## 3 Results
### Conductive Polymers  
Conductive polymers (CPs) and their derivatives are commonly used in biomedical engineering and have gained much importance in the last 20 years, because they exhibit chemical and physical characteristics of organic polymers along with electrical properties of metals [25]. Conductive polymers provide electrical stimulus and a physical environment for tissue genesis, cell growth and allow precise control over the duration and level of stimulation [26]. Researches showed that they are widely used in biological applications and they have the capability to modulate and support the growth of various cells including bone cells and nerve cells [27]. In addition, conductive polymers are also used to design polymeric composites with enhanced structural, mechanical and electrical properties and hence proved to be helpful in regenerative medicine including cardiac and neural tissue engineering [28]. CPs mainly used in biomedical area are polypyrrole (PPy), polyaniline (PANI), and polythiophene (PEDOT), with their electrical and optical properties [29; 30; 31; 32]. Hereinafter, several details for each type of material. * _Polypyrrole (PPy)_--PPy is conductive conjugated polymer with excellent mechanical, electrical and stimulus-responsive characteristics, which makes it one of the most conductive biomaterials, appropriate to be used in biomedicine [33]. Polypyrrole possesses great chemical stability in water and air [34; 35], and high electrical conductivity under biological conditions [36; 37; 38; 39]. It can be synthesized with various different porosities and can be adjusted to make it more feasible for biomedical applications by incorporating with bioactive molecules [40; 41; 42]. Moreover, its stimulus responsive nature allows to control its properties by applying electrical potential [39; 43]. As abiomaterial, PPy also supports cell growth and adhesion of a number of different types of cell, which makes it a suitable for scaffold fabrication in tissue engineering [44; 45; 46; 47]. * _Polyaniline (PANI)_--The second most studied conductive polymer is polyaniline (PANI) which is commonly known as aniline black. It is classified into three types depending on its oxidation level, such as the fully oxidized form is pernigraniline base, half-oxidized form is emeraldine base and fully reduced form is leucoemeraldine base. Among these, most conductive and stable is PANI emeraldine [48; 49]. PANI offers many advantages over other conducting polymers, such as low-cost, easy to synthesize, and able to electrically switch between its resistive and conductive states [50; 51; 52; 53; 54]. Studies have shown that PANI and its derivative support cell growth [55] and hence can be used for scaffold fabrication. * _Poly (3,4-ethylenedioxythiophene) (PEDOT)_--Another conductive polymer is PEDOT which is a polythiophene (PTh) derivative [48; 56]. PEDOT possesses good electrical, environmental and chemical stability [56]. It also have better thermal stability and conductivity than PPy [49; 56]. [PERSON] et al. (2008) [57] carried out an in vivo study and examined the biocompatibility of PEDOT by seeding NIH3T3 fibroblasts cells on PEDOT glass films. The results showed good inflammatory response at the implantation site with low intrinsic cytotoxicity, hence making them suitable for biological and biosensing applications e.g., in neural electrodes [49; 56; 58], heart muscle patches, and nerve grafts [56]. A summary of the specific properties of each material are reported in Table 1. By using these polymers is possible to produce conductive scaffolds, with the aim of defining platforms for cell sensing. The cell growth and colonization of the scaffold brings changes in its electrochemical impedance [59] and this change can be used to track cell growth.