Autonomous Bio-Mag-MEMS based on permanent micro-magnets

Orateur : Soutenance de Thèse de Luiz Fernando ZANINI (Institut Néel/G2Elab)

The range of applications for magnetic micro- and nano-particles is constantly expanding, in particular in medicine and biology. A number of applications involve particle trapping and deviation under the effect of a magnetic field and field gradient. In most publications, the required magnetic fields are produced either using soft magnetic elements polarized by an external magnetic field, electromagnets or bulk permanent magnets. Micromagnets produce high fields and favor autonomy and stability while downscaling leads to an increase of field gradients. The challenge is to produce good quality, hard magnetic films in the range of 1 to 100 μm both in thickness and lateral dimensions and to integrate them into a Bio-Mag-MEMS. Physical vapor deposition (triode sputtering) is used to prepare high quality rare earth magnets in thick film form. In order to obtain field gradients in the lateral directions, three techniques have been developed : - Topographic patterning, in which the film itself is patterned either by sputtering onto pre-etched substrates or by etching the magnetic film. - Thermo-magnetic patterning, which exploits the temperature dependance of coercivity to locally reorient the magnetization. - Micro magnetic imprinting, which consists of organizing magnetic powder with the aid of the above-cited magnets, then embedding the powder into a polymeric matrix. Such micro-magnets are autonomous, having no requirements for a cumbersome external field source nor power supply. Here we demonstrate the potential to develop autonomous devices based on micromagnet arrays. Controlled positioning using superparamagnetic particles as a model is shown at first. Then, the magnet arrays are used to study endocytic processes using magnetically labelled biological elements. In a step towards device integration, microfluidic channels are produced above the magnet arrays. Magnetic and non-magnetic particles are pumped through the devices and precise positioning, as well as guiding and sorting are performed. High purity is obtained in the sorted solutions. The good results obtained in the development of micromagnetic flux sources, integration into microdevices and particle/cell handling and sorting indicate the high potential of this work for actual biological and medical applications. Moreover, the biocompatibility and autonomy of such devices allow their use in micro-total-analysis systems, point-of-care or implantable devices.

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