Graduation date: 2018The Brownian motion of micron-scale particles reflects the viscoelastic response of the local environment of the medium. Tracking the thermal fluctuations of these particles is a measure of the rheology of the material at the microscopic scale. This technique is called passive microrheology. Microrheology has been developed to assess the microscopic structural and mechanical properties of complex materials. This probing method is well suited for studying evolving materials and rare biological materials, since it only causes small deformations that are driven by the thermal energy and since it only requires micro-liter quantities of sample.\ud \ud Video microrheology is a method that involves recording the thermal fluctuation of the microscopic probes to track the particle motions. The trajectories of particles are analyzed from videos that are recorded by the video microscopy system and used to compute the mean-squared displacement that reflects the microscopic environment where the particles reside. Moreover, the properties of materials that are characterized by microrheological techniques are highly comparable to conventional macroscopic methods, such as conventional rheometry.\ud \ud We applied video microrheology to characterize the concentration-dependent rheology of artificial sputum medium (ASM) and transient microrheology of platelet poor plasma (PPP). The development of ASM is achieved by increasing the entanglement of polymers, but the plasma coagulation is caused by the addition of initiators, and the evolution of a fibrin clot is achieved by the time-dependent development of the crosslink of fibrin. Using video microrheology, we computed the shear modulus and identified the gel points of both materials
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