Photocurable Polymer Research Articles

A prediction model for photopatternable thickness of photocurable polymer nanocomposites containing carbon-based high-aspect-ratio fillers

The spatial patterning of photocurable polymer nanocomposites (PnCs) with electrical conductivity provides high flexibility in fabricating microscale conductors on surfaces of any geometry. A quantitative characterization of the photopatternability of photocurable PnCs is of great concern in their lithography process. It is, however, still regarded as challenging to theoretically predict the photopatternable thickness of photocurable PnCs. Here, we establish a theoretical model on the phtopatternable thickness of photocurable PnCs containing carbon-based high-aspect-ratio (HAR) fillers. Our model is derived by modifying the Beer-Lambert law to fully consider UV light absorption and reflection in the fillers, after describing HAR fillers as spherical ones with an out-of-plane orientation parameter. The accuracy of the proposed model is verified by comparing the predicted results with the experimental data on graphite nanoflake (GnF)-reinforced SU-8 PnCs, GnF/SU-8 PnCs. The effect of filler content and UV exposure energy on the photopatterning error of photocurable PnCs containing carbon-based HAR filler is also extensively addressed.

Experimental and theoretical investigations of the rheological and electrical behavior of nanocomposites with universal percolation networks

Electrically conductive ceramic/polymer nanocomposites with universal percolation networks and varying contents of conductive nanoparticles were prepared herein; the effects of the dispersed state of the conductive nanoparticles on the electrical conductivity of the nanocomposites were investigated. The conductive nanocomposites were prepared by coating carbon black (CB) nanoparticles with a silane coupling agent, followed by their subsequent dispersion in the 1,6-hexanediol diacrylate (HDDA) photocurable polymer. The physical properties of the conductive nanocomposites, such as viscosity, photocurability, flowability, dispersibility, and electrical conductivity were investigated with respect to the loaded CB content. A correlation between conductivity and internal dispersibility was established by conducting theoretical analysis based on conditions of particle dispersion, aspect ratio, orientation, and interface. A comparison of the experimental values and theoretically obtained results assisted in identifying the nanoparticle network structure in the polymer matrix as universal percolation networks with imperfect/tunneling interfaces and a percolation threshold (c*) of 0.016. The electrical conductivity, heat deflection temperature (HDT), and tensile strength of 3D-printed conductive nanocomposite products were analyzed; scanning electron microscopy (SEM) was also employed to examine these samples. This study suggests a new development strategy for improving the quality of nano-products based on the quantitative dispersibility analysis of nanocomposite materials.

Fabricating Robust Constructs with Internal Phase Nanostructures via Liquid-in-Liquid 3D Printing.

The ability to print soft materials into predefined architectures with programmable nanostructures and mechanical properties is a necessary requirement for creating synthetic biomaterials that mimic living tissues. However, the low viscosity of common materials and lack of required mechanical properties in the final product present an obstacle to the use of traditional additive manufacturing approaches. Here, a new liquid-in-liquid 3D printing approach is used to successfully fabricate constructs with internal nanostructures using in situ self-assembly during the extrusion of an aqueous solution containing surfactant and photocurable polymer into a stabilizing polar oil bath. Subsequent photopolymerization preserves the nanostructures created due to surfactant self-assembly at the immiscible liquid-liquid interface, which is confirmed by small-angle X-ray scattering. Mechanical properties of the photopolymerized prints are shown to be tunable based on constituent components of the aqueous solution. The reported 3D printing approach expands the range of low-viscosity materials that can be used in 3D printing, and enables robust constructs production with internal nanostructures and spatially defined features. The reported approach has broad applications in regenerative medicine by providing a platform to print self-assembling biomaterials into complex tissue mimics where internal supramolecular structures and their functionality control biological processes, similar to natural extracellularmatrices.

High dielectric properties, TiO2 nanoparticles doped PDLC devices for lower switching voltage

ABSTRACT Polymer dispersed liquid crystal (PDLC) films were prepared using a nematic liquid crystal, photo-curable polymer and TiO2 nanoparticles by polymerisation-induced phase separation (PIPS) method. Electro-optical properties of doped and undoped samples including transmittance, driving voltage, contrast ratio and response time of the transmittance-voltage were measured, compared and analysed. The morphology of polymer network has been investigated by means of SEM. The phase separation of LC droplets was found to be dependent on the content of prepolymer, LC and nanoparticles used. The high dielectric properties and high refractive index of TiO2 nanoparticles make PDLC have low driving voltage and high contrast. In particular, the nanoparticles concentration can be optimised to obtain promising electronic materials with minimum threshold and high contrast for display applications.

Self-assembled photocurable polymer biconvex microlens array based on double-faced discontinuous hydrophobic surface

Biconvex microlens arrays (MLAs) are key parts in optical systems. In this work, a facile method was developed for the fabrication of biconvex MLAs on ultrathin glass substrates, in which both sides were modified with microholes patterned hydrophobic layers. The difference of the hydrophobicity inside and outside the microholes pattern were very large. The photocurable polymer formed droplets array on the discontinuous hydrophobic layer self-assembly, and polymeric biconvex MLAs were obtained after UV curing. Each polymeric dome formed on front and back sides was concentric and preserved the same size. The as-obtained biconvex MLAs showed an average diameter of 297 μm, a focal length of 669 μm, a numerical aperture (NA) of 0.21, and a maximum resolution of 45.3 lp/mm. Compared to plano-convex MLAs using the same materials with the same size, which exhibits the maximum resolution of 16 lp/mm, the biconvex MLAs displayed highly improved optical resolution. In sum, the advantages of the proposed method in terms of simple fabrication, good optical performances and high consistency in large areas make it promising for use in 3D displays, image processing, fiber coupling, optical data storage, light extraction, and biomedical processing.

Viscoelastic Properties of Cell Structures Manufactured Using a Photo-Curable Additive Technology-PJM.

This research paper reviews the test results involving viscoelastic properties of cellular structure models made with the PolyJet Matrix—PJM additive technology. The designed test specimens were of complex cellular structure and made of three various photo-curable polymer resin types. Materials were selected taking into account the so-called “soft” and “tough” material groups. Compressive stress relaxation tests were conducted in accordance with the recommendations of standard ISO 3384, and the impact of the geometric structure shape and material selection on viscoelastic properties, as well as the most favorable geometric variants of the tested cellular structure models were determined. Mathematica and Origin software was used to conduct a statistical analysis of the test results and determine five-parameter functions approximating relaxation curves. The most favorable rheological was adopted and its mean parameters determined, which enables to match both printed model materials and their geometry in the future, to make a component with a specific rheological response. Furthermore, the test results indicated that there was a possibility of modelling cellular structures within the PJM technology, using support material as well.

Synthesis and characterization of UV-Curable pyrimidine-based Poly(Acrylate) and zirconium acrylate nanocomposite with high refractive index

Highly refractive polymers are widely used in the optics industry. They are typically synthesized as matrices containing relatively high refractive index inorganic fillers, resulting in transparent, practical, and useful thin materials. This research introduces novel photo-curable pyrimidine-based acrylate monomers containing aromatic groups or aliphatic groups with sulfur atoms. Diphenylacrylate sulfanyl-methylthio-pyrimidine (DPASMTP) and trisphenylacrylate-sulfanyl-pyrimidine (TPASP) were designed and synthesized for optical applications. The polymers were obtained after a simple photo-polymerization, and exhibited good thermal stabilities (Td > 350) and high transmittance (>85% at λcutoff). All of the ZrA nanocomposites (NCs) showed well-dispersed particles at the nanometer level, high refractive index (>1.68 at 637 nm) and very low birefringence (<0.0135 at 637 nm). The ZrA contents were correlated with the optical properties of the photo-cured polymer systems, and were confirmed to enhance the refractive index.

Three-dimensional printing of gastro-floating tablets using polyethylene glycol diacrylate-based photocurable printing material

Extruded three-dimensional (3D) printing based on photocurable materials has shown good application prospects in the medical field. This has been attributed to the operational aspect that can be performed at room temperature and the high mechanical strength of the extrudate and final product. However, the commonly used photocurable polymer, polyethylene glycol diacrylate (PEGDA), has a low viscosity and exhibits a long crosslinking time. Therefore, additives are added to improve the printability of the extrudate. In this study, various hydrogels were used to improve the mixing uniformity and rheological behavior of PEGDA-based printing materials. Printing accuracy and mechanical strength were evaluated to optimize print material composition and process parameters. Hydroxypropyl methylcellulose K100M was found to improve the shear thinning and self-supporting properties of printing materials, which were essential for printability. Although the storage modulus of the photocured material proportionally increased with curing time in the range of 20–80 s, the minimal layer time of the 3D samples remained at 65 s, ensuring interlayer adhesion. Gastro-floating tablets with different infill densities were printed to illustrate the application of 3D extrusion printing in personalized medicine. The weight, crushing strength, and floating time were regulated by the infill density of the models. Overall, this study demonstrates that extrusion printing with a photocurable material is an easy way to prepare customized oral preparations with complex internal structures and tunable properties.

Graphene oxide/epoxy acrylate nanocomposite production via SLA and importance of graphene oxide surface modification for mechanical properties

PurposeTraditional nanocomposite production methods such as in situ polymerization, melt blending and solvent technique, have some deficits. Some of these are non-homogeneous particle distribution, setup difficulties, time-consuming and costly. On the other hand, three-dimensional printing technology is a quite popular method. Especially, Stereolithography (SLA) printing offers some benefits such as fast printing, easy setup and smooth surface specialties. Furthermore, surface modification of Graphene Oxide (GO) and its effects on polymer nanocomposites are quite important. The purpose of this study is to examine the effect of surface modification of GO nanoparticles on the mechanical properties and morphology of epoxy acrylate (BisGMA/1,6 hexane diol diacrylate) matrix nanocomposites.Design/methodology/approachIn this study, Ultraviolet (UV) curable end groups of synthesized resin were linked to functional groups of graphene oxide, which are synthesized by the Tour method, which is a kind of modified Hummer method. In addition, synthesized GO nanoparticle’s surfaces were modified by 3-(methacryloyloxy) propyl trimethoxysilane. Significant weight percentages of GO were added into the epoxy acrylate resin. Different Wt.% of modified graphene oxide/acrylate resins was used to print test specimens with SLA type three-dimensional printer.FindingsSurface modification has a significant effect on tensile strength for graphene oxide nanoparticles contained composites. In addition, a specific trend was not observed for tensile test results of non-modified graphene oxide. The tendency of impact and hardness test finding were similar for both surfaces modified and non-modified nanoparticles. Finally, the distribution of particles was homogeneous.Originality/valueThis paper is unique because of the inclusion of both surface modifications of graphene oxide nanoparticles and SLA production of nanocomposites with its own production of three-dimensional printer and photocurable polymer resin.

Lithium bis(trifluoromethanesulfonyl)imide blended in polyurethane acrylate photocurable solid polymer electrolytes for lithium-ion batteries

The increased demand of electronic devices promotes the development of advanced and more efficient energy storage devices, such as batteries. Lithium-ion batteries (LIBs) are the most studied battery systems due to their high performance. Among the different battery components, the separator allows the control of lithium ion diffusion between the electrodes. To overcome some drawbacks of liquid electrolytes, including safety and environmental issues, solid polymer electrolytes (SPEs) are being developed. In this work, a UV photocurable polyurethane acrylate (PUA) resin has been blended with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) up to 30 wt% LiTFSI content to reach a maximum ionic conductivity of 0.0032 mS/cm at room temperature and 0.09 mS/cm at 100 °C. Those values allowed applying the developed materials as photocurable SPE in Swagelok type Li/C-LiFePO4 half-cells, reaching a battery discharge capacity value of 139 mAh.g−1 at C/30 rate. Those results, together with the theoretical studies of the discharge capacity at different C-rates and temperatures for batteries with LiTFSI/PUA SPE demonstrate the suitability of the developed photocurable SPE for LIB applications.

Post-gel polymerisation shrinkage profiling of polymer biomaterials using a chirped fibre Bragg grating

A strain profile measurement technique using a chirped fibre Bragg grating (CFBG) sensor by implementing an integration of differences (IOD) method is reported in this paper. Using the IOD method the spatial distribution of strain along the length of the CFBG is extracted from its power reflectance spectra. As a proof of concept demonstration, the developed technique is applied to measure the polymerisation shrinkage strain profile of a photo-cured polymer dental composite which exhibits a non-uniform strain distribution attributed to the curing lamp characteristics. The result from the CFBG technique is compared with that of an FBG array embedded in the dental composite and is correlated with the degree of conversion of the material which also depends on the curing lamp intensity distribution. This technology will have significant impact and applications in a range of medical, materials and engineering areas where strain or temperature gradient profile measurement is required in smaller scales.

Leakage-Free Nucleic Acid Biochip Featuring Bioinert Photocurable Inhibitor

A leakage-free and disposable biochip for deoxyribonucleic acid (DNA) separation and detection is developed in this study. The biochip comprises of 50 mm long polydimethylsiloxane (PDMS) microchannel and copper electrodes engraved on flame retardant (FR-4) printed circuit board (PCB) substrate. An inhibitor made from photocurable diacrylate bisphenol-A polymer (DABA) was used to establish a permanent bonding between PDMS and PCB substrates. Pull-off test experiments resulted in average strength of 287.4 kPa and a standard deviation of ± 23.8 kPa. These results are comparable to recent studies on leak-free microfluidic applications. Meanwhile, the leakage test showed that the biochip could withstand a pressure of more than 190 kPa, which is sufficiently high for most DNA measurements. Finally, experiments performed on two different DNA samples indicated that the proposed design could accurately detect DNA fragments with current sensitivity higher than 100 nA, under electric field strength of 20 V/cm. The new design effectively seals the biochip, thus preventing leakage of liquid from the sensor matrix. Together with its biologically and electrochemically inert characteristic, it opens up possibilities in building a truly portable biosensing device.

4D Printing of Glass Fiber-Regulated Shape Shifting Structures with High Stiffness.

4D printing allows 3D printed structures to change their shapes overtime under external stimuli, finding a wide range of potential applications in actuators, soft robotics, active metamaterials, flexible electronics, and biomedical devices. However, most 4D printing uses soft polymers to accommodate large strain shape-changing capability at the price of low stiffness, which impedes their engineering applications. Here, we demonstrate an approach to design and manufacture self-morphing structures with large deformation and high modulus (∼4.8 GPa). The structures are printed by multimaterial direct ink writing (DIW) using composite inks that contain a high volume fraction of solvent, photocurable polymer resin, and short glass fibers as well as fumed silica. During printing, the glass fibers undergo shear-induced alignment through the nozzle, leading to highly anisotropic mechanical properties. The solvent is then evaporated, during which the aligned glass fibers enable anisotropic shrinkage in the parallel and perpendicular directions to the fiber alignment for shape shifting. A final postphotocuring step is applied to further increase the stiffness of the composite from ∼300 MPa to ∼4.8 GPa. A finite element analysis (FEA) model is developed to predict the influence of the solvent, fiber contents, and fiber orientation on the shape shifting. We demonstrate the anisotropic volume shrinkage of the structures can be used as active hinges to transform printed two-dimensional structures into complex three-dimensional structures with large shape-shifting and outstanding mechanical properties. This strategy for fabricating composite structures with programmable architectures and excellent mechanical properties shows potential applications in morphing lightweight structures with load-bearing capabilities.

Relationship between mechanical properties of ceramic green body and structures of photo-cured acrylate polymer for ceramic 3D printing based on photo polymerization

3D printing technologies using photo polymerization of photo-curable monomer and oligomers as an organic binder have been studied to fabricate ceramics with a complicated shape. For minimizing distortion of ceramics during the manufacturing process and fast 3D printing of ceramic green body, high mechanical strength of ceramic green body and fast photo polymerization of the photo-curable resin are required, respectively. In this study, the ceramic green bodies with various compositions were fabricated by photo radical polymerization of the slurry-type resin composed of fused silica bead, and tri- or (and) mono-functional acrylate. Photo radical polymerization behaviors of mono-, tri-functional acrylate monomer, and blend of two monomers were analyzed by photo-DSC and FT-IR measurements. The structure analysis of photo-cured polymers made by each monomer was performed by thermo-mechanical analysis. Through mixing of mono- and tri-functional acrylate monomer, we confirmed that polymerization rate more increased compared with those of only mono-, tri-functional monomer. Unreacted vinyl groups in the polymers prepared with blend of two monomers decreased by an addition of mono-functional monomer in tri-functional monomer. The polymers prepared with the blend showed higher storage modulus and broader viscoelastic behavior compared to those fabricated with tri-functional monomer. Thus, to achieve high fracture strength of the green body, we verified that the photo-cured polymer in the green body should have high crosslinking density and low free volume based on reduction of unreacted vinyl groups in the polymer. Additionally, through analysis of cross-sectional SEM of the green body, we confirmed that acrylate monomer should include proper content in the slurry-type resin to maximize the fracture strength of the body regardless of the type of the used acrylate monomer. This was because low content of acrylate monomer in the slurry-type resin makes it difficult to form neckings composed with photo-cured polymers between the silica beads.

Photocurable polymer composite materials with an improved combination of strength and service properties

Photocurable polymer composite materials with an improved combination of strength and service properties

Mechanical characterization and constitutive modeling of visco-hyperelasticity of photocured polymers

In this work, we study the nonlinear behavior of soft photocured polymers typically used in 3D-printing. We perform experimental testing of 3D-printed samples cured at various controlled light intensities. The experimental data show the dependency of the material elasticity and rate-sensitivity on the curing light intensity. To elucidate these relations, we develop a physically-based visco-hyperelastic model in the continuum thermodynamics framework. In our model, the macroscopic viscoelastic behavior is bridged to the microscopic molecular chain scale. This approach allows us to express the material constants in terms of polymer chain physical parameters. We consider different physical mechanisms governing hyperelasticity and rate-dependent behaviors. The hyperelastic behavior is dictated by the crosslinked network; whereas, the viscous part originates in the free and dangling chains. Based on our experimental data, we illustrate the ability of the new constitutive model to accurately describe the influence of the light intensity on photocured polymer viscoelasticity.

Prolonged recovery of 3D printed, photo-cured polylactide shape memory polymer networks.

Shape memory polymers are materials that are able to retain a deformed state until an external stimulus, most typically heat, triggers recovery to the original geometry. Whereas typically, shape memory polymers are required to recover fast (seconds to minutes), many applications, particularly in the medical field, would benefit from a slow recovery (days to weeks). In this work, we exploit the broad glass transition range of photo-cured poly(D,L-lactide) dimethacrylate networks to obtain recovery times of up to 2 weeks, at 11 °C below the peak glass transition temperature of 58 °C. Recovery times decreased considerably for higher recovery temperatures, down to ∼10 min at 55 °C. A large spread in glass transition values (53.3–61.0 °C) was observed between samples, indicating poor reproducibility in sample preparation and, hence, in predicting shape recovery kinetics for individual samples. Furthermore, a staged recovery was observed with different parts of the samples recovering at different times. The ability to prepare complex structures using digital light processing stereolithography 3D printing from these polymers was confirmed. To the best of our knowledge, this work provides the first experimental evidence of prolonged recovery of shape memory polymers.

3D printed piezoelectric BNNTs nanocomposites with tunable interface and microarchitectures for self-powered conformal sensors

Abstract 3D printing of arbitrary shapes and unique architectures offers unparalleled flexibility and simplicity for fabrication of highly complex 3D conformal electronics. It drives up high demands in electronic materials with excellent processability and functionality simultaneously. Herein, we overcome this challenge in prepared nanofiller/polymer piezoelectric composite by incorporating ultralow loadings (0.2 wt%) of boron nitride nanotubes (BNNTs) in photocurable polymer solution. Furthermore, two effective approaches are introduced to significantly boost the piezoelectric responses through tuning inorganic-polymer interfacial compatibility and structural strain variation. The microstructured piezoelectric composites containing 0.2 wt% functionalized BNNTs exhibits an unprecedentedly high relative sensitivity of (120 mV/(kPa·wt%)) over a broad press region (1–400 kPa), which is 10-fold higher than that of flat composite containing unmodified BNNTs. This dramatic enhancement is ascribed to synergistic contribution from effective stress transfer efficiency between strong piezoelectric BNNTs and nonpiezoelectric polymers, and the improved structural strain variations by topology optimization of microstructures. The as-printed piezoelectric materials are successfully demonstrated as self-powered and conformal tactile sensor array to enable haptic sensing of robotic hand and detect spatial distribution of force on uneven surfaces. Our works provide a promising route for design and fabrication of novel conformal electronics with target performance by high-resolution 3D printing from rational design of materials to optimization of microstructures topology.

In vitro controlled release of extracellular vesicles for cardiac repair from poly(glycerol sebacate) acrylate-based polymers

Cell therapy to restore cardiac function in chronic heart failure has been extensively studied. However, its therapeutic value is limited due to poor cell engraftment and survival and the therapeutic outcomes have been attributed to paracrine secretions such as extracellular vesicles (EV). The direct use of EV is an attractive therapeutic strategy and it has been shown that the kinetics of delivery of the EV to the targeted tissue may impact the outcomes. However, there are currently no technologies to deliver EV to the heart in a controlled and tunable manner. The objective of this study was to design a controlled release system, based on a photocurable adhesive polymer, to locally deliver EV to the cardiac tissue. We have first demonstrated that the adhesive polymer, PGSA-g-EG, did not impact the EV bioactivity in vitro and was biocompatible in vivo when tested in a rat model. Importantly, the polymer remained attached to the heart surface for at least 1 month. We have then evaluated and optimized the in vitro release kinetics of the EV from the PGSA-g-EG polymer. Freeze-dried EV formulations were developed to tune the release kinetics and maximize the loading in the polymeric material. Moreover, despite the instability of the EV in aqueous medium at 37°C, the PGSA-g-EG polymer was able to release bioactive EV for at least 14 days. Overall, these results suggest that the PGSA-g-EG is a suitable material to promote the controlled delivery of bioactive EV over an extended period of time. Statement of SignificanceExtracellular vesicles (EV) are an investigational class of therapeutics that has shown promise to restore cardiac function following an ischemic event. Furthermore, its translation to the clinics is expected to pose less regulatory challenges than cell-based therapies. However, EV therapeutic outcomes are likely to be impacted by the route of administration and the kinetics of delivery to the target tissue. Therefore, there is a need for biomaterial-based technologies to deliver, in a controlled and tunable manner, EV to the heart. The present study describes the use of PGSA-g-EG polymer as an adhesive cardiac patch with potential to enable the controlled delivery of bioactive EV over an extended period of time to the cardiac tissue.

Photocurable Polymer Composition Based on Heat-Resistant Aromatic Polyamide for the Formation of Optical Elements by Two-Photon Polymerization

Optical properties of a polymer composition based on heat-resistant aromatic polyamide are established and an approach to the formation of three-dimensional microoptical structures by two-photon polymerization on the base of this composition is developed. Formation of prototype polymer microoptical elements is proven in several regimes involving a two-photon polymerization system with the use of a laser source with a wavelength of 525 nm. The formed structures corresponded to the initial three-dimensional model, were optically transparent in the range from 450 nm, and preserved optical transparency after several cycles of heating up to 300°C.