Microbial fuel cells use bacteria as the catalysts to oxidize organic and inorganic matter to generate current that supplies implantable medical devices (Logan, 2006). A critical review from Microbial Fuel Cells Focus Group at Penn State University reports that a widely used and inexpensive type of microbial fuel cell is designed with two chambers connected by a tube containing a carton exchange membrane. The choice of membrane in this design is crucial: the membrane has to allow protons to pass between the chambers, but not the substrate or election acceptor in the cathode chamber (Logan, 2006). The design of microbial fuel cells hence involves knowledge in microbiology, electrochemistry, materials, and environmental engineering. Development in microbial fuel cells has great potential to be used as a renewable and bio-compatible energy source for commercial as well as medical applications. However, it is a field of research that currently lacks established terminology and systematic method of analysis.
Since the introduction of the pacemaker, lithium batteries were used to sustain power in implantable medical devices. Reasons that lithium batteries were the most popular power source include their comparatively compact sizes and long durability up to 10 years (approaches). However, there are safety risks and compatibility difficulties involved with using lithium batteries in a human body. Understanding these challenges gives context to the significance of our group’s research on alternative energy sources to implantable medical devices. Take a look at the usage of lithium batteries in pacemakers. There are two sources of biological incompatibility between lithium batteries and the human body. Lithium has extremely high specific heat, making it an ideal source of energy. However, because reacts violently with water, non-aqueous electrolytes must be used. Because most biological reactions occur in an aqueous environment, lithium batteries are hence incompatible to the environment within the human body. Secondly, electrical impulses are transmitted to the heart by a lead, which is attached to the pulse generator on the pacemaker by the connector block. The tip of the lead is implanted into the endocardial surface of the heart (trends). Metals are also a highly incompatible material with biotic tissues.
Our group plans to research possible ways to harness energy from biotic materials, such as bacteria or human adipose tissue, to power implanted devices. As nanotechnology becomes increasingly mature, implantable medical devices gains greater role in disease treatment and prevention, physiological data collection, and living quality improvement. The ability to power implantable devices within human bodies hence becomes more relevant than ever. Additionally, energy sources that are compatible with the human body have great potentials to be engineered into environmentally sustainable commercial fuels. One of such energy sources is bacteria. There has been years of research on harnessing fuel from E. coli to substitute petroleum. A more recent study discovers a potentially cheaper and “greener” method producing biofuel: directly converting cellulose to biobutanol using the TG57 strain bacteria. There remains room for research on how these biofuels can be applied to implantable medical devices within the human body. On the other hand, with its inherent compatibility with the human body, human adipose tissue presents an almost ideal alternative for biotic source of energy. Furthermore, lipid holds 9 calories of energy per gram, making it potentially an efficient source of energy. While there is little research on conversion of lipid in adipose to usable power for electrical devices, there has been significant progress on using enzymatic biofuel cells to power a wireless device in a mammal for approximately two months.