Millimeter-Sized Hole Damming.

Valves used to control liquid filling and draining processes from storage typically need to be actuated. Here, we show that similar flow enabling and restricting operations can be achieved through millimeter scale holes that function according to the amount of hydrostatic pressure applied without any other intervention. This phenomena is exhibited using receptacles where the base is made of either a hydrophilic or superhydrophobic substrate with hole sizes ranging from 1.

Drops on a Superhydrophobic Hole Hanging On under Evaporation.

Drops with larger volumes placed over a superhydrophobic (SH) surface with a hole do not fall through unless they are evaporated to a size that is small enough. This feature offers the ability to preconcentrate samples for biochemical analysis. In this work, the influence of pinning on the behavior of drops placed on a 0.

Linear Stepper Actuation Driving Drop Resonance and Modifying Hysteresis.

In this work, 2 μL water drops are placed on substrates that are created to have a circular hydrophilic region bounded by superhydrophobicity so that they exhibit high contact angles. When the substrate is translated by a linear stepper actuator, the random force components present in the actuator are shown to cause the drop to rock resonantly. When the substrate is translated downward at inclination angles of up to 6° with respect to the horizontal, the contact angle hysteresis increases progressively to a limiting condition.

Stabilized dried blood spot collection.

During the collection phase of the dried blood spot method, practitioners need to ensure that there is no smearing of the blood sample on the filter paper or else readings from it will be invalid. This can be difficult to accomplish in the field if there is relative motion between the site of blood discharge on the finger and the filter paper. In this article, a gyroscope stabilization method is introduced and demonstrated to provide consistent and improved dried blood spot collection within a circular guide region notwithstanding the presence of rocking.

Adapting a Low-Cost Selective Compliant Articulated Robotic Arm for Spillage Avoidance.

Flexible automation systems provide the needed adaptability to serve shorter-term projects and specialty applications in biochemical analysis. A low-cost selective compliant articulated robotic arm designed for liquid spillage avoidance is developed here. In the vertical-plane robotic arm movement test, the signals from an inertial measurement unit (IMU) and accelerometer were able to sense collisions.

Liquid-body resonance while contacting a rotating superhydrophobic surface.

We advance a scheme in which a liquid body on a stationary tip in contact with a rotating superhydrophobic surface is able to maintain resonance primarily from stick-slip events. With tip-to-surface spacing in the range 2.73 ≤ h < 2.

Controlled transport of captive bubbles on plastrons.

Captive bubbles that reside on superhydrophobic surfaces with plastrons move uncontrollably when tilted. A system based on creating moveable local apexes on flexible superhydrophobic foils is shown to allow controlled transport. Simulations done reveal that specific bubble transport speeds are needed to form concentration gradients suited for aerotaxis study and sensing.

Concentrating nanoparticles in environmental monitoring.

There are significant challenges in assessing the toxicity of nanoparticles in the environment in which effective methods for detection are crucial. An inexpensive method that uses superhydrophobic well with an evaporating droplet followed by a simple squeeze flow is described here and found to provide practical high nanoparticle collection from samples for detection. The process could be hastened by placing a radiant heater close to the droplet if temperature rises in the sample can be tolerated.

Plastron-Mediated Growth of Captive Bubbles on Superhydrophobic Surfaces.

Captive bubbles on a superhydrophobic (SH) surface have been shown to increase in volume via injection of air through the surrounding plastron. The experimental contact diameter against volume trends were found to follow that predicted by the Surface Evolver simulation generally but corresponded with the simulated data at contact angle (CA) = 158° when the volume was 20 μL but that at CA = 170° when the volume was increased to 180 μL. In this regime, there was a simultaneous outward movement of the contact line as well as a small reduction in the slope that the liquid-air interface makes with the horizontal as air was injected.

Particles replaced axially in an optical trap.

Flow-based measures to automate optical trapping have significant limitations. A scheme is advanced here where a spherical bead is first located in a trap, and a second bead below the focus point is selectively drawn into the trap to replace the original particle. Experimentation conducted showed that it was possible to do so with little perturbation of other surrounding particles.

Drop transfer between superhydrophobic wells using air logic control.

Superhydrophobic surfaces aid biochemical analysis by limiting sample loss. A system based on wells here tolerated tilting up to 20° and allowed air logic transfer with evidence of mixing. Conditions for intact transfer on 15 to 60 μL drops using compressed air pressure operation were also mapped.

Optical trapping map of dielectric spheres.

Many applications use a focused Gaussian laser beam to manipulate spherical dielectric particles. The axial trapping efficiency of this process is a function of (i) the particle radius r, (ii) the ratio of the refractive index of particle over the medium, and (iii) the numerical aperture of the delivered light beam. During what we believe is the first comprehensive simulation of its kind, we uncovered optical trapping regions in the three-dimensional (3D) parameter space forming an iso-surface landscape with ridge-like contours.

Optical stirring in a droplet cell bioreactor.

In the context of a bioreactor, cells are sensitive to cues from other cells and mechanical stimuli from movement. The ability to provide the latter in a discrete fluidic system presents a significant challenge. From a prior finding that the location of the focus of a laser below particles relative to the beam axis producing a pushing effect in a predominant lateral sense, we advance an approach here that generates a gentle and tunable stirring effect.

Sorting of brownian rods by the use of an asymmetric potential.

We present here a method for sorting nanometer scale brownian rods by using a switching asymmetric periodic potential. A two stage sorting process is used to isolate particles with specific dimensions, with acceptable sorting times as well as realizable potential barrier lengths. The method was tested using computer simulations.