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.
There are available examples of technology that can convert body heat into electricity. The technology is made to where thermoelectric generators are used to harvesting electricity from body heat. This can be seen as an amazing finding for possibly powering nanotechnology that is small in size and weight, due to the lack in need of batteries and other bulky components. This could possibly be incorporated with a compatible heart rate monitor or blood sugar monitor for patients to easily access. The thermoelectric generators, only 2 millimeters in thickness, generates electricity by using the temperature differential that is found between the air surrounding the body and the body itself. Understanding this, this technology would be difficult to work with for technology that would be implanted within the body, but could be altered to fit the different environment.
Lightweight, Wearable Tech Efficiently Converts Body Heat to Electricity
It is possible to harness power from muscle contractions within the human body. By using a small electromagnetic induction generator to stimulate strong muscle contractions in different parts of the body, another device which can convert those contractions into a rotational motion can generate electricity. In a study which used a leg muscle in a frog, it was proved that it required minimal electrical power in order to stimulate the muscle, and the power which was generated from the contraction was significantly higher that what was required. This new usage of relatively simple technology has the potential to replace lithium-ion batteries in powering implantable biotechnology.
Biofuel cell technology is another option to power nanotechnology inside the human body. The article below discusses renewable biofuel cells that are glucose-based. Instead of using batteries, an implantable device can extract its source of energy from biofuel cells within the body. The article discusses how biofuel cells can convert the chemical energy of biofuels like glucose into electrical energy through oxidation. This energy could then power devices like pacemakers, insulin pumps, and other technology inside the body. Right now, glucose-based biofuel cells are limited in lifespan and production of power, but further research could make them an ideal substitute to batteries that are currently being used inside the body. Converting glucose into electrical energy to power nanotechnology is another option that our group should consider as it is sustainable source and would be a safer alternative to lithium batteries.
The average adult human has about the same amount of energy stored within their body as a 1 ton battery.
Current designs for implants in knees, both through transplant surgeries and braces can harvest kinetic energy to power small devices. Other devices harnessing the power of thermodynamics and kinetic energy have been used in constantly changing/moving parts of the human body such as the heart, lungs, legs, etc.
Another source of energy is the endocochlear potential – a potential generated in the space in the ear across the membrane. This potential created from vibrations in the eardrum has enough power to theoretically power a small hearing aid/device. This could result in the first piece of biotech which is fully powered by the body, and is one step closer to actual integration.
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.
One source of energy that I came across an article mentioning of a single implanted glucose biofuel cell, or GBFC, that is capable of generating sufficient power from a mammal’s bodily fluids to act as a power source for electronic devices. This type of energy generation would be the most suitable for bio/nanotechnology that would be within the body. One of the most intriguing portions of the report was that the implant didn’t have any signs of rejection or inflammation within the rat after nearly four months of the cell being implanted in the abdominal cavity. The autopsies even showed within the first two to three weeks that a thin layer of vascularized tissue begins to cover the external side of the implant, ensuring how biocompatible it would be. With this in mind, I would also begin to think about how the energy would be stored efficiently and then used appropriately for various technologies? Would the human body have the same reaction to such an implant?
Human movement is another source of energy that can be harvested to power nanotechnology. One article I found discusses the research done at Vanderbilt University to harvest energy from low-frequency human motion (as slow as 0.01 Hertz). Ultrathin layers of black phosphorous nanosheets are being used to extract energy directly from human motion. The materials developed are so thin that they can be easily incorporated into clothing. According to another article, MIT researchers found a new method to harness energy from human movements. They developed a flexible electrochemical battery that begins to bend with human motion. Pressure builds up when the battery bends and an electrical current is made. This current can then be used to power other nanodevices. As we consider how we want to harvest energy to power nanotechnologies inside the body, our group might think about the ways in which humans create energy and how this energy can be transferred for internal use.
The group “Biofueling Change” will be researching human “biofuels.” These are different power sources within the human body. Currently, there is lots of research being done on harnessing the power of the human body in order to power biotechnology. Biotechnological innovations such as a pacemaker currently require a lithium-ion battery. Not only are these harmful to the environment when disposed of, but they are foreign sources of power which are unnatural and potentially harmful to the human body. As biomedical engineering grows and becomes more extensive, natural and recyclable forms of power will be needed. Biomedical Engineers researching this hope that one day, technology will be developed that can essentially plug somewhere into the body, generating power and powering the devices of tomorrow.
The three branches of research that I have found are as follows. First, there is the power from human movement. Are bodies are constantly moving, from walking to our beating hearts. Piezoelectric materials such as the crystal in lighters which generates an electric spark are being used throughout the human body. Scientists have successfully generated a small amount of electricity by attaching a very small piece of piezoelectric cloth/material to internal organs. Second, there is the power from human body heat (thermodynamics). Certain materials have been recently developed which can generate electricity when exposed to high temperatures. When heated to the temperature of the human body, scientists have successfully generated a small amount of power. Finally, there is the power flowing through our blood. Artificial cells called Enzymatic Biofuel Cells (EFCs) target the plasma in human blood, extracting the glucose and using it to generate electricity. An EFC has been successfully implanted in a rat, where it generated a small amount of electricity successfully for 11 days.
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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.