**5. Conclusions**

Appeared on scene as a painless alternative to syringes, MNDs have conquered the biomedicine. The flexibility of these innovative devices makes these technological platforms really attractive for even new fields of application. Almost all materials can be used in the fabrication of MNDs: noble metals (gold and silver), semiconductors (silicon), plastics (polymers and hydrogels), amorphous materials (ceramics) and artificial nanostructured materials (porous silicon). MNDs have been used for drug delivery, cosmetic industry or biosensing, where the MN microstructures have been used as electrodes for electrochemical transduction. For biosensing systems, pros and cons have been highlighted for each device type in terms of analytical performances such as LoD, detection time, sensitivity and so on. In all the application cases, considerations about the safety of MNDs is due, since MNDs are conceived for being in contact with the human body. Then, inert, biocompatible, or physiologically dissolvable materials have to be engaged for device fabrication, even if they show lower analytical or delivery performances. After the overcoming of the skin natural barrier, MNs are directly in contact with human ISF. Hollow, coated, and swelling MNDs are all used in two ways: sensing of analytes and delivery of drugs; biosensing and administration; therapy and diagnosis.
