Biomedical Engineering Reference
In-Depth Information
11
Charge Transport and Electrical Switching
in Composite Biopolymers
Gabriel Katana
1
and Wycliffe Kipnusu
2
1
Physics Department, Pwani University College, P.O. Box 195 Kilifi,
2
Institute of Experimental Physics I, University of Leipzig, 04103 Leipzig,
1
Kenya
2
Germany
1. Introduction
Polymers are long chain macromolecules made up of many repeating units called
monomers. They are found in nature and can also be made synthetically. Natural/bio
polymers are considered to be environmental benign materials as opposed to synthetic
polymers. Research geared toward producing innocuous products from biopolymers has
intensified. Improved understanding of properties of biopolymers allows for the design of
new eco-friendly materials that have enhanced physical properties and that make more
efficient use of resources. Biopolymers also have the advantage of being biodegradable and
biocompatible. They are therefore of interest for application in advanced biomedical
materials, for instance tissue engineering, artificial bones or gene therapy (Eduardo et al.,
2005). Other possible fields of applications are related to electrical properties, making this
class of materials attractive for potential uses in electronic switches, gates, storage devices,
biosensors and biological transistors (Finkenstadt & Willett 2004). Plant biopolymers
constitute the largest pool of living organic matter most of which can be attributed to four
distinct classes of organic compounds; lignin, cellulose, hemicellulose and cuticles. Cuticles
are mainly made up of polymethylenic biopolymers which include cutin and suberin. Cutin-
containing layers are found on the surfaces of all primary parts of aerial plants, such as
stems, petioles, leaves, flower parts, fruits and some seed coats. In addition, cutin may be
found on some internal parts of plants such as the juice-sacs of citrus fruits (Heredia, 2003).
Composition, structure and biophysical data of plant cuticles have recently been reviewed
(Jeffree, 2003; Pollard et al. 2008; and Dom
́
ınguez et al., 2011) and will only be mentioned
briefly. The main constituents of cutin are esterified fatty acids hydroxylated and epoxy
hydroxylated with chain lengths mostly of 16 and 18 carbon atoms. It also contains some
fraction of phenolic and fluvanoid compounds.
2. Charge transfer mechanism in biopolymers
Several biopolymers have well documented properties as organic semiconductors (Eley et
al., 1977; Leszek et al., 2002; Radha & Rosen, 2003; Mallick & Sakar, 2000; Lewis & Bowen,
2007; Ashutosh & Singh 2008). DNA-based biopolymer material possesses unique optical
and electromagnetic properties, including low and tunable electrical resistivity, ultralow
