Multi‐Material 3D Printing of Soft Dielectric Actuators With Optimized Electrodes

Emerging classes of soft robotics with flexible actuation, intelligent sensibility, and biomimetic functionality are driving significant advances in academic researches and commercial applications. Such new generation robotics relies heavily on important breakthroughs in soft matter engineering and flexible actuation systems. Unlike conventional rigid robots, soft robots generally have unique sporting styles and manufacturing strategies. Recently, a series of newly developed soft materials—gallium‐based liquid metals (LMs) are found to display dramatical roles in making soft machines and robotics with their unusual properties in soft robotic actuation and self‐driven field. With superior merits of both high stretchability and electroconductivity over conventional soft materials, LM is increasingly innovated as flexible sensors and actuators in constructing intelligent soft robots. Typical advances in LM enabled soft machines and robotics are summarized and interpreted, herein, with special focus on the driving principles of the LM objects, the preparation methods of LM flexible electronics for making soft robots, and the applications of LM in biomedicines and intelligent robots, together with the consideration of key challenges facing LM‐based soft robotics and its future prospects.

Continuum robots play the role of end effectors in various surgical robots and endoscopic devices. While soft continuum robots (SCRs) have proven advantages such as safety and compliance, more research and development are required to enhance their capability for specific medical scenarios. This research aims at designing a soft robot, considering the concepts of geometric and kinematic similarities. The chosen application is a semi-invasive medical application known as transesophageal echocardiography (TEE). The feasibility of fabrication of a soft endoscopic device derived from the Chorda dorsalis paragon was shown empirically by producing a three-segment pneumatic SCR. The main novelties include bioinspired design, modeling, and a navigation control strategy presented as a novel algorithm to maintain a kinematic similarity between the soft robot and the rigid counterpart. The kinematic model was derived based on the method of transformation matrices, and an algorithm based on a self-organizing map (SOM) network was developed and applied to realize kinematic similarity. The simulation results indicate that the control method forces the soft robot tip to follow the path of the rigid probe within the prescribed distance error (5 mm). The solution provides a soft robot that can surrogate and succeed the traditional rigid counterpart owing to size, workspace, and kinematics.

Soft robots are inherently compliant and adaptive, therefore they are promising candidates for interacting with humans. However robotic manipulators utilizing soft actuators are often constrained by a series of actuator performance limitations. In this work we design a novel linear soft robotic actuator with significantly improved performances over the existing products, achieving 300% deformation ratio, quasi-constant output force over a wide motion range, while maintaining passive compliance and adaptability. Moreover, the novel actuator is less prone to friction, and could be fabricated using inject molding and 3D printing, hence having high repeatability at very low cost. An analytical model was developed to characterize the actuator behavior and provide a guideline for actuator design according to performance specifications. A 6 DOF soft manipulator was designed and fabricated utilizing the novel soft actuator. The manipulator arm had a serial kinematic structure with a biomimetic wrist and was driven by 12 soft actuators mounted onto the arm links. With 1.2m workspace radius and 1kg payload, the working air pressure could be as low as 1bar. Preliminary results have shown the validity of the novel soft actuator and manipulator designs, as well as the strong potential of soft robots in human-oriented applications.

<div>The development of soft materials for various smart applications, such as in</div><div>soft robotic devices derived from elastomers, naturally occurring rubbers and polymers,</div><div>can be traced back to 1940s. Contrary to conventional robotics, soft robotic research</div><div>was primarily dedicated to reproducing and mimicking the elasticity and compliance of</div><div>biological substrates. In the last few decades, however, subsequent progress in soft</div><div>robotic devices and manipulators has been witnessed within the subcategories of</div><div>material & processing, sensor and actuators. In this chapter, a comprehensive</div><div>introduction to soft robotics engineering is highlighted exclusively from the perspective</div><div>of materials development. Soft material prototypes are eventually exploited towards</div><div>designing biomimetic prosthetic devices with sensing capabilities and soft actuating</div><div>bodies. We present an elaborate discussion on soft materials engineering, including</div><div>elastomers, polymer composites containing fillers and associated processing</div><div>methodologies. Despite high flexibility and inherent biocompatibility, conventional</div><div>soft elastomer-based (silicone and polyurethane) matrices often suffer from either poor</div><div>mechanical strength or reduced mechanical output at higher temperatures. This review</div><div>briefly summarizes and critically discusses the different types of compliant materials,</div><div>i.e. elastomers, fluids, gels and others, which are currently being employed in soft</div><div>robotics. This chapter also highlights new opportunities and paves some potential</div><div>avenues to address several challenges, particularly the ones concerning and soft robotic</div><div>materials. Moreover, utilization of soft rubber for sensors and other applications could</div><div>ameliorate the versatility of soft material applications. Therefore, challenges and future</div><div>direction in soft robotics research have to be explicitly integrated within the subdomain</div><div>of materials development and processing and, therefore, addressed in-depth in this</div><div>chapter, with an emphasis on autonomous soft robotic arms capable of stimuliresponsive</div><div>operations.</div>

SummaryA design and manufacturing method is described for creating a motor tendon–actuated soft foam robot. The method uses a castable, light, and easily compressible open-cell polyurethane foam, producing a structure capable of large (~70% strain) deformations while requiring low torques to operate (<0.2 N·m). The soft robot can change shape, by compressing and folding, allowing for complex locomotion with only two actuators. Achievable motions include forward locomotion at 13 mm/s (4.3% of body length per second), turning at 9◦/s, and end-over-end flipping. Hard components, such as motors, are loosely sutured into cavities after molding. This reduces unwanted stiffening of the soft body. This work is the first demonstration of a soft open-cell foam robot locomoting with motor tendon actuators. The manufacturing method is rapid (~30 min per mold), inexpensive (under $3 per robot for the structural foam), and flexible, and will allow a variety of soft foam robotic devices to be produced.

Conventional robots are constructed with rigid parts and materials, restricting their ability to deform freely and adapt to the external environment. Performing tasks such as handling delicate materials and navigating narrow pathways is challenging for these typical robots made of stiff materials. However, there is a growing demand for such functions in various industries. Recent advances in soft robotics have garnered considerable attention as solutions to these challenges. Soft robotic systems in various forms present a systematic solution for performing unique tasks. The goal of soft robotics research is to develop advanced technologies, incorporating innovative robotic mechanisms based on soft materials and structures to enhance adaptability. Soft robots find broad applications in diverse fields, including industry, healthcare, and field exploration. Soft component technology plays a crucial role in configuring soft robots. Soft actuators introduce new types of motion and operation mechanisms, while soft sensors measure the deformation of the actuators with a tiny stiffness change. These advancements in soft actuators and sensors encourage researchers to explore new robotic designs and applications. Additionally, the component technology enables the integration of soft and typical robots into hybrid B Youngsu Cha

A systematic trend analysis of 3D printing techniques used in specific soft robotic elements

Soft robotics is a fast growing field of engineering where there are significant opportunities to realize new forms of actuation and sensing. However, there is also a challenge to translate some of the lab-based developments into a robust industrial manufacturing process. Linked to this is also the opportunity to create new forms of functionality in soft robotic devices by employing a flexible, digital manufacturing process for their creation. Overcoming these hurdles, and unlocking the possibilities for greater functionality, is likely to be a key enabler for wider applications and adoption of soft robotics in practical applications. We present a system of computer-controlled Aerosol Jet Printing that will enable complex soft robotic structures to be manufactured. The process is demonstrated through the deposition of a carbon-based conductive ink on to elastomeric substrates for high resolution, conformal and multilayer patterning. Functional demonstrators, in the form of a dielectric elastomer actuator and strain sensor, are produced to showcase the potential of the technique.

In the contemporary era, novel manufacturing technologies like additive manufacturing (AM) have revolutionized the different engineering sectors including biomedical, aerospace, electronics, etc. Four-dimensional (4D) printing aka AM of smart materials is gaining popularity among the scientific community, which has the excellent ability to make soft structures such as soft robots, actuators, and grippers. These soft structures are developed by applying various stimuli such as pH, temperature, magnetic field, and many combinations onto soft materials. Stimuli in 3D printing permit various shape-morphing behaviors such as bending, twisting, folding, swelling, rolling, shrinking, origami, or locomotion. A wide variety of soft magnetic structures can be fabricated through the incorporation of soft or hard magnetic particles into soft materials resulting in magneto-active soft materials (MASMs). With this integration, magneto-thermal coupling actuation allows diverse magneto-deformations, facilitating the development of personalized devices that are capable of enhanced deformation. In this review, guidelines are provided on the 3D printing for MASMs such as magneto-active polymers (MAPs), magneto-active composites, and magneto-active hydrogels (MAHs) on the booming development of various smart and flexible devices such as soft robots, wearable electronics, and biomimetic devices. Moreover, 3D-printed soft robotics have an outstanding capacity to adapt to complicated situations for many advanced actuating applications. Finally, some current challenges and emerging areas in this exciting technology have been proposed. Lastly, it is anticipated that technological advancements in developing smart and intelligent magneto-active structures will have a significant impact on the design of real-world applications.

Vertebrate animals benefit from a combination of rigidity for structural support and softness for adaptation. Similarly, integrating rigidity and softness can enhance the versatility of soft robotics. However, the challenges associated with creating durable bonding interfaces between soft and rigid materials have limited the development of hybrid robots. Existing solutions require specialized machinery, such as polyjet 3D printers, which are not commonly available. In response to these challenges, we have developed a 3D printing technique that can be used with almost all commercially available FDM printers. This technique leverages the common issue of underextrusion to create a strong bond between soft and rigid materials. Underextrusion generates a porous structure, similar to fibrous connective tissues, that provides a robust interface with the rigid part through layer fusion, while the porosity enables interlocking with the soft material. Our experiments demonstrated that this method outperforms conventional adhesives commonly used in soft robotics, achieving nearly 200% of the bonding strength in both lap shear and peeling tests. Additionally, we investigated how different porosity levels affect bonding strength. We tested the technique under pressure scenarios critical to soft and hybrid robots and achieved three times more pressure than the current adhesion solution. Finally, we fabricated various hybrid robots using this technique to demonstrate the wide range of capabilities this approach and hybridity can bring to soft robotics.

Today's use of large-scale industrial robots is enabling extraordinary achievement on the assembly line, but these robots remain isolated from the humans on the factory floor because they are very powerful, and thus dangerous to be around. In contrast, the soft robotics research community has proposed soft robots that are safe for human environments. The current state of the art enables the creation of small-scale soft robotic devices. In this article we address the gap between small-scale soft robots and the need for human-sized safe robots by introducing a new soft robotic module and multiple human-scale robot configurations based on this module. We tackle large-scale soft robots by presenting a modular and reconfigurable soft robotic platform that can be used to build fully functional and untethered meter-scale soft robots. These findings indicate that a new wave of human-scale soft robots can be an alternative to classic rigid-bodied robots in tasks and environments where humans and machines can work side by side with capabilities that include, but are not limited to, autonomous legged locomotion and grasping.

Fabrication and assembly of flexible sensors and soft actuators play important roles in improving the performance of wearable electronics and soft robots. Traditional manufacturing techniques have limitations in controlling the geometry and architecture of many soft actuation and sensing systems, which compromise their performance as well as applications. With the emergence of 3D printing, directly transforming 3D models into real objects becomes possible. In particular, vat photopolymerization techniques, represented by stereolithography, are capable of printing all‐in‐one and lab‐on‐a‐chip devices with fast speed and high accuracy. Novel polymer formulations, including functional resins, hydrogels, elastomers, polymer blends, composites, and biological materials, have been developed for vat photopolymerization 3D printing to produce highly stable architectures, which prompts a remarkable revolution in mechanics and materials for soft electronics. This review looks into the recent developments of vat photopolymerization 3D printing technology for lightweight engineering, personalized electronics, and soft robots.

More than 130,000 people have strokes each year in the United States [1]. Of these victims, 76% are left with disabilities that cost the nation over $54 billion in lost work and medical fees. One prominent disability is upper extremity hemiplegia, which occurs among approximately 50% of stroke sufferers [2]. Robotic technology has the potential to provide an automated platform for controlled rehabilitation and assisted, task-oriented therapy. Several systems have been designed to assist in patient articulation of an impaired hand using rigid robotic components. While these products have been successful in articulating the pure bending motions of the four fingers, the limited capabilities of rigid technologies fail to reproduce the complicated motion path [5] of the thumb during opposition grasp (see Figure 1). This is the most important articulation for normal hand function and specifically for picking up everyday objects. To date, robotic systems for thumb rehabilitation have not been widely investigated [3] apart from some recent work [4] that used a multi-joint rigid robot.

This study presents a novel rolled self-sensing artificial muscle that integrates shape memory alloy actuators and interdigitated capacitive sensors within a monolithic polydimethylsiloxane matrix. An innovative 3D printing-based fabrication process is introduced for the co-design of actuator and sensor, allowing for the measurement of deformation during actuation. Experimental tests demonstrate the high signal stability and repeatability of the sensors, with gauge factor up to 0.76 and hysteresis lower than 0.013 pF. The actuators achieve peak forces of 12 N, approximately 100 times their self-weight, and displacements of 2.5 mm, corresponding to 3% strain. Actuation time ranges between 85–90 s and is primarily dependent on thermal effects. The dynamic characterization of the self-sensing artificial muscle incorporates both electromechanical and thermal effects, with a temperature compensation term introduced to correct for temperature-induced capacitance variations during actuation. As a proof of concept, a soft robot is developed, realized with three rolled self-sensing artificial muscles arranged in a parallel configuration. A kinematic model is derived to describe the relationship between the measured displacements of the artificial muscles in the actuation space and the three degrees of freedom pose (roll, pitch, and vertical displacement) in the workspace. The findings highlight the effectiveness of the proposed design and fabrication approach for achieving compact, integrated actuation and sensing in a soft robotic device. The proposed rolled, self-sensing artificial muscle is fabricated by integrating shape-memory alloy actuators and interdigitated capacitive sensors within a monolithic polydimethylsiloxane matrix. To validate the design and fabrication process, a 3-DOF soft robot is constructed that uses three self-sensing actuators arranged in a parallel configuration. • A novel rolled self-sensing artificial muscle is proposed which is realized by integrating shape memory alloy actuators and interdigitated capacitive sensors within a monolithic polydimethylsiloxane matrix. • A novel dynamic characterization of the self-sensing actuator incorporates both electromechanical and thermal effects, with a temperature compensation term introduced to correct for temperature-induced capacitance variations during actuation. • A proof of concept of a soft robot, actuated by three rolled self-sensing artificial muscles arranged in a parallel configuration, validates the proposed design and fabrication.

Over the past two decades, researchers have advanced and employed integrated microfluidic circuitry to enable a wide range of chemical and biological ‘lab-on-a-chip’ capabilities. Yet in recent years, a wholly different field, soft robotics, has begun harnessing microfluidic circuitry as a promising means to enhance soft robot autonomy. Unfortunately, key challenges associated with not only the fabrication of microfluidic circuitry, but also its integration with soft robotic systems represent critical barriers to progress. To overcome such issues, here we present a strategy that leverages ‘in situ direct laser writing (isDLW)’—a submicron-scale additive manufacturing (or ‘three-dimensional (3D) printing’) approach developed previously by our group—to fabricate microfluidic circuit elements and soft microrobotic actuators directly inside of enclosed microchannels. In addition, we introduce ‘normally closed’ microfluidic transistors that comprise free-floating sealing discs designed to block source-to-drain fluid flow until the application of a target gate pressure. As an exemplar, we printed microfluidic transistors with distinct gate activation properties as well as identical soft microgrippers downstream of each drain within 40 µm-tall microchannels. Experimental results for a source pressure of 100 kPa revealed that microgripper deformation was prevented in the absence of a gate input; however, increasing the gate pressure to 300 kPa induced actuation of one set of microgrippers, while a further increase to 400 kPa led to both sets of microgrippers actuating successfully. These results suggest that the presented isDLW-based strategy for manufacturing and integrating 3D microfluidic circuit elements and microrobotic end effectors could offer unique potential for emerging soft robotic applications.