High-resolution Printing Research Articles

Towards industry-ready additive manufacturing: AI-enabled closed-loop control for 3D melt electrowriting.

Melt electrowriting (MEW) is an emerging high-resolution 3D printing technology used in biomedical engineering, regenerative medicine, and soft robotics. Its transition from academia to industry faces challenges such as slow experimentation, low printing throughput, poor reproducibility, and user-dependent operation, largely due to the nonlinear and multiparametric nature of the MEW process. To address these challenges, we applied computer vision and machine learning to monitor and analyze the process in real-time through imaging of the MEW jet between the nozzle-collector gap. To collect data for training we developed an automated data collection methodology that eases the experimental time from days to hours. A feedforward neural network, working in concert with optimization methods and a feedback loop, is used to develop closed-loop control ensuring reproducibility of the printed parts. We demonstrate that machine learning allows streamlining the MEW operation via closed-loop control of the highly nonlinear 3D printing technology.

Green Synthesis of Soybean Oil-Derived UV-Curable Resins for High-Resolution 3D Printing

Green Synthesis of Soybean Oil-Derived UV-Curable Resins for High-Resolution 3D Printing

Dynamic interface printing

Additive manufacturing is an expanding multidisciplinary field encompassing applications including medical devices1, aerospace components2, microfabrication strategies3,4 and artificial organs5. Among additive manufacturing approaches, light-based printing technologies, including two-photon polymerization6, projection micro stereolithography7,8 and volumetric printing9–14, have garnered significant attention due to their speed, resolution or potential applications for biofabrication. Here we introduce dynamic interface printing, a new 3D printing approach that leverages an acoustically modulated, constrained air–liquid boundary to rapidly generate centimetre-scale 3D structures within tens of seconds. Unlike volumetric approaches, this process eliminates the need for intricate feedback systems, specialized chemistry or complex optics while maintaining rapid printing speeds. We demonstrate the versatility of this technique across a broad array of materials and intricate geometries, including those that would be impossible to print with conventional layer-by-layer methods. In doing so, we demonstrate the rapid fabrication of complex structures in situ, overprinting, structural parallelization and biofabrication utility. Moreover, we show that the formation of surface waves at the air–liquid boundary enables enhanced mass transport, improves material flexibility and permits 3D particle patterning. We, therefore, anticipate that this approach will be invaluable for applications where high-resolution, scalable throughput and biocompatible printing is required.

Low-cost fabrication of digital light processing 3D printed conical microneedles for biomedical applications

The 3D printing of microneedles has become an emerging area of research focus due to its ability to rapidly create microneedle arrays with parametrically variable geometry and composition. Through direct fabrication or via replica molding, 3D printed microneedles can facilitate iterative array assessment and act as a screening tool to quickly establish optimal parameters for tissue insertion and capacity for biomarker monitoring or drug release. However, the widespread adoption of 3D printing by microneedle array researcher group faces multiple barriers: (1) Investment in 3D printing systems that are traditionally associated with high-resolution pose a significant financial cost, (2) Current high-resolution printing methods are often slow and not conducive to rapid manufacturing, (3) Material selection can be limited in some ‘proprietary’ 3D printing systems (e.g. CLIP, SLA, or 2PP), (4) Given the multidisciplinary nature of the microneedle-field, researchers may not have the expertise to optimize printing parameters for a given material or printer. This work explores how ultra-low-cost digital light processing (DLP) printers can rapidly produce functional microneedle arrays for a variety of purposes, whether direct print, master mold production, or creation of coated microneedles, at a fraction of the cost of currently used systems. Further, this work highlights that high quality microneedle arrays can be created using DLP printing methods with reliability exceeding 98 %, tip radii on the order of 30 µm, and with appropriate parameter input optimization, high quality microneedle arrays can be fabricated that express desirable characteristics for multiple forms of solid microneedle array production.

Versatile binder system as enabler for multi-material additive manufacturing of ceramics by vat photopolymerization

Vat photopolymerization is an additive manufacturing process for producing ceramics with high printing resolution. Extending this approach to multi-material additive manufacturing, the aim is to combine two or more different ceramics in a single component to aggregate their advantages. For this, binders for different ceramic materials are required. To enhance the debinding step, this work aimed to develop a versatile binder system suitable for different ceramic materials. Finally, a binder system was developed and qualified for several different ceramic materials. By thermogravimetrical analyses, a suitable temperature curve for debinding was derived. In a final sintering step, the components were densified almost defect-free. Therefore, this work serves as an enabler for multi-material vat photopolymerization.

Enhancing alginate dialdehyde-gelatin (ADA-GEL) based hydrogels for biofabrication by addition of phytotherapeutics and mesoporous bioactive glass nanoparticles (MBGNs)

This study explores the 3D printing of alginate dialdehyde-gelatin (ADA-GEL) inks incorporating phytotherapeutic agents, such as ferulic acid (FA), and silicate mesoporous bioactive glass nanoparticles (MBGNs) at two different concentrations. 3D scaffolds with bioactive properties suitable for bone tissue engineering (TE) were obtained. The degradation and swelling behaviour of films and 3D printed scaffolds indicated an accelerated trend with increasing MBGN content, while FA appeared to stabilize the samples. Determination of the degree of crosslinking validated the increased stability of hydrogels due to the addition of FA and 0.1% (w/v) MBGNs. The incorporation of MBGNs not only improved the effective moduli and conferred bioactive properties through the formation of hydroxyapatite (HAp) on the surface of ADA-GEL-based samples but also enhanced VEGF-A expression of MC3T3-E1 cells. The beneficial impact of FA and low concentrations of MBGNs in ADA-GEL-based inks for 3D (bio)printing applications was corroborated through various printing experiments, resulting in higher printing resolution, as also confirmed by rheological measurements. Cytocompatibility investigations revealed enhanced MC3T3-E1 cell activity and viability. Furthermore, the presence of mineral phases, as confirmed by an in vitro biomineralization assay, and increased ALP activity after 21 days, attributed to the addition of FA and MBGNs, were demonstrated. Considering the acquired structural and biological properties, along with efficient drug delivery capability, enhanced biological activity, and improved 3D printability, the newly developed inks exhibit promising potential for biofabrication and bone TE.

Digital Light Processing (DLP) 3D Printing of Caprolactone Copolymers with Tailored Properties through Crystallinity.

Digital light processing (DLP) 3D printing has shown great advantages such as high resolution in the fabrication of 3D objects toward a range of applications. Despite the rapid development of photocurable materials for DLP printing, tailoring properties to meet the specific demands for various applications remains challenging. Herein, we introduce copolymers of caprolactone and allyl caprolactone offering built-in functionality for thiol-ene photochemistry, thereby omitting the need for postfunctionalization. A crystalline block copolymer and an amorphous statistical copolymer were synthesized with the same comonomer composition and molecular weight. Thio-ene photocuring with a tetrafunctional thiol cross-linker was studied at different thiol to double-bond ratios for the copolymers and their blends. All formulations undergo rapid photocuring within several seconds of irradiation with slightly higher gel fractions observed for the statistical copolymer over the block copolymer under the same conditions, suggesting a somewhat higher cross-link density. Thermal properties of the networks were dependent on the presence of the semicrystalline block copolymer, where higher melting enthalpies were reached at higher block copolymer content. Similarly, crystallinity was found to be the main contributor to the mechanical properties. For a comparable composition, the modulus of a block copolymer network was found to be 31 times higher than that of the statistical copolymer network (27.7 vs 0.89 MPa). Intermediate moduli could be obtained by blending the two copolymers. DLP-printed scaffolds from these copolymers retained their thermal properties, therefore offering an efficient approach to tailoring mechanical properties, through crystallinity. Moreover, the printed scaffold displayed shape memory properties as the first example of poly(carprolactone) (PCL) copolymers in DLP printing. These materials are readily synthesized, offer fast and high-resolution 3D printing, and are degradable and cell compatible. They offer a straightforward approach to tailoring properties of PCL-based biomaterials and devices.

Oxime esters: Potential alternatives to phosphine oxides, for overcoming oxygen inhibition in material jetting applications

Material jetting technology is emerging as a prominent technique within the additive manufacturing domain for printing multi-material objects. Despite its various advantages, including high printing resolution, oxygen inhibition remains the main issue for UV-curable materials. Oxime esters are interesting photoinitiators for this application due to their ability to undergo a photocleavage reaction followed by decarboxylation, limiting the diffusion of oxygen. A series of four commercially available oxime esters were studied as Type I photoinitiators, with the photoinitiating ability and photochemical properties of two of them never having been investigated before. Initially, their UV–visible absorption properties were studied, revealing significant absorption up to 420nm. Photopolymerization kinetic studies indicate that the oxime esters can outperformed benchmark photoinitiators such as phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO) by reaching around 80% of double bond conversion in 12µm layer under air (for O-16) against 60% for BAPO under the same conditions. Finally, the oxime esters were tested in 3D-inkjet printing applications, displaying highly promising results with tack-free surfaces.

Printing of 3D photonic crystals in titania with complete bandgap across the visible spectrum.

A photonic bandgap is a range of wavelengths wherein light is forbidden from entering a photonic crystal, similar to the electronic bandgap in semiconductors. Fabricating photonic crystals with a complete photonic bandgap in the visible spectrum presents at least two important challenges: achieving a material refractive index > ~2 and a three-dimensional patterning resolution better than ~280 nm (lattice constant of 400 nm). Here we show an approach to overcome such limitations using additive manufacturing, thus realizing high-quality, high-refractive index photonic crystals with size-tunable bandgaps across the visible spectrum. We develop a titanium ion-doped resin (Ti-Nano) for high-resolution printing by two-photon polymerization lithography. After printing, the structures are heat-treated in air to induce lattice shrinkage and produce titania nanostructures. We attain three-dimensional photonic crystals with patterning resolution as high as 180 nm and refractive index of 2.4-2.6. Optical characterization reveals ~100% reflectance within the photonic crystal bandgap in the visible range. Finally, we show capabilities in defining local defects and demonstrate proof-of-principle applications in spectrally selective perfect reflectors and chiral light discriminators.

3D-Printed Latticed Microneedle Array Patches for Tunable and Versatile Intradermal Delivery.

Using high-resolution 3D printing, a novel class of microneedle array patches (MAPs) is introduced, called latticed MAPs (L-MAPs). Unlike most MAPs which are composed of either solid structures or hollow needles, L-MAPs incorporate tapered struts that form hollow cells capable of trapping liquid droplets. The latticestructures can also be coated with traditional viscous coating formulations, enabling both liquid- and solid-state cargo delivery, on a single patch. Here, a library of 43 L-MAP designs is generated and in-silico modeling is used to down-select optimal geometries for further characterization. Compared to traditionally molded and solid-coated MAPs, L-MAPs can load more cargo with fewer needles per patch, enhancing cargo loading and drug delivery capabilities. Further, L-MAP cargo release kinetics into the skin can be tuned based on formulation and needle geometry. In this work, the utility of L-MAPs as a platform is demonstrated for the delivery of small molecules, mRNA lipid nanoparticles, and solid-state ovalbumin protein. In addition, the production of programmable L-MAPs is demonstrated with tunablecargo release profiles, enabled by combining needle geometries on a single patch.

Synthesis and Solvent Free DLP 3D Printing of Degradable Poly(Allyl Glycidyl Ether Succinate).

Digital light processing (DLP) printing forms solid constructs from fluidic resins by photochemically crosslinking polymeric resins with reactive functional groups. DLP is used widely due to its efficient, high-resolution printing, but its use and translational potential has been limited in some applications as state-of-the-art resins experience unpredictable and anisotropic part shrinkage due to the use of solvent needed to reduce resin viscosity and layer dependent crosslinking. Herein, poly(allyl glycidyl ether succinate) (PAGES), a low viscosity, degradable polyester, was synthesized by ring opening copolymerization and used in combination with degradable thiol crosslinkers to afford a solvent free resin that can be utilized in DLP printing. Varying resin formulations of PAGES polymer are shown to decrease part shrinkage from 14% to 0.3%. Photochemically printed parts fabricated from PAGES possess tensile moduli between 0.43 and 6.18 MPa and degradation profiles are shown to vary between 12 and 40 days under accelerated conditions based on degree of polymerization and crosslink ratio.

Inkjet Printing of a Gate Insulator: Towards Fully Printable Organic Field Effect Transistor

In this work, a gate insulator poly (4-vinylphenol) (PVP) of an organic field effect transistor (OFET) was deposited using an inkjet printing technique, realized via a high printing resolution. Various parameters, including the molecular weight of PVP, printing direction, printing voltage, and drop frequency, were investigated to optimize OFET performance. Consequently, PVP with a smaller molecular weight of 11 k and a printing direction parallel to the channel, a printing voltage of 18 V, and a drop frequency of 10 kHz showed the best OFET performance. With a direct ink writing-printed organic semiconductor, this work paves the way for fully inkjet-printed OFETs.

3D-Printed Interfacially Jammed Emulsion Aerogels.

3D printing ultralightweight porous structures using direct ink writing (DIW) while maintaining their mechanical robustness is highly challenging. This difficulty is amplified when low ink concentrations are used to create complex geometries. Herein, this shortfall was addressed by interfacially jammed emulsion gels. The gel emerged from the electrostatic interaction among synergized nanomaterials (graphene oxide (GO) and cellulose nanocrystals (CNCs)) in the aqueous phase and a ligand in the oil phase. This interaction led to the jamming of the nanoparticles and the creation of stable emulsion gels. The formed interfacial assemblies were further treated by post-jamming ionic cross-linking with NaHCO3, which dictated the emulsion gels' rheological characteristics, enhancing the ink's viscoelastic properties for high-resolution 3D printing. The customizable emulsion system allows control over porosity from the macro- to the micro-scale and generates complex geometries with desired compositions. By manipulating post-annealing processes and varying concentrations, it is possible to achieve aerogels that feature a remarkably low density (∼2.63 mg/cm3) and adjustable mechanical robustness (elastic modulus of 0.45 MPa). Additionally, this method allows for producing aerogels with flexible or stiff characteristics as required, alongside the capability to tailor specific electromagnetic shielding effectiveness (ranging from 6791 to 19615 dB cm2/g), showcasing the technique's versatility and engineerability.

Decolorization of Lignin for High-Resolution 3D Printing of High Lignin-Content Composites.

Lignin, one of the most abundant biomaterials and a large-scale industrial waste product, is a promising filler for polymers as it reduces the amount of fossil resources and is readily available. 3D printing is well-known for producing detailed polymer structures in small sizes at low waste production. Especially light-assisted 3D printing is a powerful technique for production of high-resolution structures. However, lignin acts as a very efficient absorber for UV and visible light limiting the printability of lignin composites, reducing its potential as a high-volume filler. In this work, the decolorization of lignin is presented for high-resolution 3D printing of biocomposites with lignin content up to 40wt.%. Organosolv lignin (OSL) is decolorized by an optimized low-energy process of acetylation and subsequent UV irradiation reducing the UV absorbance by 71%. By integration of decolorized lignin into bio-based tetrahydrofurfuryl acrylate (THFA), a lignin content of 40wt.% and a resolution of 250µm is achieved. Due to the reinforcing properties of lignin, the stiffness and strength of the material is increased by factors of 15 and 2.3, respectively. This work paves the way for the re-use of a large amount of lignin waste for 3D printing of tough materials at high resolution.

Surface modification strategies for improved cellulose nanocrystal integration in 3D-Printed bio-based acrylate matrix

The current application of renewable resources in vat photopolymerization (VP) 3D printing is rather limited, emphasizing the importance of incorporating bio-based materials into additive manufacturing (AM). In this study, VP 3D printing technology was applied to create composites (derived from soybean oil-based resin) reinforced with cellulose nanocrystals (CNC). Two distinct modifications for CNC, i.e., the acrylation and functionalization with methyl methacrylate, were selected to achieve strong bonding with the UV-curable acrylate matrix. With the use of 0.1 wt% of modified CNC, the resins retain remarkable performance and support the creation of high-resolution prints. The successful integration of modified CNC showed significant improvements in tensile and flexural properties, e.g., elongation at break increased by 75 % and 295 %, respectively. The addition of modified CNC fillers also increased tensile strength by 147 % and flexural strength by 121 %. Fourier-transformation infrared (FTIR) spectroscopy and dynamic mechanical analysis (DMA) testified to the enhanced interface between filler and matrix. The morphological features and print quality were examined with microscopic analysis, UV-VIS spectroscopy, and colorimetry. The resin showed exceptional printing resolution, characteristic of VP printing, and yielded double bond conversion rates greater than 70 %. The findings presented here indicate that the addition of 0.1 wt% of modified CNC to bio-based resins results in an exceptional increase in the mechanical performance and dimensional stability of printed materials.

Microfluidic Lab-on-CMOS Packaging Using Wafer-Level Molding and 3D-Printed Interconnects.

Lab-on-a-chip (LoC) technologies continue to promise lower cost and more accessible platforms for performing biomedical testing in low-cost and disposable form factors. Lab-on-CMOS or lab-on-microchip methods extend this paradigm by merging passive LoC systems with active complementary metal-oxide semiconductor (CMOS) integrated circuits (IC) to enable front-end signal conditioning and digitization immediately next to sensors in fluid channels. However, integrating ICs with microfluidics remains a challenge due to size mismatch and geometric constraints, such as non-planar wirebonds or flip-chip approaches in conflict with planar microfluidics. In this work, we present a hybrid packaging solution for IC-enabled microfluidic sensor systems. Our approach uses a combination of wafer-level molding and direct-write 3D printed interconnects, which are compatible with post-fabrication of planar dielectric and microfluidic layers. In addition, high-resolution direct-write printing can be used to rapidly fabricate electrical interconnects at a scale compatible with IC packaging without the need for fixed tooling. Two demonstration sensor-in-package systems with integrated microfluidics are shown, including measurement of electrical impedance and optical scattering to detect and size particles flowing through microfluidic channels over or adjacent to CMOS sensor and read-out ICs. The approach enables fabrication of impedance measurement electrodes less than 1 mm from the readout IC, directly on package surface. As shown, direct fluid contact with the IC surface is prevented by passivation, but long-term this approach can also enable fluid access to IC-integrated electrodes or other top-level IC features, making it broadly enabling for lab-on-CMOS applications.

A study on the synergistic chondro-inductive effects of collagen II and its high-resolution 3D-printed scaffolds

Collagen II is the most essential component of the cartilage-specific extracellular matrix (ECM). However, research on collagen II-based scaffold fabrication, structural optimization, and correlation to the chondrogenic activities of stem cells is currently limited, presumably due to challenges related to its hydrogel processability. Existing collagen II-containing scaffolds are mainly produced by freeze-drying and exhibit limited properties, such as pore interconnectivity and tortuosity. Additionally, the chondro-inductive capability of collagen II composition and its underlying mechanism remains unclear, warranting further research. In this study, we addressed the aforementioned issues by investigating and enhancing the rheological properties of collagen II-based hydrogel, resulting in a high printing resolution exceeding 150 μm. The collagen II composition reportedly facilitated the condensation and chondrogenic activities of mesenchymal stem cells (MSCs) compared to gelatin. Moreover, high-resolution collagen II-based scaffolds promoted cell proliferation and chondrogenic differentiation to a higher degree. Therefore, we optimized the compositional and structural characteristics of collagen II-based scaffolds for enhancing chondrogenic activities. We anticipate that this study will broaden our understanding of collagen II-based scaffold designs and condition optimizations for cartilage tissue engineering.

Ex vivo liquid core fiber photometry with high-resolution 3D printing

High resolution 3D printing emerges as an alternative to microfabrication due to its fine resolution along with one-step manufacturing. Thus, it is broadly used in many fields, such as biological and chemical applications. We introduce such a technique to the design of the optofluidic probe by integrating optics and microfluidics as an ex vivo liquid core fiber photometry. We build the optofluidic probes with various T-shapes and conduct the transmission measurements and the ray tracing simulations, where the results are comparable. Through the transmission and fluorescence measurements, we obtain optimized curl T-shape dimensions of 524 µm wide, ∼50 µm thick, and 350 µm long with longitudinal spaces between them of 260 um. Furthermore, a heightened level of complexity in structure, characterized by a feature size of 25 µm, is attained through the improvement process. We conclude the feasibility of this optofluidic system with two applications: the in vivo-like setting consisting of thyroid biopsy training phantom and human plasma and the ex vivo-like setting consisting of the mice brain slices stained with wheat germ agglutinin (WGA). This prototype is an important step of establishing a 3D printing optofluidic applications for various in vivo research.

Preoperative planning of craniectomy and reconstruction using three-dimension-printed cranioplasty for treatment of calvarial lesion.

Common calvarial lesions include fibrous dysplasia (FD), intraosseous meningioma, osteoma, Langerhans cell histiocytosis (LCH), intraosseous hemangioma, dermoid and epidermoid cyst, and malignancy. Surgical removal with removal of the involved skull is the choice of treatment for these lesions. Previously, the skull defect was repaired using allograft, and alloplastic materials have been replaced with newer polyetheretherketone (PEEK) material, which is more resistant, biocompatible, and can be 3-dimension (3D)--printed. High-resolution 3D printing uses very fine extruders to put materials in fine layers to recreate patients' anatomy authentically, which gives superior cosmetic outcomes. Our objectives were preoperative planning of craniectomy and reconstruction for calvarial lesions and reconstruction of skull defects using 3D-printed cranioplasty with PEEK materials. In this series, we describe 11 cases in which skull lesions were removed and reconstructed in the same sitting using a 3D-printed PEEK implant designed preoperatively using high-resolution computer tomography. All the cases were done in the neurosurgery department of Bangabandhu Sheikh Mujib Medical University from 2021 to 2023. Patients were followed up for 6 months after surgery. Regarding 11 cases, six cases were FD, three cases were intraosseous meningioma, one case was intraosseous hemangioma, and one case was LCH. Average lesion size were 12.73-5.77 cm. Cranioplasty was done with PEEK material. Minor complications were treated conservatively. Seroma, postoperative fever, and nausea were among these. The human bone-like biocompatibility and resistance to physical forces leads to more frequent use of PEEK, which enables to repair of complex craniofacial defects with better cosmesis. Despite some limitations, the PEEK cranioplasty implant continued to thrive and showed its promise to be an excellent material. Further, research and investment should be put into developing the technique.

3D printable and biocompatible PEDOT:PSS-ionic liquid colloids with high conductivity for rapid on-demand fabrication of 3D bioelectronics

3D printing has been widely used for on-demand prototyping of complex three-dimensional structures. In biomedical applications, PEDOT:PSS has emerged as a promising material in versatile bioelectronics due to its tissue-like mechanical properties and suitable electrical properties. However, previously developed PEDOT:PSS inks have not been able to fully utilize the advantages of commercial 3D printing due to its long post treatment times, difficulty in high aspect ratio printing, and low conductivity. We propose a one-shot strategy for the fabrication of PEDOT:PSS ink that is able to simultaneously achieve on-demand biocompatibility (no post treatment), structural integrity during 3D printing for tall three-dimensional structures, and high conductivity for rapid-prototyping. By using ionic liquid-facilitated PEDOT:PSS colloidal stacking induced by a centrifugal protocol, a viscoplastic PEDOT:PSS-ionic liquid colloidal (PILC) ink was developed. PILC inks exhibit high-aspect ratio vertical stacking, omnidirectional printability for generating suspended architectures, high conductivity (~286 S/cm), and high-resolution printing (~50 µm). We demonstrate the on-demand and versatile applicability of PILC inks through the fabrication of 3D circuit boards, on-skin physiological signal monitoring e-tattoos, and implantable bioelectronics (opto-electrocorticography recording, low voltage sciatic nerve stimulation and recording from deeper brain layers via 3D vertical spike arrays).