**7. New development and future trend**

composites also showed good MG63 cell differentiation ability, which showed its potentiality as

SMPU can be made in the form of fibers (macro-, micro-, and nanofibers), solutions, films, and foams for textile and apparel applications, such as non-woven materials, coatings, finishing, lamination, weaving, and knitting [46–49]. Various methods such as wet spun, melt spun, dry

Shape memory films and foams have a number of applications in laminated smart fabrics [54, 55]. The functions of SMP films applied to textiles include waterproofing, water vapor permeability (WVP), seam sewing, crease recoverability, and crease fixing [56, 57]. SMPU has a potential for making breathable fabrics due to its good WVP sensitivity. Jeong et al. studied the WVP properties of SMPUs, and breathable fabrics were invented by coating the SMPU membranes on a fabric substrate [26]. Mondal and Hu also designed SMPU-coated fabrics, which abruptly increased

gested that the breathable textiles require possessing a high WVP at higher temperatures and a low WVP at lower temperatures. Additionally, Mondal and Hu incorporated a small percentage of carbon nanotube in SMPUs and then coated on cotton. They reported that the fabricated cotton fabric provided excellent UV protection, along with a required WVP and wearing coziness [58]. In addition to that, Chen et al. also investigated adjusting the size and shape of the free-volume holes in a fabricated membrane to control the WVP by adjusting the temperature [59]. Further, Mondal and Hu attempted to find the influence of hydrophilic groups and crystalline soft segments on the WVP of SMPU films [60]. They found that the WVP increased with the increase of PEG due to the enhancement of hydrophilicity. However, PCL or polytetramethylene glycolbased SMPUs have low WVP because of the increased interaction among the polymer chains.

Hu et al. also fabricated a fabric-based thermoelectric generator using coating of waterborne PU composite on yarn [61]. They reported that this coated fabric showed satisfactory thermoelectric performance and good processability. In addition to that, medical stockings are also fabricated using SMPU for the treatment of chronic venous disorders [62–64]. This SMPUbased stocking allows controlling or managing the pressure exerted in a wrapped position and also produces extra pressure (up to 50%) by simply heating the stocking. This type of stocking possesses a great potential to overwhelm the restriction of conventional stockings. It can be used as a smart wound-care product, during the course of compression therapy. Selfhealing textiles are also developed using SMPU. In this context, Hu et al. fabricated stimuli-

SMP security label film is made from SMPU. SMP security label film can store embossed logo/ text shape information in the synthetic-paper-like film, and release these information when exposed to stimuli (**Figure 6**). This kind of SMP security label is just not only an exclusive anticounterfeit label but also a tamper evidence label [66]. These labels are used for security label,

responsive fiber using SMPU which showed 94% healing efficiency [65].

tamper evidence, security packaging, security ticket, and so on.

**6.4. Anti-counterfeiting application of SMPU**

) compared to low temperature [58]. These results sug-

an alternative biomaterial for bone regeneration in a comprehensive manner [45].

spun, and electrospun are used for the production of SMPU fiber [50–53].

**6.3. Textile application of SMPU**

64 Aspects of Polyurethanes

WVP properties at room temperature (*T*<sup>r</sup>

Even though an enormous progress in the field of SMPU is already done, several future directions and related challenges still remain, which may be considered in future research:

