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1. Selective imaging of diamond nanoparticles within complex matrices using magnetically induced fluorescence contrast

   https://doi.org/10.1039/C9EN01008D  

   Jones, Zachary R. ; Niemuth, Nicholas J. ; Robinson, Margaret E. ; Shenderova, Olga A. ; Klaper, Rebecca D. ; Hamers, Robert J. ( February 2020 , Environmental Science: Nano)

   The use of fluorescence microscopy to study fate and transport of nanoparticles in the environment can be limited by the presence of confounding background signals such as autofluorescence and scattered light. The unique spin-related luminescence properties of nitrogen vacancy (NV) centers in diamond nanoparticles (NVND) enable new types of imaging modalities such as selective imaging of nanoparticles in the presence of background fluorescence. These techniques make use of the fact that the spin properties, which affect the fluorescence of NV centers, can be modulated using applied magnetic or radio-frequency fields. This work presents the use magnetic fields to modulate themore »fluorescence of NVND for background-subtracted imaging of nanoparticles ingested by a model organism, C. elegans . With the addition of modest time-modulated magnetic fields from an inexpensive “hobby” electromagnet, the fluorescence of 40 nm NVND can be modulated by 10% in a widefield imaging configuration. Herein, differential magnetic imaging is used to image and to isolate the fluorescence arising from nanodiamond within the gut of the organism C. elegans . This method represents a promising approach to probing the uptake of nanoparticles by organisms and to assessing the movement and interactions of nanoparticles in biological systems.« less
2. Magnetic bio-hybrid micro actuators

   https://doi.org/10.1039/d2nr00152g  

   Quashie, David ; Benhal, Prateek ; Chen, Zhi ; Wang, Zihan ; Mu, Xueliang ; Song, Xiaoxia ; Jiang, Teng ; Zhong, Yukun ; Cheang, U Kei ; Ali, Jamel ( March 2022 , Nanoscale)

   Over the past two decades, there has been a growing body of work on wireless devices that can operate on the length scales of biological cells and even smaller. A class of these devices receiving increasing attention are referred to as bio-hybrid actuators: tools that integrate biological cells or subcellular parts with synthetic or inorganic components. These devices are commonly controlled through magnetic manipulation as magnetic fields and gradients can be generated with a high level of control. Recent work has demonstrated that magnetic bio-hybrid actuators can address common challenges in small scale fabrication, control, and localization. Additionally, it ismore »becoming apparent that these magnetically driven bio-hybrid devices can display high efficiency and, in many cases, have the potential for self-repair and even self-replication. Combining these properties with magnetically driven forces and torques, which can be transmitted over significant distances, can be highly controlled, and are biologically safe, gives magnetic bio-hybrid actuators significant advantages over other classes of small scale actuators. In this review, we describe the theory and mechanisms required for magnetic actuation, classify bio-hybrid actuators by their diverse organic components, and discuss their current limitations. Insights into the future of coupling cells and cell-derived components with magnetic materials to fabricate multi-functional actuators are also provided.« less
3. Size-dependent magnetic and magnetothermal properties of gadolinium silicide nanoparticles

   https://doi.org/10.1039/D0RA05394E  

   Nauman, Muhammad ; Alnasir, Muhammad Hisham ; Hamayun, Muhammad Asif ; Wang, YiXu ; Shatruk, Michael ; Manzoor, Sadia ( July 2020 , RSC Advances)

   Gadolinium silicide (Gd 5 Si 4 ) nanoparticles are an interesting class of materials due to their high magnetization, low Curie temperature, low toxicity in biological environments and their multifunctional properties. We report the magnetic and magnetothermal properties of gadolinium silicide (Gd 5 Si 4 ) nanoparticles prepared by surfactant-assisted ball milling of arc melted bulk ingots of the compound. Using different milling times and speeds, a wide range of crystallite sizes (13–43 nm) could be produced and a reduction in Curie temperature ( T C ) from 340 K to 317 K was achieved, making these nanoparticles suitable formore »self-controlled magnetic hyperthermia applications. The magnetothermal effect was measured in applied AC magnetic fields of amplitude 164–239 Oe and frequencies 163–519 kHz. All particles showed magnetic heating with a strong dependence of the specific absorption rate (SAR) on the average crystallite size. The highest SAR of 3.7 W g −1 was measured for 43 nm sized nanoparticles of Gd 5 Si 4 . The high SAR and low T C , (within the therapeutic range for magnetothermal therapy) makes the Gd 5 Si 4 behave like self-regulating heat switches that would be suitable for self-controlled magnetic hyperthermia applications after biocompatibility and cytotoxicity tests.« less
4. Regulating Tissue-Mimetic Mechanical Properties of Bottlebrush Elastomers by Magnetic Field

   https://doi.org/10.1021/acsami.1c12860  

   Kostrov, Sergei A. ; Dashtimoghadam, Erfan ; Keith, Andrew N. ; Sheiko, Sergei S. ; Kramarenko, Elena Yu. ( August 2021 , ACS Applied Materials & Interfaces)

   We report on a new class of magnetoactive elastomers (MAEs) based on bottlebrush polymer networks filled with carbonyl iron microparticles. By synergistically combining solvent-free, yet supersoft polymer matrices, with magnetic microparticles, we enable the design of composites that not only mimic the mechanical behavior of various biological tissues but also permit contactless regulation of this behavior by external magnetic fields. While the bottlebrush architecture allows to finely tune the matrix elastic modulus and strain-stiffening, the magnetically aligned microparticles generate a 3-order increase in shear modulus accompanied by a switch from a viscoelastic to elastic regime as evidenced by a ca.more »10-fold drop of the damping factor. The developed method for MAE preparation through solvent-free coinjection of bottlebrush melts and magnetic particles provides additional advantages such as injection molding of various shapes and uniform particle distribution within MAE composites. The synergistic combination of bottlebrush network architecture and magnetically responsive microparticles empowers new opportunities in the design of actuators and active vibration insulation systems.« less
5. Soft Capsule Magnetic Millirobots for Region-Specific Drug Delivery in the Central Nervous System

   https://doi.org/10.3389/frobt.2021.702566  

   Mair, Lamar O. ; Adam, Georges ; Chowdhury, Sagar ; Davis, Aaron ; Arifin, Dian R. ; Vassoler, Fair M. ; Engelhard, Herbert H. ; Li, Jinxing ; Tang, Xinyao ; Weinberg, Irving N. ; et al ( July 2021 , Frontiers in Robotics and AI)

   Small soft robotic systems are being explored for myriad applications in medicine. Specifically, magnetically actuated microrobots capable of remote manipulation hold significant potential for the targeted delivery of therapeutics and biologicals. Much of previous efforts on microrobotics have been dedicated to locomotion in aqueous environments and hard surfaces. However, our human bodies are made of dense biological tissues, requiring researchers to develop new microrobotics that can locomote atop tissue surfaces. Tumbling microrobots are a sub-category of these devices capable of walking on surfaces guided by rotating magnetic fields. Using microrobots to deliver payloads to specific regions of sensitive tissues ismore »a primary goal of medical microrobots. Central nervous system (CNS) tissues are a prime candidate given their delicate structure and highly region-specific function. Here we demonstrate surface walking of soft alginate capsules capable of moving on top of a rat cortex and mouse spinal cord ex vivo , demonstrating multi-location small molecule delivery to up to six different locations on each type of tissue with high spatial specificity. The softness of alginate gel prevents injuries that may arise from friction with CNS tissues during millirobot locomotion. Development of this technology may be useful in clinical and preclinical applications such as drug delivery, neural stimulation, and diagnostic imaging.« less