## 5 Discussion  
The advancement of SMPNCs represents a significant step forward in the development of smart materials with enhanced mechanical, thermal, and actuation properties. This review has extensively examined the fundamental aspects of SMPNCs, including their structural composition, mechanisms of shape recovery, and diverse applications across various fields such as biomedical technology, robotics, electronics, and automotive systems. While SMPNCs have demonstrated superior performance compared to conventional SMPs, certain challenges and limitations still persist, necessitating further exploration. One of the key challenges in the field of SMPNCs is achieving uniform dispersion of nanofillers within the polymer matrix. The effectiveness of nanofillers in enhancing the properties of SMPs depends on their homogeneous distribution and strong interfacial  
Figure 30: (**a**) The antimicrobial properties of PLLA and PCL-TiO\({}_{2}\)/PLLA were tested against \(B\). _subtilis_, \(B\). _licheniformis_, and mold. Reproduced with permission from ref. [126]. Copyright 2023 Elsevier. (**b**) Photos of the 5f-t667 yarn sensor sewn onto silk fabric and a cotton glove, alongside relative resistance changes in the sensor when attached to a bending finger. Reproduced with permission from ref. [46]. Copyright 2023 Elsevier. (**c**) Illustration of rewritable photonic papers, along with optical and SEM images of a red photonic nanocomposite under 0%, 50%, and 100% tensile strain. Reproduced with permission from ref. [317]. Copyright 2018 John Wiley and Sons. (**d**) Fabrication of microcone arrays involved assembly procedures and showing the lossless transfer of droplets in both the “captured” and “detached” conditions. Reproduced with permission from ref. [121]. Copyright 2020 American Chemical Society. (**e**) Illustration of the shape-recovery procedure using several Morse codes based on different activation techniques. Reproduced with permission from ref. [320]. Copyright 2017 American Chemical Society. adhesion with the polymer chains. However, agglomeration of nanoparticles, particularly at high concentrations, can lead to non-uniform mechanical and thermal properties, negatively impacting the shape-memory performance. To address this, advanced fabrication techniques, such as surface functionalization of nanofillers, in situ polymerization, and the use of compatibilizers, have been investigated to improve the dispersion and interaction of nanofillers within SMP matrices. Another significant consideration is the mode of actuation. While thermally triggered SMPNCs are the most widely studied, they often require direct heat sources, which can be challenging for remote or spatial control applications. Recent developments have focused on alternative actuation methods, including electrical, magnetic, and light-based stimuli. Magnetic and photothermal activation have shown promise in enabling remote actuation, but challenges such as the efficiency of energy conversion and potential overheating need to be addressed. Moreover, achieving multi-stimuli responsiveness in SMPNCs remains an area of active research, as integrating multiple activation mechanisms could lead to more versatile and application-specific material responses. In biomedical applications, the biocompatibility and biodegradability of SMPNCs are critical factors that must be considered. Although certain nanofillers, such as gold and iron oxide nanoparticles, have demonstrated compatibility for medical applications, concerns remain regarding long-term stability, cytotoxicity, and potential accumulation in biological systems. Extensive in vivo studies and regulatory evaluations are required to ensure the safe implementation of SMPNC-based medical devices. Additionally, the long-term durability and fatigue resistance of SMPNCs under cyclic loading conditions are crucial aspects that need further investigation.