RESEARCH PAPER Design optimisation and fabrication of SU-8 based electro-thermal micro-grippers Ruth E. Mackay & Huirong R. Le & Robert P. Keatch Received: 12 July 2010 / Revised: 27 September 2010 / Accepted: 20 October 2010 # Springer-Verlag 2010 Abstract This paper describes the design and simulation of an integrated micro-electro-mechanical system (MEMS) to be used for micromanipulation. Electrothermal micro- grippers were designed for micro-tensile tests of biological materials which require relatively low force and tempera- ture. Finite element analysis (FEA) was performed to examine gripper opening displacements, tip temperature and stresses. The feasibility of various materials including silicon, plated nickel and SU-8 was examined for applica- tions in biological environment. The paper looks at fabrication techniques employed to allow a cheaper, wet etching solution, to the fabrication of SU-8 micro-grippers. The structure was successfully fabricated and tested. The results showed that the micro-gripper could be actuated by fairly low voltage. Keywords Micro-electro-mechanical systems . Micro- gripper . Finite element simulation . Tissue manipulation 1 Introduction The mechanical characterization of tissues and cells will help scientists to understand fundamental cell physiology. With respect to cancer normal mechanical properties of cells could be compared to those of abnormal cells. This could lead to new early diagnostic tools and therapies in the treatment of cancer [1]. A number of micro-electro-mechanical systems and nanosystems have been developed to study biomechanics of cells and tissues. Atomic force microscopy (AFM) using a simple cantilever beam has been used to study mechanical properties of cells. Cross et al found Young’ s modulus of metastatic cancer cells had a modulus that was 70% lower compared to healthy cells taken from the same person [2]. Micropipette aspiration [3] and optical stretchers [4] have also been used to study biomechanics of cancerous cells or tissues. However, there is difficulty to attach biological samples to commercial force sensors for micro-tensile tests. Researchers have used miniaturised grippers to investigate cellular mechanics in vitro [5] or tissue hardness in vivo [6]. Micro-grippers allow for direct, mechanical gripping of small scale tissues or cells. Integrating micro-grippers with force sensor on the same system would facilitate mechan- ical characterisation of soft cells and tissues. Micro-gripping of constructs smaller than 50 μm diameter is a challenging problem. Several types of micro-grippers have been designed. Electrostatic micro-grippers, which operate due to electrostatic attraction forces, cannot be used in a biological medium which has electrolytic properties [7, 8]. Electrostatic micro-grippers operate at a high voltage, for example 90 V, high voltages may damage biological cells [9]. Thermoelectric micro-grippers such as bimorph actua- tors, developed by Guckel [10] operate due to joule heating. These have high operating temperatures (300–1,500 K) which could invalidate the experiment [11–13]. Piezoelectric micro-grippers require high actuation voltages for small displacements (0–70 V) [14]. Piezoelectric actuators must be amplified to give a large gripping stroke or a macro piezoelectric actuator could be used to actuate micro- grippers [15]. Shape Memory Alloy (SMA) micro-grippers work for a limited number of cycles before losing their shape memory effect [16]. Various researchers reported cage type R. E. Mackay (*) : H. R. Le : R. P. Keatch School of Engineering, Physics and Mathematics, University of Dundee, Dundee DD1 4HN, UK e-mail: r.z.mackay@dundee.ac.uk J. Micro-Nano Mech. DOI 10.1007/s12213-010-0029-y