Three-dimensional Inkjet Printing Research Articles

Preparation of thiolated poly (lactic acid) microspheres by amine ester reaction to simulate three-dimensional inkjet printing (3DP) biocompatible scaffolds

3D inkjet printing (3DP) technology offers the advantages of fast processing speed and high precision, but achieving a strong combination of “powder” and “ink“ in polymer materials remains a great challenge. In this work, thiolated poly(lactic acid) (PLA) microspheres are fabricated through the amine-ester reaction between cysteine and PLA in a “green” water environment. 3DP is then simulated using thiolated PLA microspheres as the “powder”, and acryloylmorpholine containing double bonds as the “ink”. By virtue of the fast “thiol-ene click” reaction, the PLA scaffolds with a covalent bonding interface are fabricated within 20 s. Both the thiolated microspheres and scaffolds exhibit good biocompatibility, and the tensile strength of the scaffolds can reach 13.2 MPa, with the Young's modulus of 722 MPa, meeting the performance requirements of bone tissue scaffolds. Therefore, a new strategy to solve the interfacial bonding problem in 3DP technology are provided, facilitating the 3DP molding of PLA powder and promoting its application in the field of life and health.

Three-dimensional inkjet printing and low temperature sintering of silica-based ceramics

The conventional LTCC fabrication route requires a series of costly molding equipment and a complicated manufacturing process. If it is achievable to fabricate ceramics using three-dimensional inkjet printing (IJP) technology, it is anticipated that LTCC components could be designed as a more efficient and flexible additive manufacturing route using IJP technology to co-print ceramic and conductive layers and co-fire them. This research represents the first attempt to utilize IJP technology in the field of LTCC, where we developed a stable SiO2-H3BO3 nanoceramic ink that can be continuously printed through a piezoelectric nozzle with an array of spray holes. The ink was supplemented with selected photosensitive resins to facilitate the curing of the printed layer under ultraviolet light irradiation. Green bodies are sintered at 950° for two hours to obtain ceramic sheets with good surface flatness and microscopic sintering degrees. The tested samples have an ultra-low dielectric constant (εr) of about 2.485 and a low dielectric loss (tan δ) of about 0.0038 (at 1 MHz), while being stable at high temperatures (< 400°) and high frequencies (< 10 GHz), indicating its ability to match the required dielectric properties required for microwave dielectric substrates.

Tightly Coupled Ultra-Wideband Phased-Array Implemented by Three-Dimensional Inkjet Printing Technique

In order to enhance the gains from antennas suitable for airplane-mounted platforms, a tightly coupled antenna array is investigated in this paper. Specifically, a three-dimensional (3-D) inkjet printing technique is used to implement the conformal characteristics needed for the array. Both the radiators and substrate of the antenna array have been fabricated by combining the fused deposition modeling and microdroplet injection molding technologies, based on an existing 3-D printer. Here, through a unique combination of 3-D and 2-D inkjet printing of dielectric material and metallic ink, respectively, we demonstrate a monolithically integrated design for a nonplanar antenna for the first time. The antenna measurements herein show the complete characterization of this new process in terms of minimum feature size and achievable conductivities. This antenna configuration offers a high-gain performance with a low-cost and rapid fabrication technique by using 3-D printing techniques. To check our design, the voltage standing wave ratio and radiation patterns were tested after adding the newly designed feed structure. The results show that the design process is very efficient. Both the antenna element and the array demonstrate positive properties and are in very good agreement with the specially mounted platform.

The Driving Waveform Design Method of Power-Law Fluid Piezoelectric Printing Based on Iterative Learning Control.

In some applications of piezoelectric three-dimensional inkjet printing, the materials used are power-law fluids as they are shear thinning. Their time-varying viscosities affect the droplet formation, which is determined by the volume flow rate at the nozzle outlet. To obtain a fine printing effect, it is necessary to present a driving waveform design method that considers the shear-thinning viscosities of materials to control the volume flow rate at the nozzle outlet, which lays the foundation for the single and stable droplet generation during the printing process. In this research, we established the relationship between the driving waveform and the volume flow rate at the nozzle outlet by modifying a model that describes the inkjet mechanism of power-law fluid. The modified model was used to present a driving waveform design method based on iterative learning control. The iterative learning law of the method was designed based on the gradient descent algorithm and demonstrated its convergence. The driving waveform design method was verified to be practical and feasible by implementing drop generation experiments.

Modelling of Power-Law Fluid Flow Inside a Piezoelectric Inkjet Printhead.

Piezoelectric three-dimensional inkjet printing has been used to manufacture heterogeneous objects due to its high level of flexibility. The materials used are non-Newtonian inks with complex rheological properties, and their behavior in the context of inkjet printing has not been fully understood: for example, the fact that the shear-thinning viscosity affects the droplet generation. Therefore, a control strategy coping with shear-thinning behaviors is needed to ensure printing consistency. In this paper, a novel model-based approach is presented to describe the shear-thinning ink dynamics inside the piezoelectric inkjet printhead, which provides the basis to design the excitation parameters in a systematic way. The dynamic equation is simplified into a quasi-one-dimensional equation through the combination of the boundary layer theory and the constitutive equation of the power-law fluid, of which the viscosity is shear-thinning. Based on this, a nonlinear time-varying equivalent circuit model is presented to simulate the power-law fluid flow rate inside the tube. The feasibility and effectiveness of this model can be evaluated by comparing the results of computational fluid dynamics and the experimental results.

Inkjet printing of small molecules, biologics, and nanoparticles

During the last decades, inkjet printing has emerged as a novel technology and attracted the attention of the pharmaceutical industry, as a potential method for manufacturing personalized and customizable dosage forms to deliver drugs. Commonly, the desired drug is dissolved or dispersed within the ink and then dispensed in various dosage forms. Using this approach, several studies have been conducted to load hydrophilic or poorly water-soluble small molecules onto the surface of different solid substrates, including films, tablets, microneedles, and smart data-enriched edible pharmaceuticals, using two-dimensional and three-dimensional inkjet printing methods, with high dose accuracy and reproducibility. Furthermore, biological drugs, such as peptides, proteins, growth factors, and plasmids, have also been evaluated with positive results, eliciting the expected biological response; nonetheless, minor changes in the structure of these compounds with significant impaired activity cannot be dismissed. Another strategy using inkjet printing is to disperse drug-loaded nanoscale particles in the ink liquid, such as nanosuspension, nanocomplexes, or nanoparticles, which have been explored with promising results. Although these favorable outcomes, the proper selection of ink constituents and the inkjet printer, the correlation of printing cycles and effectively printed doses, the stability studies of drugs within the ink and the optimal analysis of samples before and after the printing process are the main challenges for inkjet printing, and therefore, this review analyzes these aspects to assess the body of current literature and help to guide future investigations on this field.

Intelligent modeling and monitoring of micro-droplet profiles in 3D printing

The inkjet 3D printing has been one of the most studied and applied additive manufacturing (AM) processes in electronic industry. In this AM process, the forming quality is greatly influenced by the micro-droplet deposition and substrate temperature. While most studies focus on the formation mechanism of droplets, there are few studies on the quantitative evaluation of the droplet surface profile and its qualitative correlation with temperature changes. In this study, the characteristics of droplet profile in three-dimensional inkjet printing were studied from two aspects, the modeling of droplet shape and the estimation of droplet temperature. For this purpose, different types of radial basis function networks (RBFN) are applied. The validity of the regularized RBFN model is developed and verified by experiments. The results show that the droplet shape can be accurately modeled and the drying temperature can be accurately estimated given the model.

High-throughput characterization of fluid properties to predict droplet ejection for three-dimensional inkjet printing formulations

Inkjet printing has been used as an Additive Manufacturing (AM) method to fabricate three-dimensional (3D) structures. However, a lack of materials suitable for inkjet printing poses one of the key challenges that impedes industry from fully adopting this technology. Consequently, many industry sectors are required to spend significant time and resources on formulating new materials for an AM process, instead of focusing on product development. To achieve the spatially controlled deposition of a printed voxel in a predictable and repeatable fashion, a combination of the physical properties of the ‘ink’ material, print head design, and processing parameters is associated. This study demonstrates the expedited formulation of new inks through the adoption of a high-throughput screening (HTS) approach. Use of a liquid handler containing multi-pipette heads, to rapidly prepare inkjet formulations in a micro-array format, and subsequently measure the viscosity and surface tension for each in a high-throughput manner is reported. This automatic approach is estimated to be 15 times more rapid than conventional methods. The throughput is 96 formulations per 13.1 working hours, including sample preparation and subsequent printability determination. The HTS technique was validated by comparison with conventional viscosity and surface tension measurements, as well as the observation of droplet ejection during inkjet printing processes. Using this approach, a library of 96 acrylate/methacrylate materials was screened to identify the printability of each formulation at different processing temperatures. The methodology and the material database established using this HTS technique will allow academic and industrial users to rapidly select the most ideal formulation to deliver printability and a predicted processing window for a chosen application.

Laser Nanostructuring and Three-Dimensional Ink-Jet Printing of Nanocoatings

High-production laser ablation is used to prepare nano-ink that is colored colloidal solutions of nanoparticles in water, characterized by a variety of physicochemical properties. Using the nano-ink, singleand multi-layered nanocoatings are printed by a jet technique and studied in detail.

A new photocrosslinkable polycaprolactone-based ink for three-dimensional inkjet printing.

A new type of photocrosslinkable polycaprolactone (PCL) based ink that is suitable for three-dimensional (3D) inkjet printing has been developed. Photocrosslinkable Polycaprolactone dimethylacrylate (PCLDMA) was synthesized and mixed with poly(ethylene glycol) diacrylate (PEGDA) to prepare an ink with a suitable viscosity for inkjet printing. The ink performance under different printing environments, initiator concentrations, and post processes was studied. This showed that a nitrogen atmosphere during printing was beneficial for curing and material property optimization, as well as improving the quality of structures produced. A simple structure, built in the z-direction, demonstrated the potential for this material for the production of 3D printed objects. Cell tests were carried out to investigate the biocompatibility of the developed ink. © 2016 The Authors Journal of Biomedical Materials Research Part B: Applied Biomaterials Published by Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1645-1657, 2017.

3D printing of ceramic scaffolds for engineering of bone tissue

The study presents results of development and investigation of processes of three-dimensional inkjet printing of scaffold structures based on microgranules of tricalcium phosphate and their further chemical modification in buffer solutions with the purpose of manufacturing bioactive ceramic scaffolds for bone tissue engineering.

Compact polymeric 3D prints of high stability

Abstract

Human cartilage tissue fabrication using three-dimensional inkjet printing technology.

Bioprinting, which is based on thermal inkjet printing, is one of the most attractive enabling technologies in the field of tissue engineering and regenerative medicine. With digital controlcells, scaffolds, and growth factors can be precisely deposited to the desired two-dimensional (2D) and three-dimensional (3D) locations rapidly. Therefore, this technology is an ideal approach to fabricate tissues mimicking their native anatomic structures. In order to engineer cartilage with native zonal organization, extracellular matrix composition (ECM), and mechanical properties, we developed a bioprinting platform using a commercial inkjet printer with simultaneous photopolymerization capable for 3D cartilage tissue engineering. Human chondrocytes suspended in poly(ethylene glycol) diacrylate (PEGDA) were printed for 3D neocartilage construction via layer-by-layer assembly. The printed cells were fixed at their original deposited positions, supported by the surrounding scaffold in simultaneous photopolymerization. The mechanical properties of the printed tissue were similar to the native cartilage. Compared to conventional tissue fabrication, which requires longer UV exposure, the viability of the printed cells with simultaneous photopolymerization was significantly higher. Printed neocartilage demonstrated excellent glycosaminoglycan (GAG) and collagen type II production, which was consistent with gene expression. Therefore, this platform is ideal for accurate cell distribution and arrangement for anatomic tissue engineering.

Reproduction in Three-Dimensional Ink Jet Printing

Three-dimensional printing is a powder-based solid freeform fabrication technique. It is based on conventional ink jet printing technology, basic materials being powders and binders (inks). As the process uses colored binders, text and graphic elements can be reproduced on the objects. The reproduction of three-dimensional prints surface elements was evaluated, also using image analysis, which was studied as a tool for reproduction evaluation. A test target, consisting of selected geometric and text elements, was placed on the surface of designed three-dimensional plate. The test plates were placed in different relative xyz positions, as well as printed with different preferences. The evaluation was done on light microscope captures, while scanned images of three-dimensional prints surfaces were used and observed as well. Changes in three-dimensional printed surface elements reproduction due to the objects' positioning and printing preferences, and binder-powder interactions were discussed. Specific image analysis procedures were researched as a tool for objective reproduction evaluation.

Application of 3-Dimensional Powder Laminating Fabrication to Metallic Components

Production of dense metal products by a three-dimensional inkjet printing system was developed. Carbonyl nickel powder with a mean particle size of 5μm was used as a raw material and two binder supply methods, (i) coating a water soluble polymer on the powder and then supplying thin polymer-dissolved water from the inkjet head; (ii) supplying a binder directly from the inkjet head were examined. The layered green product was sintered in a hydrogen atmosphere at a temperature in the range of 1073-1623K. Microstructure observation was done and sintering procedure was discussed. Sintered samples fabricated from the coated powder had non-uniform microstructure with different densities due to agglomeration of the coated powder. The inhomogeneous microstructure was improved by screening the agglomerated particles, or agglomerating most of the powder to the contrary. However, the elimination of the density variegation was not achieved in the method using the coated powder. In samples made from the powder bonded by the binder directly, microstructure was fairly homogeneous. The homogeneous microstructure helped uniform sintering, and the macroscopic shape was retained after high temperature sintering at 1623K, and a high density of over 90% was achieved.

Dense P/M Component Produced by Solid Freeform Fabrication (SFF)

Using fine metal powders, we were able to fabricate dense P/M (powder metallurgy) products by a three-dimensional inkjet printing system. We used carbonyl nickel powder with a mean particle size of 5 mm as a raw material and examined two binder supply methods: (i) supplying a binder directly from the inkjet head (DB method), and (ii) coating the powder with a water-soluble polymer and then supplying thin polymer-dissolved water from the inkjet head (CB method). The layered green product was sintered in a hydrogen atmosphere at a temperature in the range of 1073–1623 K. Sintered samples fabricated by the CB method had non-uniform microstructure due to agglomeration of the coated powder. In samples made by the DB method, the macroscopic shape was retained after high-temperature sintering at 1623 K, and a high density of over 90% was achieved, which was attributed to uniform powder cohesion in the laminating process.