Polypyrrole-based conducting polymers and interactions with biological tissues
D.D Ateh
()
H.A Navsaria
P Vadgama
0
Centre for Cutaneous Research, Institute of Cell and Molecular Sciences, Barts and The London School of Medicine and Dentistry, Queen Mary University of London
, London E1 2AT,
UK
1
IRC in Biomedical Materials, Queen Mary University of London
, London E14NS,
UK
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Polypyrrole-based conducting polymers
and interactions with biological tissues
D. D. Ateh1,2,*, H. A. Navsaria2 and P. Vadgama1
Polypyrrole (PPy) is a conjugated polymer that displays particular electronic properties
including conductivity. In biomedical applications, it is usually electrochemically generated
with the incorporation of any anionic species including also negatively charged biological
macromolecules such as proteins and polysaccharides to give composite materials. In
biomedical research, it has mainly been assessed for its role as a reporting interface in
biosensors. However, there is an increasing literature on the application of PPy as a
potentially electrically addressable tissue/cell support substrate. Here, we review studies
that have considered such PPy based conducting polymers in direct contact with biological
tissues and conclude that due to its versatile functional properties, it could contribute to a
new generation of biomaterials.
1. INTRODUCTION
Through new combined knowledge of molecular biology
and the biophysical correlates of material surface
properties (Kasemo 1998; Castner & Ratner 2002;
Tiefenauer & Ros 2002), local interactions between
cells and their immediate microenvironments are
increasingly better understood and recapitulated for
the design of practical biomaterials (Discher et al. 2005;
Liu & Chen 2005; Stevens & George 2005). Tissue
engineering (Langer & Vacanti 1993) is probably one of
the most likely avenues for exploitation of such new
generation materials along with other niche areas such
as neuroprosthetics, biosensors and drug delivery.
In tissue engineering, especially with regard to
bioreactors for optimal tissue growth in artificial
constructs prior to implantation, the majority of
cellsupporting scaffolds currently used are porous and
degradable polymers (Seal et al. 2001). Such structures
may be fabricated from natural materials, such as
collagen or fibrin or synthetic polymers such as
polyglycolide or polylactide. However, such scaffolds
(or substrates) and their associated bio-functionality
are now known to be important in tissue growth and
guidance beyond any mesoscopic organization. For
example, their topography (Curtis & Wilkinson 1997),
mechanics (Wong et al. 2004) and incorporated
controlled release growth factors and signal molecules
(Saltzman & Olbricht 2002) can have profound effects
on cell behaviour.
Tailoring specific material properties, bulk as well as
surface, could provide novel solutions for
tissueengineered systems including controlled cell assembly
(micro and nanopatterned surfaces), drug release
(degradable polymers), tissue release
(thermoresponsive polymers) and integrated biosensing (electroactive
polymers). In addition, such materials provide a
platform for the study of the fundamental underpinning
science relating to tissue-material surface interactions.
It is in recognition of these special requirements that
researchers have engaged unique classes of materials for
trial use in biological applications. Conducting
polymers such as polypyrrole (PPy) offer a new class of
material in this regard. This review presents research
where PPy is in contact with biological tissue and
outlines current achievements with an assessment of
future opportunities.
2. POLYPYRROLE-BASED CONDUCTING POLYMERS
2.1. Conducting polymers
Letheby in 1862 first reported the anodic oxidation of
aniline in dilute sulphuric acid, yielding an insoluble
blueblack shiny powdered deposit on a platinum
electrode. Further experiments led Goppelsroeder in
1876 to establish that oligomers were formed by the
PPy with biological tissues
D. D. Ateh and others
oxidation of aniline (Heinze 1989). Natta et al. (1958)
synthesized polyacetylene and Dallolio et al. (1968)
discovered yet another compound, PPy, at the time
called pyrrole black. However, it was not until 1977
that Shirakawa and his co-workers wrote their seminal
paper showing that halogen doping of polyacetylene
dramatically increased its conductivity (to around
103 s mK1 in the case of I-doped trans-polyacetylene).
The major breakthrough with regard to the routine
synthesis of conducting polymers, however, was
achieved by Diaz and co-workers (Diaz & Kanazawa
1979; Kanazawa et al. 1979; Diaz 1981) when they
reported the formation of a highly conductive, stable
and manageable PPy film under controlled
electrochemical conditions. Since then, in the cont (...truncated)