The rapid development of additive manufacturing has fueled a revolution in various research fields and industrial applications. Among the myriad of advanced three-dimensional printing techniques, two-photon polymerization lithography (TPL) uniquely offers a significant electron microscope (SEM) images of SMP structures before and after programming and after recovery, respectively. Reproduced under terms of the CC-BY license. [114] Copyright 2021, The Authors, published by Nature Publishing Group. b) Stiff SMPs for high-resolution reversible nanophotonics. I-II) The deformed and recovered nanopillars under optical microscope and SEM, respectively. Reproduced with permission. [115] Copyright 2022, American Chemical Society. c) Vapor-responsive photonic arrays. I-IV) Optical image of a grid array in air, in water vapors ~ 20 s, saturation with water vapors ~ 88s, and after the gas flow stopped, respectively.Reproduced under terms of the CC-BY license. [116] Copyright 2021, The Authors, published by Royal Society of Chemistry. d) SEM image of a 40-layer face-cantered-cubic photonic structure printed by SU-8. Reproduced with permission. [117] Copyright 2004, Nature Publishing Group. e) SEM image of helices with an axial pitch of 800 nm and a radius of 800 nm fabricated by the two-step absorption photoresist. Reproduced with permission. [118]

Photopolymerization of (meth)acrylate-based formulations has become a widespread method for industry due to the high energy efficiency and low curing times of this technology. Various products from simple coatings to more complex applications such as additive manufacturing technologies are based on this versatile method. Common industrial radical photoinitiators are generally based on aromatic ketones. Benzaldehyde is an organic compound consisting of a benzene ring with a formyl substituent. It is the simplest aromatic aldehyde and one of the most industrially useful; for instance in the preparation of various aniline dyes, perfumes, flavorings, and pharmaceutics. Parallel to this, triphenylamines are extensively used for the design of dyes used for solar energy conversion. In this work, three triphenylamine derivatives bearing formyl groups are as a new substance class of multi-photon lithography photoinitiators. Besides their efficient formulations, they show high biocompatibilty by investigating the adhesion, viability and proliferation of dental stem cells on photopolymerized thin films.

A novel dual cure photopolymerizable system was developed by combining two plant-derived acrylic monomers, acrylated epoxidized soybean oil and vanillin dimethacrylate, as well as the thiol monomer pentaerythritol tetrakis (3-mercaptopropionate). Carefully selected resin composition allowed the researchers to overcome earlier stability/premature polymerization problems and to obtain stable (up to six months at 4 °C) and selectively-polymerizable resin. The resin demonstrated rapid photocuring without an induction period and reached a rigidity of 317.66 MPa, which was more than 20 times higher than that of the other vanillin-based polymers. Improved mechanical properties and thermal stability of the resulting cross-linked photopolymer were obtained compared to similar homo- and copolymers: Young’s modulus reached 4753 MPa, the compression modulus reached 1634 MPa, and the temperature of 10% weight loss was 373 °C. The developed photocurable system was successfully applied in stereolithography and characterized with femtosecond pulsed two-beam initiation threshold measurement for the first time. The polymerization threshold of the investigated polymer was determined to be controlled by the sample temperature, making the footprint of the workstations cheaper, faster, and more reliable.

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