Electrically Conducting Polymers and Their Composites for Tissue Engineering

Conductive polymers are a new generation of intelligent electroactive biomaterials that are capable of delivering electrical stimulation to cells and are considered to have a broad range of potential healthcare applications. This book systematically summarizes the synthesis, physical, chemical and biological properties of conductive polymers, as well as their applications in tissue regeneration. Meanwhile, the limitations, challenges and impracticalities of using conductive polymers for these healthcare applications are also presented.

Electrically conducting polymers are widely used in various advanced fields including energy, sensing, photovoltaics, biomedical, and so on due to their novel physicochemical properties. Owing to their unique properties over traditional polymers, conductive polymers (CPs) have been extensively researched in the past few decades and the range of applications have increased due to their tunable surface area, electrical conductivity, and high electrochemical response. Various strategies have been reported for the synthesis of conducting polymers including chemical oxidation, electrochemical polymerization, vapor phase synthesis, template-assisted, electrospinning, etc. Conductive polymers show the combined characteristics of conventional polymers with fascinating electrical conductivity due to the free movement of electrons within their band positions. The research in this field reveals that manipulating the morphology can be used to further enhance the physicochemical properties and performance of the conducting polymers. Therefore, it is essential to establish a connection between morphological structure and performance. Here in this chapter, the brief discussion on various synthesis strategies and morphology of the conducting polymers are discussed.

Composites based on conducting polymers (CBCPs) have great properties that make them a good choice for a variety of applications. This chapter presents an overview of various methods of preparing CBCPs. In this regard, the various techniques for making CBCPs such as melt blending, solution casting, in-situ polymerization, electrospinning, and some unconventional and specific preparation techniques were discussed. The properties of CBCPs are significantly influenced by the introduction of various fillers, including carbon materials, metal, and metal oxide nanoparticles, enzymes, polymers, etc. Although the introduced methods can resolve the problem of the design and synthesis of CBCPs, there are still some limitations. Depending on the manufacturing process, conductive networks in CBCPs may have various morphologies that can be controlled by different strategies. Several approaches can be employed to reduce the limitations, control the network structure and subsequently customize the properties of CBCPs, including random and selective nanofiller dispersion in the polymeric matrix. In general, this chapter covers the fabrication and various morphological control strategies of CBCPs.

Conducting polymers are conjugated polymers with highly delocalized p-electrons that flow through the polymer chain. While the electrical conductivity of polymers in their pure form is usually low, dopants have been added to substantially increase the conductivity properties. Dopants have also been used to increase the mechanical, thermal, and optical properties of polymers. These physicochemical and mechanical properties of conducting polymers are discussed in this chapter as to how different substituents, ions, side chains, or additions to the polymers have an influence on these properties and how they can be tailored for various applications.

Antioxidants inhibit and prevent the oxidation of other substances by scavenging free radicals and reactive oxygen species (ROS). With the prolonged applications of antioxidants, especially in the food processing industry, to increase the shelf life of materials, researchers have started using various types of materials as antioxidants. Among various types of materials investigated as antioxidants, conductive polymers have been recently explored due to their unique structure and their ability to scavenge free radicals. The antioxidant activity of conductive polymers has significant advantages such as protecting vulnerable polymers from active scavenging radicals, along with the associated anti-inflammatory, antimicrobial, and immunomodulatory properties benefiting biological systems. This chapter describes the antioxidant features of various conductive polymers and discusses the effective parameters for enhancing the antioxidant activities of electroconductive polymers and their composites. Furthermore, the antioxidant mechanisms of electroconductive polymers and their composites will also be discussed. Moreover, we will summarize the antioxidant activity of conductive polymers and their composites.

One of the critical challenges for tissue engineering tissues is that the proliferation and adhesion of cells are prevented through bacterial colonization on the scaffold and their activity. Antibacterial scaffolds have been advanced to the cardiac, and cartilage tissues. Conducting polymers, such as Poly(3,4-ethylene dioxythiophene) (PEDOT), polyaniline (PANI), polypyrrole (PPY), and Polythiophene (PTH) with positive charges can form electrostatic interaction with bacterial membrane, induce cell death, and interact with another molecule inside cells. Conducting polymers (CPs) can produce composites with metal, and carbon-based materials as novel groups of antimicrobial agents with increased antibacterial activity. The increase of high levels of reactive oxygen species (ROS) from composites of polymers-based metal nanomaterials has destructive effects and makes the death of the cell. Efforts are needed to investigate the mixture of conducting polymers and their nanocomposites with natural molecules with antimicrobial properties in tissue engineering and the progress of antimicrobial scaffolds. Consequently, such scaffolds with low cytotoxicity are anticipated to destroy microorganisms.

Conducting polymers and their composites has lately piqued the interest of academic and industry researchers interested in exploring their potential in biomedical applications including drug delivery systems, biosensors, biomedical implants, and tissue engineering. Conventional conductive polymers have potential conductivity for these applications, but their processability, biocompatibility, and mechanical characteristics have some limitations. As a result, conductive polymeric composites made of durable and biocompatible polymers with dispersed conductive fillers including metallic nanoparticles, carbon nanotubes, graphene, etc. have recently come under scrutiny. One of the key requirements for the therapeutic application of these materials is biocompatibility. The evaluation of cytotoxicity, which could be determined in vitro employing a range of different target primary cells or cell lines, is essential to the testing of biocompatibility. Consequently, this book chapter provides a brief overview of the cytotoxicity and biocompatibility of conducting polymers and their composites.

The hierarchical, multiphase, and anisotropic structure of bone is coupled with piezoelectric characteristics. Each hierarchical structural level of bone affects its rigidity, ductility, and hardness. Bone is a dynamic structure mostly composed of collagen, hydroxyapatite, and water. It has been demonstrated that the complicated mechanism of piezoelectricity creation in bone is essential for both bone adaptability and repair. Since the term "tissue engineering" was first used, bone tissue engineering has been steadily improving. In bone tissue engineering, the biomaterials that serve as the building blocks for the creation of scaffolds are essential. Smart materials called piezoelectric materials may produce electrical activity in reaction to slight deformations. Investigations devoted to piezoelectric materials for bone tissue engineering have significantly increased. This chapter reviews the structure, mechanical characteristics, and components of natural bone as well as the techniques used in bone tissue engineering. Then, the application of electroconductive biomaterials for bone tissue engineering is discussed. Finally, current challenges and prospects are highlighted.

Conductive materials to promote the activity of cells through electrical stimulation have become an attractive and effective approach for wound healing acceleration. This technology is proposed to supplement current wound care management technologies that unfortunately have not fully satisfied clinicians and patients in complete and rapid wound closure. Polymers with conductive properties have demonstrated great potential in skin tissue engineering, owing to their similar conductivity to human skin, good antibacterial activities, electrically controlled drug delivery, and photothermal effect. Herein, we provide an overview of electrical stimulation in wound healing by focusing on advancements in conductive materials and incorporating them with non-conducting polymers to construct electroactive wound dressings. The mechanisms of how they promote wound repair are discussed at the cellular and molecular levels and potential directions and perspectives for the future development of regenerative electroactive formulations are also summarized.

The human nervous system consists of two parts of central (CNS) and peripheral (PNS) nerve systems. Severe CNS and PNS nerve degeneration often need intervention to be cured. However, therapeutic strategies have not been entirely successful till now, especially in the repair of the CNS. In the case of spinal cord injury (SCI), healthcare strategies are started before hospital admission and followed by surgery and drug administration such as corticosteroids. Notwithstanding, in the case of PNS, there are few commercial nerve conduits in the market. However, they suffer different limitations, such as improper spatial/physical guidance. Electrically conducting polymers have received much interest as tissue engineering materials because they can transmit electrical cues to specific areas while providing physical support for cell development. Regarding the nervous system’s electrical, mechanical, and chemical interactions, conductive polymers (CPs) are intriguing biomaterials providing a substrate for ongoing contact with regenerating neural tissue. Electrically CPs with similar chemical structures, such as polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) (PEDOT), and polyaniline (PANI), are the most investigated CPs as scaffolds in nerve regeneration. Polypyrrole (PPy) has emerged as a viable candidate material both in-vitro and in-vivo. CNS investigations. The present chapter discussed the use of CPs as scaffolds, drug delivery systems, and theranostic systems in CNS and PNS regeneration. It was highlighted in vivo studies as a helpful criterion for developing toward clinical trials before the ultimate translation from bench to bed.

Myocardial infarction (MI) and other cardiovascular diseases, as a leading cause of morbidity and mortality, have gradually become the number one killer threatening human health worldwide. Advanced Electrical-active scaffold based cardiac tissue engineering (CTE) is one of the most promising solutions for cardiac regeneration and injury repair. In this chapter, we give an introduction of advanced electrically conducting polymers and their composites and an overview of their applications and underlying mechanism for CTE. We hope this work can provide more new research ideas for future researchers, and it is believed that with the continuous progress of technology and researchers’ exploration, the research of engineered myocardial tissue constructed with conductive materials in cardiac repair and regeneration will make further progress.