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Thermoresponsive hydrogels were 3D-printed with embedded gold nanorods (GNRs), which enable shape change through photothermal heating. GNRs were functionalized with bovine serum albumin and mixed with a photosensitizer and poly(N-isopropylacrylamide) (PNIPAAm) macromer, forming an ink for 3D printing by direct ink writing. A macromer-based approach was chosen to provide good microstructural homogeneity and optical transparency of the unloaded hydrogel in its swollen state. The ink was printed into an acetylated gelatin hydrogel support matrix to prevent the spreading of the low-viscosity ink and provide mechanical stability during printing and concurrent photocrosslinking. Acetylated gelatin hydrogel was introduced because it allows for melting and removal of the support structure below the transition temperature of the crosslinked PNIPAAm structure. Convective and photothermal heating were compared, which both triggered the phase transition of PNIPAAm and induced reversible shrinkage of the hydrogel–GNR composite for a range of GNR loadings. During reswelling after photothermal heating, some structures formed an internally buckled state, where minor mechanical agitation recovered the unbuckled structure. The BSA-GNRs did not leach out of the structure during multiple cycles of shrinkage and reswelling. This work demonstrates the promise of 3D-printed, photoresponsive structures as hydrogel actuators. [ABSTRACT FROM AUTHOR]

Artificial magnetic cilia are hair‐like structures that can respond to magnetic fields. Using hard magnetic materials in magnetic cilia makes possible programming and reprogramming of the magnetization state and corresponding actuation behaviors. Hard‐magnetic cilia are fabricated through self‐assembly by solvent casting of a slurry of NdFeB microparticles dispersed in a solution of a thermoplastic polyurethane elastomer. These hard‐magnetic cilia are capable of attractive and repulsive responses to magnetic fields, determined by the remanent magnetization of the NdFeB microparticles. An array of cilia can be magnetically reprogrammed through immobilization in ice, applying a damped alternating magnetic field first to reduce the remanent magnetization, and then remagnetizing the cilia with a large field. This demagnetization process significantly improves the reprogrammability of the cilia array. Different responses to magnetic fields can be programmed, including spatially nonuniform behaviors. Reprogrammed hard‐magnetic cilia exhibit unique behaviors in rotating magnetic fields. After reprogramming the magnetization direction along the width of the cilia, rotation and torsion cause them to slowly coil and then quickly uncoil in a snapping behavior. Modeling the magnetic and elastic torques during actuation provides additional insights and aids the design of magnetic cilia actuators based on hard magnets. [ABSTRACT FROM AUTHOR]

Transition metal chalcogenide nanoparticles (NPs) are of interest for energy applications, including batteries, supercapacitors, and electrocatalysis. Many methods have been established for synthesizing Ni NPs, and conversion chemistry to form Ni oxide and phosphides from template Ni NPs is well‐understood. Sulfidation and selenidation of Ni NPs have been much less explored, however. We report a method for the conversion of Ni template NPs into sulfide and selenide product NPs using elemental sulfur, 1‐hexadecanthiol, thiourea, trioctylphosphine sulfide, elemental selenium, and selenourea. While maintaining mole ratios of 2 mmol sulfur/selenium precursor: mmol Ni, products with phases of Ni3S2, Ni9S8, NiS, NiSO4·6H2O, Ni3S4, Ni3Se2, and NiSe have been obtained. The products have voids that form through the Kirkendall effect during interdiffusion. Trends relating the chemical properties of the precursors to the phases of the products have been identified. While some precursors contained phosphorus, there was no significant incorporation of phosphorus in any of the products. An increase of the NP size during sulfidation and selenidation is consistent with ripening. The application of Ni sulfide and selenide NPs as electrocatalysts for the hydrogen evolution reaction is also demonstrated. [ABSTRACT FROM AUTHOR]

Stimulus‐responsive polymers are attractive for microactuators because they can be easily miniaturized and remotely actuated, enabling untethered operation. In this work, magnetic Fe microparticles are dispersed in a thermoplastic polyurethane shape memory polymer matrix and formed into artificial, magnetic cilia by solvent casting within the vertical magnetic field in the gap between two permanent magnets. Interactions of the magnetic moments of the microparticles, aligned by the applied magnetic field, drive self‐assembly of magnetic cilia along the field direction. The resulting magnetic cilia are reconfigurable using light and magnetic fields as remote stimuli. Temporary shapes obtained through combined magnetic actuation and photothermal heating can be locked by switching off the light and magnetic field. Subsequently turning on the light without the magnetic field drives recovery of the permanent shape. The permanent shape can also be reprogrammed after preparing the cilia by applying mechanical constraints and annealing at high temperature. Spatially controlled actuation is demonstrated by applying a mask for optical pattern transfer into the array of magnetic cilia. A theoretical model is developed for predicting the response of shape memory magnetic cilia and elucidates physical mechanisms behind observed phenomena, enabling the design and optimization of ciliary systems for specific applications. [ABSTRACT FROM AUTHOR]

The first collision-induced dissociation tandem mass spectrometry (CID MS/MS) of a thiolate-protected Au nanoparticle is described that has a crystallographically determined structure. CID spectra has shown that dissociation pathways for the mixed monolayer [Na.sub.x][Au.sub.25][(S[C.sub.2][H.sub.4]Ph).sub.18-y][(S[([C.sub.2][H.sub.4]O).sub.5]C[H.sub.3]).sub.y] has centrally involved the semi-ring [Au.sub.2][L.sub.3] coordination that constitutes the nanoparticle's protecting structure.

Intact molecular ions of the organothiolate-protected nanoparticles [Au.sub.25][(SC[H.sub.2]C[H.sub.2]Ph).sub.18], including their isotopic resolution, is observed as 1- and 1+ ions in negative and positive mode by MALDI-TOF mass spectrometry when using a tactic of threshold laser pulse intensities and trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-propenylidene]malononitrile (DCTB) as matrix. The studies have shown that the first fragmentation step for the [Au.sub.25][(SC[H.sub.2]C[H.sub.2]Ph).sub.18] nanoparticle has resulted in losses of AuL units and also the loss of [Au.sub.4][(SC[H.sub.2]C[H.sub.2]Ph).sub.4].

The various size limitations to be considered during the formation of ordered striped nanoparticles (NPs), are discussed. The analysis proves that such size limitations highly affect the properties of the rippled NPs.

New approaches are described for electrospray ionization mass spectrometry (ESI-MS) with exact compositional assignments of small ([Au.sub.25]) nanoparticles with uniform and mixed protecting organothiolate monolayers. Mass spectrometry is the only method that has can be used for measuring the exact distribution of ligand-exchange products.

The high-resolution nanoparticle, electrospary ionization mass spectroscopy (ESI-MS) is widely used for investigating biological molecules and noncovalent interactions and hence is used for successful incorporation of the poly(ethylene glycol) (PEG) ligands. The analysis suggests that different sizes of Au nanoparticles can be used for the described purpose, which gives different PEG ligands and different ESI tags as well.

Quantum dots with a core/shell structure consisting of an alloyed core of As(sub X)P(sub 1-X), an intermediate shell of InP and an outer shell of ZnSe are developed. Alloyed core dots of the As(sub X)P(sub 1-X) show tunable emission in the near-infrared (NIR) region and the InP shell leads to a red-shift and an increase in the quantum yield.

A phosphine oxide gel is developed using bis(dichlorophosphino)ethane and poly(ethylene glycol) that can be used to transfer various nanoparticles from organic solvents to water. These aqueous nanoparticles have physical properties and reactivities comparable to those in organic solvent.