Functional inks for 3D printing: a review of materials, rheology and industrial applications

Recent advances in 3D printing technologies for wearable (bio)sensors

Advanced 3D-printed phase change materials

The emergence of additive manufacturing technologies has brought about a significant transformation in several industries. Among these technologies, Fused Deposition Modeling/Fused Filament Fabrication (FDM/FFF) 3D printing has gained prominence as a rapid prototyping and small-scale production technique. The potential of FDM/FFF for applications that require improved mechanical, thermal, and electrical properties has been restricted due to the limited range of materials that are suitable for this process. This study explores the integration of various reinforcements, including carbon fibers, glass fibers, and nanoparticles, into the polymer matrix of FDM/FFF filaments. The utilization of advanced materials for reinforcing the filaments has led to the enhancement in mechanical strength, stiffness, and toughness of the 3D-printed parts in comparison to their pure polymer counterparts. Furthermore, the incorporation of fillers facilitates improved thermal conductivity, electrical conductivity, and flame retardancy, thereby broadening the scope of potential applications for FDM/FFF 3D-printed components. Additionally, the article underscores the difficulties linked with the utilization of filled filaments in FDM/FFF 3D printing, including but not limited to filament extrusion stability, nozzle clogging, and interfacial adhesion between the reinforcement and matrix. Ultimately, a variety of pragmatic implementations are showcased, wherein filled filaments have exhibited noteworthy benefits in comparison to standard FDM/FFF raw materials. The aforementioned applications encompass a wide range of industries, such as aerospace, automotive, medical, electronics, and tooling. The article explores the possibility of future progress and the incorporation of innovative reinforcement materials. It presents a plan for the ongoing growth and application of advanced composite materials in FDM/FFF 3D printing.

Ink formulation is one of the main challenges with ceramic 3D printing. Here, we present a new, reactive-colloidal hybrid ink for 3D printing by robocasting of BaTiO3-based ceramics. The hybrid ink combines a titanium isopropoxide-based sol-gel base with a colloidal dispersion of powder, here demonstrated with BaTiO3 both as the sol-gel (by reaction of titanium isopropoxide and barium oxide) and colloidal (by addition of BaTiO3 powder) parts. Addition of glycerol was necessary to avoid fast precipitation and poor dispersion of BaTiO3 from the reaction of BaO and Ti-isopropoxide. With a solid loading of 40 ​vol% BaTiO3, 10 ​mm tall structures could be printed with minimal deformation from slumping. The BaTiO3 shows good piezo-, ferro- and dielectric properties after sintering, with a piezoelectric charge coefficient (d33 ​= ​159 ​pC/N) in the range commonly reported for BaTiO3. The hybrid inks developed in this work are therefore suitable for robocasting of BaTiO3-based electroceramics.

To reduce the carbon footprint of manufacturing processes, it is necessary to reduce the number of stages in the development process. To this end, integrating additive manufacturing processes with three-dimensional (3D) printing makes it possible to eliminate the need to use tooling for component manufacturing. Furthermore, using 3D printing allows the generation of complex models to optimize different components, reducing the development time and realizing lightweight structures that can be applied in different industries, such as the mobility industry. Printing process parameters have been studied to improve the mechanical properties of printed items. In this regard, although the failure of most structural components occurs under dynamic load, the majority of the evaluations are quasistatic. This work highlights an improvement in fatigue strength under dynamic loads in 3D-printed components through heat treatment. The fatigue resistance was improved regarding the number of cycles and the dispersion of results. This allows 3D-printed polylactic acid components to be structurally used, and increasing their reliability allows their evolution from a prototype to a functional component.

Flexible electronics and 3D printing are quickly reshaping the world in many aspects spanning from science, technology to industry and social society. However, there still exist many barriers to impede further progress of the areas. One of the biggest bottlenecks lies in the strong shortage of appropriate functional inks. Among the many printable materials ever tried such as conductive polymers, powdered plastic, metal particles or other adhesive materials, the liquid metal or its alloy is quickly emerging as a powerful electronic ink with diverse capabilities from which direct printing of flexible electronics and room temperature 3D printing for manufacturing metal structures are enabled. All these fabrication capabilities are attributed to the unique properties of such metal’s low melting point (generally less than 100 °C), flowable feature and high electrical conductivity etc. To better push forward the research and application of the liquid metal printed electronics and 3D manufacture, this article is dedicated to present an overview on the fundamental research advancements in processing and developing the liquid metal inks. Particularly, the flow, thermal, phase change and electrical properties of a group of typical liquid metals and their alloy inks will be systematically summarized and comparatively evaluated. Some of the practical applications of these materials in a wide variety of flexible electronics fabrication, 3D printing and medical sensors etc. will be briefly illustrated. Further, we also explained the basic categories of the liquid metal material genome towards discovering new functional alloy ink materials as initiated in the authors’ lab and interpret the important scientific and technical challenges lying behind. Perspective and future potentials of the liquid metal inks in more areas were also suggested.

PurposeThe purpose of this paper is to prepare and characterise various ink formulations for inkjet printing on nylon 66 carpet.Design/methodology/approachVarious ink formulations were prepared using CI Acid Red 57, synthetic thickeners (BYK425 and BYK420), ethylene glycol, diethylene glycol, isopropanol with auxiliaries. The inks were characterised for their rheological, wetting and storage stability properties. The inks were jetted using a Printos P16 drop‐on‐demand jet print‐head onto nylon 66 carpet materials. The printed images were characterised using an ImageXpert system.FindingsIt is found that the inks containing the synthetic thickeners at the optimum ratio give good printing and image properties, such as optical density, drop size, and depth of penetration into the substrate at pH 4‐5. The optimised ink formulation is found to have good storage stability.Research limitations/implicationsThe study focuses on ink formulations based on CI Acid Red 57. Ink formulations based on other colorants could also be studied in order to assess the applicability of the ink formulation system found for other colorants.Practical implicationsThe ink formulations developed could find use in industrial scale printing.Originality/valueLow cost ink formulations for printing of nylon carpets are novel.

Characterizing properties of scaffolds 3D printed with peptide-polymer conjugates

Additive manufacturing, particularly 3D printing, has revolutionized the manufacturing industry by allowing the production of complex and intricate parts at a lower cost and with greater efficiency. However, 3D-printed parts frequently require post-processing or integration with other machining technologies to achieve the desired surface finish, accuracy, and mechanical properties. Ultra-precision machining (UPM) is a potential machining technology that addresses these challenges by enabling high surface quality, accuracy, and repeatability in 3D-printed components. This study provides an overview of the current state of UPM for 3D printing, including the current UPM and 3D printing stages, and the application of UPM to 3D printing. Following the presentation of current stage perspectives, this study presents a detailed discussion of the benefits of combining UPM with 3D printing and the opportunities for leveraging UPM on 3D printing or supporting each other. In particular, future opportunities focus on cutting tools manufactured via 3D printing for UPM, UPM of 3D-printed components for real-world applications, and post-machining of 3D-printed components. Finally, future prospects for integrating the two advanced manufacturing technologies into potential industries are discussed. This study concludes that UPM is a promising technology for 3D-printed components, exhibiting the potential to improve the functionality and performance of 3D-printed products in various applications. It also discusses how UPM and 3D printing can complement each other.

Various ink formulations for inkjet printing on nylon66 carpet are prepared by using CI Acid Red 57, Natrosol and sodium alginate thickeners, ethylene glycol, diethylene glycol, and isopropanol with auxiliaries. The inks are characterised for their rheological, wetting, and storage stability properties. They were jetted by using a Printos P16 drop-on-demand jet print-head onto the nylon66 carpet materials, and the printed images were characterised by using an Image Xpert system. The inks that contained the synthetic thickeners at the optimum ratio provide good printing and imaging properties, such as optical density, drop size, and depth of penetration into the substrate at pH 4-5. The optimised ink formulation is found to have good storage stability. The study has focused on ink formulations based on CI Acid Red 57. Ink formulations based on other colorants could also be studied in order to assess the applicability of the ink formulation system found for other colorants. The ink formulations developed could find both uses in industrial scale printing and low cost ink formulations for printing of nylon66 carpets.

In the era of digital manufacturing, 3D printing has great potential in the spare parts supply chain due to its characteristics of real-time response manufacturing. In order to improve the docking efficiency of the supply and demand sides in 3D printing, the development of 3D printing cloud platform has received more and more attention. However, the traditional 3D printing platform can neither meet the needs of rapid production in actual production scenes nor create a safe and efficient data sharing mode. In order to meet these challenges, this paper proposes a 3D printing platform based on blockchain. First of all, the production standard identification and coordination solutions of spare parts suppliers are established to carry on the rapid qualification certification to the supplier. Secondly, the blockchain technology on-chain off-chain storage scheme is developed to achieve efficient sharing of 3D printed digital files under the premise of full property rights protection. Third, the product traceability service is developed to ensure the safety and transparency of spare parts. Finally, the effectiveness of the blockchain 3D printing platform is confirmed through the development of the prototype system.

Bone diseases such as osteomyelitis, osteosarcoma, and osteoarthritis, as well as conditions caused by metabolic imbalances, including osteoporosis, require more efficient and optimized therapies. Systemic drug administration entails major disadvantages like cytotoxicity and adverse reactions, which can lead to serious complications or death. Therefore, local drug administration alternatives are currently under investigation for different pharmacological therapies. New vectors were created to improve control over administration, and 3D-printed and patient-specific drug delivery systems have been tested, revealing great potential. Moreover, 3D-printed platforms that mimic human tissues for drug testing are innovative solutions emerging for the pharmaceutical industry. Situated between in vitro and in vivo testing on human patients, they offer the advantage of reproducing functional architecture, providing results that are closer to those encountered in clinical trials performed on patients. In our article, we present the two categories of 3D systems, from the perspective of main drug groups (antibiotics, anticancer, and anti-inflammatory) as well as other categories, alongside their advantages, limitations, and their adaptations to 3D printing technologies. This article also highlights the technological drawbacks encountered in both delivery and screening systems, as well as the printing methods and materials used, including their physical and biological properties.

3D printed graphene aerogels using conductive nanofibrillar network formulation

The recent interest in 3D printing with concrete has generated great interest on how inhomogeneities arise and affect performance parameters, in particular strength and durability. With respect to durability, of particular interest is how 3D‐printed layer interfaces can impact transport of species of interest, such as moisture, chlorides or carbon dioxide in carbonation processes. This is of particular interest considering that the primary use case of 3D‐printed concrete has been as a lost formwork for a cast structural concrete, and thus it is of interest to determine the carbonation resistance. This study consists of a preliminary look at the microstructure after accelerated carbonation of a 3D‐printed concrete used as a lost formwork. Preferential carbonation is observed in the layer interfaces compared to the bulk of the printed filaments, possibly related to porosity from air voids or a locally high capillary porosity corresponding to the lubrication layer.

Three-dimensional (3D) printing technologies have revolutionized bioengineering by enabling the fabrication of complex, customized structures with high morphological compatibility for specific functions. Most advances in the materials aspect of 3D printing have focused on developing inks that provide high stability and precise deposition for specific printing techniques. A new generation of printable materials not only ensures structural and mechanical integrity, but also incorporates additional functionalities directly into the material. The integration of rational structural design with functional materials offers powerful tools for biomedical applications. In this study, we developed a platform for investigating thermoresponsiveness in cell culture. By inducing controllable, localized heating, we examined the effects of hyperthermia on cancer cells, an emerging treatment modality gaining increasing attention as a promising anticancer strategy. We demonstrate that structurally controlled 3D-printed objects composed of polymer and iron oxide (IO) can generate defined thermal gradients upon exposure to infrared irradiation, thereby inducing differential cellular responses. Using precise spatial control with Digital Light Processing (DLP) printing, we created hyperthermia models. We demonstrated that the experimental conditions can detect changes in cell sensitivity, showing that pre-exposure of cancer cells to the cryoprotective compound trehalose alters their heat resistance. Moreover, repeated thermal cycles promoted the emergence of a cell subpopulation with enhanced heat resistance and increased aggressiveness, highlighting the platform's ability to drive adaptive cell selection based on thermal tolerance. Our findings indicate that thermal conditioning via 3D-printed platforms can serve as a robust tool for studying cellular responses to hyperthermia and may contribute to optimizing hyperthermia-based cancer therapies.