Controlled microrobotic navigation in the vascular system can revolutionize minimally invasive medical applications, such as targeted drug and gene delivery. Magnetically controlled surface microrollers have emerged as a promising microrobotic platform for controlled navigation in the circulatory system. Locomotion of micrororollers in strong flow velocities is a highly challenging task, which requires magnetic materials having strong magnetic actuation properties while being biocompatible. The L10‐FePt magnetic coating can achieve such requirements. Therefore, such coating has been integrated into 8 µm‐diameter surface microrollers and investigated the medical potential of the system from magnetic locomotion performance, biocompatibility, and medical imaging perspectives. The FePt coating significantly advanced the magnetic performance and biocompatibility of the microrollers compared to a previously used magnetic material, nickel. The FePt coating also allowed multimodal imaging of microrollers in magnetic resonance and photoacoustic imaging in ex vivo settings without additional contrast agents. Finally, FePt‐coated microrollers showed upstream locomotion ability against 4.5 cm s−1 average flow velocity with real‐time photoacoustic imaging, demonstrating the navigation control potential of microrollers in the circulatory system for future in vivo applications. Overall, L10‐FePt is conceived as the key material for image‐guided propulsion in the vascular system to perform future targeted medical interventions.
Biological cilia play essential roles in self-propulsion, food capture, and cell transportation by performing coordinated metachronal motions. Experimental studies to emulate the biological cilia metachronal coordination are challenging at the micrometer length scale because of current limitations in fabrication methods and materials. We report on the creation of wirelessly actuated magnetic artificial cilia with biocompatibility and metachronal programmability at the micrometer length scale. Each cilium is fabricated by direct laser printing a silk fibroin hydrogel beam affixed to a hard magnetic FePt Janus microparticle. The 3D-printed cilia show stable actuation performance, high temperature resistance, and high mechanical endurance. Programmable metachronal coordination can be achieved by programming the orientation of the identically magnetized FePt Janus microparticles, which enables the generation of versatile microfluidic patterns. Our platform offers an unprecedented solution to create bioinspired microcilia for programmable microfluidic systems, biomedical engineering, and biocompatible implants.
Controlled
plastic forming of nanoscale metallic objects by applying
mechanical load is a challenge, since defect-free nanocrystals usually
yield at near theoretical shear strength, followed by stochastic dislocation
avalanches that lead to catastrophic failure or irregular, uncontrolled
shapes. Herein, instead of mechanical load, we utilize chemical stress
from imbalanced interdiffusion to manipulate the shape of nanowhiskers.
Bimetallic Au–Fe nanowhiskers with an ultrahigh bending strength
were synthesized employing the molecular beam epitaxy technique. The
one-sided Fe coating on the defect-free, single-crystalline Au nanowhisker
exhibited both single- and polycrystalline regions. Annealing the
bimetallic nanowhiskers at elevated temperatures led to gradual change
of curvature and irreversible bending. At low homological temperatures
at which grain boundary diffusion is a dominant mode of mass transport
this irreversible bending was attributed to the grain boundary Kirkendall
effect during the diffusion of Au along the grain boundaries in the
Fe layer. At higher temperatures and longer annealing times, the bending
was dominated by intensive bulk diffusion of Fe into the Au nanowhisker,
accompanied by a significant migration of the Au–Fe interphase
boundary toward the Fe layers. The irreversible bending was caused
by the concentration dependence of the lattice parameter of the Au(Fe)
alloy and by the volume effect associated with the interphase boundary
migration. The results of this study demonstrate a high potential
of chemical interdiffusion in the controlled plastic forming of ultrastrong
metal nanostructures. By design of the thickness, microstructure,
and composition of the coating as well as the parameters of heat treatment,
bimetallic nanowhiskers can be bent in a controlled manner.
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