**6. Conclusions**

The main advantages of electrospinning process are the production of nanometer scale fibers with large surface areas, good mechanical properties, easy functionalization of these fibers for various purposes such as protective clothing, drug release material, or an air filter. These advantages provide many opportunities for their use in wide range of different applications [126]. PU is often chosen as a material for composing a nanoweb due to its chemical stability, mass transport, good mechanical properties, and also excellent nanofiber forming characteristic. Main reason for chosing PUs in electrospinning is that, the properties of PUs can vary in a wide range, so it is possible to adopt PUs to many applications by varying the structure of PUs. Electrospun PU nanofiber mats exhibiting good mechanical properties may have a wide variety of potential applications in high-performance air filters, protective textiles, wound dressing materials, sensors, in biomedical applications, drug delivery, as well as in wound dressing studies because of its good barrier properties and oxygen permeability. For these applications, electrospinning assembly can be varied in different ways for combining materials properties with different morphological structures. PUs can also be mixed either with a natural polymer or with a synthetic polymer for special applications such as collagen, dextran, and hydroxypropyl cellulose (HPC). Beside, from an industrial point of view, an enhancement in both mechanical and physical properties of the electrospun fiber mats is very important and it is possible to mix the PUs with SWCNTs or MWCNTs to overcome this problem.

Although there is ever increasing literature on use of PU nanofibers for various applications but still the field is in its infancy. For example, there are also lots of questions for biomedical applications, like interaction of scaffolds with biological systems, toxicity, in vivo studies etc. There is no doubt that PU electrospun materials are going to take major place in future for above mentioned applications. Thus, all these applications have to be thoroughly investigated before the technology can be used for any real practical application.
