Artificial-goosebump-driven microactuation

Microactuators provide controllable driving forces for precise positioning, manipulation and operation at the microscale. Development of microactuators using active materials is often hampered by their fabrication complexity and limited motion at small scales. Here we report light-fuelled artificial goosebumps to actuate passive microstructures, inspired by the natural reaction of hair bristling (piloerection) on biological skin. We use light-responsive liquid crystal elastomers as the responsive artificial skin to move three-dimensionally printed passive polymer microstructures. When exposed to a programmable femtosecond laser, the liquid crystal elastomer skin generates localized artificial goosebumps, resulting in precise actuation of the surrounding microstructures. Such microactuation can tilt micro-mirrors for the controlled manipulation of light reflection and disassemble capillary-force-induced self-assembled microstructures globally and locally. We demonstrate the potential application of the proposed microactuation system for information storage. This methodology provides precise, localized and controllable manipulation of microstructures, opening new possibilities for the development of programmable micromachines.

microhair actuated by the fs laser.By relocating the laser spot alternately between the two sides of the microactuator, we observed that the microhair deflected in the subsequent frame (10 ms later), which indicates the utilization of the fs laser empowers our microactuation system to achieve a swift response time within 10 ms.
Achieving perfectly synchronized motions among different microstructures using a single laser source can be challenging at the physical level.However, we can attain a state of quasi-synchronous actuation of the fs laser for these microactuators at the microscale, by considering the high scanning speed, reaching up to 10 5 µm/s.For example, when we generate an array of laser spots with diameters of 1 µm while scanning at a moderate speed of 10 4 µm/s, the time interval between individual spots is approximately 0.1 ms.This time difference is significantly faster (approximately two orders of magnitude) than the response time of the microstructures' actuation.We recorded the laser using a frame rate of 10 Hz, which confirmed that these laser spot arrays were positioned on the LCE skin within the 10 ms frame duration (see Supplementary Fig. 5).Consequently, these laser spots can be considered as effectively applied simultaneously to the LCE skin.
Besides, the total processing time required to open each assembled microstructure in Fig. 6 currently is approximately 0.88 seconds (Supplementary Video 11).This duration encompasses three essential steps: the time dedicated to actuating the assembly, stage movement to reach the next targeted assembly, and the automated interface finding process.Among these steps, the most time-consuming elements are the stages of moving the stage and conducting subsequent interface finding.Notably, the actual disassembly of the microstructure itself constitutes only a fraction of the overall timeframe.To expedite processing and enhance information writing efficiency, we can optimize the laser programming codes by reducing the frequency of stage movements and automated interface finding and incorporating Galvo scanning mode for the laser.The Galvo scanner integrated into the laser system plays a pivotal role in swiftly steering the laser beam across the substrate's xy-plane, thereby facilitating high-speed writing within each addressable view field.During each stage movement, followed by a single automated interface finding step, the laser traverses and rapidly actuate these assemblies within the view field at an high speed (optimized key code using Galvo scanners: "X(/Y)offset n", where 'n' represents the distance between each pixel).Consequently, a substantial number of pixels within the field of view can be disassembled concurrently.This strategic optimization eliminates the need for repetitive stage movements and automated interface finding for each individual pixel.
As a result of these measures, the processing time for each pixel has been notably reduced to approximately 0.20 seconds, significantly enhancing the efficiency of our microstructure disassembly process.

Supplementary Note 3. Controllable micro-mirrors for light steering
Our microactuation systems achieve precise manipulation of the reflective plane for light steering, catering to both subtle and large steering angles.Micro-mirrors with precise control over small steering angles are essential for high-resolution applications, such as laser-based spectroscopy and microscopy, where precise control of the reflective plane is necessary to achieve accurate measurements and observations.As shown in Extended Data Fig. 4a, the degree of tilting angle (α) of the reflection plane increases as we enhance the scanning powers or diameters of the laser spots, which amplifies the laser dosage or heating areas required for generating enlarged artificial goosebumps and higher uplifts.Our FE simulation (Fig. 5d) corroborates these results, aligning with the experimental results (Supplementary Video 6).In addition, we provide a solution for achieving large steering angles of the reflective plane by uniformly scaling down the micro-mirrors (Extended Data Figs.4b   and 4c).The micro-mirrors are miniaturized, while the generated artificial goosebump remains the same, which induces more pronounced deformations to the micro-mirrors and consequently augmenting the plane's tilt.Additionally, we can also achieve free tilting direction (0-360 o ) of the mirror plane through the quasi-synchronous actuation of laser spots (Supplementary Note 2, Supplementary Fig. 5).A single laser spot can cause the individual supporting pillars of the micro-mirror to lift up and tilt the mirror plane toward the direction of the activated pillar (Fig. 5d), while simultaneous actuation of two spots on adjacent pillars can enable the tilt direction between these two pillars (Extended Data Fig. 4d).By rationally tuning the dosage (thus obtaining different geometries of artificial goosebumps) of the two laser spots acting on any two adjacent pillars, we can realize free rotation of the mirror plane with controllable angular tilt.

Fig. 1
Mechanical properties of the LCE materials.a, Strain-stress curves of LCE films (without doping) measured along (D∥) and transverse to (D⊥) the director direction.b, Detailed strain-stress curves showing the anisotropic mechanical properties of the LCE films (without doping).c, Hysteresis loops of LCE film with a 25% dopant of 5CB at various strains.Inset shows the corresponding dissipation factors (tanδ) across different strains.d, Strain-stress curves of LCE films with varying content of 5CB doping under a 60% strain of loading-unloading test.