In this work we present a novel microfabrication process that is based on combined use of dielectrophoresis (DEP) to
attract particles or cells to electrodes and to follow this step by an electrodeposition of polypyrrole (PPy) to entrap the
particles or cells on electrode surface. This process can be used for mass-production of high surface area structures as
well as to the creation of functionally graded materials. DEP was employed to pull the microparticles toward the surface
of the electrodes and hold them in place while PPy was electrodeposited. Polystyrene microbeads with diameters ranging
from 1 to 10 microns were employed in this study. Experimental results demonstrated that PPy can entrap the particles
attracted to the electrode surface by the positive DEP. It was also demonstrated that hierarchical structures can be created
where smaller microbeads are attached to, caught and secured on the surface of larger microbeads entrapped on the
electrode surface. Furthermore, as DEP can be employed for manipulating of wide variety of polarizable materials, this
process can also entrap inorganic and biological microparticles in the fabricated structure. Applications of this work
include, but are not limited to, the development of biomedical, electrokinetic, and energy storage devices,
electrochemical sensors, and scaffolds.
Polypyrrole (PPy)-based microactuators hold a promise for a wide variety of engineering applications from robotics and
microassembly to biosensors and drug delivery systems. The main advantages of using PPy/Au actuator structures (vs
competing solid-state actuator technologies) include ease of fabrication, low actuation energy, and large motion range of
microactuators. We present advances in two areas of application - in the extended-life biosensor platform and in
micromixers.
High specific surface area structures are used in a variety of applications including production of highly sensitive
biosensors, fabrication of separation membranes, manufacturing of high throughput catalytic microreactors, and
development of efficient electrodes for batteries and fuel cells. In many electrochemical applications (i.e. sensors and
batteries) it's also critical to have good conductive properties of the fabricated high surface area structures.
For energy harvesting technologies such as batteries and fuel cells, careful design of surface-to-volume ratio of the
electrode surface is important, because while high specific surface area facilitates electrochemical reaction rates, it also
increases overall electrode resistance. Thus, it is desirable to construct electrodes with a range of hierarchical features
(for example with fractal structures).
We invented a novel fabrication technology for creating three-dimensional conductive high surface area structures based
on the deposition and subsequent processing of the electroactive polymers (EAP). The proposed fabrication technique is
capable of fast and inexpensive production of high surface area structures with the designed geometry, porosity, and
conductivity.
Present study is looking at the problem of integrating drug delivery microcapsule, a bio-sensor, and a control mechanism into a biomedical drug delivery system. A wide range of medical practices from cancer therapy to gastroenterological treatments can benefit from such novel bio-system. Drug release in our drug delivery system is achieved by electrochemically actuating an array of polymeric valves on a set of drug reservoirs. The valves are bi-layer structures, made in the shape of a flap hinged on one side to a valve seat, and consisting of thin films of evaporated gold and electrochemically deposited polypyrrole (PPy). These thin PPy(DBS) bi-layer flaps cover access holes of underlying chambers micromachined in a silicon substrate. Chromium and polyimide layers are applied to implement "differential adhesion" to obtain a voltage induced deflection of the bilayer away from the drug reservoir. The Cr is an adhesion-promoting layer, which is used to strongly bind the gold layer down to the substrate, whereas the gold adheres weakly to polyimide. Drug actives (dry or wet) were pre-stored in the chambers and their release is achieved upon the application of a small bias (~ 1V). Negative voltage causes cation adsorption and volume change in PPy film. This translates into the bending of the PPy/Au bi-layer actuator and release of the drug from reservoirs. This design of the drug delivery module is miniaturized to the dimensions of 200μm valve diameter. Galvanostatic and potentiostatic PPy deposition methods were compared, and potentiostatic deposition method yields film of more uniform thickness. PPy deposition experiments with various pyrrole and NaDBS concentrations were also performed. Glucose biosensor based on glucose oxidase (GOx) embedded in the PPy matrix during elechtrochemical deposition was manufactured and successfully tested. Multiple-drug pulsatile release and continuous linear release patterns can be implemented by controlling the operation of an array of valves. Varying amounts of drugs, together with more complex controlling strategies would allow creation of more complex drug delivery patterns.
This work presents manufacturing and testing of a closed-loop drug delivery system where drug release is achieved by an electrochemical actuation of an array of polymeric valves on a set of drug reservoirs. The valves are based on bi-layer structures made of polypyrrole/gold in the shape of a flap that is hinged on one side of a valve seat. Drugs stored in the underlying chambers are released by bending the bi-layer flaps back with a small applied bias. These polymeric valves simultaneously function as both drug release components and biological/chemical sensors responding to a specific biological or environmental stimulus. The sensors may send signals to the control module to realize closed-loop control of the drug release. In this study a glucose sensor has been integrated with the polymeric actuators through immobilization of glucose oxidase(GOx) within polypyrrole(PPy) valves. Sensitivities per unit area of the integrated glucose sensor have been measured and compared before and after the actuation of the sensor/actuator PPy/DBS/GOx film. Other sensing parameters such as linear range and response time were discussed as well. Using an array of these sensor/actuator cells, the amount of released drug, e.g. insulin, can be precisely controlled according to the surrounding glucose concentration detected by the glucose sensor. Activation of these reservoirs can be triggered either by the signal from the sensor, or by the signal from the operator. This approach also serves as the initial step to use the proposed system as an implantable drug delivery platform in the future.
The most common methods for the drug delivery are swallowing pills or receiving injections. However, formulations that control the rate and period of medicine (i.e., time-release medications) are still problematic. The proposed implantable devices which include batteries, sensors, telemetry, valves, and drug storage reservoirs provide an alternative method for the responsive drug delivery system [1]. Using this device, drug concentration can be precisely controlled which enhances drug efficiency and decreases the side effects. In order to achieve responsive drug delivery, a reliable release valve has to be developed. Biocompatibility, low energy consumption, and minimized leakage are the main requirements for such release method. A bilayer structure composed of Au/PPy film is fabricated as a flap to control the release valve. Optimized potentiostatic control to synthesize polypyrrole (PPy) is presented. The release of miniaturize valve is tested and showed in this paper. A novel idea to simultaneously fabricate the device reservoirs as well as protective packaging is proposed in this paper. The solution of PDMS permeability problem is also mentioned in this article.
Fluid flow in capillary microchannels is used in numerous applications in biotechnology (such as protein separation, fast DNA analysis, drug deliveries systems and viral filtration), in solid-state devices, and in catalytic devices. The current work presents the experimental validation for the electrokinetic theory in microchannels. Retardation of polar liquids, including de-ionized water, ethanol and propyl alcohol, is studied in microfabricated channels of several diameters. It was found that polar liquids flow about 6 percent more slowly than predicted by the classical hydrodynamic theory in microchannels, with the hydraulic diameter equal to 90 microns. For small microchannels with a hydraulic diameter of several microns, observed retardation is on the order of 70 percent. Collected experimental data have good correspondence with the electrokinetic model presented. Electrokinetic retardation of polar liquids in microchannels is based on the charge separation principle. Electrical charges are separated at the interface (near the channel wall). When liquid is forced downstream, it causes charge accumulation at one end of the microchannel. The streaming potential produced causes an upstream current that creates upstream counterflow. The resultant fluid flow is less than it would be for non-polar liquids. The higher the zeta-potential at the microchannel wall and the smaller the channel, the larger the resulting retardation. Modifications for the friction factor, as applied to microfluidics, are suggested. Recommendations to improve fluid flow in microchannels are made.
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