J colloid sci interface

J colloid sci interface can you

Sonophoresis is commonly used in the treatment of muscle soreness, tendonitis and bursitis. Although considerable attention has been given to the investigation of sonophoresis in the past years, its mechanisms were not clearly understood, reflecting the fact that several phenomena may occur in the skin upon ultrasound exposure.

These include: - Cavitation (generation and oscillation of gas bubbles). Accordingly, if one idenjpgies the dominant phenomena responsible j colloid sci interface sonophoresis, a better selection of ultrasound parameters and surrounding physiochemical conditions can be made to selectively enhance the favourable phenomena, thereby broadening the types of drugs that can be administered transdermally (15). In order to understand the mechanisms of sonophoresis, it is important to idenjpgy various effects of ultrasound exposure on human tissue since one or more this effects may contribute to j colloid sci interface mechanism of sonophoresis.

Cavitation involves the generation and oscillation of gaseous bubbles in a liquid medium and their subsequent collapse when such a medium is exposed to a sound wave, which may be an j colloid sci interface. It can generate violent microstreams, which increase the bioavailability of the drugs (16).

Cavitation occurs due to the nucleation of small gaseous cavities during the negative pressure cycles of ultrasound, followed by the growth of these bubbles throughout subsequent pressure cycles.

Whenever small gaseous j colloid sci interface already exist in a medium, cavitation takes place preferentially at those nuclei j colloid sci interface. This cavitation leads to the disordering j colloid sci interface the lipid bilayers and formation of aqueous channels in the skin through which drugs can permeate (18,19,20).

The minimum ultrasound intensity required for the onset of cavitation, referred to as cavitation threshold, increases rapidly with ultrasound frequency (16,18). But as cavitational effects vary inversely with ultrasound frequency, it was found that any frequency lower than that corresponding to therapeutic ultrasound was more effective in enhancing transdermal transport.

This is a direct consequence of reduced acoustic cavitation (formation, growth, and collapse of gas bubbles) at high ultrasound frequencies. Application of ultrasound generates oscillating pressures in liquids and nucleates cavitation bubbles. At higher frequencies it becomes increasingly difficult to generate cavitation due to the fact that the time between the positive and negative acoustic pressures becomes too short, diminishing the ability of dissolved gas within the medium to diffuse into the cavitation nuclei.

The number and size of cavitation bubbles is inversely oiii with application frequency (21, 23). Cavitation occurs in a variety of mammalian tissues, including muscle, white hair and liver, upon exposure to ultrasound in different conditions. This occurrence of cavita-tion in Celecoxib Oral Solution (Elyxyb)- FDA tissue is attributed to the existence of a large number of gas nuclei.

These nuclei are gas pockets trapped Naldemedine Tablets (Symproic)- FDA either intracellular or intercellular structures. It has been shown that cavitation inside the skin plays a dominant role in enhancing transdermal transport upon ultrasound exposure (15).

Cavitation inside the SC can potentially take place in the keratinocytes or in the lipid regions or in both. Since the effect of ultrasound on transdermal transport depends strongly on the dissolved air content in the surrounding buffer and because most of the water in the SC is present in the keratinocytes, it can be said that cavitation inside the SC takes place in the keratinocytes (Fig.

Oscillations of the ultrasound-induced cavitation bubbles near the keratinocyte-lipid bilayer interfaces may, in turn cause oscillations in the lipid bilayers, thereby causing structural disorder of the SC lipids. Shock waves generated by the collapse of cavitation bubbles at the interfaces may also contribute to the structure disordering effect. Because the diffusion of permeants through a disordered bilayer phase can be significantly faster than that through a normal j colloid sci interface, transdermal transport in the presence of ultrasound is higher than passive transport.

This, in essence, is the mechanism of sonophoresis. Cavitation in the saline surrounding the skin does occur after ultrasound exposure. These cavitation bubbles can potentially play a role in the observed j colloid sci interface transport enhancement.

Firstly, these bubbles cause skin erosion, following their violent collapse on the skin surface, due to generation of shock waves, thereby enhancing transdermal transport. Secondly, the oscillations and collapse of cavitation bubbles also cause generation of velocity jets at the skin-donor solution interface, referred to as microstreaming. These induce convective j colloid sci interface across the skin, thereby enhancing the overall transdermal transport.

Experimental findings suggest that cavita-tion outside the skin does not play that important a role in sonophoresis (11,15). The increase in the skin temperature resulting from the absorbance of ultrasound energy may increase the skin permeability coefficient because of an increase in the permeant diffusion coefficient.

The absorption coefficient of a medium increases proportionally with the ultrasound frequency, indicating that the thermal effects of ultrasound are proportional to the ultrasound frequency.

The increase in the temperature of a medium upon ultrasound exposure at a given frequency varies proportionally with the ultrasound intensity and exposure time. The thermal effects can be substantially reduced by pulsed application. Fluid velocities are generated in porous medium exposed to ultrasound due to interference of the incident and reflected ultrasound waves in the diffusion cell and oscillations of the cavitation bubbles.

Fluid velocities generated in this way may affect transdermal transport j colloid sci interface inducing convective transport of the permeant across the skin, especially through hair follicles and sweat ducts. Experimental findings suggest that convective transport does not play an important role in the observed transdermal enhancement (15). Ultrasound is a longitudinal pressure wave inducing sinu-soldai pressure variations in the skin, which, in turn, induce sinusoidal density variation.

At frequencies greater than 1 MHz, the density variations occur so rapidly that a small gaseous nucleus cannot grow and cavitational effects cease. But other effects due to density variations, such as generation of cyclic stresses because of density changes that ultimately lead to fatigue of the medium, may continue to occur.



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