Editing Transdermal patch (section)

=== Types of microneedle ===
There are many types of microneedle that are distinguished by the shape and other characteristics. The types include: Dissolvable MNPs, solid non-soluble MNPs, and hollow MNPs. Different MNPs may be chosen depending on the situation and the drug properties.

==== Soluble or dissolvable MNPs ====
One of the types of MNPs are water-soluble needles made out of soluble polymers or saccharide. However, dissolvable needles cannot efficiently deliver drugs to the dermal layer. Drug maximum concentration cannot be carried out to the skin, as the needles will dissolve beforehand. Fortunately, researchers have developed a water-insoluble backing layer, making the needle last longer in the human body environment. This design enables efficient delivery of more than 90% of the drug within 5 minutes of application of MNPs to the skin.<ref name="Li 2103359">{{Cite journal|last1=Li|first1=Song|last2=Xia|first2=Dengning|last3=Prausnitz|first3=Mark R.|date=2021-06-21|title=Efficient Drug Delivery into Skin Using a Biphasic Dissolvable Microneedle Patch with Water-Insoluble Backing|journal=Advanced Functional Materials|volume=31|issue=44|page=2103359|doi=10.1002/adfm.202103359|pmid=34744551 |pmc=8570388 |issn=1616-301X}}</ref>

==== Non-soluble or undissolvable MNPs ====
Other than dissolvable MNPs, needles can also be made out of metal or ceramic that will not dissolve in the body environment. These coated drug needles can deliver consistent concentration of drugs without the needles dissolving in the body. This kind of MNPs has better performance, but compared to the soluble MNPs, metal or ceramic MNPs are the older version of MNPs. Even if the patches are small, the metal or ceramic MNPs may cause several waste issues. Recycling the metal and ceramic are very hard, as the quantity is very small to overcome the cost to recycle. That is why researchers try to develop the dissolvable MNPs with similar characteristic and performance of drug delivery in non-soluble MNPs.<ref name="Li 2103359"/>

==== Hollow MNPs ====
Among all of the MNPs, hollow needles allow a bigger amount of delivery up to 200μL. The mechanism mimics the operation of a hypodermic, but the fabrication is hard and complex. The hollow needles introduce a potential failure if the insertion is improper. That is why, among the others, hollow MNPs are the least popular because of the complex manufacturing and applying process.<ref name=":1" />