## 4 Applications  
### Biomedical Applications  
SMPCs exhibit significant potential in biomedical applications due to their inherent nontoxicity, biocompatibility, and ease of processing. These properties facilitate the use of SMPNCs in a range of biomedical applications, including tissue engineering, drug delivery, stents, biological sutures, and minimally invasive surgery, where they transition from a compact temporary structure to their original expanded shape in response to external stimuli. Moreover, SMP-based scaffolds excel in self-healing and self-adaptation, allowing them to precisely conform to defect boundaries upon shape restoration, further underscoring their versatility and effectiveness in medical applications. Congenital heart diseases (CHDs) are the most prevalent congenital anomalies that seriously threaten human health and life [26]. Interventional therapy, which utilizes occluders for percutaneous nonsurgical closure, has emerged as an effective treatment modality for CHDs [27]. However, the use of nondegradable materials such as nitinol (Ni-Ti) alloys and polyethylene terephthalalate (PET) fabric in occluders has raised concerns regarding long-term foreign body reactions and associated complications [275]. Although nitinol-based occlusion devices are clinically effective in isolating the left atrial appendage (LAA), their limited biocompatibility, non-degradability, and mechanical property mismatch with adjacent tissues may lead to complications, including allergies, corrosion, tissue wear, and perforation [276,277]. [PERSON] and coworkers designed a 4D-printed biocompatible and absorbable left atrial appendage occluder (LAAO) that can match the deformation of LAA tissue to minimize complications [278]. The LAAOs were fabricated through 4D printing from shape-memory PLA-based magnetic nanocomposites (PLA-MNCs), where incorporating MNPs facilitate self-heating and enable remote-controlled 4D transformation. A feasibility test for transcatheter closure of the LAA was performed using a 13 Fr catheter, which successfully and minimally invasive delivered the double-layer LAAO into a  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Nanofilers** & **Polymer Matrix** &
\begin{tabular}{c} **Temperature** \\ **(T\({}_{\text{ram}}\))** **s**  
freshly isolated swine heart. The LAAO exhibited excellent magnetic response, supporting its remote-controlled magnetism-induced 4D transformation and affirming its suitability for minimally invasive transcatheter closure in an isolated swine heart (Figure 27a) [278]. In another study, a 4D-printed biodegradable occlusion device for the treatment of atrial septal defects was developed by incorporating Fe\({}_{3}\)O\({}_{4}\) particles into a shape-memory PLA matrix, enabling magnetically remote controllability post-implantation (Figure 27b) [279]. These biodegradable occluders emerge as a next-generation solution designed to overcome complications associated with non-degradable implants by offering a temporary mechanism that promotes in situ tissue regeneration and addresses issues related to permanent foreign bodies [280]. Upon endothelialization, the devices gradually decompose into benign substances that are metabolized, featuring self-expandable double-umbrella structures to facilitate healing within the heart defect [80]. In a related study, [PERSON] and coworkers incorporated polyethylene glycol-modified gold nanorods (AuNR/PEG) into poly(L-lactide-co-\(\varepsilon\)-caprolactone) (PLCL) to fabricate biodegradable occluders using PLCL-GNR/PEG nanocomposites [80]. The addition of 10% caprolactone (CL) structural units to PLCL enhances toughness and lowers the T\({}_{\text{g}}\) to a level more suitable for tissue acceptance. The occluders, featuring a \"double umbrella\" structure, were designed for easy catheter loading and selective spatiotemporal expansion under NIR light to occlude defects (Figure 27c).