Simultaneous Photopolymerization Research Articles

Fabrication of a Novel Fluorescein Embedded Photocomposite Based on Interpenetrating Polymer Network (IPN) and Its Application in 4D Printing

AbstractWith the rapid development of the 3D printing technique, the concept of 4D has emerged, defining time as the fourth dimension. This concept allows for changes in the appearance, function, or other properties of 3D printed objects in response to certain controlled external stimuli over time. In this work, a new photocomposite containing fluorescein based is designed on an interpenetrating polymer network (IPN) system, this system can be generated by the simultaneous photopolymerization of acrylate and epoxide monomers under visible LED@405 nm irradiation. Unexpectedly, combining the reversible fluorometric turn‐on property of fluorescein and the deformation of the IPN in the presence of water, the 3D flower structure printed from this photocomposite would demonstrate a novel dual responsive behavior with both fluorescence and shape changes when it is exposed to water for a short time. This work would present a novel functional photocomposite material and also expand the application prospect of 4D printing.

Hybrid Free-Radical/Cationic Phase-Separated UV-Curable System: Impact of Photoinitiator Content and Monomer Fraction on Surface Morphologies and Gloss Appearance.

Simultaneous photopolymerization of radical and cationic systems is one strategy to generate polymer network architectures named interpenetrating polymer networks (IPNs). In these hybrid systems, phase separation and final polymer morphology are ultimately governed by thermodynamic incompatibility and polymerization kinetics. This behavior is quite complex, as numerous factors can affect polymerization kinetics including monomer/oligomer viscosity and structure, light intensity, photoinitiator content and absorbance, cross-linking, vitrification, etc. In this work, the impact of photoinitiator concentration and monomer fraction on surface morphologies in a hybrid radical/cationic phase-separated system was examined. Wrinkles formed on the surface of photopolymerized films depend on the polymerization rate and acrylate/epoxy ratio. This phenomenon is partially explained by the rapid polymerization rate associated with the development of an epoxy matrix and a smaller acrylate domain. The size and shape of the wrinkles can be controlled by varying formulation parameters (mainly, composition) and photoinitiator content. It was possible to create surface roughness and consequently decrease the gloss by controlling the polymerization kinetics and phase-separated morphology. This study demonstrates that the morphology, polymerization kinetics, and film properties (e.g., gloss, transparency) can be manipulated with the ratio of the acrylate/epoxy mixture and the photoinitiator content.

Mechanically tough dry‐free ionic hydrogel microfibers swollen in aqueous electrolyte prepared by microfluidic devices

AbstractSoft conducting materials in the shape of microfibers with various functional geometries are crucial for soft electronics. To develop highly stretchable conducting microfibers, a microfluidic method is used to prepare hydrogels in a double‐network structure. Based on the coagulation of chitosan in cold water and simultaneous photopolymerization and photocrosslinking of N‐isopropylacrylamide and N‐diethylacrylamide, long microfibers with controlled uniform diameters can be obtained at the junction of a coaxially aligned microchannel device. After further reinforcement of the chitosan chain and exchange of the medium of the hydrogel microfiber with an aqueous electrolyte of lithium bis(trifluoromethanesulfonyl)imide, the prepared ionic hydrogel exhibits high conductivity and stretchability and dry‐free properties. Owing to its mechanical robustness and ionic conductivity, we envision a highly stretchable soft electrode with the prepared ionic hydrogel microfiber that can be stretched up to 900%. This fiber has potential for applications in soft electronics and wearable devices.

In Situ Super-Resolution Imaging of Organoids and Extracellular Matrix Interactions via Phototransfer by Allyl Sulfide Exchange-Expansion Microscopy (PhASE-ExM).

3D organoid models have recently seen a boom in popularity, as they can better recapitulate the complexity of multicellular organs compared to other in vitro culture systems. However, organoids are difficult to image because of the limited penetration depth of high-resolution microscopes and depth-dependent light attenuation, which can limit the understanding of signal transduction pathways and characterization of intimate cell-extracellular matrix (ECM) interactions. To overcome these challenges, phototransfer by allyl sulfide exchange-expansion microscopy (PhASE-ExM) is developed, enabling optical clearance and super-resolution imaging of organoids and their ECM in 3D. PhASE-ExM uses hydrogels prepared via photoinitiated polymerization, which is advantageous as it decouples monomer diffusion into thick organoid cultures from the hydrogel fabrication. Apart from compatibility with organoids cultured in Matrigel, PhASE-ExM enables 3.25× expansion and super-resolution imaging of organoids cultured in synthetic poly(ethylene glycol) (PEG) hydrogels crosslinked via allyl-sulfide groups (PEG-AlS) through simultaneous photopolymerization and radical-mediated chain-transfer reactions that complete in <70 s. Further, PEG-AlS hydrogels can be in situ softened to promote organoid crypt formation, providing a super-resolution imaging platform both for pre- and post-differentiated organoids. Overall, PhASE-ExM is a useful tool to decipher organoid behavior by enabling sub-micrometer scale, 3D visualization of proteins and signal transduction pathways.

Two-photon lithography of subwavelength plasmonic microstructures in metal-polymer composite resin

Two-photon lithography has emerged as a tool of prime importance for additive manufacturing of 2D and 3D micro/nanostructures in metal-polymer composite resins with resolutions beyond the diffraction limit. Two-photon absorption dyes used are not only expensive, difficult to synthesize but also proprietary. To mitigate these challenges, we report formulation of two-photon polymerizable metal doped resin. Two-photon polymerization and reduction of metal-polymer composite resins is used for fabricating plasmonic micro/nanostructures. Simultaneous photopolymerization and photoreduction restricts the diffusion of the photoreduced metal-ions from the metal doped polymeric voxel, resulting in metal doped precisely fabricated micro/nanostructures. The impact of gold loading in the composite resin and fabrication process parameters on resolution of fabricated structureswere systematically studied. Minimum linewidth of ~350 nm using an 800 nm laser excitation was achieved for 10 wt% metal loaded polymer. A two-dimensional plasmonic mesh structure have been fabricated over millimetre scale, and structural colouration is demonstrated. This technique holds great potential to initiate new developments in additive manufacturing of metal-dielectric composite structures and expected to create a paradigm shift in areas such as metaphotonics and plasmonic metamaterials, among others.

Investigation on mechanical and conductive properties of polypyrrole/UV cured acrylate nanocomposite coatings

Conductive polypyrrole/UV cured acrylate nanocomposite coatings were prepared via a facile approach called simultaneous photopolymerization. In our previous study, the mechanisms of the polymerizations of pyrrole and acrylate in this process were discussed. In the current work, the mechanical and conductive properties were investigated by correlating them with the structural and compositional changes observed in the coating systems. Various percentages of pyrrole and acrylate monomers along with their corresponding UV activators, AgNO3 and DAROCUR 1173 respectively, were used to prepare the polypyrrole/UV cured acrylate composite coatings. The percentage of the mixture of pyrrole and AgNO3 in the formulation varied from 25 % to 60 %. Scanning electron microscopy (SEM) results indicated that the deposition of polypyrrole/Ag composite particles occur closer to the substrate. Based on the conductive atomic force microscopy (AFM) results, all the coatings in this study exhibited higher current densities on the bottom side of the coatings and the only coatings prepared with the formulations containing 45 % or higher of pyrrole and AgNO3 mixture exhibited conductivity on top side of the coatings. From the thermogravimetric analysis (TGA) results, it can be inferred that the increase in percentage of polypyrrole/Ag in the coating results in changes in the chemical structure of the UV cured acrylate binder. Dynamic mechanical analysis (DMA)results suggested that the incorporation of polypyrrole/Ag composite during the photopolymerization process leads to plasticization of polymer network causing an increase in dissipative-like behavior in the coatings.

Multifunctional alginate-based hydrogel with reversible crosslinking for controlled therapeutics delivery

Glycan-based alginate hydrogels have great potential in creating new vehicles with responsive behavior and tunable properties for biomedicine. However, precise control and tunability in properties present major barrier for clinical translation of these materials. Here, we report the synthesis of pH responsive anthracene modified glycan-based hydrogels for selective release of therapeutic molecules. Hydrogels were crosslinked through simultaneous photopolymerization of vinyl groups and photodimerization of anthracene. Incorporation of anthracene into these gels leads to reversible control on crosslinking and transition between gel/sol states through dimerization/dedimerization of anthracene groups. Chemotherapeutic drug doxorubicin-loaded hydrogels were then tested in a cancer mimetic microenvironment where 85% of the drug was released from anthracene-conjugated hydrogels at pH 2 for 6 days. Control on gelation with anthracene incorporation was observed through alterations in modulus, where storage modulus was increased two-fold with anthracene conjugation during photopolymerization and photodimerization. Furthermore, cell survival analysis revealed that anthracene conjugation could selectively compromise cancer cell viability without inducing significant toxicity on healthy fibroblasts. This study combines light-induced control of crosslink density due to anthracene and pH-triggered therapeutics delivery with alginate. The approach would be applicable for systems where multiple control is required with high precision.

Bioprinting Cartilage Tissue from Mesenchymal Stem Cells and PEG Hydrogel.

Bioprinting based on thermal inkjet printing is one of the most attractive enabling technologies for tissue engineering and regeneration. During the printing process, cells, scaffolds , and growth factors are rapidly deposited to the desired two-dimensional (2D) and three-dimensional (3D) locations. Ideally, the bioprinted tissues are able to mimic the native anatomic structures in order to restore the biological functions. In this study, a bioprinting platform for 3D cartilage tissue engineering was developed using a commercially available thermal inkjet printer with simultaneous photopolymerization . The engineered cartilage demonstrated native zonal organization, ideal extracellular matrix (ECM ) composition, and proper mechanical properties. Compared to the conventional tissue fabrication approach, which requires extended UV exposure, the viability of the printed cells with simultaneous photopolymerization was significantly higher. Printed neocartilage demonstrated excellent glycosaminoglycan (GAG) and collagen type II production, which was consistent with gene expression profile. Therefore, this platform is ideal for anatomic tissue engineering with accurate cell distribution and arrangement.

Conductive polypyrrole and acrylate nanocomposite coatings: Mechanistic study on simultaneous photopolymerization

Abstract Facile preparation of conductive polypyrrole coatings with optimized binding and conductive properties for various electronic applications such as printing circuit boards and conductive inks using simultaneous photopolymerization method was investigated in this article. This method involves independent polymerization processes of pyrrole and acrylate monomers occurring simultaneously to produce conductive coating. While AgNO 3 was used as oxidizing agent for photopolymerization of pyrrole, Irgacure 907 was used as the photoinitiator for the acrylate monomer, 1,6-hexanediol diacrylate. Based on Real-time Fourier Transform Infrared (RT-FTIR) spectroscopy characterization on polymerization rates and mechanisms, it was deduced that the selection of proper initial concentrations of monomers and their corresponding photoinitiators was essential to obtain optimized conductive and binding properties of the final coating. In addition, microscopic techniques such as TEM and SEM revealed that the size, morphology and dispersion of polypyrrole were also affected by the initial concentrations. Finally, conductivity measurements obtained via four-point probe method and conductive AFM were correlated with the spectroscopic and microscopic characterization to determine the optimal conditions for the preparation of conductive polypyrrole/acrylate coatings via this method.

Fabrication of Conductive 3D Gold-Containing Microstructures via Direct Laser Writing.

3D conductive microstructures containing gold are fabricated by simultaneous photopolymerization and photoreduction via direct laser writing. The photoresist employed consists of water-soluble polymers and a gold precursor. The fabricated microstructures show good conductivity and are successfully employed for 3D connections between gold pads.

Synthesis and characterization of simultaneous IPNs. Evidence of the IPN structure by selective chemical attack on the cross-linker

Interpenetrating polymer network hydrogels based on fluoro-, siloxane-acrylates and N-vinylpyrrolidone were synthesized using simultaneous photopolymerization technique in presence of poly(ethylene glycol diacrylate) as cross-linker. These hydrogels were characterized by Fourier-transform infrared spectroscopy and by their swelling properties. Evidence of the semi-IPN structure was shown thanks to the selective chemical attack on the cross-linker. Poly(ethylene glycol diacrylate) crosslinks of prepared hydrogels were attacked by concentrated basic solution leading to the hydrolysis of the poly(ethylene glycol diacrylate) molecules and the degradation of the polymer network. The solid residue and the liquid phase after degradation were analyzed by gas chromatography with mass spectrometry analyzer and by FTIR spectroscopy. These analyses gave evidence of the presence of non-crosslinked poly(N-vinylpyrrolidone) chains in the acrylate network. Henceforth, the synthesized hydrogel should be associated to a semi-IPN structure.

Inkjet-bioprinted acrylated peptides and PEG hydrogel with human mesenchymal stem cells promote robust bone and cartilage formation with minimal printhead clogging.

Inkjet bioprinting is one of the most promising additive manufacturing approaches for tissue fabrication with the advantages of high speed, high resolution, and low cost. The limitation of this technology is the potential damage to the printed cells and frequent clogging of the printhead. Here we developed acrylated peptides and co-printed with acrylated poly(ethylene glycol) (PEG) hydrogel with simultaneous photopolymerization. At the same time, the bone marrow-derived human mesenchymal stem cells (hMSCs) were precisely printed during the scaffold fabrication process so the cells were delivered simultaneously with minimal UV exposure. The multiple steps of scaffold synthesis and cell encapsulation were successfully combined into one single step using bioprinting. The resulted peptide-conjugated PEG scaffold demonstrated excellent biocompatibility, with a cell viability of 87.9 ± 5.3%. Nozzle clogging was minimized due to the low viscosity of the PEG polymer. With osteogenic and chondrogenic differentiation, the bioprinted bone and cartilage tissue demonstrated excellent mineral and cartilage matrix deposition, as well as significantly increased mechanical properties. Strikingly, the bioprinted PEG-peptide scaffold dramatically inhibited hMSC hypertrophy during chondrogenic differentiation. Collectively, bioprinted PEG-peptide scaffold and hMSCs significantly enhanced osteogenic and chondrogenic differentiation for robust bone and cartilage formation with minimal printhead clogging.

Human cartilage tissue fabrication using three-dimensional inkjet printing technology.

Bioprinting, which is based on thermal inkjet printing, is one of the most attractive enabling technologies in the field of tissue engineering and regenerative medicine. With digital controlcells, scaffolds, and growth factors can be precisely deposited to the desired two-dimensional (2D) and three-dimensional (3D) locations rapidly. Therefore, this technology is an ideal approach to fabricate tissues mimicking their native anatomic structures. In order to engineer cartilage with native zonal organization, extracellular matrix composition (ECM), and mechanical properties, we developed a bioprinting platform using a commercial inkjet printer with simultaneous photopolymerization capable for 3D cartilage tissue engineering. Human chondrocytes suspended in poly(ethylene glycol) diacrylate (PEGDA) were printed for 3D neocartilage construction via layer-by-layer assembly. The printed cells were fixed at their original deposited positions, supported by the surrounding scaffold in simultaneous photopolymerization. The mechanical properties of the printed tissue were similar to the native cartilage. Compared to conventional tissue fabrication, which requires longer UV exposure, the viability of the printed cells with simultaneous photopolymerization was significantly higher. Printed neocartilage demonstrated excellent glycosaminoglycan (GAG) and collagen type II production, which was consistent with gene expression. Therefore, this platform is ideal for accurate cell distribution and arrangement for anatomic tissue engineering.

Obtaining of hybrid nanocomposites by simultaneous photopolymerization of some urethane monomers and photoinduced formation of gold nanoparticles

Urethane–urea dimethacrylates were synthesized and used in the preparation of nanocomposites containing gold nanoparticles (Au NPs) in situ photogenerated during the UV-curing process in the absence of reducing agent. A study of the photopolymerization kinetics showed that the photoreactivity of the monomers alone or in combination with a dual urethane benzophenone (BP) macromer is dependent on the nature of photoinitiator (Irgacure819, BP/amine) and the formulation composition. It was found that the addition of 1 wt % AuBr3 in monomers slightly improved the polymerization rate and the degree of conversion. The formation of Au NPs into the network was confirmed through UV–vis, XRD, EDX, SAXS, and TEM analyses, the last indicating the existence of NPs with size around 8.5 nm and spherical/triangle shapes. On addition of 10 wt % 2[N-methacryloyloxyethyl-(N'-2-thioethyl)] (urea) in formulation, the Au NPs (200 nm) became predominantly cubic/hexagonal in shape. The composite films emit fluorescence at 575 nm, and this property could be exploited in the field of fluorescent bio/sensors. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 728–738

Direct Human Cartilage Repair Using Three-Dimensional Bioprinting Technology

Current cartilage tissue engineering strategies cannot as yet fabricate new tissue that is indistinguishable from native cartilage with respect to zonal organization, extracellular matrix composition, and mechanical properties. Integration of implants with surrounding native tissues is crucial for long-term stability and enhanced functionality. In this study, we developed a bioprinting system with simultaneous photopolymerization capable for three-dimensional (3D) cartilage tissue engineering. Poly(ethylene glycol) dimethacrylate (PEGDMA) with human chondrocytes were printed to repair defects in osteochondral plugs (3D biopaper) in layer-by-layer assembly. Compressive modulus of printed PEGDMA was 395.73±80.40 kPa, which was close to the range of the properties of native human articular cartilage. Printed human chondrocytes maintained the initially deposited positions due to simultaneous photopolymerization of surrounded biomaterial scaffold, which is ideal in precise cell distribution for anatomic cartilage engineering. Viability of printed human chondrocytes increased 26% in simultaneous polymerization than polymerized after printing. Printed cartilage implant attached firmly with surrounding tissue and greater proteoglycan deposition was observed at the interface of implant and native cartilage in Safranin-O staining. This is consistent with the enhanced interface failure strength during the culture assessed by push-out testing. Printed cartilage in 3D biopaper had elevated glycosaminoglycan (GAG) content comparing to that without biopaper when normalized to DNA. These observations were consistent with gene expression results. This study indicates the importance of direct cartilage repair and promising anatomic cartilage engineering using 3D bioprinting technology.

Crosslinked microparticle preparation in supercritical carbon dioxide with photopolymerization

An antisolvent processing technique by simultaneous compressed antisolvent precipitation and photopolymerization for cross-linked polymer microparticles formation was presented in this paper. In this process, photopolymerization of the homogeneous solution composed of methylene chloride, poly(ethylene glycol)600 diacrylate (PEG600DA) as monomer and diphenyl-(2,4,6-trimethylbenzoyl)-phosphine oxide (TPO) or 2,2-dimethoxy-2-phenylacetophenone (DMPA) as photoinitiator resulted to microparticle when it was sprayed into supercritical carbon dioxide (scCO2) and simultaneously exposed to initiating light. High miscibility of the solvent in scCO2 made methylene chloride quickly extracted from the dispersion phase, leaving very high concentrations of monomer (PEG600DA) dispersed in scCO2. The high monomer concentration combined with photo initiating polymerization facilitates rapid reaction rates and ultimately lead to polymer precipitation. Particle size and morphology were adjustable by changing the processing conditions, such as temperature and pressure. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Subwavelength Direct Laser Patterning of Conductive Gold Nanostructures by Simultaneous Photopolymerization and Photoreduction

This article presents a new method for fabricating highly conductive gold nanostructures within a polymeric matrix with subwavelength resolution. The nanostructures are directly written in a gold precursor-doped photoresist using a femtosecond pulsed laser. The laser energy is absorbed by a two-photon dye, which induces simultaneous reduction of gold in the precursor and polymerization of the negative photoresist. This results in gold nanoparticle-doped polymeric lines that exhibit both plasmonic effects, due to the constituent gold nanoparticles, and relatively high conductivity (within an order of magnitude of the bulk metal), due to the high density of particles within these lines. Line widths from 150 to 1000 nm have been achieved with this method. Various optically functional structures have been prepared, and their structural and optical properties have been characterized. The influence of laser intensity and scan speed on feature size have been studied and found to be in agreement with predictions of a mathematical model of the process.

Spatially controlled synthesis of silver nanoparticles and nanowires by photosensitizedreduction

The present paper reports on the spatially controlled synthesis of silver nanoparticles (NPs)and silver nanowires by photosensitized reduction. In a first approach, directphotogeneration of silver NPs at the end of an optical fiber was carried out. Control of bothsize and density of silver NPs was possible by changing the photonic conditions. In afurther development, a photochemically assisted procedure allowing silver to be depositedat the surface of a polymer microtip was implemented. Finally, polymer tips terminated bysilver nanowires were fabricated by simultaneous photopolymerization and silverphotoreduction.The silver NPs were characterized by UV–visible spectroscopy and scanning electronmicroscopy.

A novel process for holographic polymer dispersed liquid crystal system via simultaneous photo-polymerization and siloxane network formation

Formation of transmission holographic polymer dispersed liquid crystal gratings was studied for matrix components of trimethylolpropane triacrylate:trimethoxysilylmethyl methacrylate:1-vinyl-2-pyrrolidone (reactive diluent) in the range from 80:10:10,wt% to 10:80:10,wt% and E7 as nematic liquid crystal under the irradiation with Nd-YAG laser (532,nm). The optimum concentration of E7 in the recording solution was 35,wt% (65,wt% of matrix components) in presence of small amounts of radical photo-initiator system (Rose Bengal 0.05,wt%, NPG 0.1,wt%). When the concentration of methacrylate in matrix components was low ( 50,wt%) of the methacrylates. Contrary to that gratings with reasonably high and stable diffraction efficiency were successfully fabricated with trimethoxysilylmethyl methacrylate, gratings with only low diffraction efficiency were obtained for non-cross-linkable trimethylsilylmethyl methacrylate. With higher concentration of photo-sensitizer and photo-initiator (0.2,wt%; 1.0,wt%), and shorter irradiation time, gratings with high diffraction efficiency could be fabricated only for the photo-initiator system of 3,3′-carbonylbis(7-diethylaminocoumarin) and diphenyliodonium hexafluorophosphate with shorter induction period (∼174,s). Grating with diffraction efficiency of 72% was obtained with trimethoxysilylpropyl acrylate (80,wt% in the matrix component) and 35,wt% E7. By increasing the concentration of diphenyliodonium hexafluorophosphate to 2,wt%, diffraction efficiency increased to 85% and induction period was shortened to 129,s, and low volume shrinkage of 8% was attained via simultaneous radical cross-linking of trimethylolpropane triacrylate and siloxane network formation of trimethoxysilyl groups of trimethoxysilylmethyl acrylate by atmospheric moisture catalyzed by cationic species produced from the initiator system. In SEM morphology, although gratings formed with high concentration of trimethoxysilylpropyl acrylate had some cracks in polymer matrix, the largest grating spacing indicating the lowest volume shrinkage and very regular and well-defined gratings were observed.

Optical ion sensing with immobilized thin films of photocrosslinked decyl methacrylate

Abstract The simultaneous photopolymerization and covalent immobilization of thin decyl methacrylate (DMA) films onto glass substrates represents a new approach for the fabrication of optical ion sensing devices. Robust and durable optical sensors for small ions are described based on photocrosslinked DMA membrane films doped with appropriate chromoionophores, ionophores, or ion-exchangers. Sensors prepared with the chromoionophore ETH 2412 and the non-specific anion-exchanger TDMAC exhibit a rapid, reproducible and reversible response towards inorganic anions with selectivity following the classical Hofmeister pattern. Sensors prepared with ETH 5350, valinomycin, and a tetraphenylborate derivative respond to potassium with excellent selectivity and reproducibility. Sensor response times of approximately 30 s compare well with similar optical sensors prepared with other membrane matrices, and are not affected by the crosslinker content of the DMA film. The ability to covalently attach the DMA films to silanized glass substrates results in optical sensing devices with substantially increased lifetimes relative to similar devices based on solvent-cast polymeric films.