Optical 3D Printing Research Articles

Nanoscale Vertical Resolution in Optical Printing of Inorganic Nanoparticles.

Direct optical printing of functional inorganics shows tremendous potential as it enables the creation of intricate two-dimensional (2D) patterns and affordable design and production of various devices. Although there have been recent advancements in printing processes using short-wavelength light or pulsed lasers, the precise control of the vertical thickness in printed 3D structures has received little attention. This control is vital to the diverse functionalities of inorganic thin films and their devices, as they rely heavily on their thicknesses. This lack of research is attributed to the technical intricacy and complexity involved in the lithographic processes. Herein, we present a generalized optical 3D printing process for inorganic nanoparticles using maskless digital light processing. We develop a range of photocurable inorganic nanoparticle inks encompassing metals, semiconductors, and oxides, combined with photolinkable ligands and photoacid generators, enabling the direct solidification of nanoparticles in the ink medium. Our process creates complex and large-area patterns with a vertical resolution of ∼50 nm, producing 50-nm-thick 2D films and several micrometer-thick 3D architectures with no layer height difference via layer-by-layer deposition. Through fabrication and operation of multilayered switching devices with Au electrodes and Ag-organic resistive layers, the feasibility of our process for cost-effective manufacturing of multilayered devices is demonstrated.

Fabrication of Glass‐Ceramic 3D Micro‐Optics by Combining Laser Lithography and Calcination

AbstractThis perspective is an overview of a recent direction in optical 3D printing, where polymerization of crosslinkable materials and nanomaterial fillers can be guided to the final structures and new composites via high temperature annealing (HTA). Defining 3D nano/micro‐structures by ultrafast laser direct writing and tailoring their precursor composition with subsequent tunability of the final properties during 750–1500 °C HTA step takes place at the large surface‐to‐volume ratio conditions favoring efficient pyrolysis and calcination, which are required for exchange of chemical materials/gases between glass/ceramic phase and surrounding. Previously, unexplored inorganic material formation conditions in terms of fast thermal quenching, composition mixing and surface tension guided formation can be harnessed by glass making for creation of new materials endowed with preferable technical properties. An immediate application perspective for a high durability, integrated, and active 3D micro‐optics is foreseen.

Versatile volumetric additive manufacturing with 3D ray tracing.

Tomographic volumetric additive manufacturing (VAM) is an optical 3D printing technique where an object is formed by photopolymerizing resin via tomographic projections. Currently, these projections are calculated using the Radon transform from computed tomography but it ignores two fundamental properties of real optical projection systems: finite etendue and non-telecentricity. In this work, we introduce 3D ray tracing as a new method of computing projections in tomographic VAM and demonstrate high fidelity printing in non-telecentric and higher etendue systems, leading to a 3x increase in vertical build volume than the standard Radon method. The method introduced here expands the possible tomographic VAM printing configurations, enabling faster, cheaper, and higher fidelity printing.

A review on fabrication of 3D printed biomaterials using optical methodologies for tissue engineering applications.

Human body comprises of different internal and external biological components. Human organs tend to fail due to continuous or sudden stress which leads to deterioration, failure, and dislocation. The choice of selection and fabrication of materials for tissue engineering play a key role in terms of suitability, sensitivity, and functioning with other organs as a replacement for failed organs. The progressive improvement of the additive manufacturing (AM) approach in healthcare made it possible to print multi-material and customized complex/intricate geometries in a layer-by-layer fashion. The customized or patient-specific implant fabrication can be easily produced with a high success rate due to the development of AM technologies with tailorable properties. The structural behavior of 3D printed biomaterials is a crucial factor in tissue engineering as they affect the functionality of the implants. Various techniques have been developed in appraising the important features and the effects of the subsequent design of the biomaterial implants. The behavior of the AM built biomaterial implants can be understood visually by an imaging system with a high spatial and spectral resolution. This review intends to present an overview of various biomaterials used in implants, followed by a detailed description of optical 3D printing procedures and evaluation of the performance of 3D printed biomaterials using optical characterization.

Photocurable Glycerol- and Vanillin-Based Resins for the Synthesis of Vitrimers.

In this study, photocurable resins based on glycerol and vanillin were designed, synthesized, and applied to digital light processing three-dimensional (3D) printing and vitrimeric abilities such as shape-memory, self-healing, and recyclability have been investigated. First, photocurable resins were prepared and synthesized by combining renewable resources and photocuring as an environmentally friendly strategy for the synthesis of vitrimers. Afterward, the most suitable resin for optical 3D printing was selected by photorheometry, and the thermal and mechanical properties of the resulting polymers were tested. Furthermore, by activating dynamic transesterification reactions at elevated temperatures, the photocured polymer exhibited self-healing, recyclability, and shape-memory properties. The vitrimer with a weight ratio of 8:2 of glycerol- and vanillin-based monomers demonstrated a welding efficiency of tensile strength up to 114.12%, 75% recyclability by alcoholysis, and shape-memory properties above and below two glass transition temperatures.

Development and optical 3D printing of acrylated epoxidized soybean oil-based composites with functionalized calcium silicate hydrate filler derived from aluminium fluoride production waste

In this study, novel photocurable biobased and biodegradable composites with functionalized fillers from industrial inorganic waste have been developed and applied in optical 3D printing technology. Hydrothermally synthesized calcium silicate hydrates from aluminium fluoride production waste were used as fillers in photoresins based on acrylated epoxidized soybean oil-based. The use of fillers synthesized from industrial waste led to an improvement in the mechanical properties of polymer composites compared to filler synthesized from impurity-free material. The high 3D printing accuracy, perfect layer adhesion, and smooth surface finishing of 3D objects printed with a commercial digital light processing (DLP) 3D printer were shown by the developed composites. The biodegradability of photocured polymer composites reached 19.6% in 60 days. The developed composites have the great potential to be a competitive alternative to conventional petroleum-derived ones and reduce the environmental impact.

Second harmonic generation of laser beams in transverse mode locking states

Nonlinear frequency conversion of structured beams has been of great interest recently. We present an intracavity second harmonic generation (SHG) of laser beams in transverse mode locking (TML) states with a specially designed sandwich such as a microchip laser. The intracavity nonlinear frequency conversion process of a laser beam in a TML state to its second harmonic is theoretically and experimentally investigated, considering different relative phase and weight parameters between the basic modes in the TML beam. Comparison between the far-field SHG beam patterns of fundamental frequency transverse modes in coherently locked and incoherently superposed states demonstrates that the SHG of TML beams can carry more information. Various rarely observed far-field SHG beam patterns are obtained, and they are consistent with the theoretical analysis and numerical simulations. With the obtained SHG beams, the characteristics of the structured fundamental frequency beams can also be conversely investigated or predicted. This work may have important applications in optical 3D printing, optical trapping of particles, and free-space optical communication areas.

Advanced optical methods and materials for fabricating 3D tissue scaffolds

Three-dimensional (3D) printing, also known as additive manufacturing (AM), has undergone a phase of rapid development in the fabrication of customizable and high-precision parts. Thanks to the advancements in 3D printing technologies, it is now a reality to print cells, growth factors, and various biocompatible materials altogether into arbitrarily complex 3D scaffolds with high degree of structural and functional similarities to the native tissue environment. Additionally, with overpowering advantages in molding efficiency, resolution, and a wide selection of applicable materials, optical 3D printing methods have undoubtedly become the most suitable approach for scaffold fabrication in tissue engineering (TE). In this paper, we first provide a comprehensive and up-to-date review of current optical 3D printing methods for scaffold fabrication, including traditional extrusion-based processes, selective laser sintering, stereolithography, and two-photon polymerization etc. Specifically, we review the optical design, materials, and representative applications, followed by fabrication performance comparison. Important metrics include fabrication precision, rate, materials, and application scenarios. Finally, we summarize and compare the advantages and disadvantages of each technique to guide readers in the optics and TE communities to select the most fitting printing approach under different application scenarios.

Vegetable Oil-Based Thiol-Ene/Thiol-Epoxy Resins for Laser Direct Writing 3D Micro-/Nano-Lithography.

The use of renewable sources for optical 3D printing instead of petroleum-based materials is increasingly growing. Combinations of photo- and thermal polymerization in dual curing processes can enhance the thermal and mechanical properties of the synthesized thermosets. Consequently, thiol-ene/thiol-epoxy polymers were obtained by combining UV and thermal curing of acrylated epoxidized soybean oil and epoxidized linseed oil with thiols, benzene-1,3-dithiol and pentaerythritol tetra(3-mercaptopropionate). Thiol-epoxy reaction was studied by calorimetry. The changes of rheological properties were examined during UV, thermal and dual curing to select the most suitable formulations for laser direct writing (LDW). The obtained polymers were characterized by dynamic-mechanical thermal analysis, thermogravimetry, and mechanical testing. The selected dual curable mixture was tested in LDW 3D lithography for validating its potential in optical micro- and nano-additive manufacturing. The obtained results demonstrated the suitability of epoxidized linseed oil as a biobased alternative to bisphenol A diglycidyl ether in thiol-epoxy thermal curing reactions. Dual cured thermosets showed higher rigidity, tensile strength, and Young’s modulus values compared with UV-cured thiol-ene polymers and the highest thermal stability from all prepared polymers. LDW results proved their suitability for high resolution 3D printing—individual features reaching an unprecedented 100 nm for plant-based materials. Finally, the biobased resin was tested for thermal post-treatment and 50% feature downscaling was achieved.

Influence of Vanillin Acrylate-Based Resin Composition on Resin Photocuring Kinetics and Antimicrobial Properties of the Resulting Polymers.

The investigation of the influence of vanillin acrylate-based resin composition on photocuring kinetics and antimicrobial properties of the resulting polymers was performed in order to find efficient photocurable systems for optical 3D printing of bio-based polymers with tunable rigidity, as well as with antibacterial and antifungal activity. Two vanillin derivatives, vanillin diacrylate and vanillin dimethacrylate, were tested in photocurable systems using phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide as a photoinitiator. The influence of vanillin acrylate monomer, amount of photoinitiator, presence and amount of dithiol, and presence of solvent on photocuring kinetics was investigated by real-time photoreometry. Polymers of different rigidity were obtained by changing the photocurable resin composition. The photocuring kinetics of the selected vanillin acrylate-based resins was comparable with that of commercial petroleum-based acrylate resins for optical 3D printing. Polymers based on both vanillin acrylates showed a significant antibacterial activity against Escherichia coli and Staphylococcus aureus. Vanillin diacrylate-based polymer films also demonstrated an antifungal activity in direct contact with Aspergillus niger and Aspergillus terreus. Vanillin diacrylate-based dual curing systems were selected as the most promising for optical 3D printing of bio-based polymers with antibacterial and antifungal activity.

3D printing enabled by light and enabling the manipulation of light: feature issue introduction

This feature issue aims at highlighting the two-way connection between optics and photonics and 3D printing. One direction concerns novel photoresist materials and technical advances in optics-based 3D additive manufacturing. The other direction uses such advanced optical 3D printing technologies for the realization of novel micro-optical components, micro-optical systems, 3D artificial materials called metamaterials, micro-robots, and more. All of these would be difficult if not impossible to manufacture otherwise.

3D printing enabled by light and enabling the manipulation of light: feature issue introduction

This feature issue aims at highlighting the two-way connection between optics and photonics and 3D printing. One direction concerns novel photoresist materials and technical advances in optics-based 3D additive manufacturing. The other direction uses such advanced optical 3D printing technologies for the realization of novel micro-optical components, micro-optical systems, 3D artificial materials called metamaterials, micro-robots, and more. All of these would be difficult if not impossible to manufacture otherwise.

(Invited) Fabrication of Polymer Gels with Double Network Using Multi-Material 2/3D Printing

Multi-material systems for additive manufacturing, also known as 3D printing, are used to fabricate the functional objects with different color materials or with the position dependent material properties such as elastic modulus or solubility. The previous work for Fused Deposition Modeling (FDM) method have demonstrated that the multiple print heads or a single head with the mixed-material systems can extrude the complex and composite materials with piling up the multi-material layers connected with the physical bonds between layers.However, few studies have focused on the fabrication of 3D printed gel materials with different materials, and the creation of chemical bonds on the interface between the multi-material layers.In our previous work, 3D printed hollow objects made of gel materials were fabricated with a customized optical 3D printing system, and the 3D printed objects of multifunctional ionic gels incorporating ionic liquid (IL) in the thiol–ene network of thiol-based end-crosslinker and acrylate monomers were fabricated using commercial stereolithography (SLA) system. It was found that optical 3D printing system utilized to fabricate gel materials could create the microscale objects.This study report the design and fabrication of 3D printed polymer gels containing two types of gels using 3D gel printer named “SWIMER”. The double network technique for hydrogels is used for the creation of chemical bonds between two types of gels. Figure shows one of examples of 3D printed gel.This gel consists of two parts: the soft body frame for structural support which is made of nonionic polymer gels and the part which is made of the ionic polymer gels. The nonionic gels with an ordered structure are synthesized by the polymerization of the monomer, N,N-Dimethylacrylamide (DMAAm), and the crosslinker, N, N'-Methylenebisacrylamide (MBAA). The ionic gels are synthesized by the polymerization of the monomer, N-(1,1-Dimethyl-2-(sodiosulfo)ethyl)acrylamide and the same chemicals as the nonionic gels. Chemicals as the ultraviolet (UV) initiator are depending on the wavelength of laser source in the process of how we fabricate the gels.The significant difference in the swelling behavior between the two parts enabled them to be actuated in one direction. We found that by controlling the ion concentration in water they enlarged the solvent-induced strains to 108% in water which is comparable to the polymer actuators driven with high voltage. Figure 1

A Bio-Based Resin for a Multi-Scale Optical 3D Printing

Materials obtained from renewable sources are emerging to replace the starting materials of petroleum-derived plastics. They offer easy processing, fulfill technological, functional and durability requirements at the same time ensuring increased bio-compatibility, recycling, and eventually lower cost. On the other hand, optical 3D printing (O3DP) is a rapid prototyping tool (and an additive manufacturing technique) being developed as a choice for efficient and low waste production method, yet currently associated with mainly petroleum-derived resins. Here we employ a single bio-based resin derived from soy beans, suitable for O3DP in the scales from nano- to macro-dimensions, which can be processed even without the addition of photoinitiator. The approach is validated using both state-of-the art laser nanolithography setup as well as a widespread table-top 3D printer - sub-micrometer accuracy 3D objects are fabricated reproducibly. Additionally, chess-like figures are made in an industrial line commercially delivering small batch production services. Such concept is believed to make a breakthrough in rapid prototyping by switching the focus of O3DP to bio-based resins instead of being restricted to conventional petroleum-derived photopolymers.

Vanillin Acrylate-Based Resins for Optical 3D Printing.

The investigation of biobased systems as photocurable resins for optical 3D printing has attracted great attention in recent years; therefore, novel vanillin acrylate-based resins were designed and investigated. Cross-linked polymers were prepared by radical photopolymerization of vanillin derivatives (vanillin dimethacrylate and vanillin diacrylate) using ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate as photoinitiator. The changes of rheological properties were examined during the curing with ultraviolet/visible irradiation to detect the influences of solvent, photoinitiator, and vanillin derivative on cross-linking rate and network formation. Vanillin diacrylate-based polymers had higher values of yield of insoluble fraction, thermal stability, and better mechanical properties in comparison to vanillin dimethacrylate-based polymers. Moreover, the vanillin diacrylate polymer film showed a significant antimicrobial effect, only a bit weaker than that of chitosan film. Thermal and mechanical properties of vanillin acrylate-based polymers were comparable with those of commercial petroleum-derived materials used in optical 3D printing. Also, vanillin diacrylate proved to be well-suited for optical printing as was demonstrated by employing direct laser writing 3D lithography and microtransfer molding techniques.

Photocross‐linked polymers based on plant‐derived monomers for potential application in optical 3D printing

ABSTRACTPhotocross linking of the resins composed of plant‐derived monomers, acrylated epoxidized soybean oil (AESO), myrcene (MYR) and vanillin dimethacrylate (VDM) or divinylbenzene (DVB, for comparison), was performed using 2,2‐dimethoxy‐2‐phenylacetophenone as photoinitiator. Photocross‐linking rate and properties of the crosslinked polymers depended on the resin compositions. The higher amount of MYR caused not only the better homogenization and lower viscosity of the resin but also the reduction of polymerization rate and the worse mechanical and thermal properties of the resulting polymers. The higher amount of aromatic component (VDM or DVB) improved mechanical and thermal properties of polymers. Moreover, the use of VDM instead of DVB in the system led to the higher photocross‐linking rate and higher yield of insoluble fraction. The resin composed of only plant‐derived monomers AESO/MYR/VDM, molar ratio 1:1:3, showed characteristics comparable to those of commercial petroleum‐derived photoresins and was selected as a potential renewable photoresin for application in optical 3D printing. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48708.

Vanillin-based thiol-ene systems as photoresins for optical 3D printing

Purpose This study aims to present a design and investigation of novel vanillin-based thiol-ene photocurable systems as candidate materials for optical three-dimensional printing. Design/methodology/approach Two vanillin acrylates, vanillin dimethacrylate and vanillin diacrylate, were tested in thiol-ene photocurable systems with 1,3-benzenedithiol. The kinetics of photocross-linking was investigated by real-time photorheometry using two photoinitiators, diphenyl (2,4,6-trimethylbenzoyl)phosphine oxide or ethyl (2,4,6-trimethylbenzoyl)phenylphosphinate in different quantities. The dependencies of rheological properties of resins on the used vanillin derivative, photoinitiator, and the presence of a solvent, as well as structure, thermal and mechanical properties of the selected polymers were investigated. Findings The most rigid polymers were obtained from vanillin diacrylate-based resins without any solvent. The vanillin diacrylate-based polymer possessed higher values of cross-linking density, the yield of insoluble fraction, thermal stability and better mechanical properties in comparison to the vanillin dimethacrylate-based polymer. Originality/value The kinetics of photocross-linking of vanillin-based thiol-ene systems was investigated by real-time photorheometry for the first time. The designed novel photocurable systems based on vanillin acrylates and 1,3-benzenedithiol are promising renewable photoresins for optical three-dimensional printing on demand.

Photoinitiator Free Resins Composed of Plant-Derived Monomers for the Optical µ-3D Printing of Thermosets.

In this study, acrylated epoxidized soybean oil (AESO) and mixtures of AESO and vanillin dimethacrylate (VDM) or vanillin diacrylate (VDA) were investigated as photosensitive resins for optical 3D printing without any photoinitiator and solvent. The study of photocross-linking kinetics by real-time photorheometry revealed the higher rate of photocross-linking of pure AESO than that of AESO with VDM or VDA. Through the higher yield of the insoluble fraction, better thermal and mechanical properties were obtained for the pure AESO polymer. Here, for the first time, we validate that pure AESO and mixtures of AESO and VDM can be used for 3D microstructuring by employing direct laser writing lithography technique. The smallest achieved spatial features are 1 µm with a throughput in 6900 voxels per second is obtained. The plant-derived resins were laser polymerized using ultrashort pulses by multiphoton absorption and avalanche induced cross-linking without the usage of any photoinitiator. This advances the light-based additive manufacturing towards the 3D processing of pure cross-linkable renewable materials.

Extremely Soft, Conductive, and Transparent Ionic Gels by 3D Optical Printing

AbstractA series of 3D printable multifunctional ionic gels (IGs) are developed incorporating ionic liquid (IL) in the thiol–ene network of thiol‐based end‐crosslinker and acrylate monomers. The resulted gels, termed as thiol‐ionic gels (T‐IGs), are highly transparent and very soft with IL content of 70–85 wt%. The mechanical and conductive properties of the T‐IGs are found to be largely dependent on the IL content, end‐crosslinker functionalities, and chain‐length of monomers. Progression of ionic conductivity is observed with an increase in IL content and conductivity as high as 5.40 mS cm−1is attained for longer acrylate group containing T‐IGs at room temperature, while further increase is observed at elevated temperature. T‐IGs in all systems are found to exhibit superior thermal stability. Three‐dimensional fabrication of these functional T‐IGs is achieved by optical 3D printing process with microscale resolution in facile steps.

Photoresins based on acrylated epoxidized soybean oil and benzenedithiols for optical 3D printing

PurposeThe purpose of this paper is the design and investigation of novel acrylated epoxidized soybean oil-based photocurable systems as candidate materials for optical 3D printing.Design/methodology/approachAromatic dithiols, benzene-1,3-dithiol or benzene-1,4-dithiol, were used as cross-linking agents of acrylated epoxidized soybean oil in these systems. Kinetics of photocross-linking was investigated by real-time photorheometry using two different photoinitiators, 2, 2-dimethoxy-2-phenylacetophenone or 2-hydroxy-2-methylpropiophenone, in different quantities. The effect of the initial composition on the rate of photocross-linking, mechanical, thermal properties and swelling of obtained polymers was investigated.FindingsThe rate of photocross-linking was higher, more cross-links and shorter polymer chains between cross-linking points of the network were formed when benzene-1,4-dithiol and 2, 2-dimethoxy-2-phenylacetophenone were used in compositions. The higher yield of insoluble fraction, glass transition temperatures and values of compressive modulus were obtained when benzene-1,3-dithiol and 2, 2-dimethoxy-2-phenylacetophenone were used in compositions.Originality/valueThis is the first study of acrylated epoxidized soybean oil-based thiol-ene system by real-time photorheometry. The designed novel photocurable systems based on acrylated epoxidized soybean oil and benzenedithiols are promising renewable photoresins for rapid optical 3D printing on demand.