For simplicity, we investigate origami structures through the most prominent kingdoms of life, namely, Animalia and Plantae, as well as other worthy nature inspirations, in order to explore the rich designs of origami engineering structures that have been inspired by nature. Each fold and crease bears witness to the ingenious perfection that evolution has brought about in organisms over millennia. In the following pages, we find not just the beauty of biologically inspired origami but also its practical applications in engineering and design. From the streamlined contours of animal anatomy to the fractal geometries of plant leaves, including both larger macrostructures and tiny nanostructures, we uncover inspiration for engineering innovation.
3.1. Animalia-Inspired Origami
In this section, we discuss how origami engineering has been inspired by the incredibly unique organisms seen in nature. We review the biomechanics and structural adaptations of crawling species, nimble insects, marine creatures, and other members of the Animalia kingdom. Through meticulous observation and in-depth study, it has been possible to identify the design principles that allow animals to move freely in various settings, manipulate things, and display seemingly unattainable levels of power and agility. This creates opportunities for creative technical solutions that mimic the effectiveness and grace of natural designs.
Interesting results can be obtained by exploring the overlap between different fields; Matthew Gardiner [
16] talked about the intersection of origami and robotics, called oribotics, and provided a number of subjects to build it up. Important subjects include oribotic origami pattern design, the incorporation of biomimetic crab joints into exoskeletons, and metaphorical depictions of the biological interaction of foraging bees, all of which encourage admiration for folded forms of nature and help to incorporate them into man-made settings.
3.1.1. Crawling Robots
The construction of an origami-based robot that moves in a similar way to an earthworm was shown by Fang et al. [
17]. The robot is inspired by the softness of origami and the morphology of earthworms. The robot’s mobility mimics that of a worm by employing origami ball constructions with different actuation methods, similar to how earthworms move. In this way, the earthworm body segments’ bidirectional deformations are replicated. Experiments demonstrated that the origami ball’s compliance and multi-stability are advantageous for the construction of robots. Three distinct robot segments were designed utilizing various actuators and an origami ball, while a six-segmented robot prototype was built using a DC motor-driven segment. The created prototype exhibited good locomotion, with various modes and speeds controlled by a gait generator modeled after earthworm movement. Future origami-based robot development appears to have a bright future thanks to its low cost of production, customizability, and scalability (
Figure 6) [
17].
Jin et al. [
18] designed an origami robot inspired by worm biomechanics that uses a paper-knitting method to perform complex movements and tasks. The backbone of the robot can flex and deform under tension, compression, and bending, and it is propelled by magnetic forces and torques. The robot can clear hurdles, scale walls, and move freight, as shown in their experiment’s numerical simulations and theoretical analysis. The robot is low-cost, lightweight, and flexible, and can be used in various environments. Ze et al. [
19] presented a “small-scale origami crawler” based on a Kresling dipole inspired by the crawling motion of earthworms. This magnetically operated crawler is proposed for biomedical application, and consists of a four-unit Kresling origami assembly that can navigate in restricted spaces. While Ze et al. aimed for smaller versions of their Kresling crawler, it would also be interesting consideration to consider a larger scale and its implications. Meanwhile, Wei et al. [
20] addressed the limitations of soft robotics by increasing the bending angle, elongation rate, and movement flexibility of a tubiform origami structure inspired by annelid somite joints. They used a Ni–Ti memory alloy wire for actuation by eliminating negative Poisson ratio and removing material, which enabled efficient and flexible extension (
Figure 7) [
20].
A biomimetic origami prototype robot in the shape of a caterpillar was presented by Cat et al. [
21], consistsing of a biomimetic origami robot that can move independently in tight spaces. This robot is highly adaptable, with a the creep pattern that can be controlled to enhance mobility. It can perform compression, deformation, six modes of locomotion, and various motion types with good stability, tunable elasticity, and adaptive locomotion. This adaptability makes the robot particularly suitable for complex environments and precise tasks. Similarly, Xu et al. [
22] expanded the field of Kresling origami by mimicking a worm, with motion originating through vacuum chambers that are capable of achieving unidirectional displacement under tight conditions.
Similarly, the Origami Robotic Snake (OriSnake) by Luo et al. [
23] is a soft robotic platform for search-and-rescue applications. Unlike traditional snake robots that use links and joints, OriSnake uses tubular origami continuous sectors driven by inner cords and electric mechanisms for distributed actuation, sensing, and control. Modeled after real snake movements, OriSnake’s lateral undulation and sidewinding gait allow it to move in 3D spaces. Experimental results show that OriSnake can move at 40.5 mm/s in lateral undulation gait and 35 mm/s in sidewinding gait. Its light weight, low cost, and origami-based flexibility enable it to navigate through narrow spaces and 3D terrain (
Figure 8) [
23]. Zuo et al. [
24] presented another snake-shaped robot; inspired by waterbomb origami concepts, their design includes modular joints with flexible hinges and soft rubber material, and can bend and deform through lasso constructions. Kinematics modeling and control system implementation allow it to move on various surfaces.
Many different authors from various backgrounds have presented aligned ideas with a range of similarities; the majority of crawlers we reviewed use the waterbomb pattern as a building block for robots, as this pattern provides the full range of desired motions while distributing the stress loads towards the confined spaces required for crawler robots. On the other hand, the Kresling and Yoshimura patterns are used only for extremely specialized areas, in particular those requiring empty inner cavity spaces and particular ranges of motion, respectively. Ultimately, crawling robots need further improvement; fully untethered capabilities and high range of motion are among the development areas where researchers are aiming to find solutions.
3.1.2. Dual Morphing
Mintchev et al. [
25] described a creative kind of origami construction modeled after insect wings. This construction exemplifies dual stiffness by fusing resilient and soft materials with the supporting strength of rigid materials and the potential to change shape. The origami structure serves as the frame for a gripper quadcopter, which operates in an aerodynamic environment and has the ability to change shape to prevent damage in the event of a collision. This property makes it possible to integrate electronic circuitry and soft actuators into the origami to provide proprioception and controlled actuation. This design opens up multipurpose shape-shifting structures for consumer applications as well as robotics and aerospace, such as morphing drone wings with distributed sensors to improve flight stability.
Intricate constructions such as those found in insect wings have inspired a number of innovative structural designs. Baek et al. [
26] examined the formation of compliant origami modules with strong “self-locking” capabilities that were modeled after the veins in ladybird beetle wings. These structures, which stray from traditional origami design, are able to support high loads and can be stored or deployed. This research examines how compliant origami can be used to improve the energy storage of a jumping robot’s mechanism and create a glider module that can be deployed for a “multimodal robot”. Additionally, Baek reviewed the use of compliant origami in intricate origami constructions with an emphasis on robotic systems applications. (
Figure 9) [
26]. However, one cause for concern that has been brought into discussion involves the activation of the gliding mechanism, as the entire system can be compromised if it fails.
The earwig wing folding mechanism has features that cannot be replicated by traditional origami; according to Faber et al. [
27], these are rapid self-folding movements using a characteristic Resilin material, a wing pattern with angled and curved creases, and stability mechanisms that keep the wings latched during flight. Inspired by this biological mechanism, the authors proposed a spring origami model that expands the scope of traditional origami (
Figure 10) [
27]. Similarly inspired by earwig wings, Rojas et al. [
28] proposed a technique using double-layered creases that contract asymmetrically in response to external input. They fabricated biomimetic earwig wings inspired by Miura’s fold and developed an analytical model to predict folding angles. They demonstrated their method on various membrane-based structures such as solar arrays through experimentation and finite element analysis, and discussed the possibility of creating self-locking mechanisms to stiffen biologically inspired origami structures. While Rojas et al. approached the challenge of mimicking an earwig’s wing and came up with relevant contributions regarding material selection and behavior, a gliding test is encouraged in order to enhance this contribution.
Saito et al. [
29] provided guidelines for biomimicry and proposed a method to create deployable structures inspired by earwig wing folding. They used X-ray microcomputed tomography to reconstruct the geometrical rules of earwig wing crease patterns. This method was applied to design artificial deployable structures for mechanical engineering, aerospace, architecture, and everyday objects. While Faber et al. [
27] and Rojas et al. [
28] focused on the mechanical and adaptive aspects of earwig folding, Saito et al. [
29] focused on the geometrical reconstruction and practical implementation of these principles in various fields and showed a more comprehensive range of applications for biomimetic deployable structures. Both approaches face unforeseen challenges and need additional research before reconstructing a synthetic earwig-inspired wing becomes possible.
Biological inspiration may be found in every living being; Kim et al. [
30] examined the pelican eel’s unusual “dual-mode” morphing, which increases the chance of engulfing prey by first unfolding and then inflating the mouth. Similar to the earwig wing, this type of morphing is not achievable with traditional single-mode morphing mechanisms. The authors suggested dual-morphing structures that consider origami unfolding and skin stretching due to fluid pressure. They demonstrated quasi-sequential dual-morphing responses in artificial organisms for adaptive grabbing, crawling, and submerged mobility using only stretchable origami pieces. The fundamental building block of this new paradigm for constructing adaptive “shape-morphing systems” in soft robotics, engineering structures, and active metamaterials is the stretching of Miura and Yoshimura origami unit cells. (
Figure 11) [
30]. The double-folding nature of Miura’s fold and the stiffness required to both remain straight and stretch provided by Yoshimura designs provides solutions based on origami patterns to address the challenges of deploying pelican eel-inspired biomimicry.
3.1.3. Inflatable Motion
Clarice et al. [
31] presented PuffBot, an inflatable origami robot with movement and inflationary properties are modeled after those of a pufferfish. PuffBot uses a chemical process to inflate an internal balloon beneath its origami exoskeleton, which enables it to move in water through surge, yaw, and heave motion. Utilizing a microcontroller, a solenoid valve controls the inflation process, which can be managed remotely. Tests carried out for design verification demonstrated that PuffBot can successfully mimic a pufferfish. In addition to the conducted research, it would be ideal to test the reaction of this inflatable robot in different water bodies as well as its fatigue life when exposed to prolonged submersion.
Similarly, marine biology and origami have inspired soft robotic jellyfish. Hu et al. [
32] used mathematical modeling and hydrodynamic simulation to select an origami polyhedra model that mimics the jet propulsion of prolate medusae. Their rope-motor-driven robotic jellyfish prototype can swim effectively, showing the system’s scalability, simplicity of fabrication, and structural efficiency (
Figure 12) [
32]. Additionally, in 2024 [
33] Hu and Li expanded the capabilities of a “Rhombic Dodecahedron” to provide an inflatable origami concept. The goal was to present a compact and modular design with adaptability to varying environmental conditions. Qiu et al. [
34] designed a biomimetic process for jellyfish origami using waterbomb tessellations. They explored geometric models and kinematic equations of the Biomimetic Jellyfish Origami Mechanism (BJOM) and optimized it for material usage, fineness ratio, and volume ratio. The optimized BJOM prototype showed better volume and fineness ratio and was able to mimic the flexible propulsion modes of natural jellyfish movement. This design could have many applications in underwater vehicles due to its effective propulsion mechanism and environmental adaptability (
Figure 13) [
34]. Though inspired by different biological systems and applications, both of these papers show the potential of biomimicry and origami in developing new robotic systems. The origami patterns selected by the authors grant these robots the ability to perform required functions without exerting unbearable stress on the structures, ideally while also mimicking biological organisms.
3.1.4. Mechanical Transitions
Daynes et al. [
35] introduced a structural idea modeled after adaptable morphing cells. A regulated bistable mechanism changes the configuration from flat to textured. Based on the concepts of kirigami, it uses silicone rubber cells strengthened by locally reinforced regions. Pneumatic actuation is used to fold or unfold the cells, while structural bistability ensures that the shape is maintained without the need for mechanisms or prolonged actuation. Finite element evaluations regarding shape and stability during actuation and a mathematical quantification of surface roughness were conducted. The authors emphasized the significance of angular rotation with respect to the deployment angle (
Figure 14) [
35]. Additional ways to improve this research could involve providing alternatives for non-flat surfaces and verifying their outcomes.
The shrimp origami pattern presented by Liu et al. [
36] allows for the creation of programmable metastable phases through mechanical phase transitions. The two-dimensional units that make up the shrimp pattern can be tessellated in either homogeneous or heterogeneous local geometries, making it possible to design intricate energy landscapes inside the metamaterial. As a result, the metamaterial can change its mechanical characteristics and structure, which is useful for applications such as energy storage systems, reconfigurable acoustic waveguides, microelectromechanical systems, and reprogrammable materials of various scales (
Figure 15) [
36].
The biomimetic origami robot called Pillbot, developed by Zhang et al. [
37], is based on the movement of pill bugs. This robot has three bionic elements: bionic pereiopods for movement in harsh conditions, soft internal muscles for functionality, and a flexible origami exoskeleton to reduce friction. The paper shows how soft robotics can use nature-inspired origami concepts to make robots more durable and usable, providing a practical example of biomimetic design in robotics. Its flat-bed origami design allows the structure to deploy, and its dynamic characteristics provide an example of how origami can impact engineering. Similarly, Baruah et al. [
38] drew inspiration from the biomechanics of pill bugs to propose new engineering structures. Their research involved using origami-inspired designs for adaptive civil engineering applications, for which they analyzed the shape-changing properties of pill bugs. They compared a computer vision method applied to a 3D printed model with a dynamic relaxation technique for quasi-static form-finding of the origami pill bug structure. Experimental validation showed the efficiency of the dynamic relaxation module. In contrast, computer vision-based tracking showed the kinematic properties and dynamic behavior of the structure during rolling (
Figure 16) [
38]. These papers show the possibilities of pill bug-inspired origami in different fields: Zhang et al. [
37] focused on applications in robotics, in particular integrating bionic elements to provide movement and durability in various conditions; in contrast Baruah et al. [
38] explored the possibilities in civil engineering, using advanced analysis to understand and replicate the shape-changing properties of pill bugs for adaptive structures. Although they focus on different applications, both papers show the versatility and innovation of biomimetic origami in engineering and robotics.
Kamrava et al. [
39] designed a mechanical string inspired by origami that can fold and position itself precisely and in specific forms with kinetic and kinematic motion based on programming. This system is actuated mechanically along a single line and has one degree of freedom, allowing it to be controlled from one end while keeping the exact position along its length. Applications include a biomimetic hand and a robotic gripper, both of which require high dexterity and sensitivity. The design is scalable across different length scales, making it suitable for scaled applications (
Figure 17) [
39]. However, it one cause for concern is how the gripper yields as the scale increases or decreases. In contrast, Green et al. [
40] used biomimicry in regenerative ophthalmology to create biomaterials for treating blindness and visual impairment. By mimicking extracellular matrix features such as topography, biomaterials can promote cell organization and tissue regeneration. Their study presented two cases: the regrowth of ocular epithelium on nanostructured insect wing surfaces, and origami-inspired membranes for ocular cell transplantation. These biomimetic materials are designed to replicate natural basement membranes to solve regenerative ophthalmology challenges by providing clinically relevant solutions through advanced materials chemistry and self-deploying membranes. While tissue regeneration is a novel topic and further research is required, defining structures that could mimic the building blocks at a cellular level can open future research opportunities in the field. Similarly, Song’s work [
41] used biomimetic design to create a compliant structural skin for biomimetic robots inspired by natural epithelium structures. The skin comprises rigid iron rings between a soft polyester fabric, and can stretch and bend with minimal resistance or energy consumption. Experimental results showed that the skin works underwater and aerially, has low cost, is easy to fabricate, and can be applied to various biologically-inspired structures such as worms, snakes, and fish robots. The flexibility and folding ratio can be adjusted by changing the number of rings, making it suitable for various robotic designs.
Kamrava et al. [
39] and Song [
41] both used biomimetic structures in robotics; Kamrava focused on mechanical actuation and control for precise movement, while Song focused on compliant materials for flexibility and adaptability in different environments. Green et al. [
40] used biomimicry in medical biomaterials, specifically in regenerative ophthalmology. Each of these studies shows that biomimetic designs can be achieved and applied to different challenges, as different origami patterns behave in multiple predictable paths when the pattern tessellation is defined.
Seo et al. [
42] used a fabric-integrated actuation module with an origami design to increase the strength and supporting force of soft pneumatic actuators. In contrast to conventional paper-based origami structures, this module features a stiff fabric origami pattern that uses less air and requires more effort. Specifically, the actuation module for the Yoshimura pattern was mathematically analyzed to adjust all design parameters in order to support the upper human limb. The module was experimentally validated lifting up to 7.5 kg at a pressure of 50 kPa or less, which is suitable for helping a person move their arm while holding a tool. The module was intended as the basis for a wearable system that would convert natural arm motion for overhead jobs (
Figure 18) [
42]. While the research was conducted and inspired by human limbs, it could also be tested beyond these limits to enhance human capabilities through robotics engineering that could take advantage of optimal origami design.
3.1.5. Grippers
Nguyen et al. [
43] provided an extensive overview of bioinspired grippers with parameters related to operating principles, materials, actuation, design complexity, fabrication techniques, and applications. Using biologically inspired designs, their review covered advancements in gripper technology, including both unyielding and soft gripper systems. The latter are inspired by living entities which work well in delicate and complex activities, while the former mimic the limbs of humans and animals to increase productivity in industrial automation and manipulation processes. Through their synergistic influence, biology and robotics have combined to create stunning gripper designs with applications across various industries. For example, Liu et al. [
44] presented a new origami chomper-based flexible gripper design combining origami and a newly developed nonlinear topology optimization (NTO) method. The gripper performed well in various experiments, including gripping range under the same load, maximum gripping ratio, adaptability to different object textures and shapes, and scalability from millimeters to decimeters. By optimizing the origami structure with the NTO method, their gripper showed better gripping effectiveness and adaptability to irregular objects. In addition, their study demonstrates the computational efficiency and design refinement of the NTO method and its application in designing high-performance flexible grippers to handle objects with different stiffness, shape, size, and orientation. In summary, this work provides a foundation for designing new flexible grippers by combining simple origami with advanced optimization techniques to improve gripping and versatility across scales. Irrespective of the particular origami pattern or what different authors have achieved through their use, it is notable that the versatility of origami-inspired structures is inspiring developments in a wide variety of engineering fields.
3.1.6. Other Applications
Zhang et al. [
45] presented a novel approach to the production of reprocessable and programmable elastomeric sheets that are selectively altered by solvent-containing active particles and laser ablation. For soft ferromagnetic origami robots, this opens up a variety of functionalities including actuation, sensing, and adaptive coloration. The suggested method provides versatility for robot development and permits the deletion and reprocessing of functionality. Numerous demonstrations show how this construction technique is broadly applicable, ranging from color-changing robots to warning systems and swimming robots inspired by nature’s chameleons and frogs.
Shark teeth have inspired structures in engineering, as shown by Guo et al. [
46], who presented a microneedle patch for smart wound care using advanced materials and biomimetic structures from shark teeth. The patch is made by laser engraving origami and can control drug release and stable adhesion for chronic wound treatment. It also has MXene electronics and microfluidic tubes for biochemical analysis and motion tracking. In vivo tests showed that the patch can promote wound healing in diabetic rats, proving that this bio-inspired design can be applied in the medical field. Although this research was targeted toward wound healing, one cause for concern is how paper origami would react when exposed to environmental conditions commonly present on the skin.
Drawing inspiration from origami-driven devices, Li et al. [
47] proposed the architecture of a new fluid-driven origami-inspired artificial muscle (FOAM) that can operate in fluid media by combining a flexible skin and a compressible skeleton. FOAMs can be combined to create multi-DOF systems and produce various motions along multiple axes, including bending, torsion, and contraction. Their ability to function at negative fluid pressures reduces the safety risks relating to fluidic artificial muscles. According to experimental findings, FOAMs can create enormous stresses, contract more than 90% of their starting length, and show peak power densities several times higher than those of natural muscle. FOAMs hold great potential for various applications.
3.2. Plantae-Inspired Origami
This section examines the role that complex plant forms and growth patterns have in origami design. As proposed by Dutta et al. [
48], there are several degrees of biomimicry, which frequently draw inspiration from specific groups of biological forms depending on their scope and application. Plants exhibit a wide range of structural adaptations for the best use of resources and interactions with the environment, from the graceful unfolding of leaves to the complex blooming flowers. By delving deeper into the biomechanics and developmental processes of plants, design principles that highlight their influences are revealed. Inspired by the kingdom Plantae, these biomimetic origami constructions pave the way for new developments in engineering structures.
Jiao et al. [
49] researched origami metamaterials by using a binary digital abstraction, which replicates the growing process of lilies and pushes floriography into the fourth spatiotemporal dimension. The floriography integrates data analysis across time with knowledge from biomimicry, opening up new possibilities for bioinspired intelligent tools and systems. Using theoretical modeling, numerical simulations, and experimental testing, the origami metamaterials’ bistable mechanical response was analyzed, showing its tunability and customizability. The bouquets’ capacity to save and send numbers and letters converted using the American Standard Code for Information Interchange (ASCII) is the most compelling evidence of their information functioning, implying that they are more than just mechanical structures. The selected crease patterns and bistable behavior allow predictable outcomes for such interpretations.
Tang et al. [
50] demonstrated how crease patterns can be designed for triangular deployable membranes for space projects via biomimetic folding. Several crease designs, including leaf-in, leaf-out, and orthogonal patterns, were developed and evaluated utilizing performance metrics, including deployment efficiency and linear dimension ratio. These designs were based on biomimetic folding principles. To comprehend how variables influencing folding behavior and deployment efficiency could impact the creases, a parametric study was conducted to determine the most suitable crease patterns and specifications for the triangle deployable membrane used in space missions (
Figure 19) [
50].
Wong et al. [
51] presented a technique for directing large-scale reconfiguration in response to specific water stimuli in soft materials, inspired by the folding of the leaflets in
Mimosa pudica. Utilizing a Janus bilayer, the system effectively transforms surface energy into kinetic and elastic energies for many-centimeter-scale self-assembly. This mechanism generates exceptional flow rates and velocities while overcoming the drawbacks of previous wicking-based systems. A regime of Mimosa origami with infinite length scaling has considerable potential for applications in biosensors, microfluidics, and water purification. System-able reversible self-assembly makes this method exceedingly adaptable and relevant to various functions in stimuli-responsive matter, artificial muscles, sensors, and other power-independent devices. It also permits the unfolding and regaining of original properties (
Figure 20) [
51]. While the research to date has been conducted with water, further research could investigate Mimosa origami’s reaction to different fluids and analyze these results.
Yasuda et al. [
52] demonstrated an origami structure inspired by natural geometric patterns in the form of a leaf that can move like a Venus flytrap. This allows for highly adjustable, uniform, and non-uniform grasping motions. It was presented as a flexible, autonomous, and self-adaptive robotic operation, showing self-adaptive grasping motion through numerical analysis and experiments. Their research mainly focused on controlling adaptive grasping motion and snap-through behavior by tuning structural parameters, demonstrating adaptive and responsive robotic mechanisms. Notably, leaf-out origami provides researchers with autonomous and versatile grasping motions that warrant the investigation due to their unique kinematics.
Li and Wang [
53] studied fluidic origami as adaptive structures inspired by origami folding and plant movements. Their work linked Miura-folded sheets to enable autonomous shape morphing or stiffness adjustment. By filling the cells between the sheets with working fluid, their research opens up new possibilities around linking autonomous motion with internal material properties. They described the structural deformation of multifunctional origami unit cells through a model combining internal fluid volume, folding motion, and material deformation. An experimental case with a 3D printed prototype, shown in
Figure 21 [
53], demonstrated the feasibility of these implementations.
Similarly, Sun et al. [
54] presented soft actuators that respond to different solvent vapors and can move in a similar way to
Dendrobium orchids and
Bauhinia variegate. They used the finite element method to study the transient response and recovery actuation parameters and applied Principal Component Analysis (PCA) to the analyte molecules. Their actuator’s origami technique was versatile, and can be applied to grippers, walkers, and snake-like robots. The results showed high addressability and reversibility in mechanical deformation, providing a way to create intelligent actuators with complex motion for various applications (
Figure 22) [
54]. These three from Yasuda, Li, and Sun show the possibilities of combining origami with adaptive and responsive mechanisms. Yasuda et al. [
52] focused on adaptive and self-regulating motion in a leaf-like structure for robotic application, while Li and Wang [
53] demonstrated fluidic origami for autonomous shape morphing and stiffness adjustment through internal material properties. Sun et al. [
54] used solvent-responsive soft actuators for programmable complex motion and showed versatility in different actuator forms. The common challenge among these studies is to model and control the complex interactions between the material properties and the responsive behavior of the structure so as to obtain precise and reliable performance in real-world applications. Ultimately, origami structures exhibit versatile characteristics that hold the promise of new discoveries in future research.
Poppinga et al. [
55] focused on intriguing plant movements and how biomimetics might leverage them. They examined the principles of plant movement and demonstrated how they might serve as an inspiration for the creation of technical systems that move. A variety of diverse principles of plant movements are emulated by original 3D printed hygroscopic shape-changing structures, including snap-through elastic instability actuation, modular aperture architectures, scale-like bending structures, origami-like curved folding kinematic amplification, and motion actuation by edge growth-driven actuation. These intricate origami-style folding, bending, and buckling motions allow for more realistic biomimicry. For example, Sidney et al. [
56] studied shape-morphing systems motivated by nastic plant motions and self-folding origami. They presented dynamic conformations such as those of plants through the printing of “composite hydrogel structures” with swelling behavior regulated by the alignment of cellulose fibrils. In order to create the necessary shapes, such alignment patterns are designed within a theoretical framework; this could enable the production of arbitrarily complex three-dimensional morphologies through programming.
The kinematics of a leaf-out origami and its potential to provide a multitransformable structure without the need to modify the crease patterns was examined by Yasuda et al. [
57], who investigated several geometrical arrangements of origami by varying the folding and unfolding techniques. Multiple potential energy routes and distinct potential energy values were discovered during transformation when the motions were modeled using linear torsion springs along the crease lines. The origami exhibited bistability, providing snap-through mechanisms as well as being readily deformable for engineering applications, architecture, and space structures. Rigid panels and hinges can be used to take advantage of the mechanics of rigid foldability associated with leaf-out origami, resulting in stiff yet multitransformable structures. Compared to previous foldable structures, the single-degree-of-freedom architecture provides easier control, and as such exhibits potential advantages for a variety of applications.
Pan et al. [
58] introduced TransfOrigami microfluidics (TOM), modeled after the nastic movements of plants. TransfOrigami is able to change its morphology in response to external stimuli, mimicking the adaptive reactions of plants to changes in temperature, humidity, and light irradiation by fusing materials that respond to stimuli with foldable geometries. Potential applications for this transformational ability include shape-adaptive flexible electronics, environmentally adaptable photomicroreactors, and dynamic artificial vascular networks. Flexible and stable configurations between flat 2D and 3D can be achieved through origami-inspired structures; however, there is room for improvement in the 4D printing mechanisms, which currently do not support embedding required microtubes (
Figure 23) [
58].