**2.3 Lipid as stabilizing agent in the formation of microbubbles**

For biomedical imaging and drug delivery, lipid-coated microbubbles are one of the most interesting and useful formulations. The lipid shell is inspired by nature, as stable microbubbles found ubiquitously in the oceans and freshwaters of earth are known to be stabilized by acyl lipids and glycoproteins [18].

During ultrasound and sonication technique, the lipid molecules which are held together by weak physical forces form the microbubble shell having property of expansion and compression without chain entanglement. Lipid-coated microbubbles therefore reduce the damping effect on resonance and reseal around the gas core during fragmentation process [12]. Thus, the lipid-coated microbubble itself is a versatile platform technology. An example of lipid microbubble is shown in **Figure 2B**, which depicts heterogeneity and phase separation of phosphatidylcholine and lipopolymers that are typically used to stabilize lipid microbubble [19].
