Electrically conductive polymeric materials have recently attracted considerable interest from academic and industrial researchers to explore their potential in biomedical applications such as in biosensors, drug delivery systems, biomedical implants and tissue engineering. Conventional conductive homopolymers such as polypyrrole and PEDOT show promising conductivity for these applications, however their mechanical properties, biocompatibility and processability are often poor. This has led to more recent attention being directed towards conductive polymeric composites comprised of biostable/biocompatible polymers with dispersed conductive fillers such as graphene, carbon nanotubes and metallic nanoparticles. The major objective of this paper is to provide an up to date review of the recent investigations conducted in the development of conductive polymer composites focussing on the methods of their preparation, underlying concepts of their conductivity and the ways to tailor their properties. Furthermore, recent progress made in conventional conducting polymers and their composites/blends for biomedical applications is also discussed.

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Electrically conductive polymers and composites for biomedical applications

Biodegradable and electrically conducting polymers for biomedical applications

Research pertaining to conductive polymers has gained significant traction in recent years, and their applications range from optoelectronics to material science. For all intents and purposes, conductive polymers can be described as Nobel Prize-winning materials, given that their discoverers were awarded the Nobel Prize in Chemistry in 2000. In this review, we seek to describe the chemical forms and functionalities of the main types of conductive polymers, as well as their synthesis methods. We also present an in-depth analysis of composite conductive polymers that contain various nanomaterials such as graphene, fullerene, carbon nanotubes, and paramagnetic metal ions. Natural polymers such as collagen, chitosan, fibroin, and hydrogel that are structurally modified for them to be conductive are also briefly touched upon. Finally, we expound on the plethora of biomedical applications that harbor the potential to be revolutionized by conductive polymers, with a particular focus on tissue engineering, regene...

Conductive Polymers: Opportunities and Challenges in Biomedical Applications

During the resorbable-polymer-boom of the 1970s and 1980s, polycaprolactone (PCL) was used in the biomaterials field and a number of drug-delivery devices. Its popularity was soon superseded by faster resorbable polymers which had fewer perceived disadvantages associated with long term degradation (up to 3-4 years) and intracellular resorption pathways; consequently, PCL was almost forgotten for most of two decades. Recently, a resurgence of interest has propelled PCL back into the biomaterials-arena. The superior rheological and viscoelastic properties over many of its aliphatic polyester counterparts renders PCL easy to manufacture and manipulate into a large range of implants and devices. Coupled with relatively inexpensive production routes and FDA approval, this provides a promising platform for the production of longer-term degradable implants which may be manipulated physically, chemically and biologically to possess tailorable degradation kinetics to suit a specific anatomical site. This review will discuss the application of PCL as a biomaterial over the last two decades focusing on the advantages which have propagated its return into the spotlight with a particular focus on medical devices, drug delivery and tissue engineering.

The return of a forgotten polymer : Polycaprolactone in the 21st century

Electrically conducting polymers arenovel In thattheir surface pries induding charge density and wettability, canbereversibly changed with anapplied electrical potential. Suchproperties might render conducting polymers unique forbiological applications. However, themajority of research onconducting polymers hasbeencarried outunder nonbio lcondits. Wesyntheoptically transparent polypyrrole thinfinms andstudied theminenvironments suitable forprotein adsorption andmammalian cell culture. In viro studies demonstrated that extracellular matrix molecules, suchasfibronectin, adsorb efficiently ontopolypyrrole thin films andsupport cell attentunder serum-free conditions. Whenaortic endothelial cells werecultured onfibronectin- coated polypyrrole (oxidized) ineither chemicall defined medium orthepresence ofserum, cells spread normally and synthesized DNA.Incontrast, whenthepolymer wasswitched toits neutral state byapplying anelectrical potntil, bothcell extension andDNAsynthesis wereinhibited without affecting cell viability. Application ofasimilar electrical potential tocells cultured onindium tin oxide surfaces hadnoeffect oncell shape orfunction. Thesedatasuggest thatdectrially conducting polymers mayrepresent atype ofculture substrate which could provide anoninvasive meanstocontrol theshape andfunction ofadherent cells, independent ofanymediumalteration. Growth andfunction ofcultured cells iscommonly controlled byaddition ofmediumsupplements, including serum, de- fined growth factors, andsoluble hormones. However, in- teractions between cells andtheir culture substrate arealso critical forregulation oftheir growth andfunction. For example, mostmammalian cells areanchorage-dependent and, thus, mustattach andextend onasurface inorder to proliferate (1-5). Furthermore, thesamecells will remain quiescent anddifferentiate intheidentical growth factor- containing medium, ifcell spreading isprevented byaltering interactions between cells andsubstrate-adsorbed extracel-

Electrically conducting polymers cannoninvasively control the shapeandgrowth ofmammalian cells

This review focuses on one of the most exciting applications area of conjugated conducting polymers, which is tissue engineering. Strategies used for the biocompatibility improvement of this class of polymers (including biomolecules' entrapment or covalent grafting) and also the integrated novel technologies for smart scaffolds generation such as micropatterning, electrospinning, self-assembling are emphasized. These processing alternatives afford the electroconducting polymers nanostructures, the most appropriate forms of the materials that closely mimic the critical features of the natural extracellular matrix. Due to their capability to electronically control a range of physical and chemical properties, conducting polymers such as polyaniline, polypyrrole, and polythiophene and/or their derivatives and composites provide compatible substrates which promote cell growth, adhesion, and proliferation at the polymer-tissue interface through electrical stimulation. The activities of different types of cells on these materials are also presented in detail. Specific cell responses depend on polymers surface characteristics like roughness, surface free energy, topography, chemistry, charge, and other properties as electrical conductivity or mechanical actuation, which depend on the employed synthesis conditions. The biological functions of cells can be dramatically enhanced by biomaterials with controlled organizations at the nanometer scale and in the case of conducting polymers, by the electrical stimulation. The advantages of using biocompatible nanostructures of conducting polymers (nanofibers, nanotubes, nanoparticles, and nanofilaments) in tissue engineering are also highlighted.

Review paper: Progress in the Field of Conducting Polymers for Tissue Engineering Applications

Hybrid materials consisting of an all-conjugated polythiophene backbone and grafted hydrophilic poly(ethylene glycol) chains

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Effect of the graft ratio on the properties of polythiophene-g-poly(ethylene glycol)

The properties, microscopic organization and behavior as the cellular matrix of an all-conjugated polythiophene backbone (PTh) and well-defined poly(ethylene glycol) (PEG) grafted chains have been investigated using different experimental techniques and molecular dynamic simulations. UV-vis spectroscopy has been used to determine the optical band gap, which has been found to vary between 2.25 and 2.9 eV depending on the length of the PEG chains and the chemical nature of the dopant anion, and to detect polaron → bipolaron transitions between band gap states. The two graft copolymers have been found to be excellent cellular matrices, their behavior being remarkably better than that found for other biocompatible polythiophene derivatives [e.g. poly(3,4-ethylenedioxythiophene)]. This is fully consistent with the hydrophilicity of the copolymers, which increases with the molecular weight of the PEG chains, and the molecular organization predicted by atomistic molecular dynamics simulations. Graft copolymers tethered to the surface tend to form biphasic structures in solvated environments (i.e. extended PTh and PEG fragments are perpendicular and parallel to the surface, respectively) while they collapse onto the surface in desolvated environments. Furthermore, the electrochemical activity and the maximum of current density are remarkably higher for samples coated with cells than for uncoated samples, suggesting multiple biotechnological applications in which the transmission with cells is carried out at the electrochemical level.

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Polythiophene-g-poly(ethylene glycol) graft copolymers for electroactive scaffolds

https://pubs.rsc.org/en/content/articlepdf/2018/PY/C8PY00762D

Anca-Dana Bendrea

Papers

Review paper: Progress in the Field of Conducting Polymers for Tissue Engineering Applications

Hybrid materials consisting of an all-conjugated polythiophene backbone and grafted hydrophilic poly(ethylene glycol) chains

Effect of the graft ratio on the properties of polythiophene-g-poly(ethylene glycol)

Polythiophene-g-poly(ethylene glycol) graft copolymers for electroactive scaffolds

Amphiphilic polypyrrole-poly(Schiff base) copolymers with poly(ethylene glycol) side chains: synthesis, properties and applications