Photocuring Process Research Articles

Hot-lithography 3D printing of biobased epoxy resins

The introduction of Hot Lithography has opened new perspective in the field of additive manufacturing especially with regard to high viscous formulations. The access to elevated temperature in the 3D printing process not only reduce the viscosity of resin but it allows to achieve higher curing kinetics and degree of conversion. Therefore, it is possible to process new type of monomers which are not reactive enough at room temperature towards UV-curing expanding the formulation design and selection to the 3D-printing of a broader range of epoxy-based formulations. With regard to climate change and the limitation of fossil resources, new needs arise for the origin of the materials. In this view, we investigated the use of two bio-based epoxy monomers (furandimethanol diglycidyl ether (FDE) and resorcinol diglycidyl ether (RDE)) in Hot Lithography 3D printing. Moreover, we compared the performance of the bio-based resins with a commercial fossil-based one, the 1,4-cyclohexanedimethanol diglycidyl ether (CDE). The photocuring process was fully characterized by means of real-time NIR/photorheology and photo-DSC analysis. The thermo-mechanical properties of the final thermosets were investigated by DMTA and tensile test. Finally, the 3D printing of complex shapes was carried out to demonstrate the possibility to obtain arbitrary self-standing shapes. • Hot-lithography 3D-printing of bio-based epoxy resin. • Photocuring of Furan-dimethanol diglycidyl ether epoxy resin. • Photocuring of 1,4-cyclohexanedimethanol diglycidyl ether.

Accurate modulation of photoprinting under stiffness imaging feedback for engineering ECMs with high-fidelity mechanical properties

Engineered extracellular matrices (ECMs) that replicate complex in-vivo features have shown great potential in tissue engineering. Biocompatible hydrogel microstructures have been widely used to replace these native ECMs for physiologically relevant research. However, accurate reproduction of the 3D hierarchical and nonuniform mechanical stiffness inside one integrated microstructure to mimic the complex mechanical properties of native ECMs presents a major challenge. Here, by using digital holographic microscopy (DHM)-based stiffness imaging feedback, we propose a novel closed-loop control algorithm to achieve high-accuracy control of mechanical properties for hydrogel microstructures that recapitulate the physiological properties of native ECMs with high fidelity. During photoprinting, the photocuring area of the hydrogel is divided into microscale grid areas to locally control the photocuring process. With the assistance of a motorized microfluidic channel, the curing thickness is controlled with layer-by-layer stacking. The DHM-based stiffness imaging feedback allows accurate adjustment of the photocuring degree in every grid area to change the crosslinking network density of the hydrogel, thus enabling large-span and high-resolution modulation of mechanical properties. Finally, the gelatin methacrylate was used as a typical biomaterial to construct the high-fidelity biomimetic ECMs. The Young’s modulus could be flexibly modulated in the 10 kPa to 50 kPa range. Additionally, the modulus gradient was accurately controlled to within 2.9 kPa. By engineering ECM with locally different mechanical properties, cell spreading along the stiff areas was observed successfully. We believe that this method can regenerate complex biomimetic ECMs that closely recapitulate in-vivo mechanical properties for further applications in tissue engineering and biomedical research.

Solvent Casting and UV Photocuring for Easy and Safe Fabrication of Nanocomposite Film Dressings.

The aim of this work was to optimize and characterize nanocomposite films based on gellan gum methacrylate (GG-MA) and silver nanoparticles (AgNPs) for application in the field of wound dressing. The films were produced using the solvent casting technique coupled with a photocuring process. The UV irradiation of GG-MA solutions containing glycerol as a plasticizer and different amounts of silver nitrate resulted in the concurrent crosslinking of the photocurable polymer and a reduction of Ag ions with consequent in situ generation of AgNPs. In the first part of the work, the composition of the films was optimized, varying the concentration of the different components, the GG-MA/glycerol and GG-MA/silver nitrate weight ratios as well as the volume of the film-forming mixture. Rheological analyses were performed on the starting solutions, whereas the obtained films were characterized for their mechanical properties. Colorimetric analyses and swelling studies were also performed in order to determine the AgNPs release and the water uptake capacity of the films. Finally, microbiological tests were carried out to evaluate the antimicrobial efficacy of the optimized films, in order to demonstrate their possible application as dressings for the treatment of infected hard-to-heal wounds, which is a demanding task for public healthcare.

Synthesis of acrylated tannic acid as bio-based adhesion promoter in UV-curable coating with improved corrosion resistance

Aiming to developing UV-curable coatings with high performance on metal surface, acrylated tannic acid (TA-GMA) was developed to be a new bio-based adhesion promoter, which was synthesized via the ring opening reaction of tannic acid (TA) and glycidyl methacylate (GMA). The acrylation of TA not only improve the compatibility of TA with UV-curable resin, but also participate in the photo-curing process, which could act as a "bridge" between the coating and the metal substrate. The structure of TA-GMA was determined by FT-IR and 1H NMR. The adhesion promotion effects of TA-GMA for UV-curable coatings on metal substrates were investigated with cross-hatch test and pull off analysis. The results showed that TA-GMA could significantly improve the adhesion strength between UV-cured coatings and metal substrates. The pull-off strength increased from 0.44 MPa to 1.65 MPa for low carbon steel plate and from 0.13 MPa to 1.11 MPa for aluminum plate with the presence of TA-GMA, respectively. A significant increase in cross-hatch adhesion level was also observed. Accompanied with the remarkably improved adhesion performance, the corrosion protection properties of the UV-cured coating with TA-GMA were significantly enhanced from both electrochemical impedance spectroscopy (EIS) test and salt spray results.

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.

INVESTIGATION OF 3D CULTURE OF HUMAN ADIPOSE TISSUE-DERIVED MESENCHYMAL STEM CELLS IN A MICROFLUIDIC PLATFORM

Mesenchymal stem cells (MSCs) are multipotent stem cells that can support various tissues including bone marrow, adipose tissue, and synovial fluids, from which they can be readily isolated. The objective of this study is to harness the advantages of microfluidic systems for controlling and enhancing the maintenance and viability, and regenerative properties of MSCs by providing a 3D culture microenvironment with gelatin methacrylate (GelMA) hydrogel and exposing the cells to a slow fluid flow and low shear stress conditions. GelMA has methacryloyl groups and can be crosslinked by a photocuring process using biocompatible photoinitiators. The most common used photoinitiator for cellular encapsulation within hydrogels is the ultraviolet (UV) initiator 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure 2959 or I2959), but due to its low water solubility and the necessity of using a shorter wavelength light (365 nm), it can lead to cellular phototoxic and genotoxic effects. To overcome these limitations, lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) have recently been used with GelMA as an alternative photoinitiator. Because LAP is highly water soluble and has a 10 times faster polymerization rate, and it requires a visible light (λ = 405 nm) which makes it much safer for the cells, we use 10% GelMA together with 0.05% LAP photoinitiator for bioprinting human adipose tissue derived MSCs (hAT-MSCs) onto a membrane that has a 40 µm mesh size. To demonstrate a microfluidic culture advancement for improving the biological activities and regenerative capacity of the cells including cell adhesion, growth, viability and proliferation capacity as ultimate goals of this study, the membrane carrying the bioprinted construct was placed in a PDMS microchannel and exposed to the fluid to obtain dynamic microenvironments found in the human body. As a result, the cells were successfully maintained in the microfluidic 3D cell culture for two days, with a high cell viability of 99%.

Thermal shrinkage reveals the feasibility of pulse-delay photocuring technique

ObjectivesTo resolve the feasibility of the pulse-delay photocuring technique as a clinical strategy for reducing the detrimental polymerization stress induced in dental composites during the photocuring process. MethodsModel dental composites with high and low-filler contents were cured with the pulse-delay photocuring technique using different combinations of photocuring variables (irradiance, exposure time, and delay time). Irradiance used ranged from 0.1W/cm2 to 4W/cm2. The exposure time of the first pulse varied from 0.2s to 27.2s and the delay times ranged from 10s to 120s. The radiant exposure was varied from 4J/cm2 to 20J/cm2. A cantilever-beam based instrument (NIST Standards Reference Instrument 6005) was used to implement the photocuring technique for the measurement of the polymerization properties (the degree of monomer conversion, polymerization stress induced due to shrinkage, and temperature change due to the reaction exotherm and curing light absorbance) simultaneously in real-time. These properties were compared with those obtained using the conventional photocuring technique (i.e., using a constant irradiance for a fixed exposure time, a uniform exposure). ResultsThere exists a minimum radiant exposure, such that a reduction in the polymerization stress can be achieved without sacrificing the degree of monomer conversion by using the pulse-delay over the conventional photocuring technique. More specifically, stress reductions of up to 19% and 32% was observed with the pulse-delay when compared with the conventional photocuring technique at an irradiance of 0.5W/cm2 and 4W/cm2, respectively. The reduction occurred when the exposure time of the first pulse was greater than, but closer to, the gelation time (i.e., lower than the vitrification time) of the composite, regardless of the delay time used. Lower thermal shrinkage (contraction) during the post-curing time, rather than the stress relaxation during the delay time or lower degree of monomer conversion as claimed in the literature, is the cause of the reduction in the polymerization stress. SignificanceThe study clarifies a long-standing confusion and controversy on the applicability of the pulse-delay photocuring technique for reducing the polymerization stress and promotes its potential clinical success for dental restorative composites.

One-Component Cationic Photoinitiators from Tunable Benzylidene Scaffolds for 3D Printing Applications

This paper describes a series of novel benzylidene scaffold-based iodonium salt one-component photoinitiators containing double bonds and dialkylamino groups synthesized in one step via classical aldol condensation reactions. Systematic investigations of structure–activity relationships were performed via quantum-chemical calculations and experimental tests. New salts can efficiently decompose under irradiation from UV to visible regions of the spectrum. The design of new iodonium salts is described, followed by a description of properties of photoinitiators prepared in this way. All presented salts were characterized in terms of their spectral properties (UV–vis spectroscopy), ability to photodecompose (steady-state photolysis), cationic polymerization of the vinyl monomer, and epoxide monomer photoinitiation (quantum efficiency of acid generation and real-time Fourier-transform infrared measurements) as well as their proposed application in 3D printing. New benzylidene iodonium salts can photoinitiate the polymerization of vinyl ethers and epoxy monomers under LED@365 and LED@405 irradiation. Investigated compounds can simultaneously initiate and monitor the polymerization process according to the change of fluorescence during the photocuring process. Formulations before photopolymerization do not exhibit fluorescence, during the photopolymerization process fluorescence is “turning on”. This phenomenon might be used to monitor photopolymerization in an “online” manner.

Phase-sensitive optical coherence tomography for non-contact monitoring photocuring process

A method combining phase-contrast technique and spectral-domain optical coherence tomography (OCT) has been recently proposed for visualizing curing behaviors inside polymers (2020 Appl. Phys. Lett. 116 054103). Here, based on the method, a non-contact and highly-sensitive optical sensor is further developed to monitor the photocuring process of light-cured polymers. Compared with the existing method, the proposed optical sensor features two distinct advantages: (a) the sensor uses a point-detection OCT, rather than a line-field OCT, to capture the interference signal, which significantly improves its practicability and the measuring speed; (b) the sensor can simultaneously monitor the shrinkage strains and refractive index variations during a photocuring process, featuring enhanced functionality in practical applications. For validation, a cure monitoring experiment was carried out, proving that the sensor can accurately monitor the shrinkage strain and refractive index variation during the polymer photocuring process. The polymer coating fabrication process and the polymer adhesive process were also monitored, showing the effectiveness and practicability of the sensor.

Highly conductive organic-ionogels with excellent hydrophobicity and flame resistance

Very different from electronic conductors, ionic conductors usually possess some unique functions such as stretchability, transparency and ionic conductivity, thus exhibiting a great promise in the flexible wearable electronic devices. Herein, we develop a novel stretchable transparent organic-ionogel (OIG-TBP-50) via a rapid photo-curing process, in which we select the mixture of tributyl phosphate (TBP) and 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)amine ([BMMIm][NTf2]) as fireproof and conductive solvent, respectively. Just benefiting from the good synergistic effect of TBP and [BMMIm][NTf2], our-designed OIGs demonstrate excellent hydrophobicity and flame resistance as well as perfect stretchability (757%), high transparency (93%) in visible region, good environmental stability, wide temperature tolerance range (from −55 °C to 180 °C) and high ionic conductivity (1.73 × 10-3 S cm−1 at room temperature). In addition, our stretchable transparent OIGs even could light LED lamps under an alternating current field when directly used as the flexible conductive substrate. Further applying such OIGs as ionic conductor to assemble flexible sensor and touch screen, both of them could transport rapid signal response under slight touch stress.

Holographic Display-Based Control for High-Accuracy Photolithography of Cellular Micro-Scaffold With Heterogeneous Architecture

Engineered three-dimensional (3D) tissues that replicate composite in-vivo architectures have shown great potential for use in biomedical research. Cell-encapsulated hydrogel micro-scaffolds have been applied widely as basic building blocks to construct these artificial tissues. However, accurate reproduction of heterogeneous hierarchical structures and different regional mechanical properties inside a single integrated micro-scaffold that mimics physiologically relevant complex tissues presents a major challenge. Here, we propose a novel fabrication control algorithm to achieve high-accuracy photolithography of micro-scaffolds that recapitulate the high fidelity of native tissues by adjusting a 3D digital mask using holographic imaging feedback. By performing digital holographic reconstruction to express the hydrogel photocuring process in a matrix form and presetting the curing duration for each discrete point, the 3D digital mask was predefined to represent the required customized micro-scaffold. During fabrication, the UV exposure area was divided into microscaled grids with relatively uniform irradiance to control the photocuring process discretely for every local region in the entire architecture. The holographic imaging feedback allowed the curing duration of each grid to be adjusted in real-time, which enabled accurate reproduction of a 3D construct integrated with different microstructural morphologies and mechanical properties. Finally, PEGDA and GelMA, as typical biomaterials, were used to fabricate the heterogeneous hierarchical micro-scaffold. The structural accuracy was improved from 65 m to 12 m and the Youngs modulus was controlled flexibly in the 27.93.5 to 91.23.5 kPa range. With different local mechanical properties, cell migration in the micro-scaffold from soft to stiff areas is observed successfully.

A Stretchable Ionic Conductive Elastomer for High‐Areal‐Capacity Lithium‐Metal Batteries

Developing high‐areal‐capacity and dendrite‐free lithium (Li) anodes is of significant importance for the practical applications of the Li‐metal secondary batteries. Herein, an effective strategy to stabilize the high‐areal‐capacity Li electrodeposition by modifying the Li metal with a stretchable ionic conductive elastomer (ICE) is demonstrated. The ICE layer prepared via an instant photocuring process shows a promising Li+‐ion conductivity at room temperature. When being used in Li‐metal batteries, the thin ICE coating (~0.27 μm) acts as both a stretchable constraint to minimize the Li loss and a protective layer to facilitate the uniform flux of Li ions. With this ICE‐modifying strategy, the reversibility and cyclability of the Li anodes under high‐areal‐capacity condition in carbonate electrolyte are significantly improved, leading to a stable Li stripping/plating for 500 h at an ultrahigh areal capacity of 20 mAh cm−2 in commercial carbonate electrolyte. When coupled with industry‐level thick LiFePO4 electrodes (20.0 mg cm−2), the cells with ICE‐Li anodes show significantly enhanced rate and cycling capability.

Microstructure and mechanical properties of 3D printed ceramics with different vinyl acetate contents

Stereolithography (SL)-based three-dimensional (3D) printing technique is an efficient method for the fabrication of alumina ceramics. The alumina slurry is difficult to obtain due to the barrier between hydrophilic alumina and oleophilic resin. It not only requires that the ceramic slurry possessed low viscosity and uniformity, but also requires that the slurry could complete the photocuring process. In this study, vinyl acetate was added in the ceramic slurry as a bridge to connect alumina and resin, and the effects of vinyl acetate content on the microstructure and mechanical properties of the alumina ceramics were systematically investigated. The results showed that the alumina ceramics were composed of three types of particles which included large aggregates, individual particles, and long-column-shaped particles. The shrinkage, bulk density, and crystallite size of the ceramics increased with the increase in vinyl acetate content. The open porosity decreased with the increase in vinyl acetate content. The flexural strength of the ceramics first increased and subsequently decreased with the increase in vinyl acetate content. The shrinkage in Z direction was much greater than that in X or Y direction. Based on the above results, the optimum vinyl acetate content for alumina slurry was 10 wt%, which resulted in sintered ceramic with the shrinkage of 15.6% in X direction, 13.5% in Y direction, 21.9% in Z direction, bulk density of 1.9 g·cm−3, open porosity of 50.1%, and flexural strength of 24.4 MPa. The sintered ceramics satisfy the requirement of alumina ceramic cores.

Automated Fabrication of the High-Fidelity Cellular Micro-Scaffold Through Proportion-Corrective Control of the Photocuring Process

Fabricated cellular micro-scaffold that recapitulates natural extracellular matrix (ECM) has shown huge potential in the study of cell behaviors. However, the reproducing of the physiological morphology with high efficiency and accuracy in the micro-scaffold still remains as a major challenge. Here, we propose a novel automated fabrication method to engineer high-fidelity cellular micro-scaffold with a proportion-corrective control algorithm to modulate the photocuring process of biodegradable hydrogel in real-time. A digital holographic microscopy (DHM) system is integrated into the micro-fabrication system based on the digital micro-mirror device (DMD) to enable the real-time detection of the photocuring process. Before the photocuring, the theoretical curing thickness is determined by the calibrated model. To fabricate a micro-scaffold with high-fidelity morphology, the incident UV light is divided into different grid areas and achieve local discrete photocuring control. For every local area, the real-time added value of the cured thickness is compared with the theoretical value to determine the distortion which is corrected by the second-step exposure controlled by the proportion-corrective algorithm. Finally, the algorithm efficiently improved the fabrication accuracy from 200μm to 50μm. With the long-term culture, the cells viabilities exceeded 96%. The experimental results verified the effectiveness and feasibility of the proposed control algorithm.

Low‐weight fractions of graphene and hydroxyapatite enhance mechanics in photocured methacrylate adhesives

AbstractIn many applications, it is desirable for photocured adhesives to have high‐mechanical strength in the cured state, but relatively low viscosity when liquid. This was achieved by adding less than 0.5 wt% hydroxyapatite and graphene to methyl methacrylate with diurethane dimethacrylate (UDMA‐MMA). Nanoindentation shows hardness increasing by 30–40% and indentation modulus by >30% compared to UDMA‐MMA on its own. Rheometry shows only a small increase in uncured viscosity for the liquid state. The additives affect the optical properties, mobility of free radicals, photocuring, and degree of conversion, the effects of which are seen in Fourier transform infrared and micro‐Raman spectra. Thermographic images taken during curing show that the additives impact the photocuring process. In addition, changes in intermolecular bonding are seen in the vibrational spectra when the additives are present. The enhanced mechanical properties are attributed to the observed changes in photocuring and bonding.

Tertiaryamine linked and polysiloxane modified polyurethane acrylate oligomer and its effects of migration/co-initiation on photo-curable inkjet printing

To resolve the issue of handle-softness inadequacy in current polyurethane acrylate (PUA) oligomers for photo-curable inkjet printing on flexible substrates, and to improve the ability of anti-oxygen inhibition and photo-initiation efficiency of the tertiaryamine macromolecular co-initiator, the hydroxyl-terminated polydimethylsiloxane co-polymerized with tertiaryamine modified polyurethane acrylate (SiPUA) oligomer was designed and synthesized by using a sequential polymerization process. The structure of the SiPUA oligomer was confirmed by titration test and FTIR analysis, and the properties of the oligomers and the resultant photo-cured films were characterized by a range of analytical and measurement techniques. During the photo-curing process, the polysiloxane chain segment moved to the surface of the photo-cured SiPUA-HEA film due to the similar "surfactant critical micelle effect", forming an interconnected microphase structure of 50-70 μm thickness enriched with siloxane. The tertiaryamine group linked with polysiloxane segment was also enriched in the surface accordingly due to the migration of polysiloxane, thus improving the ability of anti-oxygen inhibition and photo-initiation efficiency. Benefiting from the both polysiloxane and tertiaryamine enriched surface and the retained PUA-HEA framework bulk in the cured film, a soft, flexible and strong photo-cured film with water-resistance and high photo-initiating efficiency was obtained.

Constitutive model for epoxy shape memory polymer with regulable phase transition temperature

ABSTRACT The epoxy shape memory polymer (SMP) with adjustable phase transition temperature is a kind of high-performance shape memory polymer, which can change its phase transition temperature and improve its mechanical properties through the process of photo curing. An epoxy SMP constitutive model combining phase transition and viscoelasticity is established by discretizing the epoxy SMP into several glass phase units and rubbery phase units in this paper. The model includes the viscoelastic constitutive equations of glass phase units and rubber phase units, the parameter expression during shape memory process, and material parameter equation during photocuring process. And the stress relaxation behavior of epoxy SMP at different temperatures and the change of material parameters during the photo-curing process are simulated numerically, and the simulation results perform consistency with the experimental data. The model can not only relate shape memory effect and phase transformation in physics but also better characterize the viscoelastic properties of SMP and predict the shape memory response of SMP.

Photocurable “all-lignocellulose” derived hydrogel nanocomposites for adsorption of cationic contaminants

Removal of contaminants from wastewater is one key element for the development of sustainable society. Here, innovative “all-lignocellulose” derived photo-curable hydrogel nanocomposites based on methacrylated carboxymethyl cellulose (M-CMC) and lignosulfonate-derived carbonaceous products were successfully designed. The carbon products were synthesized by microwave-assisted hydrothermal carbonization (MAHC), followed by oxidation and methacrylation. This yielded nano-graphene oxide (nGO) and methacrylated nGO (M-nGO). The structure of the carbon products was confirmed by several spectroscopic techniques. The photo-curing process, mechanical properties, swelling degree, adsorption efficiency towards cationic contaminants and recycling efficiency of the produced hydrogel nanocomposites containing different amounts of nGO or M-nGO were evaluated. Rapid photo-curing was demonstrated for all studied compositions. However, the shielding effect caused by the addition of aromatic nGO increased the time required for reaching gel point (8.5–19.5 s, instead of 4.8 s for pure M-CMC). This was partially compensated by the addition of M-nGO, that could participate in the photo-curing process. The photo-cured nanocomposites, M-CMC/nGO and M-CMC/M-nGO, demonstrated good mechanical properties, extremely high swelling degrees, outstanding adsorption capacity (up to 350 and 145 mg/g for MB and Cu(II) adsorption, respectively) and very good recyclability for at least 3 cycles. The designed “all-lignocellulose” derived hydrogel nanocomposites are, thus, promising candidates for wastewater purification to ensure access to clean water.

Improving mechanical properties of porous calcium phosphate scaffolds by constructing elongated gyroid structures using digital light processing

The present study reports the manufacturing of a novel type of porous calcium phosphate scaffolds with elongated gyroid structures using digital light processing (DLP), in order to offer significantly enhanced mechanical properties. In particular, solid camphor was employed as the diluent, in order to offer sufficiently low viscosity at high solid loading for conventional layer-by-layer DLP process. Four types of porous CaP scaffolds with different percent elongation (%EL = 0, 20, 40, and 60) were manufactured, and their porous structures and mechanical properties were characterized. All porous CaP scaffolds showed that CaP walls were elongated along the z-direction, while the degree of pore elongation increased with an increase in the designed %EL. Owing to the use of controlled processing parameters, such as layer thickness and exposure time for layer-by-layer photocuring process, and carefully designed debinding process, the photocured layers could be completely bonded together with high densification after sintering at 1,200 °C for 3 h. Such elongation of a gyroid structure offered significantly enhanced mechanical properties − compressive strengths of 4.33 ± 0.26 MPa and 11.51 ± 1.75 MPa were obtained for the porous CaP scaffold with the %EL of 0 and 60, respectively.

Synthesis and photo-curing properties of polyurethane acrylates with difunctional acrylate

Although a photo curing is more efficient in terms of time, solvent, and cost than a thermal one, photo-curable coatings require low viscosity and fast curing speed due to workability and time saving, respectively. A high viscous oligomer with multi-acryl groups is one of main components to determine its physical property after curing and then viscosity of coatings is controlled by adding a diluent. The polyurethane acrylates were newly synthesized by using ethylene diamine as a chain extender in poly(ε-caprolactone) polyol, dicyclohexylmethane 4,4′-diisocyanate, and isocyanato acrylate (ICA) containing diacrylate and diisocyanate groups. IR spectra were used to identify the synthesis and photo curing process. The mechanical properties of the cured films were analyzed by UTM. The results showed that the tensile strength of the UV-cured films was depended on the ICA content in the polyurethane acrylates.