Mechanical Characterization Of Erythrocyte-Derived Optical Microparticles By Quantitative Phase Imaging And Optical Tweezers

We have fabricated constructs from erythrocytes that contain the near-infrared (NIR) dye, indocyanine green (ICG). We refer to these constructs as NIR erythrocyte mimicking transducers (NETs). Mechanical properties of NETs can play an important role in the circulation kinetics and biodistribution of these particles. We characterize the mechanical properties of erythrocytes, hemoglobin-depleted erythrocytes ghosts (EGs), and micron-sized NETs (mu NETs) through analysis of membrane fluctuations measured by quantitative phase imaging, and forces associated with membrane tethers pulled by optical tweezers. EGs were prepared from erythrocytes by hypotonic treatment. mu NETs were prepared through hypotonic loading of 25 mu M ICG into EGs. Quantitative phase images were obtained by a common-path interferometric phase-shifting system. Approximating the membrane as a sheet of springs, we estimated the stiffness of the membrane of erythrocytes, EGs, and mu NETs as 3.0 +/- 0.6 pN/mu m, 6.5 +/- 2.1 pN/mu m, and 8.0 +/- 2.1 pN/mu m. Optical tweezers experiments yielded a similar trend. Differences in membrane stiffness suggest that the circulation dynamics of mu NETs may be altered as compared to native erythrocytes.