Microneedles

Microneedles (MNs) are small micron-sized needles which whenapplied on the skin breaches the SC to create microchannels throughthe skin thereby assisting drug delivery. Drug can be deliveredby variousmodes using these techniques.

These modes are:

(a) piercingan array of solidmicroneedles into the skin followed by application of adrug patch at the treated site

(b) coating drug ontomicroneedlesand inserting them into the skin for subsequent dissolution of the coateddrug within the skin

(c) encapsulating drug within biodegradable, polymericmicroneedles followed by insertion into the skin for controlleddrug release and  

(d) injecting drug through hollow microneedles. The microchannels thus created help topically applied drugmolecules to by pass the SC which is the major rate limiting barrier for transdermal permeation.Moreovermicroneedles areminimally invasiveand painless as they do not penetrate up to the papillary dermis wherenerve endings are situated.

In vivo delivery has been shown forpeptides, such as insulin and desmopressin, genetic material, includingplasmid DNA and oligonucleotides, disease-modifying antirheumaticdrugs (DMARDs)  and vaccines directed against hepatitisB, anthrax and Japanese encephalitis. Apart fromthat,MNsmadefrom insoluble metal and silicon is painless, though it has its own prosand cons viz. poor safety and inconvenience for self-administration.This may be a main reason that Mn-based TDDS is yet not commercialized. A remarkable finding by S. Liu et al. proves that the hyaluronicacid (HA)-based novel MNs loaded with insulin have several advantagesover formerly prepared MNs as it prevents serious skin damage.