## 3 Shape-Memory Polymer Nanocomposites (SMPNCs)
### Metal-Based Nanocomposites
#### 3.1.3 Silver Nanoparticle (AgNP) Nanocomposites  
Silver nanoparticles ( AgNPs) have attracted significant attention in recent years due to their promising characteristics, including superior thermal and electrical conductivity, chemical stability, and antibacterial properties [103; 104; 105]. [PERSON] et al. reported that incorporating 22% AgNPs into high-density polyethylene enhances thermal conductivity by approximately 4.5 times when processed via extrusion, simultaneously imparting electrical functionalities [106]. [PERSON] and [PERSON] explored the effects of AgNPs on the shape-memory behavior of epoxy nanocomposites, produced through casting with in situ reduction of silver nitrate (AgNO\({}_{3}\)), carbon black, and carbon nanofibers (4 wt.%) [107]. They demonstrated that applying 220 V to both the terminal and lateral zones of the material achieved the required temperature for activating the SME where T \(>\) T\({}_{\text{g}}\), within 60 s.  
Reversible two-way SMPs utilized in soft actuators offer advantages such as significant output stress, low driven voltage, straightforward construction, and cost-effectiveness [108; 109]. The key to achieving a two-way SME lies in generating internal stress within the polymer composites [110]. Additional factors, such as two-layer structures, cross-linked networks, three-dimensional structures with reversible covalent bonds, and materials with dual-crystal components, also contribute to reversibility [111; 112; 113]. Despite the merits of two-way SMP-based actuators, opportunities for improvement remain, including more stable multilayer structures, simplified multi-molecular network designs, and enhanced reversible deformation. Consequently, [PERSON] et al. designed an AgNPs-integrated sandwich structure for a shape-memory soft actuator that features reversible electric and moisture actuation, along with strain sensing capabilities [44]. The actuator consists of a middle layer of AgNPs for electrothermal activation, sandwiched between a hygroscopically deformable polyvinyl alcohol (PVA) layer and a flexible shape-memory polymer (FSMP) layer (Figure 9a). The PVA-AgNPs-FSMP (PAF) composite, containing 6 mol/m\({}^{2}\) AgNPs, exhibited enhanced performance, particularly at 2 V, achieving recovery within 10 s at a 98% rate (Figure 9b). In a moist environment, the composite bends and returns to its original shape in 40-50 s under electric power below 2 V, demonstrating effective Joule heat generation for shape recovery (Figure 9c) [44]. Researchers also have a notable interest in AgNP-embedded nanocomposites due to the SPR properties of the NPs, which offer potential for light-triggered remote activation with precise spatial and temporal resolutions across a broad spectrum of light [114]. [PERSON] et al. utilized in situ ring-opening polymerization (ROP) of thermoset polycarbonate (PmBz) and thermoplastic PCL composites embedded with plasmonic AgNPs for laser-triggered SMP applications [57]. Benzoxazine (Bz) is known for developing permanent cross-linking or network points in thermoset polymers, thereby enhancing the thermo-mechanical performance of SMPs [115; 116]. It also plays a crucial role in forming the PmBz network and providing numerous hydroxyl groups for conjugation with the thermoplastic PCL [117]. The selection of AgNPs is based on their ability to be activated by a low-energy violet laser (408 nm, 780 mW) and surface modification with disulfide polycaprolactone (SS-PCL) to ensure high miscibility and easy dispersal in PCL matrices. An investigation into the impact of AgNP concentration on shape recovery revealed that composites with varying AgNP weights exhibited no shape recovery at 0.001 wt.% after 40 s of laser irradiation, while those with 0.01 wt.%, 0.1 wt.%, and 0.3 wt.% AgNPs displayed clear SMEs (Figure 10a). This experiment determined that a minimal content of 0.01 wt.% AgNPs is required for the phenomenon to be visually observable [57].