Roel Wirix-Speetjens

On-chip manipulation and magnetization assessment of magnetic bead ensembles by integrated spin-valve sensors

Manipulation and detection of magnetic beads on a semiconductor chip opens up new perspectives for analysis of magnetically labeled specimens in biomechanical micro-electromechanical systems for biological applications. Sensitive spin-valve sensors were integrated with magnetic field generating conductors to assess the behavior of ensembles of superparamagnetic nanoparticles 300 nm in diameter that contain 75%–80% magnetite. The spin-valve multilayer including a nanooxide layer achieves 8% magnetoresistance (MR) for an integrated device of 2×16 μm2. Motion of the magnetic particles towards and across the sensor is achieved by two tapered magnetic field generating current conductors. The spin-valve sensor detects the stray magnetic field that emanates from the ensemble of magnetic particles. We study the transients in the magnetic signal on the order of 1% MR. These results lead to a model that describes magnetization configurations of the cluster of beads.

Experimental demonstration of nonreciprocal amplified spontaneous emission in a CoFe clad semiconductor optical amplifier for use as an integrated optical isolator

Experimental results are presented for an integrated-optical-waveguide-isolator concept. This concept is based on inducing the transverse magneto-optic Kerr effect in a semiconductor InP-based optical amplifier (SOA) by using a transversely magnetized ferromagnetic metal as an electrical contact. As a result, the SOA exhibits nonreciprocal loss/gain for TM polarized light and is easily monolithically integrated with other InP-based active photonic devices. We have designed, fabricated and characterized prototype ferromagnetic metal-clad optical amplifiers for an operation wavelength of 1300nm. In these first generation devices we obtained isolation strengths of up to 2.0dB∕mm.

On-chip separation of magnetic particles with different magnetophoretic mobilities

Recent integrations of giant magnetoresistive sensor into laboratory-on-a-chip systems enable the direct detection of biological entities such as cells coated with magnetic particles on chip. However, before detection the different biological entities need to be separated. As a model system, we investigated the separation of two types of magnetic particles (4.5 and 2μm in diameter). The motion of the particles was studied when actuated using an alternating traveling magnetic field produced by four-phase conductors on chip. Different magnetic particles migrate with different speeds in the same traveling magnetic field. By carefully choosing the frequency of the magnetic field, different magnetic particles can be separated in a microfluidic system.

On-chip magnetic particle transport by alternating magnetic field gradients

We have demonstrated an on-chip magnetic bead transport device based on a set of two tapered current conductors. We have fabricated and tested two types of devices. Both devices are capable of trapping single magnetic microbeads and guiding them along a defined magnetic track. We examined scaling of the basic repetitive element and found good agreement among experiment, theory, and simulations. This novel magnetic transport mechanism opens possibilities for controlled manipulation of magnetically labeled biomolecules.

Single magnetic particle detection: Experimental verification of simulated behavior

In the past, magnetoresistive sensor based biosensors, using superparamagnetic particles, have shown to be promising candidates for highly sensitive biosensors. These sensors can detect a single micron-sized magnetic particle. For single particle detection, research groups have developed models to predict the signal per particle. In these models, the separation distance plays an important role for the quantitative determination of the signal. However, mostly only the passivation layer thickness is included as the separation distance. In this paper, we describe a detection system based on a magnetic spin-valve sensor that is capable of giving position-time information of the magnetic behavior of one single bead. The results obtained with this system for the detection of a single particle signature are then compared with simulations. For this comparison, we developed a model where an additional particle-substrate separation distance is included. This distance is determined by a force balance of the perpendi...

Fully controlled precessional switching of a macrospin in a cross-wire geometry

Ultrafast scanning Kerr microscopy measurements of half-precession-cycle, quasiballistic magnetization switching in a Permalloy™ macrospin are presented. The 20×7 μm2, 15-nm ellipse-shaped element is embedded in a continuous film of thinner Py, which effectively eliminates the remanent state closure domains and strongly increases coherence of dynamic motions in the large element. A perpendicular crossing-wire geometry allows pulse excitations to both the easy and hard axes. Data for well-terminated, ringing-suppressed ballistic switching and poorly-terminated switching with ringing are presented with hard axis pulses as small as 12 Oe and as short as ∼400-ps driving precessional switching. With addition of an easy-axis overlapping pulse, half-select precessional switching into a metastable state is observed; however, large spatial nonuniformities are introduced into the element dynamics, which ultimately defeat the half-select switching process.

Enhanced magnetic particle transport by integration of a magnetic flux guide : Experimental verification of simulated behavior

In the past, magnetic biosensors have shown to be promising alternatives for classical fluorescence-based microarrays, replacing the fluorescent label by a superparamagnetic particle. While on-chip detection of magnetic particles is firmly established, research groups continue to explore the unique ability of manipulating these particles by applying controlled magnetic forces. One of the challenging tasks in designing magnetic force generating structures remains the generation of large forces for a minimal current consumption. Previously, a simple transporting device for single magnetic particles has been demonstrated using a magnetic field that is generated by two tapered current carrying conductors [R. Wirix-Speetjens, W. Fyen, K. Xu, J. De Boeck, and G. Borghs, IEEE Trans. Magn. 41(10), 4128 (2005)]. We also developed a model to accurately predict the motion of a magnetic particle moving in the vicinity of a solid wall. Using this model, we now present a technique that enhances the magnetic force up to...

Virtual reconstruction of glenoid bone defects using a statistical shape model

BACKGROUND Description of the native shape of a glenoid helps surgeons to preoperatively plan the position of a shoulder implant. A statistical shape model (SSM) can be used to virtually reconstruct a glenoid bone defect and to predict the inclination, version, and center position of the native glenoid. An SSM-based reconstruction method has already been developed for acetabular bone reconstruction. The goal of this study was to evaluate the SSM-based method for the reconstruction of glenoid bone defects and the prediction of native anatomic parameters. METHODS First, an SSM was created on the basis of 66 healthy scapulae. Then, artificial bone defects were created in all scapulae and reconstructed using the SSM-based reconstruction method. For each bone defect, the reconstructed surface was compared with the original surface. Furthermore, the inclination, version, and glenoid center point of the reconstructed surface were compared with the original parameters of each scapula. RESULTS For small glenoid bone defects, the healthy surface of the glenoid was reconstructed with a root mean square error of 1.2 ± 0.4 mm. Inclination, version, and glenoid center point were predicted with an accuracy of 2.4° ± 2.1°, 2.9° ± 2.2°, and 1.8 ± 0.8 mm, respectively. DISCUSSION AND CONCLUSION The SSM-based reconstruction method is able to accurately reconstruct the native glenoid surface and to predict the native anatomic parameters. Based on this outcome, statistical shape modeling can be considered a successful technique for use in the preoperative planning of shoulder arthroplasty.

Statistical Shape Modeling and Population Analysis of the Aortic Root of TAVI Patients

The new transcatheter technique to implant synthetic aortic valves offers a treatment to patients previously considered untreatable. However, the majority of patients suffer from leakage alongside the implant. Using a statistical shape model of the anatomy, a correlation was discovered between leakage and the shape of the sinuses of Valsalva.

Evaluation of predicted knee function for component malrotation in total knee arthroplasty

Soft-tissue balancing for total knee arthroplasty (TKA) remains subjective and highly dependent on surgical expertise. Pre-operative planning may support the clinician in taking decisions by integrating subject-specific computer models that predict functional outcome. However, validation of these models is essential before they can be applied in clinical practice. The aim of this study was to evaluate a knee modelling workflow by comparing experimental cadaveric measures to model-based kinematics and ligament length changes. Subject-specific models for three cadaveric knees were constructed from medical images. The implanted knees were mounted onto a mechanical rig to perform squatting, measuring kinematics and ligament length changes with optical markers and extensometers. Coronal malrotation was introduced using tibial inserts with a built-in slope. The model output agreed well with the experiment in all alignment conditions. Kinematic behaviour showed an average RMSE of less than 2.7mm and 2.3° for translations and rotations. The average RMSE was below 2.5% for all ligaments. These results show that the presented model can quantitatively predict subject-specific knee behaviour following TKA, allowing evaluation of implant alignment in terms of kinematics and ligament length changes. In future work, the model will be used to evaluate subject-specific implant position based on ligament behaviour.