3D Printing Strategy Research Articles

Innovations in craniofacial bone and periodontal tissue engineering – from electrospinning to converged biofabrication

ABSTRACT From a materials perspective, the pillars for the development of clinically translatable scaffold-based strategies for craniomaxillofacial (CMF) bone and periodontal regeneration have included electrospinning and 3D printing (biofabrication) technologies. Here, we offer a detailed analysis of the latest innovations in 3D (bio)printing strategies for CMF bone and periodontal regeneration and provide future directions envisioning the development of advanced 3D architectures for successful clinical translation. First, the principles of electrospinning applied to the generation of biodegradable scaffolds are discussed. Next, we present on extrusion-based 3D printing technologies with a focus on creating scaffolds with improved regenerative capacity. In addition, we offer a critical appraisal on 3D (bio)printing and multitechnology convergence to enable the reconstruction of CMF bones and periodontal tissues. As a future outlook, we highlight future directions associated with the utilisation of complementary biomaterials and (bio)fabrication technologies for effective translation of personalised and functional scaffolds into the clinics.

A robust, autonomous, volumetric quality assurance method for 3D printed porous scaffolds

Bone tissue engineering strategies aimed at treating critical-sized craniofacial defects often utilize novel biomaterials and scaffolding. Rapid manufacturing of defect-matching geometries using 3D-printing strategies is a promising strategy to treat craniofacial bone loss to improve aesthetic and regenerative outcomes. To validate manufacturing quality, a robust, three-dimensional quality assurance pipeline is needed to provide an objective, quantitative metric of print quality if porous scaffolds are to be translated from laboratory to clinical settings. Previously published methods of assessing scaffold print quality utilized one- and two-dimensional measurements (e.g., strut widths, pore widths, and pore area) or, in some cases, the print quality of a single phantom is assumed to be representative of the quality of all subsequent prints. More robust volume correlation between anatomic shapes has been accomplished; however, it requires manual user correction in challenging cases such as porous objects like bone scaffolds. Here, we designed porous, anatomically-shaped scaffolds with homogenous or heterogenous porous structures. We 3D-printed the designs with acrylonitrile butadiene styrene (ABS) and used cone-beam computed tomography (CBCT) to obtain 3D image reconstructions. We applied the iterative closest point algorithm to superimpose the computational scaffold designs with the CBCT images to obtain a 3D volumetric overlap. In order to avoid false convergences while using an autonomous workflow for volumetric correlation, we developed an independent iterative closest point (I-ICP10) algorithm using MATLAB®, which applied ten initial conditions for the spatial orientation of the CBCT images relative to the original design. Following successful correlation, scaffold quality can be quantified and visualized on a sub-voxel scale for any part of the volume.

Recent advances in 3D printing for catalytic applications

Diversified printing mechanism and various applicable materials endow 3D printing technology with a wide range of applications in catalysis. Hence, the purpose of this review is to provide a general overview of various 3D printing strategies and catalytic applications, and future outlook towards the catalysis field. • Various 3D printing strategies and mechanisms are introduced. • Applications of 3D printing in catalysis are reviewed. • The prospect and challenges of 3D printing in catalysis are expected. Three-dimensional (3D) printing is changing the way of designing and manufacturing 3D objects by transforming digital models into solid models. 3D printing, known as a revolutionary additive manufacturing, also has an impact on catalysis with its continuous progress. Currently, 3D printing technology is widely combined with some related catalytic reactions and processes. Different from the traditional manufacture mode, the computer-aided digital and intelligent manufacturer makes the research on monolithic catalysts, reactors, mixers and ancillaries more in-depth. 3D printing gives more diversity and provides broader applications for catalysis. This review mainly introduces different 3D printing technologies, processes and printing mechanisms, and epitomizes their research and applications in the field of catalysis.

Coaxial 3D-printing constructing all-in-one fibrous lithium-, sodium-, and zinc-ion batteries

For battery manufacturing, 3D printing has merits of the unique intelligent and continuous characteristics. To construct the battery anode, cathode, and electrolyte network skeletons simultaneously via one-step 3D printing is a promising development direction. Here, a universal coaxial 3D printing approach was applied to construct the all-in-one fibrous lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and aqueous zinc-ion batteries (AZIBs) skeletons in one-step. The obtained anode, cathode, and separator inks can be scaled up to kilograms scale and have the obvious shear thinning characteristics, which are conducive to the large-scale coaxial 3D printing. Moreover, all the 3D printing constructed all-in-one fibrous LIBs, SIBs, and AZIBs have good electrochemical performances. The obtained all-in-one fibrous LIBs exhibit the capacity of 60 mAh g−1, high-rate capability up-to 510 mA g−1 with 33 mAh g−1, and long cycle stability up-to 1000 cycles. Meanwhile, the all-in-one fibrous SIBs deliver the high capacity (50 mAh g−1), high-rate capability (31 mAh g−1 at 500 mA g−1), and long cycle stability (2000 cycles). Similarly, the prepared AZIBs reveal the high capacity (121 mAh g−1), high-rate capability (68 mAh g−1 at 1600 mA g−1), and long cycle stability. This coaxial 3D printing strategy to construct all-in-one fibrous filaments provides a new method for the functional fibrous energy storage system.

3D Printing Ultraflexible Magnetic Actuators via Screw Extrusion Method.

Soft magnetic actuators with programmable structure design and controllable deformation ability based on 3D printing technology have attracted extensive attention. In this paper, a novel 3D printing strategy is developed to manufacture the ultraflexible magnetic actuator, in which the printed material is composed of magnetic particles and thermoplastic rubber materials. Different from the traditional fused deposition printing, this printing strategy introduces screw extrusion technology to the heating components of the printer to overcome the problem of filament buckling in the flexible material. Thus, the tensile modulus of the printed products can be reduced to as low as ≈2 MPa. Based on the above method, biomimetic magnetic actuators of the sucker and the pump are constructed for adhering and releasing object and pumping liquid. The contraction performance of the magnetic actuator is studied via a series of experiments and the magnetic field‐induced deformation is analyzed by the multiphysics‐based finite element model. This work proves that ultraflexible magnetic actuators fabricated by this 3D printing strategy show broad prospects in the fields of soft robotics and bionics.

Emerging 3D Printing Strategies for Enzyme Immobilization: Materials, Methods, and Applications.

As the strategies of enzyme immobilization possess attractive advantages that contribute to realizing recovery or reuse of enzymes and improving their stability, they have become one of the most desirable techniques in industrial catalysis, biosensing, and biomedicine. Among them, 3D printing is the emerging and most potential enzyme immobilization strategy. The main advantages of 3D printing strategies for enzyme immobilization are that they can directly produce complex channel structures at low cost, and the printed scaffolds with immobilized enzymes can be completely modified just by changing the original design graphics. In this review, a comprehensive set of developments in the fields of 3D printing techniques, materials, and strategies for enzyme immobilization and the potential applications in industry and biomedicine are summarized. In addition, we put forward some challenges and possible solutions for the development of this field and some possible development directions in the future.

Combining Solid-State Shear Milling and FFF 3D-Printing Strategy to Fabricate High-Performance Biomimetic Wearable Fish-Scale PVDF-Based Piezoelectric Energy Harvesters.

High-performance flexible piezoelectric polymer-ceramic composites are in high demand for increasing wearable energy-harvesting applications. In this work, a strategy combining solid-state shear milling (S3M) and fused filament fabrication (FFF) 3D-printing technology is proposed for the fabrication of high-performance biomimetic wearable piezoelectric poly(vinylidene fluoride) (PVDF)/tetraphenylphosphonium chloride (TPPC)/barium titanate (BaTiO3) nanocomposite energy harvesters with a biomimetic fish-scale-like metamaterial. The S3M technology could greatly improve the dispersion of BaTiO3 sub-micrometer particles and the interfacial compatibility, resulting in better processability and piezoelectric performance of the nanocomposites. Typically, the FFF 3D printed energy harvester incorporating 30 wt % BaTiO3 showed the highest piezoelectric outputs with an open-circuit voltage of 11.5 V and a short-circuit current of 220 nA. It could hence drive nine green LEDs to work normally. In addition, a 3D-printed biomimetic wearable energy harvester inspired by an environmentally adaptive fish-scale-like metamaterial was further fabricated. The fish-scale-like energy harvester could harvest energy through different deformation motions and successfully recharge a 4.7 μF capacitor by being mounted on a bicycle tire and the tire's rolling. This work not only provides a 3D printing strategy for designing diversified and complex geometric structures but also paves the way for further applications in flexible, wearable, self-powered electromechanical energy harvesters.

Embedded 3D Printing of Ultrasound‐Compatible Arterial Phantoms with Biomimetic Elasticity

AbstractHere, a class of ink materials and an embedded 3D printing strategy for the fabrication of macroscale elastic tissue‐mimetic constructs are presented. Novel inks composed of 10 wt% glycidyl methacrylated poly(vinyl alcohol) (PVAGMA) with different degrees of substitution (DOS) and 4 wt% cellulose nanocrystals (CNCs) (PVAGMA(DOS)/CNC) with strong shear‐thinning property are developed. By controlling the DOS of PVAGMA, hydrogels with desired mechanical stiffness mimicking that of healthy and diseased artery are designed to construct vascular phantoms. Cyclic tensile tests and in vitro hemodynamic study performed on phantoms demonstrate their excellent mechanical stability and low hysteresis. The burst pressure is found to be about 273 mmHg for PVAGMA2/CNC and 102 mmHg for PVAGMA4/CNC and the printed vascular phantoms are able to withstand 863K cycles over 10 days. Further, their suitability for ultrasonic imaging is demonstrated. Via B‐mode imaging, it is found that the vessel strains under a pulsatile flow are 11.7 ± 1.0% and 6.5 ± 1.5% for PVAGMA2/CNC and PVAGMA4/CNC vessels, respectively, perfectly matching the behaviors of healthy and atherosclerotic arteries. It exemplifies that the ink materials and printing strategy can have broad applications in biomedical research, especially for the fabrication of complex elastic tissue phantoms.

Additive Manufacturing in Orthopedics: A Review.

Additive manufacturing is an advanced manufacturing manner that seems like the industrial revolution. It has the inborn benefit of producing complex formations, which are distinct from traditional machining technology. Its manufacturing strategy is flexible, including a wide range of materials, and its manufacturing cycle is short. Additive manufacturing techniques are progressively used in bone research and orthopedic operation as more innovative materials are developed. This Review lists the recent research results, analyzes the strengths and weaknesses of diverse three-dimensional printing strategies in orthopedics, and sums up the use of varying 3D printing strategies in surgical guides, surgical implants, surgical predictive models, and bone tissue engineering. Moreover, various postprocessing methods for additive manufacturing for orthopedics are described.

Phase-Change-Enabled, Rapid, High-Resolution Direct Ink Writing of Soft Silicone.

Soft silicone is an ideal flexible material for application, e.g., in soft robotics, flexible electronics, bionics, or implantable biomedical devices. However, gravity-driven sagging, filament stretching, and deformation can cause inevitable defects during rapid manufacturing, making it hard to obtain complex, high-resolution 3D silicone structures with direct ink writing (DIW) technology. Here, rapid DIW of soft silicone enabled by a phase-change-induced, reversible change of the ink's hierarchical microstructure is presented. During printing, the silicone-based ink, containing silica nanoparticles and wax microparticles, is extruded from a heated nozzle into a cold environment under controlled stress. The wax phase change (solid-liquid-solid) during printing rapidly destroys and rebuilds the particle networks, realizing fast control of the ink flow behavior and printability. This high-operating-temperature DIW method is fast (maximum speed ≈3100mm min-1 ) and extends the DIW scale range of soft silicone. The extruded filaments have small diameters (50± 5µm), and allow for large spans (≈13-fold filament diameter) and high aspect ratios (≈1), setting a new benchmark in the DIW of soft silicone. Printed silicone structures exhibit excellent performance as flexible sensors, superhydrophobic surfaces, and shape-memory bionic devices, illustrating the potential of the new 3D printing strategy.

A triple-layer structure flexible sensor based on nano-sintered silver for power electronics with high temperature resistance and high thermal conductivity

With the rapid development of the aerospace, military, electronics, electric power, automotive, and other fields, flexible sensors with high temperature resistance and good thermal conductivity are increasingly in demand. These sensors need to be highly reliable and maintain resistance to heat, humidity, and physical shock so that their terminal units can withstand extreme environments. In this context, conductive adhesives have attracted considerable interest due to their unparalleled potential for the development of high-temperature flexible sensors and power electronics. In this work, a three-layer structure containing silver nanomixes (Ag-NMs), silver microflakes (Ag-MFs), and polyimide (PI) layers was prepared for use in flexible resistive strain sensor by combining the high electrical and thermal conductivity of sintered nano-silver and the flexibility of micron silver using a 3D printing strategy. This resistive strain sensor exhibits low volume resistivity (1.37 × 10−5 Ω·cm), high thermal conductivity (39 W·m−1·K−1), high temperature resistance (capable of stable operation at 250 °C), high sensitivity (ΔR/R0 values of up to 0.43 and 0.45 after bending to 100° at 25 °C and 250 °C, respectively; ΔR/R0 values of up to 0.31 and 0.18 after stretching 2.5% at 25 °C and 250 °C, respectively), and low fatigue after 1000 load-unload cycles. The Ag-NMs/Ag-MFs/PI flexible resistive strain sensor effectively operates at temperatures up to 250 °C for long periods of time, showing great promise for application in harsh environments.

3D Printing of Ceramic Biomaterials

• Five additive manufacturing strategies for printing bioceramics are described herein. • Printing bioceramics lead to highly porous, bioactive microstructures as favored by tissue-engineered scaffolds, grafts, and implant coatings. • The strengths and weaknesses of these 3D printed constructs depend on the factors like specific application goal, additive manufacturing method, and choice of materials. Bioceramics are a popular class of materials used in biomedical applications due to their mechanical stability and biocompatibility. They exist in a variety of fields including hip joints for orthopedics, tooth fillings for dentistry, and scaffolds for tissue engineering; however, the standard processes currently used to manufacture these ceramic products can be time-consuming and costly. In response, current literature alternatively proposes additive manufacturing (3D printing) strategies to fabricate bioceramic materials in a cost-effective and efficient manner. Herein, we briefly cover five common processes and materials used in additive manufacturing bioceramics: fused deposition modeling, material jetting, binder jetting, powder bed fusion, and vat photopolymerization. Furthermore, we discuss the potential of these 3D printed ceramic structures when applied to different biomedical technologies such as bone tissue scaffolds and structural implants.

Directional Freezing Assisted 3D Printing to Solve a Flexible Battery Dilemma: Ultrahigh Energy/Power Density and Uncompromised Mechanical Compliance

AbstractFlexible lithium‐ion batteries (LIBs) have been in the spotlight with the booming development of flexible/wearable electronics. However, the dilemma of simultaneously balancing excellent energy density with mechanical compliance in flexible electrodes impedes their practical applications. Here, for the first time, a directional freezing assisted 3D printing strategy is proposed to construct flexible, compressible, and ultrahigh energy/power density LIBs. Cellulose nanofibers (CNFs) and carbon nanotubes (CNTs) are entangled with each other to form an interwoven network and uniformly wrap the active materials, ensuring fast electron transfer and stress release through the entire printed electrode. Furthermore, vertical channels induced by directional freezing can act as high‐speed ion diffusion paths, which effectively solve the sluggish ion transport limitation of flexible 3D printed electrodes as the mass loading increases. As expected, the 3D printed LIB delivers a record‐high energy density (15.2 mWh cm–2) and power density (75.9 mW cm–2), outperforming all previously reported flexible LIBs. Meanwhile, the printed flexible full LIBs maintains favorable electrochemical stability in both bending and compression states. This work suggests a feasible avenue for the design of LIBs that resolves the long‐standing issue of high electrochemical performance and mechanical deformation in wearable and smart electronics.

Facile and Universal Method to Obtain Negative Poisson's Ratio via Support‐Free 3D Printing Tetrahedron‐Framework

Negative Poisson's ratio (NPR) structures, based on concave shapes, can improve mechanical properties effectively. Via methods of compression, vacuum, supercritical, and so on, foams can obtain reentrant cells and NPR properties, but they may suffer mass‐ or heat‐transfer gradient, causing uneven cells and performance. 3D printing technology can fabricate uniform NPR structures, whereas the common 3D‐printed concave shapes own downward concave points that should be supported, and removing the support materials complicates the preparation severely. Thus, to propose a facile method for building NPR structures, a 3D‐repeating tetrahedron‐framework with 2D NPR origami facets is designed. One edge of the tetrahedron is designed to be vertical, and thus all the facets are not horizontal. Then, the concave points on the facets are obliquely downward instead of totally downward so that the framework can be 3D‐printed without support. The Poisson's ratio of that structure is controlled from −0.8 to 0.4 via adjusting the facet thickness, and the mechanism is confirmed by differential geometry calculation and finite element analysis. Notably, improvement in specific modulus is found in different materials with that structure, and the support‐free 3D printing strategy can further be used to design customized shapes (such as lightweight aerial vehicle devices and NPR soles here).

A new stereolithographic 3D printing strategy for hydrogels with a large mechanical tunability and self-weldability

3D printing hydrogels with a good resolution, diversified geometries, and a tunable mechanical performance is still a big challenge, which is mainly due to the low photo-reactivity of the high-water containing precursor and the low modulus of the photo-cured hydrogel. In the present work, an acryloylmorpholine - acrylic acid - PEG diacrylate drygel was firstly printed with a good fidelity and subsequently post- treated with an aqueous solution containing specific ions, during which hydration of the hydrophilic network and coordination between the carboxyl and ions occurred simultaneously. The obtained dual-crosslinked hydrogel combined a complex geometry and a good stretchability. This approach decoupled the printability and mechanical properties of the hydrogels. To furtherly show this advantage over conventional direct hydrogel 3D printing, ultrasoft hydrogel lattice structures which cannot be self-supported and purely ionic crosslinked hydrogels with a good self-weldability were demonstrated.

3D-Printed Flexible Phase-Change Nonwoven Fabrics toward Multifunctional Clothing.

Functional phase-change fabrics hold great promise as wearable clothing. However, how to enable a phase-change fabric with the combined features of excellent structural flexibility and robustness, integrated multifunctionality, superior stability, and durability, as well as facile and scalable manufacturing, still remains a significant challenge. Herein, we demonstrated a scalable and controllable three-dimensional (3D) printing strategy for manufacturing flexible, thin, and robust phase-change nonwoven fabric (PCNF), with abundant and regular breathable pores as well as uniform and tight embedment of highly interconnected single-walled carbon nanotubes (SWNTs) into hydrophobic filaments built by intertwining solid-solid phase-change polymer chains together. The remarkable architectural features enabled an integral whole of the fabric, ready air exchange, superior water impermeability, highly efficient heat harvesting and storage, and effective absorption and reflection of electromagnetic waves, thereby delivering an exceptional combined function of breathability, waterproofness, thermal regulation, and radiation resistance, and meanwhile featuring superior thermal stability and outstanding resistance to stretching/folding fatigue even at cycles up to 2000. This work sheds light on effective strategies for manufacturing wearable phase-change fabrics with multifunctionality and high stability in a scalable manner toward future uses.

3D-printed NiFe-layered double hydroxide pyramid electrodes for enhanced electrocatalytic oxygen evolution reaction

Electrochemical water splitting has been considered one of the most promising methods of hydrogen production, which does not cause environmental pollution or greenhouse gas emissions. Oxygen evolution reaction (OER) is a significant step for highly efficient water splitting because OER involves the four electron transfer, overcoming the associated energy barrier that demands a potential greater than that required by hydrogen evolution reaction. Therefore, an OER electrocatalyst with large surface area and high conductivity is needed to increase the OER activity. In this work, we demonstrated an effective strategy to produce a highly active three-dimensional (3D)-printed NiFe-layered double hydroxide (LDH) pyramid electrode for OER using a three-step method, which involves direct-ink-writing of a graphene pyramid array and electrodeposition of a copper conducive layer and NiFe-LDH electrocatalyst layer on printed pyramids. The 3D pyramid structures with NiFe-LDH electrocatalyst layers increased the surface area and the active sites of the electrode and improved the OER activity. The overpotential (η) and exchange current density (i0) of the NiFe-LDH pyramid electrode were further improved compared to that of the NiFe-LDH deposited Cu (NiFe-LDH/Cu) foil electrode with the same base area. The 3D-printed NiFe-LDH electrode also exhibited excellent durability without potential decay for 60 h. Our 3D printing strategy provides an effective approach for the fabrication of highly active, stable, and low-cost OER electrocatalyst electrodes.

3D Dip‐Pen Nanolithography

AbstractDip‐pen nanolithography (DPN) can directly write a variety of materials on the substrates at the sub‐50 nm to micrometer length scale. While this tool has been extensively exploited to construct functional nanostructures and address important scientific questions, extending the capability from low‐dimensional molecular patterning to direct additive 3D manufacturing has yet to be demonstrated. In this work, the development of 3D‐DPN is reported to enable the microscale 3D printing capability via designing a rapidly UV‐curable liquid copolymer ink with appropriate viscoelastic properties. Two categories of 3D printing strategies via patterning dot and line pixels are explored, through which micrometer‐high, arbitrary 3D structures could be programmed to generate. It is believed that this development will arouse the fundamental research and functional application interest in the field of tip‐based additive 3D nanofabrication.

An investigation of the influence of 3d printing parameters on the tensile strength of PLA material

Fused Deposition Modelling (FDM), also known as 3d printing, is one of the most widespread Additive Manufacturing (AM) technologies based on the extrusion of a thermoplastic filament. This layerwise technology allows lightweight products to be built using different infill strategies and percentages. Furthermore, by varying other parameters, such as temperature, printing speed or layer thickness, it is possible to obtain components with different characteristics. Polylactic Acid (PLA) is one of the cheapest and most sustainable materials for 3d printing because it is a biobased and biodegradable plastic. Its use in 3D printing is widely spread among hobbyists and in the communities, such as the ones of Fablabs or the Makers movement.Nevertheless, to reduce the number of uncompliant parts that may fail into operation since they do not meet the expectations of the user, it is important to know in advance the mechanical performance that different 3d printing strategies can ensure for PLA parts.In this paper, Design of Experiment (DOE) is applied to investigate how main 3D printing parameters influence the tensile strength of PLA products. For this purpose, a 3x3 factorial plane with one replication was constructed and used for 3d printing tensile specimens of PLA Tough material using a Makerbot Replicator machine. The tensile test results show that the layer thickness is more significant than the infill percentage for the resistance of PLA products. A regression model is also proposed to allow the user to predict the ultimate tensile strength of PLA products depending on the values of those two parameters.

An approach to 3D print liquid ceramic slurries

Many industrial processes employed for making ceramics are wet processes that start with a liquid and highly concentrated ceramic slurry that is shaped and consolidated into a ceramic. As 3D printing methods develop, industries are urged to adopt additive manufacturing (AM) to keep up with Industry 4.0. However, current AM methods demand not only new equipment but also new material feedstocks. For example, liquid-based 3D printing relies on the development of printable inks. To address this issue and facilitate the transition to Industry 4.0 for industries producing ceramic parts using traditional wet processes, we propose herein a 3D printing strategy in which inks are liquid ceramic slurries like those used in traditional ceramic industry. A slurry containing BN and SiO2 nanoparticles suspended in water with a total solid loading of 44 vol% and exhibiting high fluidity was selected for our proof-of-concept experiments. Direct ink writing (DIW) was the 3D printing method used to extrude the slurry through a thin nozzle and deposit it onto a porous substrate. As the substrate removes the water from the deposited ink by capillary forces, the printed material consolidates. As a demonstration of this approach, bulk and porous parts were attempted that showed a print resolution of about 0.5 mm and a continuous, defect-free microstructure. These results are promising and could be further explored to print overhanging and larger structures using liquid ceramic slurries of various compositions.