Micro-Electro-Mechanical System for Measuring Mechanical Properties of Cell Aggregates
Authors: Moghimi Negar , Jedlicka Sabrina , Tatic-Lucic Svetlana 
Published: October 2015

This paper presents design and finite element analysis (FEA) modeling of a novel micro-electro-mechanical system for determining mechanical properties of cell aggregates. The main components of this system are the electrostatic actuator array for applying force onto the cell aggregate and piezoresistive sensor for measuring it. A novel actuator array that allows for a set of five predefined displacements up to 100 μm was designed and modeled. FEA modeling of the components was performed to optimize the design and performance. While the device described is specifically designed for on-chip mechanical characterization of cell aggregates in vitro, it could also be translated to other applications.
Application of MEMS in biomedical devices has expanded vastly over the last few decades. MEMS devices have been developed to measure different characteristics of cells. The study of cell biomechanics is of growing importance in biology and medical science, as mechanical properties of cells can be related to the cause, progress and cure of certain diseases [1].
The key motivation is to develop systems for controlled mechanical stimulation and characterization of cells. Previously we have developed BioMEM device for measuring mechanical characteristics of single cells [2]. Our new study is focused on a novel method to measure biomechanical properties of cell aggregates, which are commonly used in stem cell culture. The biomechanical measurement of cell aggregates could elucidate how cellular aggregates change with age, differentiation, and other cellular processes or states [3, 4]; which could further inform decisions regarding future use of the cells of interest.
The actuation in this work is done by comb drive actuators [5] because of a relatively large displacement and independency of the electrostatic force from displacement. The springs need to be properly designed to achieve the maximum range of stable displacement. Folded flexure spring design combined with initially bent beams was used in our design because of great compliance in lateral direction, larger linear deflection range, lower side instability and minimal area usage [6, 7]. Coupled electromechanical modeling was performed to verify the actuator design.
The actuator array consists of a central shuttle and five pairs of comb drives each provide different displacements ranging from 52 μm to 100 μm which correspond to 5 % to 25 % deformation of the targeted cell aggregate. Custom-designed springs that will support the central actuator shuttle and allow for the large displacements were designed and the ratio of shuttle stiffness in perpendicular direction to actuation direction was maximized in order to increase the stable range of shuttle forward movement. FEA of sensor part was also done to maximize the sensor sensitivity by modeling different designs with varied design parameters.
This paper presents design of a novel MEMS actuator and sensor system. FEA modeling and optimization of device components was performed and the device is currently being fabricated.