**6.2. Biomedical applications of SMPU**

SMPs are also well suitable for the use in different biomedical applications, even though several requirements must be addressed and a range of problems must be overwhelmed for advanced application in this field [33]. For example, one major issue with thermo-responsive SMP is the heating of it inside the human body. Various approaches are developed to overcome this problem. One route is the use of noncontact triggering stimulus such as infrared (IR), lasers, and so on [34, 35]. These can heat SMP inside the body at the accurate location. Another way is the incorporation of magnetic nanoparticles in SMP. This magnetic nanoparticle can be triggered by an external magnetic field for the selective heating of the SMP. Biocompatible and nontoxic nature of SMP is also a crucial concern for biomedical applications. In this regard, it is pertinent to mention that the several SMPUs are developed, which are biocompatible. Generally, PCL, PEG, and polylactic acid-based SMPU are found to be nontoxic and biocompatible [36–38]. Besides these academic studies, DiAPLEX is a commercially available SMPU which also showed biocompatibility. Such biocompatible SMPU can be utilized in several biomedical applications, such as endovascular devices (clot-removal devices, aneurysm occlusion devices, and vascular stents), repair of cardiac valves, tissue engineering, orthopedics, orthodontics, endoscopic surgery, kidney dialysis, photodynamic therapy, and so on.

Thermo-responsive SMP-based mechanical clot extraction devices to treat ischemic stroke was reported by Maitland et al. [39]. Their fabricated catheter is photothermally activated, so it can easily remove the clot and finally relieve of the ischemia. Moaddeb and coworkers invented SMPU-based devices for treating heart failure patients suffering from various levels of heart dilation [40]. Such heart dilation is treated by reshaping the heart anatomy with the use of SMPU. The concept of biodegradable thermo-responsive SMP sutures was showed by Lendlein and Langer [41]. The suture was fabricated using oligo(ε-caprolactone)diol-based SMP. An abdominal wound in a rat was loosely sutured using the SMP fiber, and then heated to body temperature to achieve wound closure (**Figure 5a**). SMPU provides an alternative to traditional materials used for the treatment of dental malocclusions. Also, SMP arch wire in orthodontic braces for aligning teeth is more aesthetically appealing than a traditional metallic arch wire. These features were studied by Jung and Cho [42]. They used extruded SMP wire, which was attached to stainless steel brackets bonded to teeth in a dental model. When heated, the teeth slowly moved into alignment (**Figure 5b**).

materials, smart suture, and so on. In this section, we described the detailed application of

SMPUs are already widely used as heat-shrinkable polymer tubings, films, and so on. The utilization of SMPU provides easier processing compared to other used polymers in such application [30]. As a consequence, these materials found a wide range of applications, for

SMPs are also well suitable for the use in different biomedical applications, even though several requirements must be addressed and a range of problems must be overwhelmed for advanced application in this field [33]. For example, one major issue with thermo-responsive SMP is the heating of it inside the human body. Various approaches are developed to overcome this problem. One route is the use of noncontact triggering stimulus such as infrared (IR), lasers, and so on [34, 35]. These can heat SMP inside the body at the accurate location. Another way is the incorporation of magnetic nanoparticles in SMP. This magnetic nanoparticle can be triggered by an external magnetic field for the selective heating of the SMP. Biocompatible and nontoxic nature of SMP is also a crucial concern for biomedical applications. In this regard, it is pertinent to mention that the several SMPUs are developed, which are biocompatible. Generally, PCL, PEG, and polylactic acid-based SMPU are found to be nontoxic and biocompatible [36–38]. Besides these academic studies, DiAPLEX is a commercially available SMPU which also showed biocompatibility. Such biocompatible SMPU can be utilized in several biomedical applications, such as endovascular devices (clot-removal devices, aneurysm occlusion devices, and vascular stents), repair of cardiac valves, tissue engineering, orthopedics, orthodontics, endoscopic surgery, kidney dialysis, photodynamic

Thermo-responsive SMP-based mechanical clot extraction devices to treat ischemic stroke was reported by Maitland et al. [39]. Their fabricated catheter is photothermally activated, so it can easily remove the clot and finally relieve of the ischemia. Moaddeb and coworkers invented SMPU-based devices for treating heart failure patients suffering from various levels of heart dilation [40]. Such heart dilation is treated by reshaping the heart anatomy with the use of SMPU. The concept of biodegradable thermo-responsive SMP sutures was showed by Lendlein and Langer [41]. The suture was fabricated using oligo(ε-caprolactone)diol-based SMP. An abdominal wound in a rat was loosely sutured using the SMP fiber, and then heated to body temperature to achieve wound closure (**Figure 5a**). SMPU provides an alternative to traditional materials used for the treatment of dental malocclusions. Also, SMP arch wire in orthodontic braces for aligning teeth is more aesthetically appealing than a traditional metallic arch wire. These features were studied by Jung and Cho [42]. They used extruded SMP wire, which was attached to stainless steel brackets bonded to teeth in a dental model. When heated,

SMPU in the different advanced areas.

62 Aspects of Polyurethanes

**6.1. Industrial applications of SMPU**

**6.2. Biomedical applications of SMPU**

therapy, and so on.

the teeth slowly moved into alignment (**Figure 5b**).

instance as a safety tag [31] or as a self-deploying chair [32].

**Figure 5.** (a) Biodegradable SMP suture for wound closure. The photo series from the animal experiment shows the shrinkage of the suture as temperature increases (reproduced with permission from Ref. [41]) and (b) photographs of the orthodontic appliance (top) before and (bottom) after treatment. The movement of the misaligned teeth due to a lateral force originating from the shape recovery of the SMP arch wire is seen (reproduced with permission from Ref. [42]).

Tissue engineering is one of the large application areas of SMPs. The introduction of biodegradable SMPU urged the study of their usage for minimally invasive tissue engineering. Usually, tissues can be grown on SMPU-based scaffolds and incorporated inside the body through minimally invasive techniques (e.g., catheter). The scaffold is implanted to initiate the repair or reconstruction of tissues or organs in the affected area of the body. The SMPU-based-implantable embolic devices and stents demonstrated potential endovascular tissue engineering applications. Such biodegradable SMPU scaffolds can also be applied in pharyngeal mucosa reconstruction, bone regeneration, and organ repair. Different research groups have investigated the use of thermally responsive SMPUs as an extracellular matrix for in situ growing of various tissues. In this context, Rickert et al. reported the growth of cells on a biodegradable PCL-based SMP [43]. Rat pharyngeal cells are grown on a porous and smooth surface of the SMP to study the prospect of reconstructing the mucosa of the upper aerodigestive tract. Neuss et al. also investigated the cellgrowing behavior of human mesenchymal stem cells, human mesothelial cells, rat mesothelial cells, and L929 mouse fibroblasts, on a similar PCL-based SMPU [44]. They found that mesothelial cells create an anti-adhesive surface layer, which may support abdominal repair or regeneration. Mesenchymal stem cells, the precursor cells of bone, fat, cartilage, and muscle, may support bone regeneration and the construction of adipose tissue. Furthermore, they also found that the use of heat as a stimulus did not affect the majority of adherent cells. SMPU/carbon nanotube composites also showed good MG63 cell differentiation ability, which showed its potentiality as an alternative biomaterial for bone regeneration in a comprehensive manner [45].
