## 3 Shape-Memory Polymer Nanocomposites (SMPNCs)
### Metal-Based Nanocomposites
#### 3.1.5 Other Metal Nanocomposites  
Metal nanostructures, in addition to those previously mentioned, are also commonly used in the design of SMP NCs. [PERSON] et al. developed an SMPNC by incorporating PCL-hybridized titanium dioxide (TiO\({}_{2}\)) nanomaterials (PCL-TiO\({}_{2}\)) into poly(L-lactide) (PLLA), resulting in a PCL-TiO\({}_{2}\)/PLLA composite [126]. In this system, the TiO\({}_{2}\) component functions as a 'heat dispersion pump' within the switching phase, with PCL acting as a 'heat dispersion bridge'. This configuration establishes an effective heat conduction pathway within the PCL-TiO\({}_{2}\)/PLLA composite, facilitating the transfer of thermal energy necessary to initiate the melting process, release stored elastic energy, and trigger the shape-memory behavior of the composite [126]. Additionally, the hybrid switching phase provides a plasticizing effect on the otherwise rigid PLLA matrix, optimizing the balance between stiffness and toughness [52,127]. The shape-memory function was demonstrated by deforming the composite into a spiral strip and bud shape at a transition temperature (T\({}_{\text{trans}}\)), freezing the temporary shape by cooling to 15 \({}^{\circ}\)C, and then recovering the original shape by reheating to 57 \({}^{\circ}\)C (Figure 13). The PCL-TiO\({}_{2}\)/PLLA composite exhibited superior reversible shape-memory properties compared to PCL/PLLA, with shape fixity (R\({}_{f}\)) and shape-recovery (R\({}_{r}\)) ratios of 93.9% and 94.4%, respectively, and achieved shape recovery in just 15 \(s\)[126]. Figure 12: (**a**) Illustration of cross-linked networks in the PEDGA/OEG-W\({}_{18}\)O\({}_{49}\) composite synthesis; (**b**) temperature vs. time plots for UV and NIR light irradiation at different wavelengths. Reproduced with permission from ref. [72]. Copyright 2019 John Wiley and Sons. [PERSON] et al. explored the use of titanium nitride (TiN) NPs as broadband plasmonic light absorbers in cross-linked PCL SMP composites [128]. Compared to gold or silver NPs, TiN exhibited higher optical absorption loss, resulting in a broader linewidth of its plasmonic resonance [128]. Analytical and experimental demonstrations revealed that the broad resonance of TiN NPs enhanced sunlight absorption efficiency [129]. The study assessed the shape-memory behavior of TiN-PCL composites with TiN concentrations ranging from 1 to 20 wt.% by programming temporary shapes through elongation above the melting temperature (T\({}_{\rm m}\)). Subsequent shape recovery was observed under five minutes of solar radiation at intensities of 100, 130, and 160 mW/cm\({}^{2}\). All composites exhibited a high and TiN concentration-independent shape-fixing ratio [128]. Under sunlight irradiance at 130 mW/cm\({}^{2}\), partial recovery occurred, while complete recovery was achieved at 160 mW/cm\({}^{2}\), suggesting a threshold irradiance for full shape recovery between these values. The incorporation of TiN NPs impacted the flexibility of the composites, with the 1 wt.% TiN-PCL sample exhibiting the most significant shape change. The biodegradable nature of PCL, combined with the chemical stability and light-responsive properties of TiN NPs, positions the TiN-PCL composite as a suitable candidate for biological and clinical applications, providing an energy-efficient approach to activating SMPs under sunlight [128]. In a related study, [PERSON] et al. prepared an SMP composite by solution blending, doping PCL and poly(vinyl chloride) (PVC) blends with various concentrations of titanium carbide (TiC) NPs [130]. This approach aimed to investigate the effects of TiC NPs on the shape-memory behavior and properties of the PCL-PVC composite.