Incavitation, gaseous bubbles are created within inner side of the skin oroutside in drug chamber and after few cycle these bubbles collapse. Enhancedpermeation of drug using cavitation could be due to formation of two types ofcavitation bubbles e.g. stable and transient bubbles. At lower frequency ofultrasound both stable and transient bubbles form while at higher frequencyfull gas bubble is not formed because the time between negative and positiveacoustic is less than the time for bubble to fully grow. Transient bubbles are formed in drug chamber and also collapse theresymmetrically and produce shock waves of amplitude 10kbar which can stir up theSC layer by high pressure or they can collapse at SC surface asymmetricallyhence producing microjet of high velocity liquid which can intrude on thestratum corneum surface in a velocity of about 100 m/s. Mitragotri et al.
, have suggested that the low frequencyultrasound are significantly better for transdermal permeation enhancement becauseof higher rate of bubble creation and collapse.Many authorshave reported and believed that cavitation is the major driving force forenhanced skin permeation and reported the enhanced delivery of polar moleculesinsulin (~6 kDa), interferon –G (~17kDa) and erythropoietin (~48 kDa) across invitro models of human skin. A novel polyamidoamine dendrimer -coupledsonophoresis-mediated enhanced permeation of diclofenac through the skin was reported by Huang et al.(2015).Manikkath et al (2017) studied thetransdermal drug delivery of ketoprofen using sonophoretic permeation with andwithout peptide dendrimers in Swiss albino mouse skin, both in vitro and invivo model. It was observed that synthetic peptide dendrimers significantlyenhance the transdermal delivery of ketoprofen ratios of up to 1369.
15 as comparedto passive diffusion. Ketoprofen-A8 dendrimer complex plasma level using TDDSwas comparable to plasma drug levels with oral absorption . Hence it isperceptible that peptide assisted drug delivery using sonophoresis caneffectively improve the transdermal permeation. .