Measurement of beating force of cardiomyocytes using an atomic force microscope
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The most commonly used transducer based methods for measurement of beating forces of cardiomyocytes have been reviewed in this thesis and they involve either direct contact with the cardiomyocytes or their manipulation in some way to measure the beating or contractile forces exerted by them. Other methods reviewed include advanced imaging techniques to capture the contraction and elongation of the cardiomyocytes from which the beating forces can be calculated. Atomic force microscope (AFM) was chosen as the most suitable measurement technique for quantifying beating forces of engineered cardiac tissues due to its long range of force measurement ranging from a few piconewtons to tens of micronewtons. Even though AFM has been used in the past to study cardiomyocytes but these efforts have required synchronizing the z piezo to the beating of the cardiomyocytes which created fluidic disturbances resulting in inaccurate measurements. This thesis work demonstrates a novel method using the AFM to measure the beating forces of cardiomyocytes. In this method, the AFM tip is kept stationary and lowered on top of the sample and the z piezo is locked in its position. Now, the tip gently touches the sample surface with a minimal contact force. The stationary tip on coming in contact with the beating cardiomyocyte sample experienced deflections in the up and down directions which on multiplying with the spring constant of the probe gave the value of beating force. AFM was also used to quantify the mechanobiological properties of pluripotent, stem cell-derived cardiomyocytes, including frequency of beats, duration, and cellular elasticity. The elasticity of some known standard samples like PDMS was measured in order to ascertain the long range of measurements as well as the accuracy of the AFM. The beating forces were observed both over a single cardiomyocyte as well as over a cluster of beating cardiomyocytes and it was found that for clusters, the beating forces exerted were higher and more rhythmic. The AFM-based method described in this thesis can serve as a screening tool for the development of cardiacactive pharmacological agents, or as a platform for studying cardiomyocyte biology.