Light-based 3D Research Articles

Manipulate dynamic chemical interactions in renewable polymers for 3D printing tunable, healable, and recyclable metamaterials

Mechanical metamaterials have garnered significant interests due to their unique properties, which arise from the periodic structures of their constituent units. However, traditional mechanical metamaterials suffer from limitations of fixed properties of the constituent units or irreversibility if they are damaged or little-to-no recyclability. Addressing this challenge, herein, a photoresin consisting of a monomer synthesized from a renewable biomass—epoxidized soybean oil (ESO)—citric acid (CA) and other components was developed for light-based 3D printing. It is discovered that the UV irradiation initiates photopolymerized of the highly photoactive epoxidized soybean oil-ethyl acrylamide (ESO-EA) monomer while enabling the epoxy-acid reaction (EAR) of the epoxy groups in ESO-EA with carboxyl groups in CA to create dynamic chemical bonds (DCBs). This formed dynamic crosslinking network endows the printed material with tunable tensile strengths (0.3–10.4 MPa) and shape memory behaviors (transition temperature: 22–48 °C) while maintaining high stretchability (fractural strain: 81 %–205 %). Thermal annealing facilitates dynamic transesterification reactions (DTER) to further improve the mechanical properties while making the printed materials healable and recyclable. By integrating these innovations into liquid crystal display (LCD) based 3D printing, we demonstrate origami metamaterials with tunable, multi-stable mechanical behaviors as well as property recovery after self-healing of the damaged structures by both simulations and experiments. Finally, the printed metamaterials can be recycled with the well-preserved properties.

Light-based 3D printing of stimulus-responsive hydrogels for miniature devices: recent progress and perspective

AbstractMiniature devices comprising stimulus-responsive hydrogels with high environmental adaptability are now considered competitive candidates in the fields of biomedicine, precise sensors, and tunable optics. Reliable and advanced fabrication methods are critical for maximizing the application capabilities of miniature devices. Light-based three-dimensional (3D) printing technology offers the advantages of a wide range of applicable materials, high processing accuracy, and strong 3D fabrication capability, which is suitable for the development of miniature devices with various functions. This paper summarizes and highlights the recent advances in light-based 3D-printed miniaturized devices, with a focus on the latest breakthroughs in light-based fabrication technologies, smart stimulus-responsive hydrogels, and tunable miniature devices for the fields of miniature cargo manipulation, targeted drug and cell delivery, active scaffolds, environmental sensing, and optical imaging. Finally, the challenges in the transition of tunable miniaturized devices from the laboratory to practical engineering applications are presented. Future opportunities that will promote the development of tunable microdevices are elaborated, contributing to their improved understanding of these miniature devices and further realizing their practical applications in various fields. Graphic abstract

Design of interpenetration network in light-based 3D printing for robust and sustainable dielectric insulators

The sustainability and additive manufacturing of dielectric insulators are the development direction of the power system. Introducing dynamic covalent bonds in light-based 3D printing have attracted considerable attention as the reversible crosslinks allow for the reprocessing of printed objects. However, there generally exists a trade-off between mechanical strength, glass transition temperature (Tg), and reconfigurability for dynamic covalent networks. The reconfiguring process of the dynamic covalent network often requires high mobility of molecular chains and large free volumes, which in turn decreases the mechanical strength, Tg, and electrical insulating performance. Herein, we demonstrate a novel strategy for developing a kind of mechanically robust and sustainable vitrimer by building a rigid-flexible coupling inter-penetration network (IPN). Specifically, a two-stage curing approach was used to prepare high-performance 3D-printing vitrimers by using the plant oil-epoxy hybrid resin, which brings a lot of ester bonds and β-hydroxyl ester for the crosslinking network. Computational techniques with molecular dynamics calculation are used for the design and optimization of the crosslinking network, and then the optimized IPN is prepared by digital light processing 3D printing and subsequent heat curing. In the IPN, the epoxy backbone is rigid to enhance the Tg and tensile strength, while the plant-based methacrylate is flexible to guarantee topological rearrangement at elevated temperatures. Compared to reported epoxy vitrimers, the resultant IPN exhibits simultaneous high Tg (111 °C), outstanding tensile strength and toughness (tensile strength of 70 MPa, elongation at break of 17.58 %), good topological rearrangement, and excellent dielectric properties (permittivity less than 4, breakdown strength of 49.3 kV/mm). This work provides a new strategy for balancing the strength, toughness, electrical insulating and sustainability of 3D-printed thermosets.

Spherical-based porous architectures: In silico design and validation

Porous (or cellular) materials, like wood and bones, are abundantly found in nature for structural purposes. Thanks to the advancements of evolving technologies, the fabrication of intricate cellular structures was possible. Notably, functionally graded porous structures offer superior mechanical and physical properties compared to their uniform counterparts. Additive manufacturing, especially light-based 3D printing (3DP) technologies, has significantly augmented the production of such materials thanks to their high speed, resolution, and cost-efficiency. However, selecting the most suitable porous architecture for one's necessities remains challenging, requiring an optimised workflow supporting 3DP methods with in silico tools to predict the functional properties of the developed porous architecture. This study introduces a preliminary step toward this workflow, involving in silico design and mechanical validation of porous architectures manufactured via low-force stereolithography 3DP. The work proposes for the first time spherical-based functionally graded porous geometries, filling the existing gap in the literature. The proposed structures, categorised upon their pore size, porosity, and pore size gradients, demonstrate potential applications in the biomedical field (e.g., tissue engineering scaffolds and soft bioreactor systems) and outperform other existing porous architectures in terms of energy absorption capabilities. These findings lay the foundation for further workflow optimisation. By coupling our fast method of generation of porous structures and a trained machine learning model to predict desired physical properties, we aim to produce functionalised cellular architectures for biomedical applications.

(Invited) 3D Printing-Assisted Casting of Conducting Polymers for Bioelectronics

3D structured conducting polymers, known for their high conductivity, low impedance, and tunable form factor, are promising candidates for various bioelectronics applications. However, achieving a balance between structural complexity, electrical conductance, and processing generality has been challenging in these materials. In this talk, I will discuss our efforts to address this trade-off through 3D printing-assisted casting. Light-based 3D printing is used to create hollow molds, providing structural complexity and design freedom, whereas the casting nature imparts material versatility. The casting molds are made of superabsorbent polymers and printed in a partially hydrated state. Their dehydration provides significant enhancement in feature resolution and excellent thermal and mechanical properties, making them versatile for casting. After casting, over-hydration of the molds facilitate their energy-efficient removal. Using poly(3,4-ethylenedioxythiophene) (PEDOT) as a model system, complex architectures such as octet and truncated octahedron can be achieved. Compositing silver flakes with PEDOT through a thermal injection process leads to prints with conductivity over 6000 S/cm and high environmental stability. This method can potentially be applied to other hard-to-print soft materials and composites.

(Invited) Reshaping Light with Hybrid Quantum Dot: Molecule Systems

Photon upconversion is an energy conversion process wherein a material absorbs two or more low-energy photons and uses their energy to generate high-energy photons. Upconversion systems that convert near-infrared light into the visible range can address current challenges in solar energy capture and near-infrared sensor design while materials that operate at higher energy, producing UV photons from visible light, can enable applications in photocatalysis and light-based 3D printing. Due to their high extinction coefficients and size-tunable optical properties, quantum dots have emerged as ideal photosensitizers for photon upconversion systems. In these systems, light absorbed by a quantum dot is passed to a molecule at its surface, placing the molecule into a spin-triplet state. Upconversion is achieved when two molecules in their triplet state encounter one another and undergo triplet fusion, a process that deexcites one molecule and promotes the other to a high-energy, emissive spin-singlet state. In this presentation, I will present spectroscopic measurements and electronic structure calculations that identify energy transfer rates and key intermediates involved in two quantum dot systems that respectively demonstrate red-to-blue and blue-to-UV photon upconversion. In the first system, which consists of silicon quantum dots functionalized with anthracene ligands, we find that by controlling the chemical structure of molecular tethers that covalently link anthracene to silicon, we can produce strongly coupled states wherein excited charge carriers are shared between silicon and anthracene. By controlling the energy of these states, we can optimize the system’s performance, achieving an upconversion quantum yield of 17.2%. In the second system, we use CsPbBr3 perovskite quantum dots to drive triplet energy transfer to naphthalene ligands. This energy transfer process is found to be highly sensitive to the structure of the chemical linker that binds naphthalene to CsPbBr3, which we attribute to modulation of the degree of wavefunction overlap between the states of the quantum dot energy donor and naphthalene energy acceptor.

Optical Fiber-Assisted Printing: A Platform Technology for Straightforward Photopolymer Resins Patterning and Freeform 3D Printing.

Light-based 3D printing techniques represent powerful tools, enabling the precise fabrication of intricate objects with high resolution and control. An innovative addition to this set of printing techniques is Optical Fiber-Assisted Printing (OFAP) introduced in this article. OFAP is a platform utilizing an LED-coupled optical fiber (LOF) that selectively crosslinks photopolymer resins. It allows change of parameters like light intensity and LOF velocity during fabrication, facilitating the creation of structures with progressive features and multi-material constructs layer-by-layer. An optimized formulation based on allyl-modified gelatin (gelAGE) with food dyes as photoabsorbers is introduced. Additionally, a novel gelatin-based biomaterial, alkyne-modified gelatin (gelGPE), featuring alkyne moieties, demonstrates near-visible light absorption thus fitting OFAP needs, paving the way for multifunctional hydrogels through thiol-yne click chemistry. Besides 2D patterning, OFAP is transferred to embedded 3D printing within a resin bath demonstrating the proof-of-concept as a novel printing technology with potential applications in tissue engineering and biomimetic scaffold fabrication, offering rapid and precise freeform printing capabilities.

Phase-separating resins for light-based three-dimensional printing of oxide glasses

Silica-based glasses can be shaped into complex geometries using a variety of additive manufacturing technologies. While the three-dimensional printing of glasses opens unprecedented design opportunities, the development of up-scaled, reliable manufacturing processes is crucial for the broader dissemination of this technology. Here, we design and study phase-separating resins that enable light-based 3D printing of oxide glasses with high-aspect-ratio features and enhanced manufacturing yields. The effect of the resin composition on the microstructure, mechanical properties and delamination resistance of parts printed by digital light processing is investigated with the help of printing experiments, compression tests and electron microscopy analysis. The chemical composition and microstructure of the cured resins were found to strongly affect the stiffness, delamination resistance, and calcination behavior of printed parts. These findings provide useful guidelines to enhance the reliability and yield of the DLP printing process of multicomponent silica-based glasses.

Architectural differences in photopolymerized PEG-based thiol-acrylate hydrogels enable enhanced mechanical properties and 3D printability

Hydrogels have been widely investigated for applications in the human body due to their tunability and biocompatibility. Nevertheless, their application is still limited by their relatively low mechanical strength relative to load-bearing tissue scaffolds like articular cartilage. In this work, we synthesized hydrogels by combining linear poly(ethylene glycol) dimethacrylate (PEGDMA) with a 3-arm-PEG end-functionalized with thiol. We demonstrate that the combination of thiol-ene click chemistry with a multifunctional crosslinker reduces the crosslink and entanglement density in comparison with the otherwise statistically crosslinked/polymerized PEGDMA, whereby the only viable mode of gelation is through radical propagation or termination at the double bond. The corresponding minimization of topological heterogeneities that arises during thiol-ene crosslinking results in hydrogels with compressive strength in the range of tens of MPa. The molar mass of the linear PEGDMA precursor is readily tunable, unlocking access to a wider range of mechanical properties. We employed photo-mediated crosslinking protocol, which is amenable to advanced processing technologies such as light-based 3D printing techniques. Such advanced fabrication processes offer high precision and control during the generation of customizable macroscopic objects. Simple prototypes were generated using digital light processing (DLP) equipment. We demonstrate that integrating a simple co-macromonomer into a widely employed hydrogel platform can unlock new mechanical regimes and mitigate the inherent brittleness associated with these materials. The simplicity of this approach, coupled with its easy tunability and adaptability to light-based techniques, holds promise for broadening hydrogel applications in tissue engineering. Our findings contribute to advancing materials and methodologies, facilitating enhanced design and fabrication of functional constructs.

Binocular structured light-based 3D reconstruction for morphological measurements of apples

Traditional plannar images lack depth information and are challenging for accurate measurement of morphological variables such as volume and deformity index of apples. This study presents a new evaluation of a custom-assembled binocular structured light system, combined with a three-dimensional (3D) reconstruction approach, for accurate estimations of the morphological variables of apples. The system was mainly composed of a digital projector for generating structured patterns and two cameras in a symmetric arrangement. The 3D reconstruction accuracy was verified by standard samples, with the relative errors concentrating within 3%, and most were within 1% (depth error of 0.5 mm). Multi-view registration based on a rotary table was used for restoring more complete 3D information of apples. A method based on the normal vector of the point cloud was presented to complement the bottom of the apple and extract the shoulders. 3D reconstruction of 82 apples with different morphologies was performed, from which morphological variables of deformity index, the maximum diameter, fruit shape index, volume and mass were estimated. The R2 values between the actual measurements and the results obtained from the 3D point cloud were 0.9941, 0.9594, 0.8015, 0.9915 and 0.9960, respectively. This study showed that high-accuracy measurement of apple morphological variables can be achieved by binocular structured light-based 3D reconstruction, which would be beneficial for subsequent apple grading and phenotyping analysis.

3D printable aliphatic polycarbonate networks from cationic ring-opening photopolymerization of spiro-orthocarbonates

We demonstrate light-based 3D printing of pure poly(ether carbonate) networks free of shrinkage stress. Expanding the recently pioneered concept of pure cationic double ring-opening photopolymerization of spiro-orthoesters at elevated temperatures, we herein investigate spiro-orthocarbonates. Thereof resulting poly(ether carbonate) networks could find manyfold applications in biological and medical settings as well as in applications searching for more sustainable material solutions. We have determined the dependence of single and double ring-opening and the presence of backbiting side reactions for three synthesized spiro-orthocarbonate monomers in combination with an oxetane crosslinker on the ring size and photopolymerization temperature to optimize the photogenerated network and thus material properties. The absence of residual stresses in the polymer network was confirmed by tracking the decrease of sample birefringence with increasing spiro-carbonate monomer content of the sample. Based on this fundamental study, the best-performing monomer was printed in combination with an oxetane crosslinker.

Design and optimization of 3D-bioprinted cell-laden scaffolds in dynamic culture

Light-based 3D printing enables the fabrication of biological scaffolds with high precision, versatility and biocompatibility, particularly the cell-laden scaffolds with architecturally complex geometric features. However, many bioprinted tissue scaffolds suffer from low cell viability due to insufficient oxygen and nutrient supply, which is heavily influenced by scaffold structure and cultivation conditions. Current practice relies mainly on resource-intensive trial-and-error methods to optimize scaffolds’ structures and cultivation parameters. In this study, we developed a comprehensive multi-physics model integrating fluid dynamics, oxygen mass transfer, cell oxygen consumption, and cell growth processes to capture cell growth behaviors in scaffolds, establishing a robust theoretical foundation for scaffold structure optimization. The modeling results showed that a large number of parameters, such as system inlet flow rate, geometric feature size, cell parameters, and material properties, significantly impact oxygen concentration and cell growth within the scaffold. A two-step optimization strategy is proposed in this paper and was applied to obtain optimal geometric parameters of channeled scaffolds to demonstrate the model’s effectiveness for scaffold optimization. The model can be employed for scaffolds with arbitrary shapes and various materials, facilitating the optimal design of sophisticated scaffolds for more advanced tissue engineering.

Light-Based 3D Multi-Material Printing of Micro-Structured Bio-Shaped, Conducting and Dry Adhesive Electrodes for Bioelectronics.

In this work, a new method of multi-material printing in one-go using a commercially available 3D printer is presented. The approach is simple and versatile, allowing the manufacturing of multi-material layered or multi-material printing in the same layer. To the best of the knowledge, it is the first time that 3D printed Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) micro-patterns combining different materials are reported, overcoming mechanical stability issues. Moreover, the conducting ink is engineered to obtain stable in-time materials while retaining sub-100µm resolution. Micro-structured bio-shaped protuberances are designed and 3D printed as electrodes for electrophysiology. Moreover, these microstructures are combined with polymerizable deep eutectic solvents (polyDES) as functional additives, gaining adhesion and ionic conductivity. As a result of the novel electrodes, low skin impedance values showed suitable performance for electromyography recording on the forearm. Finally, this concluded that the use of polyDES conferred stability over time, allowing the usability of the electrode 90 days after fabrication without losing its performance. All in all, this demonstrated a very easy-to-make procedure that allows printing PEDOT:PSS on soft, hard, and/or flexible functional substrates, opening up a new paradigm in the manufacturing of conducting multi-functional materials for the field of bioelectronics and wearables.

Thiol-ene-based degradable 3D printed network from bio resource derived monomers ethyl-lactate and isosorbide

A polymeric ene-based thiol-ene network is reported that was demonstrated for light-based 3D printing. Allyl poly (acrylate ethyl lactate) (PAEL) was synthesized starting from ethyl lactate in an efficient and scalable manner. Ethyl lactate is a biobased material obtained naturally or chemically in high yields in the form of ethyl ester of lactic acid. Isosorbide, which is also a bio based resource was converted into thiol derivative and was used along with Pentaerythritol tetrakis(3-mercaptopropionate) (PETMP) as multifunctional thiol. The polymeric nature of the ene (i.e. PAEL) imparted exceptionally high mechanical properties like Young's modulus of 1.75 GPa as well as high thermal stability with a decomposition temperature (Td,10%) exceeding 350 °C for all the networks studied. The properties could also be customized by fine tuning the type and stoichiometric ratio of the thiol crosslinked employed. For instance, the Young's modulus range from 1.75 GPa to 1.03 GPa and glass transition temperature range from 44 °C to 54 °C could be achieved. DLP 3D printing was used to demonstrate the printability of the resins with high resolution and structural fidelity. The study also highlights the base-mediated rapid hydrolytic degradation efficiency of the 3D printed parts, demonstrating the applicability of these novel polymeric ene based thiol-ene for sustainable and eco-friendly 3D printable formulations.

Visible light-based 3D bioprinted composite scaffolds of κ-carrageenan for bone tissue engineering applications.

Three-dimensional (3D) printing of bone scaffolds using digital light processing (DLP) bioprinting technology empowers the treatment of patients suffering from bone disorders and defects through the fabrication of cell-laden patient-specific scaffolds. Here, we demonstrate the visible-light-induced photo-crosslinking of methacrylate-κ-carrageenan (MA-κ-CA) mixed with bioactive silica nanoparticles (BSNPs) to fabricate 3D composite hydrogels using digital light processing (DLP) printing. The 3D printing of complex bone structures, such as the gyroid, was demonstrated with high precision and resolution. DLP-printed 3D composite hydrogels of MA-κ-CA-BSNP were prepared and systematically assessed for their macroporous structure, swelling, and degradation characteristics. The viscosity, rheological, and mechanical properties were also investigated for the influence of nanoparticle incorporation in the MA-κ-CA hydrogels. The in vitro study performed with MC3T3-E1 pre-osteoblast-laden scaffolds of MA-κ-CA-BSNP revealed high cell viability, no cytotoxicity, and proliferation over 21 days with markedly enhanced osteogenic differentiation compared to neat polymeric scaffolds. Furthermore, no inflammation was observed in the 21-day study involving the in vivo examination of DLP-printed 3D composite scaffolds in a Wistar rat model. Overall, the observed results for the DLP-printed 3D composite scaffolds of MA-κ-CA and BSNP demonstrate their biocompatibility and suitability for bone tissue engineering.

3D printing polymerizable eutectics via RAFT polymerization

Polymerizable eutectic resins featuring a Z-connected bis-RAFT agent are applied to light-based 3D printing to prepare network copolymers with controlled microstructures, high strength, and thermoresponsive behavior.

Direct restoration of photocurable cross-linkers for repeated light-based 3D printing of covalent adaptable networks.

Light-based processing of thermosets has gained increasing attention because of its broad application field including its use in digital light processing (DLP) 3D printing. This technique offers efficient design and fabrication of complex structures but typically results in non-recyclable thermoset-based products. To address this issue, we describe here a photocurable, dynamic β-amino ester (BAE) based cross-linker that is not only suitable for DLP printing but can also be chemically degraded via transesterification upon the addition of 2-hydroxyethyl methacrylate (HEMA) as a decross-linker. This conceptually new protocol allows for efficient depolymerization with the direct restoration of curable monomers in a single step without the addition of external catalysts or solvents. By implementing this protocol, we have established a chemical recycling loop for multiple cycles of photo-cross-linking and restoration of cross-linkers, facilitating repeatable DLP 3D printing without generating any waste. The recycled materials exhibit full recovery of thermal properties and Young's modulus while maintaining 75% of their tensile strength for at least three cycles. Simultaneously, the presence of BAE moieties enables the (re)processability of these materials through compression molding.

Active biosoluble composite material obtained by real-time LbL photoreduction of silver via light-based 3D printing

In this study, a silver-containing photopolymerizable resin was developed and synthesized to create an active biosoluble composite for various applications, including biomedical devices. The main goal was to investigate the properties of this material, which can be produced through real-time LbL (Layer-by-Layer) in situ silver photoreduction during resin photopolymerization. This process uses the 405 nm LEDs of an MSLA (Masked Stereolithography Apparatus) 3D printer. Characterization techniques reveal chemical changes caused by the photoreduction of silver as well as an improvement in physical properties attributed to the presence of metallic silver. The silver nanocomposite has the potential for applications such as 3D-printed antimicrobial structures for biomedicine and engineering. To demonstrate the application of the developed material, a PoC (Proof of Concept) of 3D printing of bioinspired microneedles is presented, aiming to contribute to methods of drug administration that bypass the stratum corneum without causing pain.

Applications of Light-Based 3D Bioprinting and Photoactive Biomaterials for Tissue Engineering

The emergence of additive manufacturing, commonly referred to as 3D printing, has led to a revolution in the field of biofabrication. Numerous types of 3D bioprinting, including extrusion bioprinting, inkjet bioprinting, and lithography-based bioprinting, have been developed and have played pivotal roles in driving a multitude of pioneering breakthroughs in the fields of tissue engineering and regenerative medicine. Among all the 3D bioprinting methods, light-based bioprinting utilizes light to crosslink or solidify photoreactive biomaterials, offering unprecedented spatiotemporal control over biomaterials and enabling the creation of 3D structures with extremely high resolution and precision. However, the lack of suitable photoactive biomaterials has hindered the application of light-based bioprinting in tissue engineering. The development of photoactive biomaterials has only recently been expanded. Therefore, this review summarizes the latest advancements in light-based 3D bioprinting technologies, including the development of light-based bioprinting techniques, photo-initiators (PIs), and photoactive biomaterials and their corresponding applications. Moreover, the challenges facing bioprinting are discussed, and future development directions are proposed.

Mechanical Properties' Strengthening of Photosensitive 3D Resin in Lithography Technology Using Acrylated Natural Rubber.

Acrylated natural rubber (ANR) with various acrylate contents (0.0-3.5 mol%) was prepared from natural rubber as a raw material and then incorporated with commercial 3D resin to fabricate specimens using digital light processing. As a result, the utilization of ANR with 1.5 mol% acrylate content could provide the maximum improvement in stretchability and impact strength, approximately 155% and 221%, respectively, over using pure 3D resin, without significant deterioration of tensile modulus and mechanical strength. According to evidence from a scanning electron microscope, this might be due to the partial interaction between the dispersed small rubber particles and the resin matrix. Additionally, the glass-transition temperature of the 3D-printed sample shifted to a lower temperature by introducing a higher acrylate content in the ANR. Therefore, this work might offer a practical way to effectively enhance the properties of the fundamental commercial 3D resin and broaden its applications. It also makes it possible to use natural rubber as a bio-based material in light-based 3D printing.