Electrothermally Activated SU-8 Microgripper for Single Cell Manipulation

The development of miniaturized systems for manipulating biological samples in solution has become a great technological challenge for the future of the rapidly growing area of genomics and proteomics. The use of microgrippers in those systems as the mechanical end-effectors that securely grasp and transport the micro object to the desired location seem to be a promising approach, offering robustness, manipulation flexibility without interfering optically or electrically with the sample. Microgrippers that are activated in ionic environment can be used for single cell manipulation and positioning, cell isolation, as well as for minimally invasive surgery and for various endoscopic operations.

In contrast to previous works, our approach is based on the development of a SU-8 microgripper with integrated electrothermally activated in plane SU-8 actuators (figure 1). Taking advantage of the structural rigidity, the chemical resistance, as well as the ability to define high aspect ratio structures on SU-8 films, we developed SU-8 microgrippers that can operate in both liquid and air environments. A critical element in our design is the large coefficient of thermal expansion of SU-8 - almost 18 times higher the polysilicon - that allows the electrothermal activation of the microgripper in ionic physiological solutions at voltages below the electrolysis point and low temperature increases.

References:

1. Chronis N. and Lee L.P., "Polymer MEMS-Based Microgripper for Single Cell Manipulation", 17th IEEE International Conference on Micro Electro Mechanical Systems, Maastricht, 25-29 January 2004, p.17-20.
2. Chronis N. and Lee L.P., "Polymer-based Actuators Integrated Into Microfluidic Systems," Proceedings of International Conference on Micro Total Analsysis Systems 2002, pp. 754-756, Nara, Japan, November 3-7, 2002.

Scanning electron micrographs and close-ups of the overhanging fabricated SU-8 microgripper. The metal (Cr/Au) heat resistors are covered by the SU-8 layer and therefore are not visible.