# Research Progress on Conducting Polymer-Based Biomedical Applications
## 3 Biomedical Applications
### Scaffolds for Tissue Engineering  
The action potential generated at the synapse plays a key role in neural communication and electrical conductivity, and is known to help the proliferation and differentiation of cells [91; 92]. A scaffold is a structural element utilized in tissue engineering that serves as a template for the regeneration of functional tissues and organs. Materials for scaffolds in tissue engineering require the following characteristics: hydrophilicity, biocompatibility, biodegradability, and mechanical properties resembling those of tissues. Therefore, the CPs are promising candidates for scaffolds for tissue engineering to regenerate or replace damaged organs such as skin, tissue, and spinal cord [93; 94; 95; 96; 97]. In early studies, pure CPs, such as PPy, PANI, and PT, that offer cytocompatibility were employed for scaffolds, as they are capable of adhesion, proliferation, and differentiation of diverse cell types [98; 99; 100; 101]. These polymers can be synthesized in the form of films on the surface of an electrode either chemically or electrochemically [41]. To adjust the mechanical properties, it is common to blend the CPs with other degradable and more flexible polymers, including poly(lactic acid) (PLA), poly(lactic-co-glycolic acid) (PLGA), and polycaprolactone (PCL). For example, PPy/polycaprolactone films are prepared by merging polycaprolactone films in a mixture of polystyrene sulfonic acid and pyrrole in water, followed by the addition of ferric chloride, as an oxidant. As a result, conductive PPy-coated polycaprolactone films are formed, which display a similar resistivity as the native cardiac tissues [102]. Polyurethane is biocompatible and has suitable mechanical and physical characteristics for scaffolds, and therefore can be used to form composite films when blended with the CPs [103]. Conducting composite films composed of polyurethane and PPy are fabricated by the polymerization of pyrrole in an emulsion mixture of polyurethane and subsequent pressing into the form of films. It should be noted that the stiffness is tunable depending on the ratio of PPy to polyurethane [104]. Conducting copolymer films are another type of modification to enable the CPs to be more widely used in tissue engineering. Since not all the CPs are natively biodegradable, their use in vivo can be limited [105]. The addition of aniline to form a copolymer with the CPs is an effective way to provide the CPs with biodegradability. Copolymers of aniline and pyrrole functionalized with hydrolyzable groups have been reported to show a similar electroactivity to the CPs while also being biodegradable [106; 107]. Nanofibrous polymeric scaffolds have been extensively researched to mimic the natural extracellular matrix (ECM). The CP nanofibers can be synthesized by electrospinning, phase separation, and molecular assembly [108; 109; 110]. In the process of electrospinning, the CPs are mixed with biodegradable polymers, then electrospun into the form of nanofibers. They possess a high surface area, porosity, and tunable diameters in the range of a few nanometers [111; 112; 113]. Scaffolds fabricated by the electrospinning of conductive nanofibers using PANI blended with PLA or gelatin have been developed and showed an electrical conductivity of \(4.2\times 10^{-3}\) S cm\({}^{-1}\), which is substantial enough to be exploited for cardiac tissue engineering [114; 115]. Figure 4: Scanning electron micrographs of an array of pure carbon nanotubes before the electrodeposition of polypyrrole (**a**) and the aligned coaxial nanowires after polypyrrole was deposited (the inset shows a single nanotube) (**b**). Anodic current response of the glucose sensor composed of polypyrrole, carbon nanotubes and glucose oxidase, depending on the concentration of glucose detected (**c**). Adapted with permission from [89]. Copyright 2003 John Wiley and Sons. Electroconductive hydrogels are hybrid materials comprised of CPs blended with conventional polymers that provide aqueous gel networks.