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Encapsulated Microbubbles: From echocardiography to noninvasive blood pressure monitoring and targeted drug delivery Kausik Sarkar Department of Mechanical and Aerospace Engineering, George Washington University Micron-size gas bubbles are intravenously injected into a patient’s body to improve the contrast of ultrasound blood flow images. Currently in the USA, two such contrast agentsOptison (GE Health Care) and Definity (Lantheus Medical Imaging)are approved by the Food and Drug Administration for echocardiography. These bubbles are encapsulated by a thin layer (4-10nm) of protein, lipids and other surface-active materials to prevent their premature dissolution in the blood. They can be chemically functionalized to attach to target tissues and aid in molecular imaging and targeted delivery. Their destruction by strong ultrasound pulses is being used in real-time blood flow velocity measurement, stimulating arteriogenesis (generation of new arteries), and targeted drug delivery. For the past decade, we have been performing experimental and analytical research on contrast microbubbles. We first proposed and subsequently developed an interface model of the encapsulationhas an intrinsic surface rheology with surface viscosities and elasticitiesthat addresses the wide disparity of scales between the overall bubble size and that of the encapsulation. In this talk, I will discuss material characterization of these contrast agents that includes determination of rheological properties of a contrast microbubble’s encapsulation using one set of in vitro experiments, followed by model validation using another set. I will present a hierarchical approach with increasing sophistication in constitutive modeling of the encapsulation as warranted by the determining experiments and underlying physics. A new model for the dissolution of microbubbles that accounts for the effects of encapsulation: the encapsulation hinders the permeability of the gas-liquid surface, and its elasticity balances the surface tension-induced dissolution stress. We investigate the use subharmonic signals to noninvasively monitor organ-level blood pressure. I will show and explain unusual behaviors of subharmonic response in sharp contrast to “plausible expectations” and classical results from free bubble dynamics. I will also briefly discuss specifically targeted and triggered cytosolic delivery of cancer drugs from “echogenic liposomes”. Time permitting, I will provide an overview of other research efforts at our lab. It includes direct numerical simulation of multiphase flowsemulsions of deformable viscous and viscoelastic drops, capsules, their rheology, adhesion and migration of leukocytes on active substrates in presence of receptor-ligand bindingas well as ultrasound mediated bone fracture healing and cancer therapy.