1. Maastricht, January 25-29, MEMS 2004 Website: http://lmis2.epfl.ch Plastic Micropump using Ferrofluid and Magnetic Membrane Actuation C. Yamahata and M. A. M. Gijs Institute of Microelectronics and Microsystems, Swiss Federal Institute of Technology Lausanne (EPFL), 1015 Lausanne, Switzerland Abstract: The objective of this project is to develop an efficient and low cost pumping device for biochemical analysis systems, based on magnetic actuation. A rapid prototyping technology is presented to realize two different types of externally actuated plastic micropumps: (i) an external magnet displaces a ferrofluid liquid plug that plays the role of a piston in a channel; (ii) an external coil actuates an integrated magnetic membrane, consisting of NdFeB magnetic powder in a polydimethylsiloxane (PDMS) matrix. Plastic Microfluidic Chip A low-cost method for the fast prototyping of microfluidic chips has been developed. The microfluidic chip is a stack of polymethylmethacrylate (PMMA) layers. Powder blasting is used to realize microchannels, while complex structures are machined with standard milling tools.  In a first step, a metallic mask is realised by laser cutting and applied on top of a 250 µm thick PMMA sheet. The micropatterning is obtained by the action of accelerated alumina (Al 2 O 3 ) particles. The minimum channel dimensions obtained with this rapid prototyping method is in the 100 µm range.  As an example, a silicone membrane has been integrated to realize a check-valve. Such valve requires the presence of a PMMA pillar structure in a cavity; this is machined using standard milling tools.  The quality of the bonding has been verified by applying a fluorescent solution at 1 bar in the microfluidic structure. Ferrofluid Micropump A ferrofluid is a stable colloidal suspension of nano-sized magnetic particles in a liquid carrier. In the presence of an external magnetic field, the whole fluid responds as a homogeneous magnetic liquid. The basic idea of the ferrofluid micropump is to generate magnetically a pressure to pump liquids.  The magnetic liquid plug, which plays the role of a piston, is externally actuated with a motorized permanent magnet.  The water based ferrofluid used in the experiments is synthesized in-house at EPFL.  The magnetic saturation of the ferrofluid is found to be 30 mT at ambient temperature, which permit larger magnetic forces. than obtainable with most commercial ferrofluids.  Water has been successfully pumped at a flow rate of 30 µL/min without backpressure; pumping is demonstrated up to a backpressure of 25 mbar. Christophe Yamahata Christophe.Yamahata@epfl.ch EPFL / IMM / LMIS CH - 1015 Lausanne Tel: +41 21 693 66 39 Fax: +41 21 693 59 50 Magnetic Membrane Micropump A diaphragm micropump with 2 diffuser elements (dynamic valves) has been integrated in a microfluidic plastic chip. The oscillating membrane is made of a polymer magnet and is actuated with an external coil.  The oscillating diaphragm micropump is actuated with a 1500 turns coil supplied with a 150 mA alternative current.  The micropump uses 2 diffuser elements. A diffuser is a constriction element that functions as a dynamic valve.  The numerical simulation of the flow in a diffuser shows that it has a lower flow resistance ….. in the positive diffuser direction than in the negative nozzle direction.  Water has been successfully pumped at a flow rate of 400 µL/min without backpressure; pumping is demonstrated up to a backpressure of 12 mbar.