Two-photon polymerization-based 4D printing and its applications

Magnetic materials, also known as magnetically responsive materials, belong to a subset of materials that exhibit a response or change in their properties when exposed to a magnetic field [126]. These materials have gained prominence due to their rapid, precise, and remote response in various environments [127]. A particularly intriguing application lies in magnetic microswimmers, where rotating magnetic fields induce rotational forces and torques, translating into the rotational motion of the magnetic components. Inspired by the structure of bacterial flagella, helical microswimmers are typically designed with corkscrew-like or spiral shapes. Utilizing a rotating magnetic field, magnetic microswimmers convert rotational motion into translational motion through self-helical propulsion, a phenomenon observed in low Reynolds number regimes [128]. The evolution of TPP-printed magnetic field-driven micro/nanostructures has progressed from simple helical designs to complex motion structures with flexible links and rigid segments [129], demonstrating significant potential in biomedical applications [130]. Given that many TPP-suitable materials (e.g. photoresists, hydrogels, etc) lack inherent magnetic properties, achieving magnetically responsive micro/nanostructures through TPP involves integrating light-curable soft materials with magnetic components. There are two approaches to achieving magnetically responsive micro/nanostructures through TPP incorporating magnetic materials: (1) the sequential post-processing approach: coating the magnetic material on the TPP-printed structure's surface; (2) the direct TPP printing approach: mixing magnetic nanoparticles with photoresist, and directly printing them via TPP technology.

3.1.1. Coating of magnetic materials.

Coating magnetic materials process involves depositing a magnetic material onto the desired substrate using various techniques. The magnetic layer adds an additional magnetic response to the coated surface, enhancing the performance in applications that require magnetic functionality. The process of selectively coating magnetic materials typically involves two steps: (1) utilizing TPP technology to create microstructures, and (2) depositing magnetic material selectively through physical vapor deposition (PVD). Tottori et al developed a straightforward fabrication approach for creating spiral micromachines by 3D DLW and PVD, enabling the creation of helical devices in versatile shapes [39]. The manufacturing process is outlined in figure 4(a). First, a negative-tone photoresist (such as SU-8 or IP-L) was employed with DLW to construct helical microswimmers. In the second step, the unpolymerized photoresist was removed through development. Finally, thin bilayers of Ni/Ti were deposited onto the surface of the polymer helical micromachine using electron beam evaporation. This coating not only facilitated magnetic actuation but also enhanced the biocompatibility of the surface. Similarly, Huang et al presented a deposit-based method for fabricating micro transporters [40]. As depicted in figure 4(b), utilizing SU-8 photoresist with TPP, these micromachines were fabricated horizontally. After the development, only the outer propeller was coated with Ni/Ti bilayers (300/5 nm thickness) via PVD. Meanwhile, non-actuated components were shielded by printing a sacrificial structure post-assembly. Notably, microfluidic channels and helical microswimmers were independently printed using this approach. Yasa et al employed TPP from a prepolymer solution containing PEGDA and a photoinitiator to create 3D microswimmers (figure 4(c)) [52]. After printing, the structures underwent magnetization through sequential sputter coating with nickel and gold. Subsequently, the structures were modified with thiol-modified PEG. These devices exhibit corkscrew motion when exposed to a sufficiently high input frequency from a rotating field.

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3.1.2. Photoresists with magnetic nanoparticles.

SMPs represent a class of smart materials that undergo controlled shape changes in response to external stimuli [131]. Among these, thermos-responsive SMPs exhibit a thermally induced shape memory effect (SME) when the temperature surpasses their glass transition temperature (T_g). This remarkable property facilitates controlled transformations between permanent and temporary shapes, with the ability to return to the original permanent state via temperature adjustments. The exploration of shape transformation within SMPs has ventured into complex 3D geometries with nanoscale attributes, supporting diverse applications ranging from miniaturized deployable biomedical devices to stimuli-responsive mechanical metamaterials.

An innovative breakthrough by Zhang et al introduced a novel shape memory photoresist that achieves an impressive ∼300 nm half-pitch resolution in printed features through TPP lithography [51]. Their work involved the development and characterization of an SMP photoresist based on Vero Clear, formulated by combining Vero Clear with an elastomeric resist composed of HPPA, BPA, and TPO at varying mass fractions. Figure 5(a) illustrates their approach, where submicron-scale grids were programmed atop a foundation layer. These structures, featuring vertical grids, acted as architectural color filters, selectively transmitting specific visible light wavelengths. Upon heating to elevated temperatures, the structures underwent deformation, flattening the nanostructures and eliminating coloration. Cooling them to room temperature maintained the structures in an invisible state. Reheating the structure restored the original geometry and color of the nanostructures, demonstrating 4D printing at the submicron scale.

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Furthermore, researchers have investigated the TPP-printed SMPs at the microscale. Spiegel et al devised a versatile ink system with a shape memory effect suitable for 4D printing at both the macro- and micro-scales, utilizing DLP and DLW technologies, respectively (figure 5(b)) [58]. They identified a common functional core system, comprising appropriate monomers, crosslinkers (IsobA, PEGDA 575, and TcddA), and the photoinitiator (Irg819), that exhibited an SME and was adaptable to both printing technologies. A variety of 3D structures were printed using TPP, including basic strips, frames, and more intricate designs such as infinity rings, double platform geometries, and cubic grids at the centimeter scale. These printing endeavors achieved efficient high-resolution microscale results, with a layer height of 8–20 µm. Moreover, both the large- and small-scale printed structures demonstrated a remarkable SME. Elliott et al introduced an ink composed of acrylate/methacrylate-based compounds [96]. Their ink formulation featured BMA as the first chain builder, a functionalized amine-methacrylate as the second chain builder, and synthetically converted pentaerythritol triacrylate as the crosslinker. The authors successfully demonstrated the SME in printed microstructures employing this particular material (figure 5(c)).

Hydrogels are 3D crosslinked polymer networks with softness, biocompatibility, and multifunctionality, making them highly valuable in various biomedical applications [132]. In the realm of 4D printing, the use of smart hydrogels is particularly advantageous due to their responsiveness to external stimuli such as temperature, humidity, pH, light, and solutions with varying ionic strengths or concentrations [133]. With their swelling properties, hydrogels can give rise to deformable structures capable of intricate shape changes such as bending, folding, twisting, and multiple deformations. It is noteworthy, however, that achieving complex shape transformations requires a swelling mismatch within the actuating region of the hydrogel to generate internal stress. This is because isotropic hydrogels expand uniformly, leading to structural linear expansion [134]. Moreover, in addition to the hydrogel application mentioned in section 3.1, where it serves as a matrix for magnetic materials in response to magnetic fields, this section will delve into the detailed design and fabrication of hydrogels responsive to other stimuli for TPP-based 4D printing.

Among these, pH-responsive hydrogels merit attention for their ability to undergo structural or chemical changes in response to shifts in pH levels within the surrounding environment, leading to altered swelling behaviors. This characteristic renders them suitable for TPP-based 4D printing due to their ease of preparation [103–110]. An advanced strategy for 4D microprinting was introduced by Jin et al, involving the creation of shape-morphing micromachines utilizing stimulus-responsive hydrogels [103]. The key polymerization reaction driving the printing process is depicted in figure 6(a), while the fabrication process is illustrated in figure 6(b). By controlling parameters such as the exposure dose of the femtosecond laser, crosslinking densities, stiffness, swelling/shrinking degrees, and other properties can be finely tuned. Finite-element methods were utilized to predict characterization and shape-changing behaviors (figure 6(b)) [104]. Furthermore, Chen et al demonstrated that bilayer-based microbeams crafted from pH-responsive smart materials via TPP could induce nonmonotonic bending deformations through a sequential size-dependent layer-by-layer swelling effect [105].

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Light-responsive hydrogels [112, 113], thermo-responsive hydrogels [113–116], and solvent-responsive hydrogels [117–119] are also pivotal components in two-photon 4D printing. Light-responsive hydrogels respond to light, enabling remote and precise spatial and temporal control. Deng et al devised a 4D printing methodology to create light-triggered micromachines with unique 3D shape-changing capabilities [112]. Through an investigation of carbon nanotube-doped NIPAM composite smart hydrogels, they highlighted distinct responsiveness degrees among structural units to light under a constant laser power (figure 6(c)). Additionally, they designed micropillars with a predetermined 45° bending angle, arranged them circularly, and thereby fabricated a smart microclamp device (figure 6(d)). Thermo-responsive hydrogels offer ease of operation and tunable temperature range responses. An innovative approach by Spratte et al employed pNIPAM-based microactuator systems designed with precision via DLW technology [114]. Their study comprehensively explored the shrinkage and swelling properties of these systems, placing emphasis on actuator size, design variations, and DLW parameter influence on material actuation. Figure 6(e) illustrates the thermally driven shrinkage of pNIPAM hydrogel microstructures with different architectures. Solvent-responsive hydrogels, while allowing reversible shape and size changes, can exhibit slow response times unsuitable for certain applications. Ennis and colleagues leveraged the flexibility of 2PP to develop a novel photoresist based on phenylboronic acid that responds to sugar [118]. As shown in figure 6(f), successful microstructure creation from sugar-responsive hydrogels using TPP is demonstrated, while figure 6(g) elucidates the mechanism behind hydrogel swelling.

LCEs stand out as a class of smart materials that exhibit substantial, anisotropic, and reversible shape changes in response to multiple stimuli. With their lightly crosslinked networks boasting oriented mesogenic orientation, LCEs have become a favored choice for realizing responsive structures [135]. Notably, LCEs have gained momentum in research due to their capacity to function without reliance on an aqueous environment or external loads [136]. These materials hold promise across diverse applications, including soft actuators and robots, artificial muscles, active structures, adaptive optics, and energy dissipators. Since the advent of TPP-based 4D printing technology, LCE actuators with more intricate 3D geometries, higher resolution, and an extended size range [137] have come to fruition.

Among the various stimuli, heat has emerged as a widely employed method, rendering thermos-responsive LCEs an optimal candidate for diverse applications. Del Pozo et al pioneered the development of a liquid crystalline photoresist, yielding a densely crosslinked polymer network that facilitates the creation of 4D-fabricated microactuators with predetermined shape changes (figure 7(a)) [50]. These 3D microstructures respond to temperature fluctuations by demonstrating reversible, anisotropic shape expansions and distinct polarization colors that hinge on the structure's geometry rather than the DLW–TPP parameters (figure 7(b)). Guo et al introduced a method for crafting microscale heterogeneous LCEs with controllable and uncoupled 3D structures through the assembly of microscale LCE voxel building blocks [120]. The anisotropic properties of LCEs in distinct directions enable the creation of devices with diverse physical properties, facilitated by employing 3D initial structures and director fields (figure 7(c)). Moreover, Del Pozo et al detailed the use of a supramolecular cholesteric LCE photonic photoresist to fabricate 4D photonic microactuators [121]. The integration of self-ordering smart materials with DLW–TPP facilitates the realization of dual-responsive 3D microstructures, exhibiting controlled expansion and corresponding color changes in response to variations in humidity and temperature.

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Light serves as a popular stimulus due to its precise spatial and temporal control. TPP enables the intricate design of 3D robots with nanometer-scale precision. Martella et al introduced a light-driven microhand capable of remote control or autonomous action based on optical properties (figure 7(d)) [122]. The chosen splayed alignment prompts the bending of the four orthogonal fingers upon stimulus application (figure 7(e)). Chen et al developed a direct laser printable photoresist incorporating gold nanorods to enhance mechanical properties and achieve NIR-responsive mechanical deformation [124]. Zeng et al fabricated an artificial microwalker equipped with LCE muscle (figures 7(f) and (g)) using acrylic resin (IP-Dip) for the limbs due to its high Young's modulus. The LCE muscle exhibits a fully reversible mechanical response to light, contracting by approximately 20% along the direction of the nematic LCE network [54]. Hsu et al proposed a straightforward strategy (figure 7(h) for crafting multi-photoresponsive 3D microstructures activated by different light wavelengths, leveraging an aligned LC ink formulation and dyes with orthogonal absorptions [125]. By successfully integrating five distinct dyes into the LC microstructure, they demonstrated the versatility of their approach, enabling actuation across varying wavelength ranges. The combination of different dyes allows the fabrication of multi-response LC microactuators, offering the flexibility to tailor responses as needed.

Micro/nanorobotics has recently garnered substantial attention in the field of biomedicine [130, 138, 139]. In comparison to traditional nanomaterials used in human healthcare, 4D-printed micro/nanorobots [30] offer a broad spectrum of applications, spanning from precise cargo transportation [140] and controlled drug release [141] to surface functionalization [53, 85], precision surgery [142], and detoxification [143].

Magnetically propelled micro/nanorobots have ushered in new possibilities for diverse biomedical applications [127, 129]. Of particular interest are magnetic helical micromachines, renowned for their capacity to generate corkscrew motion under the influence of rotating magnetic fields. The combination of self-propelled mechanisms and controlled navigation renders them highly suitable for a multitude of environments and applications [128]. A significant advancement is the helical micromachine developed by Tottori et al, featuring a microholder and helical body capable of controlled swimming and cargo transport in a frequency magnetic field [39]. The transportation process of colloidal microparticles involves four stages: approaching, loading, transporting, and releasing (figure 8(a)). Cabanach et al created zwitterionic 3D-printed microrobots with nonimmunogenic properties to evade immune cell recognition [53]. Through functionalization with inorganic magnetic nanoparticles and surface modification for various functionalities (figure 8(b), these microrobots interact with immune cells, leading to either capture upon detection or release if not detected (figure 8(c)). Ceylan et al presented an integrated strategy for designing and fabricating a biodegradable microswimmer capable of therapeutic and diagnostic release in vitro [98]. Responsive to the pathological marker matrix metalloproteinase-2 (MMP-2), this microswimmer rapidly releases embedded cargo molecules upon detecting pathological enzyme concentrations (figure 8(d)). A theranostic application scenario for biomedical imaging post-therapeutic transfer procedures utilizing microswimmers is envisioned in figure 8(e).

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Furthermore, beyond magnetically actuated microswimmers, several other micro/nanorobots have found utility in active biomedical delivery systems. Huang et al devised wirelessly controlled microtransporters employing an Archimedes screw pumping mechanism for controlled microparticle and magnetic nanohelix transport within microfluidic channels [40]. The process of loading and releasing is succinctly depicted in figure 8(f), where the revolving screw draws fluid and particles into the capsule while the piston seals the capsule's back to trap the particles. Upon reverse actuation, the piston slides into an open state, and the ensuing reverse flow expels the trapped particles. Figure 8(g) outlines the four stages of transporting and delivering helical microstructures: (I) loading, (II) transporting, (III) releasing, and (IV) deployment. Villangca et al introduced an advanced light-triggered microrobot for cargo loading and release, employing photothermally driven convection currents [91]. Designed as a miniature container for material transportation, this microtool features an anterior opening for cargo manipulation (figure 8(h). The spherical handles enable optical selection, trapping, manipulation, and real-time reorientation. Through the traversal of a heating beam across the microtool, cargo ejection is facilitated via the perturbation of the microbubble, leading to the expulsion of fluid containing particles (figure 8(i)). Figure 8(j) illustrates the collection and release of captured particles, showcasing the potential of this novel light-driven robot in nanofluidic injection and targeted drug delivery applications.

TPP-based 4D printing technology has facilitated the creation of bioinspired microactuators that emulate the movements and functions of natural organisms to accomplish specific tasks. These intelligent actuators incorporate stimuli-responsive materials, enabling them to perform precise and controlled grasping and releasing actions. Drawing inspiration from the human hand, Martella et al developed a light-powered microhand capable of remote or autonomous operation through optical illumination [122]. This microhand selectively captures target microelements based on their unique absorption properties. Figure 9(a) illustrates the optical control that transitions the hand from an open to a closed state. This concept can be extended to object recognition based on distinct absorption spectra. Similarly, Zhang et al devised a TPP-based approach for crafting intelligent and flexible 3D microactuators using a common photopolymer material [117]. By encoding 3D microstructures with carefully designed networks, these actuators demonstrate predictable deformations in response to specific stimuli. This is achieved through meticulous control of voxel size and distribution at the nanoscale. The manipulation of microclaws for collecting and releasing target microspheres is shown in figure 9(b). Wang et al drew inspiration from the flytrap mechanism to demonstrate an asymmetric 4D-printed hydrogel microactuator with intelligent response properties [107]. By directly writing a responsive photoresist with a femtosecond laser, they fabricated a biometric microactuator. The adjustment of manufacturing parameters such as power density and scanning route yields controllable driving behavior. As depicted in figure 9(c), pH-triggered shape changes are harnessed to achieve and fine-tune the microactuator's gripping and releasing behavior for micro-objects.

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Liu et al utilized TPP-based 4D microprinting to achieve bidirectional and reversible self-assembly of microstructures driven by capillary force [92]. The engineered curvature, thickness, and smooth morphology of the fabricated microstructures enable transitions between a vertical and curved state. These microstructures exhibit three reversible states in diverse evaporating solvents: (I) a curved state, (II) distance-dependent coalescing clusters through conventional self-assembly, and (III) distance-independent random self-assemblies oriented in curving directions. The foundational concept of programmed self-assembly is illustrated through the 4D-printed micro butterfly wings in figure 9(d). Deng et al introduced a 4D printing method utilizing NIPAM-based hydrogels and asymmetric mechanical metamaterial unit cells to achieve precise and complex 3D geometry deformation of light-driven micromachines [112]. This technique enables the creation of high-performance smart micromachines without intricate shape programming and material integration. Figure 9(e) depicts a biomimetic aortic valve microstructure, demonstrating rapid and reliable light-stimulus response and control. The valve remains closed when hydrated and promptly opens upon light stimulation due to the hydrogel's photothermal conversion efficiency and thermal conductivity. Figure 9(f) indicates that the amplitude of the semilunar valve opening can be controlled by varying the power of light stimulation. These bioinspired microactuators have the potential to revolutionize various fields by offering advanced capabilities for precise and efficient manipulation and control of microscale objects and systems.

Autonomous mobile microrobots are gaining attention due to their inherent advantages, such as miniaturization, autonomous movement, high efficiency, and remote control. These microrobots demand sophisticated functionalities, including navigation, localization, path planning, and motion control, which can be realized through TPP-based 4D printing. This technology empowers the creation of intricate structures with precise control over size and shape, leading to microrobots with advanced capabilities such as self-propulsion and navigation. Moreover, the utilization of biocompatible materials renders them suitable for biomedical applications. The potential of autonomous mobile microrobots to revolutionize diverse industries by offering an efficient microscale task execution avenue is undeniable.

Biomimetic-legged locomotion serves as one strategy to achieve autonomous mobility in microrobots, drawing inspiration from natural organisms such as insects or arachnids to develop microrobots capable of walking, crawling, or jumping. These microrobots generally feature multiple legs that coordinate to generate propulsion. Inspired by inchworm crawls, Chen et al designed bionic multilegged microcrawlers with enhanced locomotion capabilities, incorporating smart microjoints (SMJs) via 4D DLW technology [105]. These microcrawlers exhibit adjustable locomotion through autonomous swelling and shrinking, as well as sequential swelling effects layer-by-layer, as illustrated in figure 10(a). Figure 10(b) shows the locomotion range versus time curves for four crawling cycles. With programmable structures and the integration of SMJ functions, the microcrawler demonstrates versatile motion types and exceptional crawling performance. Figure 10(c) illustrates the crawling steps of microcrawlers with three SMJs sequentially responding to time-dependent pH stimuli, transitioning from an acidic to an alkaline environment. Zeng et al introduced a light-propelled microscopic walker with LCE muscles crafted through DLW using acrylic resin to create limbs with high elastic moduli E [54]. This synthetic walker can autonomously move on diverse surfaces and undergo reversible shape-morphing under modulated laser beams. Its locomotion is governed by design and environmental interactions, enabling arbitrary or directional walking, rotation, and jumping (figure 10(d)).

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Modular assembly presents another avenue for achieving autonomous mobility in microrobots. This method involves integrating external modules, such as magnetic propulsion and electrostatic actuation, to achieve the desired motion. Such an approach allows for greater flexibility in designing and customizing microrobots for specific tasks and adaptability to changing environments. Hu et al engineered soft magnetic micromachines composed of interconnected microactuator networks, linking Janus microparticle-based magnetic microactuators using TPP [144]. Through magnetic field-based torques, each microactuator is positioned at an intended location and orientation and then linked with temporarily fixed counterparts via 3D-printed soft or rigid linkages. These connected 2D microactuator networks facilitate programmable 2D and 3D shape changes, as demonstrated by limbless and limbed untethered micromachine models showcasing diverse robotic gaits for surface movement. Figure 10(e) illustrates the movement of a lizard-inspired walking microrobot with rigid legs, displaying surface movement under an oscillating field. Meanwhile, the soft-legged robot exhibits programmed robotic gaits under the alternating field. Alapan et al demonstrated how shape-encoded programmed interactions between structural and motor components could dynamically assemble mobile micromachines into expected configurations [145]. By encoding dielectrophoretic interactions in the 3D geometry of each unit, they successfully assembled micromachines featuring magnetic and self-propelled motor parts. Various micromachines are hierarchically assembled through shape-encoded dielectrophoretic (DEP) interactions, with a two-stage assembly between micromachines (figure 10(f)). The second unit assembles with the first unit in the second stage due to the weak electric field beneath its ledges (figure 10(g)). Parallel assembly preserves linear displacement, whereas anti-parallel assembly yields rotating locomotion (figure 10(h)).

The emergence of transformable devices and robots introduces a category of intelligent machines that can modify both shape and function in response to varying environmental stimuli. Jin et al pioneered 4D-DLW technology utilizing phototunable stimuli-responsive hydrogels to fabricate reconfigurable micromachines with exceptional mechanical properties [103]. Unlike bilayered structures, this approach permits extensive shape transformations. Figure 11(a) illustrates diverse reconfigurable micromachines, such as microcages, microstents, and microumbrellas, demonstrating their capacity for rapid, precise, uniaxial and biaxial contraction, reversible changes, and articulated bar folding. The 4D-DLW process involves (1) integrating deformation amplification mechanisms, (2) design, (3) prediction, (4) laser writing, and (5) shape morphing. In response to environmental pH alterations, these structures can function as actuators, transitioning between open and closed positions. Inspired by modular robots and Lego-like blocks, Huang et al introduced a programmable design approach to directly construct 3D reconfigurable microstructures, enabling sophisticated shape transformations using stimuli-responsive hydrogel micro-blocks created through TPP-based 4D printing [104]. Varying crosslinked polymer networks are achieved via temporal and spatial control of direct writing. The transformer, equipped with multiple distinct deformations, can morph from a race car to a human-like robot.

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Alcântara et al introduced an inventive design and fabrication methodology for designing and fabricating hybrid micro-interlock structures, ingeniously combining TPP, mold casting, and electrodeposition processes [146]. They devised a novel cage (or helix) configuration of interconnected rods, resulting in structures with predictable behaviors. These structures are adaptable and can be reshaped through passive or preprogrammed means initiated by an external magnetic field. Figure 11(b) depicts the interlinked helical cage-rod rings that exhibit both in-plane rotation and out-of-plane tumbling motions. An aspect ratio structure with multiple magnetic elements (figure 11(c)) allows for advancing, rolling, and trajectory alteration upon manipulation of the external magnetic field. The rolling mechanism enables out-of-plane tumbling and rolling motion in silicone oil and deionized (DI) water (figure 11(d)). Similarly, in cases where the cage intersects with the bar through in-plane rotation, the structure undergoes rotation without significant net locomotion. The agility of rolling robots in maneuvering obstacles is depicted in figure 11(e), highlighting their adeptness in combining forward rolling and out-of-plane axis rotation. This innovative approach demonstrates the potential of transformable devices and robots in navigating complex and dynamic scenarios.

4D printing based on TPP technology offers remarkable precision, flexibility, and customization capabilities, positioning it as a pivotal player in the advancement of anti-counterfeiting microdevices. These microdevices are designed to safeguard products and brands from counterfeit activities through the incorporation of distinctive attributes such as specific patterns, colors, or concealed messages. Del Pozo et al devised liquid crystalline photoresist microstructures endowed with controlled deformation capabilities and distinct polarization colors for real-time identification and authentication [50]. The hexagonal arrays engineered in this study exhibited altered anisotropy upon heating within the 20 °C–220 °C range, resulting in perpendicular expansion and parallel shrinkage to the alignment direction (figure 12(a)). Figure 12(b) displays microstructures demonstrating distinct polarization colors—wooden pile structures exhibiting yellow hues and spiral disks displaying a diverse array of colors. The thermal response of the 3D woodpile and spiral disk microstructures led to variations in structure thickness and birefringence, corresponding to changes in optical path difference responsible for polarized color (figure 12(c)). These findings hold promise for the integration of these microstructures into sensing and anti-counterfeiting microdevices.

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Zhang et al introduced a method to manipulate the optical response of nanostructures by modifying the refractive index, exemplified by grids with size-tunable multi-colors designed to explore shape memory effects through customized nanoscale structure deformation [51]. Diverse colors can be achieved by adjusting the printing parameters. Figure 12(d) shows the printed color palette in its printed, compressed, and recovered states, each exhibiting distinct colors. SEM images of the original, programmed, and recovered states are illustrated in figure 12(e). As a demonstration, the authors printed artwork featuring an octopus and a mountainous landscape. The programmed print transitioned from translucent and featureless to its original state upon heating (figure 12(f)). This platform's exceptional resolution printing capabilities and remarkable reversibility offer potential applications in the creation of temperature-sensitive labels, anticounterfeiting devices, and adaptable photonic products. Moreover, TPP technology has enabled the generation of angle-insensitive coloration in biomimetic nanostructures, inspired by the blue Morpho butterfly [95]. Through the design of disordered structures, researchers achieved reduced angle dependence, setting them apart from traditional photonic crystals. The manipulation of processing parameters facilitated hue control. Given that these biomimetic structures exhibited structural colors comparable to biological and bioinspired structures in distinct liquid environments [147] or demonstrated heightened selectivity in vapor response [148], this technology provides a potential application for the development of anticounterfeiting microdevices.