Visible Light Cross-Linked Methacrylated Silk Fibroin Enables Enhanced Osteogenic Response in Bioprinted Dual-Layer Guided Bone Regeneration Membrane

Precise design and fabrication of photo-cross-linked hydrogels with controlled network architecture and tailored mechanical properties are essential for advancing complex tissue engineering applications. In this study, a visible-light-activated type II photo-cross-linking system was developed using eosin Y/triethanolamine/N-vinylpyrrolidone (VE) to fabricate methacrylated silk fibroin (SFM) hydrogels through oxygen-mediated controlled photolysis. In comparison to conventional UV-initiated lithium phenyl-2,4,6-trimethylbenzoylphosphinate cross-linking, which rapidly yields mechanically stiffer networks with pronounced β-structures, the VE system (0.02 mM eosin Y, 100 mM triethanolamine, and 50 mM N-vinylpyrrolidone) enabled the fabrication of gradually formed compliant homogeneous networks. This tunability allowed using VE cross-linked SFM in light-assisted extrusion bioprinting to fabricate a dual-layer guided bone regeneration membrane incorporating a collagen I-rich ECM layer. Under calcium-supplemented conditions, the dual-layer membrane exhibited robust osteogenic potential, evidenced by significantly elevated ALP activity and distinctive nodular mineralization patterns compared with single-layer controls. Gene expression profiles revealed coordinated regulation of early (RUNX2, COL1A1), mid-to-late (SPP1, SPARC), and late-stage (BGLAP) markers, indicating successful progression through the osteogenic program. The heterogeneous design achieved a desired balance between its barrier function and tissue integration with an interconnected porous architecture that limits soft tissue downgrowth while supporting matrix organization conducive to bone regeneration. These findings establish critical structure-function relationships in photo-cross-linked biomaterials and highlight how mechanistic understanding of cross-linking chemistry can guide the rational design of functional scaffolds for biomedical applications.

3D Printed Ion-Responsive Personalized Transdermal Patch

Microneedle patches are easy-to-use medical devices for transdermal administration. However, the insufficient insertion of microneedles due to the gap between planar patches and contoured skin affects drug delivery. Herein, we formulate a prepolymer for high-fidelity three-dimensional (3D) printed personalized transdermal patches. With the excellent photoinitiation ability of 2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine (Tz), a high-fidelity and precise microneedle patch is successfully fabricated. Upon irradiation of the white illuminator, the doped gold nanoparticles (AuNPs) in the patch release heat and promisingly induce sweat production. With the introduction of Na+, the dominant component of sweat, the curvature of the produced transdermal patch is observed due to the ion-induced network rearrangement. The alkanethiol-stabilized AuNP with an end group of a carboxyl group causes controlled drug release behavior. Furthermore, the irradiation-induced photothermal heating of AuNP can facilitate the sustainability of drug release thanks to the substantially increased particle size of AuNP. These findings demonstrate that the developed prepolymer is a promising candidate for the production of transdermal patches fitting the curvature of the body surface.

Optimization of Gelatin Methacryloyl Hydrogel Properties through an Artificial Neural Network Model

Gelatin methacryloyl (GelMA) hydrogels are promising materials for tissue engineering applications due to their biocompatibility and tunable properties. However, the time-consuming process of preparing GelMA hydrogels with desirable properties for specific biomedical applications limits their clinical use. Visible-light-induced cross-linking is a well-known method for the preparation of GelMA hydrogels; however, a comprehensive investigation on the influence of critical parameters such as Eosin Y (EY), triethanolamine (TEA), and N-vinyl-2-pyrrolidone (NVP) concentrations on the stiffness and gelation time has yet to be performed. In this study, we systematically investigated the effect of these critical parameters on the stiffness and gelation time of GelMA hydrogels. We developed an artificial neural network (ANN) model with three input variables, EY, TEA, and NVP concentrations, and two output variables, Young's modulus and gelation time, derived from our experimental design. Through the alteration of individual chemical concentrations, [EY] between 0.005 and 0.5 mM and [TEA] and [NVP] between 10 and 1000 mM, we studied the impact of these alterations on the real-time values of stiffness and gelation time. Furthermore, we demonstrated the validity of the ANN model in predicting the properties of GelMA hydrogels. We also studied cell survival to establish nontoxic concentration ranges for each component, enabling safer use of GelMA hydrogels in relevant biomedical applications. Our results showed that the ANN model can accurately predict the properties of GelMA hydrogels, allowing for the synthesis of hydrogels with desirable stiffness for various biomedical applications. In conclusion, our study provides a comprehensive library that characterizes the stiffness and gelation time and demonstrates the potential of the ANN model to predict these properties of GelMA hydrogels depending on the critical parameters. The ANN models developed here can facilitate the optimization of GelMA hydrogels with the most efficient mechanical properties that resemble a native extracellular matrix and better address the need in the in vivo microenvironment. The approach of this study is to bring research about the synthesis of GelMA hydrogels to a new level where the synthesis of these hydrogels can be standardized with minimum cost and effort.

Switchable DNA Photocatalysts for Radical Polymerization Controlled by Chemical Stimuli

Polymerization catalysts that activate in response to specific chemical triggers offer spatial and temporal control over polymer synthesis, facilitating the development of responsive materials and custom polymer coatings. However, existing catalysts switch their activity through mechanisms that are not generalizable to chemically diverse stimuli. To approach the level of control exhibited in biological polymer synthesis, switchable polymerization catalysts need to be configurable for activation in response to diverse chemical stimuli. Here, we combine synthetic photocatalysts with conformation-switching DNA aptamers to create polymerization catalysts that respond to diverse chemical stimuli. We use the secondary structure of DNA to bring a photocatalyst and quencher dye into proximity, turning off photocatalysis. The DNA structure can be precisely designed to change conformation in response to a molecular trigger, moving the photocatalyst far from the quencher and activating photocatalysis. We show these photocatalysts can initiate free-radical polymerization to form bulk hydrogels in response to complementary DNA, a metal ion (Zn2+), or small molecules (glucose and hydrocortisone). We demonstrate the biocompatibility of these switchable photocatalysts by triggering their activation on the surface of yeast cells. Finally, we perform reversible-deactivation radical polymerization through photoinduced electron/energy transfer reversible addition-fragmentation chain-transfer in a dual-stimulus manner, in which catalytic activity is regulated reversibly by photoirradiation and the conformational state of the DNA catalyst. These results demonstrate that DNA conformational changes triggered by chemically diverse stimuli can regulate the activity of radical polymerization photocatalysts. This platform offers new capabilities in spatially and temporally controlled polymer synthesis, with potential applications in diagnostics, sensing, and environmentally responsive materials.

Dual Photoredox Catalysis Strategy for Enhanced Photopolymerization-Based Colorimetric Biodetection

Catalytic redox reactions have been employed to enhance colorimetric biodetection signals in point-of-care diagnostic tests, while their time-sensitive visual readouts may increase the risk of false results. To address this issue, we developed a dual photocatalyst signal amplification strategy that can be controlled by a fixed light dose, achieving time-independent colorimetric biodetection in paper-based tests. In this method, target-associated methylene blue (MB⁺) photocatalytically amplifies the concentration of eosin Y by oxidizing deactivated eosin Y (EYH^3-) under red light, followed by photopolymerization with eosin Y autocatalysis under green light to generate visible hydrogels. Using the insights from mechanistic studies on MB⁺-sensitized photo-oxidation of EYH^3-, we improved the photocatalytic efficiency of MB⁺ by suppressing its degradation. Lastly, we characterized 100- to 500-fold enhancement in sensitivity obtained from MB⁺-specific eosin Y amplification, highlighting the advantages of using dual photocatalyst signal amplification.

Systematic optimization of visible light-induced crosslinking conditions of gelatin methacryloyl (GelMA)

Gelatin methacryloyl (GelMA) is one of the most widely used photo-crosslinkable biopolymers in tissue engineering. In in presence of an appropriate photoinitiator, the light activation triggers the crosslinking process, which provides shape fidelity and stability at physiological temperature. Although ultraviolet (UV) has been extensively explored for photo-crosslinking, its application has been linked to numerous biosafety concerns, originated from UV phototoxicity. Eosin Y, in combination with TEOA and VC, is a biosafe photoinitiation system that can be activated via visible light instead of UV and bypasses those biosafety concerns; however, the crosslinking system needs fine-tuning and optimization. In order to systematically optimize the crosslinking conditions, we herein independently varied the concentrations of Eosin Y [(EY)], triethanolamine (TEOA), vinyl caprolactam (VC), GelMA precursor, and crosslinking times and assessed the effect of those parameters on the properties the hydrogel. Our data showed that except EY, which exhibited an optimal concentration (~ 0.05 mM), increasing [TEOA], [VA], [GelMA], or crosslinking time improved mechanical (tensile strength/modulus and compressive modulus), adhesion (lap shear strength), swelling, biodegradation properties of the hydrogel. However, increasing the concentrations of crosslinking reagents ([TEOA], [VA], [GelMA]) reduced cell viability in 3-dimensional (3D) cell culture. This study enabled us to optimize the crosslinking conditions to improve the properties of the GelMA hydrogel and to generate a library of hydrogels with defined properties essential for different biomedical applications.

Photo-cross-linked Gelatin Glycidyl Methacrylate/N-Vinylpyrrolidone Copolymeric Hydrogel with Tunable Mechanical Properties for Ocular Tissue Engineering Applications

Corneal transplantation is currently the primary treatment for corneal blindness. However, severe global scarcity of donor corneas is driving the scientific community to find novel solutions. One potential solution is to replace the damaged tissue with a biocompatible artificial cornea. Here, gelatin glycidyl methacrylate (GM) and N-vinylpyrrolidone (VP) were cocrosslinked to afford a hybrid bicomponent copolymeric hydrogel with excellent mechanical, structural, and biological properties. Our studies showed that the GM/VP ratio can be adjusted to generate a construct with high tensile modulus and strength of 1.6 and 1.0 MPa, respectively, compared to 14 and 7.5 MPa for human cornea. The construct can tolerate up to 22.4 kPa pressure before retention sutures can tear through it. Due to the presence of a synthetic component, it has a significantly higher stability against collagenase induced degradation, yet it is biocompatible and promotes cellular adhesion, proliferation, and migration under in vitro settings.

Effect of TEOA on the Process of Photopolymerization at 532 nm and Properties of Nanogels

Nanogel is an important kind of biomaterials applied for wound dressings, drug delivery, medical diagnostics and biosensors. The properties of nanogels closely depend on the density of the crosslinking network. In this study, the role of triethanolamine (TEOA) in the effect on the crosslinking degree of nanogels based on poly(ethylene glycol) diacrylate (PEGDA) was investigated and illustrated. The effect of TEOA on the process of photopolymerization at 532 nm and properties of the nanogels was systematically investigated by using UV-vis spectroscopy, FT-IR spectroscopy, ¹ H NMR, DLS, SEM, AFM and DSC. In brief, the double bond conversion of photopolymerization and the crosslinking degree of nanogels can be effectively regulated by TEOA.

Exponential Amplification Using Photoredox Autocatalysis

Exponential molecular amplification such as the polymerase chain reaction is a powerful tool that allows ultrasensitive biodetection. Here, we report a new exponential amplification strategy based on photoredox autocatalysis, where eosin Y, a photocatalyst, amplifies itself by activating a nonfluorescent eosin Y derivative (EYH^3-) under green light. The deactivated photocatalyst is stable and rapidly activated under low-intensity light, making the eosin Y amplification suitable for resource-limited settings. Through steady-state kinetic studies and reaction modeling, we found that EYH^3- is either oxidized to eosin Y via one-electron oxidation by triplet eosin Y and subsequent 1e^-/H⁺ transfer, or activated by singlet oxygen with the risk of degradation. By reducing the rate of the EYH^3- degradation, we successfully improved EYH^3--to-eosin Y recovery, achieving efficient autocatalytic eosin Y amplification. Additionally, to demonstrate its flexibility in output signals, we coupled the eosin Y amplification with photoinduced chromogenic polymerization, enabling sensitive visual detection of analytes. Finally, we applied the exponential amplification methods in developing bioassays for detection of biomarkers including SARS-CoV-2 nucleocapsid protein, an antigen used in the diagnosis of COVID-19.

Metal-Free Organocatalyzed Atom Transfer Radical Polymerization: Synthesis, Applications, and Future Perspectives

Reversible deactivation radical polymerization (RDRP) is a class of powerful techniques capable of synthesizing polymers with a well-defined structure, properties, and functionalities. Among the available RDRPs, ATRP is the most investigated. However, the necessity of a metal catalyst represents a drawback and limits its use for some applications. O-ATRP emerged as an alternative to traditional ATRP that uses organic compounds that catalyze polymerization under light irradiation instead of metal. The friendly nature and the robustness of O-ATRP allow its use in the synthesis of tailorable advanced materials with unique properties. In this review, the fundamental aspects of the reductive and oxidative quenching mechanism of O-ATRP are provided, as well as insights into each component and its role in the reaction. Besides, the breakthrough recent studies that applied O-ATRP for the synthesis of functional materials are presented, which illustrate the significant potential and impact of this technique across diverse fields.

Visible-Light-Curable Solvent-Free Acrylic Pressure-Sensitive Adhesives via Photoredox-Mediated Radical Polymerization

Owing to their excellent properties, such as transparency, resistance to oxidation, and high adhesivity, acrylic pressure-sensitive adhesives (PSAs) are widely used. Recently, solvent-free acrylic PSAs, which are typically prepared via photopolymerization, have attracted increasing attention because of the current strict environmental regulations. UV light is commonly used as an excitation source for photopolymerization, whereas visible light, which is safer for humans, is rarely utilized. In this study, we prepared solvent-free acrylic PSAs via visible light-driven photoredox-mediated radical polymerization. Three α-haloesters were used as additives to overcome critical shortcomings, such as the previously reported low film curing rate and poor transparency observed during additive-free photocatalytic polymerization. The film curing rate was greatly increased in the presence of α-haloesters, which lowered the photocatalyst loadings and, hence, improved the film transparency. These results confirmed that our method could be widely used to prepare general-purpose solvent-free PSAs-in particular, optically clear adhesives for electronics.

Experimental validation of eosin-mediated photo-redox polymerization mechanism and implications for signal amplification applications

When eosin-mediated, photo-redox polymerization is used to amplify signals in biosensing, oxygen has dual, opposing roles.

Radical polymerization reactions for amplified biodetection signals

This review summarizes various radical polymerization chemistries for amplifying biodetection signals and compares them from the practical point of view.

Liposome-Enhanced Polymerization-Based Signal Amplification for Highly Sensitive Naked-Eye Biodetection in Paper-Based Sensors

Polymerization-based signal amplification (PBA) is a material-based approach to improving the sensitivity of paper-based diagnostic tests. Eosin Y is used as an assay label to photo-initiate free-radical polymerization to produce colored hydrogels in the presence of target analytes captured by bioactive paper. PBA achieves high-contrast and time-independent signals, but its nanomolar detection limit makes it impractical for early diagnosis of many diseases. In this work, we demonstrated efficient localization of large quantities of eosin Y per captured target analyte by incorporating eosin Y-loaded liposomes into PBA. This new "materials approach" allowed 30-fold signal enhancement compared to conventional PBA. To further improve the detection limit of liposome-enhanced PBA, we used a continuous flow-through assay format with 100 μL of analyte solution, achieving sub-nanomolar detection limits with high-contrast signals that were easily discernible to the unaided eye.

Physico-mechanical Characterization of Liquid versus Solid Applications of Visible Light Cross-Linked Tissue Sealants

The limitations of commercially available tissue sealants have resulted in the need for a new tissue adhesives with adequate adhesion, improved mechanical properties, and innocuous degradation products. To address current limitations, a visible light cross-linking method for the preparation of hydrogel tissue sealants, based on natural polymers (chitosan or alginate), is presented. Water-soluble chitosan was generated via modification with vinyl groups. To form hydrogels, alginate and chitosan were cross-linked by green light illumination, with or without the use of a bifunctional cross-linker. Evaluation of the mechanical properties through rheological characterization demonstrated an increased viscosity of polymer blends, and differences in shear moduli despite similar gelation points upon photo-cross-linking. A comparative study on the burst pressure properties of liquid versus solid material applications was performed to determine if the tissue sealants can perform under physiological lung pressures and beyond using different application methods. Higher burst pressure values were obtained for the sealants applied as a liquid compared to the solid application. The hydrogel tissue sealants revealed no cytotoxic effects toward primary human mesenchymal stem cells. This is the first report of a direct comparison between hydrogel tissue sealants of the same formulation applied in liquid versus solid form.