A Facile Approach for 4D Microprinting of Multi‐Photoresponsive Actuators

Abstract

For microscale 4D photoresponsive actuators, light is crucial in two ways. First, the underlying additive manufacturing techniques rely on photopolymerization processes triggered by the absorption of light. Second, the absorption of light serves as the actuation stimulus. The two absorptions can be conflicting. While the microstructure requires strong absorption at the actuation wavelength(s), this absorption should not interfere with that of the manufacturing process. Herein, a simple strategy is proposed to overcome these limitations and allow for the fabrication of multi‐photoresponsive 3D microstructures that can be actuated at different wavelengths of light. Two‐photon 3D laser printing is selected as the fabrication technique and liquid crystalline (LC) elastomers as the functional materials. In a first step, 3D microstructures are fabricated using an aligned LC ink formulation. Thereafter, up to five different dyes exhibiting absorptions that extend over the entire visible regime (400–700 nm) are successfully incorporated into the LC microstructures by an exchange process enabling a programmable actuation by irradiating with the suitable wavelength. Furthermore, by combining dyes exhibiting orthogonal absorptions, wavelength‐selective actuations are demonstrated.

Recent Advances in the Additive Manufacturing of Stimuli‐Responsive Soft Polymers

“…[417][418][419] These polymers offer relatively higher controllability and create multifunctional structures and permit the fabrication of highly precise and intricate structures with more favorable mechanical characteristics. [420][421][422][423] Multiple types of polymers such as thermo-photo, thermo-magnetic, thermo-pH, and others have been used for tissue regeneration applications in real physiological conditions. AM of multi-SRPs has been gaining significant attraction in recent years.…”

Smart Nematic Liquid Crystal Polymers for Micromachining Advances

“…For light actuation, azobenzene molecules or photothermal-responsive colorants are also used, and generally for NIR light because the light penetration into polymer or tissues is better at these wavelengths. Another recent study on micro-actuators activated with light comes from Blasco et al [ 61 ] ( Figure 7 C) where micro-clamps were developed. Here, a two-step method is presented that begins with the fabrication of a micro-actuator in a pre-aligned LC cell that is immersed in a dye solution.…”

“…( B ) Light actuation of a micro-structure with a photothermal effect generated by gold nanoparticles [ 60 ]. ( C ) LC microstructures actuated with light at different wavelengths depending on the dye used [ 61 ]. Reproduced under the terms of the Creative Commons CC BY 4.0 license.…”

Highly Efficient Photoninitiators Based on 4H‐Pyranylidene Derivatives for Two‐Photon Laser Printing

“…BAPO is a commercially available PI commonly used in formulation for 2PLP and here used as a reference. [38][39][40][41] Comparing the printing parameters of the 3D printed microstructures using the chromophores with the reference photoresist containing BAPO reveal the significantly higher efficiency of 1a-b and 2a-b (Table 3).…”