Marcus Hoop

Degradable Magnetic Composites for Minimally Invasive Interventions: Device Fabrication, Targeted Drug Delivery, and Cytotoxicity Tests

Superparamagnetic nanoparticles and a functional, degradable polymer matrix based on poly(ethylene glycol) are combined to enable fully degradable magnetic microdevices for minimally invasive biomedical applications. A bioinspired helical microrobot platform mimicking Escherichia coli bacteria is fabricated and actuated using weak rotating magnetic fields. Locomotion based on corkscrew propulsion, targeted drug delivery, and low-degradation-product cytotoxicity are demonstrated.

Magnetically driven Bi2O3/BiOCl-based hybrid microrobots for photocatalytic water remediation

In this work, we have developed 3D hybrid microstructures consisting of a short ferromagnetic CoNi segment for wireless magnetic control, coupled to a photocatalytic Bi2O3/BiOCl segment for water remediation under UV-visible light. These hybrid microstructures (pillars and helices) were fabricated using 3D photolithography and template-assisted electrodeposition, followed by in situ creation of a Bi2O3/BiOCl heterojunction after oxidation of Bi. This heterojunction is not only active under a wider solar spectrum but also ensures sufficient charge separation and hence low electron–hole recombination rate. As a result, these hybrid microstructures were able to degrade rhodamine B dye with a 90% efficiency in 6 hours. On application of magnetic fields we were able to precisely control the structures and collect them for reuse. Cytotoxicity tests were performed on our hybrid structures and a 95% cell viability was reported showing that our structures are biocompatible.

Hybrid Magnetoelectric Nanowires for Nanorobotic Applications: Fabrication, Magnetoelectric Coupling, and Magnetically Assisted In Vitro Targeted Drug Delivery

An FeGa@P(VDF-TrFE) wire-shaped magnetoelectric nanorobot is designed and fabricated to demonstrate a proof-of-concept integrated device, which features wireless locomotion and on-site triggered therapeutics with a single external power source (i.e., a magnetic field). The device can be precisely steered toward a targeted location wirelessly by rotating magnetic fields and perform on-demand magnetoelectrically assisted drug release to kill cancer cells.

Multisegmented FeCo/Cu nanowires: electrosynthesis, characterization and magnetic control of biomolecule desorption

In this paper, we report on the synthesis of FeCo/Cu multisegmented nanowires by means of pulse electrodeposition in nanoporous anodic aluminum oxide arrays supported on silicon chips. By adjustment of the electrodeposition conditions, such as the pulse scheme and the electrolyte, alternating segments of Cu and ferromagnetic FeCo alloy can be fabricated. The segments can be built with a wide range of lengths (15-150 nm) and exhibit a close-to-pure composition (Cu or FeCo alloy) as suggested by energy-dispersive X-ray mapping results. The morphology and the crystallographic structure of different nanowire configurations have been assessed thoroughly, concluding that Fe, Co, and Cu form solid solution. Magnetic characterization using vibrating sample magnetometry and magnetic force microscopy reveals that by introduction of nonmagnetic Cu segments within the nanowire architecture, the magnetic easy axis can be modified and the reduced remanence can be tuned to the desired values. The experimental results are in agreement with the provided simulations. Furthermore, the influence of nanowire magnetic architecture on the magnetically triggered protein desorption is evaluated for three types of nanowires: Cu, FeCo, and multisegmented FeCo15nm/Cu15nm. The application of an external magnetic field can be used to enhance the release of proteins on demand. For fully magnetic FeCo nanowires the applied oscillating field increased protein release by 83%, whereas this was found to be 45% for multisegmented FeCo15nm/Cu15nm nanowires. Our work suggests that a combination of arrays of nanowires with different magnetic configurations could be used to generate complex substance concentration gradients or control delivery of multiple drugs and macromolecules.

Magnetoelectric micromachines with wirelessly controlled navigation and functionality

The use of a single energy source for both manipulating micromachines and triggering their functionalities will result in highly integrated devices and simplify the design of the controlling platform. Here, we demonstrate this concept employing magnetoelectric Janus particle-based micromachines, which are fabricated by coating SiO2 microspheres with a CoFe2O4–BaTiO3 bilayer composite. While the inner magnetic CoFe2O4 layer enables the micromachines to be maneuvered using low magnitude rotating magnetic fields, the magnetoelectric bilayer composite provides the ability to remotely generate electric charges upon the application of a time-varying magnetic field. To demonstrate the capabilities of these micromachines, noble metals such as Au, Ag and Pt are magnetoelectrochemically reduced from their corresponding precursor salts and form nanoparticles on the surface of the micromachines. Magnetoelectric micromachines are promising devices for their use as metal scavengers, cell stimulators and electric field-assisted drug delivery agents.

Ultrasound-mediated piezoelectric differentiation of neuron-like PC12 cells on PVDF membranes

Electrical and/or electromechanical stimulation has been shown to play a significant role in regenerating various functionalities in soft tissues, such as tendons, muscles, and nerves. In this work, we investigate the piezoelectric polymer polyvinylidene fluoride (PVDF) as a potential substrate for wireless neuronal differentiation. Piezoelectric PVDF enables generation of electrical charges on its surface upon acoustic stimulation, inducing neuritogenesis of PC12 cells. We demonstrate that the effect of pure piezoelectric stimulation on neurite generation in PC12 cells is comparable to the ones induced by neuronal growth factor (NGF). In inhibitor experiments, our results indicate that dynamic stimulation of PVDF by ultrasonic (US) waves activates calcium channels, thus inducing the generation of neurites via a cyclic adenosine monophosphate (cAMP)-dependent pathway. This mechanism is independent from the well-studied NGF induced mitogen-activated protein kinases/extracellular signal-regulated kinases (MAPK/ERK) pathway. The use of US, in combination with piezoelectric polymers, is advantageous since focused power transmission can occur deep into biological tissues, which holds great promise for the development of non-invasive neuroregenerative devices.

Small‐Scale Machines Driven by External Power Sources

Micro- and nanorobots have shown great potential for applications in various fields, including minimally invasive surgery, targeted therapy, cell manipulation, environmental monitoring, and water remediation. Recent progress in the design, fabrication, and operation of these miniaturized devices has greatly enhanced their versatility. In this report, the most recent progress on the manipulation of small-scale robots based on power sources, such as magnetic fields, light, acoustic waves, electric fields, thermal energy, or combinations of these, is surveyed. The design and propulsion mechanism of micro- and nanorobots are the focus of this article. Their fabrication and applications are also briefly discussed.

PCR quantification of SiO2 particle uptake in cells in the ppb and ppm range via silica encapsulated DNA barcodes

There is a strong interest in studying the cellular uptake of silica nanoparticles, particularly at medically relevant concentrations (ppb-ppm range) to understand their toxicology. At present, uptake analysis at these exposure levels is impeded by the high silica background concentration. Here we describe the use of DNA encapsulated within silica particles as a tool to quantify silica nanoparticles in in vitro cell-uptake experiments at low concentrations (down to 10 fg cell(-1)).

Piezoelectrically Enhanced Photocatalysis with BiFeO3 Nanostructures for Efficient Water Remediation

Summary Designing new catalysts that can efficiently utilize multiple energy sources can contribute to solving the current challenges of environmental remediation and increasing energy demands. In this work, we fabricated single-crystalline BiFeO3 (BFO) nanosheets and nanowires that can successfully harness visible light and mechanical vibrations and utilize them for degradation of organic pollutants. Under visible light both BFO nanostructures displayed a relatively slow reaction rate. However, under piezocatalysis both nanosheets and nanowires exhibited higher reaction rates in comparison with photocatalytic degradation. When both solar light and mechanical vibrations were used simultaneously, the reaction rates were elevated even further, with the BFO nanowires degrading 97% of RhB dye within 1 hr (k-value 0.058 min−1). The enhanced degradation under mechanical vibrations can be attributed to the promotion of charge separation caused by the internal piezoelectric field of BFO. BFO nanowires also exhibited good reusability and versatility toward degrading four different organic pollutants.