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This article describes a versatile method to fabricate magnetic microstructures with complex two-dimensional geometric shapes using magnetically assembled iron oxide (Fe3O4) and cobalt ferrite (CoFe2O4) nanoparticles. Magnetic pole patterns are imprinted into magnetizable media, onto which magnetic nanoparticles are assembled from a colloidal suspension into defined shapes via the shaped magnetic field gradients. The kinetics of this assembly process are studied by evaluation of the microstructure features (e.g., line width and height) as a function of time, particle type, and volume fraction. After assembly, the iron oxide particles are cross-linked in situ and subsequently released by dissolving a sacrificial layer. The free-floating magnetic structures are shown to retain their patterned shape during manipulation with external magnetic fields.
The fabrication and integration of microactuators with 3D micromechanisms are necessary to develop microrobots with higher capability and complexity. In this work, a twostep fabrication method combining 3D printing with two-photon polymerization (TPP) and aluminum sputtering is demonstrated. Actuators using two different transduction mechanisms (thermal and electrostatic) were fabricated in this process, and a thermal actuator was printed with a mechanism in three-dimensional space without additional assembly steps. This work also provides parameterized characterizations which can be used as design guidelines for building actuators and mechanisms. A design approach to electrically isolate the actuators from the substrate is introduced so that the device can be functional after two fabrication steps without patterning the metal layer. Metal coverage on the sidewalls of trenches are characterized, which provides a design space for deciding electrode gaps and heights in electrostatic actuators. Using these guidelines, 500 µm long thermal actuators showed a maximum displacement of 18.0 µm at 8.31mW and reliably actuated up to 8,500 cycles. An interdigitated electrostatic comb-drive actuator was also successfully demonstrated, displacing 12.7 µm when 160V was applied. Finally, a 3D actuated mechanism was designed by incorporating a thermal actuator with 3D compliant mechanisms to flap 250 µm long wings. Flapping motion was successfully demonstrated.
Goal
This paper investigates the practicality of using a small, permanent magnet to capture magnetic particles out of high-viscosity biological fluids, such as synovial fluid.
Methods
Numerical simulations are used to predict the trajectory of magnetic particles toward the permanent magnet. The simulations are used to determine a “collection volume” with a time-dependent size and shape, which determines the number of particles that can be captured from the fluid in a given amount of time.
Results
The viscosity of the fluid strongly influences the velocity of the magnetic particles towards the magnet, hence the collection volume after a given time. In regards to the design of the magnet, the overall size is shown to most strongly influence the collection volume in comparison to the magnet shape or aspect ratio.
Conclusion
Numerical results showed good agreement with in vitro experimental magnetic collection results.
Significance
In the long-term, this work aims to facilitate optimization of the collection of magnetic particle-biomarker conjugates from high-viscosity biological fluids without the need to remove the fluid from a patient.
We demonstrate GaN-based thin light-emitting diodes (LEDs) on flexible polymer and paper substrates covered with chemical vapor deposited graphene as a transparent-conductive layer. Thin LEDs were fabricated by lifting the sapphire substrate off by Excimer laser heating, followed by transfer of the LEDs to the flexible substrates. These substrates were coated with tri-layer graphene by a wet transfer method. Optical and electrical properties of thin laser lift-offed LEDs on the flexible substrates were characterized under both relaxed and strained conditions. The graphene on paper substrates remained conducting when the graphene/paper structure was folded. The high transmittance, low sheet resistance and high failure strain of the graphene make it an ideal candidate as the transparent and conductive layer in flexible optoelectronics.
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