High-Efficiency Dynamic Scanning Strategy for Powder Bed Fusion by Controlling Temperature Field of the Heat-Affected Zone

Improvement of fabrication efficiency and part performance was the main challenge for the large-scale powder bed fusion(PBF)process.In this study,a dynamic monitoring and feedback system of powder bed temperature field using an infrared thermal imager has been established and integrated into a four-laser PBF equipment with a working area of 2000 mm×2000 mm.The heat-affected zone(HAZ)temperature field has been controlled by adjusting the scanning speed dynamically.Simultaneously,the relationship among spot size,HAZ temperature,and part performance has been established.The fluctuation of the HAZ temperature in four-laser scanning areas was decreased from 30.85℃to 17.41℃.Thus,the consistency of the sintering performance of the produced large component has been improved.Based on the controllable temperature field,a dynamically adjusting strategy for laser spot size was proposed,by which the fabrication efficiency was improved up to 65.38%.The current research results were of great significance to the further industrial applications of large-scale PBF equipment.

Functionalized alginate-based bioinks for microscale electrohydrodynamic bioprinting of living tissue constructs with improved cellular spreading and alignment

Bioprinting has been widely investigated for tissue engineering and regenerative medicine applications.However,it is still difficult to reconstruct the complex native cell arrangement due to the limited printing resolution of conventional bioprinting techniques such as extrusion-and inkjet-based printing.Recently,an electrohydrodynamic(EHD)bioprinting strategy was reported for the precise deposition of well-organized cell-laden constructs with microscale filament size,whereas few studies have been devoted to developing bioinks that can be applied for EHD bioprinting and simultaneously support cell spreading.This study describes functionalized alginate-based bioinks for microscale EHD bioprinting using peptide grafting and fibrin incorporation,which leads to high cell viability(>90%)and cell spreading.The printed filaments can be further refined to as small as 30μm by incorporating polyoxyethylene and remained stable over one week when exposed to an aqueous environment.By utilizing the presented alginate-based bioinks,layer-specific cell alignment along the printing struts could be observed inside the EHD-printed microscale filaments,which allows fabricating living constructs with cell-scale filament resolution for guided cellular orientation.

Embedding aligned nanofibrous architectures within 3D-printed polycaprolactone scaffolds for directed cellular infiltration and tissue regeneration

Three-dimensional(3D) printing provides a promising way to fabricate biodegradable scaffolds with designer architectures for the regeneration of various tissues.However,the existing3D-printed scaffolds commonly suffer from weak cell-scaffold interactions and insufficient cell organizations due to the limited resolution of the 3D-printed features.Here,composite scaffolds with mechanically-robust frameworks and aligned nanofibrous architectures are presented and hybrid manufactured by combining techniques of 3D printing,electrospinning,and unidirectional freeze-casting.It was found that the composite scaffolds provided volume-stable environments and enabled directed cellular infiltration for tissue regeneration.In particular,the nanofibrous architectures with aligned micropores served as artificial extracellular matrix materials and improved the attachment,proliferation,and infiltration of cells.The proposed scaffolds can also support the adipogenic maturation of adipose-derived stem cells(ADSCs)in vitro.Moreover,the composite scaffolds were found to guide directed tissue infiltration and promote nearby neovascularization when implanted into a subcutaneous model of rats,and the addition of ADSCs further enhanced their adipogenic potential.The presented hybrid manufacturing strategy might provide a promising way to produce additional topological cues within 3D-printed scaffolds for better tissue regeneration.

Transfer film effects induced by 3D-printed polyether-ether-ketone with excellent tribological properties for joint prosthesis

Based on the building principle of additive manufacturing,printing orientation mainly determines the tribological properties of joint prostheses.In this study,we created a polyether-ether-ketone(PEEK)joint prosthesis using fused filament fabrication and investigated the effects of printing orientation on its tribological properties using a pin-on-plate tribometer in 25% newborn calf serum.An ultrahigh molecular weight polyethylene transfer film is formed on the surface of PEEK due to the mechanical capture of wear debris by the 3D-printed groove morphology,which is significantly impacted by the printing orientation of PEEK.When the printing orientation was parallel to the sliding direction of friction,the number and size of the transfer film increased due to higher steady stress.This transfer film protected the matrix and reduced the friction coefficient and wear rate of friction pairs by 39.13%and 74.33%,respectively.Furthermore,our findings provide a novel perspective regarding the role of printing orientation in designing knee prostheses,facilitating its practical applications.

3D printing of functional bioengineered constructs for neural regeneration: a review

Three-dimensional(3D)printing technology has opened a new paradigm to controllably and reproducibly fabricate bioengineered neural constructs for potential applications in repairing injured nervous tissues or producing in vitro nervous tissue models.However,the complexity of nervous tissues poses great challenges to 3D-printed bioengineered analogues,which should possess diverse architectural/chemical/electrical functionalities to resemble the native growth microenvironments for functional neural regeneration.In this work,we provide a state-of-the-art review of the latest development of 3D printing for bioengineered neural constructs.Various 3D printing techniques for neural tissue-engineered scaffolds or living cell-laden constructs are summarized and compared in terms of their unique advantages.We highlight the advanced strategies by integrating topographical,biochemical and electroactive cues inside 3D-printed neural constructs to replicate in vivo-like microenvironment for functional neural regeneration.The typical applications of 3D-printed bioengineered constructs for in vivo repair of injured nervous tissues,bio-electronics interfacing with native nervous system,neural-on-chips as well as brain-like tissue models are demonstrated.The challenges and future outlook associated with 3D printing for functional neural constructs in various categories are discussed.

A Prediction Model of Effective Thermal Conductivity for Metal Powder Bed in Additive Manufacturing

In current research,many researchers propose analytical expressions for calculating the packing structure of spherical particles such as DN Model,Compact Model and NLS criterion et al.However,there is still a question that has not been well explained yet.That is:What is the core factors affecting the thermal conductivity of particles?In this paper,based on the coupled discrete element-finite difference(DE-FD)method and spherical aluminum powder,the relationship between the parameters and the thermal conductivity of the powder(ETC_(p))is studied.It is found that the key factor that can described the change trend of ETC_(p) more accurately is not the materials of the powder but the average contact area between particles(a_(ave))which also have a close nonlinear relationship with the average particle size d_(50).Based on this results,the expression for calculating the ETC_(p) of the sphere metal powder is successfully reduced to only one main parameter d_(50)and an efficient calculation model is proposed which can applicate both in room and high temperature and the corresponding error is less than 20.9%in room temperature.Therefore,in this study,based on the core factors analyzation,a fast calculation model of ETC_(p) is proposed,which has a certain guiding significance in the field of thermal field simulation.

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.

Fiber Traction Printing:A 3D Printing Method of Continuous Fiber Reinforced Metal Matrix Composite

A novel metal matrix composite freeform fabrication approach,fiber traction printing(FTP),is demonstrated through controlling the wetting behavior between fibers and the matrix.This process utilizes the fiber bundle to control the cross-sectional shape of the liquid metal,shaping it from circular to rectangular which is more precise.The FTP process could resolve manufacturing difficulties in the complex structure of continuous fiber reinforced metal matrix composites.The printing of the first layer monofilament is discussed in detail,and the effects of the fibrous coating thickness on the mechanical properties and microstructures of the composite are also investigated in this paper.The composite material prepared by the FTP process has a tensile strength of 235.2 MPa,which is close to that of composites fabricated by conventional processes.The complex structures are printed to demonstrate the advantages and innovations of this approach.Moreover,the FTP method is suited to other material systems with good wettability,such as modified carbon fiber,surfactants,and aluminum alloys.

In vivo evaluation of additively manufacturedmulti-layered scaffold for the repair of large osteochondral defects

The repair of osteochondral defects is one of the major clinical challenges in orthopaedics.Well-established osteochondral tissue engineering methods have shown promising results for the early treatment of small defects.However,less success has been achieved for the regeneration of large defects,which is mainly due to the mechanical environment of the joint and the heterogeneous nature of the tissue.In this study,we developed a multi-layered osteochondral scaffold to match the heterogeneous nature of osteochondral tissue by harnessing additive manufacturing technologies and combining the established art laser sintering and material extrusion techniques.The developed scaffold is based on a titanium and polylactic acid matrix-reinforced collagen“sandwich”composite system.The microstructure and mechanical properties of the scaffold were examined,and its safety and efficacy in the repair of large osteochondral defects were tested in an ovine condyle model.The 12-week in vivo evaluation period revealed extensive and significantly higher bone in-growth in the multi-layered scaffold compared with the collagen–HAp scaffold,and the achieved stable mechanical fixation provided strong support to the healing of the overlying cartilage,as demonstrated by hyaline-like cartilage formation.The histological examination showed that the regenerated cartilage in the multi-layer scaffold group was superior to that formed in the control group.Chondrogenic genes such as aggrecan and collagen-II were upregulated in the scaffold and were higher than those in the control group.The findings showed the safety and efficacy of the cell-free“translation-ready”osteochondral scaffold,which has the potential to be used in a one-step surgical procedure for the treatment of large osteochondral defects.

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.

Experimental investigation on electromechanical deformation of dielectric elastomers under different temperatures

Under an applied voltage, dielectric elastomers(DEs) produce an actuation strain that is nonlinear, partly because of the material properties. In this study, an experimental characterization is conducted to evaluate how the ambient temperature and pre-stretch affected the actuation performance. For DEs with a pre-stretch of 2 × 2, an increase of temperature from-10° to 80° results in a variation in the actuation strain of more than 1700%. Low pre-stretched DEs are more susceptible to temperature change; while highly pre-stretched DEs are relatively insensitive to temperature, because in this case the energy conversion was dominated by mechanical stretching, rather than thermal conduction, during the actuation.

Effects of bionic mechanical stimulation on the properties of engineered cartilage tissue

Tissue-engineered cartilage(TEC)remains a potential alternative for the repair of articular cartilage defects.However,there has been a significant different between the properties of TEC and those of natural cartilage.Studies have shown that mechanical stimulation such as compressive load can help regulate matrix remodelling in TEC,thus affecting its biomechanical properties.However,the influences of shear induced from the tissue fluid phase have not been well studied and may play an important role in tissue regeneration especially when integrated with the compressive load.Therefore,the aim of this study was to quantitatively investigate the effects of combined loading mechanisms on TEC in vitro.A bespoke biosimulator was built to incorporate the coupled motion of compression,friction and shear.The specimens,encapsulating freshly isolated rabbit chondrocytes in a hydrogel,were cultured within the biosimulator under various mechanical stimulations for 4 weeks,and the tissue activity,matrix contents and the mechanical properties were examined.Study groups were categorized according to different mechanical stimulation combinations,including strain(5-20%at 5%intervals)and frequency(0.25 Hz,0.5 Hz,1 Hz),and the effects on tissue behaviour were investigated.During the dynamic culture process,a combined load was applied to simulate the combined effects of compression,friction and shear on articular cartilage during human movement.The results indicated that a larger strain and higher frequency were more favourable for the specimen in terms of the cell proliferation and extracellular matrix synthesis.Moreover,the combined mechanical stimulation was more beneficial to matrix remodelling than the single loading motion.However,the contribution of the combined mechanical stimulation to the engineered cartilaginous tissue matrix was not sufficient to impede biodegradation of the tissue with culture time.

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.

Oxygen tension modulates cell function in an in vitro three-dimensional glioblastoma tumor model

Hypoxia is a typical feature of the tumor microenvironment,one of the most critical factors affecting cell behavior and tumor progression.However,the lack of tumor models able to precisely emulate natural brain tumor tissue has impeded the study of the effects of hypoxia on the progression and growth of tumor cells.This study reports a three-dimensional(3D)brain tumor model obtained by encapsulating U87MG(U87)cells in a hydrogel containing type I collagen.It also documents the effect of various oxygen concentrations(1%,7%,and 21%)in the culture environment on U87 cell morphology,proliferation,viability,cell cycle,apoptosis rate,and migration.Finally,it compares two-dimensional(2D)and 3D cultures.For comparison purposes,cells cultured in flat culture dishes were used as the control(2D model).Cells cultured in the 3D model proliferated more slowly but had a higher apoptosis rate and proportion of cells in the resting phase(G0 phase)/gap I phase(G1 phase)than those cultured in the 2D model.Besides,the two models yielded significantly different cell morphologies.Finally,hypoxia(e.g.,1%O2)affected cell morphology,slowed cell growth,reduced cell viability,and increased the apoptosis rate in the 3D model.These results indicate that the constructed 3D model is effective for investigating the effects of biological and chemical factors on cell morphology and function,and can be more representative of the tumor microenvironment than 2D culture systems.The developed 3D glioblastoma tumor model is equally applicable to other studies in pharmacology and pathology.

3D-printed Metamaterials with Versatile Functionalities

Metamaterials are artificial structures that have been engineered to exhibit properties that do not occur naturally in conventional materials.They were firstly made up of periodic unit cells that interact with electromagnetic(EM)waves to manipulate their behavior,showing extraordinary phenomena like EM cloaking,negative index,beam deflection and so on.In recent years,the concept of metamaterial has been penetrating in various physical do-main and various metamaterials with versatile functionalities have been proposed and fabricated by 3D printing technology to manipulate the interactions between matter and electromagnetic,thermal,acoustic,and mechan-ical energy.With the increasing of structural complexity,material types,precision additive manufacturing serve as a powerful tool to achieve novel metamaterials with extraordinary performance and fusion of functionalities.In this paper,we reviewed the remarkable properties enabled by 3D printed metamaterials in different fields,and analyzed the consilience relationship between structure,function,and manufacturing process.

3D Bioprinted Skin Substitutes for Accelerated Wound Healing and Reduced Scar

The shortage of skin for grafting continues to be a major problem in the treatment of serious skin injuries.3D bioprinting provides a new way to solve this problem.However,current 3D printed skin is less effective in treatment of large wounds because of severe shrinkage and scarring.In this study,bionically designed bilayer skin was fabricated using an extrusion-based bioprinter and a gelatin/sodium alginate/gelatin methacrylate hydrogel with excellent physical and biological properties.Full-thickness skin wounds were created in the back of nude mice and treated with bioprinted skin or hydrogel.Bioprinted skin accelerated wound healing,reduced wound contraction and scarring,and facilitated wound skin epithelialization compared with the bioprinted hydrogel or untreated wound.The skin from the wound was collected 28 days after grafting for histology and immunofluorescence analysis.The thickness of the dermis and epidermis of the bioprinted skin was similar to that of nude mice.Microvascular formation in the dermis and dense keratinocytes in the epidermis of the bioprinted skin were observed.This study provides a potential treatment strategy for reducing skin contraction and scar in large skin wounds.

Roadmap for Additive Manufacturing:Toward Intellectualization and Industrialization

With the rapid development of Additive Manufacturing(AM)technology in the past 30 years,AM has been shift-ing from prototyping to advanced manufacturing of functional components in industry.Intellectualization and industrialization of AM process and equipment could be the bottlenecks to the wide industrial applications of AM technology in the future,which have been highlighted in this paper,aiming at describing the technological research roadmaps for the next 5 to 10 years.According to the data flow in the process and value chains of AM technologies,state-of-art of design methodology,material,process&equipment,smart structures,and ap-plications in extreme scales and environments has been elaborated respectively.Some suggestions on potential challenges for research and development in AM technologies have been provided in each section,which would finally establish a critical technical platform for the future industrial innovation and entrepreneurship.

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.