Direct ink writing to fabricate porous acetabular cups from titanium alloy

Acetabular cups,which are among themost important implants in total hip arthroplasty,are usually made from titanium alloys with high porosity and adequate mechanical properties.The current three-dimensional(3D)printing approaches to fabricate customized acetabular cups have some inherent disadvantages such as high cost and energy consumption,residual thermal stress,and relatively low efficiency.Thus,in this work,a direct ink writing method was developed to print a cup structure at room temperature,followed by multi-step heat treatment to form microscale porous structure within the acetabular cup.Our method is facilitated by the development of a self-supporting titanium-6 aluminum-4 vanadium(Ti64)ink that is composed of Ti64 particles,bentonite yield-stress additive,ultraviolet curable polymer,and photo-initiator.The effects of Ti64 and bentonite concentrations on the rheological properties and printability of inks were systematically investigated.Moreover,the printing conditions,geometrical limitations,and maximum curing depth were explored.Finally,some complex 3D structures,including lattices with different gap distances,honeycomb with a well-defined shape,and an acetabular cup with uniformly distributed micropores,were successfully printed/fabricated to validate the effectiveness of the proposed method.

A systematic printability study of direct ink writing towards high-resolution rapid manufacturing

Direct ink writing(DIW)holds enormous potential in fabricating multiscale and multi-functional architectures by virtue of its wide range of printable materials,simple operation,and ease of rapid prototyping.Although it is well known that ink rheology and processing parameters have a direct impact on the resolution and shape of the printed objects,the underlying mechanisms of these key factors on the printability and quality of DIW technique remain poorly understood.To tackle this issue,we systematically analyzed the printability and quality through extrusion mechanism modeling and experimental validating.Hybrid non-Newtonian fluid inks were first prepared,and their rheological properties were measured.Then,finite element analysis of the whole DIW process was conducted to reveal the flow dynamics of these inks.The obtained optimal process parameters(ink rheology,applied pressure,printing speed,etc)were also validated by experiments where high-resolution(<100μm)patterns were fabricated rapidly(>70 mm s^(-1)).Finally,as a process research demonstration,we printed a series of microstructures and circuit systems with hybrid inks and silver inks,showing the suitability of the printable process parameters.This study provides a strong quantitative illustration of the use of DIW for the high-speed preparation of high-resolution,high-precision samples.

Direct Ink Writing of Highly Conductive MXene Frames for Tunable Electromagnetic Interference Shielding and Electromagnetic Wave-Induced Thermochromism

The highly integrated and miniaturized next-generation electronic products call for high-performance electromagnetic interference(EMI)shielding materials to assure the normal operation of their closely assembled components.However,the most current techniques are not adequate for the fabrication of shielding materials with programmable structure and controllable shielding efficiency.Herein,we demonstrate the direct ink writing of robust and highly conductive Ti3C2Tx MXene frames with customizable structures by using MXene/AlOOH inks for tunable EMI shielding and electromagnetic wave-induced thermochromism applications.The as-printed frames are reinforced by immersing in AlCl_(3)/HCl solution to remove the electrically insulating AlOOH nanoparticles,as well as cross-link the MXene sheets and fuse the filament interfaces with aluminum ions.After freeze-drying,the resultant robust and porous MXene frames exhibit tunable EMI shielding efficiencies in the range of 25-80 dB with the highest electrical conductivity of 5323 S m−1.Furthermore,an electromagnetic wave-induced thermochromic MXene pattern is assembled by coating and curing with thermochromic polydimethylsiloxane on a printed MXene pattern,and its color can be changed from blue to red under the high-intensity electromagnetic irradiation.This work demonstrates a direct ink printing of customizable EMI frames and patterns for tuning EMI shielding efficiency and visualizing electromagnetic waves.

Direct ink writing of 3D-Honeycombed CL-20 structures with low critical size

3D-Honeycombed CL-20 structures with low critical size of detonation have been fabricated successfully for intelligent weapon systems using a micro-flow direct ink writing(DIW) technology.The CL-20-based explosive ink for DIW technology was prepared by a two-component adhesive system with waterborne polyurethane(WPU) and ethyl cellulose(EC).Not only the preparation of the explosive ink but also the principle of DIW process have been investigated systematically.The explosive ink displayed stro ng shea rthinning behavior that permitted layer-by-laye r deposition from a fine nozzle onto a substrate to produce complex shapes.The EC content was varied to alter the pore structure distribution and rheological behavior of ink samples after curing.The deposited explosive composite materials are of a honeycombed structure with high porosity,and the pore size distribution increases with the increase of EC content.No phase change was observed during the preparation process.Both WPU and EC show good compatibility with CL-20 particles.Apparently high activation energy was realized in the CL-20-based composite ink compared with that of the refined CL-20 due to the presence of non-energetic but stable WPU.The detonation performance of the composite materials can be precisely controlled by an adjustment in the content of binders.The 3D honeyco mbed CL-20 structures,which are fabricated by DIW technology,have a very small critical detonation size of less than 69 μm,as demonstrated by wedge shaped charge test.The ink can be used to create 3D structures with complex geometries not possible with traditional manufacturing techniques,which presents a bright future for the development of intelligent weapon systems.

Reshapeable,rehealable and recyclable sensor fabricated by direct ink writing of conductive composites based on covalent adaptable network polymers

Covalent adaptable network(CAN)polymers doped with conductive nanoparticles are an ideal candidate to create reshapeable,rehealable,and fully recyclable electronics.On the other hand,3D printing as a deterministic manufacturing method has a significant potential to fabricate electronics with low cost and high design freedom.In this paper,we incorporate a conductive composite consisting of polyimine CAN and multi-wall carbon nanotubes into direct-ink-writing 3D printing to create polymeric sensors with outstanding reshaping,repairing,and recycling capabilities.The developed printable ink exhibits good printability,conductivity,and recyclability.The conductivity of printed polyimine composites is investigated at different temperatures and deformation strain levels.Their shape-reforming and Joule heating-induced interfacial welding effects are demonstrated and characterized.Finally,a temperature sensor is 3D printed with defined patterns of conductive pathways,which can be easily mounted onto 3D surfaces,repaired after damage,and recycled using solvents.The sensing capability of printed sensors is maintained after the repairing and recycling.Overall,the 3D printed reshapeable,rehealable,and recyclable sensors possess complex geometry and extend service life,which assist in the development of polymer-based electronics toward broad and sustainable applications.

Direct ink writing of multifunctional gratings with gel-like MXene/norepinephrine ink for dynamic electromagnetic interference shielding and patterned Joule heating

Intelligent electromagnetic interference(EMI)shielding modulators with a wide tuning range and cyclic stability are urgently needed but their fabrication remains challenging.A gel-like MXene/norepinephrine ink is developed and multifunctional MXene gratings with wide EMI shielding effectiveness(SE)tuning range,superior reversibility,and high mechanical flexibility are constructed by direct ink writing approach for dynamic EMI shielding and patterned Joule heating applications.The modulable MXene/norepinephrine grating with a high conductivity of 3510 S·cm-1 can conveniently realize the seamless modulation of the EMI SE by adjusting the angle between the MXene grating filaments and the electric field of the incident electromagnetic waves,offering highly reversible switching between shielding“On”(28.0 dB)and“Off”(0.5 dB)states.Notably,due to the optimized integration of the MXene ink and the rationally designed pattern,a superior specific EMI SE of 95,688.2 dB·cm^(2)·g^(-1) is achieved in the“On”state.Furthermore,the MXene/norepinephrine ink can be used to fabricate many complex patterned gratings with superior stability,instant responsibility,and superb mechanical flexibility,exhibiting a unique patterned Joule heating behavior.Direct writing of multifunctional gratings paves a means for developing intelligent EMI shielding materials,wearable electronic devices,and advanced thermal management materials.

Enhancing electrolyte ion diffusion via direct ink writing pillar array structure of graphene electrodes for high-performance microsupercapacitors

The graphene-based microsupercapacitors(MSCs)suffer from graphene aggregation issue in electrodes.It reduces the electrolyte ions transportation in the electrodes to degrade the charge storage ability of MSCs,hampering their practical application.Increasing the electrolyte ions transportation in the electrodes can boost the charge storage ability of MSCs.Herein,we design and experimentally realize pillar array structure of graphene electrodes for MSCs by direct ink writing technology.The graphene electrodes with pillar array structure increase the contact area with electrolyte and short the electrolyte ions transport path,facilitating electrolyte ions transport in electrodes.The MSCs exhibit high areal capacitance of 25.67 mF·cm^(−2),high areal energy density of 20.54μWh·cm^(−2),and high power density of 1.45 mW·cm^(−2).One single MSCs can power timer for 10 min and pressure sensor more than 160 min,showing high practical application possibility.This work provides a new avenue for developing high performance MSCs.

Highly conductive calcium ion-reinforced MXene/sodium alginate aerogel meshes by direct ink writing for electromagnetic interference shielding and Joule heating

Although MXene sheets possess high electrical conductivity and rich surface chemistry and are well suit-able for fabricating electrically conductive nanocomposites for electromagnetic interference(EMI)shield-ing applications,it remains challenging for MXene nanocomposites to achieve tunable EMI shielding per-formances and customized geometries.Herein,an aqueous MXene/sodium alginate ink is developed to print aerogel meshes with customized geometries using a direct ink writing approach.An ion-enhanced strategy is proposed to reinforce the printed aerogel meshes by multi-level cross-linking.The resultant 3D printed aerogel mesh exhibits an ultrahigh electrical conductivity of 2.85×10^(3)S m^(−1),outstanding mechanical properties,and excellent structural stability in wet environment.More importantly,a wide range of tunable EMI shielding efficiencies from 45 to 100 dB is achieved by the structural design of the 3D printed ion-enhanced MXene/sodium alginate aerogel meshes.As a Joule heater,in addition,the printed aerogel meshes can achieve a wide temperature range of 40-135℃at low driving voltages.This work demonstrates a direct ink writing approach for the fabrication of ion-enhanced MXene/sodium al-ginate aerogel meshes with tunable EMI shielding properties and multi-functionalities for applications in many scenarios.

Porous bio-high entropy alloy scaffolds fabricated by direct ink writing

Porous tantalum-titanium-niobium-zirconium(Ta-Ti-Nb-Zr)bio-high entropy alloy(bioHEA)scaffolds are fabricated using direct ink writing 3D printing technology in this study.A composite ink is prepared using four metal powders as raw materials:Ta,Ti,Nb and Zr.Ink extrusion is used to build 3D scaf-folds with interconnected porous structures at room temperature,which are then sintered in a vacuum environment.The interdiffusion of metal elements yields porous bioHEA scaffolds with a body-centered cubic(BCC)structure.The fabricated scaffolds have uniform compositions with a significant alloying ef-fect and good biocompatibility.The scaffolds have a compressive strength of 70.08-149.95 MPa and an elastic modulus of 0.18-0.64 GPa,indicating that the mechanical properties can be controlled over a wide range.The scaffolds have a compressive strength close to that of human cortical bone and thus meet the requirements for porous structure characteristics and biological and mechanical properties of orthopedic implants.

Engineering 3D-printed aqueous colloidal ceramic slurry for direct ink writing

The construction of rapid prototyping for structured ceramics has a promoting effect on potential applications.In this work,engineering slurry with different formulations were used to develop aqueous colloidal ceramic slurry for direct ink writing(DIW).Optimized slurry of Formulation 5 possessed good printing effect for DIW with stable mechanical properties.Related characteristics,including shrinkage,compressive strength,rheological behavior,and chemical property,were also examined.DIW ceramics prepared from optimized slurry can be preliminarily applied to adsorption of Rhodamine B and chlortetracycline,and possessed the advantages of easy separation and operation compared with powder adsorbents.This work provides a strategy for the design of 3D-printed kaolin ceramic slurry,and also extends to potential application in adsorption.

Direct ink writing of metal-based electrocatalysts for Li–S batteries with efficient polysulfide conversion

Thanks to the significantly higher energy density compared with universal commercialized Li-ion batteries,lithium–sulfur(Li–S)batteries are being investigated for use in prospective energy storage devices.However,the inadequate electrochemical kinetics of reactants and intermediates hinder commercial utilization.This limitation results in substantial capacity degradation and short battery lifespans,thereby impeding the battery's power export.Meanwhile,the capacity attenuation induced by the undesirable shuttle effect further hinders their industrialization.Considerable effort has been invested in developing electrocatalysts to fix lithium polysulfides and boost their conversion effectively.In the conventional process,the planar electrodes are prepared by slurry-casting,which limits the electron and ion transfer paths,especially when the thickness of the electrodes is relatively large.Compared with traditional manufacturing methods,direct ink writing(DIW)technology offers unique advantages in both geometry shaping and rapid prototyping,and even complex three-dimensional structures with high sulfur loading.Hence,this review presents a detailed description of the current developments in terms of Li–S batteries in DIW of metal-based electrocatalysts.A thorough exploration of the behavior chemistry of electrocatalysis is provided,and the adhibition of metal-based catalysts used for Li–S batteries is summarized from the aspect of material usage and performance enhancement.Then,the working principle of DIW technology and the requirements of used inks are presented,with a detailed focus on the latest advancements in DIW of metal-based catalysts in Li–S battery systems.Their challenges and prospects are discussed to guide their future development.

Parameter Optimization via Orthogonal Experiment to Improve Accuracy of Metakaolin Ceramics Fabricated by Direct Ink Writing

Kaolin/metakaolin-insulating ceramic components fabricated using direct ink writing(DIW)have important ap-plication prospects in architecture and aerospace.The accuracy of the entire process including the forming and sintering accuracy of ceramics greatly limits the application scope,and high-accuracy ceramic samples can meet the usage requirements in many scenarios.The orthogonal experiment was designed with four process parame-ters,including nozzle internal diameter,filling rate,printing layer height/nozzle internal diameter,and printing speed,to investigate the evolution of the DIW forming accuracy,sintering shrinkage rate and surface roughness of metakaolin-based ceramics with different process parameters.The influence of each process parameter and its mechanism were analyzed to obtain the DIW parameters for high-accuracy metakaolin ceramics.Multiple linear regression models between the dimensional change rate,surface roughness,and process parameters of the ceramic samples were established and validated.The results show that comprehensively considering the forming accuracy of the ceramic green bodies,sintering shrinkage rate and surface roughness,the optimal DIW process parameters were a 0.41 mm nozzle internal diameter,100%filling rate,50%printing layer height/nozzle inter-nal diameter,and a 15 mm/s printing speed.Multiple linear regression models were developed for the process parameters and the printing accuracy,sintering shrinkage rate and surface roughness.The error rates between the theoretical results obtained by substituting the optimal process parameters into the multiple linear regression models and the actual results obtained by printing the samples with the optimal parameters were extremely small,all less than 0.8%.This verified the correctness and predictability of the multiple linear regression models.This work provides a reference basis for rapid fabrication of high-accuracy ceramics via DIW and accuracy prediction with different process parameters.

Direct ink writing of conductive materials for emerging energy storage systems

Direct ink writing(DIW)has recently emerged as an appealing method for designing and fabricating three-dimensional(3D)objects.Complex 3D structures can be built layer-by-layer via digitally controlled extrusion and deposition of aqueous-based colloidal pastes.The formulation of well-dispersed suspensions with specific rheological behaviors is a prerequisite for the use of this route.In this review article,the fundamental concepts of DIW are presented,including the operation principles and basic features.Typical strategies used for ink formulation are discussed with a focus on the most widely used electrode materials,including graphene,Mxenes,and carbon nanotubes.The recent progress in printing design of emerging energy storage systems,encompassing rechargeable batteries,supercapacitors,and hybrid capacitors,is summarized.Challenges and future perspectives are also covered to provide guidance for the future development of DIW.

Direct ink writing of programmable functional silicone-based composites for 4D printing applications

Polydimethylsiloxane(PDMS)has been widely used in flexible electronics,soft robotics,and bioelectronics.However,the fabrication of PDMS-based devices has mostly relied on conventional approaches,such as casting and molding,thereby limiting their potential.Here we fabricate PDMS-based composites with programmable microstructures by direct ink writing and realize their practical functionalities of four-dimensional(4D)printing.The mechanical,thermomechanical and magnetic properties of the three-dimensional-printed composites can be well tailored by using carbon,metal,or ceramic functional fillers.By taking advantage of the printable,flexible,and magnetic PDMS composites,we demonstrate new practical functionalities of 4D printing by designing programmable architectures,including magnetic-field-driven battery cases and patchworks,as well as arbitrary morphing ceramic structures.In particular,4D-printed batteries are constructed by PDMS-based battery cases for the first time,which can be actuated via external magnetic field.This study broadens the paradigm of 4D printing for prospective applications,such as implant batteries,biomimetic engineering,and customized biomedical devices.

Bioinspired Multi-Metal Structures Produced via Direct Ink Writing

Bioinspired Multi-Metal Structures(MMSs)combine distinct properties of multiple materials,benefiting from improved properties and providing superior designs.Additive Manufacturing(AM)exhibits enormous advantages in applying different materials and geometries according to the desired functions at specific locations of the structure,having great potential in fabricating multi-materials structures.However,current AM techniques have difficulty manufacturing 3D MMSs without material cross-contamination flexibly and reliably.This study demonstrates a reliable,fast,and flexible direct ink writing method to fabricate 3D MMSs.The in-situ material-switching system enables the deposition of multiple metallic materials across different layers and within the same layer.3D Fe-Cu MMSs with complex geometries and fine details are fabricated as proof of concept.The microstructures,chemical and phase compositions,and tensile fracture surfaces of the Fe-Cu interfaces indicate a well-bonded interface without cracks,delamination,or material cross-contamination.We envision this novel method making other metallic combinations and even metal-ceramic components.It paves the way for manufacturing 3D MMSs using AM and establishes the possibilities of numerous MMSs applications in engineering fields.

High-rate metal-free MXene microsupercapacitors on paper substrates

MXene is a promising energy storage material for miniaturized microbatteries and microsupercapacitors(MSCs).Despite its superior electrochemical performance,only a few studies have reported MXene-based ultrahigh-rate(>1000 mV s^(−1))on-paper MSCs,mainly due to the reduced electrical conductance of MXene films deposited on paper.Herein,ultrahigh-rate metal-free on-paper MSCs based on heterogeneous MXene/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS)-stack electrodes are fabricated through the combination of direct ink writing and femtosecond laser scribing.With a footprint area of only 20 mm^(2),the on-paper MSCs exhibit excellent high-rate capacitive behavior with an areal capacitance of 5.7 mF cm^(−2)and long cycle life(>95%capacitance retention after 10,000 cycles)at a high scan rate of 1000 mV s^(−1),outperforming most of the present on-paper MSCs.Furthermore,the heterogeneous MXene/PEDOT:PSS electrodes can interconnect individual MSCs into metal-free on-paper MSC arrays,which can also be simultaneously charged/discharged at 1000 mV s^(−1),showing scalable capacitive performance.The heterogeneous MXene/PEDOT:PSS stacks are a promising electrode structure for on-paper MSCs to serve as ultrafast miniaturized energy storage components for emerging paper electronics.

Preparation and combustion properties of laminated sticks of B-CuO and B-Bi_(2)O_(3)

To explore the composite process of B-CuO and B-Bi_(2)O_(3) two-component laminated sticks,obtain the corresponding sticks with good printing effect,and explore the energy release behavior.In this study,boron,copper oxide,and bismuth trioxide powders were dispersed in the dispersed phase (DMF) using F_(2602) as a binder,and the construction of two-component B-CuO,B-Bi_(2)O_(3),three-component microcomposite,and three-component macro-composite sticks were realized with the help of double nozzle direct ink writing (DIW) technique respectively.The resulting sticks were ignited by a nichrome wire energized with a direct current,and a high-speed camera system was used to record the combustion behavior of the sticks,mark the flame position,and calculate the rate of ignition.The results showed that the B-CuO stick burning rate (42.11 mm·s^(-1)) was much higher than that of B-Bi_(2)O_(3)(17.84 mm·s^(-1)).The formulation with the highest CuO content (ω_(CuO)=58.7%) in the microscale composite of the sticks also had the fastest burning rate of 60.59 mm·s^(-1),as the CuO content decreased (ω_(CuO)=43.5%,29.3%),its burning rate decreased to 34.78 mm·s^(-1),37.97 mm·s^(-1).The stick with the highest copper oxide content(ω_(CuO)=60%) also possessed the highest burning rate (48.84 mm·s^(-1)) in the macro-composite sticks,and the burning rates of the macro-composite sticks with component spacing of 0.1 mm,0.2 mm,and 0.5 mm were 43.34 mm·s^(-1),48.84 mm·s^(-1),and 40.76 mm·s^(-1).

Direct writing of electronics based on alloy and metal （DREAM） ink： A newly emerging area and its impact on energy, environment and health sciences

Electronics, such as printed circuit board （PCB）, transistor, radio frequency identification （RFID）, organic light emitting diode （OLED）, solar cells, electronic display, lab on a chip （LOC）, sensor, actuator, and transducer etc. are playing increasingly important roles in people＇s daily life. Conventional fabrication strategy towards integrated circuit working steps, generally （IC）, requesting at least six consumes too much energy, material and water, and is not environmentally friendly. During the etching process, a large amount of raw materials have to be abandoned. Besides, lithography and microfabrication are typically carried out in ＂Clean room＂ which restricts the location of IC fabrication and leads to high production costs. As an alternative, the newly emerging inkjet printing electronics are gradually shaping modem electronic industry and its related areas, owing to the invention of a series of conductive inks composed of polymer matrix, conductive fillers, solvents and additives. Nevertheless, the currently available methods also encoun ter some technical troubles due to the low electroconduc tivity, complex sythesis and sintering process of the inks. As an alternative, a fundamentally different strategy was recently proposed by the authors＇ lab towards truly direct writing of electronics through introduction of a new class of conductive inks made of low melting point liquid metal or its alloy. The method has been named as direct writingof electronics based on alloy series of functional circuits, and metal （DREAM） ink. A sensors, electronic elements and devices can thus be easily written on various either soft or rigid substrates in a moment. With more and more technical progresses and fundamental discoveries being kept made along this category, it was found that a new area enabled by the DREAM ink electronics is emerging, which would have tremendous impacts on future energy and environmental sciences. In order to promote the research and development along this direction, the present paper is dedicated to draft a comprehensive picture on the DREAM ink technology by summarizing its most basic features and principles. Some important low melting point metal ink candidates, especially the room temperature liquid metals such as gallium and its alloy, were collected, listed and analyzed. The merits and demerits between conventional printed electronics and the new direct writing methods were comparatively evaluated. Important scientific issues and technical strategies to modify the DREAM ink were suggested and potential application areas were proposed. Further, digestions on the impacts of the new technology among energy, health, and environmental sciences were presented. Meanwhile, some practical challenges, such as security, environmentfriendly feature, steady usability, package, etc. were summarized. It is expected that the DREAM ink technology will initiate a series of unconven tional applications in modem society, and even enter into peoples＇ daily life in the near future.

A focus review on 3D printing of wearable energy storage devices

Three-dimensional(3D)printing has gained popularity in a variety of applications,particularly in the manufacture of wearable devices.Aided by the large degree of freedom in customizable fabrication,3D printing can cater towards the practical requirements of wearable devices in terms of light weight and flexibility.In particular,this focus review aims to cover the important aspect of wearable energy storage devices(WESDs),which is an essential component of most wearable devices.Herein,the topics discussed are the fundamentals of 3D printing inks used,the optimizing strategies in improving the mechanical and electrochemical properties of wearable devices and the recent developments and challenges of wearable electrochemical systems such as batteries and supercapacitors.It can be expected that,with the development of 3D printing technology,realization of the full potential of WESDs and seamless integration into smart devices also needs further in-depth investigations.

Extrusion-Based 3D-Printed Supercapacitors:Recent Progress and Challenges

Supercapacitors have been regarded as promising power supplies for future electronics due to their high power density,superior stability,easy integration,and safety.Extrusion-based three-dimensional printing technologies hold promise to satisfy the demands for integrated and flexible supercapacitors because of their highly versatile manufacturing process.In this review article,a comprehensive and timely review of these state-of-theart technologies is presented.We start with a brief introduction of fundamental concepts of supercapacitors,including energy storage mechanisms and device structures.Then,the latest progress of extrusionbased three-dimensional printing technologies(e.g.,fused deposition modeling,inkjet printing,and direct ink writing)along with their applications for manufacturing supercapacitors is summarized.The choice of printable materials(e.g.,graphene,carbon nanotubes,metal oxides,and MXenes),printing process,and the resulted electrochemical performances of supercapacitors are especially emphasized.Finally,the development of extrusion-based three-dimensional printing supercapacitors is summarized,with existing challenges diagnosed,possible solutions proposed,and future outlooks forecasted.We hope this review can offer insights to further improve the performance of three-dimensional-printed supercapacitors for practical applications.