Two‐Photon Polymerization: Fundamentals, Materials, and Chemical Modification Strategies

Abstract

Two-photon polymerization (TPP) has become a premier state-of-the-art method for microscale fabrication of bespoke polymeric devices and surfaces. With applications ranging from the production of optical, drug delivery, tissue engineering, and microfluidic devices, TPP has grown immensely in the past two decades. Significantly, the field has expanded from standard acrylate-and epoxy-based photoresists to custom formulated monomers designed to change the hydrophilicity, surface chemistry, mechanical properties, and more of the resulting structures. This review explains the essentials of TPP, from its initial conception through to standard operating principles and advanced chemical modification strategies for TPP materials. At the outset, the fundamental chemistries of radical and cationic polymerization are described, along with strategies used to tailor mechanical and functional properties. This review then describes TPP systems and introduces an array of commonly used photoresists including hard polyacrylic resins, soft hydrogel acrylic esters, epoxides, and organic/inorganic hybrid materials. Specific examples of each class-including chemically modified photoresists-are described to inform the understanding of their applications to the fields of tissue-engineering scaffolds, micromedical, optical, and drug delivery devices.

3D Security Labels: Photostable Multimaterial Multilayered QR Codes via Two-Photon Lithography

“…PR’s absorbance peaks are observed at λ = 226, 284, 445, and 580 nm (Figure A), whereas PY’s absorbance peaks fall at λ = 217, 259, 443, and 470 nm (Figure B). This allows unhindered two-photon absorption of the photoinitiator molecules in the acrylate photoresist to initiate two-photon polymerization (TPP) . Additionally, when excited by a green laser (λ ex = 550 nm), only PR emits red fluorescence peaking at λ ≫ 600 nm (Figures A and S3C).…”

Two‐Photon Polymerization Lithography for Optics and Photonics: Fundamentals, Materials, Technologies, and Applications

“…[67,106] Several combinations of monomer/oligomer and photoinitiators have been investigated in TPL. [107][108][109] Like the case in UV lithography, there are both positive and negative TPL photoresists. The most widely used and tested are negatives photoresists, [110][111][112] in which two-photon exposure of the photoresist results in a cross-linked or polymerized 3D structure, allowing the uncured photoresist to be washed away after printing.…”

Triplet Upconversion under Ambient Conditions Enables Digital Light Processing 3D Printing

“…In recent years, various strategies have been developed to address these particular limitations of UV photocuring. This includes photocatalysts that directly operate using visible and near-infrared light − as well as more sophisticated multiphoton excitation modes for catalysts that require higher energy, such as two-photon absorption, two-step absorption, and photon upconversion. , Notably, the latter three techniques have an inherent quadratic relationship between incident light intensity and photocuring rate. This superlinear relationship stems from the requisite combination of multiple photons to generate the radical species that initiate polymerization.…”