Active-passive calibration for biomechanical force sensing by optical tweezers

Biomechanical force sensing in living organisms requires accurate calibration of the applied force probes. Since biomechanical cues in cell development, cell migration, cell pathologies such as cancer or vascular diseases are gaining more and more relevance, we witness an increasing demand for in vivo force sensing. It opens the path towards active microrheology. In our contribution, we envision red blood cells as dynamic, easily available probes for in vivo force sensing in multicellular structures such as vessels. To this end, we combine active-passive calibration protocols in optical tweezers (OT) with direct force sensing for improved accuracy of force calibration. OT enable the three dimensional manipulation of microscopic particles, representing an exciting biophotonic tool for in vivo force metrology. However, established assays are limited in temporal resolution and ease-of-applicability. We thus extend the standard OT configuration by active driving and direct force sensing. We show improved in vitro calibration and discuss requirements for in vivo biomechanical analysis. Our results pave the way to in vivo force sensing, advancing OT-based metrology to clinical studies.