The skin as a barrier to drugs and actives
The major barrier to the delivery of drugs and other actives through and into the skin is the 10-20 micrometre thick outer layer of skin, the stratum corneum. This is composed of around 15-25 flattened dead cells filled with protein, resembling bricks embedded in a mortar of intercellular lipid. It creates a formidable barrier, preventing water loss from the skin and protecting the body from physical damage and penetration of chemicals, microbes and allergens. The stratum corneum presents a mixed lipid (oily) and protein structure, which greatly reduces the range of chemicals that can penetrate.
A number of methods have been developed to disrupt the stratum corneum and so increase the permeability of the skin to certain chemicals, and these can be divided into chemical and physical means. Chemical means include penetration enhancers, (chemicals that can push apart the lipid layers and disrupt their integrity), soaps and solvents that extract some of the lipids (such as acetone). Physical means include use of a variety of energy devices, including heat, laser, electric fields, ultrasound, and also mechanical damage by tape stripping, microneedles and dermabrasion.
Plasma as a penetration enhancer
NeoGen produces a controlled burst of heat, and heat is known to increase stratum corneum permeability. As with other modalities, like ultrasound, thermal ablation and laser, it would be expected that NeoGen-induced rapid heating would cause increased permeability through pore formation, enhancing and joining the discontinuous pore network. It is known that gas plasma jet treatment can enhance penetration of 56nm diameter particles, presumably by enhancing pore formation, and plasma has been shown to increase permeation of fluorescein, galantamine hydrobromide, Phenol Red, fluorescently labelled dextran, and, interestingly, epidermal growth factor.
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