Author: Gurmeen Kaur, Training Research Editor
Institution: Lady Hardinge Medical College, Delhi
When one has invented something, there is a feeling of achievement and elation that words can never fully define! This past year, I attended a summer certification program in nanotechnology. There was a varied group of people there from the various spheres of science engineering students, masters in biotechnology and so on. I was the only completely "medical" person in the bunch, and I'd determined that my project in the program would center on nanomedicine.
My project centered on creating a creative hypothesis on the use of a direct glucose fuel cell in medicine. I worked hard throughout the summer, putting the best of my abilities into practice, and here's what I created Blood As A Potential Source For Carbohydrate In An Implantable Biofuel Cell A Proposal.'
The use of blood as a source for deriving energy by external devices placed in the human body environment is a previously unexplored field. A "blood battery-derived circuit" such as this has wonderful implications for its use in medicine--pacemakers, an intestinal motility regulator, and various nerve dysfunction and spinal cord lesions could all benefit from this nanotechnology. The potential uses are unending and enchanting!
Life was good--I was pleased with my project, as were others, and it was an overall success. But, then came the catharsis: when I decided to try to publish my work, I found that the fuel cell I had designed had been patented by scientists 40 years ago! Confirmation that my "invention" had merit, yes, but a shock none-the-less. After more investigation, however, I noticed that while our projects had the same theme, my idea was still uniquely different.
First, a little history behind what a fuel cell is. A fuel cell is an electrochemical conversion device. It produces electricity from various external quantities of fuel (on the anode side) and an oxidant (on the cathode side). These react in the presence of an electrolyte. Generally, the reactants flow in and reaction products flow out while the electrolyte remains in the cell. Fuel cells can operate virtually continuously as long as the necessary flows are maintained. A fuel cell works by catalysis, separating the component electrons and protons of the reactant fuel, and forcing the electrons to travel though a circuit, hence converting them to electrical power. The catalyst is typically comprised of a platinum group metal or alloy. Another catalytic process takes the electrons back in, combining them with the protons and the oxidant to form waste products (typically simple compounds like water and carbon dioxide).
The existing carbohydrate-based fuel cell consists of a vanadium flow battery in which the vanadium ions are reduced by sugar (from a carbohydrate) to oxidation state +3 on one side of a membrane, and are oxidized to state +5 on the other side by oxygen. The theoretical upper limit to the conversion efficiency of the energy in sugar by this method under standard conditions is 54%.
For an implantable biofuel cell, it would be excellent if we could trap a natural source of blood glucose in our body as a source for carbohydrate. This cell would go a long way in the development of medical science, as it will help us make pacemakers which can make the heart function using the power of the blood itself, thus eliminating the need for an external battery system.
In their patented implantable fuel cell, Danial Y.C. et al (1) have extensively described the engineering design of their cell, which is perfectly structured. The light weight of a mere 600 gms and really small dimensions are pretty suitable for implantation. Something that has been overlooked, however, is that there is a problem associated with a cell that uses free air and hence requires a percutaneous connection.
They have stated "Just as the artificial heart and its pump are encased in a biologically acceptable plastic, for example a silicone rubber, tissue contacting parts of the air-breathing assembly, fuel cell, and storage battery are constructed or coated with such material."
Additionally, they have proposed creating a small pore on the skin and maintaining it as an open incision. In their words "The pore opening may be located at the base of the neck which is an area that can be kept open to the atmosphere in the manner commonly done with permanent tracheostomy of laryngectomy patients. However, the pore may be adapted to be placed in any convenient location, and where necessary or desired, the pore can be moved or revived from time to time."
Theoretically, this appears acceptable, but if you ask a surgeon, he/she may express concern that this design may lead to increased chances of air embolism into the body, which is a dreaded and potentially deadly event.
Also, another cause for worry is that the anode and cathode of this fuel cell are widely separated. Though the authors have talked about the use of a non- hemolytic material compatible to the blood (i.e., satisfies criteria for a low percentage of mechanical or chemical (hemolytic) damage to the blood during the pumping action, blood pressure cycling, etc), what they additionally need to worry about is the thrombogenic potential that such a device may have. Also, since the critical location of the anode is either the heart pump mechanism (the outflow tract of the prosthetic heart pump or at some remote location where a portion of the venous blood can be diverted through the fuel cell on its way to the heart), extensive research is needed before the possibility of thrombosis or accelerated atherosclerosis due to substance placement in areas of high turbulence can be ruled out.
While such a cell has major potential cardiovascular and other medical uses, inventors will have to make sure that, in the process of increasing the ejection fraction of the heart, they are not harming the normal anti-thrombotic factors existing in the blood stream.
As for the membrane, they have stated "The membrane is permeable only to a plasma ultrafiltrate containing the oxidizable organic compounds such as glucose which are oxidized in the fuel cell."
This is where the importance of my hypothesis comes in. Potential issues regarding the membrane include its ability to initiate an immunological foreign body reaction in the body and its inability to successfully draw enough glucose into the cell amongst other things. This problem can be tackled by using a membrane with GLUT 4 receptors. Since these receptors are vital to our existence and are the main mechanism of how almost the entire body draws its glucose from the blood, it is bound to be the most efficient way of extracting glucose as substrate. A non-reacting membrane with genetically-engineered receptors are not likely to excite any immunological responses in the body.
Some suggested changes for the patented model of the implantable biofuel cell are:
The whole cell will have to be made of, or completely covered in, a substance against which the body does not illicit a foreign body reaction like PMMA or a similar polymer. This will prevent the immune defense mechanism against the host and promote fruitful survival and working of the fuel cell in the body.
There would be a nanofilter attached to the outer aspect of the fuel cell so that blood is filtered before it enters the cell.
This will prevent contamination of the fuel cell and will also delay the accumulation of impurities (which calls for a need of replacement or removal and cleaning)
The cell will have an extra membrane before the fuel enters the fuel chamber. This membrane will mimic the natural cell membrane possessed by each human cell. It will have GLUT 4 receptors which are responsible for insulin-mediated entry of the glucose into the cell.
The gluconic acid produced cannot cross this membrane and hence can continue serving as a minor fuel in the microenvironment between the membrane and the cell as suggested by the designing authors.
Though the cell can produce current even without this membrane, it would be of very low voltage. Addition of this membrane will facilitate increased concentration of glucose in the fluid finally entering the fuel chamber of the cell, and thus facilitate increased efficiency of the cell.
A diagrammatic view of the membrane-promoting insulin- mediated entry of glucose through cell membrane having GLUT 4 receptors is shown here. [image #2 ]
So the final representation of the fuel cell would be as shown below:[image #3 ]
Togo et al(2) have used the electron mediator based in Vitamin K3 at the anode, which naturally exists in our bodies, making it an extremely safe choice as an enzyme-based microfluidic biofuel cell. Additionally, it has the major advantage of being non-toxic. This could serve as another modification in the Daniel model of the fuel cell for better functioning in-vivo.
A very strong point of the original design of the fuel cell is that it may be connected in parallel with a storage battery, preferably of the silver- or nickel-cadmium type to form a hybrid power system. In such a system, each component is selected to be capable of powering the blood pump alone. This important feature gives the fuel cell-storage battery hybrid system an outstanding redundancy capability. In the case of failure of the main fuel cell unit, the hybrid power battery can easily take over till the patient is taken to the hospital.
OTHER POTENTIAL USES OF SUCH AN IMPLANTABLE BIOFUEL CELL:
1. Use as a pacemaker for the weakened or failing heart this is the primary used suggested by Daniel et al.
2. Use as a peristaltic motility controller. It can be used to increase the intestinal motility in selected cases.
3. Use as an impulse provider in case of nerve dysfunction/ damage. It can provide stimulus to the muscles whose nerve is damaged due to trauma or disease like myasthenia gravis or multiple sclerosis.
4. With more sophistication in design it may be used in spinal cord injury patients to provide signal output to the organs.
Though we have undoubtedly come a long way since 1969, the ingenious design of the original authors still holds valid relevance. Despite such good designing propositions, there are no existing biofuel cell pacemakers or other such implantable devices available yet. Scientists should strive to carve into reality such a biofuel cell that will beautifully serve the hearts of the masses--utilizing their own blood!
1. Daniel Y. C., Wolfson Jr., Sidney K, Appleby, Anthony J. Implantable fuel cell. http://www.freepatentsonline.com/3837922.html.
2. M. Togo, A, Takamura, T. Asai, H. Kaji, and M. Nishizawa, (2007) "An enzyme-based microfluidic biofuel using vitamin K3-mediated glucose oxidation," Electrochim. Acta 52(14): 46694674.
I would like to express my sincere thanks to Mr Sundar of Appin India and Mr Avneesh Dwivedi for their support and encouragement.
Author: Gurmeen Kaur
Reviewed and Published by Senior News and Features Editor Falishia Sloan