Patent Application
20250055010
The present invention concerns an electronic device comprising a biofuel cell and a printed circuit board (PCB) with an air-breathing aperture, the biofuel cell comprising an external layer air-breathing aperture (through GDL), the electronic device being characterized in that the air-breathing aperture formed into the PCB is opposite the external layer air-breathing aperture, the biofuel cell being attached to the PCB. In the description below, references in square brackets ([]) refer to the list of references at the end of the text.
Biological fuel cells (or biofuel cells) offer an attractive means to provide eco-friendly and sustainable power to electronic devices, particularly for small portable devices for applications such as healthcare, environmental monitoring, bio-defense, etc. Given that enzyme-based fuel cells can operate using substrates that are abundant in the biological fluids and environmental effluent (i.e., glucose and oxygen) whilst exhibiting power densities that are often superior to microbial fuel cells, they offer an attractive proposition to augment or self-power miniaturized wearable or implantable devices [1,2,3]. Furthermore, paper-based devices are gaining popularity as propositions for these types of applications owing to their low mass, small form factor and flexibility, allowing them to conform to a range of different surfaces.
It is well documented that the current density at the cathode is one of the limiting factors in biological fuel cell performances where oxidoreductase enzymes are used within one of the two half-cell reactions, and this is largely due to the lower concentration of dissolved oxygen available at the electrode—solution interface. It is therefore often advantageous to increase the amount of oxygen at the cathode surface, for example by optimizing its morphology to expose part of the cathode to air [4,5,6]. Such devices are commonly referred to as having an ‘air breathing’ cathode.
Whilst increasing the availability of oxygen is important to improve global performance of an oxygen-based fuel cell, it is also important to maintain enough liquid, which is required to provide transport of ionic species, often in the form of an electrolyte. Simply providing an open aperture can lead to the fuel cell drying, ceasing the ability for the reactions to ensue.
Therefore, a membrane which supports the flux of oxygen whilst limiting the loss of liquid is typically implemented. Gas diffusion layers (GDLs), made often of carbon, are frequently employed as they can double as an electrical current collector. Carbon-based GDLs are porous materials composed of a dense array of carbon fibers, which may also be modified with other carbon micro-/nano-structures. This structure provides intrinsic hydrophobicity, reducing loss of liquid, but may also be further treated (e.g., inclusion of PTFE) to increase hydrophobicity.
As aforementioned, one of the main factors reducing the operational lifetime is the loss of liquid within the fuel cell. It is therefore interesting to increase the available volume of liquid within the device. If a constant/continuous supply of liquid cannot be provided (for instance where a body could provide a steady supply of biological fluid), one option, particularly for miniaturized, single-use devices, is to provide a liquid reservoir [7] in order to provide a mechanism to maintain wetting of the interfaces.
However, this liquid reservoir will naturally occupy a volume. In many applications (wearable health/medical patches, packaging), it is interesting to provide a thin, flexible, and conformable biofuel cell. In these instances, it is interesting to reduce the overall thickness of the device. Naturally, by reducing the thickness of the device (z-axis), the volume must be spread across the plane of the device (x, y-axes). By occupying the full extent of the x-y plane, the total thickness can be minimized. The consequence of this technique is that this surface cannot be used to provide an aperture for the provision of an air-breathing cathode, particularly when the optimum location for the aperture is in the center of the active area (center of electrode) of the device.
Assuming a thin biofuel cell (whereby the thickness is so minute that we can consider two flat surfaces surrounded by edges that pose no functional surfaces for design, a 2D structure rather than a 3D structure), if one surface is occupied by the liquid reservoir, the other surface must be used for all other function. Functionality would typically include the provision of electrical terminals (anode and cathode), as well as an aperture for the flux of air (for oxygen provision) to provide air-breathing capability [8].
Looking at the attachment of such an embodiment to an electronic device, conductive films (such as a singular anisotropic conductive film (ACF) or multiple isotropic conductive films (ICF) are championed due to their low cost and low thickness (typically less than 100 micron), and ability to be used in mass production (such as roll-to-roll processing), otherwise surface mount technology (SMT) ribbon cable connectors may be employed for reusable applications.
Thus biofuel cells are usually made as standalone devices, or they are made as a part of a PCB. Indeed combination of a standalone biofuel cell with a functional PCB presents some challenges such as delivery of oxygen to the cathode of the fuel cell through the PCB for example. Furthermore, combination of a biofuel cell with a functional PCB requires spatial constraint and specific arrangement e.g. the place for the contact pads, the place for the inlet, the electronic component, the location of the sensors, etc. . . . In the case of wearable applications or medical patches, the biofuel cell and the PCB are usually connected via electrical wires [9]. Nevertheless, the use of electric wires is a real weakness for a wearable biosensor as it can easily break and would not suit a real-life use or a mass production. In either case, the biofuel cell would be brought into close proximity (<200 μm) with the electronic device. Advantageously, the electronic device would directly be connected to the two electrodes by sticking the PCB on one side of the biofuel cell (using conductive tape for instance). However, the consequence of this technique is a high probability of blocking the air-breathing cathode because of the electronic device size (usually larger than the contact pads used to connect the electrical chemicals of the biofuel cell and the electronic device), thus decreasing the capacity of the biofuel cell.
Thus there is still a need to provide a novel electronic device combining a biofuel cell with a functional PCB, that does not have the disadvantages of the prior art devices, i.e. that allows a sufficient flux of air to arrive to the biocathode to get full performance of the biofuel cell.
Therefore the Inventors solved the technical problem by providing an electronic “sandwich” device comprising a biofuel cell (International Application WO 2019/234573) [7] and a printed circuit board (PCB) having an air-breathing aperture formed opposite the external layer air-breathing aperture of the biofuel cell attached to the PCB, with the purpose to solve the problems of:
In other words, the claimed electronic device maximizes the flux of air available for an oxygen reduction reaction, whilst providing a maximum volume of liquid to improve longevity as well as minimum overall thickness of the solution. The glucose-oxygen biofuel cell consists of two carbon electrodes functionalized by different enzymes for the oxidation of glucose (e.g., glucose oxidase or glucose dehydrogenase), and reduction of oxygen (e.g., laccase or bilirubin oxidase), with a cellulose separator, a gas diffusion layer (GDL) (to provide current collection and flux of oxygen/air) at the biocathode, and encapsulated by a robust cellulose paper (water proof, grease proof, and heat proof) that includes different types of apertures for electrical contacts, flux of oxygen/air, and a liquid inlet, bonded with a liquid reservoir to provide increased longevity by reducing the time taken for the liquid to be lost via the gas diffusion layer. Thus the current technology of said biofuel cell is based on 7 layers: External layer; Current collector (carbon felt; e.g. from Panasonic EYGS, sgl carbon, ProGraphiteShop); Anode (nanotube felt with mediators and enzymes; e.g. from DSM, SHIN NIHON CHEMICAL, Sigma Aldrich); Microfluidic layer (cellulosic paper; e.g. from VWR European, Ahlstrom Munksjo); Cathode (nanotube felt with promoter and enzymes; e.g. from Creative enzymes, Sigma Aldrich); Current collector and gas diffusion layer (GDL, ideally with microporous layer (MPL)) (hydrophobic carbon felt; e.g. from sgl carbon, FuelCellStore); then External layer. In turn, the paper biofuel cell with liquid reservoir is then attached to a PCB which includes an air-breathing aperture aligned to the (external layer) air-breathing aperture into the biofuel cell providing flux of oxygen/air to the biocathode.
In either case (use of a liquid reservoir or as medical patches), the orientation effect of this “sandwich” device is a key factor to the success of its application and mass production. For instance, in case of wearable applications/medical patches:
An object of the present invention is therefore an electronic device comprising a biofuel cell and a printed circuit board (PCB) with an air-breathing aperture (or hole), the biofuel cell comprising an external layer air-breathing aperture, the electronic device being characterized in that the air-breathing aperture formed into the PCB is opposite the external layer air-breathing aperture, the biofuel cell being attached to the PCB.
According to a particular embodiment of the present invention, the electronic device is a portable electronic device, wherein:
According to a particular embodiment of the present invention, the electronic device is in the form of a wearable medical patch, wherein:
According to a particular embodiment of the present invention, the air-breathing aperture into the PCB is at least one hole.
According to a particular embodiment of the present invention, the air-breathing aperture into the PCB has an area from e 1/10 to 2 times the external layer air-breathing aperture of the biofuel cell.
According to a particular embodiment of the present invention, the air-breathing aperture into the PCB is equipped with a material that is permeable to the oxygen. For example, the material is in the form selected from the group consisting of a grid, and a membrane. According to a particular embodiment of the present invention, the air-breathing aperture into the PCB is in the form of a plurality of contiguous holes made in the PCB itself, the said holes together forming a grid opposite the GDL air breathing aperture of the biofuel cell.
According to a particular embodiment of the present invention, the biofuel cell is attached to the PCB by an ACF (Anisotropic Conductive Film) tape, by a Teflon tape (e.g. from Techniflon) or by any biodegradable or lowest environmental impact means (e.g. a biodegradable adhesive such as paper tape or water-dissolving tape, e.g. from Adhesives Research) or by a snap-fit means.
According to a particular embodiment of the present invention, the snap-fit means comprises at least one spur formed either onto the surface of the biofuel cell in contact with the surface of the PCB or onto the surface of the PCB in contact with the surface of the biofuel cell, and at least one slot complementary to said at least one spur formed either onto the surface of the PCB in contact with the surface of the biofuel cell or onto the surface of the biofuel cell in contact with the surface of the PCB, respectively, such that the said at least one spur slots into the said at least one slot to attach thereby the biofuel cell to the PCB. Preferably, the said at least one spur and the said at least one slot surrounds the (external layer) air-breathing aperture of the biofuel cell and the air-breathing aperture formed into the PCB, while the air-breathing aperture formed into the PCB is opposite the external layer air-breathing aperture of the biofuel cell. According to a particular embodiment of the present invention, the snap-fit means comprises several spurs formed either onto the surface of the biofuel cell in contact with the surface of the PCB or onto the surface of the PCB in contact with the surface of the biofuel cell, and several slots complementary to said several spurs formed either onto the surface of the PCB in contact with the surface of the biofuel cell or onto the surface of the biofuel cell in contact with the surface of the PCB, respectively, such that the said several spurs slot into the said several complementary slots to attach thereby the biofuel cell to the PCB. Preferably, the said several spurs and the said several slots surround the (external layer) air-breathing aperture of the biofuel cell and the air-breathing aperture formed into the PCB, while the air-breathing aperture formed into the PCB is opposite the GDL air-breathing aperture of the biofuel cell.
According to a particular embodiment of the present invention, the biofuel cell is an enzymatic fuel cell.
According to a particular embodiment of the present invention, the PCB is composed of different electronic components. For example, the PCB comprises sensors, microprocessors, user interactions, communication modules, etc. . . . or a combination thereof.
Material for film substrate: Polyimide (PI) or similar polymer, Polyester (PET), Polyethylene naphthalate (PEN), PTFE, Aramid. There are approximately 2000 additional plastic film categories which can be potentially suitable for the Flexible PCB manufacturing.
FPCBs (Flexible Printed Circuit Boards) usually consist of 3 layers: substrate, adhesive and copper foil. Adhesive reduces the FPCB performance, both electrical and mechanical, therefore 2-layer FPCBs with no adhesive exist. Methods of manufacturing the 2-layer FPCBs include electroplating, film coating and lamination. Electroplating is usually used for small scale cheaper boards, film coating is better for low-cost mass production and lamination is usually used for double-sided FPCB manufacturing. Since all our boards are double sided, they are most likely manufactured using the lamination process.
Manufacturing process steps:
All of the above steps are applicable to standard PCBs as well as Flex PCBs with some adjustments to some of the steps. In our case it does not matter if me use a standard rigid PCB or the Flex PCB, the holes for the air, blister and inlet would need to be cut anyway. The biggest difference would be during the cutting step as it is harder to cut the rigid PCB with a die due to its thickness, so laser or more realistically mechanical routing techniques would be used.
Same is applicable to the PCBs with more than 2 layers. In this case they are produced as separate PCBs, but prior to copper plating step they would be bonded together to make up a single board with internal layers. For example, for a 4-layer board two 2-layer boards would be made, then an insulator would be applied to one side of one of the boards and the other one would be glued on top of it. A result would be a board with 2 external and 2 internal layers, connections between layers would be done with the help of vias (which need to be plated, hence this happens before the plating step.
For our purposes the shape and dimensions of the boards are arbitrary as we do adjust their shape and size based on the application. In addition, we also do put the components on both sides of the boards for some use cases.
The device for the production of electrical energy comprises an anode and a cathode. In order to ensure the redox reaction allowing the production of electrical energy, the anode and cathode are made of materials allowing ion exchange. The anode and cathode must have specific properties (thickness, conductivity, surface resistance), chosen according to the application. These elements can be impregnated with enzymes and mediators. For example the anode and cathode comprise nanotube sheets, and in particular sheets composed of multi-walled carbon nanotubes (MWNT) as described above. In the case of glucose batteries, the nanotube sheet is impregnated with mediators and enzymes that enable the oxidation of glucose at the anode and the reduction of oxygen from the air to water at the anode. For example, the anode may comprise the enzyme glucose oxidase and/or FAD dehydrogenase for the oxidation of glucose as well as naphthoquinone and/or phenanthrolinequinone as a redox mediator transferring electrons to the electrode! The cathode may include the enzyme laccase, bilirubin oxidase and ABTS as mediators.
A microfluidic diffusion layer is placed between the anode and the cathode. The latter allows the diffusion of a solution triggering the production of electrical energy by redox between the anode and the cathode. The microfluidic layer can, for example, be a simple gap or, more advantageously, comprise or consist of a paper-like material in which the solution triggering redox can diffuse by capillarity. A compromise must be made between its thickness and its cellular capacity (volume of the voids).
This layer forms a separating layer between the anode and the cathode and can also constitute, at least partially, the diffusion support of the electrolyte.
The device for producing electrical energy can also include the usual elements of electrochemical cells and in particular of fuel cells. Thus, the device may comprise conductive elements in contact with an electrode (in particular on the opposite side of the electrode face in contact with the microfluidic layer).
When the device is supplied with a gas, means of diffusion of this gas (GDL) are arranged to allow the supply of the gas.
Finally, the electrical energy production device can comprise a support, preferably quite rigid, and a covering element (blister, liquid reservoir, protective materials), for example a glass fiber, plastic or polystyrene band, or preferably a bio-sourced material, surrounding all the elements described above, with the exception of the reservoir, which is accessible in order to be able to release its contents. The purpose of this element is to secure and protect the device.
A resulting electronic device with a liquid reservoir is represented in
A resulting electronic device in the form of a wearable medical patch is represented in
Thus the apertures and air-breathing aperture of the external layers of the bioanode and the biocathode of the electronic device of the present invention, respectively, does not exhibit the same function.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21306926.3 | Dec 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/087544 | 12/22/2022 | WO |
