3D printing in space:from mechanical structures to living tissues

3D printing stands at the forefront of transforming space exploration,offering unprecedented on-demand and rapid manufacturing capabilities.It adeptly addresses challenges such as mass reduction,intricate component fabrication,and resource constraints.Despite the obstacles posed by microgravity and extreme environments,continual advancements underscore the pivotal role of 3D printing in aerospace science.Beyond its primary function of producing space structures,3D printing contributes significantly to progress in electronics,biomedicine,and resource optimization.This perspective delves into the technological advantages,environmental challenges,development status,and opportunities of 3D printing in space.Envisioning its crucial impact,we anticipate that 3D printing will unlock innovative solutions,reshape manufacturing practices,and foster self-sufficiency in future space endeavors.

Development Trends in Additive Manufacturing and 3D Printing

Additive manufacturing and 3D printing tech-nology have been developing rapidly in the last 30 years, and indicate great potential for future development. The promising future of this technology makes its impact on traditional industry unpredictable. 3D printing will propel the revolution of fabrication modes forward, and bring in a new era for customized fabrication by realizing the five "any"s: use of almost any material to fabricate any part, in any quantity and any location, for any industrial field. Innovations in material, design, and fabrication processes will be inspired by the merging of 3D-printing technology and processes with traditional manufacturing processes. Finally, 3D printing will become as valuable for manufacturing industries as equivalent and subtractive manufacturing processes.

Medical Additive Manufacturing: From a Frontier Technology to the Research and Development of Products

1.Research and development(R&D)and the challenges of raw materials for medical additive manufacturing Raw materials for medical additive manufacturing have a wide range of commonalities that are also seen in many other fields,making them an important basis in the field of three-dimensional(3D)printing.Problems and challenges related to material types,powder properties,formability,viscoelasticity,and so forth also share common features.For example,many metal materials are used in the field of aviation,while metals,polymers,and inorganic materials are used in the field of biomedicine.The most widely used materials in biomedicine are biocompatible.Various homogeneous and non-homogeneous composites are also available for 3D printing,and impose an additional challenge in additive manufacturing;the use of heterogeneous composites in 3D printing is particularly challenging.

Research center of biomanufacturing in Xi'an Jiaotong University

Xi'an Jiaotong University (XJTU)has carded out the research of additive manufacturing (AM)since 1993,who is one of the earliest institutes majoring in AM.After 20years of effort,XJTU has made great progress on the additive manufacturing of polymer,metals,ceramics,composite materials and intelligent materials.XJTU has established a research team that features the engineering application of rapid manufacturing system.

Additive manufacturing frontier： 3D printing electronics

3D printing is disrupting the design and manufacture of electronic products. 3D printing electronics offers great potentialto build complex object with multiple functionalities. Particularly, it has shown the unique ability to make embedded electronics,3D structural electronics, conformal electronics, stretchable electronics, etc. 3D printing electronics has beenconsidered as the next frontier in additive manufacturing and printed electronics. Over the past five years, a large numberof studies and efforts regarding 3D printing electronics have been carried out by both academia and industries. In thispaper, a comprehensive review of recent advances and significant achievements in 3D printing electronics is provided.Furthermore, the prospects, challenges and trends of 3D printing electronics are discussed. Finally, some promising solutionsfor producing electronics with 3D printing are presented.

Editorial for Additive Manufacturing

Since its emergence in the 1980s,additive manufacturing has rapidly evolved into many forms.With capabilities that are impossible with conventional manufacturing processes,additive manufacturing has been recognized as a new paradigm for the manufacturing industry and its applications have expanded in numerous areas,including the medical,aerospace,automotive,construction,defense,and consumable sectors.However,despite the great potential of this technology,the widespread adoption of additive manufacturing in mainstream manufacturing has encountered barriers and challenges,which include manufacturing repeatability and reliability,affordability,and a lack of standards.

Application of printed nanocrystalline diamond film for electron emission cathode

The low-cost and large area screen-printed nano-diamond film (NDF) for electronic emission was fabricated. The edges and corners of nanocrystalline diamond are natural field-emitters. The nano-diamond paste for screen-printing was fabricated of mixing nano-graphite and other inorganic or organic vehicles. Through enough disperse in isopropyl alcohol by ultrasonic nano-diamond paste was screen-printed on the substrates to form NDF. SEM images showed that the surface morphology of NDF was improved, and the nano-diamond emitters were exposed from NDF through the special thermal-sintering technique and post-treatment process. The field emission characteristics of NDF were measured under -6 all conditions with 10 Pa pressure. The results indicated that the field emission stability and emission uniformity of NDF were improved through hydrogen plasma post-treatment process. The turn-on field decreased from 1.60 V/ μm to 1.25 V/ μm . The screen-printed NDF can be applied to the displays electronic emission cathode for low-cost outdoor in large area.

3D printing of bone tissue engineering scaffolds

Tissue engineering is promising in realizing successful treatments of human body tissue loss that current methods cannot treat well or achieve satisfactory clinical outcomes.In scaffold-based bone tissue engineering,a high performance scaffold underpins the success of a bone tissue engineering strategy and a major direction in the field is to produce bone tissue engineering scaffolds with desirable shape,structural,physical,chemical and biological features for enhanced biological performance and for regenerating complex bone tissues.Three-dimensional(3D)printing can produce customized scaffolds that are highly desirable for bone tissue engineering.The enormous interest in 3D printing and 3D printed objects by the science,engineering and medical communities has led to various developments of the 3D printing technology and wide investigations of 3D printed products in many industries,including biomedical engineering,over the past decade.It is now possible to create novel bone tissue engineering scaffolds with customized shape,architecture,favorable macro-micro structure,wettability,mechanical strength and cellular responses.This article provides a concise review of recent advances in the R&D of 3D printing of bone tissue engineering scaffolds.It also presents our philosophy and research in the designing and fabrication of bone tissue engineering scaffolds through 3D printing.

Cryogenic 3D printing of dual-delivery scaffolds for improved bone regeneration with enhanced vascularization

Three-dimensional(3D)printing has been increasingly employed to produce advanced bone tissue engineering scaffolds with biomimetic structures and matched mechanical strengths,in order to induce improved bone regeneration in defects with a critical size.Given that the successful bone regeneration requires both excellent osteogenesis and vascularization,endowing scaffolds with both strong bone forming ability and favorable angiogenic potential would be highly desirable to induce improved bone regeneration with required vascularization.In this investigation,customized bone tissue engineering scaffolds with balanced osteoconductivity/osteoinductivity were produced via cryogenic 3D printing ofβ-tricalcium phosphate and osteogenic peptide(OP)containing water/poly(lactic-co-glycolic acid)/dichloromethane emulsion inks.The fabricated scaffolds had a hierarchically porous structure and were mechanically comparable to human cancellous bone.Angiogenic peptide(AP)containing collagen I hydrogel was then coated on scaffold surface to further provide scaffolds with angiogenic capability.A sequential release with a quick AP release and a slow but sustained OP release was obtained for the scaffolds.Both rat endothelial cells(ECs)and rat bone marrow derived mesenchymal stem cells(MSCs)showed high viability on scaffolds.Improved in vitro migration and angiogenesis of ECs were obtained for scaffolds delivered with AP while enhanced osteogenic differentiation was observed in scaffolds containing OP.The in vivo results showed that,toward scaffolds containing both AP and OP,the quick release of AP induced obvious angiogenesis in vivo,while the sustained OP release significantly improved the new bone formation.This study provides a facile method to produce dual-delivery scaffolds to achieve multiple functions.

3D Printing of Continuous Fiber Reinforced Polymer Composites:Development,Application,and Prospective

Continuous fiber reinforced polymer composites(CFRPC)have been widely used in the field of automobile,air-craft,and space due to light weight,high specific strength and modulus in comparison with metal as well as alloys.Innovation on 3D printing of CFRPCs opened a new era for the design and fabrication of complicated composite structure with high performance and low cost.3D printing of CFRPCs provided an enabling technol-ogy to bridge the gaps between advanced materials and innovative structures.State-of-art has been reviewed according to the correlations of materials,structure,process,and performance as well as functions in 3D printing of CFRPCs.Typical applications and future perspective for 3D printing of CFRPCs were illustrated in order to grasp the opportunities and face the challenges,which need much more interdisciplinary researches covering the advanced materials,process and equipment,structural design,and final smart performance.

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.

Rapid in situ alloying of CoCrFeMnNi high-entropy alloy from elemental feedstock toward high-throughput synthesis via laser powder bed fusion

High-entropy alloys(HEAs)are considered alternatives to traditional structural materials because of their superior mechanical,physical,and chemical properties.However,alloy composition combinations are too numerous to explore.Finding a rapid synthesis method to accelerate the development of HEA bulks is imperative.Existing in situ synthesis methods based on additive manufacturing are insufficient for efficiently controlling the uniformity and accuracy of components.In this work,laser powder bed fusion(L-PBF)is adopted for the in situ synthesis of equiatomic CoCrFeMnNi HEA from elemental powder mixtures.High composition accuracy is achieved in parallel with ensuring internal density.The L-PBF-based process parameters are optimized;and two different methods,namely,a multi-melting process and homogenization heat treatment,are adopted to address the problem of incompletely melted Cr particles in the single-melted samples.X-ray diffraction indicates that HEA microstructure can be obtained from elemental powders via L-PBF.In the triple-melted samples,a strong crystallographic texture can be observed through electron backscatter diffraction,with a maximum polar density of 9.92 and a high ultimate tensile strength(UTS)of(735.3±14.1)MPa.The homogenization heat-treated samples appear more like coarse equiaxed grains,with a UTS of(650.8±16.1)MPa and an elongation of(40.2%±1.3%).Cellular substructures are also observed in the triple-melted samples,but not in the homogenization heat-treated samples.The differences in mechanical properties primarily originate from the changes in strengthening mechanism.The even and flat fractographic morphologies of the homogenization heat-treated samples represent a more uniform internal microstructure that is different from the complex morphologies of the triple-melted samples.Relative to the multi-melted samples,the homogenization heat-treated samples exhibit better processability,with a smaller composition deviation,i.e.,≤0.32 at.%.The two methods presented in this study are expected to have considerable potential for developing HEAs with high composition accuracy and composition flexibility.

Letter from the Editors-in-Chief

Chinese Journal of Mechanical Engineering:Additive Manufacturing Frontiers(AMF)has been launched finally!As the very FIRST English peer-reviewed journal of China in the field of additive manufacturing,AMF focuses on serving the scientific innovation,spreading the frontier scientific achievements,and building a high-level comprehensive aca-demic exchange platform.