Drew Owen

Magnetic microbeads for sampling and mixing in a microchannel

Microfluidics provides exciting possibilities for miniaturized biosensors systems allowing for highly parallel automated high throughput tests to be performed. Detection of low concentrations of bacteria, viral particles and parasites in food samples is a challenging process. The capture of the target can be more effectively carried out with efficient mixing. We present a simple microfluidic system capable of controlled transport of rotating magnetic beads among soft magnetic patterns. Low aspect ratio NiFe discs (200 nm tall, diameter 3 μm) are patterned onto a silicon wafer. A PDMS channel is bonded onto the wafer to create the microfluidic channel. An external permanent magnet attached to a motor provides a magnetic field, which can be rotated at different speeds while magnetizing the NiFe disks in the channel. Microbeads (Dynabeads M-280, Invitrogen) introduced into the channel with a syringe pump are trapped at the poles of the now magnetized soft magnetic discs. Rotation of the external permanent magnet induced magnetic poles in the soft magnetic discs which will in turn rotate the trapped microbeads. We have already demonstrated the capacity to capture particles from flow with rotating M-280 beads in this device.

Active fluid mixing with magnetic microactuators for capture of salmonella

Detection of low concentrations of bacteria in food samples is a challenging process. Key to this process is the separation of the target from the food matrix. We demonstrate magnetic beads and magnetic micro-cilia based microfluidic mixing and capture, which are particularly useful for pre-concentrating the target. The first method we demonstrate makes use of magnetic microbeads held on to NiFe discs on the surface of the substrate. These beads are rotated around the magnetic discs by rotating the external magnetic field. The second method we demonstrate shows the use of cilia which extends into the fluid and is manipulated by a rotating external field. Magnetic micro-features were fabricated by evaporating NiFe alloy at room temperature, on to patterned photoresist. The high magnetic permeability of NiFe allows for maximum magnetic force on the features. The magnetic features were actuated using an external rotating magnet up to frequencies of 50Hz. We demonstrate active mixing produced by the microbeads and the cilia in a microchannel. Also, we demonstrate the capture of target species in a sample using microbeads.

Spatiotemporal mechanical variation reveals critical role for rho kinase during primitive streak morphogenesis.

Large-scale morphogenetic movements during early embryo development are driven by complex changes in biochemical and biophysical factors. Current models for amniote primitive streak morphogenesis and gastrulation take into account numerous genetic pathways but largely ignore the role of mechanical forces. Here, we used atomic force microscopy (AFM) to obtain for the first time precise biomechanical properties of the early avian embryo. Our data reveal that the primitive streak is significantly stiffer than neighboring regions of the epiblast, and that it is stiffer than the pre-primitive streak epiblast. To test our hypothesis that these changes in mechanical properties are due to a localized increase of actomyosin contractility, we inhibited actomyosin contractility via the Rho kinase (ROCK) pathway using the small-molecule inhibitor Y-27632. Our results using several different assays show the following: (1) primitive streak formation was blocked; (2) the time-dependent increase in primitive streak stiffness was abolished; and (3) convergence of epiblast cells to the midline was inhibited. Taken together, our data suggest that actomyosin contractility is necessary for primitive streak morphogenesis, and specifically, ROCK plays a critical role. To better understand the underlying mechanisms of this fundamental process, future models should account for the findings presented in this study.

The Role of Actomyosin Contractility During Early Avian Gastrulation

Actin-myosin contraction has been shown to play a major role in early morphogenetic movements in Drosophila (fly) and Xenopus (frog) [1,2]. However, the specific role of actomyosin contractility in amniote embryos (reptiles, birds, and mammals) during primitive streak (PS) formation, the “organizing center” for gastrulation (formation of three primary germ layers), is not known. Current theories regarding primitive streak formation in higher order amniotes center around cell-cell intercalation or chemotactic cell movement [3,4]. We hypothesize that contraction via actin-myosin (AM) filaments is conserved from anamniotes and drives formation of the PS and the associated morphogenetic cell movements.Copyright