PU Electrospun Fibers

Electrospinning process is a very useful technique used to fabricate suitable polymeric fibers with small diameter [137] due to the possibility of producing three dimensional structures that enable the development of advanced materials with sophisticated applications [138-140], However, thermal stability and decomposition kinetic of nanofibers may be different from micron-sized particles of a same polymer. In particular, in this chapter, we focus the attention on the electrospun fibers of PU and of PU-based 

In general, a constant amount of material is supplied to the tip of the needle by a syringe pump, and a high voltage is applied between the syringe and the collector, in which the electrospun fibers were deposited [143]. A difference of potential is applied between the tip and the collector in order to contrast with the surface tension of the solution or of the melt, able to produce an elongation of the drop of the polymer and so, the electrospun fibers are obtained. 

That is, the thermal degradation of metalized hybrid PU nanofibers was extended to higher temperature, suggesting the suppression of thermal decomposition due to the protective copper layer deposited on the surface of nanofibers. In addition, the degradation patterns of metalized hybrid PU nanofibers are different from pure PU 

Im et al. have prepared polyurethane fibers with aluminum hydroxide and multi-walled CNTs as flame-retardant additives by electrospinning, in order to improve the thermal oxidation stability of the polyurethane fibers [146]. The PU electrospun 

Pourmortazavi et al. studied both azidodeoxy nitrate cellulose (ACN) and PU electrospun fibers, thus comparing their thermal stability with their bulk materials, respectively, reporting that nanofibers of both ACN and PU have lower thermal stabilities in comparison with their bulk form [147]. 

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Figure 7.5 PU electrospun fibers prepared from polymer solution.

Sun D, Chang C, Li S, Lin L. Near-field elecUrospinning. Nano Lett 2006 6(4) 839 2. Fuh YK, Chen S Y, Ye JC. Massively parallel aligned microfibers-based harvester deposited via in situ, oriented poled near-field electro spinning. Appl Phys Lett 2013 103(3) 033114. Pu J, Yan X, Jiang Y, Chang C, Lin L. Piezoelectric actuation of direct-write electrospun fibers. Sensor Actuat A- Phys 2010 164(l) 131-6. 

Biodegradable PUs can be processed into various products such as freeze-dried foams [67], electrospun fibers [115], and 3D-printed scaffolds [68], by the use of solvent or heat. In the case of thermal processing, the moisture must be removed to avoid heat-induced hydrolysis [72], Biodegradable PU has been used as scaffolds for the repair of bones, cartilages, and blood vessels [68,116,117], demonstrating the potential in a wide range of medical applications. 

Our group also developed rapamycin (RM)-eluting stents using electrospun PU vascular grafts that could effectively suppress local smooth muscle cell proliferation. We observed that the release kinetics was characteristic of a Fickian diffusion for at least 77 days in vitro. RM-PU fibers generafed via powder blending showed the highest encapsulation efficiency. 

Figure 8.13 SEM images of electrospun rapamycin-PU fibers at a relative RM/SPU ratio (w/w) of 0,1, 5, 10, or 20% via three different blending methods. Scale bar 2 pm. Adapted from Ref. [101].

Therefore, electrospun RM-containing PU fibers can serve as effective drug carriers for the local suppression of cell proliferation and could be used as RM-eluting scaffolds for vascular grafts [101,102]. 

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