# Shape Memory Polyurethane and its Composites for Various Applications
## 2 Shape Memory Polyurethane in Different Applications
### Bone Tissue Engineering
[PERSON] and coworkers [42] developed a chitosan based scaffold which possess shape memory ability triggered by hydration. The same group [43] added bioactive glass nanoparticles in chitosan by sol-gel method in order to enhance bioactivity and biomineralization ability of chitosan scaffold without affecting shape memory with a 89.9% recovery ratio. A bone like apatite layer was formed due to presence of bioactive glass when the scaffold was subjected to simulated body fluid (SBF), which suggested the suitability of the material for bone tissue engineering. The developed dehydrated composite scaffold with the temporary shape was placed in a defect of pig femur bone model which was occupied the defect contour after rehydration (Figure 5). The hydration driven shape memory permits a relatively good fixation trough a press-fitting effect. Figure 5: Demonstration of recovery in a defect produced in a pig femur bone using chitosan bioglass nanoparticle (CHT/BG-NPs) composite scaffold [43]. Similarly, [PERSON] et al. [44] prepared chitosan based shape memory spheres driven by hydration by incorporating bioactive glass nanoparticles using sol-get method and using genipin used as a cross-linker. An apatite layer was formed on the surface of the spheres immersed in SBF which confirmed the compatibility to bone tissue formation. They demonstrated the shape memory ability of chitosan composite sphere for bone regeneration using a self-fitting technique. Chitosan spheres with an optimized percentage of bioactive glass (10%) and genipin (10%) can be added to the bone defects with predefined shape followed by self-fitting due to rehydration (Figure 6) with a shape recovery ratio of more than 88%. The spheres were demonstrated to be used for drug delivery purposes. They postulated that, after hydration, the presence of an interconnecting porous network between spheres may work as pores allowing transport of oxygen, cellular invasion, and nutrient access. Along with the biopolymers, biobased and biodegradable polymer-based polyurethanes are being used for the purpose of bone tissue engineering. In the recent past, superparamagnetic iron oxide (SPIO) nanoparticles have been widely employed for several applications such as tissue repair, detoxification of biological fluids, hyperthermia, drug delivery, etc. [45]. [PERSON] and coworkers [46] have utilized SPIO's ability to promote the osteogenic induction of human bone derived mesenchymal stem cells (hBMSCs) [47] for the development of bone scaffold based on waterborne SMPs which contain SPIO nanoparticles along with polyethylene oxide or gelatin as thickener. Three-dimensional scaffold was printed using low-temperature fuse deposition manufacturing platform and used for bone tissue regeneration. The matrix of polyurethane was made of using PCL, PLA, and diisocyanate. The developed scaffold demonstrated an effective shape memory property when fixed in predefined defect and exposed to warm water. The results indicated that the release of SPIO promoted the osteogenesis of hBMSCs in scaffolds (Figure 7) and secretion and deposition of collagen and calcium. Figure 6: Digital picture of shape recovery of chitosan spheres containing 10% bioactive glass nanoparticles and 10% genipin in a defect created in a rabbit femur bone: (**A**) before hydration, (**B**) after hydration [44]. Similarly, [PERSON] and coworkers [48] utilized hydroxyapatite (HA) nanoparticles in the fabrication of SMP foam using gas foaming technique for the treatment of load bearing bone defects. Chemical similarity to natural bone matrix (\(\sim\)69 wt % HA) [49] make HA exhibit strong affinity toward host hard tissues. In addition, HA has advantages such as osteoconductivity, osteoinductivity, biocompatibility which make HA useful for bone repair and bone augmentation [50; 51]. [PERSON] et al. found that SMP foam with HA revealed excellent biocompatibility for bone tissue regeneration and promoted bone ingrowth and neovascularization. They also found that the time of 12 weeks was sufficient for the bone repairing (Figure 8).