Grayscale Color 3D/4D Printing via Orthogonal Photochemistry

Photothermal Nanotrigger Enables Rapid Gelation and Spatially-Programmable Printability Under Broad-Spectrum Light

Controllable and versatile manufacturing of nanocomposite hydrogels is highly desirable for attaining preferential performance and pushing their applications. However, the conventional thermal-initiated method suffers from sluggish and uncontrollable bulky gelation, whereas the photo-initiated method is controllable yet is limited by a special wavelength of light and is ineffective for hydrogel precursors containing light-absorbing conductive/magnetic nanomaterials. Herein, these limitations are fundamentally overcome, and a new concept of photothermal nanotrigger (PTNT) is discovered that leverages the classic photothermal effect of light-absorbing nanomaterials to transform uncontrollable thermal initiation into a new photo-controlled initiation. The design of PTNT is universal and can be extended for arbitrary photothermal nanomaterials from 2D nanosheets to 1D nanotubes and 0D nanoparticles, exhibiting high gelation efficiency and superior compatibility to broad-spectrum light from visible to ultraviolet and near-infrared. Intriguingly, the PTNT approach can be imparted with excellent spatially-programmable printability by introducing viscous and low thermally-conductive glycerol to confine the photothermal-generated heat and eliminate the diffusion of the formed free radicals to the unexposed region, enabling the manufacturing of high-resolution and heterogenous architecture. Moreover, in addition to the basic initiation function, the PTNT can parasitize the hydrogel network to find many additional applications in the fields of flexible electronics, light/magnetic-manipulated soft robotics, and beyond.

Non-monotonic Information and Shape Evolution of Polymers Enabled by Spatially Programmed Crystallization and Melting

Stimuli-responsive polymer materials are a kind of intelligent material which can sense and respond to external stimuli. However, most current stimuli-responsive polymers only exhibit a monotonic response to a single constant stimulus but cannot achieve dynamic evolution. Herein, we report a method to achieve a non-monotonic response under a single stimulus by regionalizing the crystallization and melting kinetics in semicrystalline polymers. Based on the influence of cross-linking on the crystallization and melting kinetics of polymers, we employ light to spatially regulate the cross-linking degree in polymers. The prepared material can realize the self-evolved encryption of pattern information and the non-monotonic shape evolution without complex multiple stimuli. By combination of pattern and shape evolution, the coupled encryption of shape and pattern can be achieved. This approach empowers polymers with the ability to evolve under constant stimulus, offering insights into the functional design of polymer materials.

Multi-color dual wavelength vat photopolymerization 3D printing via spatially controlled acidity

Dual wavelength vat photopolymerization (DW-VP) has emerged as a powerful approach to create multimaterial objects. However, only a limited range of properties have been showcased. In this work, we report the 3D printing (3DP) of multi-color objects from a single resin vat using DW-VP. This was accomplished by concurrently curing resin with visible light and modulating local resin color with 365-nm ultraviolet (UV) light. The key advance was to use a photoacid generator (PAG) in combination with pH responsive dyes in the 3DP resins. The specific color is dictated by the extent of reaction, or local acidity in our case, and controlled by the light dosage and pattern of UV light applied. Multi-color object formation was implemented in two-step processes involving first 3DP to set the object structure, followed by UV exposure, as well as single processes that leveraged DW-VP to create a broad range of vibrant colors and patterns.