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Babak Ziaie

Publications and source records attributed to Babak Ziaie.

7 recordsLinked to original sources
PubMed2006

A hydrogel-based implantable micromachined transponder for wireless glucose measurement.

In this paper, we report on the design and characterization of a new hydrogel-based implantable wireless glucose sensor. The basic device structure is a passive [inductor/capacitor (LC)] micromachined resonator coupled to a stimuli-sensitive hydrogel, which is confined between a stiff nanoporous membrane and a thin glass diaphragm. As glucose molecules pass through the nanoporous membrane, the hydrogel swells and deflects the flexible glass diaphragm, which is the movable plate of the variable capacitor in the totally integrated passive LC resonator. The corresponding change in resonant frequency can be remotely detected. A glucose- sensitive phenylboronic acid-based hydrogel was loaded into the microtransponder, and its sensitivity and time response were measured. Prior to hydrogel loading, the sensitivity of the pressure sensor to applied air pressure was measured to be -222 kHz/kPa over the frequency range 51-->42 MHz. The sensor showed a sensitivity of -34.3 kHz/mM over the glucose concentration range 0-20 mM (at pH 7.4), and a response time of 90 min. The dynamic response, although unacceptable at such values, can be easily improved by decreasing the hydrogel thickness and reducing the sensor and porous membrane thicknesses. The transponder's overall dimensions were 5x5x0.8 mm3, small enough for subcutaneous implantation.

Biosensing Techniques↗
PubMed2005

Modeling and characterization of a valved glaucoma drainage device with implications for enhanced therapeutic efficacy.

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.

Computer Simulation↗
PubMed2005

Thin-film coupled fluid-solid analysis of flow through the Ahmed glaucoma drainage device.

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.

Aqueous Humor↗
PubMed2004

Application of the lag-after-pulsed-separation (LAPS) flow meter to different protein solutions.

A lag after pulsed separation (LAPS) meter was previously developed to measure flow rates of protein solutions. The LAPS meter operates on the time-of-flight principle. An upstream event (electrophoretic concentration of the particles in one section of the device) is detected downstream (by change in ac resistance). The time lag between the event and its detection is inversely proportional to the fluid flow rate. We demonstrate the ability of the LAPS meter to measure the flow rate of solutions containing one or more charged biomacromolecules or particles. A prototype of the LAPS meter was used to measure flow rates of solutions of model proteins [bovine serum albumin (BSA), lysozyme and hemoglobin] and mixtures of BSA and lysozyme. Flow rates of 10-50 microl min(-1)(average velocities of 0.24-1.2 mm s(-1)) were measured. When a single ac measurement was used, the results were solution-dependent, which we attribute to the interface between the protein solution and the ac electrodes. A differential mode, in which the signal from a positive and a negative dc pulse were subtracted from each other, eliminated interfacial effects and led to a single universal (solution-independent) calibration curve. The LAPS meter can be used as a non-invasive, no-moving-parts flow sensor in any microfluidic system (such as drug delivery devices or micro-reactor arrays) where one needs to measure the flow rate of a solution or a suspension containing charged species such as proteins or cells.

Animals↗
PubMed2004

Hard and soft micromachining for BioMEMS: review of techniques and examples of applications in microfluidics and drug delivery.

Recent development in microfabrication (micromachining, microelectromechanical systems, MEMS) permits the integration of hard and soft structures, and enables the design of controllable microfluidic systems, which may be applied to drug delivery. In this paper, we present a tutorial review of both classical "hard" and more recent "soft" micromachining techniques. We then provide examples where these techniques are combined to produce hydrogel-based microfluidic control systems. The most complex of these systems utilizes a very small hydrogel based on phenylboronic acid to control the flow of an insulin solution in response to changes in glucose concentration.

Drug Delivery Systems↗