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

Design considerations for digital light processing bioprinters

With the rapid development and popularization of additive manufacturing, different technologies, including, but not limited to, extrusion-, droplet-, and vat-photopolymerization-based fabrication techniques, have emerged that have allowed tremendous progress in three-dimensional (3D) printing in the past decades. Bioprinting, typically using living cells and/or biomaterials conformed by different printing modalities, has produced functional tissues. As a subclass of vat-photopolymerization bioprinting, digital light processing (DLP) uses digitally controlled photomasks to selectively solidify liquid photocurable bioinks to construct complex physical objects in a layer-by-layer manner. DLP bioprinting presents unique advantages, including short printing times, relatively low manufacturing costs, and decently high resolutions, allowing users to achieve significant progress in the bioprinting of tissue-like complex structures. Nevertheless, the need to accommodate different materials while bioprinting and improve the printing performance has driven the rapid progress in DLP bioprinters, which requires multiple pieces of knowledge ranging from optics, electronics, software, and materials beyond the biological aspects. This raises the need for a comprehensive review to recapitulate the most important considerations in the design and assembly of DLP bioprinters. This review begins with analyzing unique considerations and specific examples in the hardware, including the resin vat, optical system, and electronics. In the software, the workflow is analyzed, including the parameters to be considered for the control of the bioprinter and the voxelizing/slicing algorithm. In addition, we briefly discuss the material requirements for DLP bioprinting. Then, we provide a section with best practices and maintenance of a do-it-yourself DLP bioprinter. Finally, we highlight the future outlooks of the DLP technology and their critical role in directing the future of bioprinting. The state-of-the-art progress in DLP bioprinter in this review will provide a set of knowledge for innovative DLP bioprinter designs.

Accuracy of soy-based resins for dental 3D printing

OBJECTIVES

To verify the accuracy of soy-based resins for dental three-dimensional (3D) printing.

MATERIALS AND METHODS

After conducting a power analysis, models of 10 consecutively treated patients were produced from four different resins using a dental 3D printer. Two of these resins were soy based and therefore biodegradable. These 20 models were measured manually with a caliper as well as digitally by software and compared based on measurement parameters in all three spatial axes.

RESULTS

No statistically significant differences were found between the four different resins or between the manual and digital measurements.

CONCLUSIONS

Soy-based resin seems to be a suitable material for orthodontic 3D printing and is a more environmentally friendly alternative to conventional dental resins. Digital model analysis seems to produce comparable results to manual measurement.

Printing Green: Microalgae-Based Materials for 3D Printing with Light

Microalgae have emerged as sustainable feedstocks due to their ability to fix CO2 during cultivation, rapid growth rates, and capability to produce a wide variety of metabolites. Several microalgae accumulate lipids in high concentrations, especially triglycerides, along with lipid-soluble, photoactive pigments such as chlorophylls and derivatives. Microalgae-derived triglycerides contain longer fatty acid chains with more double bonds on average than vegetable oils, allowing a higher degree of post-functionalization. Consequently, they are especially suitable as precursors for materials that can be used in 3D printing with light. This work presents the use of microalgae as "biofactories" to generate materials that can be further 3D printed in high resolution. Two taxonomically different strains -Odontella aurita (O. aurita, BEA0921B) and Tetraselmis striata (T. striata, BEA1102B)- are identified as suitable microalgae for this purpose. The extracts obtained from the microalgae (mainly triglycerides with chlorophyll derivatives) are functionalized with photopolymerizable groups and used directly as printable materials (inks) without the need for additional photoinitiators. The fabrication of complex 3D microstructures with sub-micron resolution is demonstrated. Notably, the 3D printed materials show biocompatibility. These findings open new possibilities for the next generation of sustainable, biobased, and biocompatible materials with great potential in life science applications.

Fully Bio-Based Polymer Composites: Preparation, Characterization, and LCD 3D Printing

The present work aimed to prepare novel bio-based composites by adding fillers coming from agro-wastes to an acrylate epoxidized soybean oil (AESO) resin, using liquid crystal display (LCD) 3D printing. Different photocurable formulations were prepared by varying the reactive diluents, iso-bornyl methacrylate (IBOMA) and tetrahydrofurfuryl acrylate (THFA). Then, two fillers derived from different industrial wastes, corn (GTF) and wine (WPL-CF) by-products, were added to the AESO-based formulations to develop polymer composites with improved properties. The printability by LCD of the photocurable formulations was widely studied. Bio-based objects with different geometries were realized, showing printing accuracy, layer adhesion, and accurate details. The thermo-mechanical and mechanical properties of the 3D-printed composites were tested by TGA, DMA, and tensile tests. The results revealed that the agro-wastes' addition led to a remarkable increase in the elastic modulus, tensile strength, and glass transition temperature in the glassy state for the systems containing IBOMA and for flexible structures in the rubbery region for systems containing THFA. AESO-based polymers demonstrated tunable properties, varying from rigid to flexible, in the presence of different diluents and biofillers. This finding paves the way for the use of this kind of composite in applications, such as biomedical for the realization of prostheses.

Improving the 3D Printability and Mechanical Performance of Biorenewable Soybean Oil-Based Photocurable Resins

The general requirement of replacing petroleum-derived plastics with renewable resources is particularly challenging for new technologies such as the additive manufacturing of photocurable resins. In this work, the influence of mono- and bifunctional reactive diluents on the printability and performance of resins based on acrylated epoxidized soybean oil (AESO) was explored. Polyethylene glycol di(meth)acrylates of different molecular weights were selected as diluents based on the viscosity and mechanical properties of their binary mixtures with AESO. Ternary mixtures containing 60% AESO, polyethylene glycol diacrylate (PEGDA) and polyethyleneglycol dimethacrylate (PEG200DMA) further improved the mechanical properties, water resistance and printability of the resin. Specifically, the terpolymer AESO/PEG575/PEG200DMA 60/20/20 (wt.%) improved the modulus (16% increase), tensile strength (63% increase) and %deformation at the break (21% increase), with respect to pure AESO. The enhancement of the printability provided by the reactive diluents was proven by Jacobs working curves and the improved accuracy of printed patterns. The proposed formulation, with a biorenewable carbon content of 67%, can be used as the matrix of innovative resins with unrestricted applicability in the electronics and biomedical fields. However, much effort must be done to increase the array of bio-based raw materials.

Additive and Lithographic Manufacturing of Biomedical Scaffold Structures Using a Versatile Thiol-Ene Photocurable Resin

Additive and lithographic manufacturing technologies using photopolymerisation provide a powerful tool for fabricating multiscale structures, which is especially interesting for biomimetic scaffolds and biointerfaces. However, most resins are tailored to one particular fabrication technology, showing drawbacks for versatile use. Hence, we used a resin based on thiol-ene chemistry, leveraging its numerous advantages such as low oxygen inhibition, minimal shrinkage and high monomer conversion. The resin is tailored to applications in additive and lithographic technologies for future biofabrication where fast curing kinetics in the presence of oxygen are required, namely 3D inkjet printing, digital light processing and nanoimprint lithography. These technologies enable us to fabricate scaffolds over a span of six orders of magnitude with a maximum of 10 mm and a minimum of 150 nm in height, including bioinspired porous structures with controlled architecture, hole-patterned plates and micro/submicro patterned surfaces. Such versatile properties, combined with noncytotoxicity, degradability and the commercial availability of all the components render the resin as a prototyping material for tissue engineers.

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.

Science and Technology of Additive Manufacturing Progress: Processes, Materials, and Applications

As a special review article, several significant and applied results in 3D printing and additive manufacturing (AM) science and technology are reviewed and studied. Which, the reviewed research works were published in 2020. Then, we would have another review article for 2021 and 2022. The main purpose is to collect new and applied research results as a useful package for researchers. Nowadays, AM is an extremely discussed topic and subject in scientific and industrial societies, as well as a new vision of the unknown modern world. Also, the future of AM materials is toward fundamental changes. Which, AM would be an ongoing new industrial revolution in the digital world. With parallel methods and similar technologies, considerable developments have been made in 4D in recent years. AM as a tool is related to the 4th industrial revolution. So, AM and 3D printing are moving towards the fifth industrial revolution. In addition, a study on AM is vital for generating the next developments, which are beneficial for human beings and life. Thus, this article presents the brief, updated, and applied methods and results published in 2020.

Graphical Abstract

The overview of analytical methods for studying of fossil natural resins

The review presents methods that are used frequently for multi-analytical study of fossil resins. The preliminary characterization relies on physical methods such as microhardness, density and fluorescence in UV light measurements. The spectroscopic methods: infrared spectroscopy, Raman spectroscopy, fluorescence spectroscopy are also presented in the paper. Besides that, the review also contains examples of the application of chromatographic methods: gas chromatography, thin layer chromatography, high-performance liquid chromatography, two-dimensional gas chromatography coupled to time-of-flight mass spectrometry as well as sample preparation methods for chromatographic studies such as pyrolysis. Additionally, thermal methods such as thermogravimetric analysis and differential scanning calorimetry also are covered by the review. Beside the examples of application, a detailed description with development history and perspective for further improvement are presented for each method. Moreover, fit-for-purpose assessment of each method is illustrated based on many examples from literature. The paper also contains examples of the application of multivariate statistical analysis and chemometric methods for comparing multiple properties of different fossil resin specimens for differentiation and classification purposes.

Biocompatibility enhancement via post-processing of microporous scaffolds made by optical 3D printer

Providing a 3D environment that mimics the native extracellular matrix is becoming increasingly important for various applications such as cell function studies, regenerative medicine, and drug discovery. Among the most critical parameters to consider are the scaffold's complicated micro-scale geometry and material properties. Therefore, stereolithography based on photopolymerization is an emerging technique because of its ability to selectively form volumetric structures from liquid resin through localized polymerization reactions. However, one of the most important parameters of the scaffold is biocompatibility, which depends not only on the material but also on the exposure conditions and post-processing, which is currently underestimated. To investigate this systematically, microporous scaffolds with pore sizes of 0.05 mm³ corresponding to a porosity of 16,4% were fabricated using the stereolithography printer Asiga PICO2 39 UV from the widely used resins FormLabs Clear and Flexible. The use of various polymers is usually limited for cells because, after wet chemical development, the non-negligible amount of remaining monomers intertwined in the photopolymerized structures is significantly toxic to cells. Therefore, the aim of this research was to find the best method to remove monomers from the 3D scaffold by additional UV exposure. For this purpose, a Soxhlet extractor was used for the first time, and the monomers were immersed in different alcohols. A Raman microspectroscopy was also used to investigate whether different post-processing methods affect DC (cross-linking) to find out if this specifically affects the biocompatibility of the scaffolds. Finally, mesenchymal stem cells from rat dental pulp were examined to confirm the increased biocompatibility of the scaffolds and their ability to support cell differentiation into bone tissue cells.

Functionalized Soybean Oil- and Vanillin-Based Dual Cure Photopolymerizable System for Light-Based 3D Structuring

A novel dual cure photopolymerizable system was developed by combining two plant-derived acrylic monomers, acrylated epoxidized soybean oil and vanillin dimethacrylate, as well as the thiol monomer pentaerythritol tetrakis (3-mercaptopropionate). Carefully selected resin composition allowed the researchers to overcome earlier stability/premature polymerization problems and to obtain stable (up to six months at 4 °C) and selectively-polymerizable resin. The resin demonstrated rapid photocuring without an induction period and reached a rigidity of 317.66 MPa, which was more than 20 times higher than that of the other vanillin-based polymers. Improved mechanical properties and thermal stability of the resulting cross-linked photopolymer were obtained compared to similar homo- and copolymers: Young's modulus reached 4753 MPa, the compression modulus reached 1634 MPa, and the temperature of 10% weight loss was 373 °C. The developed photocurable system was successfully applied in stereolithography and characterized with femtosecond pulsed two-beam initiation threshold measurement for the first time. The polymerization threshold of the investigated polymer was determined to be controlled by the sample temperature, making the footprint of the workstations cheaper, faster, and more reliable.

Multifunctional Medical Grade Resin with Enhanced Mechanical and Antibacterial Properties: The Effect of Copper Nano-Inclusions in Vat Polymerization (VPP) Additive Manufacturing

Vat photopolymerization (VPP) is an additive manufacturing process commonly used in medical applications. This work aims, for the first time in the literature, to extend and enhance the performance of a commercial medical-grade resin for the VPP process, with the development of nanocomposites, using Copper (Cu) nanoparticles as the additive at two different concentrations. The addition of the Cu nanoparticles was expected to enhance the mechanical properties of the resin and to enable biocidal properties on the nanocomposites since Cu is known for its antibacterial performance. The effect of the Cu concentration was investigated. The nanocomposites were prepared with high-shear stirring. Specimens were 3D printed following international standards for mechanical testing. Their thermal and spectroscopic response was also investigated. The morphological characteristics were examined. The antibacterial performance was evaluated with an agar well diffusion screening process. The experimental results were analyzed with statistical modeling tools with two control parameters (three levels each) and eleven response parameters. Cu enhanced the mechanical properties in all cases studied. 0.5 wt.% Cu nanocomposite showed the highest improvement (approximately 11% in tensile and 10% in flexural strength). The antibacterial performance was sufficient against S. aureus and marginal against E. coli.

Preparation and Characterization of 3D-Printed Biobased Composites Containing Micro- or Nanocrystalline Cellulose

Stereolithography (SLA), one of the seven different 3D printing technologies, uses photosensitive resins to create high-resolution parts. Although SLA offers many advantages for medical applications, the lack of biocompatible and biobased resins limits its utilization. Thus, the development of new materials is essential. This work aims at designing, developing, and fully characterizing a bio-resin system (made of poly(ethylene glycol) diacrylate (PEGDA) and acrylated epoxidized soybean oil (AESO)), filled with micro- or nanocellulose crystals (MCC and CNC), suitable for 3D printing. The unfilled resin system containing 80 wt.% AESO was identified as the best resin mixture, having a biobased content of 68.8%, while ensuring viscosity values suitable for the 3D printing process (>1.5 Pa s). The printed samples showed a 93% swelling decrease in water, as well as increased tensile strength (4.4 ± 0.2 MPa) and elongation at break (25% ± 2.3%). Furthermore, the incorporation of MCC and CNC remarkably increased the tensile strength and Young’s modulus of the cured network, thus indicating a strong reinforcing effect exerted by the fillers. Lastly, the presence of the fillers did not affect the UV-light penetration, and the printed parts showed a high quality, thus proving their potential for precise applications.

The Use of Graphene and Its Derivatives for the Development of Polymer Matrix Composites by Stereolithographic 3D Printing

Significant advances in graphene-based materials have facilitated the development of various composites structures in a diverse range of industry sectors. At present, the preparation of graphene-added materials is mainly developed through traditional methods. However, in recent years, additive manufacturing emerged as a promising approach that enables the printing of complex objects in a layer-by-layer fashion, without the need for moulds or machining equipment. This paper reviews the most recent reports on graphene-based photopolymerizable resins developed for stereolithography (SLA), with particular consideration for medical applications. The characteristics of the SLA technology, the most suitable raw materials and formulations and the properties of final 3D products are described. Throughout, a specific focus is placed on the mechanical properties and biocompatibility of the final 3D-printed object. Finally, remaining challenges and future directions are also discussed.

Customized 3D-printed stackable cell culture inserts tailored with bioactive membranes

There is a high demand in various fields to develop complex cell cultures. Apart from titer plates, Transwell inserts are the most popular device because they are commercially available, easy to use, and versatile. While Transwell inserts are standardized, there are potential gains to customize inserts in terms of the number of layers, height between the layers and the size and composition of the bioactive membrane. To demonstrate such customization, we present a small library of 3D-printed inserts and a robust method to functionalize the inserts with hydrogel and synthetic membrane materials. The library consists of 24- to 96-well sized inserts as whole plates, strips, and singlets. The density of cultures (the number of wells per plate) and the number of layers was decided by the wall thickness, the capillary forces between the layers and the ability to support fluid operations. The highest density for a two-layer culture was 48-well plate format because the corresponding 96-well format could not support fluidic operations. The bottom apertures were functionalized with hydrogels using a new high-throughput dip-casting technique. This yielded well-defined hydrogel membranes in the apertures with a thickness of about 500 µm and a %CV (coefficient of variance) of < 10%. Consistent intestine barrier was formed on the gelatin over 3-weeks period. Furthermore, mouse intestinal organoid development was compared on hydrogel and synthetic filters glued to the bottom of the 3D-printed inserts. Condensation was most pronounced in inserts with filters followed by the gelatin membrane and the control, which were organoids cultured at the bottom of a titer plate well. This showed that the bottom of an insert should be chosen based on the application. All the inserts were fabricated using an easy-to-use stereolithography (SLA) printer commonly used for dentistry and surgical applications. Therefore, on demand printing of the customized inserts is realistic in many laboratory settings.

Translation of 3D printed materials for medical applications

During the past 30 years, 3D printing (3DP) technologies significantly influenced the manufacturing world, including innovation in biomedical devices. This special issue reviews recent advances in translating 3DP biomaterials and medical devices for metallic, ceramic, and polymeric devices, as well as bioprinting for organ and tissue engineering, along with regulatory issues in 3DP biomaterials. In our introductory article, besides introducing selected 3DP processes for biomaterials, current challenges and growth opportunities are also discussed. Finally, it highlights a few success stories for the 3D printed biomaterials for medical devices. We hope these articles will educate engineers, scientists, and clinicians about recent developments in translational 3DP technologies.

Photocurable Coatings Based on Bio-Renewable Oligomers and Monomers

Due to long-term problems related to environmental protection, economic aspects, and waste management in the chemical industry, it is justified to develop renewable polymers as an alternative to synthetic polymers. Two kinds of acrylic bio-renewable components were used for the modification of acrylated epoxidized soybean oil (AESO). The bio-based compositions used as photocurable binders to obtain the photocurable coatings with satisfactory properties and high bio content were then prepared. The kinetic of curing reaction of the oligomers and monomers towards radical photopolymerization and the properties of the cured coatings were fully investigated; the results are discussed in relation with the compounds’ structures. Important information about how to design and obtain renewable photocurable coatings with satisfactory properties was provided in this study. In this study, AESO resin was modified with renewable oligomer or (math)acrylate monomer to increase the reactivity and reduce the viscosity of the photoreactive system in order to obtain renewable and viable alternatives to petroleum-based polymeric materials with perfect film-forming properties. It turned out that both photopolymerization rate and hardness of cured coatings were increased significantly with the addition of modifiers; the use of a thiol modifier and change of the photoinitiator concentration allowed to improve the adhesion, hardness, and control of the photo-curing process.

Laser 3D Printing of Inorganic Free-Form Micro-Optics

A pilot study on laser 3D printing of inorganic free-form micro-optics is experimentally validated. Ultrafast laser direct-write (LDW) nanolithography is employed for structuring hybrid organic-inorganic material SZ2080TM followed by high-temperature calcination post-processing. The combination allows the production of 3D architectures and the heat-treatment results in converting the material to inorganic substances. The produced miniature optical elements are characterized and their optical performance is demonstrated. Finally, the concept is validated for manufacturing compound optical components such as stacked lenses. This is an opening for new directions and applications of laser-made micro-optics under harsh conditions such as high intensity radiation, temperature, acidic environment, pressure variations, which include open space, astrophotonics, and remote sensing.

Multiphoton Laser Fabrication of Hybrid Photo-Activable Biomaterials

The possibility to shape stimulus-responsive optical polymers, especially hydrogels, by means of laser 3D printing and ablation is fostering a new concept of “smart” micro-devices that can be used for imaging, thermal stimulation, energy transducing and sensing. The composition of these polymeric blends is an essential parameter to tune their properties as actuators and/or sensing platforms and to determine the elasto-mechanical characteristics of the printed hydrogel. In light of the increasing demand for micro-devices for nanomedicine and personalized medicine, interest is growing in the combination of composite and hybrid photo-responsive materials and digital micro-/nano-manufacturing. Existing works have exploited multiphoton laser photo-polymerization to obtain fine 3D microstructures in hydrogels in an additive manufacturing approach or exploited laser ablation of preformed hydrogels to carve 3D cavities. Less often, the two approaches have been combined and active nanomaterials have been embedded in the microstructures. The aim of this review is to give a short overview of the most recent and prominent results in the field of multiphoton laser direct writing of biocompatible hydrogels that embed active nanomaterials not interfering with the writing process and endowing the biocompatible microstructures with physically or chemically activable features such as photothermal activity, chemical swelling and chemical sensing.

Superior Properties through Feedstock Development for Vat Photopolymerization Additive Manufacturing of High-Performance Biobased Feedstocks

Vat photopolymerization additive manufacturing (Vat AM) technologies have found niche industrial use being able to produce personalized parts in moderate quantity. However, Vat AM lacks in its ability to produce parts of satisfactory thermal and mechanical properties for structural applications. The purpose of this investigation was to develop high-performance resins with glass transition temperatures (Tg) above 200 °C for Vat AM, evaluate the properties of the produced thermosets and establish a structure–property relationship of the thermosets produced. Herein, we have developed SLA-type resins that feature bio-derived monomer hesperetin trimethacrylate (HTM) synthesized from the flavonone hesperetin. Diluents 4-acryloyl morpholine, styrene, 4-methyl styrene and 4-tert butylstyrene (tbutylsty) were photocured with HTM as the monomer and all produced thermosets with Tg values above 200 °C. Investigations of suitable crosslinkers urethane dimethacrylate, the vinyl ester CN 151 and Ebecryl 4859 (Eb4859) showed that each crosslinker displayed different benefits when formulated with HTM as the monomer and tbutylSty as the diluent (HTM:crosslinker:tbutylSty with mass ratio 2:1:2). The crosslinker CN 151 produced the thermoset of greatest onset of thermal decomposition temperature (T₀) of 352 °C. Eb4859 produced the thermoset of highest tensile strength, 19 ± 7 MPa, amongst the set of varied crosslinkers. The formulation featuring UDM (HTM:UDM:tbutysty) offered ease of processing and was seemingly the easiest to print. Investigations of reactive diluent showed that styrene produced the thermoset of the highest extent of cure and the overall highest tensile strength, 25 ± 5 MPa, while tbutylSty produced the thermoset with the greatest Tan-δ Tg, 231 °C. HTM was synthesized, formulated with diluents, crosslinkers and initiators. The HTM resins were then 3D printed to produce thermosets of Tg values greater than 200 °C. The polymer properties were evaluated and a structure–reactivity relationship was discussed.

Bio-Based Crosslinked Polymers Synthesized from Functionalized Soybean Oil and Squalene by Thiol-Ene UV Curing

The development of polymers photopolymerized from renewable resources are extensively growing as fulfills green chemistry and green engineering principles. With the rapid growth of consumerism, research on innovative starting materials for the preparation of polymers may help to reduce the negative impact of petroleum-based plastic materials on the global ecosystem and on animal and human health. Therefore, bio-based crosslinked polymers have been synthesized from functionalized soybean oil and squalene by thiol-ene ultra-violet (UV) curing. First, thiol-ene UV curing of squalene was performed to introduce thiol functional groups. Then, hexathiolated squalene was used as a crosslinker in click UV curing of acrylated epoxidized soybean oil. Two photoinitiators, 2-hydroxy-2-methylpropiophenone and ethylphenyl (2,4,6-trimethylbenzoyl) phosphinate, were tested in different quantities. Rheological properties of the resins were monitored by real-time photorheometry. The characterization of obtained polymers was performed by differential scanning calorimetry, thermogravimetry, and Shore A hardness measurements. Polymers possessed higher storage modulus, thermal characteristics, Shore A hardness, and lower swelling value when ethylphenyl (2,4,6-trimethylbenzoyl) phosphinate was used as photoinitiator.

UV-Light Curing of 3D Printing Inks from Vegetable Oils for Stereolithography

Typical resins for UV-assisted additive manufacturing (AM) are prepared from petroleum-based materials and therefore do not contribute to the growing AM industry trend of converting to sustainable bio-based materials. To satisfy society and industry's demand for sustainability, renewable feedstocks must be explored; unfortunately, there are not many options that are applicable to photopolymerization. Nevertheless, some vegetable oils can be modified to be suitable for UV-assisted AM technologies. In this work, extended study, through FTIR and photorheology measurements, of the UV-curing of epoxidized acrylate from soybean oil (AESO)-based formulations has been performed to better understand the photopolymerization process. The study demonstrates that the addition of appropriate functional comonomers like trimethylolpropane triacrylate (TMPTA) and the adjusting of the concentration of photoinitiator from 1% to 7% decrease the needed UV-irradiation time by up to 25%. Under optimized conditions, the optimal curing time was about 4 s, leading to a double bond conversion rate (DBC%) up to 80% and higher crosslinking density determined by the Flory-Rehner empirical approach. Thermal and mechanical properties were also investigated via TGA and DMA measurements that showed significant improvements of mechanical performances for all formulations. The properties were improved further upon the addition of the reactive diluents. After the thorough investigations, the prepared vegetable oil-based resin ink formulations containing reactive diluents were deemed suitable inks for UV-assisted AM, giving their appropriate viscosity. The validation was done by printing different objects with complex structures using a laser based stereolithography apparatus (SLA) printer.

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.