Applied Materials Today
Volume 24, September 2021, 101117
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Electroconductive multi-functional polypyrrole composites for biomedical applications

https://doi.org/10.1016/j.apmt.2021.101117Get rights and content

Highlights

  • Polypyrrole (PPy) used in the biomedical arena, due to its good biocompatibility.

  • Synthesis, physicochemical and mechanical properties of PPy summarized.

  • Fabrication and biological activities of PPy nanocomposites summarized.

  • Biomedical applications of PPy and its nanocomposites summarized.

Abstract

Polypyrrole is an example of inherently electrically conductive polymer that is employed in the biomedical arena because of its low cost, excellent electroconductive properties, and good biocompatibility. Because many body tissues respond to electrical fields, polypyrrole-based nanocomposites have become an important class of bio-conductive material. Nanocomposites prepared by blending polypyrrole with other biopolymers or nanomaterials show marked improvements in physicochemical, mechanical, and biological properties. The present review outlines the structure and synthesis of polypyrrole, as well as the physical and mechanical properties of polypyrrole-containing nanocomposites. The antimicrobial and antioxidant activities and possible cytotoxicity of these nanocomposites are summarized and critiqued. A survey of the biomedical applications of polypyrrole as biosensors, drug delivery systems, tissue engineering scaffolds, or photo-thermal therapeutic agents is presented to spur further advances in this exciting field of research.

Introduction

Polymers have been perceived as highly promising materials for biomedical applications [1], [2], [3]. Because of their versatility, polymers have been utilized in bulk (e.g. scaffolds or hydrogels) or in colloidal form (e.g. nanoparticles or nanogels) to satisfy diverse medical needs [4,5]. Polymers are highly valuable because of their tunable mechanical properties and adjustable chemistry [6,7]. The choice of an optimal polymer for biomedical applications is determined by the physicochemical properties of the specific macromolecule. For example, a biologically stable polymer would be a better choice than a biodegradable polymer for the construction of an implantable medical device in which long-term stability is the primary concern. Likewise, a natural polymer is preferred over a synthetic polymer in a biomedical product in which cellular interactions are essential [1,8]. A major disadvantage of polymers in the construction of medical prosthetic devices to replace bone, heart or nerves is their lack of electrical conductivity. This is because the atoms in most polymer chains are joined together by strong covalent bonds with no freely movable electrons or ions. This feature renders most polymers effective as insulators but not conductors [9]. Nevertheless, some polymers may be tailored to be conductive when they are subjected to an electrical field. Properties such as the dielectric constant, dissipation factor and resistivity are used to define the electrical characteristics of a polymer [10].

Polymers that possess distinctive optoelectronic properties are termed inherently conducting polymers. The alternating single and double carbon-carbon bonds in these polymers have delocalized π-electrons and render them easily polarizable. Many studies have been conducted in this domain since Hegger, MacDiarmid and Shirakawa discovered the first inherently conducting polymer in 1977 [9,11,12]. Polypyrrole is the most widely used inherently conducting polymer in the biomedical field, as well as in other areas such as sensors, actuators, or energy generators (batteries and solar cells) because of its low cost and good electrical properties [13]. Another advantage of polypyrrole is its microbicidal and antioxidant properties, which have been attributed to the positive charges generated on the backbone during synthesis. There have been concerns over the toxicity of polypyrrole and related polypyrrole-based nanoparticles. The current trend is to combine polypyrrole with other organic or inorganic materials to improve the biocompatibility of the final product [14,15].

The present review outlines the structure and synthesis of polypyrrole, as well as the physical, chemical and mechanical properties of polypyrrole-containing nanocomposites. The antimicrobial and antioxidant properties and possible cytotoxicity of these nanocomposites are outlined and critiqued. The application of polypyrrole as biosensors, drug delivery systems, tissue engineering scaffolds and photo-thermal therapeutic agents is subsequently presented to spur further advances in this exciting field of research.

Section snippets

Structure and prepration

Polypyrrole is an electrically conducting polymer that is composed of heterocyclic monomers joined together. The molecular structure comprises five-membered pyrrole rings linked to each other at the 2- and 5-positions. It was first synthesized in 1963 by the pyrolysis of tetraiodopyrrole [16]. Nowadays, polypyrrole is usually prepared via electrochemical or chemical oxidation polymerization approaches (Fig. 1) [17,18].

Electrochemical polymerization of pyrrole is based on anodic oxidation of the

Physicochemical and mechanical properties

The electrical conductivity of polypyrrole is due to the ease with which electrons pass along and between the polymer backbones [35]. Polypyrroles possess a conjugated backbone, meaning that it is made up of a series of alternating single and double bonds with sp2-hybridized carbon atoms. Dopants play a key role in enhancing the electrical conductivity of polypyrrole. In its pristine (non-doped) state, polypyrrole has a band gap of 4 eV and is an electronic insulator. Once the polypyrrole is

Cytotoxicity and biocompatibility

Because polypyrrole and its composites have been used for biomedical applications extensively, it is logical to identify the factors that affect their biocompatibility so that these materials may be evaluated in clinical trials. Polypyrrole has been used for delivery of dexamethasone to the eye. The half maximal inhibitory concentration (IC50) of polypyrrole, which is a measure of its potency in inhibiting a specific biological function, 0.77 mM. This value indicates that the polypyrrole is

Antimicrobial activity

Polypyrrole is a conductive polymer with bactericidal activity. This activity is attributed to the strong electrostatic interactions between the positive charges along the polymer structure and the negatively charged bacterial cell wall [81]. These positive charges (double bondNH+) are repeated every three to five units and are produced using dopants such as HCl, H2SO4, or HNO3. Polypyrroles can destroy bacterial cell wall, interact with the cell membranes of bacteria, disrupt the balance of proton

Drug delivery

Controlling the release rate of drugs loaded within polymeric carriers is an important challenge in drug delivery [111]. Polypyrrole has been employed as a component of drug delivery platforms because of its biocompatibility as well as its electrical properties. These properties enable polypyrrole to control the release of drugs and improve the overall efficacy of the drugs [112], [113], [114]. Drug release may be controlled by altering the degree of protonation of the polypyrrole to produce a

Biosensors

The requirements of biosensors include high selectivity, high sensitivity, stability, high accuracy, reusability, low-cost and user-friendliness. Biosensors are used for many biomedical applications, the most important of which is the early detection of biomarkers related to diseases or infections. Many studies have been conducted to identify useful materials for the fabrication of biosensors [217,218]. Conductive polymers with electrical conductivity are cost-effective, biocompatible and

Conclusions and future perspectives

In the present review, polypyrrole and its nanocomposites, their advantages and associated challenges were concisely reviewed. Issues including the preparation, physical, chemical, mechanical properties and biological properties, as well as biomedical applications were thoroughly discussed.

Tissue engineering strongly depends on the ability to expose cells that migrate into the damaged tissue to accurately defined biophysical, biochemical and biomechanical cues. The incorporation of

Declaration of Competing Interest

The authors declare no conflict of interest.

Acknowledgments

M.-A. Shahbazi acknowledges the financial support from the Academy of Finland (grant no. 317316). MR Hamblin was supported by US NIH grants R01AI050875 and R21AI121700.

References (269)

  • J. Zhao et al.

    Facile synthesis of polypyrrole nanowires for high-performance supercapacitor electrode materials

    Prog. Nat. Sci. Mater. Int.

    (2016)
  • F. Yin et al.

    Synthesis of mesoporous hollow polypyrrole spheres and the utilization as supports of high loading of Pt nanoparticles

    Mater. Lett.

    (2017)
  • B. Maharjan et al.

    In-situ polymerized polypyrrole nanoparticles immobilized poly(ε-caprolactone) electrospun conductive scaffolds for bone tissue engineering

    Mater. Sci. Eng. C

    (2020)
  • M.J.L. Santos et al.

    Study of polaron and bipolaron states in polypyrrole by in situ Raman spectroelectrochemistry

    Electrochim. Acta

    (2007)
  • J. Stejskal et al.

    Conductivity and morphology of polyaniline and polypyrrole prepared in the presence of organic dyes

    Synth. Met.

    (2020)
  • Z. Capáková et al.

    The biocompatibility of polyaniline and polypyrrole 21: doping with organic phosphonates

    Mater. Sci. Eng. C

    (2020)
  • J. John et al.

    Doped polypyrrole with good solubility and film forming properties suitable for device applications

    Mater. Today Proc.

    (2018)
  • M. Aghelinejad et al.

    Processing parameters to enhance the electrical conductivity and thermoelectric power factor of polypyrrole/multi-walled carbon nanotubes nanocomposites

    Synth. Met.

    (2019)
  • A. Adhikari et al.

    Biosurfactant tailored synthesis of porous polypyrrole nanostructures: a facile approach towards CO2 adsorption and dopamine sensing

    Synth. Met.

    (2018)
  • J. Li et al.

    The effect of thermal annealing on dopant site choice in conjugated polymers

    Org. Electron.

    (2016)
  • T. Shoa et al.

    Electro-stiffening in polypyrrole films: dependence of Young’s modulus on oxidation state, load and frequency

    Synth. Met.

    (2010)
  • J.Y. Lee et al.

    Synthesis of soluble polypyrrole of the doped state in organic solvents

    Synth. Met.

    (1995)
  • W. Huang et al.

    Scalable dextran-polypyrrole nano-assemblies with photothermal/photoacoustic dual capabilities and enhanced biocompatibility

    Carbohydr. Polym.

    (2020)
  • A.M. Kumar et al.

    Promising bio-composites of polypyrrole and chitosan: surface protective and in vitro biocompatibility performance on 316L SS implants

    Carbohydr. Polym.

    (2017)
  • Z. Neisi et al.

    Synthesis, characterization and biocompatibility of polypyrrole/Cu(II) metal-organic framework nanocomposites

    Colloids Surf. B Biointerfaces

    (2019)
  • H. Yang et al.

    COX-2 in liver fibrosis

    Clin. Chim. Acta

    (2020)
  • J. Upadhyay et al.

    Antibacterial and hemolysis activity of polypyrrole nanotubes decorated with silver nanoparticles by an in-situ reduction process

    Mater. Sci. Eng. C

    (2015)
  • C. Wan et al.

    Cellulose aerogels functionalized with polypyrrole and silver nanoparticles: in-situ synthesis, characterization and antibacterial activity

    Carbohydr. Polym.

    (2016)
  • H. Huang et al.

    Multifunctional polypyrrole-silver coated layered double hydroxides embedded into a biodegradable polymer matrix for enhanced antibacterial and gas barrier properties

    J. Bioresour. Bioprod.

    (2019)
  • R. Kumar et al.

    Hybrid chitosan/polyaniline-polypyrrole biomaterial for enhanced adsorption and antimicrobial activity

    J. Colloid Interface Sci.

    (2017)
  • M. Maruthapandi et al.

    Antibacterial activities of microwave-assisted synthesized polypyrrole/chitosan and poly (pyrrole-N-(1-naphthyl) ethylenediamine) stimulated by C-dots

    Carbohydr. Polym.

    (2020)
  • A.L. Martinez et al.

    Immobilization of Zn species in a polypyrrole matrix to prevent corrosion and microbial growth on Ti-6Al-4V alloy for biomedical applications

    Prog. Org. Coatings

    (2020)
  • F.A.G. da Silva et al.

    Synthesis and characterization of highly conductive polypyrrole-coated electrospun fibers as antibacterial agents

    Compos. Part B Eng.

    (2017)
  • A. Talebi et al.

    A conductive film of chitosan-polycaprolcatone-polypyrrole with potential in heart patch application

    Polym. Test.

    (2019)
  • J. Upadhyay et al.

    Biocompatibility and antioxidant activity of polypyrrole nanotubes

    Synth. Met.

    (2014)
  • P. Poprac et al.

    Targeting free radicals in oxidative stress-related human diseases

    Trends Pharmacol. Sci.

    (2017)
  • M.S. Shoichet

    Polymer scaffolds for biomaterials applications

    Macromolecules

    (2010)
  • M. Wallis et al.

    3D printing for enhanced drug delivery: current state-of-the-art and challenges

    Drug Dev. Ind. Pharm.

    (2020)
  • Y. Ding et al.

    Electrospun fibrous architectures for drug delivery, tissue engineering and cancer therapy

    Adv. Funct. Mater.

    (2019)
  • F. Pinelli et al.

    Coating and functionalization strategies for nanogels and nanoparticles for selective drug delivery

    Gels

    (2020)
  • Y. Zhang et al.

    Polymer fiber scaffolds for bone and cartilage tissue engineering

    Adv. Funct. Mater.

    (2019)
  • E.N. Zare et al.

    Progress in conductive polyaniline-based nanocomposites for biomedical applications: a review

    J. Med. Chem.

    (2020)
  • W. Su

    Principles of Polymer Design and Synthesis

    (2013)
  • N.M. Barkoula et al.

    Flame-retardancy properties of intumescent ammonium poly(phosphate) and mineral filler magnesium hydroxide in combination with graphene

    Polym. Polym. Compos.

    (2008)
  • J. Huang et al.

    Conjugated Polymers: Theory, Synthesis, Properties, and Characterization

    (2006)
  • T. Nezakati et al.

    Conductive polymers: opportunities and challenges in biomedical applications

    Chem. Rev.

    (2018)
  • L. Vinet et al.

    A “Missing” Family of Classical Orthogonal Polynomials

    (2011)
  • J. Heinze et al.

    Electrochemistry of conducting polymers-persistent models and new concepts

    Chem. Rev.

    (2010)
  • N. Eser et al.

    Synthesis, characterization and some physicochemical properties of polypyrrole/halloysite composites

    J. Macromol. Sci. Part A Pure Appl. Chem.

    (2020)
  • K.C. Khulbe et al.

    Polymerization of pyrrole by potassium persulfate

    J. Polym. Sci. A1

    (1982)
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