Micropumps

Devices for converting electrical signals to other, nonelectrical signals and effects. This group includes electroosmotic micropumps, different types of balancing devices, color indicators, and so on. 

Finally, at the Texas Heart Institute, we are developing a concept device that will consist of a catheter deployed micropump in the descending aorta and fixated with metallic struts to the aortic wall. It is designed to accelerate blood flow in the descending aorta to unload the heart. Its power will be supplied through a transarterial power cable to an outside power source. Though still in the conceptual phase only, it may be truly implantable in the cath lab without surgery. 

Fig. 89. Schematic cross-section of the magnetostrictive membrane type micropump. After Quandt (1997).

During the experiments, a micropump made circulating the sample through a reservoir. The optical path of the sample cell was 0.5 mm. The temperature of the sample was kept at 50 °C. The photographic quantum yield was measured at room temperature. 

Zahn, J.D., et al. 2004. Continuous on-chip micropumping for microneedle enhanced drug delivery. Biomed Microdevices 6 183. 

A number of patented technologies for multiparticulate dosage forms have been described recently, such as the Micropump system, which is an osmotically driven coated microparticle system designed to increase the absorption time for rapidly absorbed drugs.59 Combination of water-soluble and water-insoluble polymers could provide enhanced controlled release rates and profiles. A patented technology (COSRx) has been reported to be capable of delivering various sophisticated release profiles. The formulation involves a guar-gum-based tablet and a combination of water-soluble and water-insoluble polymeric tablet coat.60... 

Microfabricated systems. Based on the characteristics, microfabricated systems include microchips and micropumps. 

Silicon micropumps offer major advantages in terms of system miniaturization and control over low flow rates with a stroke volume 160 nL.14 The micropump has the characteristics of very small in size, implantability in the human body, low flow rates (in the range of 10 pL/min), moderate pressure generation from the microactuator to move the drug, biocompatibility, and most important, a reliable design for safe operation. The implantable device is particularly suitable (over the injectable drug delivery systems) for patients with Parkinson s disease, Alzhiemer s disease, diabetes, and cancer, as well as chronically ill patients, because the catheter that is attached to the device can transport drug to the required site. 

Micropumps based on piezoelectrics are made of pumping chambers that are actuated by three piezoelectric lead zirconate titanate disks (PZT). The pump consists of an inlet, pump chambers, three silicon membranes, three normally closed active valves, three bulk PZT actuators, three actuation reservoirs, flow microchannels, and outlet. The actuator is controlled by the peristaltic motion that drives the liquid in the pump. The inlet and outlet of the micropump are made of a Pyrex glass, which makes it biocompatible. Gold is deposited between the actuators and the silicon membrane to act as an upper electrode. Silver functions as a lower electrode and is deposited on the sidewalls of the actuation reservoirs. In this design, three different pump chambers can be actuated separately by each bulk PZT actuator in a peristaltic motion. 

Micropumps have been designed using polymers such as polymethyl methacrylate (PMMA) as the base material. The basic design of this pump consists of six layers. The first is made of a PMMA plate that has an opening at the center for fixing a peizodisk, which, in turn, works as both the actuator and the pump membrane. The peizodisk and a second PMMA plate act as the pump chamber. The second PMMA plate has two... 

As described earlier, the basic design of the micropump involves a drug reservoir attached to a pumping device with or without a sensor. The inclusion of a sensor with the device makes it a closed-loop system, where the device can check the levels of marker molecules such as glucose and deliver the therapeutic agent. In many systems the devices are implanted such that the reservoir can be charged when it is exhausted. The device may pump at a basal rate or may be controlled by a circuit connected in a closed loop with a sensor or by a handheld remote control device by the patient. 

In polymeric membrane and matrix-based micropumps, the membrane or the matrix makes the essential component of the delivery device that controls the rate of release. In matrix controlled delivery, the rate of the hydrolytic breakdown of the matrix is the governing process. In polymeric membrane-controlled release, the rate of hydration of the membrane and the subsequent diffusion of drug are the rate-controlling steps. 

Maillefer, D., Rey-Mermet, G., Hirschi, R. A high-performance silicon micropump for an implantable drug delivery system. 12th IEEE MEMS 1999, Technical Digest, Orlando, FL, 1999. 

Dorner and Cole [27 ] determined aflatoxins in peanuts by LC with post-column iodination and modified micropump clean-up. /i-Cyclodcxtrin enhances the... 

If large amounts of materials have to be transported, a favorable design should instead consider large pumps rather than arrangements with many micropumps, which, in most cases, are commercially unattractive for cost reasons and technically less suitable because of their comparatively low efficiency. 

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