IOP PUBLISHING JOURNAL OF MICROMECHANICS AND MICROENGINEERING J. Micromech. Microeng. 18 (2008) 075020 (8pp) doi:10.1088/0960-1317/18/7/075020 A polymer V-shaped electrothermal actuator array for biological applications Wenyue Zhang 1 , Markus Gnerlich 1 , Jonathan J Paly 2 , Yaohua Sun 1 , Gaoshan Jing 1 , Arkady Voloshin 2,3 and Svetlana Tatic-Lucic 1,2 1 Sherman Fairchild Center, Electrical & Computer Engineering Department, Lehigh University, Bethlehem, PA 18015, USA 2 Bioengineering Program, Lehigh University, Bethlehem, PA 18015, USA 3 Department of Mechanical Engineering & Mechanics, Lehigh University, Bethlehem, PA 18015, USA E-mail: svt2@lehigh.edu Received 27 March 2008, in final form 8 May 2008 Published 9 June 2008 Online at stacks.iop.org/JMM/18/075020 Abstract A polymer V-shaped electrothermal actuator (ETA) array that is capable of compressing a live biological cell with a desired strain was designed, fabricated and characterized. This polymer electrothermal array is the core of a microelectromechanical systems (MEMS) device to measure the mechanical compliance of a cell. A polymer electrothermal actuation mechanism was selected because it is able to operate in an electrolytic solution (cell medium), which was needed to keep cells alive during testing. The MEMS-based device was optimized utilizing finite element analysis and the devices were fabricated using surface micromachining techniques. Characterization of these devices was conducted in air, deionized water and cell mediums. Operating these devices in liquid environments was performed using direct current voltages less than 2.0 V or high-frequency (800 kHz) alternating current voltages. The actuator displacement was up to 9 μm in air and 3 μm in liquids, i.e. it achieves 30% displacement of that in air when operating in liquids. Such remarkable performance is due to the large coefficient of thermal expansion and low thermal conductivity of the structural polymer (SU-8). Finally, we demonstrated the suitability of this actuator for biological applications by compressing a cultured NIH3T3 fibroblast in the cell medium. (Some figures in this article are in colour only in the electronic version) 1. Introduction A study of the mechanical compliance of biological cells is critical to improve research to benefit public health because measurements of the compliance contribute to the study of the pathophysiology of various diseases and the search for effective treatments. Biologists hypothesize that the biomechanical properties of osteoblasts (bone formation cells) change as a function of age, and this change could be a contributing factor to the pathogenesis of osteoporosis [1]. This hypothesis of the osteoblasts’ mechanosensitivity has not been examined due to the limitations of current measurement techniques. Biomechanical research could be traced back to the 19th century where it started from a gross anatomical level of investigation and has advanced to the cellular level today. In early research, strain gages were attached to the midshaft of live animal bone to record the variations of strains during the animal’s natural activities in vivo for 1–2 days [2]. Later, accelerometers were employed to obtain quantitative values necessary to evaluate the shock-absorbing capacity of the human locomotion system [3]. Recently, mechanical properties of live cells have been investigated by atomic force microscopy (AFM) [4], soft substrate stretching [5], magnetic beads attachment [6], cytoindentation [7] and modified tensile testing [8], among other techniques. AFM has broad applications in characterizing the elasticity of biological materials [9]. It has been effective, not only for imaging the morphology of developing neurons and their processes three-dimensionally, but also for studying the elastic properties of a live osteoblast on a submicrometer scale [10]. However, AFM has several drawbacks when used 0960-1317/08/075020+08$30.00 1 © 2008 IOP Publishing Ltd Printed in the UK