Cellular strain assessment tool (CSAT): Precision-controlled cyclic uniaxial tensile loading

Abstract

The development of a multi-sample strain device and elastomeric culture wells designed to systematically assess strain effects on cell cultures is presented in this report. This device enables one to precisely conduct experimental analyses in sterile conditions while delivering cyclic uniaxial tensile strain. The input to the computer interface allows one to alter variables of frequency, duration, and amplitude of strain. The influence of strain on the migration of human umbilical vein endothelial cell (HUVEC) cultured on 2D polydimethylsiloxane (PDMS) surfaces was examined to verify the utility of this system.

Introduction

Cells throughout our body are exposed to various forms of mechanical stimuli (Smith and Kampine, 1990; O’Rourke et al., 1992). To examine effects of mechanical cyclic strain on vascular cells, several types of strain devices have been developed, and the methods of force application range from the use of dynamic indenters (Vandenburgh, 1988) to vacuum pressures (both positive, as reported in Winston et al., 1989 or negative, as reported in Banes et al., 1985; Gilbert et al., 1994) to stretch the bottom surface of the elastic substrate to which the cells are cultured. A number of custom uniaxial strain devices have been developed to examine cells that are normally exposed to lateral stresses (Vandenburgh and Karlisch, 1989; Murray and Rushton, 1990; Neidlinger-Wilke et al., 1994; Pfister et al., 2003; Carano and Siciliani, 1996). However, a limitation to most uniaxial strain devices is that they can only accommodate a limited number of samples (Murray and Rushton, 1990; Neidlinger-Wilke et al., 1994; Pfister et al., 2003; Carano and Siciliani, 1996; Waters et al., 2001) at one time. Most devices also lack a platform to perform consistent clamping and loading of samples, which can significantly alter substrate strain (Murray and Rushton, 1990; Neidlinger-Wilke et al., 1994; Jones et al., 1991) and ultimately, introduce large variations between experiments.

Here, we present a computer-controlled precision strain application system (Fig. 1) composed of a custom multi-well uniaxial cellular strain assessment tool (CSAT) (Fig. 2), a microscope adaptable mini CSAT (Fig. 3), and custom elastomeric polydimethylsiloxane (PDMS) plates (Fig. S1). The effect of cyclic tensile strain on the migration of endothelial cells (ECs) was also analyzed in this study. Human umbilical vein endothelial cells (HUVECs), cultured in 2D directly on elastomeric polydimethylsiloxane substrates were exposed to physiologic levels of cyclic tensile strain, and strain-enhanced directional EC migration.