Remotely Controlled Micromanipulation by Buckling Instabilities in Fe₃O₄ Nanoparticle Embedded Poly(N-isopropylacrylamide) Surface Arrays

Abstract

The micromanipulation of biological samples is important for microbiology, pharmaceutical science, and related bioengineering fields. In this work, we report the fabrication and characterization of surface-attached microbeam arrays of 20 μm width and 25 μm height made of poly(N-isopropylacrylamide), a thermoresponsive polymer, with embedded spherical or octopod FeO nanoparticles. Below 32 °C, the microbeams imbibe water and buckle with an amplitude of approximately 20 μm. Turning on an AC-magnetic field induces the microbeam array to expel water due to the heating effect of the nanoparticles (magnetic hyperthermia), leading to a reversible transition from a buckled to nonbuckled state. It is observed that the octopod nanoparticles have a heating rate 30% greater (specific absorption rate, SAR) than that of the spherical nanoparticles, which shortens the time scale of the transition from the buckled and nonbuckled state. The return of the microbeams to the buckled state is accomplished by turning off the AC magnetic field, the rate of which is dictated by dissipation of heat and is independent of the type of nanoparticle. It is further demonstrated that this transition can be used to propel 50 μm spherical objects along a surface. While the motion is random, this study shows the promise of harnessing shape-shifting patterns in microfluidics for object manipulation.

Topographical Manipulation of Microparticles and Cells with Acoustic Microstreaming

“…The recent development of manipulation technologies in the micro/nanoscale offers considerable promise in nanomachines, microfactories, lab on chip systems, cell biology, and tissue engineering. − For practical applications, robust control over the propulsion and directionality are essential to steer and navigate micro/nanoobjects toward their destination. To date, conventional manipulation methods have been reported to be successful in specific applications, including the use of optical tweezers, − external magnetic fields, − electrokinetic forces, − hydrodynamic flows, − and surface acoustic waves. − Although optical tweezers have been successfully used to manipulate microobjects, there may be irreversible damage to the sample by laser-induced heating. − The use of magnetic field manipulation offers fast propulsion and orientation control but requires complex systems to operate, magnetized materials, and sophisticated feedback actuation strategies for achieving guidance of a single element. − Electrokinetic forces are determined by particle conductivity and can destroy biological species by current-induced heating. − Hydrodynamic interaction can use grooves or steps to give rise to sliding and directional motion, − yet microobjects can be steered only temporally along simple pathways. Surface acoustic waves are capable of precisely manipulating diverse microobjects, but the reproducible navigation with complex topographical guidance remains an unmet challenge. − Recent advances in acoustofluidics have made it possible to collect or sort microparticles in a simple manner but cannot address th...…”

Controllable Hierarchical Surface Patterns of Supramolecular Hydrogels: Harnessing Buckling Instability by Confinement

“…2), the surface becomes mechanically unstable, resulting in spontaneous disordered patterns such as folds and creases through buckling instability without the need for external loads . Although theoretical and experimental studies on the formation of buckling patterns on different geometries, such as stripes, disks, tubes, spheres bound to a hard substrate, and freestanding porous films have been reported, taking advantage of buckling hydrogel films has been rarely extended to create hierarchical patterns with long‐range orders …”

“…It is well known that hydrogels can undergo huge volume changes upon swelling through immersion in aqueous media.I nt hin films, the swelling is, however,c onstrained by the rigid substrate and thus expansion can occur only in the direction normalt ot he surface,g enerating ab iaxial compressive stress within the hy-drogel films. [32,33] Herein, we report on the controllable and long-range ordered hierarchical surface patterns in hydrogel thin films by combining nanoembossing methodology with intrinsic buckling instability.Apoly(ethylene glycol)( PEG)-based polyurethane-urea (PUU) supramolecular hydrogel is selected as the model compound as it shows excellent solution processability,h igh mechanical strengtha nd fast stimuli responsiveness through self-complementary PUU units encapsulated within hydrophobic domains. 2), [26] the surfaceb ecomes mechanically unstable, resulting in spontaneous disordered patterns such as folds andc reases through bucklinginstability without the need for externalloads.…”

“…[27][28][29][30] Althought heoretical and experimental studies on the formation of buckling patterns on different geometries, such as stripes, disks, tubes, spheres bound to ah ard substrate, and freestanding porous films have been reported, [28,31] taking advantage of bucklingh ydrogel films has been rarely extended to create hierarchical patternsw ith long-range orders. [32,33] Herein, we report on the controllable and long-range ordered hierarchical surface patterns in hydrogel thin films by combining nanoembossing methodology with intrinsic buckling instability.Apoly(ethylene glycol)( PEG)-based polyurethane-urea (PUU) supramolecular hydrogel is selected as the model compound as it shows excellent solution processability,h igh mechanical strengtha nd fast stimuli responsiveness through self-complementary PUU units encapsulated within hydrophobic domains. [34,35] The supramolecular hydrogel was firstly patterned into arrays of nanostripesb yn anoembossing techniques.…”

Self-Competitive Growth of CsPbBr3 Planar Nanowire Array

“…6−8 Great progress has been made in the fabrication of PNAs, which can be categorized into "postgrowth assembly" and "bottom-up growth" routes. The PNA fabrication with "post-growth assembly", such as Langmuir− Blodgett assembly, 9 micromanipulation, 10 and optical tweezers, 11 usually involves multiple steps for collecting, transferring, and rearranging nanowires on substrates, leading to challenges in terms of poor crystal quality, inefficiency, and high cost.…”