## 3 Shape-Memory Polymer Nanocomposites (SMPNCs)
### Metal-Based Nanocomposites
#### 3.1.5 Other Metal Nanocomposites
[PERSON] and colleagues reported the incorporation of manganese oxide (MgO) NPs into PLA-based electrospun fibers at concentrations of 0.1, 0.5, 1, and 3 wt.% relative to  
Figure 13: (**a**) Schematic of the PCL-TiO\({}_{2}\) synthesis process; (**b**) visual demonstration of shape-memory behavior (left) and shape fixty (R\({}_{\rm f}\)) and shape-recovery (R\({}_{\rm r}\)) ratios of the polymer composites (right). Reproduced with permission from ref. [126]. Copyright 2023 Elsevier. the PLA matrix, and introduced 20 wt.% oligomers as a plasticizer to adjust the glass transition temperature (T\({}_{\text{g}}\)) (Figure 14a) [131]. The thermally-activated shape-memory behavior of these composites was examined at various temperatures to assess the effects of NP and plasticizer incorporation. At 60 \({}^{\circ}\)C, composites containing 0.1 and 0.5 wt.% MgO NPs did not exhibit shape-memory behavior, whereas those with 1 and 3 wt.% MgO NPs demonstrated excellent shape-memory responses, achieving shape fixity ratio (R\({}_{\text{f}}\)) values over 97% for effective shape fixation. In contrast, at 45 \({}^{\circ}\)C, while neat PLA electrospun fibers lacked thermally-activated shape memory, the addition of MgO NPs within 0.1-3 wt.% range preserved the high shape-memory performance of the PLA matrix (20 wt.% oligomers), with consistent shape fixity (R\({}_{\text{f}}\) > 99%) and shape-recovery ratio (R\({}_{\text{r}}\) > 82%) values across multiple thermo-mechanical cycles [131]. By incorporating citric acid-modified Prussian blue nanoparticles (PBNPs), [PERSON] and coworkers developed NIR-responsive shape-memory polyurethane (SMPU-PB) composites [132]. PBNPs are known for their cubic hexacyanoferrate structure, featuring a mixed valence state of Fe\({}^{2+}\) and Fe\({}^{3+}\), which endows them with unique photophysical, magnetic, electrochemical, and electrochromic properties [133]. The cyano groups (C\(\equiv\)N) in their hexacyanoferrate cubic structure act as a coordination link between the iron ions [134]. Additionally, as an excellent NIR photothermal agent similar to AuNPs, PBNPs have strong absorption at 808 nm [135]. The incorporation of photothermal PBNPs into the polymer matrix allows the resulting composite to exhibit an NIR response, as evidenced by the  
Figure 14: (a) FESEM images of MgO NPs with MgO-loaded electrospun fibers containing 0.1, 0.5, 1, and 3 wt.% MgO. Reproduced with permission from ref. [131]. Copyright 2022 MDPL (b) Photographs depicting the shape recovery of a “box”, as well as the processes of “Jump” and “Cross Obstacle” for a SMPU-PB material under 808 nm NIR light exposure. Reproduced with permission from ref. [132]. Copyright 2023 American Chemical Society. unfolding and recovery of a fabricated \"box\" shape upon NIR irradiation (Figure 14b). The material displayed consistent shape fixation and recovery ratios of 98.9% and 95.7% respectively, over five cycles, indicating its resilience to repeated shape-memory cycles, although it did not achieve 100% shape recovery due to potential permanent deformation in the thermoplastic composite. The study also explored a light-activated bionic \"athlete\" that exhibits a jumping motion initiated by NIR light for 25.6 s, covering 17 mm in 0.06 s, and demonstrated its ability to adeptly overcome obstacles with consistent \"cross-obstacle\" performance even after five iterations (Figure 14b) [132]. Copper sulfide (CuS) NPs are used as nanofillers to enhance the behavior of SMP composites. As a p-type semiconductor with a direct bandgap ranging from 1.2 to 2.0 eV, CuS exhibits notable photothermal conversion driven by the efficient d-d energy band transition of Cu(II) ions under NIR laser irradiation [136]. [PERSON] et al. developed a cost-effective, stable light-sensitive SMP composite by embedding CuS NPs, synthesized on modified cellulose nanocrystal (CuS NPs@MCNC) through chemical precipitation, into a polyurethane matrix [137].