Camilo Velez

Magnetic Assembly and Cross-Linking of Nanoparticles for Releasable Magnetic Microstructures.

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.

Investigation of the Capture of Magnetic Particles From High-Viscosity Fluids Using Permanent Magnets

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 toward 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 paper 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.

Automated 2D micro-assembly using diamagnetically levitated milli-robots

In this article, we demonstrate the application of diamagnetically levitated milli-robots for the 2D micro-assembly of 10-μm polymer microspheres and other silicon microfabricated parts. By using an optical microscope for feedback (imaged at 27 Hz), we are able to demonstrate long-term open-loop stability (up to 78 hr) and sub-micron stability of the levitated micro-robots. Furthermore, due to the low hysteresis and high compliance in the magnetic drive of the milli-robots, we are able to directly use the milli-robots in conjunction with machine vision as a force sensor. Soft polymer-based end effectors are used for the micromanipulation of parts and show modest reliability of pick (>70%) and high reliability of place (>99%) that is insensitive to the pick surface material. Finally, we implement autonomous micro-assembly from randomly deposited microspheres into ordered arrays.

Collection of magnetic particles from synovial fluid using Nd-Fe-B micromagnets

In this paper, the collection of magnetic particles from synovial fluid using Nd-Fe-B micromagnets is quantitatively studied to determine the influence of fluid viscosity and magnet geometry on the velocity distribution and collection rate. Magnetic capture is validated in highly viscous fluids, such as bovine synovial fluid (η~ 1 Pa·s). A first-order theoretical model has been developed to predict the particle motion, as well as a numerical multiphysics model. Both models exhibit good agreement with in vitro experimental magnetic collection results. The velocity of the magnetic particles is shown to be inversely proportional to fluid viscosity, and two magnetic structures are compared in term of collection efficiency: a cylindrical Nd-Fe-B permanent magnet and a laser-machined conical Nd-Fe-B permanent magnet.

Microneedle Based ECG – Glucose Painless MEMS Sensor with Analog Front End for Portable Devices

A portable microelectromechanical system (MEMS) for mobile phones, or other portable devices, that measures body electrical signals, as well as, extracts transdermal biological fluid for invivo analysis is proposed. This system integrates two sensing methods: three points finger electrocardiography (ECG) and glucose monitoring, through one electrode with a microneedle-array. This work presents the: (1) device modeling and microneedle-array’ fabrication method, (2) signal processing and biasing circuitry’ design and simulation, (3) Analog Front End (AFE) for measured signals, and (4) Glucose sensor characterization. Design parameters and geometries are obtained by solving the capillarity model inside the microneedles and running optimization numeric methods. The AFE consists in a differential band pass filter that provides amplification, filtering, and noise rejection. This work presents clear technological innovation, for its miniaturization and integration of known biological signals’ measurement methods in a portable Smart System, which points in the direction of Internet of Things’ goals.

Direct measurement and microscale mapping of nanoNewton to milliNewton magnetic forces

This paper describes the direct measurement and mapping of magnetic forces/fields with microscale spatial resolution by combining a commercial microforce sensing probe with a thin-film permanent micromagnet. The main motivation of this work is to fill a critical metrology gap with a technology for direct measurement of magnetic forces from nN to 10’s of mN with sub-millimeter spatial resolution. This capability is ideal for measuring forces (which are linked to magnetic field gradients) produced by small-scale magnetic and electromagnetic devices including sensors, actuators, MEMS, micromotors, microfluidics, biomedical devices. This new measuring technique is validated by comparison of measured forces from small permanent magnets with the analytical models.

Fabrication of patterned magnetic microstructures using magnetically assembled nanoparticles

This work describes the modeling and experimental characterization of a fabrication method for forming magnetic microstructures using self-assembled iron oxide (Fe3O4) magnetic nanoparticles. This method can potentially be used in roll-to-roll production of magnetic structures patterned onto substrates or optionally lifted off to create free-floating micromagnetic actuators. This article reports: (1) the use of a selective magnetization process to create magnetic microstructures with complex, photolithographically defined shapes, (2) development of multi-physics simulations that model key fabrication steps (selective magnetization and particle assembly), and (3) experimental evaluation of the microstructure features (line width and height) as functions of process variables. The primary accomplishment is obtaining well-defined microstructures with complex shape and demonstrating their magnetic actuation when released as free-floating structures.