Recent Trends in Advanced Photoinitiators for Vat Photopolymerization 3D Printing

Abstract

3D printing has revolutionized the way of manufacturing with a huge impact on various fields, in particular biomedicine. Vat photopolymerization‐based 3D printing techniques such as stereolithography (SLA) and digital light processing (DLP) attract considerable attention owing to their superior print resolution, relatively high speed, low cost, and flexibility in resin material design. As one key element of the SLA/DLP resin, photoinitiators or photoinitiating systems have experienced significant development in recent years, in parallel with the exploration of 3D printing (macro)monomers. The design of new photoinitiating systems cannot only offer faster 3D printing speed and enable low‐energy visible light fabrication, but also can bring new functions to the 3D printed products and even generate new printing methods in combination with advanced optics. This review evaluates recent trends in the development and application of advanced photoinitiators and photoinitiating systems for vat photopolymerization 3D printing, with a wide range of small molecules, polymers, and nanoassemblies involved. Personal perspectives on the current limitations and future directions are eventually provided.

Boron-Methylated Dipyrromethene as a Green Light Activated Type I Photoinitiator for Rapid Radical Polymerizations

“…At this stage, the hypothesis was put forward that free radical polymerization was caused by light-induced homolytic βscission at the boron−carbon bond (B−CH 3 ) for the methylated BODIPYs. This bond is considered β as it is separated from π-conjugation by one atom, boron, which is sp 3 -hybridized. Additionally, the small extent of polymerization observed for resins with BODIPY-F-Br was rationalized by inefficient homolytic β-scission at the meso-methyl C−O bond, as previously reported for coumarin-based photocages.…”

“…Visible light has emerged as a promising stimulus to drive polymerizations for a variety of applications, − particularly in the biomedical and advanced manufacturing (e.g., 3D printing) arenas. This arises in part from the inherent spatiotemporal control, high penetration depth, low energy, and discrete absorption it offers to enable benign and wavelength-selective fabrication of multifunctional soft materials .…”

Skin-interfaced microfluidic systems with spatially engineered 3D fluidics for sweat capture and analysis

“…In the context of microfluidics, the use of 3D printing is well established ( 29 ) for the rapid, cost-effective fabrication of high-resolution templates for soft lithography. In particular, vat photopolymerization techniques [e.g., resin-based printing, stereolithography, digital light processing (DLP), and continuous liquid interface polymerization] ( 30 ) enable rapid production of microscale features (>100 μm) over large areas (>600 mm 2 ) with high precision ( 31 ). Innovations in printer hardware, software processing, and materials chemistry further extend these 3D printing capabilities to enable the direct production of enclosed microfluidic channels for lab-on-chip applications.…”

“…Successful fabrication requires optimization of other critical factors including printing technology (e.g., vat photopolymerization versus extrusion), feature design and spatial location, and printer-dependent parameters. AM process optimization, particularly for vat photopolymerization, demands careful attention to the chemistry of printed materials ( 30 , 32 ). Resin formulations must simultaneously satisfy application specific requirements, such as biocompatibility or optical clarity, while preserving printability.…”

Enhanced dual photo/thermal initiating systems for preparation of few layer graphene filler-based composites and 3D printing

“…31–40 Therefore, its 3D printing technology (mainly referring to VAT photopolymerization) is also highly preferred due to its low cost, fast speed of response, and the ability to accomplish rapid and mass production of customized structures. 41–46 However, the preparation of such FLG composite is hardly done by photopolymerization process because it is hindered by problems such as light penetration. However, different from well-known preparation technique, we have recently demonstrated that polymerization of opaque resins (high iron filler content) can be achieved directly by a photopolymerization process, 13 which enables the fabrication and printing of metal composites with thick curing depths by combining charge transfer complexes which feature lower thermal initiation temperatures.…”