Photosensitive Resin Research Articles

Exploring three-dimensional photoinhibition to enhance vat photopolymerization: A preliminary study

Vat photopolymerization (VPP) based additive manufacturing (AM) technologies print 3D components by using light to selectively cure photosensitive resins. In VPP-based AM, one outstanding challenge remains in controlling the over-curing, which is mainly caused by the diffusive and/or excessive photo-induced species such as free radicals and can severely affect the geometric properties of as-printed parts. Common practices rely on formulating proper resins or optimizing exposure parameters to address the vertical over-curing but often ignore the lateral over-curing. In this work, we develop a new VPP process of photoinhibition aided photopolymer AM (PinPAM) to comprehensively address over-curing issues in both vertical and lateral dimensions for enhancing the properties of as-printed geometry. The PinPAM method incorporates an adaptive photoinhibition zone, generated both surrounding and underneath the curing zone on a layer basis. This differs from current literature approaches that utilize photoinhibition to create a higher deadzone to increase print speed or constrain vertical profiles for achieving volumetric VPP AM. We present several preliminary experimental study cases involving pillar array sample printing. By comparing part dimensions and shapes resulting from traditional VPP and PinPAM, our experiments prove the concept of PinPAM and demonstrate its potential to address over-curing in VPP. Furthermore, we present an initial case study on optimizing the PinPAM process for printing cylinder samples with targeted dimensions, illustrating the planning and implementation of PinPAM. A discussion on future research directions to establish PinPAM is included. The developed PinPAM opens up a new avenue for improving VPP printed parts’ geometrical properties and facilitating its adoption in precision fabrications that demand dimensional accuracy and resolution.

Simulation of UV curing of photosensitive resins with phase change materials

Based on the mechanism of the resin polymerization reaction and free radical diffusion under UV irradiation, here, a mathematical model of the curing process was established for the mixture of photosensitive resin (PAA) and polyethylene glycol (PEG, as the phase change material), and the factor influencing the mechanical performance of the cured samples was analyzed. The yield stress (σs) of the pure resin sample can reach 50 MPa when the monolayer curing depth is 5 mm. σs decreases with the increase in the PEG content and monolayer curing depth. With increasing the monolayer exposure time, the yield stress increases and then decreases, and there is an optimum value. The material has the maximum stress at the monolayer exposure time of 13.5 s when the resin content is 50 %.

Piezoelectric properties and biocompatibility of barium titanate prepared via digital light processing

Barium titanate (BT) is widely studied in bone repair engineering due to its high dielectric constant, excellent ferroelectric properties, and non-toxic nature. However, one of the research focuses on the preparation of high-precision BT ceramics and enhances their limited mineralization bioactivity. BT is difficult to use for high-precision ceramic molding using Digital Light Processing (DLP) due to its high refractive index and strong ultraviolet absorption. In this manuscript, BT was doped with calcium silicate (CS) which has a refractive index close to photosensitive resin. The printing parameters of the composite ceramic scaffolds were determined to obtain a balance between printing efficiency and accuracy. Experimental results have demonstrated that within a CS doping ratio of up to 20 wt%, the scaffolds simultaneously meet the piezoelectric coefficient and mechanical properties of natural bone. Furthermore, mineralization and cell experiments have shown that the composite scaffold exhibits improved degradation rate, cell activity, and osteoinductivity. Subsequently, bone scaffolds with a doping ratio of 20 wt% were selected, which meet the requirements of natural bone and exhibit significantly enhanced biological activity. Research findings revealed that ceramic scaffolds after piezoelectric stimulation are more conducive to cell proliferation and growth compared to before stimulation.

SonoPrint: Acoustically Assisted Volumetric 3D Printing for Composites.

Advances in additive manufacturing in composites have transformed aerospace, medical devices, tissue engineering, and electronics. A key aspect of enhancing properties of 3D-printed objects involves fine-tuning the material by embedding and orienting reinforcement within the structure. Existing methods for orienting these reinforcements are limited by pattern types, alignment, and particle characteristics. Acoustics offers a versatile method to control the particles independent of their size, geometry, and charge, enabling intricate pattern formations. However, integrating acoustics into 3D printing has been challenging due to the scattering of the acoustic field between polymerized layers and unpolymerized resin, resulting in unwanted patterns. To address this challenge, SonoPrint, an innovative acoustically assisted volumetric 3D printer is developed that enables simultaneous reinforcement patterning and printing of the entire structure. SonoPrint generates mechanically tunable composite geometries by embedding reinforcement particles, such as microscopic glass, metal, and polystyrene, within the fabricated structure. This printer employs a standing wave field to create targeted particle motifs-including parallel lines, radial lines, circles, rhombuses, hexagons, and polygons-directly in the photosensitive resin, completing the print in just a few minutes. SonoPrint enhances structural properties and promises to advance volumetric printing, unlocking applications in tissue engineering, biohybrid robots, and composite fabrication.

Effect of multi-walled carbon nanotubes on the properties of DLP 3D printing photosensitive resin

To improve the mechanical properties of photosensitive resin, a technique for manufacturing multi-walled carbon nanotubes (MWCNTs) composite resin using DLP 3D printing was proposed. MWCNTs were used as reinforcing materials for photosensitive resins. The molding accuracy and comprehensive mechanical properties of the resin were significantly improved, and the content of MWCNTs was 0.06 wt%, which obtained the best properties. Tests with different thickness layers further confirmed the advantages of MWCNTs as reinforcing materials. The oil–water separation membrane was prepared by DLP 3D printing with the optimum content.

Preparation of short carbon fiber reinforced photosensitive resin and composite material properties study

AbstractLight‐curing rapid prototyping (SLA) has become an emerging technology in the manufacturing industry because of its high precision, rapid prototyping, and the ability to mold complex parts. To enhance the mechanical properties and thermal stability of its raw material photosensitive resin (PR), carbon fiber (CF) was surface modified by chemical oxidation and grafting of amino silane (KH550) to obtain KH550‐modified carbon fiber (ACF). Then, ACF was composited with photosensitive resin to obtain modified carbon fiber/photosensitive resin (ACF/PR) composites. The viscosities of ACF/PR composites, including the viscosity, curing shrinkage, mechanical properties, and thermal stability of the ACF/PR composites, were characterized. The results showed that KH550 was successfully grafted onto CF. When the addition of ACF in the composites was 0.6%, the tensile strength, elongation at break, and impact strength of ACF/PR reached 39.48 MPa, 20.32%, and 13.62 kJ/m2, which were 120%, 27.15%, and 154% higher than that of the pure resin; the thermal decomposition temperatures and the maximum thermal decomposition temperatures at 50% mass loss of ACF/PR increased to 457.66°C and 442.44°C at 50% mass loss, which is 3.95% and 3.63% higher than that of the pure resin. Currently, the composites have excellent strength, toughness, and thermal stability. This paper gives a cost‐efficient method for improving the functioning of PR.Highlights Mixed acid oxidation and amino silane modification of CFs. Preparation of modified CF/photosensitive resin composites. Composites with excellent mechanical properties and thermal stability.

Photopolymerization initiated by p-diethylene glycol monomethyl ether cinnamyl formamide-based disulfide under 455 nm LED with minimized volume shrinkage

This study introduces a novel p-diethylene glycol monomethyl ether cinnamyl formamide-based disulfide monomer, N,N′-(disulfanediylbis(2,1-phenylene)) bis(4-(4-(2-(2-methoxyethoxy)ethoxy) phenyl)-2-oxobut-3-enamide) (Mp-BSCF), designed to reduce the volume shrinkage of photosensitive resins and initiate monomer polymerization under 455 nm LED light irradiation. The photochemical properties and photoinitiation efficiency of Mp-BSCF are systematically investigated using UV–vis absorption spectroscopy, electron paramagnetic resonance (EPR) and real-time infrared spectroscopy. Although its weak absorption around 455 nm, Mp-BSCF can generate arylthiyl radicals under 455 nm LED irradiation, and then effectively initiate the polymerization of triethylene glycol dimethacrylate (TEGDMA)/A glycerolate dimethacrylate (Bis-GMA) system. Increasing Mp-BSCF addition enhances the final double bond conversion and maximum polymerization rate of the TEGDMA/Bis-GMA system, reaching up to 82.0 % and 2.02 % s−1, respectively. Notably, Mp-BSCF significantly reduces the volume shrinkage of the photopolymerization system, with the addition of 10 % Mp-BSCF resulting in a 50 % reduction compared to the control system. This reduction is attributed to the dynamic reversible nature of the SS bond “breaking-recovery” and the intermolecular hydrogen bond interaction. Additionally, Mp-BSCF improves the thermal stability, friction resistance, and hardness of the TEGDMA/Bis-GMA photopolymerization system.

Hydrophilic coating of membrane by UV-induced radical and cationic curing of photosensitive resins: Lower shrinkage, smoother surface and better anti-fouling performance

Hydrophilic coating is frequently used to enhance the anti-fouling performance of membrane. However, traditional strategies often suffer from defects of cumbersome steps, high energy consumption, and unstable coating. Herein, radical and cationic photopolymerization are used for hydrophilic coating of membranes. Two photosensitive resins were first synthesized either by direct radical copolymerization of 3-ethyl-3-(methacryloyloxy) methyloxetane and 2-hydroxyethyl acrylate (Poly(HEA-EMO)) or through post-polymerization modification of poly(2-hydroxyethyl acrylate) with vinyl groups (Poly(HEA-MA)). Subsequently, hydrophilic coating was conducted on the membrane surface by UV-induced curing of different photosensitive resins, either through radical photopolymerization of vinyl-functional Poly(HEA-MA) or cationic photopolymerization of Poly(EMO-HEA) with pendent oxetane groups. The modified membranes showed enhanced hydrophilicity and underwater oleophobicity than the original membrane. Moreover, the coating (PAN / HEA(C5)) by cationic photopolymerization exhibited lower shrinkage, smoother surface, and more excellent antifouling performance than that by radical photopolymerization. After bovine albumin fouling-cleaning cycles, the flux recovery rate (FRR) of the original membrane was only 68.6 %, while the FRR of PAN / HEA(C5) was as high as 98.0 %. Furthermore, it showed superior long-term operational stability, proving the stability of the coating formed by cationic photopolymerization.

Synthesis and Characterization of Furan-Based Methacrylate Oligomers Containing the Imine Functional Group for Stereolithography.

Herein, a furan-based methacrylate oligomer (FBMO) featuring imine functional groups was synthesized for application in stereolithography. The preparation involved the imination reaction of 5-hydroxymethylfurfural (5-HMF) and amino ethanol. Utilizing 5-HMF as a sustainable building block for furan-based polymers, FBMO was formulated and subsequently integrated into photosensitive resin formulations along with methacrylate-containing diluents, such as PEGDMA and TEGDMA. The synthesized furan-based methacrylate oligomers underwent comprehensive characterization using FTIR, 1H NMR spectroscopy, and size exclusion chromatography. The impact of methacrylate-containing diluents on various properties of the formulated resins and the resulting 3D-printed specimens was systematically evaluated. This assessment included an analysis of rheological behavior, printing fidelity, mechanical properties, thermal stability, surface morphology, and cytotoxicity. By adjusting the ratios of FBMO to methacrylate-containing diluents within the range of 50:50 to 90:10, the viscosity of the resulting resins was controlled to fall within 0.04 to 0.28 Pa s at a shear rate of 10 s-1. The 3D-printed specimens exhibited precise conformity to the computer-aided design (CAD) model and demonstrated compressive moduli ranging from 0.53 ± 0.04 to 144 ± 6.70 MPa, dependent on the resin formulation and internal structure. Furthermore, cytotoxicity assessments revealed that the 3D-printed specimens were noncytotoxic to porcine chondrocytes. In conclusion, we introduce a new strategy to prepare the furan-based methacrylate oligomer (FBMO) and 3D-printed specimens with adjustable properties using stereolithography, which can be further utilized for appropriate applications.

UV-curing 3D printing of high-performance, recyclable, biobased photosensitive resin enabled by dual-crosslinking networks

UV-curing 3D printing technologies based on vat photopolymerization have gained increasing interest in rapidly manufacturing high-quality custom-designed objects. However, they are still challenged by the non-renewability of photosensitive resins in future large-scale applications. Herein, a high-performance, recyclable, biobased carboxyl-terminated unsaturated polyester is developed from itaconic acid and bio-diols, which involves the formation of dual-crosslinking networks, i.e., covalent crosslinking of unsaturated double bonds and non-covalent coordination interaction between terminal carboxyl and ZnCl2. Dual-crosslinking networks greatly increase tensile strength from 31 to 43 MPa by 40 %. More importantly, taking advantage of the dynamic reversibility of coordination and thermally-activated transesterification by ZnCl2, the universal problem, i.e. the anisotropic mechanical property in 3D printing caused by printing layers, can be effectively solved, attributed to reversible rearrangement and reassociation between printing layers. Moreover, after the 3D printing products are pulverized into microparticles, the powders can be thermally compressed into new materials with a 70 % recovery in tensile strength. In addition, these powders can also be used as reinforcing fillers to enhance the virgin resin, the optimum tensile strength and elastic modulus further increase to 52 MPa and 1019 MPa by 40 % with 1 wt% dosages. Therefore, this study is a pioneering pathway for the concurrent achievement of good mechanical properties (52 MPa) and high biomass content (96 wt%) for UV-curable 3D printing photosensitive resin.

Evaluation of Mechanical Properties of Self-cured, Heat-cured, and Photosensitive 3D Printing Resins After the Addition of Silica Nanoparticles

This study evaluated investigate the addition of silica nanoparticles in autopolymerizable resin and into liquid resin for 3D printing and compare them with CAD-CAM blocks and thermopolymerizable resin, regarding flexural strength and surface roughness. Eight groups (n=12) were created according to the types of materials: autopolymerizable resin (G1-G4), photosensitive resin for 3D printing (G5-G6), PMMA block (G7) and thermopolymerizable resin (G8). Functionalized silica nanoparticles (0.5-1.5 wt%) were added in groups G2-G4 and G6. Mechanical flexural strength, surface roughness and morphological analysis were carried out to evaluate the properties of the samples. One-way ANOVA, followed by Tukey's post-hoc test, was used to evaluate the data. The average surface roughness was higher in group G7 and lower in the G8 group, with a statistical difference (p < 0.001). The G8 and G1-G4 showed no significant difference in surface roughness. The G5 and G6 presented surface roughness higher than that recommended by Borchers and Bollen (Ra=0.2 µm). The incorporation of nanoparticles into self-polymerizing acrylic resins negatively affected the mechanical properties of the material, reducing flexural strength. The G5 and G6 demonstrated the lowest flexural strength (p<0.001), presenting values lower than those recommended by ISO (σ >60 MPa) regardless of the incorporation or not of silica nanoparticles. The G7 presented the highest flexural strength value followed by the G8. Within the limits of this study, it may be concluded that the addition of silica nanoparticles did not improve the flexural strength the G6 and also affected negatively the mechanical properties of self-polymerizing acrylic resins.

Fabrication of biphasic scaffold composed of bioceramic‐loaded and water‐based photosensitive resins through vat photopolymerization

Fabrication of biphasic scaffold composed of bioceramic‐loaded and water‐based photosensitive resins through vat photopolymerization

Preparation, characterization, and mechanical properties of dental photosensitive resin composites: effect of amalgamation with boron nitride nanosheets

Preparation, characterization, and mechanical properties of dental photosensitive resin composites: effect of amalgamation with boron nitride nanosheets

Co-pyrolytic drivers and volatiles of 3D printing waste and textile dyeing sludge and their multi-objective optimization

Textile dyeing sludge (TDS) disposal poses a critical environmental challenge due to its complex and hazardous nature. This study explored the co-pyrolysis of 3D printing waste (3DPW), comprising photosensitive resin waste (PRW) and polycaprolactone waste (PCLW), with TDS as a potential co-circularity strategy. Drivers, interactions, and resultant products of the co-pyrolysis were characterized through thermogravimetric experiments. Kinetically, the co-pyrolysis process followed a second-order reaction (F2) model. The co-pyrolysis with PRW enhanced the releases of ketones, aldehydes, and esters, with 2-pentene (26.70%) and 2-ethylacrolein (34.67%) as the primary products. Conversely, the co-pyrolysis with PCLW reduced CO emission and generated tetrahydrofuran (27.28%) and cyclopentanone (44.58%). The co-pyrolysis with 3DPW offers a promising approach for mitigating environmental pollution by transforming hazardous wastes into value-added valuable precursors for fuels and organic chemicals.

Simultaneous Manufacture of Magnetic and Locally Conductive Millimeter Scale Bifunctional Devices via Single‐Material Projection‐Based Stereolithography

AbstractThe development of projection‐based stereolithography 3D printing techniques has provided a powerful approach to fabricate millimeter scale functional devices with complex structures. However, the current processes face challenges in frequent switching between multiple materials or processes, resulting in low efficiency and accuracy during the fabrication of bifunctional devices. To address these challenges, chemical deposition is utilized to modify graphene nanoplatelets (GNs) with Fe3O4 magnetic particles and incorporate them into the photosensitive resin, resulting in the development of a novel bifunctional printing material with magnetic and locally conductive properties. Furthermore, the localized conductivity of devices is controlled by an electric‐field‐assisted alignment process of the magnetic GNs (mGNs) during the printing process. Herein, this single‐material projection‐based stereolithography allows for the simultaneous fabrication of magnetic and locally conductive millimeter scale bifunctional devices without switching between multiple materials or processes. A magnetically driven circuit switch and signal coding gear are fabricated as demonstrations. This work significantly improves the efficiency and accuracy of fabricating millimeter scale bifunctional devices, thereby facilitating their application in the fabrication of miniaturized and integrated devices.

A study of mechanical properties of photosensitive resins used in vat photopolymerization process

In recent years, the rapid advancement of Additive Manufacturing (AM) technology has led to resource-efficient processes and reduced gaps between design and product/prototypes. Particularly, sectors like medicine and dentistry stand to gain from these advancements if materials with suitable mechanical characteristics for clinical use are available. One such evolving AM process is VAT photopolymerization through LCD 3D Printer technology, characterized by the curing of photosensitive polymeric resins. This study aims to assess the impact of the angle of layer photopolymerization of UV resin in three positions (horizontal, vertical, and inclined at 45°) using a cost-effective LCD 3D Printer. Additionally, specimens, distributed across five positions on the printing platform, underwent testing with three types of UV light-curing resin. Mechanical properties, including tensile stress, elasticity modulus, and hardness, were evaluated and analyzed statistically. Results indicate that both the chosen manufacturing platform position and the inclined layer angle significantly influence the final characteristics of the workpiece.

Advances in 3D printing for polymer composites: A review

AbstractThe potential of three‐dimensional (3D) printing technology in the fabrication of advanced polymer composites is becoming increasingly evident. This review discusses the latest research developments and applications of 3D printing in polymer composites. First, it focuses on the optimization of 3D printing technology, that is, by upgrading the equipment or components or adjusting the printing parameters, to make them more adaptable to the processing characteristics of polymer composites and to improve the comprehensive performance of the products. Second, it focuses on the 3D printable novel consumables for polymer composites, which mainly include the new printing filaments, printing inks, photosensitive resins, and printing powders, introducing the unique properties of the new consumables and different ways to apply them to 3D printing. Finally, the applications of 3D printing technology in the preparation of functional polymer composites (such as thermal conductivity, electromagnetic interference shielding, biomedicine, self‐healing, and environmental responsiveness) are explored, with a focus on the distribution of the functional fillers and the influence of the topological shapes on the properties and functional characteristics of the 3D printed products. The aim of this review is to deepen the understanding of the convergence between 3D printing technology and polymer composites and to anticipate future trends and applications.image

Synthesis and characterization of polyurethane acrylate with bio-oil modification for photo-curing 3D printed flexible structures

The use of renewable resources for additive manufacturing has grown significantly as a means of advancing the ongoing shift to a green economy. This study uses bio-oil generated from the rapid pyrolysis of forest waste as a bio-based chemical to partially replace polyethylene glycol to synthesize a new type of bio-oil modified polyurethane acrylate, used in photo-curing 3D printing technology. The study explores the impact of the ratio of bio-oil to polyethylene glycol on the properties of polyurethane resin. As the amount of bio-oil added increases, the molecular weight of polyurethane acrylate decreases. Modified photosensitive resin showcases better suitability for photo-curing 3D printing, with lower viscosity and volume shrinkage, and its printed samples exhibit enhanced mechanical strength and improved thermal stability. In particular, when the bio-oil substitution rate is 20 wt%, the tensile strength of the 3D printed sample increases by 70 %, and the double bond conversion rate reaches 58.07 %. Meanwhile, the hollow and branching structures of 3D printing have the characteristics of high precision and flexibility. Introducing bio-oil into 3D printing technology not only expands the application fields of bio-oil but also provides new considerations for the transition of photosensitive resins from petroleum-based to renewable fields.

How to Improve the Curing Ability during the Vat Photopolymerization 3D Printing of Non-Oxide Ceramics: A Review.

Vat photopolymerization (VP), as an additive manufacturing process, has experienced significant growth due to its high manufacturing precision and excellent surface quality. This method enables the fabrication of intricate shapes and structures while mitigating the machining challenges associated with non-oxide ceramics, which are known for their high hardness and brittleness. Consequently, the VP process of non-oxide ceramics has emerged as a focal point in additive manufacturing research areas. However, the absorption, refraction, and reflection of ultraviolet light by non-oxide ceramic particles can impede light penetration, leading to reduced curing thickness and posing challenges to the VP process. To enhance the efficiency and success rate of this process, researchers have explored various aspects, including the parameters of VP equipment, the composition of non-oxide VP slurries, and the surface modification of non-oxide particles. Silicon carbide and silicon nitride are examples of non-oxide ceramic particles that have been successfully employed in VP process. Nonetheless, there remains a lack of systematic induction regarding the curing mechanisms and key influencing factors of the VP process in non-oxide ceramics. This review firstly describes the curing mechanism of the non-oxide ceramic VP process, which contains the chain initiation, chain polymerization, and chain termination processes of the photosensitive resin. After that, the impact of key factors on the curing process, such as the wavelength and power of incident light, particle size, volume fraction of ceramic particles, refractive indices of photosensitive resin and ceramic particles, incident light intensity, critical light intensity, and the reactivity of photosensitive resins, are systematically discussed. Finally, this review discusses future prospects and challenges in the non-oxide ceramic VP process. Its objective is to offer valuable insights and references for further research into non-oxide ceramic VP processes.

Low viscosity and highly flexible stereolithographic 3D printing resins for flexible sensors

Flexible sensors show the wide range of applications in electronic products. However, challenges remain in developing sensors with internal complex construction, excellent flexibility, elasticity and strength. In this paper, a prepolymer (PU-PDMS-OH-HEMA) contain polyurethane (PU) segments and polysiloxane (PDMS) segments was synthesized, and the photosensitive resins with low viscosity for 3D printing were prepared by mixing prepolymers with diluents and photoinitiators. The resultant cured photosensitive resins showed the improved mechanical properties. The PDMS-OH-30 sample exhibit the excellent mechanical properties, with tensile strength and elongation at break of 10.03 MPa and 1046.15 %, respectively, and the resin viscosity of 62 cP. Conductive ionic liquids were added to the above photosensitive resins to prepare flexible sensors, which show the electrical sensitivity and stability. The findings in the work propose a contribution to the development of highly flexible 3D printing resins for fabricating flexible sensors.