Evaluation needle length and density of microneedle arrays in the pretreatment of skin for transdermal drug delivery

Microneedle characterisation: the need for universal acceptance criteria and GMP specifications when moving towards commercialisation

“…A strong inverse correlation between skin permeability and skin electrical impedance has been demonstrated [58,60]. Yan et al [6] recognised a linear relationship between acyclovir flux and the inverse of skin electrical resistance. Typically, the method involves a test/measurement electrode measuring electrical resistance at the site of MN penetration, while a counter reference electrode is placed nearby to complete the electrical circuit [58,59].…”

“…In this context, impedance is the phase dependant resistance of the skin to the flow of alternating current. The SC represents the main barrier for transdermal delivery of drugs [6]. The electrical impedance technique, Figure 7, exploits the SC's electrical insulating properties to provide information on skin barrier function and confirm if MNs have successfully compromised the SC [48].…”

“…The majority of studies document a rapid rise in TEWL values from baseline following MN penetration. Yan et al [6] recorded an immediate 10-25 fold increase with values returning to baseline over time, indicating skin barrier recovery. This method has been applied to MN experiments investigating the effect of different MN parameters on skin barrier function and also aids in observing the resealing kinetics of the skin's integrity [6,51,53].…”

“…Yan et al [6] recorded an immediate 10-25 fold increase with values returning to baseline over time, indicating skin barrier recovery. This method has been applied to MN experiments investigating the effect of different MN parameters on skin barrier function and also aids in observing the resealing kinetics of the skin's integrity [6,51,53]. Gomaa et al [53] observed an approximate correlation between the number of trypan-blue stained pores visualised on the MN pretreated skin and TEWL values measured at 1 h post MN application.…”

“…MNs are arrays consisting of multiple MN projections (ranging from 50-900 µm in height) [5]. Their micron scale allows them to successfully bypass the SC, without stimulating nociceptors (pain receptors) in the underlying epidermal/dermal tissue layers [5,6,7,8]. Over the past decade, an extensive range of potential MN applications have been proposed.…”