Search Results (180)

Background: This study aimed to assess the impact of methacrylate-functionalized polyhedral oligomeric silsesquioxanes dispersed in nanosilica (MA/Ns-POSS) on the mechanical properties of light-curable dental resins and composites. The primary goal was to evaluate how different concentrations of MA/Ns-POSS (0.5–20 wt.%) affect the hardness, flexural strength, modulus, diametral tensile strength, polymerization shrinkage stress, and degree of conversion of these materials. Methods: A mixture of Bis-GMA, UDMA, TEGDMA, HEMA, and camphorquinone, with a tertiary amine as the photoinitiator, was used to create resin and composite samples, incorporating 45 wt.% silanized silica for the composites. Hardness (Vickers method, HV), flexural strength (FS), and flexural modulus (E_f) were assessed using three-point bending tests, while diametral tensile strength (DTS) polymerization shrinkage stresses (PSS), and degree of conversion (DC) analysis were analyzed for the composites. Results: The results showed that resins with 10 wt.% MA/Ns-POSS exhibited the highest E_f and FS values. Composite hardness peaked at 20 wt.% MA/Ns-POSS, while DTS increased up to 2.5 wt.% MA/Ns-POSS but declined at higher concentrations. PSS values decreased with increasing MA/Ns-POSS concentration, with the lowest values recorded at 15–20 wt.%. DC analysis also showed substantial improvement for 15–20 wt.% Conclusion: Incorporating MA/Ns-POSS improves the mechanical properties of both resins and composites, with 20 wt.% showing the best results. Further studies are needed to explore the influence of higher additive concentrations. Full article

The demand for polymer composite materials in the dental market is increasing every year. This rise is due to their excellent properties and ongoing technological advancements. The goal of this study was to develop new photoinitiators included in the liquid organic matrix, which is one of the main components of dental composites. Therefore, a series of compounds based on the indenoquinoxaline skeleton was synthesized, differing in the substituent. The spectroscopic properties of these compounds allowed their use as visible-light photoinitiators of radical polymerization in combination with (phenylthio)acetic acid. In addition to the polymerization kinetics, the lifetime and quantum yield of the triplet-state formation and the rate constants of its quenching by (phenylthio)acetic acid were determined. The durability of the designed composites was also assessed. Ageing tests included hydrothermal ageing, allowing for the determination of sorption, solubility, and mass change. Solutions imitating the oral cavity environment—distilled water, artificial saliva, n-heptane, and 3% acetic acid—as well as solutions containing pigments were used for these studies. Determination of the mass change and colour stability allowed for the assessment of how these materials react to long-term exposure in the oral environment. It was found that the solution simulating the natural oral environment has a significant impact on the hydrolytic stability and colour stability of the materials. Full article

As far as history tells, people have set efforts both to improve the conditions and to change the visual outfit of the skin, nails, and hair. The first information on nail cosmetics is found in ancient China and Egypt, where various nature-derived compositions were used for changing the colour of the nails. Nowadays more mechanically and chemically durable systems for nail polishes are elaborated. This review focuses on the latest achievements in the field of UV-curable nail polishes. Herein, the polymerization mechanisms of various systems (acrylates, as well as epoxides and thiols) occurring in nail polishes are described. Besides plausible side reactions of the polymerization process are characterized. Thus, the main drawbacks for forming a uniform, perfect layer are illuminated. For effective curing, the choice of photoinitiators may be crucial; thus, various types of photoinitiators as well as their main advantages and disadvantages are characterized. Ensuring effective adhesion between the substrate (human nail) and the polymer film is one of the challenges for the nail polish industry—thus the plausible interactions between the adhesion promoters and the keratin are described. Regarding the film-forming agents, a comprehensive overview of the composition of the traditional UV-curing nail polishes is provided, but the main emphasis is devoted to alternative, nature-derived film-forming agents that could introduce renewable resources into nail cosmetics. Additionally, this review gives short insight into the latest innovations in UV-curing nail cosmetics, like (1) nail polishes with improved pealability, (2) covalently polymer-bonded dyes and photoinitiators, thus reducing the release of the low-molecular compounds or their degradation products, and (3) UV-curing nail polishes as delivery systems for nail treatment medicine. Full article

Challenges in the traditional cast-and-cure manufacturing of composite solid propellants, such as the use of mandrels and the toxicity of curing agents, are being addressed through new propellant formulations and additive manufacturing techniques. Within this framework, this study aimed to investigate the properties of UV-curable composite solid rocket propellants, focusing on their compatibility with advanced 3D printing technologies. Polybutadiene-based propellants incorporating a specific photoinitiator were examined. Key rheological properties, including the pseudoplasticity and pot-life, were assessed to evaluate the material’s behavior during the printing process. Furthermore, photopolymerization tests were performed using a customized delta illuminator to evaluate the conversion efficiency under UVA and UVC light sources. Concurrently, a modular Cartesian 3D printer was developed and preliminary tests were performed. Rheological tests also revealed a flow index n of 0.32 at 60 °C and 0.46 at 80 °C, indicating significant pseudoplastic behavior. The pot-life tests showed that the viscosity of the propellant reached the upper limit of ${10}^6$ cP more quickly at higher temperatures, indicating a shorter time range of printability. UVA irradiation resulted in a polymerization conversion rate of about 90%, while UVC exposure did not significantly enhance the conversion rate beyond this value. Finally, the 3D printing tests confirmed the feasibility of producing solid propellant, though challenges related to material segregation and the extrusion consistency were observed. Material separation resulted in a significant impact on the printability, causing underextrusion and nozzle clogging, particularly with smaller nozzle diameters and higher extrusion pressures. Overall, this research represents a significant step forward in the development of UV-curable propellants for additive manufacturing, building on previous advancements by the research group. It demonstrates tangible progress in addressing key challenges such as the printability, material performance, and curing efficiency, while also highlighting areas requiring further refinement. These findings underscore the continuous evolution of this technology toward higher readiness levels, paving the way for its broader application in composite solid propellant manufacturing. Full article

Protein–polymer bioconjugates offer numerous advantages in biomedical applications by integrating the benefits of functional proteins and tunable synthetic polymers. Developing drug-loaded protein–polymer nanoparticles, with a receptor-targeting protein forming the nanoparticle shell, would be ideal for the targeted delivery of drugs to cancer cells that overexpress specific receptors for more effective cancer therapy. In this study, we report the synthesis of reduction-responsive protein–polymer nanoparticles by a photoinitiated polymerization-induced self-assembly (photo-PISA) approach. Anti-cancer drugs can be efficiently encapsulated at high concentrations within the nanoparticles during the photo-PISA process. These protein–polymer nanoparticles present transferrin (Tf) on their surfaces, capable of targeting the overexpressed Tf receptors found on cancer cells. It was found that the nanoparticles demonstrate enhanced cellular uptake and delivery of the anti-cancer drug, curcumin, to cancer cells via Tf receptor-mediated endocytosis, compared to the control PEGylated nanoparticles that lack targeting capability. Moreover, the nanoparticles can release the encapsulated curcumin in response to a reducing environment, a characteristic of cancer cells compared to health cells. Consequently, the synthesized protein–polymer nanoparticles are more effective in inducing cancer cell death compared to the control nanoparticles, demonstrating their potential as an effective and targeted drug delivery system for cancer therapy. Full article

Background/Objectives: Glioblastoma is the most common and lethal primary brain tumor. Patients often suffer from tumor- and treatment induced vasogenic edema, with devastating neurological consequences. Intracranial edema is effectively treated with dexamethasone. However, systemic dexamethasone requires large doses to surpass the blood brain barrier in therapeutic quantities, which is associated with significant side effects. The aim of this study was to investigate a biodegradable, dextran-hydroxyethyl methacrylate (dex-HEMA) based hydrogel, containing polymeric micelles loaded with dexamethasone and liposomes encapsulating dexamethasone phosphate for localized and prolonged delivery. Methods: Poly(ethylene glycol)-b-poly(N-2-benzoyloxypropyl methacrylamide (mPEG-b-p(HPMA-Bz)) micelles were loaded with dexamethasone and characterized. The dexamethasone micelles, together with dexamethasone phosphate liposomes, were dispersed in an aqueous dex-HEMA solution followed by radical polymerization using a photoinitiator in combination with light. The kinetics and mechanisms of drug release from this hydrogel were determined. Results: The diameter of the nanoparticles was larger than the mesh size of the hydrogel, rendering them immobilized in the polymer network. The micelles immediately released free dexamethasone from the hydrogel for two weeks. The dexamethasone phosphate loaded in the liposomes was not released until the gel degraded and intact liposomes were released, starting after 15 days. The different modes of release result in a biphasic and sequential release profile of dexamethasone followed by dexamethasone phosphate liposomes. Conclusions: The results show that this hydrogel system loaded with both dexamethasone polymeric micelles and dexamethasone phosphate loaded liposomes has potential as a local delivery platform for the sequential release of dexamethasone and dexamethasone phosphate, for the intracranial treatment of glioblastoma associated edema. Full article

In this study we report on the efficiency of a furane-indole-chromenone-based organic derivative (FIC) as a photocatalyst in the α-arylation of enol acetate upon LED irradiation at 405 nm, and as a photoinitiator/photocatalyst in the free radical polymerization of an acrylate group in the presence of bis-(4-tert-butylphenyl)iodonium hexafluorophosphate (Iod) as an additive, or in the presence of both Iod and ethyl-4-(dimethyl amino) benzoate (EDB) under LED irradiation at 365 nm. The photochemical properties of this new light-sensitive compound are described, and the wide redox window (3.27 eV) and the high excited-state potentials FIC*/FIC^●− (+2.64 V vs. SCE) and FIC^●+/FIC* (−2.41 V vs. SCE) offered by this photocatalyst are revealed. The chemical mechanisms that govern the radical chemistry are discussed by means of different techniques, including fluorescence-quenching experiments, UV-visible absorption and fluorescence spectroscopy, and cyclic voltammetry analysis. Full article

Hydrogels are three-dimensional polymeric matrices capable of absorbing significant amounts of water or biological fluids, making them promising candidates for biomedical applications such as drug delivery and wound healing. In this study, novel hydrogels were synthesized using a photopolymerization method and modified with cisplatin-loaded protein carriers, as well as natural extracts of nettle (Urtica dioica) and chamomile (Matricaria chamomilla L.). The basic components of the hydrogel were polyvinylpyrrolidone and polyvinyl alcohol, while polyethylene glycol diacrylate was used as a crosslinking agent and 2-methyl-2-hydroxypropiophenone as a photoinitiator. The hydrogels demonstrated high swelling capacities, with values up to 4.5 g/g in distilled water, and lower absorption in Ringer’s solution and simulated body fluid (SBF), influenced by ionic interactions. Wettability measurements indicated water contact angles between 51° and 59°, suggesting balanced hydrophilic properties conducive to biomedical applications. Surface roughness analyses revealed that roughness values decreased after incubation, with Ra values ranging from 6.73 µm before incubation to 5.94 µm after incubation for samples with the highest protein content. Incubation studies confirmed the stability of the hydrogel matrix, with no significant structural degradation observed over 20 days. However, hydrogels containing 2.0 mL of protein suspension exhibited structural damage and were excluded from further testing. The synthesized hydrogels show potential for application as carriers in localized drug delivery systems, offering a platform for future development in areas such as targeted therapy for skin cancer or other localized treatments. Full article

This study aimed to evaluate the depth of cure (DoC) of bulk-fill composite resins, measured by the bottom-to-top Vickers microhardness ratio, using different light-curing units (LCUs): single-wave LED, polywave LED, and halogen. Six bulk-fill composites—Tetric EvoCeram Bulk Fill, X-tra base, SonicFill, Venus Bulk Fill, SDR, and Filtek Bulk Fill—were tested. Four LCUs, including one halogen (Elipar Trilight) and three LEDs (Demi Ultra, Valo, and Bluephase style), were employed for polymerization. Vickers hardness measurements were taken at depths of 1 mm to 5 mm. One- and two-way ANOVA (α = 0.05) were used for data analysis. The results revealed significant differences in microhardness and microhardness ratios among the composites at depths of 4 mm and beyond, depending on the LCU used. It was observed that most bulk-fill composites showed an adequate DoC up to 4 mm, but the effectiveness varied with different LCUs. Importantly, polywave LED LCUs did not exhibit a superior advantage in achieving depth of cure compared to monowave LED LCUs for composites containing multiple photoinitiators. These findings suggest that while several factors affect the DoC, the type of LCU plays a crucial role, and polywave LEDs may not offer additional benefits over monowave LEDs. Full article

The chain-length-dependent nature of the termination reaction in radical polymerization (RP) renders the overall termination rate coefficient, <k_t>, a complex parameter in the usual situation where the radical chain-length distribution is non-uniform. This applies also for the activation energy of termination, E_a(<k_t>), which we subject to detailed mechanistic investigation for the first time. The experimental side of this work measures E_a(<k_t>) for the dilute-solution, low-conversion, chemically initiated homopolymerization of styrene (ST), methyl methacrylate (MMA), butyl methacrylate, and dodecyl methacrylate. Values of 25–39 kJ mol⁻¹ are obtained, consistent with strong chain-length-dependent termination (CLDT) for short chains. On other hand, the reanalysis of analogous bulk polymerization data for ST and MMA finds E_a(<k_t>) values of 18–24 kJ mol⁻¹, consistent with weak CLDT for long chains. Both these results are as expected from the so-called composite model for CLDT. A simple analytic framework for understanding and predicting E_a(<k_t>) values is presented for the standard RP situation of continuous initiation. All the results of this work can be rationalized via this framework, which clearly establishes that E_a(<k_t>) is determined by far more than just the E_a of radical diffusion. This framework is extended to activation energy for the number-average degree of polymerization, E_a(DP_n), which we measure and successfully scrutinize via our CLDT model. In the final section of this work, we make interesting, testable predictions about E_a(<k_t>) and/or E_a(DP_n) in various RP systems of different natures to those studied here, most notably, systems involving acrylates, continuous photoinitiation, or dominant chain transfer. Full article

Aim: Polyurethane-based aligners, created through photoinitiated free-radical polymerization, have been the subject of numerous studies focusing solely on their mechanical properties. In contrast, we investigate their thermomechanical properties, which are crucial for their efficacy. This paper aims to investigate the effects of different UV light exposure durations on the complex modulus of elasticity, tan delta, glass transition temperature, and the degree of conversion (DC). Methods: Aligners were printed using Tera Harz TC-85 and NextDent Ortho Flex resin with specific exposure times (2, 2.4, 3, 4, and 4.5 s for Tera Harz; 5, 6, 7, and 8 s for NextDent) and processed per manufacturer guidelines. The degree of conversion was analyzed using Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy, while Dynamic Mechanical Analysis (DMA) characterized the mechanical properties (complex modulus and tan delta) and the glass transition. Results: Tera Harz TC-85 showed a higher degree of conversion (90.29–94.54%), suggesting fewer residual monomers, which is potentially healthier for patients. However, its lower glass transition temperature (35.60–38.74 °C) might cause it to become rubbery in the mouth. NextDent Orto Flex, with a higher storage modulus (641.85–794.55 MPa) and Tg (49.36–50.98 °C), offers greater rigidity and stability at higher temperatures (greater than temperature in the oral cavity), ideal for orthodontic forces, though its lower degree of conversion raises health concerns. Conclusions: Tera Harz TC 85 generally achieves higher DC and more stable polymerization across different UV exposure times than NextDent Orto Flex. Optimal polymerization times significantly impact both the mechanical and thermal properties of these dental resins, with NextDent showing optimal properties at 7 s and Tera Harz benefiting from both very short and extended exposure times. Full article

In this work, two novel acridone-based photoinitiators were designed and synthesized for the free radical polymerization of acrylates with a light-emitting diode emitting at 405 nm. These acridone derivatives were employed as mono-component Type II photoinitiators and as multicomponent photoinitiating systems in the presence of an iodonium salt or an amine synergist (EDB) in which they achieved excellent polymerization initiating abilities and high final conversions of the acrylate group. Photoinitiation mechanisms through which reactive species are produced were investigated employing different complementary techniques including steady-state photolysis, steady-state fluorescence, cyclic voltammetry, UV–visible absorption spectroscopy, and electron spin resonance spectroscopy. Finally, these molecules were also used in the direct laser writing process for the fabrication of 3D objects. Full article

Stepwise photopolymerization is a miraculous strategy modulating the polymer skeleton and electro-optical properties of light modulators based on liquid crystal/polymer composites. However, owing to the indistinct polymerization mechanism and curing condition discrepancy, the required polymer structures and electro-optical properties are hard to be controlled precisely. Herein, a novel polymer-stabilized liquid crystal film based on acrylate/epoxy resin is proposed, fabricated and the relationships between preparation process, polymer content, polymer morphology and electro-optical properties are studied. The in-situ photopolymerization of acrylate/epoxy resin liquid crystalline polymer is fulfilled using cation photo-initiator UV 6976. The distinct photopolymerization speed between acrylate and epoxy resin benefits the polymer morphology control, and with accurate containment of the polymerization process and polymer composition, the superior electro-optical properties at a higher polymer content are acquired. The polymer morphology and electro-optical properties are influenced by the polymer content and mass ratio between acrylate and epoxy resin. The best electro-optical properties among samples are attained by controlling the mass ratio between acrylate and epoxy resin to 1:1, integrating higher densities of scattering centers and lower anchoring effect. With higher polymer content, the strategy of increasing the mass ratio of E6M benefits the improvement of E-O properties for alleviating polymer density. This work provides insights to stepwise polymerization of liquid crystalline monomers and offers a fancy strategy for the preparation of novel liquid crystal dimming films. Full article

Photopolymerization is becoming increasingly popular in industry due to its copious advantages. The vital factor in the entire pre-polymerization formulation is the presence of photoinitiators. Depending on the application, photoinitiators have different features. Hence, scientists are particularly interested in developing new photoinitiators that can expand the scope of applications and be used to create products with the features demanded by current trends. This brief review summarizes the photoinitiators used in dental materials and hydrogels and those obtained from natural and synthetic sources. Full article

The miniaturization and high-power density of modern electronic devices pose significant thermal management issues, particularly affecting their performance and lifetime. Ladder-like polysilsesquioxanes (LPSQs) offer a promising solution due to their remarkable thermal, mechanical, and chemical properties. By incorporating thermally conductive fillers, LPSQ composites can achieve high thermal conductivity (TC), making them ideal for thermal management in advanced electronic applications. In this study, LPSQ-based nanocomposites containing functionalized alumina nanoparticles were prepared by solution casting and UV curing, and the effects of varying amounts of Irgacure-184 photoinitiator on their structural and thermal properties were investigated. Three sets of samples were prepared with a fixed amount of LPSQs, 80 wt.% of nanoparticles, and 1, 5, or 10 wt.% of photoinitiator with respect to the matrix. TC was evaluated from the measured values of heat capacity, density, and thermal diffusivity. TC values increased by 60%, 71.2%, and 93.1% for the three samples, respectively, compared to the neat matrix. Results indicate that an intermediate amount of photoinitiator (5%) preserved LPSQs’ structural integrity, namely the presence of long linear silsesquioxane chains, and provided good filler dispersion and distribution, high polymerization degree, thermal stability, and high TC. Full article