## 3 Shape-Memory Polymer Nanocomposites (SMPNCs)
### Carbon-Based Nanocomposites
#### 3.2.1 Carbon Nanotube (CNT) Nanocomposites
In their experiments, a rectangular sample of the PCL-CAN composite network was stretched and then quickly returned to its original shape within two minutes through Joule heating, demonstrating efficient localized heating in stretched regions while avoiding overheating of the entire sample (Figure 15). Figure 15: (**a**) Illustration of step-by-step network formation through maleimide-furan Diels-Alder addition; (**b**) shape-memory cycles of PCL-CAN, measured by DMA, starting from panels A to D; and (**c**) standard and infrared images illustrating the electroactive shape-memory recovery process driven by the Joule effect. Reproduced with permission from ref. [55]. Copyright 2023 Elsevier. [PERSON] and coworkers fabricated a nanocomposite with fast healing capabilities based on dynamic bonds, utilizing carboxyl-functionalized MWCNT\({}_{\text{COOH}}\) and a cross-linked polyurea (CPU) matrix through a facile two-step method. This method involved in situ photo-induced polymerization followed by hot compression [152]. The resultant nanocomposites exhibited exceptional photo-induced SME, capable of unfolding round-shaped films under NIR light irradiation within 20 s and returning them to their original shape in 120 s. In contrast, pure CPU films remained unchanged even after 120 s of exposure, highlighting the significant role of MWCNT\({}_{\text{COOH}}\) in enhancing photo-induced SME through its photothermal properties. Furthermore, the self-healing capabilities under NIR light were investigated, revealing that while visible scratches on pure CPU matrices persisted even after prolonged NIR exposure, nanocomposites containing 0.5 wt.% and 1.0 wt.% MWCNT\({}_{\text{COOH}}\) achieved rapid and complete scratch healing within 40 s, reaching a 100% self-healing efficiency (Figure 16). In another study, [PERSON] and coworkers added polydopamine (PDA)-modified MWCNTs to an epoxy vitrimer to improve the interfacial interaction between nanofillers and the polymer matrix while maintaining high photothermal efficiency [153]. The incorporation of 1 wt.% MWCNTs resulted in shape-memory composites demonstrating initial shape fixty and recovery ratio 80.1% and 92.1%, respectively. This approach not only improved the performance of the composites but also underscored the synergy between material innovation and scientific advancement in the field of materials engineering. [PERSON] and colleagues utilized a sol-gel method to synthesize silica-coated multi-walled carbon nanotubes (MWCNT@SiO\({}_{2}\)). These were subsequently incorporated into a cyanate ester-based SMPNC [154]. The optimal loading of 0.9 wt.% MWCNT@SiO\({}_{2}\) not only enhanced the moisture resistance but also significantly improved the mechanical properties, as evidenced by increased strength and toughness. Furthermore, the inclusion of MWCNT@SiO\({}_{2}\) facilitated an accelerated shape-memory process, with the composites demonstrating excellent  
Figure 16: (a) Images depict the production process of CPU@CNT using hot compression, with photos of a pure polymer film and a nanocomposite film before and after bending, along with SEM images of the cross-sectional and surface views of [EMAIL_ADDRESS]; (b) illustration of the scratch-healing process under NIR light; and (c) images of shape recovery for CPU@CNT and pure CPU. Reproduced with permission from ref. [152]. Copyright 2022 Elsevier. shape fixity (R\({}_{\text{f}}\)) and recovery (R\({}_{\text{r}}\)) ratios exceeding 98% after 10 testing cycles. In a related study, [PERSON] et al. reinforced the mechanical and shape-memory characteristics of shape-memory polyurethane (SMPU) with a mixture of two types of nanofillers: MWCNTs and halloysite nanotubes (HNTs) [155]. This reinforcement strategy yielded composites with impeccable 100% shape recovery from their programmed temporary shapes, alongside a reduction in recovery time as the filler concentration increased.