Naveen Shamsudhin

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.

Cooperative manipulation and transport of microobjects using multiple helical microcarriers

Manipulation and transport of microscale objects in 3D with high spatiotemporal resolution require precise control over the applied forces. We report a strategy that uses specially engineered microbars having engagement points and multiple helical microcarriers that can apply reversible loads onto these holders. The helical microcarriers are actuated by externally generated, low strength magnetic fields. By optimizing the design of helical structures for precise manipulation, we fabricated microcarriers that swim with little wobbling even at low rotating frequencies. The cooperation of microcarriers generates higher propulsive forces while application of forces at multiple locations results in motion control with multiple degrees of freedom (DOF). The microbar loaded with multiple microcarriers can be employed as a single mobile device for the realization of higher order manipulation tasks.

Massively Parallelized Pollen Tube Guidance and Mechanical Measurements on a Lab-on-a-Chip Platform

Pollen tubes are used as a model in the study of plant morphogenesis, cellular differentiation, cell wall biochemistry, biomechanics, and intra- and intercellular signaling. For a “systems-understanding” of the bio-chemo-mechanics of tip-polarized growth in pollen tubes, the need for a versatile, experimental assay platform for quantitative data collection and analysis is critical. We introduce a Lab-on-a-Chip (LoC) concept for high-throughput pollen germination and pollen tube guidance for parallelized optical and mechanical measurements. The LoC localizes a large number of growing pollen tubes on a single plane of focus with unidirectional tip-growth, enabling high-resolution quantitative microscopy. This species-independent LoC platform can be integrated with micro-/nano-indentation systems, such as the cellular force microscope (CFM) or the atomic force microscope (AFM), allowing for rapid measurements of cell wall stiffness of growing tubes. As a demonstrative example, we show the growth and directional guidance of hundreds of lily (Lilium longiflorum) and Arabidopsis (Arabidopsis thaliana) pollen tubes on a single LoC microscopy slide. Combining the LoC with the CFM, we characterized the cell wall stiffness of lily pollen tubes. Using the stiffness statistics and finite-element-method (FEM)-based approaches, we computed an effective range of the linear elastic moduli of the cell wall spanning the variability space of physiological parameters including internal turgor, cell wall thickness, and tube diameter. We propose the LoC device as a versatile and high-throughput phenomics platform for plant reproductive and development biology using the pollen tube as a model.

Characterization of size-dependent mechanical properties of tip-growing cells using a lab-on-chip device

Quantification of mechanical properties of tissues, living cells, and cellular components is crucial for the modeling of plant developmental processes such as mechanotransduction. Pollen tubes are tip-growing cells that provide an ideal system to study the mechanical properties at the single cell level. In this article, a lab-on-a-chip (LOC) device is developed to quantitatively measure the biomechanical properties of lily (Lilium longiflorum) pollen tubes. A single pollen tube is fixed inside the microfluidic chip at a specific orientation and subjected to compression by a soft membrane. By comparing the deformation of the pollen tube at a given external load (compressibility) and the effect of turgor pressure on the tube diameter (stretch ratio) with finite element modeling, its mechanical properties are determined. The turgor pressure and wall stiffness of the pollen tubes are found to decrease considerably with increasing initial diameter of the pollen tubes. This observation supports the hypothesis that tip-growth is regulated by a delicate balance between turgor pressure and wall stiffness. The LOC device is modular and adaptable to a variety of cells that exhibit tip-growth, allowing for the straightforward measurement of mechanical properties.

Micro-cantilevers with AIN actuators and PtSi tips for multi-frequency atomic force microscopy

We report the design, fabrication, and characterization of cantilevers with integrated AlN actuators and conductive PtSi tips for multi-frequency atomic force microscopy. These cantilevers also possess a stepped-rectangular geometry. The excellent dynamic behavior of these cantilevers is investigated using both finite-element simulations and experimental methods. Several imaging experiments are presented to illustrate the efficacy and versatility of these cantilevers.

Magnetically guided capsule endoscopy

Wireless capsule endoscopy (WCE) is a powerful tool for medical screening and diagnosis, where a small capsule is swallowed and moved by means of natural peristalsis and gravity through the human gastrointestinal (GI) tract. The camera-integrated capsule allows for visualization of the small intestine, a region which was previously inaccessible to classical flexible endoscopy. As a diagnostic tool, it allows to localize the sources of bleedings in the middle part of the gastrointestinal tract and to identify diseases, such as inflammatory bowel disease (Crohns disease), polyposis syndrome, and tumors. The screening and diagnostic efficacy of the WCE, especially in the stomach region, is hampered by a variety of technical challenges like the lack of active capsular position and orientation control. Therapeutic functionality is absent in most commercial capsules, due to constraints in capsular volume and energy storage. The possibility of using body-exogenous magnetic fields to guide, orient, power, and operate the capsule and its mechanisms has led to increasing research in Magnetically Guided Capsule Endoscopy (MGCE). This work shortly reviews the history and state-of-art in WCE technology. It highlights the magnetic technologies for advancing diagnostic and therapeutic functionalities of WCE. Not restricting itself to the GI tract, the review further investigates the technological developments in magnetically guided microrobots that can navigate through the various air- and fluid-filled lumina and cavities in the body for minimally invasive medicine.

Magnetic microrobots with addressable shape control

Shape shifting soft microrobots are generated from self-folding hydrogel bilayer structures. The folding conditions are analyzed to develop an optimal strategy for producing desired three-dimensional shapes. We present two different methods for programming magnetization in these microrobots that are variant and invariant to folding. The microrobots can be navigated through user-defined trajectories using rotating magnetic fields, and the morphing in response to temperature changes can be tuned for adaptive behavior. On-demand modulation of the mobility of individual microrobots is demonstrated by morphing their shape using selective near infrared light (NIR) exposure.

Micro-cantilever design and modeling framework for quantitative multi-frequency AFM

Recently several multi-frequency imaging techniques have been proposed that have opened up a multitude of information channels to probe surface properties in atomic force microscopy (AFM). However, the dynamics involved are significantly more complicated than in the traditional AFM modes, and hence quantitative multi-frequency AFM (MF- AFM) remains a key challenge. In this paper, we introduce custom-made micro-cantilevers with integrated actuators and a systems-theoretic modeling framework for MF-AFM, which together provide powerful experimental and theoretical tools for quantitative measurement of tip-sample interaction forces and sample properties.