes that can integrate different functional nanostructures onto specific substrates,so as to meet the fast-growing need for broad applications in nanoelectronics,nanophotonics,and fexible optoelectronics.Existing direct-lithography methods are difficult to use on fexible,nonplanar,and biocompatible surfaces.Therefore,this fabrication is usually accomplished by nanotransfer printing.However,large-scale integration of multiscale nanostructures with unconventional substrates remains challenging because fabrication yields and quality are often limited by the resolution,uniformity,adhesivity,and integrity of the nanostructures formed by direct transfer.Here,we proposed a resist-based transfer strategy enabled by near-zero adhesion,which was achieved by molecular modification to attain a critical surface energy interval.This approach enabled the intact transfer of wafer-scale,ultrathin-resist nanofilms onto arbitrary substrates with mitigated cracking and wrinkling,thereby facilitating the in situ fabrication of nanostructures for functional devices.Applying this approach,fabrication of three-dimensional-stacked multilayer structures with enhanced functionalities,nanoplasmonic structures with~10 nm resolution,and MoS2-based devices with excellent performance was demonstrated on specific substrates.These results collectively demonstrated the high stability,reliability,and throughput of our strategy for optical and electronic device applications.

Advancements in transfer printing techniques for flexible electronics:adjusting interfaces and promoting versatility

The burgeoning interest in flexible electronics necessitates the creation of patterning technology specifically tailored for flexible substrates and complex surface morphologies.Among a variety of patterning techniques,transfer printing emerges as one of the most efficient,cost-effective,and scalable methods.It boasts the ability for high-throughput fabrication of 0–3D micro-and nano-structures on flexible substrates,working in tandem with traditional lithography methods.This review highlights the critical issue of transfer printing:the flawless transfer of devices during the pick-up and printing process.We encapsulate recent advancements in numerous transfer printing techniques,with a particular emphasis on strategies to control adhesion forces at the substrate/device/stamp interfaces.These strategies are employed to meet the requirements of competing fractures for successful pick-up and print processes.The mechanism,advantages,disadvantages,and typical applications of each transfer printing technique will be thoroughly discussed.The conclusion section provides design guidelines and probes potential directions for future advancements.

Biomimetic 3D printing of composite structures with decreased cracking

The development of tissue engineering and regeneration research has created new platforms for bone transplantation.However,the preparation of scaffolds with good fiber integrity is challenging,because scaffolds prepared by traditional printing methods are prone to fiber cracking during solvent evaporation.Human skin has an excellent natural heat-management system,which helps to maintain a constant body temperature through perspiration or blood-vessel constriction.In this work,an electrohydrodynamic-jet 3D-printing method inspired by the thermal-management system of skin was developed.In this system,the evaporation of solvent in the printed fibers can be adjusted using the temperature-change rate of the substrate to prepare 3D structures with good structural integrity.To investigate the solvent evaporation and the interlayer bonding of the fibers,finite-element analysis simulations of a three-layer microscale structure were carried out.The results show that the solvent-evaporation path is from bottom to top,and the strain in the printed structure becomes smaller with a smaller temperaturechange rate.Experimental results verified the accuracy of these simulation results,and a variety of complex 3D structures with high aspect ratios were printed.Microscale cracks were reduced to the nanoscale by adjusting the temperature-change rate from 2.5 to 0.5℃s-1.Optimized process parameters were selected to prepare a tissue engineering scaffold with high integrity.It was confirmed that this printed scaffold had good biocompatibility and could be used for bone-tissue regeneration.This simple and flexible 3D-printing method can also help with the preparation of a wide range of micro-and nanostructured sensors and actuators.

Vat-based photopolymerization 3D printing:From materials to topical and transdermal applications

Three-dimensional(3D)printing is an innovative manufacturingmethod with the potential to revolutionize topical and transdermal dosage forms.Nowadays,it is established that Vatbased photopolymerization(VP)3D printing technologies offer superior printing efficiency and versatility compared to other 3D printing technologies available on the market.However,there are some limitations that impair their full application in pharmaceutical contexts,such as the lack of a range of biocompatiblematerials for topical and transdermal applications.This reviewarticle explores all types of VP-based 3D printing and discusses the relevance of implementing this kind of technology.We start with a detailed description of the printing process,focusing on the commercial materials available and lab-made resins proposed by different authors.We also review recent studies in this field,which mainly focus on the fabrication of transdermal devices based on microneedle arrays.In the future,it is expected that the manufacturers of 3D printers invest in modifications to the printing apparatus to allow the simultaneous printing of different resins and/or compound types,which will open frontiers to the personalization of treatment approaches.

3D printing of poly(ethyleneimine)-functionalized Mg-Al mixed metal oxide monoliths for direct air capture of CO_(2)

Direct air capture(DAC)of CO_(2)plays an indispensable role in achieving carbon-neutral goals as one of the key negative emission technologies.Since large air flows are required to capture the ultradilute CO_(2)from the air,lab-synthesized adsorbents in powder form may cause unacceptable gas pressure drops and poor heat and mass transfer efficiencies.A structured adsorbent is essential for the implementation of gas-solid contactors for cost-and energy-efficient DAC systems.In this study,efficient adsorbent poly(ethyleneimine)(PEI)-functionalized Mg-Al-CO_(3)layered double hydroxide(LDH)-derived mixed metal oxides(MMOs)are three-dimensional(3D)printed into monoliths for the first time with more than 90%adsorbent loadings.The printing process has been optimized by initially printing the LDH powder into monoliths followed by calcination into MMO monoliths.This structure exhibits a 32.7%higher specific surface area and a 46.1%higher pore volume,as compared to the direct printing of the MMO powder into a monolith.After impregnation of PEI,the monolith demonstrates a large adsorption capacity(1.82 mmol/g)and fast kinetics(0.7 mmol/g/h)using a CO_(2)feed gas at 400 ppm at 25℃,one of the highest values among the shaped DAC adsorbents.Smearing of the amino-polymers during the post-printing process affects the diffusion of CO_(2),resulting in slower adsorption kinetics of pre-impregnation monoliths compared to post-impregnation monoliths.The optimal PEI/MeOH ratio for the post-impregnation solution prevents pores clogging that would affect both adsorption capacity and kinetics.

Effect of fractures on mechanical behavior of sand powder 3D printing rock analogue under triaxial compression

In practical engineering applications,rock mass are often found to be subjected to a triaxial stress state.Concurrently,defects like joints and fractures have a notable impact on the mechanical behavior of rock mass.Such defects are identified as crucial contributors to the failure and instability of the surrounding rock,subsequently impacting the engineering stability.The study aimed to investigate the impact of fracture geometry and confining pressure on the deformation,failure characteristics,and strength of specimens using sand powder 3D printing technology and conventional triaxial compression tests.The results indicate that the number of fractures present considerably influences the peak strength,axial peak strain and elastic modulus of the specimens.Confining pressure is an important factor affecting the failure pattern of the specimen,under which the specimen is more prone to shear failure,but the initiation,expansion and penetration processes of secondary cracks in different fracture specimens are different.This study confirmed the feasibility of using sand powder 3D printing specimens as soft rock analogs for triaxial compression research.The insights from this research are deemed essential for a deeper understanding of the mechanical behavior of fractured surrounding rocks when under triaxial stress state.