## 3 Shape-Memory Polymer Nanocomposites (SMPNCs)
### Metal-Based Nanocomposites
utilized silane-functionalized nanodiamond@Fe\({}_{3}\)O\({}_{4}\) (S-NDF) hybrid NPs to create highly sensitive and multifunctional magnetic nanocomposites [69]. The resulting nanocomposites, with 9 wt.% S-NDF loading exhibited superior shape recovery (above 96%) in a small magnetic field (H = 0.76 kA/m), along with faster magnetic responsiveness compared to Fe\({}_{3}\)O\({}_{4}\)-loaded counterparts. Figure 4: **(a) Illustration of the structure of Fe\({}_{3}\)O\({}_{4}\) NPs embedded in V-fa/ECO copolymers and object pushing actuation under a magnetic field using 5 wt.% NPs. Reproduced with permission from ref. [51]. Copyright 2023 Kingfa Scientific and Technological Co. Ltd. (b) Schematic of the manufacturing procedure for the composites used in 3D printing and the magneto-responsive shape-memory process of a honeycomb structure. Reproduced with permission from ref. [67]. Copyright 2022 Elsevier. **  
The SMPNCs filled with Fe\({}_{3}\)O\({}_{4}\) NPs also demonstrated photothermal conversion capabilities, efficiently absorbing near-infrared (NIR) light to generate thermal energy [70; 71]. This property enables non-contact actuation through NIR laser and magnetic attraction, offering a localized triggering mechanism for shape memory, distinct from traditional thermal activation methods [72; 73; 74]. [PERSON] et al. synthesized a cellulose/PCL composite with notable strength, toughness, degradability, and multi-stimuli responsiveness by grafting soft PCL side chains onto a rigid cellulose backbone and incorporating a cross-linking network with hexamethylenediamine-modified MNPs [75]. This composite achieved exceptional toughness (up to 107 MJ/m\({}^{3}\)), displayed significant thermal stability, and rapidly heated to 75 \({}^{\circ}\)C under 808 nm NIR light exposure, maintaining photothermal conversion efficiency and stability across multiple light on/off cycles. The shape-memory behavior of the composite was demonstrated by its significant ability to lift heavy objects and self-tightening knots under NIR light, suggesting potential for intelligent gripping applications (Figure 5a). Similarly, [PERSON] et al. developed polyhydroxyurethane (PHU)-based SMPNCs by integrating poly(2-oxo-1,3-dioxolane-4-y)methyl methacrylate-modified Fe\({}_{3}\)O\({}_{4}\) NPs, exhibiting shape-memory activation via non-contact NIR light exposure [76]. When subjected to NIR light, the pure PHU specimen failed to revert to its original shape even after two minutes of irradiation, while the nanocomposites displayed efficient recovery, transforming from a \"bud\" to a \"blooming flower\" shape within 39 s at a 30 wt.% filler content (Figure 5b). This suggests that the photothermal effect of Fe\({}_{3}\)O\({}_{4}\) NPs effectively activates the shape-memory behavior in the nanocomposites. [PERSON] et al. fabricated epoxy-based nanocomposites incorporating Fe\({}_{3}\)O\({}_{4}\) NPs and poly(\(\alpha\)-lipoic acid) as a cross-linker [77]. The resulting SMPNCs enable non-contact and photothermally induced shape recovery, exemplified by the rapid restoration of the extended rectangular specimen to its original shape when irradiated with an 808 nm NIR laser (Figure 5c). In another study, [PERSON] et al. designed multiple-stimulus responsive SMPNCs  
Figure 5: **(a)** Schematic diagrams illustrating the chemical composition of EC-g-PCL/Fe\({}_{3}\)O\({}_{4}\) composites, stress-strain curves, the cyclic photothermal conversion process, and self-tightening knots of the composites. Reproduced with permission from ref. [75]. Copyright 2022 Elsevier. **(b)** Shape-memory behavior transitioning from a “bud” to a “blooming flower” of laser-triggered PHU-Fe\({}_{3}\)O\({}_{4}\) nanocomposites containing 30 wt.% of PDOMA-grafted Fe\({}_{3}\)O\({}_{4}\). Reproduced with permission from ref. [76]. Copyright 2021 Elsevier. **(c)** NIR-triggered shape recovery of a rectangular specimen. Reproduced with permission from ref. [77]. Copyright 2023 Elsevier. **(d)** NIR-triggered shape recovery of a rectangular specimen. Reproduced with permission from ref.