Micropump diffusion

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. 

Fig. 16. Schematic of the nozzle/diffuser parallel connected micropumps [36]...

Fig. 12 Diffusion micropump, (a) Schematic set-up. (b) Operating principle, (c) Pump characteristics (1) peristaltic mode, (2) pulsatile mode. Reproduced from (Richter et al. 2009a) by permission of The Royal Society of Chemistry...

Unlike diffusion devices the displacement micropump pumps at increasing actuator volume (Fig. 13b) and fills the pump chamber at hydrogel shrinkage. The flow direction of the pump is defined by the valves placed inlet- and outletsided. 

Compared to other micropumps hydrogel-based devices can be classified as pumps with small dead volume suitable for low- (diffusion micropump) and medium-performance (displacement micropump) applications (Nguyen et al. 2002 Laser and Santiago 2004). 

The controlled-release micropump (Figure 2) is a recently invented device that uses the principles of membrane transport and controlled release of drugs to deliver insulin at variable rates (20,26). With a suitable supply of insulin connected to the pump, the concentration and/or pressure difference across the membrane results in diffusion or bulk transport through the membrane ). This process is the basal delivery and requires no external power source. Augmented delivery is achieved by repeated compression of the foam membrane by the coated mild-steel piston. The piston is the core of the solenoid, and compression is effected when current is applied to the solenoid coil. Interruption of the current causes the membrane to relax, drawing more drug into the membrane in preparation for the next compression cycle. 

Microactuators, Fig. 4 In-plane micropump for drug delivery composed of diffuser, nozzle, pumping chamber, and electrothermal microactuator (Image courtesy of Texas Microfactory Lab, ARRI-UTA)... 

Chao et al. [12] reported an ultrasound-actuated micropump which uses nonporous one-way membranes. The device consists of a PMMA pumping chamber with nanonozzles and diffusers. If the device is submerged in ultrasonic bath, it starts pumping the fluid. A flow rate of 0.603 pL/s against a back pressure of 200 mm H2O was reported. 

Chao C, Cheng CH, Liu Z, Yang M, Leung WWF (2008) An ultrasound-actuated micropump that uses nanoporous one-way membrane as nozzle-diffuser. In IEEE intematiraial ultrasonies symposium proceedings... 

One of the passive mixers was developed using capillary forces to insert and hold the liquids in separate chambers, which are connected via a small gap [45]. It is a self-filling micromixer device and does not require micropumps referring it as an automixing device. This device was developed on a chip with two channels with variable volumes that are separated by a thick porous plate through which mixing takes place by diffusion. The idea was to use the capillary forces to fill one capillary with two liquids. 

A micropump driven by piezoelectrics was developed at the Technical University of Ilmenau. The privileged direction of flow is determined by two pyramid-shaped diffusers etched into silicon (Fig. 6.119). Due to their geometry, these diffusers exhibit different flow resistances for each direction at higher flow speeds (Reynolds number > 100). This characteristic enables alternating flows to be rectified through a two paces forward, one pace back principle. With valve channel widths between 80 pm and 300 pm depending... 

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