Contractile force measurement of cardiomyocytes using a hybrid biopolymer microcantilever array

This paper reports a novel method for quantitative and real-time contractile force measurement of cardiomyocytes using a hybrid biopolymer micracrocantilver array. Measuring contractile force of cardiomyocyte is important for quantitative understanding of the mechanism of heart failure and molecular alterations in diseased heart cells [1]. Previously, many researchers developed their own methods using micro-technology to measure contractile force of cardiomyocyte. A force transducer with clampers and hinges was fabricated by MEMS technology [2]. However, this technical approach involves cell manipulations with probes, gluing, and clamping, which may have some unknown effect on the cell and their function. Another method was proposed by Tan et al. [3]. They developed an array of micrometer scale elastomeric posts. Each post in the array independently bends according to the level of local forces exerted by the attached cell. However, the hard contact between the cell and a bed of needles or pillars may have some effect on the cell membrane and myocyte function. Furthermore, since cell spreading and morphology are quite different between on a flat surface and on micropillars, the contractile force measurement via micropillars should be verified when cells are on the flat surface. In this paper, we designed and fabricated a hybrid biopolymer microcantilever array made of PDMS (polydimethylsiloxane) elastomer to overcome the above problems. Culturing primary cardiomyocytes on PDMS microcantilver array leads to self-organization of cells on the structure, which enables to make massively paralleled arrangement of cells in the hybrid system. The system can avoid inefficient dissection and attachment of the muscle tissue by hand to be implemented to the microsystem. The important feature in our system over previous contractile force measurement techniques is that our method can measure quantitatively contractile force on the specific micro-sized area in real-time using well-known microcrocantilever structure. A schematic diagram of the measurement system to monitor the motion of hybrid biopolymer microcantilever is shown in Figure 1. To make a hybrid biopolymer microcantilever array, sandwich molding process was adopted, which is presented by Jo et al [4]. Since the fresh PDMS surface is hydrophobic, preventing adhesion from protein and cells, reactant ion etcher (RIE) treatment were applied to increase adhesion forces among PDMS surface, extracellular matrix and cardiac cells. The plasma-treated surface was then coated with 0.5% of fibronectin and 0.02% of gelatin. Figure 2 shows ESEM images of hybrid biopolymer microcantilever array before and after cell seeding. The displacements of the microcantilever by contractile force of cardiomyocytes were measured at 96hrs after cell seeding by obtaining the images at the edge of the microcantilver as shown in Figure 3. These experimental results were analyzed with analytical solution based on Stoney's equation (Figure 4). The presented method is safe and noninvasive, because the whole material in this study is biocompatible and there is not any hard contact, which can affect myocyte function or morphology. It can open opportunities to better understand mechanism of heart failure and furthermore, to design optimal hybrid biopolymer actuators or microdevice in microscale.