**2.5 Microbubbles used as polyelectrolyte multilayer shells**

Polyelectrolyte multilayer (PEM) is a modified type of polymer surfactant shell for the formulation of perforated microbubbles. These microbubbles are coated with charged surfactant which acts as a substrate. To absorb oppositely charged polymer, the layer by layer assembly technique is used [26]. Borden et al. [27] used trimethylammonium propane (TAP) which is a phospholipid containing the cationic head group for creating PEM microbubble where TAP serves as shell. Lentacker et al. [28] described multilayer microbubble. The coating material is DNA and PAH which protect the DNA from enzymatic degradation.

**105**

*Using Microbubbles as Targeted Drug Delivery to Improve AIDS*

vascular system as blood pool act as carrier.

1.Perfluorocarbon-filled microbubble, which is stable for circulating in the

3.Albumin-encapsulated microbubble, which adheres to vessel walls.

2.Ultrasound microbubble, when applied over skin surface where it bursts and releases drug. It is use in low concentration. It also increases therapeutic index. It is advantageous for those drugs which have hazardous and toxic effect.

4.Phospholipid-coated microbubble, which has a high affinity for chemothera-

1.Microbubbles increase adherence to damaged vascular endothelium. As the viral proteins obtain in immune response within target tissue the use of viral vector is limited in gene therapy. It has been seen that viral vector causes an

2.Ultrasound when applied over the skin surface bursts the microbubbles which causes localized release of drug [29–32]. This technique require lower concentration of drug systemically and the concentration of drug only where it is needed therefore the therapeutic index may be increased which is advantageous in case of drug with hazardous systemic side such as cytotoxic agents [33].

3.In diagnostic ultrasound, microbubbles create an acoustic impedance mismatch between fluids and tissues to increase reflection of sound which is used in radiology and cardiology for the detection of perfusion and characterization of tissues. Microbubbles not only increase reflection of sound, they also

4.Ultrasound to contrast agents creates extravasation points in skeletal muscle capillaries. High-intensity ultrasound can rupture capillary vessel resulting in the deposition of protein and genetic material into the tissues. Only a small capillary rupture was required to deliver large quantities of colloidal particles

5.Ultrasound increases the transmembrane current as a direct result of mem-

6.Ultrasound-induced cavitation may then be used to destabilize the carriers and affect local drug release. Applications of sonodynamic therapy may include tumor ablation and treating vascular disease such as atherosclerotic plaques. To make targeted microbubbles, targeting ligands were developed and were called bioconjugates suitable for incorporation into membranes

7.The anchor locks the bioconjugate into the membrane surrounding the

microbubble, and the linker gives the peptide-based targeting ligand enough motional freedom to bind to its target (see **Figure 3**). Thrombus-specific

intense inflammatory activation of endothelial cells [55].

increase the absorption of sonic energy [34].

brane resistance due to pore formation [36].

*DOI: http://dx.doi.org/10.5772/intechopen.87157*

peutic drugs [55].

to the muscles [35].

stabilizing microbubbles.

**4. Applications**

**3. Types**
