We report on modeling and bench test results targeted at better understanding of valved glaucoma drainage devices (GDDs), a common current surgical treatment for glaucoma. A simple equivalent circuit is described to model fluid mechanical behavior of the aqueous humor in an eye with glaucoma, both before and after implantation of a valved GDD. Finite element method simulations (FEM), based on the lubrication-von Kármán model, are then performed to analyze the valve's mechanical and fluidic performance. Using nanoporous membranes to mimic the in vivo fibrous capsule, we have developed a microfluidic bench test to simulate the aqueous humor flow and the post-implantation fibrous tissue encapsulation around the GDD back plate. Our numerical and bench test results show that, contrary to the prevailing belief, the valve significantly contributes to the total pressure drop even after fibrous capsule formation. Furthermore, we show that bypassing the valve through a simple polyimide tube insertion will dramatically lower the intraocular pressure (IOP) after fibrous capsule formation. This may offer a new treatment option in some patients with advanced glaucoma.

The interaction among convection, diffusion, and geometry causes significant differences in biodistribution between large and small molecules or across species. These differences should be considered in the design of delivery strategies or animal studies.

We present a robust low-cost PDMS peristaltic micropump with magnetic drive. The fabrication process is based on the soft molding and bonding of three PDMS layers. A base layer incorporates the microchannel while a middle layer contains the actuation membrane. The top layer encapsulates three small permanent magnetic rods (Ni-plated-NdFeB) in three small chambers. A small DC motor (6 mm in diameter and 15 mm in length) with three permanent magnets stagger-mounted on its shaft is used to pull down and actuate the membrane-mounted magnets to generate a peristaltic waveform. A maximum pumping rate of about 24 muL/min at the speed of 1700 rpm with power consumption of 11 mW was demonstrated. A preliminary numerical analysis of the peristaltic pump was performed, which showed the characteristic membrane deflection and fluid flow of pumping.

SUMMARYA method is developed for performing a local reduction of the governing physics for uid problems with domains that contain a combination of narrow and non-narrow regions, and the computational accuracy and performance of the method are measured. In the narrow regions of the domain, where the uid is assumed to have no inertia and the domain height and curvature are assumed small, lubrication, or Reynolds, theory is used locally to reduce the two-dimensional Navier-Stokes equations to the one-dimensional Reynolds equation while retaining a high degree of accuracy in the overall solution. The Reynolds equation is coupled to the governing momentum and mass equations of the non-narrow region with boundary conditions on the mass and momentum ux. The localized reduction technique, termed 'stitching,' is demonstrated on Stokes ow for various geometries of the hydrodynamic journal bearing-a non-trivial test problem for which a known analytical solution is available. The computational advantage of the coupled Stokes-Reynolds method is illustrated on an industrially applicable fullyooded deformable-roll coating example. The examples in this paper are limited to two-dimensional Stokes ow, but extension to three-dimensional and Navier-Stokes ow is possible.

The Ahmed glaucoma valve (AGV) is a popular glaucoma drainage device, allowing maintenance of normal intraocular pressure in patients with reduced trabecular outflow facility. The uniquely attractive feature of the AGV, in contrast to other available drainage devices, is its variable resistance in response to changes in flow rate. As a result of this variable resistance, the AGV maintains a pressure drop between 7 and 12 mm Hg for a wide range of aqueous humor flow rates. In this paper, we demonstrate that the nonlinear behavior of the AGV is a direct result of the flexibility of the valve material. Due to the thin geometry of the system, the leaflets of the AGV were modeled using the von Kármán plate theory coupled to a Reynolds lubrication theory model of the aqueous humor flow through the valve. The resulting two-dimensional coupled steady-state partial differential equation system was solved by the finite element method. The Poisson's ratio of the valve was set to 0.45, and the modulus was regressed to experimental data, giving a best-fit value 4.2 MPa. Simulation results compared favorably with previous experimental studies and our own pressure-drop/flow-rate data. For an in vitro flow of 1.6 microL/min, we calculated a pressure drop of 5.8 mm Hg and measured a pressure drop of 5.2 +/- 0.4 mm Hg. As flow rate was increased, pressure drop rose in a strongly sublinear fashion, with a flow rate of 20 microL/min giving a predicted pressure drop of only 10.9 mm Hg and a measured pressure drop of 10.5 +/- 1.1 mm Hg. The AGV model was then applied to simulate in vivo conditions. For an aqueous humor flow rate of 1.5-3.0 microL/min, the calculated pressure drops were 5.3 and 6.3 mm Hg.

Because of the significance of diffusion on the microfluidic length scale, diffusion-based mixers are a valuable and popular component in lab-on-a-chip designs, with many variations emerging. The design of such mixers, however, is limited by existing simulation tools, which are often slow and poorly suited to the special geometry of microchannels. In this article, we derive the necessary conditions for a reduced-dimension model of flow and diffusion in a thin (i.e., height much less than width) channel. We subsequently show that the resulting mass transport equation can be solved in a streamfunction-pressure coordinate system, providing a simpler, more accurate, and more stable solution than is possible using standard methods in the x–y coordinate system. Simulations by this method were fast, requiring less than 30 min even for complex domains; the bulk of the time was spent on noncomputational tasks such as mesh generation. The approach was applied to three problems: a simple mixer based on the T sensor of Yager and co-workers, and then two variations on the base case in which obstructions were introduced to increase the available diffusion time. Although the obstructions changed the flow pattern significantly, there was little effect on the outlet concentration profile. It was observed from the model equations that if the flow rate is unchanged, the improvement in mixing can be expressed in terms of an upper bound based on the increase in pressure drop. In the case studied, the pressure drop change was small, so the mixing was not improved very much.