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This investigation explores the fabrication of polymer matrix nanocomposites via additive manufacturing (AM), using a UV photopolymerization resin and copper nanoparticles (Cu-NPs) with vat photopolymerization 3D printing technology. The aim in this study is to investigate the mentioned materials in different formulations in terms of inexpensive processing, the property related variability, and targeting multifunctional applications. After the AM process, samples were post-cured with UV light in order to obtain better mechanical properties. The particles and resin were mixed using an ultrasonicator, and the particle contents used were 0.0, 0.5, and 1.0 wt %. The process used in this investigation was simple and inexpensive, as the technologies used are quite accessible, from the 3D printer to the UV curing device. These formulations were characterized with scanning electron microscopy (SEM) to observe the materials' microstructure and tensile tests to quantify stress-strain derived properties. Results showed that, besides the simplicity of the process, the mixing was effective, which was observed in the scanning electron microscope. Additionally, the tensile strength was increased with the UV irradiation exposure, while the strain properties did not change significantly.

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The flexural resistence is one of the most used test in researchs of mechanical characterization of resin composites for dental restoration. ISO 4049 photopolymerization technique performed static application stages of light tip. To polymerize the entire area of the specimen some areas must receive extra radiation. These areas with extra radiation are called overlap areas. In an attempt to remedy this problem, this research compared the ISO method with a new method using constant movement (CM) during photopolymerization. Twenty specimens (SPs) were produced with 25 x 2 x 2 mm, for each group, 10 specimens being polymerized by the static technique recommended by the ISO-4049 and 10 specimens polymerized by the CM technique for each LED curing light used. After Tukey's statistical analysis, it was found that there was no statistical difference in relation to flexural strength (FS) and for the flexural modulus of elasticity (EF). However, the standard deviation of both FS and EF were much lower in MC than in ISO. Therefore, the photopolymerization by CM of the samples for the flexural strength test proved to be a possible solution to the problem of overlap of the technique proposed by ISO.

O teste de flexão é um dos mais utilizados em pesquisa de caracterização mecânica de compósitos resinosos para restauração dentária. A técnica ISO 4049 é feita em etapas com aplicação estática da luz. Para que toda a área do corpo de prova receba esta radiação é preciso que outras áreas recebam radiação extra. Na tentativa de sanar tal problema, esta pesquisa comparou o método da ISO com um método que utiliza um movimento constante (MC) durante a fotopolimerização. Foram produzidos 20 corpos de provas (CPs) com 25 x 2 x 2 mm, para cada grupo, sendo 10 polimerizados pela técnica estática recomendada pela normativa ISO-4049 e 10 polimerizados pela técnica de movimentação contínua (MC) para cada fotopolimerizador LED utilizado. Após análise estatística de Tukey apurou-se que não houve diferença estatística em relação à resistência à flexão (RF) e para o módulo de elasticidade em flexão. Porém, percebe-se, que o desvio padrão tanto da RF quanto do EF foram bem menores em MC do que em ISO. Sendo assim, a fotopolimerização em movimentação constante (MC) das amostras para o teste de resistência à flexão se mostrou como uma possível solução para o problema de sobreposição na técnica proposta pela ISO.

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Additive manufacturing and nanotechnology have been used as fundamental tools for the production of nanostructured parts with magnetic properties, expanding the range of applications in additive processes through tank photopolymerization. Magnetic cobalt ferrite (CoFe2O4) and barium ferrite (BaFe12O19) nanoparticles (NPs) with an average size distribution value (DTEM) of 12 ± 2.95 nm and 37 ± 12.78 nm, respectively, were generated by the hydroxide precipitation method. The dispersion of the NPs in commercial resins (Anycubic Green and IRIX White resin) was achieved through mechanochemical reactions carried out in an agate mortar for 20 min at room temperature, with limited exposure to light. The resulting product of each reaction was placed in amber vials and stored in a box to avoid light exposure. The photopolymerization process was carried out only at low concentrations (% w/w NPs/resin) since high concentrations did not result in the formation of pieces, due to the high refractive index of ferrites. The Raman spectroscopy of the final pieces showed the presence of magnetic NPs without any apparent chemical changes. The electron paramagnetic resonance (EPR) results of the pieces demonstrated that their magnetic properties were maintained and not altered during the photopolymerization. Although significant differences were observed in the dispersion process of the NPs in each piece, we determined that the photopolymerization did not affect the structure and superparamagnetic behavior of ferrite NPs during processing, successfully transferring the magnetic properties to the final 3D-printed piece.

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This work presents a post-cured treatment alternative for photopolymer substrates considering the plasma produced via the sputtering process. The sputtering plasma effect was discussed, analyzing the properties of zinc/zinc oxide (Zn/ZnO) thin films deposited on photopolymer substrates, with and without ultraviolet (UV) treatment as a post-treatment process, after manufacturing. The polymer substrates were produced from a standard Industrial Blend resin and manufactured using stereolithography (SLA) technology. After that, the UV treatment followed the manufacturer's instructions. The influence of the sputtering plasma as an extra treatment during the deposition of the films was analyzed. Characterization was performed to determine the microstructural and adhesion properties of the films. The results showed the effect of plasma as a post-cured treatment alternative: fractures were found in thin films deposited on polymers with previous UV treatment. In the same way, the films showed a repetitive printing pattern due to the phenomenon of polymer shrinkage caused by the sputtering plasma. The plasma treatment also showed an effect on the thicknesses and roughness values of the films. Finally, according to VDI-3198 standards, coatings with acceptable adhesion failures were found. The results provide attractive properties of Zn/ZnO coatings on polymeric substrates produced by additive manufacturing.

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In recent years significant efforts have been made to develop new materials for wound dressing with improved healing properties. However, the synthesis methods usually employed to this end are often complex or require several steps. We describe here the synthesis and characterization of antimicrobial reusable dermatological wound dressings based on N-isopropylacrylamide co-polymerized with [2-(Methacryloyloxy) ethyl] trimethylammonium chloride hydrogels (NIPAM-co-METAC). The dressings were obtained with a very efficient single-step synthesis procedure based on visible light (455 nm) by photopolymerization. To this end, F8BT nanoparticles of the conjugated polymer (poly(9,9-dioctylfluorene-alt-benzothiadiazole) - F8BT) were used as macro-photoinitiators, and a modified silsesquioxane was employed as crosslinker. Dressings obtained by this simple and gentle method show antimicrobial and wound healing properties, without the incorporation of antibiotics or any other additives. The physical and mechanical properties of these hydrogel-based dressings were evaluated, as well as their microbiological properties, through in vitro experiments. Results show that dressings with a molar ratio of METAC of 0.5 or higher exhibit high swelling capacity, appropriate water vapor transmission rate values, stability and thermal response, high ductility and adhesiveness. In addition, biological tests showed that the dressings have significant antimicrobial capacity. The best inactivation performance was found for hydrogels synthesized with the highest METAC content. The dressings were tested several times with fresh bacterial cultures, showing a bacterial kill efficiency of 99.99 % even after three repetitions in a row, employing the same dressing, demonstrating the intrinsic bactericidal property of the materials and their reusability. In addition, the gels show low hemolytic effect, high dermal biocompatibility and noticeable wound healing effects. Overall results demonstrate that some specific hydrogel formulations have potential application as dermatological dressings for wound healing and disinfection.

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Natural porous materials adjust their resulting mechanical properties by the optimal use of matter and space. When these are produced synthetically, they are known as mechanical metamaterials. This paper adds degrees of tailoring of mechanical properties by producing double levels of gradation in lattice structures via cross-section variation in struts in uniformly periodic lattice structures (UPLS) and layered lattice structures (LLS). These were then additively manufactured via material extrusion (ME) and vat photopolymerization (VP). Their effective mechanical properties under compressive loads were characterized, and their stiffness contrasted with finite element models (FEM). According to the simulation and experimental results, a better correlation was obtained in the structures manufactured via VP than by ME, denoting that printing defects affect the correlation results. The brittle natural behavior of the resin caused a lack of a plateau region in the stress-strain curves for the UPLS structures, as opposed to those fabricated with ME. The LLS increased energy absorption up to 244% and increased the plateau stress up to 100% compared to the UPLS. The results presented in this paper demonstrate that the mechanical properties of lattice structures with the same base topology could be modified by incorporating variations in the strut diameter and then arranging these differently.

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In this work, a photo-polymerization route was used to obtain potassium acrylate-co-acrylamide hydrogels with enhanced mechanical properties, well-defined microstructures in the dry state, and unique meso- and macrostructures in the hydrated state. The properties of the hydrogels depended on the concentration of the crosslinking agent. Mechanical properties, swelling capacity, and morphology were analyzed, showing a well-defined transition at a critical concentration of the crosslinker. In terms of morphology, shape-evolving surface patterns appeared at different scales during swelling. These surface structures had a noticeable influence on the mechanical properties. Hydrogels with structures exhibited better mechanical properties compared to unstructured hydrogels. The critical crosslinking concentration reported in this work (using glycerol diacrylate) is a reference point for the future preparation of multistructured acrylic hydrogel with enhanced properties.

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This study describes the synthesis of a curing agent derived from limonene as well as its application to prepare biobased thermoset polymers via the epoxy/thiol-ene photopolymerization (ETE) method. A biobased commercial epoxy resin was used to synthesize a crosslinked polymeric matrix of polyether-polythioether type. The preparation of the curing agent required two steps. First, a diamine intermediate was prepared by means of a thiol-ene coupling reaction between limonene and cysteamine hydrochloride. Second, the primary amino groups of the intermediate compound were alkylated using allyl bromide. The obtained ditertiary amine-functionalized limonene compound was purified and characterized by FTIR and NMR spectroscopies along with GC-MS. The curing agent was formulated with a tetrafunctional thiol in stoichiometric ratio, and a photoinitiator at 1 mol % concentration, as the components of a thiol-ene system (TES). Two formulations were prepared in which molar concentrations of 30 and 40 mol % of the TES were added to the epoxy resin. The kinetics of the ETE photopolymerizations were determined by means of Real-Time FTIR spectroscopy, which demonstrated high reactivity by observing photopolymerization rates in the range of 1.50-2.25 s-1 for the epoxy, double bonds and thiol groups. The obtained polymers were analyzed by thermal and thermo-mechanical techniques finding glass transition temperatures (Tg) of 60 °C and 52 °C for the polymers derived from the formulations with 30 mol % and 40 mol % of TES, respectively. Potential applications for these materials can be foreseen in the area of coatings.

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This work reports the synthesis of a monomer 2-((2-(3-(prop-1-en-2-yl)phenyl)propan-2-yl)carbamoyl)oxy)ethyl methacrylate (MVTPM) and the evaluation of its performance as an additive in the formulation of Bis-GMA/TEGDMA based composite resins. Experimental composite resins formulated with the MVTPM monomer were compared with a control reference. Double bond conversion, polymerization kinetics, shrinkage and associated stress, sorption, and aqueous solubility, cell viability, as well as mechanical properties were evaluated according to international measurements standards. The experimental composite resins show comparable mechanical properties with the control reference and improvements in other properties, such as better hydrolytic and hygroscopic behavior and lower shrinkage stress, are reported. This makes MVTPM monomer potentially useful in the formulation of dental composite resins.

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An eco-friendly epoxy/thiol-ene photopolymerization (ETEP) process was employed to prepare epoxy bio-composites using a commercial biobased epoxy resin and a woven jute fabric as reinforcement. In this process the components of the thiol-ene system, an allyl-functionalized ditertiary amine curing agent, a multifunctional thiol and a radical photoinitiator, were added to the epoxy resin to produce a polyether-polythioether crosslinked co-network. Moreover, the jute fibers were functionalized with thiol groups using the 3-mercaptopropyl (trimethoxysilane) with the purpose of creating a chemically bonded polymeric matrix/fiber system. The obtained bio-composites prepared with the thiol-functionalized cellulose fibers exhibited an increase up to 52% and 40% in flexural modulus and strength with respect to the non-functionalized counterparts. Under the three-point bending loadings, the composites displayed higher deformation at break and toughness due to the presence of polythioethers in the co-network. The prepared bio-composites developed in this work are excellent candidates to extend the use of cellulose fibers for structural applications.

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This article describes a comprehensive study to obtain polymeric porous materials via a photopolymerization technique, using acrylate-based high internal phase emulsions (HIPEs), as a template. The aim of obtaining these polymers was to use them as hydrocarbon absorbing materials. Kinetics of photopolymerization of the acrylate monomers and of the HIPEs were conducted to optimize the process. The obtained monoliths were characterized by thermal analysis such as differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The morphology and surface area were analyzed by scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis. The compression properties of the materials were determined, as well as their absorption properties of hydrocarbons such as hexane, diesel, toluene and chloroform. The findings show that the acrylate-HIPEs displayed high reactivity photopolymerizing in 20 min. The glass transition temperature of the materials were in the range of 2 to 83 °C, depending on the ratio of acrylates in the photocurable formulation, displaying the characteristic morphology with voids and interconnecting windows. The polyHIPEs exhibited superior properties of absorption of the studied hydrocarbons. The order of capability of absorption was chloroform > toluene > hexane > diesel. The optimum absorbing material was that with trimethylolpropane triacrylate, ethylhexyl acrylate and isobornyl acrylate in a 1:0.9:2.1 ratio, which absorbed 778% of chloroform, 378% of toluene, 306 % of hexane and 236% of diesel.

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Aim: This study aimed to evaluate the effect of polymerization with either a monowave (MW) or a polywave (PW) light-curing unit (LCU) on the degree of conversion (DC) and marginal adaptation following thermomechanical aging of an ormocer bulk-fill resin composite (RC) (Admira fusion X-tra Bulk Fill - AB), a methacrylate-based bulk-fill RC (Tetric N-Ceram Bulk Fill - TB) and a conventional RC (Tetric N-Ceram - TC). Methods: DC was assessed in five samples of each RC using Fourier transform infrared spectroscopy. For determination of marginal adaptation, standard preparations were made in 60 bovine incisors, divided into three groups, according to the RC. The bulk-fill RC was inserted in a single increment of 4 mm. In contrast, the conventional RC was inserted in three increments. Marginal gap was evaluated after thermomechanical aging. Data were analyzed using a two-way analysis of variance (ANOVA) and Tukey's tests for multiple comparisons (α = 0.05). Results: The two-way ANOVA showed a significant effect (p<.05) of the RC factor but not of the LCU factor. The Tukey test showed that TB had the significantly lowest DC followed by TC, and with AB having the significantly highest DC. For the marginal adaptation, a significant effect was found for the LCU factor and the for the interaction RC × LCU (p<.05). Groups light-cured with PW showed significantly wider marginal gaps than MW. TC presented wider marginal gaps (17.36 µm) when cured with PW than when cured with MW (13.05 µm). The two bulk-fill RC resulted in similar marginal gap formation to each other. Conclusion: The ormocer-based bulk-fill RC showed a higher DC than the methacrylate-based bulk-fill RC but similar marginal adaptation. The LCU, MW or PW, had no significant influence on the DC, and no relevance on the marginal adaptation.

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This work reports the use of two monomers with two tertiary amines and four methacrylic (TTME) or acrylic (TTAC) terminal groups as co-initiators in the formulation of experimental resin adhesive systems. Both monomers were characterized by FT-IR and 1H NMR spectroscopies. The control adhesive was formulated with BisGMA, TEGDMA, HEMA, and the binary system CQ-EDAB as a photo-initiator system. For the experimental adhesives, the EDAB was completely replaced for the TTME or the TTAC monomers. The adhesives formulated with TTME or TTAC monomers achieved double bond conversion values close to 75%. Regarding the polymerization rate, materials formulated with TTME or TTAC achieved lower values than the material formulated with EDAB, giving them high shelf-life stability. The degree of conversion after shelf simulation was only reduced for the EDAB material. Ultimate tensile strength, translucency parameter, and micro-tensile bond strength to dentin were similar for control and experimental adhesive resins. Due to their characteristics, TTME and TTAC monomers are potentially useful in the formulation of photopolymerizable resins for dental use with high shelf-life stability.

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In this paper, we study the capabilities of two additive manufacturing technologies for the production of lattice structures, namely material extrusion and vat photopolymerization additive manufacturing. A set of polymer lattice structures with diverse unit cell types were built using these additive manufacturing methods and tested under compression. Lattice structures built using material extrusion had lower accuracy and a lower relative density caused by the air gaps between layers, but had higher elastic moduli and larger energy absorption capacities, as a consequence of both the thicker struts and the relatively larger strength of the feedstock material. Additionally, the deformation process in lattices was analyzed using sequential photographs taken during the compression tests, evidencing larger differences according to the manufacturing process and unit-cell type. Both additive manufacturing methods produced miniature lattice structures with similar mechanical properties, but vat polymerization should be the preferred option when high geometrical accuracy is required. Nevertheless, as the solid material determines the compressive response of the lattice structure, the broader availability of feedstock materials gives an advantage to material extrusion in applications requiring stiffer structures or with higher energy absorption capabilities.

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Photopolymerized microparticles are made of biocompatible hydrogels like Polyethylene Glycol Diacrylate (PEGDA) by using microfluidic devices are a good option for encapsulation, transport and retention of biological or toxic agents. Due to the different applications of these microparticles, it is important to investigate the formulation and the mechanical properties of the material of which they are made of. Therefore, in the present study, mechanical tests were carried out to determine the swelling, drying, soluble fraction, compression, cross-linking density (Mc) and mesh size (ξ) properties of different hydrogel formulations. Tests provided sufficient data to select the best formulation for the future generation of microparticles using microfluidic devices. The initial gelation times of the hydrogels formulations were estimated for their use in the photopolymerization process inside a microfluidic device. Obtained results showed a close relationship between the amount of PEGDA used in the hydrogel and its mechanical properties as well as its initial gelation time. Consequently, it is of considerable importance to know the mechanical properties of the hydrogels made in this research for their proper manipulation and application. On the other hand, the initial gelation time is crucial in photopolymerizable hydrogels and their use in continuous systems such as microfluidic devices.

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We describe the synthesis of polymer monoliths inside polypropylene tubes from ink pens. These tubes are cheap, chemically stable, and resistant to pressure. UV-initiated grafting with 5 wt% benzophenone in methanol for 20 min activated the internal surface, thus enabling the covalent binding of ethylene glycol dimethacrylate, also via photografting. The pendant vinyl groups attached a poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) monolith prepared via photopolymerization. These tubes measured 100-110 mm long, with 2 mm of internal diameter. The parent monoliths were functionalized with Na2 SO3 or iminodiacetate to produce strong and weak cation exchangers, respectively. The columns exhibited permeabilities varying from 2.7 to 3.3 × 10-13  m2 , which enabled the separation of proteins at 500 µL/min and back pressures <2.8 MPa. Neither structure collapse nor monolith detachment occurred at flow rates as high as 2.0 mL/min, which produced back pressures between 6.9 and 9.0 MPa. The retention times of ovalbumin, ribonuclease A, cytochrome C, and lysozyme in salt gradient at pH 7.0 followed the order of increasing isoelectric points, confirming the cation exchange mechanism. Separation and determination of lysozyme in egg white proved the applicability of the columns to the analysis of complex samples.

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Two liquid monomers (CT-AL and CT-ACR) were synthesized from the acylation of tert-butyl catechol with different acid chlorides. The monomers were used to prepare photopolymerizable dental composite for completely replacing TEGDMA. Properties such as flexural strength, modulus of elasticity, degree of double bond conversion, polymerization shrinkage, as well as the polymerization stress were studied. Also, color alteration, translucency, and cytotoxicity were evaluated. The results show that the experimental materials formulated with CT-AL and CT-ACR have similar mechanical properties to a control material formulated with BisGMA/TEGDMA, similar polymerization shrinkage, and less polymerization stress. The composite formulated with the CT-AL monomer shows a similar degree of conversion (72%), while the composite formulated with the CT-ACR monomer has a degree of conversion lower (58%) than the control resin (71%). These results suggest that both monomers could have potential applications in the formulation of composites for dental restorations.

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The development of convenient synthetic methods and improved materials for the production of high load-capacity and biocompatible drug delivery systems is a challenging task with important implications in health sciences. In this work, acrylamide/2-hydroxyethylmethacrylate and N-isopropylacrylamide/2-hydroxyethylmethacrylate hydrogels were synthesized by photopolymerization using energy-efficient green-LEDs. A functionalized silsesquioxane was used as both crosslinker and co-initiator for the photopolymerization. The hybrid organic-inorganic nature of the silsesquioxane improved the resulting hydrogels' properties increasing their swelling capacity and biocompatibility. Additionally, the mild conditions used during the photopolymerization allowed the synthesis of hydrogels in the presence of antibiotics yielding high load-capacity materials in which the drug preserves its molecular structure and antimicrobial activity (as confirmed by HPLC and microbiological assays). The materials were characterized by FTIR, DSC and SEM. Additionally, the kinetics of gels´ swelling and drug release were studied under physiological conditions (pH 7.4 and 37 °C). The results demonstrate how hydrogel composition affects the antibiotics-release kinetics. The final drug release percentage increased with increasing molar fraction of acrylamide or N-isopropylacrylamide and in most cases exceeded 85%. Finally, the antibacterial effect of loaded gels was characterized using a number of assays against Gram negative and Gram positive bacteria. The observed antibacterial effect correlated well with swelling and drug release results. Furthermore, gels are not toxic for isolated erythrocytes as demonstrated by haemolytic tests. Overall, our results indicate that the produced hydrogels are promising materials to develop controlled drug-delivery devices such as capsules, dermatological patches and others.

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A novel filler-resin matrix interphase structure was developed and evaluated for dental composite restoratives. Nanogel additives were chemically attached to the filler surface to use this created interphase as a potential source of compliance to minimize stress development during polymerization. In addition, we evaluated the effects of free nanogel dispersion into the resin matrix, combined or not with nanogel-modified fillers. Nanogels with varied characteristics were synthesized (i.e., size, 5 and 11 nm; glass transition temperature, 28 °C to 65 °C). Glass fillers were treated with trimethoxyvinylsilane and further reacted with thiol-functionalized nanogels via a free radical thiol-ene reaction. γ-Methacryloxypropyltrimethoxysilane-surface treated fillers were used as a control. Composites were formulated with BisGMA/TEGDMA resin blend with 60 wt% fillers with nanogel-modified fillers and/or free nanogel additives at 15 wt% in the resin phase. Polymerization kinetics, polymerization stress, volumetric shrinkage, and rheological and mechanical properties were evaluated to provide comprehensive characterization. Nanogel-modified fillers significantly reduced the polymerization stress from 2.2 MPa to 1.7 to 1.4 MPa, resulting in 20% stress reduction. A significantly greater nanogel content was required to generate the same magnitude stress reduction when the nanogels were dispersed only in the resin phase. When the nanogel-modified filler surface treatment and resin-dispersed nanogel strategies were combined, there was a stress reduction of 50% (values of 1.2 to 1.1 MPa). Polymerization rate and volumetric shrinkage were significantly reduced for systems with nanogel additives into the resin. Notably, the flexural modulus of the materials was not compromised, although a slight reduction in flexural strength associated with the nanogel-modified interphase was observed. Overall, modest amounts of free nanogel additives in the resin phase can be effectively combined with a limited nanogel content filler-resin interphase to lower volumetric shrinkage and dramatically reduce overall polymerization stress of composites.

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PURPOSE: The aim of this study was to evaluate the influence of indirect restorative material type and thickness on the transmission of different wavelengths from a broad-banded dental curing light. METHODS: Four dental indirect restorative materials for computer-aided design and computer-aided manufacturing (CAD/CAM) were evaluated: [RC] resin/ceramic hybrid material (Lava Ultimate), [FC] feldspathic ceramic (VitaBlocs), and two zirconia-based ceramics ([ZK] Katana; and [ZL] Lava). Total loss of irradiance (TL) was measured for blue (WB, 425-490nm) and violet (WV, 350-425nm) wavelengths. Specimens of 15×15mm with varying thicknesses (0.5, 1.0, 1.5, and 2.0mm) were fabricated (n=5). A plasma-arc dental light-curing unit was used (Arc Light-II). To assess TL as a function of wavelength, a software (Spectra Suite v5.1) connected to a spectroradiometer (USB2000) and an integrating sphere (CTSM-LSM-60-SF) was used. Data was subjected to statistical analysis (two-way ANOVA and post-hoc Tukey test, α=0.05). RESULTS: A 0.5mm interposition resulted in TL from 50.5 to 67.2%, depending on material. Increased thickness resulted in higher TL for all materials. FC showed less TL compared to ZK. In general, WV showed higher TL than did WB, and WV/WB proportion decreased with increasing thickness. CONCLUSIONS: Indirect materials significantly reduced TL, and this effect is greater with increasing thickness. WV showed lower penetration compared to WB.

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