Photoinitiator Concentration Research Articles

Influence of Photoinitiator Type and Curing Conditions on the Photocuring of Soft Polymer Network

The presented work deals with the photocuring of telechelic macromonomers derived from plant-based fatty acids to obtain a soft polymer network. Compositions were made by mixing macromonomers with three different concentrations (0.5, 1, and 2%) of two type I photoinitiators (Omnirad 2022 and Omnirad 819). All formulations were then subjected to photopolymerization studies by applying UV-assisted differential scanning calorimetry (UV-DSC) measurements at isothermal conditions at 37 °C with a narrow light source wavelength of 365 nm and irradiation (light intensity) of 20 and 50 mW/cm2. The percentage conversions, reaction orders, and constants were estimated based on autocatalytic Sestak–Berggen and Avrami models. In this work, for the first time, the influence of the curing conditions on the photopolymerization process, such as the photoinitiator concentration, light intensity, and oxygen presence/absence, were investigated for these novel systems. The results indicated significant differences between the two commercially available photoinitiators and their effects on photopolymerization kinetics. The maximum reaction rate was found to be considerably higher for Omnirad 2022 (which is a blend of three different compounds), especially at a lower light intensity, i.e., 20 mW/cm2, compared to Omnirad 819. However, it led to lower maximum conversion in an air atmosphere. The dynamic thermomechanical analysis (DMTA) revealed that light intensity, photoinitiator concentration, and oxygen presence had a strong effect on the storage modulus and loss modulus values. It was concluded that the chemical structure of the photoinitiator and curing conditions had a strong effect on the photopolymerization kinetics and properties of the prepared soft polymer networks.

Hydrogels based on poly(2-hydroxyethyl methacrylate) and nettle extract

New types of hydrogels based on linear poly(2-hydroxyethyl methacrylate) and poly(ethyleneglycol) diacrylate (PHEMA-PEGDA) and nettle extract were obtained. A solution of poly(2-hydroxyethylmethacrylate) in monomer (S-PHEMA) was obtained by bulk photopolymerization. Common nettle extractwas used as an ingredient that facilitates wound healing. The influence of the photoinitiator content(1-[4-(2-hydroxymethyl)-phenyl]-2-hydroxy-2-methylpropanone) on the photopolymerization kinetics,as well as the equilibrium swelling ratio (ESR), thermal and mechanical properties of the hydrogelswere examined. Complete HEMA conversion was achieved at the lowest photoinitiator dose. ReplacingHEMA with S-PHEMA causes an increase in ESR (24%) and Tg (50°C) and the amorphous phase content.At the same time, the tensile strength and Young’s modulus decrease. However, the addition of nettleextract (0.3 wt%) requires a significant increase in the amount of photoinitiator (up to 2.5 wt%). As theconcentration of the photoinitiator in the system increases, ESR and Tg decrease, but tensile strengthand Young’s modulus increase.

Customization of an Ultrafast Thiol-Norbornene Photo-Cross-Linkable Hyaluronic Acid-Gelatin Bioink for Extrusion-Based 3D Bioprinting.

Light-based three-dimensional (3D) bioprinting has been widely studied in tissue engineering. Despite the fact that free-radical chain polymerization-based bioinks like hyaluronic acid methacrylate (HAMA) and gelatin methacryloyl (GelMA) have been extensively explored in 3D bioprinting, the thiol-ene hydrogel system has attracted increasing attention for its ability in building hydrogel scaffolds in an oxygen-tolerant and cell-friendly way. Herein, we report a superfast curing thiol-ene bioink composed of norbornene-modified hyaluronic acid (NorHA) and thiolated gelatin (GelSH) for 3D bioprinting. A new facile approach was first introduced in the synthesis of NorHA, which circumvented the cumbersome steps involved in previous works. Additionally, after mixing NorHA with macro-cross-linker GelSH, the customized NorHA/GelSH bioinks exhibited fascinating superiorities over the gold standard GelMA bioinks, such as an ultrafast curing rate (1-5 s), much lowered photoinitiator concentration (0.03% w/v), and flexible physical performances. Moreover, the NorHA/GelSH hydrogel greatly avoided excess ROS generation, which is important for the survival of the encapsulated cells. Last, compared with the GelMA scaffold, the 3D-printed NorHA/GelSH scaffold not only exhibited excellent cell viability but also guaranteed cell proliferation, revealing its superior bioactivity. In conclusion, the NorHA/GelSH system is a promising candidate for 3D bioprinting and tissue engineering applications.

Boron-Methylated Dipyrromethene as a Green Light Activated Type I Photoinitiator for Rapid Radical Polymerizations.

Unimolecular (Type I) radical photoinitiators (PIs) have transformed the chemical manufacturing industry by enabling (stereo)lithography for microelectronics and emergent 3D printing technologies. However, the reliance on high energy UV-violet light (≤420 nm) restricts the end-use applications. Herein, boron-methylated dipyrromethene (methylated-BODIPY) is shown to act as a highly efficient Type I radical PI upon irradiation with low energy green light. Using a low intensity (∼4 mW/cm2) light emitting diode centered at 530 nm and a low PI concentration (0.3 mol %), acrylic-based resins were polymerized to maximum conversion in ∼10 s. Under equivalent conditions (wavelength, intensity, and PI concentration), state-of-the-art visible light PIs Ivocerin and Irgacure 784 show no appreciable polymerization. Spectroscopic characterization suggests that homolytic β-scission at the boron-carbon bond results in radical formation, which is further facilitated by accessing long-lived triplet excited states through installment of bromine. Alkylated-BODIPYs represent a new modular visible light PI platform with exciting potential to enable next generation manufacturing and biomedical applications where a spectrally discrete, low energy, and thus benign light source is required.

Occurrence, Fate, Human Exposure, and Toxicity of Commercial Photoinitiators.

Photoinitiators (PIs) are a family of anthropogenic chemicals used in polymerization systems that generate active substances to initiate polymerization reactions under certain radiations. Although polymerization is considered a green method, its wide application in various commercial products, such as UV-curable inks, paints, and varnishes, has led to ubiquitous environmental issues caused by PIs. In this study, we present an overview of the current knowledge on the environmental occurrence, human exposure, and toxicity of PIs and provide suggestions for future research based on numerous available studies. The residual concentrations of PIs in commercial products, such as food packaging materials, are at microgram per gram levels. The migration of PIs from food packaging materials to foodstuffs has been confirmed by more than 100 reports of food contamination caused by PIs. Furthermore, more than 20 PIs have been detected in water, sediment, sewage sludge, and indoor dust collected from Asia, the United States, and Europe. Human internal exposure was also confirmed by the detection of PIs in serum. In addition, PIs were present in human breast milk, indicating that breastfeeding is an exposure pathway for infants. Among the most available studies, benzophenone is the dominant congener detected in the environment and humans. Toxicity studies of PIs reveal multiple toxic end points, such as carcinogenicity and endocrine-disrupting effects. Future investigations should focus on synergistic/antagonistic toxicity effects caused by PIs coexposure and metabolism/transformation pathways of newly identified PIs. Furthermore, future research should aim to develop "greener" PIs with high efficiency, low migration, and low toxicity.

Clinical Applicability of Visible Light-Mediated Cross-linking for Structural Soft Tissue Reconstruction.

Visible light-mediated cross-linking has utility for enhancing the structural capacity and shape fidelity of laboratory-based polymers. With increased light penetration and cross-linking speed, there is opportunity to extend future applications into clinical spheres. This study evaluated the utility of a ruthenium/sodium persulfate photocross-linking system for increasing structural control in heterogeneous living tissues as an example, focusing on unmodified patient-derived lipoaspirate for soft tissue reconstruction. Freshly-isolated tissue is photocross-linked, then the molar abundance of dityrosine bonds is measured using liquid chromatography tandem mass spectrometry and the resulting structural integrity assessed. The cell function and tissue survival of photocross-linked grafts is evaluated ex vivo and in vivo, with tissue integration and vascularization assessed using histology and microcomputed tomography. The photocross-linking strategy is tailorable, allowing progressive increases in the structural fidelity of lipoaspirate, as measured by a stepwise reduction in fiber diameter, increased graft porosity and reduced variation in graft resorption. There is an increase in dityrosine bond formation with increasing photoinitiator concentration, and tissue homeostasis is achieved ex vivo, with vascular cell infiltration and vessel formation in vivo. These data demonstrate the capability and applicability of photocrosslinking strategies for improving structural control in clinically-relevant settings, potentially achieving more desirable patient outcomes using minimal manipulation in surgical procedures.

Digital light processing of poly(ε-caprolactone)-based resins into porous shape memory scaffolds

Digital light processing (DLP) is a promising 3D printing technique with excellent resolution, enabling the fabrication of complex structures to serve the tissue engineering (TE) field. However, its full potential in this regard remains insufficiently explored by the scarcity of ‘smart’ photoresponsive biodegradable and biocompatible polymers. By combining biodegradable shape memory polymers with DLP printing, complex thermo-responsive structures can be developed, allowing minimally invasive TE. The current study focuses on the development of biodegradable and biocompatible photosensitive resins consisting of poly(ε-caprolactone) acrylate-endcapped urethane-based polymers (AUPs) to create thermo-responsive porous scaffolds with a shape shift close to body temperature. The molar mass of the AUP along with the photo-initiator concentration are varied, enabling the investigation of the influence of these parameters on the resin properties and the DLP processability. The newly developed resins exhibit excellent properties in terms of viscosity, photocrosslinking kinetics, polymer fraction, and swelling capacity. Compression tests demonstrated that the porous scaffolds exhibit a compressive modulus around 75 kPa, making them suitable to serve a variety of soft TE applications. Additionally, the 3D printed scaffolds are biocompatible as indicated by a cell viability and metabolic activity exceeding 85%. Finally, the scaffolds’ shape memory properties are evidenced both qualitatively as quantitatively via Dynamic Mechanical Analysis (DMA) experiments. These experiments indicate a shape shift around body temperature and shape fixity and shape recovery values superior to 94%, rendering them excellent candidates for, among others, minimally invasive TE strategies.

Effect of Photoinitiator Concentration and Film Thickness on the Properties of UV-Curable Self-Matting Coating for Wood-Based Panels

Matte coatings have found wide-ranging applications across diverse industries. In this study, self-matting films with surface wrinkles were produced by exposing UV-curable polyurethane acrylate (UV-WPUA) resin to 172 nm Xe2* excimer and medium-pressure mercury lamps. The gloss values, micromorphologies, water contact angles (WCAs), roughness values, and friction behaviors of UV-WPUA films with different photoinitiator (PI) concentrations and thickness were investigated for the first time. The results indicate that the gloss values of the films at the same thickness enhance with the increase of PI concentration, while the amplitude of wrinkles, roughness, and WCAs decrease; however, the friction coefficient shows insignificant variations. While the PI concentration is unchanged, an increase in film thickness results in a decrease in gloss value and an increase in roughness and friction coefficient. Nevertheless, the WCA is relatively constant. The PI concentration of 0.5 wt% (lowest gloss value of cured film) was utilized to prepare the UV-WPUA wood coating. The cured coating film exhibited low gloss (4.9 GU at 60° and 5.2 GU at 85°) and outstanding mechanical properties, including 3H pencil hardness, grade 0 adhesion, excellent wear resistance, and tensile property. These findings can be utilized to guide the development of self-matting wood coatings and the production of wood-based panels used in industrial finishing.

Research on mechanical properties of ink‐jet, UV‐thermal dual‐cured 3D printing materials and a comparison of the properties of ink‐jet, LCD and UV‐thermal dual‐cured 3D printing materials

AbstractIn this work, ink‐jet 3D printing materials were developed and investigated. Additionally, a UV‐thermal dual‐curable prepolymer was synthesized and introduced into liquid crystal display (LCD) 3D printing material. Subsequently, a UV‐thermal dual‐cured 3D printing material was developed as well. The different light stabilizers, photoinitiator content and different thermal annealing time were studied to reveal these effects on the mechanical properties of the ink‐jet 3D printed samples. FTIR was used to analyze the deblocking effect of blocked isocyanate in the synthesized resin. The mechanical properties of the UV‐thermal dual‐cured materials at different thermal annealing time and different ratios of UV content to thermal content were discussed. Scanning electron microscopy (SEM) was utilized to reveal the microscopic morphology of UV‐thermal dual‐cured material before and after thermal annealing. Finally, the dissipated energies of different 3D printing materials were revealed to indicate the difference in internal structure between ink‐jet, LCD and UV‐thermal dual‐cured 3D printing materials.

Initiation and recovery of damage initiated by UV irradiation in luminescent solar concentrators deposited in ambient conditions

Photopolymerization of thin, dye-doped acrylate-based layers under ambient conditions often requires high concentrations of photoinitiators. The radical storm created during polymerization has been shown to cause damage to the embedded fluorescent dyes; some of this damage is repaired upon exposure to air, but a fraction of the damaged molecules do not repair. This work presents a more detailed optical study of the environmental effects, nature of the initiator, and resulting fluorescence of the dye molecules caused by photopolymerization, all factors necessary to understand and control to allow ambient inkjet printing of these luminescent species.

Highly Efficient Photoninitiators Based on 4H‐Pyranylidene Derivatives for Two‐Photon Laser Printing

AbstractA series of four donor–acceptor–donor derivatives bearing 4H‐pyranylidene and 4‐methylcyclohexan‐1‐one units as donor and acceptor groups respectively is designed, synthesized, and photophysically characterized. Both experimental and theoretical studies reveal good two‐photon absorption (2PA) properties for these systems. Decoration of the exocyclic position of the 4H‐pyranylidene moiety with a thiophene ring results in high 2PA cross‐section values (σ2PA) ≈700 nm, and remarkably, in the region between 900 and 1000 nm. Furthermore, all chromophores are evaluated as photoinitiators (PIs) for two‐photon‐laser printing at 780 nm, showing superior performance compared to the commonly used commercially available PI, phenylbis(2,4,6‐trimethylbenzoyl)phosphine oxide. Among the studied PIs, the ones equipped with a thiophene unit at the exocyclic position of the 4H‐pyranylidene moiety exhibit the highest efficiency, enabling fast printing using low laser powers with even lower concentrations of PI. Overall, this study shows the great potential of this new class of PIs for application in the field of 3D nanoprinting.

Effect of solvent type on porous structure of emulsion templated poly(glycerol sebacate)-methacrylate

Polymerised emulsion templating is a common method for the fabrication of biomaterials with interconnected porous structures. Here, we present the fabrication of poly(glycerol sebacate)-methacrylate (PGSM) porous structures via emulsion templating. The mixing speed and photoinitiator concentration for emulsions were optimised (350 rpm, 16 wt%, respectively). The resulting emulsion separation before/after mixing and pore morphology of PGSM emulsions was then assessed by altering the emulsion formulation using four different types of diluting solvent (chloroform, dichloromethane, dichloroethane, toluene) for the first time. By altering the type and volume of solvents, the overall pore morphology of polymerised emulsions was tuned.

Gelatin acrylamide with improved UV crosslinking and mechanical properties for 3D biofabrication

Photocrosslinkable gelatin has attracted increasing interest in the field of biofabrication, with the most studied and widely used photocrosslinkable gelatin being gelatin methacrylate (GelMa). However, the 3D fabrication of GelMa has presented several limitations and challenges, primarily due to its slow crosslinking speed. It is generally known that acryl-based functional groups have faster reaction kinetics than methacryl-base groups. However, gelatin acrylamide (GelAc) has not been widely investigated, largely due to its increased complexity of synthesis relative to GelMA. In this study, we developed a novel synthesis method for GelAc. By varying the reaction ratio of reagents, GelAc with a degree of substitution from 20% to 95% was produced. The UV crosslinking properties of GelAc was studied, demonstrating significantly faster crosslinking kinetics than GelMa, especially at lower concentrations and low photoinitiator concentrations. The swelling ratio and mechanical properties of the crosslinked GelAc hydrogel were also characterized, and biocompatibility experiments conducted via both surface seeding and hydrogel encapsulation of cells, with good cell viability observed. The application of GelAc for 3D biofabrication was demonstrated by 3D printing. GelAc can be a useful material for the fabrication of 3D conduits for tissue engineering applications.

Retracted: A Photoclick Thiol‐Ene Collagen‐Based Hydrogel Platform for Skeletal Muscle Tissue Engineering

AbstractUV‐cured collagen‐based hydrogels hold promise in skeletal muscle regeneration due to their soft elastic properties and porous architecture. However, the complex triple helix conformation of collagen and environmental conditions, i.e., molecular oxygen, pose risks to reaction controllability, wet‐state integrity, and reproducibility. To address this challenge, a photoclick hydrogel platform is presented through an oxygen‐insensitive thiol‐ene reaction between 2‐iminothiolane (2IT)‐functionalized type I collagen and multiarm, nonhomopolymerizable norbornene‐terminated polyethylene glycol (PEG). UV‐induced network formation is demonstrated by oscillatory time sweeps on the reacting thiol‐ene mixture, so that significantly increased storage moduli are measured and adjusted depending on the photoinitiator concentration. Variations in PEG functionality (4‐arm and 8‐arm) and PEG content generate hydrogels with skeletal muscle native stiffness (Ec = 1.3 ± 0.2‒11.5 ± 0.9 kPa), diffusion‐controlled swelling behavior and erosion‐driven degradability. In vitro, no cytotoxic effect is detected on C2C12 murine myoblasts, while myogenic differentiation is successfully accomplished on hydrogel‐seeded cells in then low serum culture medium. In vivo, 7 d subcutaneous implantation of selected thiol‐ene hydrogel in rats reveal higher cell infiltration, blood vessel formation, and denser tissue interface compared to a clinical gold standard collagen matrix (Mucograft, a trademark of Geistlich Biomaterials). These results, therefore, support the applicability and further development of this hydrogel platform for skeletal muscle regeneration.

Microstructural study of different thick dimethacrylate-based samples using different amounts of photoinitiator

The influence of the thickness and concentration of photoinitiator on the free volume properties of a dental material based on dimethacrylate was investigated in situ by positron annihilation lifetime spectroscopy.

Preparation and performance of reversible thermochromic phase change microcapsules based on negative photochromic spiropyran

Thermochromic phase change materials have been widely studied for their importance in energy-efficient buildings, thermal control clothing, and low-temperature energy storage. Herein, we successfully designed and synthesized a spiropyran compound with negative photochromic properties in a solid matrix, 3-(3′,3′-dimethyl-6,8-dinitrospiro[chromene-2,2′-indolin]−1′-yl) propyl methacrylate (SPMA), as a thermochromic dye. The synthesized spiropyran was copolymerized with methyl methacrylate (MMA) using photoinitiation, and then n-octadecane was encapsulated by the copolymer to prepare reversible thermochromic phase change microcapsules (TC-microPCMs) through the solvent evaporation technique. The encapsulation efficiency of n-octadecane by copolymers prepared with different photoinitiator concentrations was also investigated. According to the results of SEM, particle size analysis (DLS), and DSC, the copolymer prepared at 3% concentration possessed the best encapsulation effect on n-octadecane, and the melting enthalpy of the microcapsules reached 168.7 J/g and the encapsulation ratio was 89.5%, which was not significantly different from that of microcapsules without the addition of thermochromic dyes. This di-functionalization process effectively avoids the "impurity effect" of dye addition. In addition, the homogeneous spherical structure and stable chemical composition of the microcapsules are the key factors to achieve a fully reversible thermochromic behavior. What's more, the functionalized film based on TC-microPCMs, TC-microPCMs@PVA, was used to explore the potential for applications in thermal storage and temperature sensing. The results demonstrated that the composite film has excellent reversible thermochromic performance, high latent heat storage performance, and good cycling durability, which make the bifunctional microcapsules highly promising candidates for thermal sensors, solar energy storage, and smart textiles.

UV curing behavior of a liquid polyborosilazane and stereolithography to SiBCN ceramic components

The ultraviolet (UV) curing behavior and kinetics both in air and in nitrogen atmosphere of a liquid polyborosilazane were investigated by differential scanning photo calorimeter (DPC) measurement and real-time FTIR techniques. The results showed that the bifunctional acrylic reactive diluent tripropylene glycol diacrylate (TPGDA) content, photo-initiator concentration, and temperature had their optimal values to get the maximum ultimate reaction rate and conversion percentage. It's noteworthy that the addition of TPGDA will greatly enhance polymerization rate and conversion percentage within a very short time-frame. While the rate in air is higher than in nitrogen atmosphere, probably owing to the effect of oxidation curing, which is coordinated with the calculation results of activation energy.Based on the above experiment, we also report on the direct fabrication of SiBCN ceramic components from preceramic polyborosilazanes by stereolithography and subsequent pyrolysis at 900 ○C for 4 h. The TGA curve shows the ceramic yield is 51.1% after pyrolysis at 1200 ○C. A linear shrinkage of 27%, associated with the polymer-to-ceramic conversion, was observable and the density of pyrolyzed SiBCN is about 2 g cm−3 with slight residual porosity. The indentation hardness is 9.83 GPa and the modulus is 77.1 GPa after heat-treatment at 1400 ○C for 3 h.

Abstract 15136: Matrix Mechanics Regulate Engineered Myocardial Microtissue Organization and Contractility

Introduction: The mechanical function of the myocardium is dictated by cardiomyocytes (CMs) and the surrounding fibrous extracellular matrix (ECM). Due to limitations in existing approaches for engineering myocardial tissue, how CMs sense and respond to mechanical microenvironmental changes remains understudied. Here, we established a method for creating arrays of cardiac microtissues with highly tunable mechanical features by integrating synthetic, fibrous matrices and iPSC-CMs. Through real-time contractility readouts enabled, we explored how biomechanical cues influence engineered cardiac tissue assembly and function. Methods: Arrayed cardiac microtissues were generated by selectively photo-crosslinking electrospun dextran vinyl sulfone fiber matrices onto pairs of microfabricated PDMS cantilevers. Subsequently, iPSC-CMs were patterned onto matrices using a microfabricated seeding mask. Matrix and cantilever stiffnesses were tuned by adjusting photoinitiator concentrations and cantilever geometry, respectively. Results: In tissues contracting against soft cantilevers (0.41 N/m), tissue contractile stress decreased with increasing matrix stiffness (E = 0.68 to 17.3 kPa). We also observed an increase in contractile stress on soft and aligned matrices, compared to non-aligned matrices. However, tissues contracting against stiffer cantilevers (1.2 N/m) exerted similar contractile stresses independent of matrix alignment. This may be explained by the enhanced alignment of myofibrils in non-aligned matrices contracting against stiffer posts. The size of vinculin-rich cell-ECM adhesion decreased on stiff matrices. Vinculin also localized to z-discs forming organized costameres on soft matrices. Tissue response to mavacamten suggests that β-cardiac myosins are required for costamere formation and myofibril maturation. Conclusions: We developed a new microfabrication strategy to create tunable cardiac microtissues and examined how biomechanical cues affect tissue assembly and function. We found that matrix stiffness, matrix alignment, and tissue constraint distinctly affect iPSC-CM function and structure, potentially due to differential influences on costamere formation and myofibrillar assembly.

Multimodal 3D printing of biodegradable shape memory elastomer resins for patient specific soft tissue repair

Acrylated poly(glycerol-dodecanedioate) (APGD), a biodegradable shape memory polymer, is a photocurable resin developed for 3D printing of biomaterial implants that is especially suited for minimally invasive procedures. 3D printing has numerous advantages over traditional manufacturing modalities including production of complex porous geometries, improved feature resolution, and lower production costs on a per part basis for low volume clinical production. Material extrusion (ME) and vat photopolymerization (VP) printing are two prevalent 3D printing modalities used in tissue engineering. Compared to VP printing, ME printing offers a higher degree of customization by allowing co- or multi-material prints, along with biologic cell printing. VP printing offers higher throughput and capability for printing more complex geometries, versus ME printing, with shorter manufacturing times, making it a more commercially viable choice for clinically translatable materials. Motivated by each printing modalities’ unique advantages, APGD resins for ME and VP printing were developed and assessed for crosslinker and photoinitiator (PI) concentration effect on resin time to gel point, storage modulus and viscosity. Increasing crosslinker concentration decreased the gel time and increased the storage modulus of cured resin. Significant differences in printed sample geometry along with material and mechanical properties resulted from using the two printing modalities. ME samples had larger void volume (6.1 ± 1.2% vs. 0.2 ± 0.4%), lower gel content (55.3 ± 2.6% vs. 68.7 ± 1.9%), and less shape fixity (77.4 ± 4.7 vs. 97.3 ± 3.7%) compared to VP samples. VP printing generated complicated 3D anatomic shapes of higher quality than ME printing. In conclusion, this manuscript provides the first report of APGD 3D printing that can be applied to shape memory, resorbable medical devices.

Analyte Enrichment via Ion Concentration Polarization with Hydrogel Plugs Polymerized in PDMS Microchannels by a Facile and Comprehensive Method for Improved Polymerization.

Hydrogels are incorporated into microfluidic devices to provide enhanced functionality by enabling processes such as enzyme immobilization, sample enrichment, and ionic current rectification. However, in the microfluidic devices with the commonly used material poly(dimethylsiloxane) (PDMS), hydrogels are very difficult to polymerize in situ in an ambient atmosphere because of the high oxygen concentration in PDMS. Even with very high (1.8%) photoinitiator concentrations, the polymerized hydrogel does not completely fill the microchannel. Here, we report a facile and broadly applicable protocol that utilizes microchannel pretreatment with 20% benzophenone in acetone to provide a hydrogel plug that completely fills the microchannel cross section by consuming the oxygen in the PDMS substrate near the microchannel wall. Both negatively charged and neutral hydrogels are polymerized from monomer solutions that utilize the photoinitiator/solvent combinations of VA-086 in water and benzophenone or IRG in DMSO. The photoinitiators were tested at different concentrations and in devices with different levels of oxidation. The hydrogel morphology is characterized using phase contrast microscopy and is related to the hydrogel's performance for concentration enrichment and ionic current rectification. A novel method is employed to confine the precursor solution in desired locations so that a photomask is not required for the spatial control of the plug location. Among six hydrogel formulations, at 100 V, the best current rectification factor obtained is ∼600 and the best analyte enrichment achieved is ∼120-fold in 5 min. This method provides a rapid and simple approach to increase the capabilities of PDMS microfluidic devices through improved polymerization of nanoporous hydrogels.