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Biological materials generally have better properties than engineered materials due to their intricate architecture, e.g., high strength-to-weight ratio, stiffness, toughness and adaptability. It has proven difficult to synthesize materials with biomimetic architecture. Recently, 3D printing techniques show great promise in bioinspired structural materials. In this paper, we propose an approach to fabricate composite materials with aligned steel fibers using a self-made 3D printer and characterized the mechanical properties of the prepared materials. To do so, we developed a DLP-based 3D printing process that can align short steel fibers in the resin matrix via magnetic assembly during the printing process. Using the developed process and raw materials, samples with ordered fibers were prepared. The mechanical properties of the printed materials, including the strength and friction, as well as morphology, were characterized. The results show that magnetically assisted scraper shear-induced 3D printing can realize the ordered arrangement of fibers. The tensile and compressive strength consistent with the direction of aligned fibers are higher than that of other directions. The friction performance perpendicular to the direction of aligned fibers is better than that of other directions. The mechanical and frictional properties of the composite contenting 5% fibers are better than that of 10% or 15%. This study provides a basis for the manufacture of biomimetic materials. A magnet-assisted assembly 3D print technology is developed to produce steel fiber-resin composites with ordered architecture by programming the traveling paths of a magnet. To demonstrate the feasibility of the proposed method, a helicoidal ladder structure with ordered reinforced fibers is printed. Finally, the mechanical properties of printed composite materials with various patterns of aligned fibers are characterized.

Shape memory polymers (SMPs) generally change shape from a temporary state to a permanent state, and the permanent shape is only determined by its initial form, which leads to the lack of design freedom for SMPs. In order to enrich morphing behavior and extend applications of SMPs, bioinspired design and fabrication methods need to be developed. Many biological dynamic materials enable shape changes ranging from bending, twisting to spiraling using site-specific aligned cellulose microfibers orientations. Here, we proposed an approach integrating bioinspired fiber architectures and varying 3D printing parameters into SMPs, to achieve tunable permanent shape and shape memory properties. The self-folded flower and sequentially deployed smart robotic hand have been developed to demonstrate the feasibility of our method. The proposed bioinspired SMPs, which is rarely seen in the previous reports, have intriguing fundamental properties and hold great potential for applications in soft actuators, smart textiles, wearable equipment, medical devices, and other intelligent apparatus.

Fiber is a crucial element in biological micro-structural materials. Replication of fiber-reinforced composites with analogous architectures of their natural counterparts has caused widespread academic concern. Recent researches indicate 3D printing technology has the potential to produce biomimetic structural materials. The aim of this study is to develop a process to fabricate fiber-reinforced composites with ordered yet spatially tunable fiber arrangement. Specifically, we present a method to align fibers during the 3D printing of fiber-reinforced composites. A modified slurry-based stereolithography process was developed, and the fibers in the fiber–resin mixture were aligned by Shear force produced during the spreading of slurry. We investigated the influence of relative factors on fiber orientation, and two models were used to uncover the internal mechanism. By controlling the speed and the direction of the moving blade, the patterns that fibers were arranged can be freely programmed. Therefore, we have extracted bioinspired sinusoidal and zigzag design motifs to analyze their mechanical properties compared with non-bioinspired motifs. The proposed method is relatively material agnostic, more efficient and more facile. It thus provides a promising route to fabricate fiber-reinforced composites, and has potential to be adopted in biological structures researches and industrial applications.

Currently, four-dimensional (4D) printing programming methods are mainly structure-based, which usually requires more than one material to endow products with site-specific attributes. Here, we propose a new 4D printing programming approach that enables site-specific shape-morphing behaviors in a single material by regulating the printing parameters. Specifically, a direct ink writing three-dimensional (3D) printer with the ability to change printing parameters (e.g., deposition speed) on the fly is reported. By site-specifically adjusting print speed and print path to control the local nematic arrangements of printed liquid crystal elastomers (LCEs), the shape-morphing behaviors of the LCEs can be successfully programmed. In this way, locally programmed popping-up, self-assembling, and oscillating behaviors can be designed by varying the print speed in specific regions. Snake-like curling is realized by uniformly boosting the print speed in a single line. Furthermore, two theories and an ultrasound image diagnostic apparatus are employed to reveal the mechanism behind this behavior. This work provides a feasible way to realize the gradient transition of material properties through a single material. It broadens the design space and pushes the envelope of 4D printing, which is expected to be helpful in the fabrication of soft robotics and flexible electronics.

In the natural composites, the reinforcement particles are subtly organized into complex structures in matrix, and its various microstructures endow the biomaterials with a variety of excellent mechanical behaviors. Among the various reinforcement building blocks used in biomaterials, short fibers are the most ubiquitous reinforcement elements. Unfortunately, because of the limitation of fabrication technique, replication of these fiber-reinforced biological composites can be extremely difficult in practice. In this paper, we developed a fiber assembly 3D printing process, which can manipulate the orientation of fibers during 3D printing procedure. Benefiting from this technology, the reinforcement particles were manipulated remotely and the arrangement of reinforcement particles with higher degree of freedom was achieved. Subsequently, based on the herringbone-modified helicoidal architecture of mantis shrimp, the bio-inspired composites with various microstructures were reconstructed by 3D magnetic printing. In addition, the influence of microstructure type and parameters of bio-inspired composites on the properties of composites was studied systematically, and the quantitative relationship between microstructure and properties of the composites was established. The results show that the impact resistance and compression resistance of the composites can be significantly improved by the simple internal microstructures design, and the regression model established in this article can be used for accurate prediction of composites properties and the reliability is higher. In a word, this study opens a new route for the design of composites with unusual features.

Soft actuators, which ensure the safety of robot–human interactions, extend the range of robotic operations to fragile and sensitive objects. Shape memory polymers are one of the building material for soft actuators due to their spontaneous shape memory properties under stimulation. However, the global, discontinuous and imprecise motion put significant limitations on their wide application. Recently, it has been demonstrated that by using motifs in nature, anisotropic, heterogeneous properties of soft actuators can be fabricated. Here, it is shown that soft actuators with local response and continuously varying shape memory properties can be realized through integrating bioinspired arranged building blocks (fibers). The modified 3D printing technique provides the pathway of assembling these fibers as designed. We have revealed the underlying mechanism of the formation of gradient shape memory properties. Simulations successfully demonstrate the feasibility of our approach to manipulate shape memory behaviors. The translation of nature’s design motifs offers synthetic soft actuators the opportunity towards unprecedented applications such as soft robot, drug carrier and other intelligent applications.

In the study of electrostatic forces of semiconductor microstructures, especially in submicrometer or nanometer orders, it is valuable to analyse the influence of the space-charge layer at the surface of the microstructures. When the distance between microstructures is larger than 1 µm, the influence of space charge is a negligible factor and the metal approximation formula can be used. When the distance is reduced to the order of submicrometers or tens of nanometers, the error introduced by the metal approximation formula increases rapidly, dominated by the distance and the doping concentration. For the commonly used material n-type silicon, whose doping concentration is 1015 cm-3, when the distance is less than 450 nm, the error caused by the metal approximation formula is more than 10%. At this time, the metal approximation formula cannot be used and the influence of the space-charge layer must be taken into account.