Polarization‐Modulated Multidirectional Photothermal Actuators

Abstract

Photothermal actuators have attracted increasing attention due to their ability to convert light energy into mechanical deformation and locomotion. This work reports a freestanding, multidirectional photothermal robot that can walk along a predesigned pathway by modulating laser polarization and on–off switching. Magnetic–plasmonic hybrid Fe3O4/Ag nanorods are synthesized using an unconventional templating approach. The coupled magnetic and plasmonic anisotropy allows control of the rod orientation, plasmonic excitation, and photothermal conversion by simply applying a magnetic field. Once the rods are fixed with desirable orientations in a bimorph actuator by magnetic‐field‐assisted lithography, the bending of the actuator can be controlled by switching the laser polarization. A bipedal robot is created by coupling the rod orientation with the alternating actuation of its two legs. Irradiating the robot by a laser with alternating or fixed polarization synergistically results in basic movement (backward and forward) and turning (including left‐, right‐, and U‐turn), respectively. A complex walk along predesigned pathways can be potentially programmed by combining the movement and turning modes of the robots. This strategy provides an alternative driving mechanism for preparing functional soft robots, thus breaking through the limitations in the existing systems in terms of light sources and actuation manners.

Engineering bioactive synthetic polymers for biomedical applications: a review with emphasis on tissue engineering and controlled release

“…261,262 Programmable actuation behaviours can be useful for overcoming the various challenges and limitations of biomedical devices; for instance, actuation may enable a fine control of biological events by adding a fourth dimension to the biological system (i.e., the temporal coordinate). The overall goal of bioactuators is to generate functional outcomes in the form of responses to various external physical or chemical stimuli, including temperature, [263][264][265] pH, [266][267][268][269] ionic strength, [270][271][272] oxidation/reduction, [273][274][275] light, [276][277][278][279][280] and electric [281][282][283][284] or magnetic fields [285][286][287] that satisfy biocompatible conditions.…”

“…306 The engineering of soft robots capable of performing complex mechanical tasks that imply a dynamic coordination in time and space (e.g., walking or swimming) is an emerging and exciting field of applications for actuators. 259,280,[307][308][309] One constraint of chemically responsive actuation is that concentrations tend to equalize or equilibrate rapidly in aqueous systems. 294 Achieving directed and coordinated displacement therefore often requires designs that consider responsiveness to external stimuli, such as electromagnetic forces or light.…”

Responsive Plasmonic Nanomaterials for Advanced Cancer Diagnostics

“…The LSPR intensity and the perceived color of Au nanorods in a colloidal solution can be quickly tuned by applying a magnetic field. A few advanced techniques enable direct colloidal synthesis of magnetic-plasmonic hybrid nanostructures, including Fe 3 O 4 @Au core/shell nanospheres (Figure 2A) (Li et al, 2020a), Fe 3 O 4 /Au nanorods ( Figure 2B) (Li et al, 2020b), Fe 3 O 4 /Ag nanorods (Li et al, 2020e), Au/Ni/Au ( Figure 2C) (Jung et al, 2018a), Au/Fe/Au multiblock nanorods (Jung et al, 2018b), and Au dimer on magnetic nanoplate hybrid structure ( Figure 2D) (Feng et al, 2019). One advantage of magnetic orientational control is the selective excitation of the two modes of Au nanorods.…”

Coupling morphological and magnetic anisotropy for assembling tetragonal colloidal crystals

“…The spatial configuration of matter and surface ligands in colloidal crystals, which control many physical and chemical properties, can be tailored in a nanometer precision by adjusting the subunit composites, sizes, shapes, and crystal structures (5)(6)(7)(8). Therefore, the colloidal assembly has become an effective strategy in producing many functional materials in photonics (9)(10)(11)(12), structural materials (13,14), robotics (15)(16)(17), and catalysis (18,19). The assembly of either spherical or highly faceted colloids is mainly dominated by entropic processes that involve depletion, hydrophobic forces, and polymer "elasticity," producing densely packed colloidal crystals with close surface contact (3,20,21).…”