Skin permeation
enhancement

Skin act as a
natural barrier for transdermal drug delivery, however skin permeability can be
enhanced by altering the nature of skin by different means like physical
approach, chemical approach or biological approach.Physical
penetration enhancement

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Physical
method of skin permeation enhancement is further subcategorized into three
categories 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 combined
together to get better systemic drug plasma concentration. In the following
section they are discussed in brief.

Structure
based permeation enhancement

Microneedles

Microneedle
arrays based TDDS have been intensively investigated in recent times for their
biocompatibility and as delivery vehicles of small and large molecules (vaccines
and drugs) commercially. Due to emergence of sophisticated
microfabrication manufacturing technology, microneedles were fabricated with
much precision and it is found to be
highly amenable to transdermal drug delivery by penetrating stratum corneum. Microneedles
size 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 on
its effective patient compliance and pain minimization.  However, it was observed that the length and
number of MN dictate this pain management. Patch having 400 microneedles
of 150?m length was reported
to be painless. When the length of needle is increases from 500 µm
to1500 µm (constant needle number) and 10 times increase in MN number (constant
length 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 arrays
on the backing of the patch and such device is known as microneedle patch. However,
this is paramount for microneedles to qualify on some characteristics for
successful drug delivery vehicle. These charcteristics are:1) they should be
inserted deep into the skin tissue without breaking;
2) they should have optimum dimension (neither too short nor too long) because
too short needle would not penetrate deeper into skin tissue or long needle
would not having enough strength and rigidness and can break before penetration.