Ductile Shape-Memory Polymer Composite with Enhanced Shape Recovery Ability

Self-Assembly of Hemimyzon Formosanus-Inspired Crescent-Shaped Nanosucker Arrays for Reversible Adhesion

Hemimyzon formosanus, a species of ray-finned fish, makes use of crescent-shaped abdominal suckers for adhering to irregular, rough, and slippery gravel in fast-flowing headwaters and minor tributaries. Bioinspired by the adhesion characteristics, two-dimensional non-close-packed colloidal crystals are self-assembled and serve as templates to pattern crescent-shaped shape memory polymer-based nanostructure arrays. By the manipulation of the configuration of nanosuckers through applying common solvent stimulations, the corresponding adhesion performances on glass, sandpaper, or even porcine kidney surfaces can be switched instantaneously and reversibly under ambient conditions. The biomimetic nanostructures indicate possible solutions to a variety of challenges, such as wound nursing, and so on.

Investigating Fundamental Principles of Nonequilibrium Assembly Using Temperature-Sensitive Copolymers

Both natural biomaterials and synthetic materials benefit from complex energy landscapes that provide the foundation for structure-function relationships and environmental sensitivity. Understanding these nonequilibrium dynamics is important for the development of design principles to harness this behavior. Using a model system of poly(ethylene glycol) methacrylate-based thermoresponsive lower critical solution temperature (LCST) copolymers, we explored the impact of composition and stimulus path on nonequilibrium thermal hysteretic behavior. Through turbidimetry analysis of nonsuperimposable heat-cool cycles, we observe that LCST copolymers show clear hysteresis that varies as a function of pendent side chain length and hydrophobicity. Hysteresis is further impacted by the temperature ramp rate, as insoluble states can be kinetically trapped under optimized temperature protocols. This systematic study brings to light fundamental principles that can enable the harnessing of out-of-equilibrium effects in synthetic soft materials.

The Current Status, Prospects, and Challenges of Shape Memory Polymers Application in Bone Tissue Engineering

Bone defects can occur after severe trauma, infection, or bone tumor resection surgery, which requires grafting to repair the defect when it reaches a critical size, as the bone's self-healing ability is insufficient to complete the bone repair. Natural bone grafts or artificial bone grafts, such as bioceramics, are currently used in bone tissue engineering, but the low availability of bone and high cost limit these treatments. Therefore, shape memory polymers (SMPs), which combine biocompatibility, biodegradability, mechanical properties, shape tunability, ease of access, and minimally invasive implantation, have received attention in bone tissue engineering in recent years. Here, we reviewed the various excellent properties of SMPs and their contribution to bone formation in experiments at the cellular and animal levels, respectively, especially for the repair of defects in craniomaxillofacial (CMF) and limb bones, to provide new ideas for the application of these new SMPs in bone tissue engineering.

Qualifying the contribution of fiber diameter on the acrylate-based electrospun shape memory polymer nano/microfiber properties

Fibrous shape memory polymers (SMPs) have received growing interest in various applications, especially in biomedical applications, which offer new structures at the microscopic level and the potential of enhanced shape deformation of SMPs. In this paper, we report on the development and investigation of the properties of acrylate-based shape memory polymer fibers, fabricated by electrospinning technology with the addition of polystyrene (PS). Fibers with different diameters are manufactured using four different PS solution concentrations (25, 30, 35, and 40 wt%) and three flow rates (1.0, 2.5, and 5.0 μL min-1) with a 25 kV applied voltage and 17 cm electrospinning distance. Scanning electron microscope (SEM) images reveal that the average fiber diameter varies with polymer concentration and flow rates, ranging from 0.655 ± 0.376 to 4.975 ± 1.634 μm. Dynamic mechanical analysis (DMA) and stress-strain testing present that the glass transition temperature and tensile values are affected by fiber diameter distribution. The cyclic bending test directly proves that the electrospun SMP fiber webs are able to fully recover; additionally, the recovery speed is also affected by fiber diameter. With the combination of the SMP material and electrospinning technology, this work paves the way in designing and optimizing future SMP fibers properties by adjusting the fiber diameter.

Bistable and Multistable Actuators for Soft Robots: Structures, Materials, and Functionalities

Snap-through bistability is often observed in nature (e.g., fast snapping to closure of Venus flytrap) and the life (e.g., bottle caps and hair clippers). Recently, harnessing bistability and multistability in different structures and soft materials has attracted growing interest for high-performance soft actuators and soft robots. They have demonstrated broad and unique applications in high-speed locomotion on land and under water, adaptive sensing and fast grasping, shape reconfiguration, electronics-free controls with a single input, and logic computation. Here, an overview of integrating bistable and multistable structures with soft actuating materials for diverse soft actuators and soft/flexible robots is given. The mechanics-guided structural design principles for five categories of basic bistable elements from 1D to 3D (i.e., constrained beams, curved plates, dome shells, compliant mechanisms of linkages with flexible hinges and deformable origami, and balloon structures) are first presented, alongside brief discussions of typical soft actuating materials (i.e., fluidic elastomers and stimuli-responsive materials such as electro-, photo-, thermo-, magnetic-, and hydro-responsive polymers). Following that, integrating these soft materials with each category of bistable elements for soft bistable and multistable actuators and their diverse robotic applications are discussed. To conclude, perspectives on the challenges and opportunities in this emerging field are considered.

Durability of Shape Memory Polymer Composite Laminates under Thermo-Mechanical Cycling

Shape memory polymer composites (SMPCs) have been manufactured by press moulding of carbon fibre-reinforced (CFR) prepregs with SMP interlayers. SMPC laminates have been produced with different numbers of CFR plies (i.e., 2, 4, 6, and 8) and different thicknesses of the SMP interlayers (i.e., 100 and 300 µm) for a sum of eight combinations. Co-curing of the prepreg plies and the SMP interlayers has led to an optimal adhesion of structural and functional plies, which has been confirmed by following testing. Single thermo-mechanical cycles at increasing strains (i.e., 0.06%, 0.12%, and 0.18%) and multiple cycling have been performed to test SMPC laminate durability. Delamination and fibre cracking were not observed during testing, and laminates showed a reproducible SM behaviour after 10 consecutive thermo-mechanical cycles. SM properties have been extracted from tests in terms of residual and memory loads as well as shape fixity and shape recovery. These data may be used for comparison of the performances of the different laminates, and as a first base for designing SMPC structures. Thin laminates exhibit lower recovery loads but higher shape fixity than thick ones, but the shape recovery is very high for all the SMPCs, with an average of 98%.

Development of Trans-1,4-Polyisoprene Shape-Memory Polymer Composites Reinforced with Carbon Nanotubes Modified by Polydopamine

In this study, which was inspired by mussel-biomimetic bonding research, carbon nanotubes (CNTs) were interfacially modified with polydopamine (PDA) to prepare a novel nano-filler (CNTs@PDA). The structure and properties of the CNTs@PDA were studied using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The CNTs and the CNTs@PDA were used as nanofillers and melt-blended into trans-1,4 polyisoprene (TPI) to create shape-memory polymer composites. The thermal stability, mechanical properties, and shape-memory properties of the TPI/CNTs and TPI/CNTs@PDA composites were systematically studied. The results demonstrate that these modifications enhanced the interfacial interaction, thermal stability, and mechanical properties of TPI/CNTs@PDA composites while maintaining shape-memory performance.

Photosensitive Composite Inks for Digital Light Processing Four-Dimensional Printing of Shape Memory Capture Devices

High-performance shape memory thermosetting polymers and their composites for four-dimensional (4D) printing are essential in practical applications. To date, most printable thermosets suffer from complicated processes, poor thermodynamic performances, and low printing speed. Here, photosensitive composite inks for fast photocuring printing are developed. The inks consist of epoxy acrylate (EPAc), polyethylene glycol dimethacrylate (PEGDMA), and carbon fillers, which form a firm network structure when exposed to UV light. EPAc is synthesized via addition esterification of epoxy resin and acrylic acid under mild conditions. It is worth noting that raw materials for the reaction are diverse, including not only various epoxy resins but also molecules with epoxy groups. The 4D printing speed of up to 180 mm/h is mainly attributed to the exothermic reaction initiated by free radicals, which accelerates the polymerization of EPAc and PEGDMA. Most importantly, by increasing the exposure time of each layer from 1 s to 3 s during the printing process, the epoxy composite-infilled carbon nanotubes and carbon fibers are printed to ensure the integrity of the microlayer structure. Furthermore, we design a claw-like catcher device based on the above printable composite inks to demonstrate its potential applications in aerospace, such as grasping end-of-service spacecraft or explosive debris. Undoubtedly, 4D printing technology opens up a new portal for the manufacturing of thermoset epoxy composites and complex structures, which make the shape memory thermosetting epoxy resins and their composites possess excellent properties and good engineering application prospects.