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In this study, fast and continuous fabrication of microscale structures by roll-to-roll UV imprinting or micromolding is demonstrated on a 121 mm wide web. This process is enabled by a UV curable thiol-ene-acrylate resin system, following the work of Stadlober and coworkers. A series of formulations were prepared with fast curing speeds at ambient conditions, low viscosities, and tunable mechanical properties. The rate and extent of curing as a function of the formulation composition were investigated with Fourier transform infrared spectroscopy. Consistent with the past work, we show that the thiol-ene-acrylate formulations reached high double bond conversions (> 80%) with the maximum conversion increasing with the relative thiol content and decreasing with the viscous urethane acrylate oligomer content. The double bond conversion of the patterned coatings (in contact with the mold) is shown to be ~ 80% for a range of UV lamp powers and web speeds up to 2.7 cm/s. Areas of the coating not covered by the mold required higher UV lamp power and/or lower web speeds to cure to a tack-free state. Microscale channels and arrays of recessed wells with various dimensions and pattern densities were continuously fabricated. Our findings show the successful use of a tetrafunctional thiol in the thiol-ene-acrylate resin system. We also discuss guidelines for the selection of processing conditions for the manufacturing of structured plastic substrates using roll-to-roll imprinting processes, opening up potential new applications.

Photocured polymers have recently gained tremendous interest for a wide range of applications, such as industrial prototyping/additive manufacturing, electronics, medical/dental devices, and tissue engineering. However, current development of photoinitiated thermosetting formulations is mostly centered on commercial monomers/oligomers that are petroleum-derived and not environmentally friendly. This work aims to develop natural phenolic-based (meth)acrylates to expand the use of sustainable and mechanically robust 3D printable formulations. Utilizing thiol–ene chemistry, bifunctional 3,6-dioxa-1,8-octanedithiol eugenol acrylate (E) was synthesized through a highly efficient, scalable method. Real-time infrared spectra and photorheology studies revealed that E exhibits rapid photocuring kinetics and that the viscosity, glass transition temperature (Tg) and thermal properties of this material can be tuned by adding a sustainable reactive diluent, guaiacyl methacrylate (G). The effect of adding a crosslinker to binary GE monomers was further investigated by incorporating vanillyl alcohol dimethacrylate (V) or trimethylolpropane trimethacrylate (T). At 20 mol%, V showed a moderate improvement in curing rate and a lower degree of cross-linking than T due to the bifunctionality of V. However, the aromaticity of V provided more resistance to chain deformation and breakage within the network, demonstrating storage moduli and tensile strengths up to 3.4 GPa and 62 MPa, respectively. The distinct impact of the crosslinkers on the tensile behaviors of glassy terpolymers was correlated to the cohesive energy density. Ternary formulations GEV 60–20–20 by mol% with 2 wt% TPO photoinitiator were successfully printed using a commercial desktop stereolithographic 3D printer with 405 nm violet laser source. This work demonstrates a versatile, sustainable, and scalable synthetic strategy to design a class of natural phenolic acrylates for sustainable photocured formulations with potential translation to high performance 3D printing.

Advanced neural research demands new electrode materials with high performance. Herein, we have developed a facile approach to synthesize amphiphilic reduced graphene oxide (rGO) and demonstrated its performance in electrically stimulating neural cells with high charge injection capacity. Synthesis of the amphiphilic rGO features covalent functionalization and simultaneous thermal reduction in a one-step manner. The covalent functionalization of methoxy poly(ethylene glycol) (mPEG) chains on the rGO surface not only provides a high dispersibility in various solvents, enabling convenient post-treatment processes, but also allows for an enhancement in double-layer charging capacitance. Calcium imaging of PC12 neural cells on the amphiphilic mPEG–rGO films has revealed a predominant increase in the percentage of cells with higher action potentials, derived from double-layer capacitance enhancement in charge injection. These results suggest that the new amphiphilic mPEG–rGO material is capable of providing a much safer and efficacious solution for neural prostheses applications.

Micromolding of UV-curable materials is a patterning method to fabricate microstructured surfaces that is an additive manufacturing process fully compatible with roll-to-roll systems. The development of micromolding for mass production remains a challenge because of the multifaceted demands of UV curable materials and the risk of demolding-related defects, particularly when patterning high-aspect-ratio features. In this research, a robust micromolding approach is demonstrated that integrates thiol-ene polymerization and UV LED curing. The moduli of cured thiol-ene coatings were tuned over 2 orders of magnitude by simply adjusting the acrylate concentration of a coating formulation, the curing completed in all cases within 10 s of LED exposure. Densely packed 50-μm-wide gratings were faithfully replicated in coatings ranging from soft materials to stiff highly cross-linked networks. Further, surface energy was modified with a fluorinated polymer, achieving a surface energy reduction of more than a half at a loading of 1 wt %, and enabling tall (100 μm) defect-free patterns to be attained. The demolding strengths of microstructured coatings were compared using quantitative peel testing, showing its decrease with decreasing surface energy, coating modulus, and grating height. This micromolding process, combining tunability in thermomechanical and surface properties, makes thiol-ene microstructured coatings attractive candidates for roll-to-roll manufacture. As a demonstration of the utility of the process, superhydrophobic surfaces are prepared using the system modified by the fluorinated polymer.

A xenon flash lamp was used to create intense pulsed light (IPL) irradiation to cure acrylate coatings at very high rates and ambient temperature; we investigate whether the achievable conversion can be increased compared to conventional irradiation and as the dose rate is increased with IPL parameters – pulse intensity, pulse duration, and pulse repeat period – and with the photoinitiator (PI) concentration and the curing temperature. Conversion of acrylate double bonds was measured using Fourier transform infrared (FTIR) spectroscopy. In all cases, cure conversion increases with the number of pulses until it plateaus at the maximum achievable value, when the reduced mobility of reactive species prevents further reaction. Changing the pulse intensity, the pulse duration, and the pulse period – and even changing the photoinitiator loading – do not appreciably affect the achievable conversion at ambient temperature. Increasing the temperature can result in somewhat higher achievable conversion, but with the loss of advantages of ambient temperature cure. Consistent with the expectation that the cure rate should depend strongly on intensity, a single measured pulse with high dose rate can achieve millisecond-timescale cure of acrylate coatings, providing adequate curing dose while avoiding damage to the substrate from excessive exposure. In multiple pulse patterns, the achievable cure can be attained more quickly with higher dose rate; as opposed to a single pulse irradiation, the introduction of dark periods can reduce the total irradiation dose needed to attain the achievable cure conversion.