Rapid High-Resolution Visible-Light 3D Printing of Hydrogels via Nanocluster-Triggered Dual-Pathway Photoinitiation

Light-driven 3D printing (vat photopolymerization) of hydrogel materials has received significant attention because of its great potential in various biomedical applications. Currently, the simultaneous achievement of the high-speed and high-resolution printing of complex hydrogel structures is still challenging. Most of the hydrogel printings are conducted using UV sources (<420 nm), and visible-light-driven systems often suffer from slower reaction times, sensitivity to ambient oxygen, and unwanted coloring of products. Here, it is presented that a nanocluster-triggered dual-pathway photoinitiation can address these key limitations. In contrast to many of the reported water-soluble photoinitiators, Ag nanocluster demonstrates a superior initiation efficiency under long wavelength (405-560 nm), and it simultaneously leads to the improved resolution due to the unique nature of nanoclusters and their generated radicals. In addition, Ag nanocluster is photodegradable which produces the highly desired, optically clear products. Spectroscopic analysis unveils the anomalous scission of the interfacial Ag-S bond (type-I) and the proton abstraction (type-II) from amino acids to Ag nanoclusters, both of which create highly reactive radicals. The dual-pathway, high photoinitiation performance, and new photochemical insights demonstrated in this work should stimulate more future exploration of nanocluster-based materials for improving the 3D printing of hydrogels and other materials systems.