Visible Light-curing Research Articles

Ultraviolet light blocking optically clear adhesives for foldable displays via highly efficient visible-light curing

In developing an organic light-emitting diode (OLED) panel for a foldable smartphone (specifically, a color filter on encapsulation) aimed at reducing power consumption, the use of a new optically clear adhesive (OCA) that blocks UV light was crucial. However, the incorporation of a UV-blocking agent within the OCA presented a challenge, as it restricted the traditional UV-curing methods commonly used in the manufacturing process. Although a visible-light curing technique for producing UV-blocking OCA was proposed, its slow curing speed posed a barrier to commercialization. Our study introduces a highly efficient photo-initiating system (PIS) for the rapid production of UV-blocking OCAs utilizing visible light. We have carefully selected the photocatalyst (PC) to minimize electron and energy transfer to UV-blocking agents and have chosen co-initiators that allow for faster electron transfer and more rapid PC regeneration compared to previously established amine-based co-initiators. This advancement enabled a tenfold increase in the production speed of UV-blocking OCAs, while maintaining their essential protective, transparent, and flexible properties. When applied to OLED devices, this OCA demonstrated UV protection, suggesting its potential for broader application in the safeguarding of various smart devices.

Ultraviolet Light Debondable Optically Clear Adhesives for Flexible Displays through Efficient Visible-Light Curing.

With growing sustainability concerns, the need for products that facilitate easy disassembly and reuse has increased. Adhesives, initially designed for bonding, now face demands for selective removal, enabling rapid assembly-disassembly and efficient maintenance across industries. This need is particularly evident in the display industry, with the rise of foldable devices necessitating specialized adhesives. A novel optically clear adhesive (OCA) is presented for foldable display, featuring a unique UV-stimulated selective removal feature. This approach incorporates benzophenone derivatives into the polymer network, facilitating rapid debonding under UV irradiation. A key feature of this method is the adept use of visible-light-driven radical polymerization for OCA film fabrication. This method shows remarkable compatibility with various monomers and exhibits orthogonal reactivity to benzophenone, rendering it ideal for large-scale production. The resultant OCA not only has high transparency and balanced elasticity, along with excellent resistance to repeated folding, but it also exhibits significantly reduced adhesion when exposed to UV irradiation. By merging this customized formulation with strategically integrated UV-responsive elements, an effective solution is offered that enhances manufacturing efficiency and product reliability in the rapidly evolving field of sustainable electronics and displays. This research additionally contributes to eco-friendly device fabrication, aligning with emerging technology demands.

Novel bis-chalcone-based carbazole derivative photoinitiators for visible light polymerization with good photobleaching and biocompatibility

Four novel bis-chalcone-based carbazole derivative photoinitiators (2E,5E)-2,5-bis((9-phenyl-9H-carbazol-3-yl)methylene)cyclopentan-1-one (KZA), 2,5-bis((E)-4-(9H-carbazol-9-yl)benzylidene)cyclopentan-1-one (KZB), (2E,5E)-2,5-bis((9-ethyl-9H-carbazol-3-yl)methylene)cyclopentan-1-one (KZC) and (2E,5E)-2,5-bis((5-(9-ethyl-9H-carbazol-3-yl)thiophen-2-yl)methylene)cyclopentan-1-one (KZD) were successfully designed and synthesized. Their maximum absorption wavelengths were 440 nm, 405 nm, 446 nm and 500 nm, respectively, and they all had high molar extinction coefficients. Furthermore, three-component photoinitiation system including bis-chalcone/iodonium/amine could quickly and efficiently trigger the photopolymerization of acrylates. For example, PEGDA coatings could cure in 10 s and the CC bond conversion exceeded 90 % in the end. Then we also conducted photosteady-state degradation, fluorescence quenching, cyclic voltammetry and ESR experiments to investigate the mechanisms of photopolymerization. Besides, all four bis-chalcones showed good photobleaching and biocompatibility, which was suitable for use in 3D printing and deep coating curing. For instance, the LCD 3D printer successfully printed clear and photobleached objects with KZD/iodonium/amine system. All these excellent properties indicated the industrial application potential of the four carbazole derivatives in visible light curing.

Design and Application of a New Visible Light-Curing 3D Printing Platform

In order to solve the safety problems that exist in traditional charging technology, a new visible light-curing 3D printing platform and energetic slurry formula were designed. Within them, the formula of light-curing slurry is 60.46% EA/PUA (prepolymer), 37.21% PETA/HDDA/BA (active diluent monomer), 0.47% CQ (visible light initiator), 0.93% DMT (curing accelerator), and 0.93% additive. The curing time of visible light-curing paste is 7.5 s, the viscosity is 22 6 mPa·s, the curing hardness is 2 H, the gel rate is 96.67%, the shrinkage rate is 98.35%, and the curing depth is 9.41 mm. The optimal formulation of energetic slurry is 20% visible light-curing slurry, 57.72% AP, 15.28% Al and 7% RDX. The 3D printing energetic powder column has a smooth surface, uniform filler distribution, a flat surface, no protrusions or other defects, and good matching. The average burning rate is 1.165 mm·s−1, the combustion is stable, and the maximum burning light intensity is 2.053 cd.

Preparation and properties of visible light-cured strippable film for radioactive decontamination

In this research, solutions of styrene-butadiene-styrene block copolymer (SBS) in 2-ethoxyethyl methacrylate (EOEMA) were used to prepare strippable films via rapid visible-light curing, where the mixture of camphorquinone (CQ), diphenylsilane (DPS) and diphenyliodonium hexafluorophosphate (Iod) was employed as the photoinitiating system, LED@405 nm, sunlight or household LED panel light as the light source and no any solvent was involved. The double bond conversion for pure EOEMA under LED@405 nm was firstly monitored by real-time FTIR and it reached 72% within 300 s. The rapid-curing of SBS/EOEMA solutions were systematically investigated and it was found that the solution with 16 wt% SBS became completely dried at the presence of 2.16 mol% crosslinker and 3.6 wt% photoinitiating system after 240 s irradiation under LED@405 nm. The tensile strength, elongation at break and glass transition temperature of the resultant strippable film were determined to be about 4.4 ± 0.5 MPa, 130 ± 11.2% and 6.9 °C, respectively, by mechanical properties testing and DSC measurements. Also, the decontamination efficiencies (DE) of household LED panel light/sunlight cured-strippable film for uranium nitrate on stainless steel, glass, and ceramic surface were evaluated to be higher than 90%. These results indicate that this rapid-curing strippable films would be a good candidate material for large-scale radioactive decontamination.

Dimensional Stability of Light-Activated Urethane Dimethacrylate Denture Base Resins.

An accurate and dimensionally stable trial denture base is required for a successful denture. The aim of this in vitro study was to assess the dimensional stability of a light-activated urethane dimethacrylate (UDMA) visible light cure (VLC) denture base with three fabrication techniques and different curing cycles. Forty-five VLC denture base samples were divided evenly into three groups. Group A used a conventional fabrication technique with a curing cycle of 5 min. Group B used a modified fabrication technique with two 4-min curing cycles. Group C used a multi-step fabrication technique with three curing cycles (4 min, plus 4 min, plus 2 min). The samples were sectioned and observed under a stereomicroscope to measure the discrepancy between the sample and the master cast. The mean dimensional discrepancy (mm) at the molar region at mid-palate, after 24 h in Group A, B and C was 0.790 mm, 0.741 mm and 0.379 mm, respectively; at the right ridge crest, it was 0.567, 0.408 and 0.185, while at the left ridge crest it was 0.475, 0.331 and 0.125, respectively. Statistical analysis showed significantly different dimensional discrepancies among the groups at all three sites; right ridge crest (F = 93.54, p < 0.001), left ridge crest (F = 105.96, p < 0.001) and mid-palate (F = 125.53, p < 0.001). Within the limitations of this laboratory study, it can be concluded that the denture base using a multi-step fabrication technique with three curing cycles provides better adaptation than the conventional technique. The significance of the study is that clinicians should consider performing denture base fabrication using a multi-step technique to enhance adaptation and hence the stability of the dentures for patients.

Visible-Light-Curable Acrylic Resins toward UV-Light-Blocking Adhesives for Foldable Displays.

Current technological advances in the organic light-emitting diode panel design of foldable smartphones demand advanced adhesives with UV-blocking abilities, beyond their conventional roles of bonding objects and relieving deformation stress. However, optically clear adhesives (OCAs) with UV-blocking ability cannot be prepared using conventional UV-curing methods relying on a photoinitiator. Herein, a new acrylic resin that can be efficiently cured using visible light without oxygen removal is presented, which may be used to develop UV-blocking OCAs for use in current flexible displays. A novel photocatalyst and a specific combination of additives facilitate sufficiently rapid curing under visible light in the presence of UV-absorbers. Only a very small amount of the highly active photocatalyst is required to prepare UV-blocking OCA films with very high transparency in the visible region. Using this system, a UV-blocking OCA that nearly meets the specifications of an OCA used in commercialized foldable smartphones is realized. This technology can also be utilized in other applications that require highly efficient visible light curing, such as optically clear resins, dental resins, and 3D/4D-printable materials.

Bio-based Non-estrogenic Dimethacrylate Dental Composite from Cloves

Bisphenol A (BPA), as an endocrine disruptor derived from petroleum-based chemicals, has been prohibited by several regulatory agencies for use in a wide variety of consumer products. For the sake of reducing human exposure to BPA derivatives and in the context of sustainability, it is far-reaching to develop high-performance and low-toxic materials from bountiful biomass sources. The objective of this work was to synthesize 2 bio-based dimethacrylate monomers, 2,2′-dially-4,4′-dimethoxy-5,5′-diglycerolate acrylatediphenylmethane (BEF-EA) and 2,2′-dially-4,4′-dimethoxy-5,5′-diglycerolate methacrylatediphenylmethane (BEF-GMA), using eugenol as the raw material. The estrogenic activity of bio-based bisphenol 2,2′-dially-4,4′-dimethoxy-5,5′-dihydroxydiphenylmethane (BEF) was evaluated and compared with estrogen and commercial bisphenols. After photopolymerization of the di(meth)acrylates diluted with tri(ethyleneglycol) dimethacrylate (TEGDMA), bio-based visible light-curing materials were prepared, and their properties were systematically investigated. Notably, di(meth)acrylates BEF-GMA and BEF-EA derived from these nonestrogenic bio-based phenols exhibited improved biocompatibility and low viscosity (down to 220–280 Pa.s). BEF-GMA and BEF-EA resin matrix exhibits lower volumetric polymerization shrinkage (about 8.5%), high photopolymerization reactivity (>50% in 60 s), and mechanical properties (fracture energy >5.5 N mm; flexural strength of 87–91 MPa, etc), which were comparable or superior to commercial Bis-GMA. The respective bio-based composites still exhibit adequate properties. Therefore, introducing eugenol-based visible light-curable dimethacrylate monomers into dental materials is a potential strategy to establish green sustainability and biocompatible dental materials without BPA.

3D printing of cell-laden visible light curable glycol chitosan bioink for bone tissue engineering

Although chitosan is the second most abundant natural polymer on earth, with a wide range of biomaterial applications, its poor water solubility limits general printing process. We selected water-soluble methacrylated glycol chitosan (MeGC) as an alternative and prepared a MeGC-based MG-63 cell-laden bioink for 3D printing using a visible light curing system. Optimal cell-laden 3D printing of MeGC was completed at 3% using 12 μM of riboflavin as a photoinitiator under an irradiation for 70 s, a 26-gauge nozzle, a pneumatic pressure of 120 kPa, and a printing speed of 6 mm/s, as confirmed by printability, protein adsorption, cell viability, cell proliferation, and osteogenic capability. In addition, in vitro tests showed that MeGC-70 has a viability above 92%, a proliferation above 96%, and a hemolysis level below 2%. The results demonstrate the potential for MeGC-70 bioinks and 3D printed scaffolds to be used as patient-specific scaffolds for bone regeneration purposes.

Color changes in bulk-fill resin composites as a result of visible light-curing.

We evaluated twelve commercially available bulk-fill resin composites to determine the colorimetric changes that occurred as a result of the photo-polymerization reaction. Samples of the resin composites were prepared as disks 8 mm in diameter and 3 mm in thickness. A colorimeter was used to measure the color of samples on a black background before and after the polymerization processed had been initiated. As results, each of the photo-initiated bulk-fill resin composites tested except for Beautifil Bulk A showed a significant color difference more than that of conventional resin composites. Bulk Base Flow became darker, whereas Beautifil Bulk Flow became clearly lighter. All resin composites except for Bulk Base Flow became less yellow. Thus, Beautifil Bulk A exhibited the least color change among all the bulk-fill resin composites. However, this color change showed a marked change (NBS units) as observed by the human naked eye.

Controlled release of bioactive IL-2 from visible light photocured biodegradable elastomers for cancer immunotherapy applications

Biodegradable elastomeric controlled-release poly (decane-co-tricarballylate) (PDET) based matrices capable of maintaining the stability and bioactivity of Interleukin-2 (IL-2) through the utilization of visible-light curing and solvent-free loading of the cytokine are reported. The elastomeric devices were fabricated by intimately mixing lyophilized IL-2 powder with the acrylated prepolymer before photocrosslinking. The bioactivity of the released protein was assessed by its ability to stimulate the proliferation of the C57BL/6 mouse cytotoxic T lymphocyte, and its concentration was analysed using ELISA. The influence of changes in the polymer's physicochemical and mechanical properties on IL-2 release kinetics and bioactivity were also studied. The increase in the device's surface area and the incorporation of trehalose in the loaded lyophilized mix increased the IL-2 release rate with drug release proceeding via typical zero-order release kinetics. Moreover, the decrease in the degree of acrylation of the prepared devices increased the IL-2 release rate. The bioactivity assay showed that IL-2 retained over 94% of its initial bioactivity throughout 28 days of the release period. A new protein delivery vehicle composed of biodegradable PDET elastomers was demonstrated to be promising and effective for linear, constant, and sustained osmotic-driven release of bioactive IL-2 and other sensitive proteins and hormones.

Analysis of the structural reliability of dental filling under the effect of mouthwash G.U.M

The application of structural reliability analysis has become very important to ensure the strength of the studied structural design, as it presents results that help in giving evidence about the acceptance of that design according to the materials used under specific operating conditions. In this research an experiment was done, to find out the effect of G.U.M mouthwash on cured and re-cured Visible Light Cured (VLC) composite dental filling material, made according to agreed international standards, where many studies have documented that the surface of restorative materials placed on the tooth may also be affected by the chemical effect of different types of oral health care products, and the experiment was analyzed mathematically by applying structural reliability analysis to know the probability of structural failure when dental filling were exposed to the mouthwash G.U.M (Operational conditions), using analysis technique: the D-vine copula. The results were that the probability of structural failure gave an indication from which to infer the extent to which the experiment was accepted or rejected.

Preparation of a Photocured Biocompatible Hydrogel for Urethral Tissue Engineering

Although studies have showed that synthetic hydrogels have the potential to be used in tissue engineering, the rapid three-dimensional (3D) molding of hydrogels with good biocompatibility is still a major challenge for researchers. In this paper, 2-hydroxyethyl methacrylate is used as a hydrophilic monomer to be cured with visible light. Combined with natural gel network sodium alginate to form a composite hydrogel, the mechanical properties, equilibrium water content, and cytotoxicity of the composite hydrogel were studied, and 3D printing of the hydrogel was attempted. Then, the feasibility of using the hydrogel in urethral tissue engineering was evaluated. The results confirmed that through the composite photoinitiator system, the visible-light curing of the poly(2-hydroxyethyl methacrylate) (p-HEMA) hydrogel under 405 nm light was realized. After adding sodium alginate, the light curing efficiency, mechanical properties, biocompatibility, and other properties of the p-HEMA hydrogel were improved. The 3D printing of the p-HEMA hydrogel was realized by using a simple and portable direct ink writing 3D printing pen. The urethral experiment preliminarily confirmed that both hydrogels had positive effects on urethral defect repair.

Orthodontic Inclined Plane Application Using a Visible Light Cure Acrylic Material for Treatment of Linguoverted Mandibular Canine Teeth.

Malocclusion is a common problem in dogs. Linguoverted canine teeth (class I malocclusion) can cause palatal defects, oronasal fistulae, dental wear, and periodontal disease. Mandibular distoclusion (class II malocclusion), in which the mandibular arch occludes caudal to its normal position relative to the maxillary arch, can further contribute to lingual displacement of mandibular canine teeth. Traditionally, a flowable self-curing bisacrylic composite material has been used. The method described here uses a light cure acrylic denture base material utilizing multiple customized segments to construct the appliance to the desired shape and size necessary to achieve a functional incline plane.

Comparison of Tensile Bond Strength of Addition Silicone with Different Custom Tray Materials Using Different Retentive Methods

To compare the bond strength of addition silicone with different commonly used custom tray materials by means of different retentive methods (mechanical, chemical, and a combination of chemical and mechanical methods). Fabrications of 90 samples of different tray resin materials were done using an aluminum mold. They were divided into three main groups. Perforations, adhesive application, and a combination of both were done according to the grouping of samples. Polyvinyl siloxane material (medium body) was loaded over the samples. A universal testing machine with a crosshead speed of 5 mm/minute was used to determine the tensile bond strength of tray resin samples to medium body impression material. Based on these values, Student's-test, group statistics, and ANOVA test were used for statistical analysis. Visible light cure (VLC) resin showed the highest bond strength in chemicomechanical methods. This was followed by repair resin material. Tray resin material showed poor bond strength in all three retentive methods. The mechanical method was the least retentive in all three resin materials. VLC tray resin material can be used with chemical and mechanical retention in clinical situations to make predictably accurate elastomeric impressions. It was concluded that VLC tray resin shows good bond strength with polyvinyl siloxane impression material when both mechanical perforations and adhesive applications were done.

Evaluation of Light-curing Intensity Output and Students’ Knowledge among Dental Schools in Riyadh City

AIM: The aim of this study is interpreting the dental student’s knowledge of light-curing units from different universities and colleges in Riyadh city and to evaluate the intensity of the light output of light-emitting diode (LED)-curing devices in dental school clinics in Riyadh, Saudi Arabia.&#x0D; METHODS: One hundred eighty-two visible light-curing (VLC) units were randomly selected to have their light intensity output evaluated using Demetron® L.E.D. Radiometer – Kerr among dental school clinics in Riyadh city. The university hospitals we visited are King Khalid University Hospital, King Saud bin Abdulaziz University Hospital, Dar Al Uloom University Hospital, Alfarabi colleges’ dental clinics, and Princess Nourah Bint Abdulrahman University Hospital. To evaluate the knowledge of dental students about light intensity output, a questionnaire was given to the students.&#x0D; RESULTS: Out of the VLC units, 22 units (12%) measured inadequate intensity, 91 units (50%) measured marginal intensity, and 69 (37%) measured adequate intensity. The statistical significance was up to p &lt; 0.05, p = 0. Most students and interns did not think that light-curing unit intensity influenced the tooth pulp (55.8%) and also reported not know the minimum wavelength of light cure intensity (62%).&#x0D; CONCLUSION: A significant difference was found between the light cure intensities in universities. As for the students’ knowledge, the research revealed poor insight toward basic concepts of VLC units and its maintenance.

Visible Light-Curable Hydrogel Systems for Tissue Engineering and Drug Delivery.

Visible light-curable hydrogels have been investigated as tissue engineering scaffolds and drug delivery carriers due to their physicochemical and biological properties such as porosity, reservoirs for drugs/growth factors, and similarity to living tissue. The physical properties of hydrogels used in biomedical applications can be controlled by polymer concentration, cross-linking density, and light irradiation time. The aim of this review chapter is to outline the results of previous research on visible light-curable hydrogel systems. In the first section, we will introduce photo-initiators and mechanisms for visible light curing. In the next section, hydrogel applications as drug delivery carriers will be emphasized. Finally, cellular interactions and applications in tissue engineering will be discussed.

A Visible-Light Curing system of Diphenyliodonium Salt/BODIPY dyes/Bisphenol-A Epoxy Resin Under Halogen Lamp

Bisphenol-A epoxy resin have attracted much attention due to its good mechanical properties after curing. In this paper, a visible light curing system of bisphenol-A epoxy resin (E51) initiated by diphenyliodonium hexafluorophosphate (IOPF) and boron dipyrromethene-based (BODIPY) photosensitizers (BODIPY-1 and (BODIPY-2) under a halogen lamp (380-580 nm) was investigated. BODIPY dyes are well known long-wavelength photosensitizers, which is good for IOPF to expand absorption to visible light region. BODIPY-1 and BODIPY-2 are intermediates that reported in our previous work. When IOPF/BODIPY-1 is 2wt%/1wt%, E51 achieves epoxy conversion up to 60% in 0.18 mm thick molds. The Illumination of the halogen lamp is as low as 25.0 mW/cm2. Under same condition, the epoxy conversions of IOPF/BODIPY-2/E51 and IOPF/E51 are about 50% and 20%. When filters were used, IOPF/BODIPY/E51 was effectively cured under light irradiation of 460 nm and 540 nm, and only IOPF is not able to initiate E51 at these wavelengths.

How Visible Light Curing came into Dentistry

This paper details the history of the introduction of visible light curing into dentistry. This history provides an excellent example of ‘out of the box’ lateral thinking translation of innovative scientific technology into dentistry. Visible light curing is an important UK contribution to the recent history and current practice of dentistry, with several million visible light curing procedures being carried out globally on a daily basis. CPD/Clinical Relevance: Given the importance of visible light curing in dentistry, its history is of relevance.

One-year Clinical Performance of Flowable Bulk-fill Composite vs Conventional Compomer Restorations in Primary Molars.

To evaluate the clinical performance of a flowable bulk-fill composite vs a compomer in Class II cavities of primary molars. In a clinical study, 100 restorations were placed in two randomly assigned comparable Class II cavities in 32 children (aged 6.7 ± 1.2 years) with at least one bulk-fill composite (Venus Bulk Fill, Heraeus Kulzer) and one compomer (Dyract eXtra, Dentsply). After caries excavation, the adhesive Scotchbond Universal (3M Oral Care) was applied in self-etching mode. According to the manufacturer's instructions, Venus Bulk Fill was used for the entire Class II cavity of primary molars without a cover layer. After visible-light curing, both restorations were finished and polished. Both restorative materials were evaluated at baseline and after one year, including esthetic, functional, and biological parameters, using the FDI criteria. The Mann-Whitney U-test was used to determine the difference in the complete scores at baseline and after one year (p < 0.05). After one year, 99 restorations were reevaluated; one tooth had exfoliated physiologically. Concerning the esthetic parameters, Dyract eXtra showed slightly higher scores than Venus Bulk Fill. Both materials showed similar scores regarding functional and biological parameters. No severe postoperative sensitivities or side-effects were reported. There was no statistically significant difference between the performance of Venus Bulk Fill and Dyract eXtra for primary molars. The flowable bulk-fill composite Venus Bulk Fill can be considered as an alternative material for clinical use in primary teeth, but longer-term studies might still be needed.