AbstractMagnetic Fe3O4 nanoparticles are employed to develop digital light processing 3D printing resin, which is used to fabricate arbitrary-shape soft actuators with multimaterials printing in a free assembly manner. Various mechanical properties and printed morphology of curing resin with different Fe3O4 nanoparticles content are explored to demonstrate the feasibility and precision. By using magnetic and nonmagnetic resins as the magnetic and nonmagnetic segments, mulitple magnetic devices and actuators are prepared by digital light processing (DLP) 3D printing technology. Moreover, the interfacial binding strength between magnetic and nonmagnetic segments and deflection with different diameters of printed lattices and content of Fe3O4 nanoparticles are investigated. DLP 3D printing enables the free assembly manufacturing of actuators with complicated architectures to achieve bending, deformation, cargo transportation, and so on. As proof-of-concept, a flexible gripper is printed through integrating magnetic responsive and nonresponsive materials into one body. This approach with special material will be promising to extend the capability of 3D printing for applications in controllable delivery with remote magnetic control in biological, medical, and robotic fields.

High-performance three-dimensional (3D) printing materials are key for the advancement and practical applications of emerging 3D printing technology. However, these are still very few in the market. In this study, photocurable polyimide inks for digital light processing (DLP) 3D printing to produce architectures with excellent comprehensive properties are reported. Maleic anhydride-terminated polyimide oligomers with a glycidyl methacrylate graft were prepared by one-step imidization of phenolic hydroxyl groups containing diamine and aromatic dianhydride in high boiling-point solvent, followed by the reaction of glycidyl methacrylate with the phenolic hydroxyl groups. The good solubility of the oligomers in reactive diluents allowed the formation of a solvent-free photocurable ink for DLP 3D printing, and this ink could be deposited in a layer-by-layer sequence into polyimides with complex shapes. The resultant photocurable polyimide inks were capable of fabricating various complicated, precise architectures with good mechanical and thermoresistant properties. As such, the 3D printing polyimides are believed to be promising in constructing parts and models, such as micro-oil filters, through-tubing materials, cooling valves, and various engine components, where heat resistance, chemical inertness, and high mechanical properties are required.

A near-infrared light triggered fast interfacial friction switch was achieved with polyelectrolyte brush grafted PDMS embedded with Fe3O4 nanoparticles, where the in situ heating up of the photothermal Fe3O4 nanoparticles in the polymer matrix changes the interface humidity and thereafter alters the hydration level of the interfacial polymer brushes.

Articular cartilage is a load-bearing and lubricious tissue covering the ends of articulating bones in synovial joints to reduce friction and wear. It ideally combines the high mechanical property and the ultralow friction performance as a result of biphasic structure and lubricious biomolecules. A biomimicking hydrogel with bilayer structure of thin porous top layer covering a compact and tough hydrogel bulk is fabricated with interfacial modulated polymerization. The top porous layer ensures the ultralow friction toward its contact pairs, while the bottom renders the high load-bearing property. Therefore, with bilayer architecture, hydrogel achieves an outstanding combination of low friction and high load bearing performance with long wear life when sliding against either steel or silicone elastomer counterpair.

The ability to control friction is quite attractive for many applications. Other than mechanical/physical methods to control friction, this letter shows how materials chemistry can regulate friction effectively. Magnetite-loaded thermosensitive poly(N-isopropylacrylamide) nanogels (Fe3O4@PNIPAM) were synthesized as nanoparticulate soft matter to reduce friction when it is used as an additive in aqueous lubricant. Interestingly, friction can be multiply regulated by temperature, magnetism, and near-infrared light through manipulating the colloidal properties of multifunctional composite nanogels in bulk solution and at the frictional interface.

The slippery mucus produced by fish skin is important to protect fish against predator attack, allowing fish to swim faster and remain elusive because of the ultra-low coefficient of friction (COF) of fish skin. To mimic this slick skin, responsive hydrogels that respond to external stimuli, including pH and temperature, were prepared. These hydrogels were found to perform better than fish skin: not only was an ultra-low COF achieved but multiple tunable COFs from ultra-low to ultra-high were discovered using sequential regulation of pH and temperature. The tunable COF was achieved through conformational changes in the molecular chains in the responsive hydrogel that were induced by the external stimuli. Swelling of both pH- and thermal-responsive polymer chains of the hydrogel resulted in an ultra-low COF; the pH-responsive component, shrink as a result of dehydration caused by a pH change, led to a moderate COF, whereas the two components simultaneous shrink brought out a very high COF. The three levels of COF under different states can be reversibly switched multiple times by sequential regulation of pH and temperature. This reversible tunability in friction performance is likely to have a significant impact on the design of hydrogel-based actuation devices.

A novel superhydrophilic material, charged polymer brushes-grafted magnetic core–shell–corona composite nanoparticles (Fe3O4@SiO2@PSPMA), was developed to harvest water through the hydration effect. Because of both the strong hydration capability and the good swelling performance, the negatively charged polymer brushes, PSPMA brushes, endow the composite nanoparticles with superhydrophilicity and a good water-absorbing performance like a sponge, while the magnetic Fe3O4 cores allow easy separation of Fe3O4@SiO2@PSPMA nanoparticles with absorbed water from oil/water mixture under an external magnetic field. The functional particles have the capability of harvesting water droplets whether floating on an oil surface or in the oil. This water-absorbing material uses selective wettability to harvest water and achieve oil–water separation and may be useful in finding novel approaches for recycling water from sewage and removing water in the petroleum industry.Keywords: charged polymer brushes; Fe3O4@SiO2@PSPMA; hydration effect; magnetic nanoparticles; oil−water separation; water harvesting

We report the fabrication of poly(3-sulfopropyl methacrylate potassium salt) (PSPMK) brushes grafted poly(N-isopropylacrylamide) (PNIPAAm) microgels and their potential as artificial synovial fluid for biomimetic aqueous lubrication and arthritis treatment. The negatively charged PSPMK brushes and thermosensitive PNIPAAm microgels play water-based hydration lubrication and temperature-triggered drug release, respectively. Under soft friction pairs, an ultralow coefficient of friction was achieved, while the hairy thermosensitive microgels showed a desirable temperature-triggered drugs release performance. Such a soft charged hairy microgel offers great possibility for designing intelligent synovial fluid. What is more, the combination of lubrication and drug loading capabilities enables the large clinical potential of novel soft hairy nanoparticles as synthetic joint lubricant fluid in arthritis treatment.Keywords: arthritis treatment; biomimetic synovial fluid; hairy microgels; hydration lubrication; polyelectrolyte brushes

A near-infrared light triggered fast interfacial friction switch was achieved with polyelectrolyte brush grafted PDMS embedded with Fe3O4 nanoparticles, where the in situ heating up of the photothermal Fe3O4 nanoparticles in the polymer matrix changes the interface humidity and thereafter alters the hydration level of the interfacial polymer brushes.