Abstract
A cell elasticity measurement method is introduced that uses polymer microtools actuated by holographic optical tweezers. The microtools were prepared with two-photon polymerization. Their shape enables the approach of the cells in any lateral direction. In the presented case, endothelial cells grown on vertical polymer walls were probed by the tools in a lateral direction. The use of specially shaped microtools prevents the target cells from photodamage that may arise during optical trapping. The position of the tools was recorded simply with video microscopy and analyzed with image processing methods. We critically compare the resulting Young’s modulus values to those in the literature obtained by other methods. The application of optical tweezers extends the force range available for cell indentations measurements down to the fN regime. Our approach demonstrates a feasible alternative to the usual vertical indentation experiments.
Highlights
Autonomous microrobots and microactuators have gained attention recently due to their ability to perform complex tasks on biological targets inside microfluidic environments without the administration of external physical tools
A cell elasticity measurement method is introduced that uses polymer microtools actuated by holographic optical tweezers
Endothelial cells grown on vertical polymer walls were probed by the tools in a lateral direction
Summary
Autonomous microrobots and microactuators have gained attention recently due to their ability to perform complex tasks on biological targets inside microfluidic environments (channels, reservoirs) without the administration of external physical tools. The complexity of microrobots spans from simple microspheres [1,9] to complex tailor-made microstructures [4,10,11,12], and sometimes a group of such structures is needed to perform specific tasks [13,14] Most often, these microtools are actuated and guided by optical means, but magnetic [15,16] or acoustic [17] controls are applied. Optical tweezers have been applied successfully earlier to measure cells’ Young’s modulus by trapping microbeads of various diameters and pushing them against the cells in an axial direction [20,22,23,24] These cell indentation experiments use optical forces of less than 10 pN combined with a larger contact surface radius than a typical AFM tip (r ≈ 1 μm vs r ≈ 10 nm), which allows only small indentations, and only smaller Young’s moduli can be measured. Our results demonstrate that the microtool-based method provides a Young’s modulus that fits in the range reported in the literature on this cell type
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