**6.3. Sonophoresis**

This transdermal drug delivery technique uses low‐frequency ultrasonic energy (15‐second burst of ultrasound at 55 kHz) to disrupt the stratum corneum and to allow drug in the reservoir or the polymeric matrix to cross the stratum corneum and then penetrate the blood vessel. Similar to the electroporation effect, the sound waves create cavitation bubbles in the tissue that disrupt the lipid bilayers of the cells of the stratum corneum creating microchan‐ nels. The ultrasound poration can increase the transport properties of the stratum corneum by 100‐fold. **Figure 13** illustrates the effect of sonophoresis.

#### **6.4. Microneedle dermal patch**

This transdermal patch technique makes use of microneedles, which are microscopic, just a few hundred microns in size. They can pierce the skin in a minimally invasive manner

**Figure 12.** Temporary disruption of the bilipid membrane after electroporation. A: Normal arrangement of the bilipid membrane B: Bilipid membrane after electroporation C: Recovery of the Bilipid membrane after an interval.

without causing pain or injury [16]. A lot of research in the literature shows that this pierc‐ ing effect increases transdermal flux of large molecular weight compounds by many folds. There are two ways of utilizing the microneedles, one of the ways in which drug delivery is achieved is to coat the drug onto microneedle shafts and insert them into the skin where they deposit the drug. The second way is upon piercing skin they create microconduits across stratum corneum and this will provide a direct route for transport of drugs into the skin from the patch reservoir (**Figure 14**).

**Figure 13.** Bubble formation after sonoporesis process, forming channel for drug penetration. A: Normal arrangement of the bilipid membrane B: Formation of bubbles in Bilipid membrane after sonoporesis.

**Figure 14.** Illustration of microneedle transdermal patch with drug reservoir.
