Magnetic actuation system

Fig. 12.4 (A) Magnetic actuation system comprising an electromagnet (coil), a magnetic yoke, and soft-magnetic poles, integrated with the microfluidic chip (B) enhanced view of the microchip showing the magnetic pole arrangement and the microfluidic channel ...

Other robotic microassembly has successfully used air jets, magnetic actuation, or vibrational energy to supply the forces for assembly. In most instances, a global vision system is used to monitor part placement on the two-dimensional assembly grid. Yet another approach popular in Japan is the microfactory which is based on macroscale concepts of fabricating and assembling parts. 

Microfluidic Control Sequential and combinatorial delivery of signals to cells or tissue in microfluidic devices can be accomplished by using built-in control systems. Several microfluidic tools including valves, pumps, mixers, fluidic oscillators, fluidic diodes, etc. have been developed to accomplish fluidic control in these devices. These components can either be passive or active. Examples of passive elements include one-way valves (flap, ball) and hydrophobic patohes which take advantage of the interactiOTi between the chemical surface properties of the substrate and Uquid. Active elements, on the other hand, typically require some type of actuation mechanism. Several mechanisms for force transduction in microfluidic devices include mechanical, thermal, electrical, magnetic, and chemical actuation systems as well as the use of biological transducers. There has been a significant amount of work in this area that has been presented in a review by Erickson and Li [5]. 

Other novel arrangements for robotic systems have been developed some examples include self-assembling robotic systems, snake and concentric tube robots, magnetically actuated manipulators, and "microrobots," Concentric tube robots allow increased surgical access without increasing invasiveness by utilizing precurved concentric tubes the... 

Niobe [41], developed by Stereotaxis Inc, is an FDA-approved magnetically actuated robotic catheter system for vascular procedures. The catheter is actuated via permanent magnets located outside the patient s body. These catheters have been reported to be significandy beneficial in reducing procedure time and radiation exposure [42],... 

Judy, J.W. and Muller, R.S. (1997) Magnetically actuated, addressable microstructures . Journal of Microelectromechanical Systems, 6(3) 249-56. 

Fig. 15 T1O2 nanotubes in drug delivery system, (a) Magnetic nanoparticle filled nanotubes with attached drug (F) for magnetically guided site selective drug delivery. Release is triggered by photocatalytic chain scission upon UV irradiation. Inset an example where a blue fluorescent molecule is released from magnetically actuated nanotubes (reproduced with permission from Ref 276). (b) Amphiphilic nanotubes loaded with drugs or biomolecules which are released upon opening the hydrophobic cap with UV irradiation (reproduced with permission from Ref 202).

A typical vibration system uses an electro-magnetic actuator to create motion. For small systems ( 1 kg), a standard electro-magnetic speaker can be used, but for larger systems a purpose-built electro-magnetic shaker is required. Piezoelectric speakers can be used for very small loads and for high frequencies. Mechanical drive using a cam is also possible [49,56,94] but is limited to sinusoidal motion. 

Active techniques improve pumping and mixing using mobile parts or external mechanical, electrical, magnetic, or aconstic forces. Active structures are based on MEMS devices, and allow the creation of actuation systems for the transport of fln-ids in microchannels. Micropumps and microvalves are examples of these structures (Rife et al., 2000 Bradley et al 1995), that can achieve proper flow rates, with values that can achieve 1 mm/s in 1.6 x 1.6 mm channels, as determined by Rife et al. (2000), or 1.15mm/s in Ixlmm channels, as obtained by Bradley etal. (1995). 

The implementation of different actuation systems in lab-on-a-chip devices requires smart materials to successfully perform the pumping, mixing, or separation actuation, while assuring an easy integration in the lab-on-a-chip devices. This section will focus on some examples of innovative materials to promote the control of fluids in a lab-on-a-chip PVDF (poly(vinylidene fluoride)), modified chitosan and magnetic particles. 

Finally, the control unit, apart from controlling voltage, has a magnetic polarity reversal switch operated by a variable timer, usually set to actuate every minute that cleverly ensures no scale can build up inside the unit, making the entire system maintenance free. ... 

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