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.
This paper describes a self‐regulating system that combines wrinkle‐patterned hydrogels with plasmonic nanoparticle (NP) lattices. In the feedback loop, the wrinkle patterns flatten in response to moisture, which then allows light to reach the NP lattice on the bottom layer. Upon light absorption, the NP lattice produces a photothermal effect that dries the hydrogel, and the system then returns to the initial wrinkled configuration. The timescale of this regulatory cycle can be programmed by tuning the degree of photothermal heating by NP size and substrate material. Time‐dependent finite element analysis reveals the thermal and mechanical mechanisms of wrinkle formation. This self‐regulating system couples morphological, optical, and thermo‐mechanical properties of different materials components and offers promising design principles for future smart systems.
more » « less- Award ID(s):
- 1848613
- NSF-PAR ID:
- 10448023
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Small
- Volume:
- 18
- Issue:
- 1
- ISSN:
- 1613-6810
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract The ability to dynamically reconfigure superlattices in response to external stimuli is an intriguing prospect for programmable DNA‐guided nanoparticle (NP) assemblies, which promises the realization of “smart” materials with dynamically adjustable interparticle spacing and real‐time tunable properties. Existing in situ probes of reconfiguration processes have been limited mostly to reciprocal space methods, which can follow larger ordered ensembles but do not provide access to real‐space pathways and dynamics. Here, in situ atomic force microscopy is used to investigate DNA‐linked NP assemblies and their response to external stimuli, specifically the contraction and expansion of on‐surface self‐assembled monolayer superlattices upon reversible DNA condensation induced by ethanol. In situ microscopy allows observation and quantification of key processes in solution, e.g., lattice parameter changes, defects, and monomer displacements in small groups of NPs. The analysis of imaging data uncovers important boundary conditions due to DNA bonding of NP superlattices to a substrate. Tension in the NP–substrate DNA bonds, which can elastically extend, break, and re‐form during contraction/expansion cycles, counteracts the changes in lattice parameter and causes hysteresis in the response of the system. The results provide insight into the behavior of supported DNA‐linked NP superlattices and establish a foundation for designing and probing tunable nanocrystal‐based materials in solution.
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Abstract A plasmonic nanolaser architecture that can produce white‐light emission is reported. A laser device is designed based on a mixed dye solution used as gain material sandwiched between two aluminum nanoparticle (NP) square lattices of different periodicities. The (±1, 0) and (±1, ±1) band‐edge surface lattice resonance (SLR) modes of one NP lattice and the (±1, 0) band‐edge mode of the other NP lattice function as nanocavity modes for red, blue, and green lasing respectively. From a single aluminum NP lattice, simultaneous red and blue lasing is realized from a binary dye solution, and the relative intensities of the two colors are controlled by the volume ratio of the dyes. Also, a laser device is constructed by sandwiching dye solutions between two Al NP lattices with different periodicities, which enables red–green and blue–green lasing. With a combination of three dyes as liquid gain, red, green, and blue lasing for a white‐light emission profile is realized.
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Oscillation plays a vital role in the survival of living organisms in changing environments, and its relevant research has inspired many biomimetic approaches to soft autonomous robotics. However, it remains challenging to create mechanical oscillation that can work under constant energy input and actively adjust the oscillation mode. Here, a steam-driven photothermal oscillator operating under constant light irradiation has been developed to perform continuous or pulsed, damped harmonic mechanical oscillations. The key component of the oscillator comprises a hydrogel containing Fe 3 O 4 /Cu hybrid nanorods, which can convert light into heat and generate steam bubbles. Controllable perturbation to the thermomechanical equilibrium of the oscillator can thus be achieved, leading to either continuous or pulsed oscillation depending on the light intensity. Resembling the conventional heat steam engine, this environment-dictated multimodal oscillator uses steam as the working fluid, enabling the design of self-adaptive soft robots that can actively adjust their body functions and working modes in response to environmental changes. An untethered biomimetic neuston-like robot is further developed based on this soft steam engine, which can adapt its locomotion mechanics between uniform and recurrent swimming to light intensity changes and perform on-demand turning under continuous light irradiation. Fueled by water and remotely powered by light, this unique hydrogel oscillator enables easy control over the oscillation dynamics and modes, offering an effective approach to self-adaptive soft robots and solar steam engines.more » « less
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Abstract Molecular motors (MM) are molecular machines, or nanomachines, that rotate unidirectionally upon photostimulation and perform mechanical work on their environment. In the last several years, it has been shown that the photomechanical action of MM can be used to permeabilize lipid bilayers, thereby killing cancer cells and pathogenic microorganisms and controlling cell signaling. The work contributes to a growing acknowledgement that the molecular actuation characteristic of these systems is useful for various applications in biology. However, the mechanical effects of molecular motion on biological materials are difficult to disentangle from photodynamic and photothermal action, which are also present when a light‐absorbing fluorophore is irradiated with light. Here, an overview of the key methods used by various research groups to distinguish the effects of photomechanical, photodynamic, and photothermal action is provided. It is anticipated that this discussion will be helpful to the community seeking to use MM to develop new and distinctive medical technologies that result from mechanical disruption of biological materials.
