Joined: 16 Mar 2004
|Posted: Fri May 15, 2009 1:40 pm Post subject: Smart Materials Mimic Biological Systems
|Lecture Describes Polymers that Replicate Nerves, Noses, Muscles & Tongues
A type of plastic that displays semi-conductor-like and metallic properties was the focus of an inaugural doctoral lecture given by Dr M A Mohamoud at the University of Leicester on June 4th, 2008. These novel smart materials, called “conducting polymers”, have the ability to mimic biological systems and can be used as components of artificial nerves and muscles, electronic noses and tongues, and drug-release/delivery systems. They can also function as energy storage devices in battery technology, electrochromic display devices (in smart window technology and light emitting diodes), and in biological sensor technology.
Conducting polymers exhibit the behaviour of metals or semi-conductors. Their backbones have a delocalised bond structure which can be augmented through “doping” with an appropriate agent (e.g. iodine), in a manner analogous to silicon. This not only controls conductivity, but can affect optical and physical properties in response to electrical stimulation (e.g. expansion/contraction, light emission, ingress or egress of molecular species). Such changes are the key features behind their potential application.
Most conducting polymers belong to one of four families: polyaniline, polypyrrole, polythiophene, and polyphenylvinylenes. In Dr Mohamoud's research he has investigated the correlation between composition (ion/molecule content) and the structural dynamics of conducting polymer thin films. A better understanding of these aspects is fundamental to the creation of novel microactuators, drug delivery vehicles and chemical/biosensors. In addition, he has further developed and fine-tuned the properties of these conducting polymers via co-polymerisation and incorporation of carbon nanotubes/metal nanoparticles.
The thickness of polymer films can be controlled in different ways: through templating (via polystyrene nanospheres, for example) or growing them on nano/microelectrodes by means of electrochemical polymerisation. The number of cycles and concentration of monomers and electrolytes are all important factors.
In microsurgery, desired drugs can be loaded into polyaniline or polypyrrole coated microelectrodes, these introduced into the appropriate part of the body and the drugs released by applying the appropriate electrical potential.
Led by Professor A. Robert Hillman and Dr. Karl S. Ryder, the research team have investigated how different anions affect the mechanical properties of conducting polymers. They have focused on polyaniline, which is the only conducting polymer that can be doped with protic acids, and show different oxidation states with pH variation. The team also investigated polypyrrole and polythiophene (and its derivatives: polyalkylthiophene and polyethydioxythiophene).
In the lecture, Dr Mohamoud showed real time movies of free standing conducting polymers at a nanoscale level, functioning as micro-muscles that have potential applications in medical surgical operations.
He explained their properties; how they function and conduct electricity and how their properties can further be improved and exploited.
He also discussed the many potential applications these new materials offer as an economic alternative to precious metals (e.g. gold, silver and platinum) with the added advantage of being able to tune their electronic and optical properties.
Dr Mohamoud said: “Traditionally, plastics have been regarded as insulators and used by the electronics industry on the basis of these properties. However, in the year 2000, the scientific community celebrated this field of materials chemistry by awarding the Nobel Prize in Chemistry to Heeger, Shirakawa and MacDiarmid for their work in the discovery of conducting polymers.
“In this presentation, I strongly highlight our contribution to the recent research in the advancement of these systems. The optimization of these systems fully relies upon the understanding of the basic principles that govern the physico-chemical processes underpinning the operations of conducting polymer systems.”
During his PhD studies, Dr Mohamoud carried out fundamental research of the correlations between composition, structure and properties of conducting polymers.
He is now a post-doctoral researcher in the Scionix laboratory in the Department of Chemistry at the University of Leicester. His current research involves metal deposition using ionic liquids (solventless liquids of mixed ions).
The lecture was based on work carried out during his postgraduate studies at the University of Leicester , where he was awarded his PhD in July 2007.