# Shape Memory Polyurethane and its Composites for Various Applications
## 2 Shape Memory Polyurethane in Different Applications
### Electromagnetic Interference Shielding  
It is known that electric and magnetic signals help to regulate the behavior of living cells and processes such as control of the cell cycle, tissue regeneration, proliferation of cells, cell wound repair, etc. [12]. The global research in the biomedical field is being conducted on testing the effects of the electric and magnetic fields on the living cells which may aid in the healing process if induced with relatively low intensity. However, high intensity electric and magnetic signals may affect the cells negatively by altering biochemical reactions. The technological modernization of society has led to the evolution of vast variety of appliances and devices such as microwave ovens, computers, radio transmitter, etc., which constantly generate range of electromagnetic waves when plugged in. Various generated signals interact with other signals which may amplify and produce intense, complex, and unpredictable energetic patterns [13]. Due to this complex electromagnetic interference (EMI), health problems in living species have been raised and have also affected the performance of other electronic devices such as navigation systems in airplane, implantable cardiac pacemakers, transportation system, etc. [14]. It is essential to use EMI shielding for aerospace applications in order to protect from lighting strikes. One of the most common health hazard due to electromagnetic radiation is skin cancer. In order to avoid these electromagnetic interferences, different shielding materials with high performance have been developed by eminent scientists. Usually, EMI shielding can be achieved using shielding materials made of metals and ceramics. However, they are heavy in weight and susceptible to corrode. On the contrary, polymers are surfacing as suitable candidates to develop shielding materials due to their extraordinary properties as compared to that of metals and ceramics. The shielding materials made of polymers are easily processable, with an ability to tune their structural properties. In addition, they can render end products to be light weight, flexible, and corrosion resistant. However, it is not possible for the pristine polyurethane to be used as shielding materials due to non-conducting nature. Shielding can be done either by reflecting electromagnetic wave from the surface or absorbing the signals [15; 16]. Most polymers (except conducting polymers) are insulators and their conductivity can be enhanced by the addition of conducting polymers into the polymer matrix. Additionally, the presence of fillers boosts thermal, mechanical, and barrier properties. It is also observed by the scientific community that improved conductivity influences the shielding effect [17]. It is also known that polyurethane and its porous composites are light weight and have the potential to absorb radiation due to the porosity and shape memory effect which can be an enrichment for the development of adjustable shielding material. [PERSON] and coworkers [18] have developed a polymer based conductive or magnetic composite which has the advantage of being flexible, light weight, highly processable, and relatively economical to produce. They have used multi-walled carbon nanotubes (MWCNTs) as fillers in the SMP matrix due to their large aspect ratio and excellent electrical and mechanical properties [19]. The presence of MWCNTs contributes to the enhancement in storage modulus of SMP composite. In addition, they obtained the conductivity of 35 S/m with 9% MWCNT loading. They concluded that electromagnetic shielding may be affected by the thickness and conductivity of the composite and they achieved \(-\)35 dB of a shielding effect when tested for 13-16 GHz with thickness of 2 mm containing 9 wt% MWCNTs. They postulated that the higher aspect ratio of the MWCNTs and the formation of percolated conductive network in the SMP matrix caused a dramatic enhancement in conductivity.