Short communicationCellular strain assessment tool (CSAT): Precision-controlled cyclic uniaxial tensile loading
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.
Section snippets
Method
For methods of design and detailed drawings (Fig. S2), please see supplementary information.
Measuring minimum power requirement
The minimum power requirement for the motor was determined by first measuring the elastic modulus of the PDMS, and calculating the force required to distend one PDMS well to 110% of its original length. This force was found to be 1.35 N (Fig. 4). To determine the load potential required for the linear motor, the force needed to distend the maximum load of 48 PDMS wells by 10–110% of its original length, was subsequently determined. This calculation yielded a minimum motor power requirement of 65
Discussion
The design and construction of CSAT and mini CSAT, and the associated components demonstrated that these devices can be effectively used to systematically deliver a micron scale cyclic uniaxial strain. Although there has been significant effort to study the effect of mechanical strain on cultured cells, many of the existing devices do not provide strain fields that are homogenous. For example, the strain profile of equi-biaxial strain (http://www.flexcellint.com/index.html; Sotoudeh et al., 1998
Conflict of interest
The authors declare no conflict of interest of any sort.
Acknowledgements
Y.Y. acknowledges technical drafting support from Mike Greenberg. Financial support was provided by the Harvard MRSEC program, under NSF Award # DMR 02-13805.
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