Skin permeationenhancement Skin act as anatural barrier for transdermal drug delivery, however skin permeability can beenhanced by altering the nature of skin by different means like physicalapproach, chemical approach or biological approach.Physicalpenetration enhancementPhysicalmethod of skin permeation enhancement is further subcategorized into threecategories a) structure based (microneedles); b) electrical based(iontophoresis, electroporation, sonophoresis, magnetophoresis, laser ablation,photomechanical waves) c) velocity based (jet propulsion).  They can used in isolation or combinedtogether to get better systemic drug plasma concentration. In the followingsection they are discussed in brief.

Structurebased permeation enhancementMicroneedlesMicroneedlearrays based TDDS have been intensively investigated in recent times for theirbiocompatibility and as delivery vehicles of small and large molecules (vaccinesand drugs) commercially. Due to emergence of sophisticatedmicrofabrication manufacturing technology, microneedles were fabricated withmuch precision and it is found to behighly amenable to transdermal drug delivery by penetrating stratum corneum. Microneedlessize varies from 150-1500 microns in length, 50-250 microns in base width, and 1-25 in diameter. The success of MN based drug delivery relies onits effective patient compliance and pain minimization.  However, it was observed that the length andnumber of MN dictate this pain management.

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Patch having 400 microneedlesof 150?m length was reportedto be painless. When the length of needle is increases from 500 µmto1500 µm (constant needle number) and 10 times increase in MN number (constantlength 620 µm), the pain score was increased by 7 and 3 fold respectively.  Microneedles cause micron  sized pore formation due to puncturing  of the skin and they are arranged in arrayson the backing of the patch and such device is known as microneedle patch. However,this is paramount for microneedles to qualify on some characteristics forsuccessful drug delivery vehicle.

These charcteristics are:1) they should beinserted deep into the skin tissue without breaking;2) they should have optimum dimension (neither too short nor too long) becausetoo short needle would not penetrate deeper into skin tissue or long needlewould not having enough strength and rigidness and can break before penetration.