# Shape Memory Polyurethane and its Composites for Various Applications
## 3 Author's Perspective on the Shape Memory Polyurethane Composites  
Our group has demonstrated the development of PCL based polyurethane composite with chitosan [106]. Chitosan has an advantage of antibacterial property along with the induction of bone formation and wound healing ability which is shadowed by the limitation of its processing temperature. Due to the overlapping of melting temperature and thermal degradation temperature, chitosan cannot be thermally processed along with other polymers in order to fabricate composites. Therefore, dispersion or blending of chitosan in polymer matrix is always a challenging task. In this regard, our group has made efforts to homogenously disperse chitosan into the polymers by in situ polymerization instead of blending chitosan with the polymer matrix. We have fabricated PCL based polyurethane by in situ polymerization in presence of micro-to-nano sized chitosan. The advantage of using nano sized chitosan is that it provides several hydroxyl groups to react with isocyanate resulting in the formation of urethane bonds which lead to homogeneous dispersion and interfacial adhesion of nano chitosan in polymer matrix. We have found that the presence of chitosan in polyurethane matrix acts as crosslinking point in the polymer matrix which possibly enhances the mechanical property along with thermo-responsive shape memory ability of the composite (Figure 18). The use of chitosan as a filler in polyurethane matrix provides opportunities for developing polymers with tailored properties. The presence of chitosan in polyurethane matrix enhances the applicability of the polyurethane in several biomedical domains such as medical bandage development, bone tissue engineering, self-healing, implants development, etc. Due to the presence of chitosan, biodegradable polymer such as polycaprolactone (PCL) based SMP composites can be used for several applications. As described in the previous section, every application is based on some specific essential properties. In order to develop the medical pressure bandage, shape memory of the polyurethane is the key property which generates the required pressure. The same can be tuned by adjusting the amount of chitosan in the polymer matrix. The usability of the pressure bandage made of PCL based polyurethane chitosan composite can be enhanced by the incorporation of essential drug into polyurethane matrix which will be delivered as and when required for wound treatment. Similarly, PCL based polyurethane chitosan composite can be used for bone tissue engineering as discussed in the previous section. Utilization of swelling ability and bone formation induction ability of chitosan along with shape memory ability of PCL polyurethane synchronously may result in an effective formulation for bone healing application. The addition of a required healing drug in the polymer matrix can enhance the applicability of the polyurethane chitosan composites. The effective use of PCL based SMP chitosan composite can be demonstrated in the production of cardiovascular implants. Polyurethane chitosan composite along with a deliverable drug can be thermally processed to stents or scaffold using 3D printing or other techniques. The developed stent may attain the shape memory ability together with drug delivery system which are the key properties required for the development of temporary self-expanded stents. The known rate of degradation of the polymers and fillers may help in the prediction of the working age of a temporary self-expandable stent after injection in the vein and thus, reducing the chances of secondary surgery. Figure 18: Demonstration of the shape memory ability of PCL based polyurethane chitosan composite [106]. The above discussion shows the significance of incorporation of fillers into the polyurethane matrix for intended applications. Materials like chitosan can enhance the usefulness of the polyurethane in several biomedical applications.