High-resolution Printing Research Articles

High-Resolution Nanotransfer Printing of Porous Crossbar Array Using Patterned Metal Molds by Extreme-Pressure Imprint Lithography.

High-resolution nanotransfer printing (nTP) technologies have attracted a tremendous amount of attention due to their excellent patternability, high productivity, and cost-effectiveness. However, there is still a need to develop low-cost mold manufacturing methods, because most nTP techniques generally require the use of patterned molds fabricated by high-cost lithography technology. Here, we introduce a novel nTP strategy that uses imprinted metal molds to serve as an alternative to a Si stamp in the transfer printing process. We present a method by which to fabricate rigid surface-patterned metallic molds (Zn, Al, and Ni) based on the process of direct extreme-pressure imprint lithography (EPIL). We also demonstrate the nanoscale pattern formation of functional materials, in this case Au, TiO2, and GST, onto diverse surfaces of SiO2/Si, polished metal, and slippery glass by the versatile nTP method using the imprinted metallic molds with nanopatterns. Furthermore, we show the patterning results of nanoporous crossbar arrays on colorless polyimide (CPI) by a repeated nTP process. We expect that this combined nanopatterning method of EPIL and nTP processes will be extendable to the fabrication of various nanodevices with complex circuits based on micro/nanostructures.

Trends in Photopolymerizable Bioinks for 3D Bioprinting of Tumor Models.

Three-dimensional (3D) bioprinting technologies involving photopolymerizable bioinks (PBs) have attracted enormous attention in recent times owing to their ability to recreate complex structures with high resolution, mechanical stability, and favorable printing conditions that are suited for encapsulating cells. 3D bioprinted tissue constructs involving PBs can offer better insights into the tumor microenvironment and offer platforms for drug screening to advance cancer research. These bioinks enable the incorporation of physiologically relevant cell densities, tissue-mimetic stiffness, and vascularized channels and biochemical gradients in the 3D tumor models, unlike conventional two-dimensional (2D) cultures or other 3D scaffold fabrication technologies. In this perspective, we present the emerging techniques of 3D bioprinting using PBs in the context of cancer research, with a specific focus on the efforts to recapitulate the complexity of the tumor microenvironment. We describe printing approaches and various PB formulations compatible with these techniques along with recent attempts to bioprint 3D tumor models for studying migration and metastasis, cell-cell interactions, cell-extracellular matrix interactions, and drug screening relevant to cancer. We discuss the limitations and identify unexplored opportunities in this field for clinical and commercial translation of these emerging technologies.

Innovative solution for relief printing without limiting heights

Abstract. By following technological developments in 3D printing, IGN experimented in 2015 with an ink jet-based relief printing solution, proposed by the Océ company. The first result was presented at the International Cartographic Conference in Rio de Janeiro in 2015, for the Belle-Ile map. The proposed technology solved several essential needs for relief mapping: high printing resolution, large size, colorimetric respect, ... But it still faced two problems: still high printing costs for the general public (compared to the prices of thermoformed maps produced in multiple copies) and still limited printing heights (less than 2–3 cm). In 2022, IGN proposed an innovative solution to overcome the problem of limiting printing heights, without increasing production costs. The new solution combines the previous ink jet relief printing technology with the Stratoconception® technology existing in the 3D printing domain. The solution is presented in detail in this paper with an example result.

3D Printing Hierarchically Nano-Ordered Structures.

Natural materials are composed of a limited number of molecular building blocks and their exceptional properties are governed by their hierarchical structure. However, this level of precision is unattainable with current state-of-the-art materials for 3D printing. Herein, new self-assembled printable materials based on block copolymers (BCPs) enabling precise control of the nanostructure in 3D are presented. In particular, well-defined BCPs consisting of poly(styrene) (PS) and a polymethacrylate-based copolymer decorated with printable units are selected as suitable self-assembled materials and synthesized using controlled radical polymerization. The synthesized library of BCPs are utilized as printable formulations for the fabrication of complex 3D microstructures using two-photon laser printing. By fine-tuning the BCP composition and solvent in the formulations, the fabrication of precise 3D nano-ordered structures is demonstrated for the first time. A key point of this work is the achievement of controlled nano-order within the entire 3D structures. Thus, imaging of the cross-sections of the 3D printed samples is performed, enabling the visualization also from the inside. The presented versatile approach is expected to create new avenues for the precise design of functional polymer materials suitable for high-resolution 3D printing exhibiting tailor-made nanostructures.

High-resolution hybrid printing of polymer and molten metal ink for printed electronics

Highly integrated, on-demand printed electronics attract lots of attention. The current fabrication methods for printed electronics are restricted to one material class and one technology, which limits the geometry design and the resolution of final products. The hybrid printing process is a potential method to effectively fabricate microscale 3D electronics with high resolution. In this paper, we developed a high-resolution (∼100 µm) hybrid printing process that integrates Electrohydrodynamic (EHD) printing and extrusion-based printing with metallic and polymeric material, respectively. Here, we characterized and verified the effect of several critical parameters, such as printing speed, pressure, voltage, and overlap on the printing process and quality of the printed features. The optimal set of printing parameters was determined for the hybrid printing process to obtain high-efficient and high-resolution printing. The best result obtained for PLA 1st layer is speed 1 mm/s, pressure 0.8 kg/cm2, overlap 25%. For the PLA 2nd layer, the best printing results are speed 0.4 mm/s, pressure 1 kg/cm2, and overlap 11%. The optimum result obtained for metal EHD printing is voltage 1.5 KV and speed 0.3 mm/s. At the end, we successfully implemented the hybrid printing process and printed high-resolution 3D electronics to demonstrate the potential capabilities of such hybrid printing in the fabrication of customized microelectronics.

Polymer nano nozzle fabricated by nanoscale electrohydrodynamic jet printing for high-resolution printing of low-viscosity inks

Electrohydrodynamic jet (E-jet) printing has emerged as a promising manufacturing technique in many areas due to its high efficiency, low cost, high resolution, and wide adaptability of materials. However, achieving further advancements in print resolution to the submicron and even nanoscale, particularly for low-viscosity inks with significant spread, requires nozzles with diameters in the hundreds of nanometers. It is particularly challenging and complicated to manufacture nozzles with such small diameters. In this paper, a concise method based on high-resolution E-jet printing was developed to fabricate nano-nozzles, which in turn enable high-resolution printing of a range of low-viscosity inks. First, the hybrid polymer nozzle mold consisting of BN303 nanomesa and SU-8 micromesa was fabricated by E-jet printing and ultraviolet (UV) lithography. Subsequently, the polymer nozzle was produced through a casting process of polydimethylsiloxane (PDMS) and subsequent bonding. In addition, the preliminary E-jet printing was performed with poly (3-hexylthiophene) (P3HT) ink using the polymer nozzle, resulting in lines as small as 140 nm. These outcomes demonstrate the compatibility of E-jet printing with high resolution and showcase the potential of the developed polymer nano-nozzles to significantly expand the scope of E-jet printing applications.

Trackable and highly fluorescent nanocellulose-based printable bio-resins for image-guided tissue regeneration

Dynamic tracking of cell migration during tissue regeneration remains challenging owing to imaging techniques that require sophisticated devices, are often lethal to healthy tissues. Herein, we developed a 3D printable non-invasive polymeric hydrogel based on 2,2,6,6-(tetramethylpiperidin-1-yl) oxyl (TEMPO)-oxidized nanocellulose (T-CNCs) and carbon dots (CDs) for the dynamic tracking of cells. The as-prepared T-CNC@CDs were used to fabricate a liquid bio-resin containing gelatin methacryloyl (GelMA) and polyethylene glycol diacrylate (GPCD) for digital light processing (DLP) bioprinting. The shear-thinning properties of the GPCD bio-resin were further improved by the addition of T-CNC@CDs, allowing high-resolution 3D printing and bioprinting of human cells with higher cytocompatibility (viability ∼95 %). The elastic modulus of the printed GPCD hydrogel was found to be ∼13 ± 4.2 kPa, which is ideal for soft tissue engineering. The as-fabricated hydrogel scaffold exhibited tunable structural color property owing to the addition of T-CNC@CDs. Owing to the unique fluorescent property of T-CNC@CDs, the human skin cells could be tracked within the GPCD hydrogel up to 30 days post-printing. Therefore, we anticipate that GPCD bio-resin can be used for 3D bioprinting with high structural stability, dynamic tractability, and tunable mechanical stiffness for image-guided tissue regeneration.

3D-Printed Microcubes for Catalase Drug Delivery.

Oxidative stress, i.e., excessive production of reactive oxygen species (ROS), plays an important role in the pathogenesis of inflammatory diseases such as cardiovascular diseases, cancer, and neurodegenerative diseases. Catalase, an antioxidant enzyme, has great therapeutic potential; however, its efficacy is limited by its delivery to target cells or tissues. In order to achieve efficient delivery, consistent drug distribution, and drug activity, small and uniformly sized drug delivery vehicles are needed. Here, three-dimensional (3D) microcubes were printed by Nanoscribe Photonic Professional GT2, a high-resolution 3D printer, and the characteristics of 3D-printed microcubes as drug delivery vehicles for the delivery of catalase were investigated. The size of the 3D-printed microcubes was 800 nm in length of a square and 600 nm in height, which is suitable for targeting macrophages passively. Microcubes were also tunable in shape and size, and high-resolution 3D printing could provide microparticles with little variation in shape and size. Catalase was loaded on 3D-printed microcubes by nonspecific adsorption, and catalase on 3D-printed microcubes (CAT-MC) retained 83.1 ± 1.3% activity of intact catalase. CAT-MC also saved macrophages, RAW 264.7, from the cytotoxicity of H2O2 by 86.4 ± 4.1%. As drug delivery vehicles, 3D-printed microparticles are very promising due to their small and uniform size, which provides consistent drug distribution and drug activity. Therefore, we anticipate numerous applications of 3D-printed microparticles for delivering therapeutic proteins.

A self-healing hydrogel and injectable cryogel of gelatin methacryloyl-polyurethane double network for 3D printing.

Three-dimensional (3D) printing of soft biomaterials facilitates the progress of personalized medicine. The development for different forms of 3D-printable biomaterials can promotes the potential manufacturing for artificial organs and provides biomaterials with the required properties. In this study, gelatin methacryloyl (GelMA) and dialdehyde-functionalized polyurethane (DFPU) were combined to create a double crosslinking system and develop 3D-printable GelMA-PU biodegradable hydrogel and cryogel. The GelMA-PU system demonstrates a combination of self-healing ability and 3D printability and provides two distinct forms of 3D-printable biomaterials with smart functions, high printing resolution, and biocompatibility. The hydrogel was printed into individual modules through an 80µm or larger nozzle and further assembled into complex structures through adhesive and self-healing abilities, which could be stabilized by secondary photocrosslinking. The 3D-printed hydrogel was adhesive, light transmittable, and could embed a light emitting diode (LED). Furthermore, the hydrogel laden with human mesenchymal stem cells (hMSCs) was successfully printed and showed cell proliferation. Meanwhile, 3D-printed cryogel was achieved by printing on a subzero temperature platform through a 210µm nozzle. After secondary photocrosslinking and drying, the cryogel was deliverable through a 16-gage (1194µm) syringe needle and can promote the proliferation of hMSCs. The GelMA-PU system extends the ink pool for 3D printing of biomaterials and has potential applications in tissue engineering scaffolds, minimally invasive surgery devices, and electronic wound dressings. STATEMENT OF SIGNIFICANCE: The 3D-printable biomaterials developed in this work are GelMA-based ink with smart funcitons and have potentials for various customized medical applications. The synthesized GelMA-polyurethane double network hydrogel can be 3D-printed into individual modules (e.g., 11×11×5mm3) through an 80μm or larger size nozzle, which are then assembled into a taller structure over five times of the initial height by self-healing and secondary photocrosslinking. The hydrogel is adhesive, light transmittable, and biocompatible that can either carry human mesenchymal stem cells (hMSCs) as bioink or embed a red light LED (620nm) with potential applications in electronic skin dressing. Meanwhile, the 3D-printed highly compressible cryogel (e.g., 6×6×1mm3) is deliverable by a 16-gage (1194μm) syringe needle and supports the proliferation of hMSCs also.

Improving glass nanostructure fabrication.

A new method offers high-resolution three-dimensional printing and low-temperature firing.

A microfluidics-assisted photopolymerization method for high-resolution multimaterial 3D printing

3D printing and bioprinting are recognized as key technologies for the construction of complex micro-devices, micro-environments, and culture models. Thanks to their potential to produce precisely heterogeneous and 3D architectures, multimaterial printing methods, which enable the production of functional 3D structures integrating multiple materials, have attracted specific attention. Nevertheless, combining multimaterial and high-resolution printing is still a major challenge, and the available technologies do not provide simultaneously the resolution and multiplexing capabilities required to create heterogeneous 3D environments. In this work, we introduce the 3D-FlowPrint concept, which involves an opto-microfluidic printhead immersed in a liquid and moved above a surface. This technology combines the convenience of microfluidics in terms of the handling and delivery of small volumes of materials with the resolution provided by laser lithography. Delivered materials are hydrodynamically confined under the printhead owing to controlled aspiration of the injected material, ensuring a continuous supply of material and avoiding cross-contamination issues. Combining microfluidics with photo-polymerization provides unique advantages as it separates the polymerization process from the material delivery, permitting high-resolution polymerization (down to 10 μm) and multimaterial handling (switching time below 60 s). We present a first proof-of-concept using poly(ethylene glycol) diacrylate (PEGDA)-based hydrogels as a photosensitive material model, along with a detailed investigation of the influence of exposure parameters, printhead velocity, and hydrodynamic parameters on the fabrication of 2D and 3D heterogeneous structures. 3D-FlowPrint allows the creation of sub-millimetric to millimetric scale objects with multimaterial designs. A first validation was performed to show the potential of the approach in biology for the creation of engineered microenvironments for cell culture.

51‐1: Distinguished Paper: High Precision and High Stability Inkjet Printing Technology for QD Color Converter‐type Micro LEDs Display

This paper proposed the inkjet head and the equipment. To realize high resolution printing with QD ink, we had to overcome the problem of robust inkjet head for QD particles. We proposed the inkjet head to eject high viscosity ink and the ink circulation system to avoid aggregation. Also, we proposed the DPN technology for high resolution printing. By combining the inkjet head technology and the equipment technology, we demonstrated QD color converter‐type Micro LEDs display panels.

BIO25: Toward a Biocompatible 3D Printing Resin for Microfluidic Organ Models

Background: Microfluidics is a desirable platform to create artificial organ models, such as organs-on-a-chip, to study disease and develop therapeutics in a 3D microenvironment. There is a gap in understanding and reproducing the microenvironment due to a lack of suitable models and means to fabricate these micron-scale architectures. 3D printed microfluidics offer a reliable fabrication approach with geometric control for replicating the tissue microenvironment at a relevant size-scale. However, gas-permeable, biocompatible materials for high-resolution microfluidic 3D printing do not exist. Here, we report a biocompatible, polydimethylsiloxane (PDMS) resin for facile 3D printing of microfluidics for tissue-based devices. Methods: 3D-printed parts were made using the Asiga MAX X UV27 digital light processing (DLP) 3D printer and our custom, high-resolution PDMS resin. Unreacted monomers and leachable components were extracted from 3D-printed well plates by soaking in ethanol for 72h and compared against untreated (no ethanol extraction) 3D-printed plates and standard cell culture plates. Absorbance of extraction media was measured to quantify the removal of leachables. Gas permeability of thin, 3D-printed films was measured for O2 and CO2 by Labthink International, Inc. according to ASTM D1434-82(R09)e1. Biocompatibility of the novel gas-permeable, high-resolution PDMS resin was tested by BioAssay Systems via a cell viability study with HepG2 cells in vitro. Results: Figure 1A shows a diminishing absorbance signal of the extractable compounds in the ethanol solution after each 24h soak of the cured resin. Reduction in the absorbance signal indicates removal of these unwanted constituents as confirmed by the lighter hue of extracted 3D-printed cell culture plate vs unextracted controls (Figure 1B). O2 and CO2 permeability are comparable to Sylgard 184 (Figure 1C). Cell viability studies performed with HepG2 cells (Figure 1D) grown on untreated 3D-printed plates, extracted 3D-printed plates, and control cell culture plates show that removal of unreacted groups and photoabsorbing compounds have a significant effect (p<0.05), improving cell growth and viability relative to the untreated and control groups. Conclusion: We have demonstrated the potential of this PDMS 3D printing resin as a biocompatible, gas-permeable material for cell-based microfluidic devices. Applications range from µALs as respiratory support devices to tissue-engineered, microfluidic organ models to study disease.Figure 1. (A) Absorbance signal of extraction media after soaking the 3D printed part in ethanol. (B) 3D printed well plates, untreated (no ethanol extraction) and extracted in ethanol (72h soak). (C) Gas permeability measurements of 100µm film made from PDMS resin. Sylgard 184 data were taken from literature. (D) Cell viability of HepG2 cells grown on control plates (standard 12-well), untreated 3D printed plates, and extracted 3D printed plates (n=3). Analyses of unpaired multiple t-tests between treatment groups (* indicates p-value<0.05) and 2-way ANOVA with Tukey’s multiple comparison test determined there was a significant interaction (p-value<0.0001) between the effects of treatment (control, untreated, and extracted) and time (24h and 72h) on cell viability (absorbance).

Microscale 3D printing of fish analogues using soy protein food ink

Plant-based meat analogues manufactured by three-dimensional (3D) food printing technology have increased in popularity nowadays. In this study, we used soy protein isolate (SPI), xanthan gum (XG) and rice starch (RS) as food ink for the 3D printing of fish analogues. We evaluated the printability of SPI/XG/RS food ink at different concentration ratios, and by adjusting the printing parameters, the high printing resolution of filaments (97.36 μm in width) in the range of real fish muscle fibers was successfully achieved. Fish analogues with similar texture properties to real fish meats were obtained by regulating their structural geometries, revealing the ability of 3D printing to tune to the myofiber-like texture of meat analogues. Thus, it was demonstrated that the high-precision 3D printing at the microscale could produce plant-based fish meat-like structures, providing a systematic approach to 3D print food analogues with the favorable mouthfeel.

3D printing of mechanically tough and self-healing hydrogels with carbon nanotube fillers.

Hydrogels have the potential to play a crucial role in bioelectronics, as they share many properties with human tissues. However, to effectively bridge the gap between electronics and biological systems, hydrogels must possess multiple functionalities, including toughness, stretchability, self-healing ability, three-dimensional (3D) printability, and electrical conductivity. Fabricating such tough and self-healing materials has been reported, but it still remains a challenge to fulfill all of those features, and in particular, 3D printing of hydrogel is in the early stage of the research. In this paper, we present a 3D printable, tough, and self-healing multi-functional hydrogel in one platform made from a blend of poly(vinyl alcohol) (PVA), tannic acid (TA), and poly(acrylic acid) (PAA) hydrogel ink (PVA/TA/PAA hydrogel ink). Based on a reversible hydrogen-bond (H-bond)-based double network, the developed 3D printable hydrogel ink showed excellent printability via shear-thinning behavior, allowing high printing resolution (~100 μm) and successful fabrication of 3D-printed structure by layer-by-layer printing. Moreover, the PVA/TA/PAA hydrogel ink exhibited high toughness (tensile loading of up to ~45.6 kPa), stretchability (elongation of approximately 650%), tissue-like Young's modulus (~15 kPa), and self-healing ability within 5 min. Furthermore, carbon nanotube (CNT) fillers were successfully added to enhance the electrical conductivity of the hydrogel. We confirmed the practicality of the hydrogel inks for bioelectronics by demonstrating biocompatibility, tissue adhesiveness, and strain sensing ability through PVA/TA/PAA/CNT hydrogel ink.

A high-absorbance water-soluble photoinitiator nanoparticle for hydrogel 3D printing: synthesis, characterization and in vitro cytotoxicity study

Light-based hydrogel crosslinking is a new approach in rapid and high-resolution 3D printing; however, using this method in tissue engineering is challenging due to the toxicity of photoinitiators, their solvents, and their low efficiency. Herein, a novel, water-soluble photoinitiator with high efficiency in light-based 3D printing is introduced. Low-cost photoinitator, 2,4,6-trimethylbenzoylphenyl phosphinate, is converted into nanoparticles via a microemulsion method and dispersed in water. Cell toxicity assays were performed to prove that these nanoparticles are non-toxic and can be used in biomedical applications. Finally, the nanoparticles were utilized in the high-accuracy 3D printing of hydrogels. The results of this study indicate that these particles are potent to be used in bioprinting.

Hydrogel-Assisted Double Molding Enables Rapid Replication of Stereolithographic 3D Prints for Engineered Tissue Design.

Tissue-engineered in vitro models are an essential tool in biomedical research. Tissue geometry is a key determinant of function, but controlling the geometry of microscale tissues remains challenging. Additive manufacturing approaches have emerged as a promising means for rapid and iterative changes in the geometry of microdevices. However, it has been shown that poly(dimethylsiloxane) (PDMS) cross-linking is often inhibited at the interface of materials printed with stereolithography. While approaches to replica mold stereolithographic three-dimensional (3D) prints have been described, these methods are inconsistent and often lead to print destruction when unsuccessful. Additionally, 3D-printed materials often leach toxic chemicals into directly molded PDMS. Here, we developed a double molding approach that allows precise replication of high-resolution stereolithographic prints into poly(dimethylsiloxane) (PDMS) elastomer, facilitating rapid design iterations and highly parallelized sample production. Inspired by lost wax casting, we used hydrogels as intermediary molds to transfer high-resolution features from high-resolution 3D prints into PDMS, while previously published work focused on enabling direct molding of PDMS onto 3D prints through the use of coatings and post-cross-linking treatments of the 3D print itself. Hydrogel mechanical properties, including cross-link density, predict replication fidelity. We demonstrate the ability of this approach to replicate a variety of shapes that would be impossible to create using photolithography techniques traditionally used to create engineered tissue designs. This method also enabled the replication of 3D-printed features into PDMS that would not be possible with direct molding as the stiffness of these materials leads to material fracture when unmolding, while the increased toughness in the hydrogels can elastically deform around complex features and maintain replication fidelity. Finally, we highlight the ability of this method to minimize the potential for toxic materials to transfer from the original 3D print into the PDMS replica, enhancing its use for biological applications. This minimization of the transfer of toxic materials has not been reported in other previously reported methods describing replication of 3D prints into PDMS, and we demonstrate its use through the creation of stem cell-derived microheart muscles. This method can also be used in future studies to understand the effects of geometry on engineered tissues and their constitutive cells.

High-Speed and High-Resolution 3D Printing of Self-Healing and Ion-Conductive Hydrogels via μCLIP

Conductive and self-healing (SH) hydrogels have been receiving continuous attention, which could broaden the design of ionotronic devices for health monitoring systems and soft robots with the ability to repair damage autonomously. So far, three-dimensional (3D) fabrication of such SH hydrogels is mainly limited to traditional molding/casting or extrusion-based 3D printing methods, which limits the formation of sophisticated structures with high-resolution features. Furthermore, the need of external stimuli (e.g., water, heat, and pH change) to achieve SH behavior could restrict their wide application. Herein, we report an ion-conductive SH hydrogel suitable for a home-built high-resolution and high-speed 3D printing process, micro continuous liquid interface production (μCLIP). This material system relies on interpenetrating polymer networks (IPN) hydrogel formed by physically cross-linked poly(vinyl alcohol) combined with chemically/ionically cross-linked poly(acrylic acid) and ferric chloride. By carefully optimizing the resin’s composition, we can balance high-resolution printability and superb SH capability, at the same time manifesting sufficient ion conductivity. Specifically, complex 3D structures with microscale features (down to 100 μm) can be printed at speeds up to 16.5 μm s–1. Upon damage occurs, hydrogen bonds within hydroxyl and carboxyl groups, as well as ionic bonds generated from ferric ions, contribute together to achieve fast and high efficiency SH, which can restore 90% (100%) of the original mechanical strength at room temperature within 4 h (8 h) without any external stimulus. In addition, both the as-printed and self-healed hydrogels manifest superior ion conductivity and stretchability. Therefore, the SH hydrogels can be rapidly printed and tailored as customized wearable sensors, and the sensing capabilities were quantitatively investigated and compared. In terms of applications, SH hydrogel-based knuckle sensors were prototyped to detect a finger’s folding and unfolding motions.

Lignin nanoparticle-enhanced biobased resins for digital light processing 3D printing: Towards high resolution and tunable mechanical properties

The more widespread applicability of photopolymerization-based three-dimensional (3D) printing is limited by the availability of light-curable resins, most of which are based on fossil-derived compounds. We developed a biobased lignin-derivable resin by utilizing methacrylated derivatives of vanillin, vanillyl alcohol, and eugenol as aromatic monomers. Lignin nanoparticles (LNPs) were incorporated as functional fillers that enhance print resolution and material properties. The crosslinking degree, and thereby the tensile properties, was modulated through the use of mono- or dimethacrylated vanillin derivatives in the resin formulation. The LNPs acted as UV absorbers, conferring better control of the photopolymerization process by preventing light penetration across unintended layers, leading to enhanced print resolution. The LNPs showed excellent dispersion stability due to their size and morphology. The inclusion of up to 2 wt% of LNPs improved the ductility of the 3D printed nanocomposites through toughening mechanisms enabled by the rigid nanoparticles. Finally, exploiting the differences in crosslinking degree of the resin formulations, a multi-material model featuring both soft and rigid domains was fabricated. This study demonstrates a simple but effective strategy for the design of biobased photocurable resins with tailorable mechanical properties that are suitable for high-resolution and multi-material 3D printing.

Fast Coating of Polydopamine Enables Scratch/Moisture Resistant Flexible Electronics

High biocompatibility and stability against water and scratch are crucial for liquid metal-based flexible electronics. Although previous studies have reported the chemical modification of liquid metal nanoparticles which can promote their water-stability and solution-processability, the modification process is complicated and hard to scale up. In particular, polydopamine (PD)-coated liquid metal nanoparticles (LMNPs) have not been used in flexible devices. We report the synthesis of the PD on LMNPs by thermal processing, which is controllable, fast, straightforward, and scalable. Because of the adhesiveness of PD, the PD@LM ink enables high-resolution printing on many substrates. The circuit printed by PD@LM shows high stability against repeated stretch in water (sustaining cardiomyocyte beating for 1 month─around 3 million times) and scratch. This conductive ink is highly biocompatible, conductive (4000 s/cm), and stretchable (up to 800% elongation). We cultured cardiomyocytes onto the PD@LM electrode and recorded the membrane potential change under electrical stimulation. For in vivo use, we fabricated a stable electrode to detect the electrocardiogram signal of a beating heart.