Electrohydrodynamic 3D Printing Research Articles

Nanodroplet Flight Control in Electrohydrodynamic Redox 3D Printing.

Electrohydrodynamic 3D printing is an additive manufacturing technique with enormous potential in plasmonics, microelectronics, and sensing applications thanks to its broad material palette, high voxel deposition rate, and compatibility with various substrates. However, the electric field used to deposit material is concentrated at the depositing structure, resulting in the focusing of the charged droplets and geometry-dependent landing positions, which complicates the fabrication of complex 3D shapes. The low level of concordance between the design and printout seriously impedes the development of electrohydrodynamic 3D printing and rationalizes the simplicity of the designs reported so far. In this work, we break the electric field centrosymmetry to study the resulting deviation in the flight trajectory of the droplets. Comparison of experimental outcomes with predictions of an FEM model provides new insights into the droplet characteristics and unveils how the product of droplet size and charge uniquely governs its kinematics. From these insights, we develop reliable predictions of the jet trajectory and allow the computation of optimized printing paths counterbalancing the electric field distortion, thereby enabling the fabrication of geometries with unprecedented complexity.

The era of digital pharmacy. 3D printing - realities and perspectives

3D printing is an innovative technology for building three-dimensional objects by laying down successive layers of material under the control of a computer software. It is entering pharmacy mainly because of its revolutionary potential to provide individualized dosage forms that meet the needs of each patient, due to the possibility to produce objects of many different sizes and shapes. An important aspect of personalized 3D tablets is the possibility to include several active substances in one dosage form, which would reduce the daily number of medications and the frequency of their administration and improve patient compliance. Another advantage of 3D printing is the possibility of producing small batches or even individual drugs for each patient. Despite the many advantages, 3D printing has several technological challenges to overcome before it becomes widely applicable in pharmacy. Five basic technologies are currently applied in pharmaceutical practice: powder-based printing, selective laser sintering, stereolithography, extrusion moulding printing, and electrohydrodynamic 3D printing. This article reviewed development, research focus, and prospects of each technology respectively.

Near thermal-electric field controlled electrohydrodynamic 3D printing of high aspect ratio microstructures

Electrohydrodynamic (EHD) printing is an effective method for high-resolution two-dimensional patterning because of its high material compatibility. The latest research on three-dimensional (3D) structure fabrication has been reported for metal nanoparticles, small molecular materials, and phase change materials by process regulation. One of the main challenges in conventional EHD 3D printing of polymers is the low accuracy of filament deposition and stacking at the microscale. It is difficult to achieve a high aspect ratio (AR) for printed structures. This study develops an external field-assisted EHD printing process for polymer materials, where the filament formation can be improved by the near thermal field and the stacking accuracy of filaments is further promoted by applying an alternating voltage between layers. The feasibility of this method is demonstrated by printing polystyrene, a typical polymer material, on the silicon substrate with. The regulatory effect of the process parameters on the filament width is explored. The influence of the external thermal field on filament formation and deposition is discussed, and a promotion mechanism is revealed of alternating voltage for accurate deposition. Based on these combinative effects, micro-scale 3D structures with a high AR are successfully printed on the insulating substrate with three kinds of polymers.

High-resolution 3D printing of angle-ply annulus fibrosus scaffolds for intervertebral disc regeneration

Intervertebral disc (IVD) degeneration is one of the leading causes of disability, and current therapies are mainly unsatisfactory. The key pathological feature during IVD degeneration is the dysfunction of annulus fibrosus (AF). Although tissue-engineered AF has shown great promise for IVD regeneration, the design and fabrication of biomimetic AF scaffold remains a challenge due to the complexity of its structure. Nowadays, 3D printing technology has drawn great attention due to its customizable processes and ability to produce complex tissue architecture. However, few existing 3D printing methods can accurately replicate the fine angle-ply architecture of native AF, which is one of the most critical steps for IVD regeneration, due to the limited printing resolution. In this study, we aimed to fabricate high-resolution polycaprolactone (PCL) scaffolds using a newly developed electrohydrodynamic 3D printing technique. The structural advantages of such scaffolds were verified by finite element analysis (FEA). The PCL scaffolds were further assembled into AF construct to replicate the angle-ply architecture of AF. The optimal assembling method was confirmed by FEA and mechanical tests. The in vitro experiments showed that the 3D printed AF scaffolds presented favorable biocompatibility and supported the adhesion and growth of AF cells. The in vivo performance of tissue-engineered IVDs (TE-IVDs), which consisted of 3D printed AF scaffold and GelMA hydrogel that simulated nucleus pulposus (NP), were evaluated using a rat total disc replacement model. We found that the implantation of TE-IVDs helped maintain the disc height, reduced the loss of NP water content, and partially restored the biomechanical function of IVD. In addition, the TE-IVDs achieved well integration with adjacent tissues and promoted new tissue formation. In summary, being able to accurately simulate the structural characteristics of native AF, the 3D printed angle-ply AF scaffolds hold potential for future applications in IVD regeneration.

Electrohydrodynamic jet printing via low-solute concentration inks for enhanced positioning accuracy

ABSTRACT Electrohydrodynamic 3D printing (EHD-3DP) employing the solution and melting liquids as inks, receives extensive applications in the manufacturing of different materials. However, the jet lagging effect associated with positioning accuracy has yet to be solved. Here, we report a new technique of non-tailing jet printing to deposit fibres precisely. By applying poly(ε-caprolactone) (PCL) solution at an ultra-low concentration of 5 wt.%, a straight-line jet profile perpendicular to the collector plane was obtained at the high motion speeds of 30–90 mm/s. This enabled the moving jet-to-collector point kept up with the projection of nozzle tip on collector plane, leading to improved positioning accuracy of PCL fibres. The optimal protocol on material and processing parameters avoided the structural staccatos of printed fibres. This work provides insights into how the printed fibres from low-concentration inks are influenced by different parameters. The technique was applicable for the complex linear and non-linear pattern printing.

Electrohydrodynamic 3D printing of orderly carbon/nickel composite network as supercapacitor electrodes

Electrohydrodynamic (EHD) 3D printing of carbon-based materials in the form of orderly networks can have various applications. In this work, microscale carbon/nickel (C-Ni) composite electrodes with controlled porosity have been utilized in electrochemical energy storage of supercapacitors. Polyacrylonitrile (PAN) was chosen as the basic material for its excellent carbonization performance and EHD printing property. Nickel nitrate (Ni(NO3)2) was incorporated to form Ni nanoparticles which can improve the conductivity and the capacitance performance of the electrode. Well-aligned PAN-Ni(NO3)2 composite structures have been fabricated and carbonized as C-Ni electrodes with the typical diameter of 9.2±2.1 μm. The porosity of the as-prepared C-Ni electrode can be controlled during the EHD process. Electrochemical results show the C-Ni network electrode has achieved a 2.3 times higher areal specific capacitance and 1.7 times higher mass specific capacitance than those of a spin-coated electrode. As such, this process offers a facile and scalable strategy for the fabrication of orderly carbon-based conductive structures for various applications such as energy storage devices and printable electronics.

Colloidal particle reaction and aggregation control in the Electrohydrodynamic 3D printing technology

The electrohydrodynamic (EHD) 3D printing technology is an Additive Manufacturing (AM) method that can be used in the manufacture of submicron-size structures. In this process, which is based on the formation of Taylor jet from a metallic ink, the investigation of particles reaction and aggregate formation in ink during printing is of great importance. In this paper, a new Finite Element model based on particle tracing in fluids is presented that couples the different physics that govern an EHD phenomenon. Vortex flow caused by boundary shear stress was observed in the ink jet; which was more like the Marangoni phenomenon in a stationary drop. By experimentally validating the presented model with the help of PIV technique, the effects of important parameters (volume fraction, number and size of particles, zeta potential, viscosity, voltage application rate) on aggregate formation were studied based on the DLVO theory. In general, any change of parameters that leads to the increase of volume fraction also boosts the amount of formed aggregates. No interaction effect was observed between the parameters of volume fraction, particle radius and number of particles. It was demonstrated that the DLVO theory by itself is not sufficient for determining colloidal ink stability, and that the parameters of volume fraction, radius and number of particles should also be investigated for this purpose. Considering the conditions of EHD printers, the amount of zeta potential needed for colloid stability increases significantly; and a minimum zeta potential of 110 mV is required for colloid stability. A too-low or too-high value of viscosity (μ > 500 mPa.s, μ < 3 mPa.s) and a low rate of applied voltage also lead to reduced aggregation.

On-Demand 3D Printing of Nanowire Probes for High-Aspect-Ratio Atomic Force Microscopy Imaging.

With the growing importance of three-dimensional (3D) nanomaterials and devices, there has been a great demand for high-fidelity, full profile topographic characterizations in a nondestructive manner. A promising route is to employ a high-aspect-ratio (HAR) probe in atomic force microscopy (AFM) imaging. However, the fabrication of HAR-AFM probes continues to suffer from extravagant cost, limited material choice, and complicated manufacturing steps. Here, we report one-step, on-demand electrohydrodynamic 3D printing of metallic HAR-AFM probes with tailored dimensions. Our additive fabrication approach yields a freestanding metallic nanowire with an aspect ratio over 30 directly on a cantilever within tens of seconds, producing a HAR-AFM probe. Furthermore, the benefits associated with unprecedented simplicity in the probe's dimension control, material selection, and regeneration are provided. The 3D-printed HAR-AFM probe exhibits a better fidelity in deep trench AFM imaging than a standard pyramidal probe. We expect this approach to find facile, material-saving manufacturing routes in particular for customizing functional nanoprobes.

Bioprinting of novel 3D tumor array chip for drug screening

Biomedical field has been seeking a feasible standard drug screening system consisting of 3D tumor model array for drug researching due to providing sufficient samples and simulating actual in vivo tumor growth situation, which is still a challenge to rapidly and uniformly establish though. Here, we propose a novel drug screening system, namely 3D tumor array chip with “layer cake” structure, for drug screening. Accurate gelatin methacryloyl hydrogel droplets (~ 0.1 μL) containing tumor cells can be automatically deposited on demand with electrohydrodynamic 3D printing. Transparent conductive membrane is introduced as a chip basement for preventing charges accumulation during fabricating and convenient observing during screening. Culturing chambers formed by stainless steel and silicon interlayer is convenient to be assembled and recycled. As this chip is compatible with the existing 96-well culturing plate, the drug screening protocols could keep the same as convention. Important properties of this chip, namely printing stability, customizability, accuracy, microenvironment, tumor functionalization, are detailly examined. As a demonstration, it is applied for screening of epirubicin and paclitaxel with breast tumor cells to confirm the compatibility of the proposed screening system with the traditional screening methods. We believe this chip will potentially play a significant role in drug evaluation in the future.

A core–shell multi-drug platform to improve gastrointestinal tract microbial health using 3D printing

Improving the proliferation of probiotics (ca. Bifidobacterium) and inhibiting the growth of pathogenic bacteria (ca. Escherichia coli) is crucial for human health. This study demonstrates the fabrication of core–shell structure fibers using electrohydrodynamic 3D printing to help improve gastrointestinal tract microbial content. These fibers have various geometries and are capable of encapsulating stachyose into cellulose acetate (shell layer) and loading proteoglycan into polyacrylic resin II (core layer). The impact of membrane geometry on drug release behavior and the effect of exchanging the loading site on physicochemical properties of the resulting fibers were studied. The printed fibrous membranes possess a biphasic drug release profile in simulated intestinal fluid with a burst release within the first 12 h and a slower sustained release up to 72 h. The speed order priority for drug release rate of the printed membrane was whole-circle > semi-circle > square. Moreover, the membranes exhibit good biocompatibility on L929 cells and excellent improvement effects on Bifidobacterium bifidum, combining inhibition effects on Escherichia coli. In summary, the dual-drug fibrous membranes presented here and their precision-fabricated patterns pave a new direction for improving the gastrointestinal tract microbial ecosystem health in the human body.

Melt electrohydrodynamic 3D printed poly (ε-caprolactone)/polyethylene glycol/roxithromycin scaffold as a potential anti-infective implant in bone repair.

Implanted scaffold or bone substitute is a common method to treat bone defects. However, the possible bone infection caused by orthopaedic surgery has created a challenging clinical problem and generally invalidate bone repair and regeneration. In this study, a poly (ε-caprolactone) (PCL)/polyethylene glycol (PEG)/roxithromycin (ROX) composite scaffold was prepared via melt electrohydrodynamic (EHD) 3D printing. Fourier transform infrared spectroscopy (FTIR) spectroscopy was performed to verify the existence of PEG and ROX in the scaffolds. By water contact angle measurement, the addition of both PEG and ROX was found to improve the hydrophilicity of the scaffolds. By in vitro drug release assay, the PCL/PEG/ROX scaffolds showed an initial burst drug release and subsequent long-term sustained release behaviour, which is favourable for the prevention and treatment of bone infections. The antibacterial assays against E. coli and S. aureus demonstrated that the composite scaffold with ROX possessed effective antibacterial activity, especially for S. aureus, the main cause of bone infection. The immunostaining and MTT assay with human osteoblast-like cells (MG63) indicated that cells showed good viability and growth on the scaffolds. Therefore, the melt EHD 3D printed PCL/PEG/ROX scaffold could be a promising anti-infective implant for bone tissue engineering.

A multiphysics model for analysis of droplet formation in electrohydrodynamic 3D printing process

Electrohydrodynamic (EHD) printing is a novel technology used for fabricating high-resolution part features from a wide range of materials. Due to the multiphysics dynamics and the multiphase nature of the microdroplet formation in the EHD printers, modeling of this phenomenon is complicated. In this paper, the formation of a droplet in an EHD printer—under a pulsed electrical field—is simulated using a new numerical model which couples the fluid flow, the electric field distribution and the movement of the electric charges under dynamic and transient conditions. The level-set method is applied to the entire multiphysics domain in order to study the formation of the droplet. The presented model is verified by comparing to the existing experimental results in the literature. In order to find the effective parameters with significant impact, at 95% confidence level, a sensitivity analysis of the process parameters is carried out based on the Plackett-Burman design of experiment approach. It is found that the voltage, the permittivity of ink, the nozzle height above substrate, the density and the conductivity of ink are the most effective parameters.

Electrohydrodynamic 3D printing of layer-specifically oriented, multiscale conductive scaffolds for cardiac tissue engineering.

Mimicking the hierarchical microarchitecture of native myocardium in vitro plays an important role in cardiac tissue engineering. Here we present a novel strategy to produce multiscale conductive scaffolds with layer-specific fiber orientations for cardiac regeneration by combining solution-based and melt-based electrohydrodynamic (EHD) printing techniques. Polycaprolactone (PCL) microfibers were printed by melt-based EHD printing and the fiber orientation was flexibly controlled in a layer-by-layer manner according to user-specific design. The as-printed microfibrous scaffolds can provide the seeded cells necessary contact cues to guide layer-specific cellular alignments. Sub-microscale conductive fibers were simultaneously incorporated inside the well-organized PCL scaffolds by solution-based EHD printing, which significantly improved the conductivity as well as the cellular adhesion and proliferation capacity. The multiscale conductive scaffolds can further direct the multiple-layer alignments of primary cardiomyocytes and facilitate cardiomyocyte-specific gene expressions, which exhibited enhanced synchronous beating behavior compared with pure microfibrous scaffolds. It is envisioned that the proposed hybrid EHD printing technique might provide a promising strategy to fabricate multifunctional micro/nanofibrous scaffolds with biomimetic architectures, electrical conductivity and even biosensing properties for the regeneration of electroactive tissues.

Designs and applications of electrohydrodynamic 3D printing.

This paper mainly reviews the designs of electrohydrodynamic (EHD) inkjet printing machine and related applications. The review introduces the features of EHD printing and its possible research directions. Significant progress has been identified in research and development of EHD high-resolution printing as a direct additive manufacturing method, and more effort will be driven to this direction soon. An introduction is given about current trend of additive manufacturing and advantages of EHD inkjet printing. Designs of EHD printing platform and applications of different technologies are discussed. Currently, EHD jet printing is in its infancy stage with several inherent problems to be overcome, such as low yielding rate and limitation of stand-off height. Some potential modifications are proposed to improve printing performance. EHD high-resolution printing has already been applied to precision components for electronics and biotechnology applications. This paper gives a review about the latest research regarding EHD used for high-resolution inkjet printing. A starting base is given to help researchers and students to get a quick overview on the recent development of EHD printing technology.

Electrohydrodynamic 3D printing of microscale poly (ε-caprolactone) scaffolds with multi-walled carbon nanotubes

Electrohydrodynamic 3D printing is a promising strategy to controllably fabricate hierarchical fibrous architectures that mimic the structural organizations of native extracellular matrix. However, most of the existing investigations are mainly based on viscous melted biopolymers which make it difficult to uniformly incorporate bioactive or functional nanobiomaterials into the printed microfibers for functionization. Here we investigated the feasibility of employing solution-based electrohydrodynamic 3D printing to fabricate microscale poly (ε-caprolactone) (PCL) scaffolds with multi-walled carbon nanotubes (MWCNTs). The effect of polyethylene oxide (PEO) content in the acetic acid solution of PCL on the 3D profile and dimension of the electrohydrodynamically printed walls was studied for an optimal PEO-PCL composition. When the contents of PEO and PCL are 8 w/v % and 5 w/v %, respectively, 3D fibrous lactic structures with different MWCNTs content could be stably printed with the fiber diameter about 10 μm, close to the size of living cells. Biological experiments showed that although the addition of MWCNTs negatively affected cellular attachment compared with PEO-PCL scaffolds, the electrohydrodynamically printed PEO-PCL-MWCNT scaffolds facilitated cell alignment. It is envisioned that the presented electrohydrodynamic 3D printing might provide a new strategy to flexibly incorporate various nanobiomaterials into microscale fibrous structures for specific functionality or mimicking of hierarchically organized nanocomposites in vivo.

Microscale electrohydrodynamic printing of biomimetic PCL/nHA composite scaffolds for bone tissue engineering

Electrohydrodynamic printing provides an innovative strategy to fabricate high-resolution tissue-engineering scaffolds with fiber orientation and scale similar to native extracellular matrix. However, few studies have been conducted to incorporate functional nanobiomaterials into microscale fibrous structures. In this study, we presented to fabricate microscale poly (ε-caprolactone) (PCL) and hydroxyapatite nanoparticles (nHA) composite scaffolds with the average fiber diameter of 8.85±1.12µm based on electrohydrodynamic 3D printing to better mimic collagen fibers and HA nanocrystals in natural bones. The composite scaffolds exhibited good biocompatibility and facilitated cell alignment and proliferation in vitro. This strategy might be useful to regulate cellular microenvironment in multiscale and multimaterial levels for improved tissue regeneration.

Development of melt electrohydrodynamic 3D printing for complex microscale poly (ε-caprolactone) scaffolds

The replication of native hierarchical structures into synthetic scaffolds is important to direct cell growth and tissue regeneration. However, most of the existing scaffold strategies lack the capability to simultaneously realize the controlled fabrication of macroscopic geometries as well as microscale architectures with the scale similar to living cells. Here we developed a melt electrohydrodynamic printing platform and verified its feasibility to fabricate three-dimensional (3D) tissue-engineered scaffolds with complex curved geometries and microscale fibrous structures. Melting temperature was studied to stably print poly (ε-caprolactone) (PCL) filaments with the size of about 10 μm, which was precisely stacked into 3D straight walls with fine surface quality. By adjusting stage moving speed and directions, 3D PCL scaffolds with curved contours and predefined fiber orientations or spacing were successfully printed. Biological experiments showed that the printed microscale scaffolds had good biocompatibility and facilitated cellular proliferation and alignment in vitro. It is envisioned that the melt electrohydrodynamic printing can potentially provide an innovative tool to fabricate hierarchical scaffolds that mimic the native tissue architectures in a multiscale level.

Towards microscale electrohydrodynamic three-dimensional printing

It is challenging for the existing three-dimensional (3D) printing techniques to fabricate high-resolution 3D microstructures with low costs and high efficiency. In this work we present a solvent-based electrohydrodynamic 3D printing technique that allows fabrication of microscale structures like single walls, crossed walls, lattice and concentric circles. Process parameters were optimized to deposit tiny 3D patterns with a wall width smaller than 10 μm and a high aspect ratio of about 60. Tight bonding among neighbour layers could be achieved with a smooth lateral surface. In comparison with the existing microscale 3D printing techniques, the presented method is low-cost, highly efficient and applicable to multiple polymers. It is envisioned that this simple microscale 3D printing strategy might provide an alternative and innovative way for application in MEMS, biosensor and flexible electronics.