Biofuel cells (BFCs) using graphene-coated carbon fiber cloth electrodes and glucose gel fuel were fabricated and evaluated. A new structure using fuel gel, in which the anode was embedded in gel and the cathode was exposed to the atmosphere, was adopted. Air-exposed biofuel cells using gel have already been reported, however, adhesion between the anode and the gel was improved by the proposed structure. In addition, the enlargement of the gel area prevented its drying. These innovations improved the power density and lifetime of the BFCs. The anode was modified with a glucose oxidase (GOD) enzyme and a mediator (ferrocene) and the cathode was modified with a bilirubin oxidase enzyme. The power density of the proposed structure was 176.4 µW/cm2 at 0.19 V, which was approximately 3.8 times higher than that of BFCs using liquid fuel (45.9 µW/cm2).

In this study, we devised a biofuel cell (BFC) by impregnating sheet-like cellulose nanofiber (CNF) with liquid fuel (fructose) and sandwiching it with the electrodes, making the structure simple and compact. CNF was considered as a suitable material for BFC because it is biocompatible, has a large specific surface area, and exhibits excellent properties as a catalyst and an adsorbent. In this BFC device, graphene-coated carbon fiber woven cloth (GCFC) was used as the material for preparing the electrodes, and the amount of enzyme modification on the surface of each electrode was enhanced. Further, as the distance between the electrodes was same as the thickness of the sheet-shaped CNF, it facilitated the exchange of protons between the electrodes. Moreover, the cathode, which requires an oxidation reaction, was exposed to the atmosphere to enhance the oxygen uptake. The maximum power density of the CNF-type BFC was recorded as 114.5 µW/cm2 at a voltage of 293 mV. This is more than 1.5 times higher than that of the liquid-fuel-type BFC. When measured after 24 h, the maximum power density was recorded as 44.9 µW/cm2 at 236 mV, and the output was maintained at 39% of that observed at the beginning of the measurement. However, it is not the case with general BFCs, where the power generation after 24 h is less than 5%. Therefore, the CNF-type BFCs have a longer lifespan and are fuel efficient.

Improvement of output and lifetime is a problem for biofuel cells. A structure was adopted in which gelation mixed with agarose and fuel (fructose) was sandwiched by electrodes made of graphene-coated carbon fiber. The cathode surface not contacting the gel was exposed to air. In addition, the anode surface not contacting the gel was in contact with fuel liquid to prevent the gel from being dry. The power density of the fuel cell was improved by increasing oxygen supply from air and the lifetime was improved by maintaining wet gel, that is, the proposed structure was a hybrid type having advantages of both fuel gel and fuel liquid. The output increased almost up to that of just using fuel gel and did not decrease significantly over time. The maximum power density in the proposed system was approximately 74.0 µW/cm2, an enhancement of approximately 1.5 times that in the case of using liquid fuel. The power density after 24 h was approximately 46.1 µW/cm2, which was 62% of the initial value.

We have developed and evaluated a prototype micro-pump for a new form of medication that is driven by a chemical reaction. The chemical reaction between citric acid and sodium bicarbonate produces carbon dioxide, the pressure of which pushes the medication out. This micropump is smaller in size than conventional diaphragm-type micropumps and is suitable for swallowing.

Incorporating a tool for administering medication, such as a syringe, is required in microneedles (MNs) for medical use. This renders it easier for non-medical personnel to administer medication. Because it is difficult to fabricate a hollow MN, we fabricated a capillary groove on an MN and its substrate to enable the administration of a higher dosage. MN grooving is difficult to accomplish via the conventional injection molding method used for polylactic acid. Therefore, biodegradable polyacid anhydride was selected as the material for the MN. Because polyacid anhydride is a low-viscosity liquid at room temperature, an MN can be grooved using a processing method similar to vacuum casting. This study investigated the performance of the capillary force of the MN and the optimum shape and size of the MN by a puncture test.

An enzymatic biofuel cell (BFC) that uses lactic acid in human sweat as fuel to generate electricity is an attractive power source for wearable devices. A BFC capable of generating electricity with human sweat has been developed. It comprised a flexible tattoo seal type battery with silver oxide vapor deposited on a flexible material and conductive carbon nanotubes printed on it. The anode and cathode in this battery were arranged in a plane (planar type). This work proposes a thin laminated enzymatic BFC by inserting a cellulose nanofiber (CNF) sheet between two electrodes to absorb human sweat (stack-type). Optimization of the anode and changing the arrangement of electrodes from planar to stack type improved the output and battery life. The stack type is 43.20μW / cm2 at 180mV, which is 1.25 times the maximum power density of the planar type.

Conventional enzymatic biofuel cells (EBFCs) use glucose solution or glucose from human body. It is desirable to get glucose from a substance containing glucose because the glucose concentration can be kept at the optimum level. This work developed a biofuel cell that generates electricity from cellulose, which is the main components of plants, by using decomposing enzyme of cellulase. Cellulose nanofiber (CNF) was chosen for the ease of decomposability. It was confirmed by the cyclic voltammetry method that cellulase was effective against CNF. The maximum output of the optimized proposed method was 38.7 μW/cm2, which was 85% of the output by using the glucose solution at the optimized concentration.

An enzymatic biofuel cell (EBFC) is a device that uses an enzyme as a catalyst to convert chemical energy into electrical energy by a redox reaction to generate electricity. EBFC has the advantage that it can operate under mild conditions (normal temperature, normal pressure, and near neutral pH) and can use various energy sources such as sugar and alcohol. Hoshi et al. reported EBFC of glucose fuel using graphene-coated carbon fiber cloth (GCFC) with a large specific surface area. However, it was considered that GOD was affected by dissolved oxygen in the fuel and generated hydrogen peroxide, which hindered the reaction. In order to further increase the output, it was necessary to improve the performance of the anode with a novel enzyme that is less affected by oxygen and generates electricity from glucose. Therefore, we focused on FAD glucose dehydrogenase (FAD-GDH). It can generate electricity with glucose fuel by using it as a catalyst like GOD. Characteristic is that it is resistant to impurities such as maltose and galactose and is not easily affected by oxygen. It was thought that this would alleviate the concern about hydrogen peroxide and improve the output.

Improvement of output and lifetime is a problem for biofuel cells. A structure was adopted in which gelation mixed with agarose and fuel (fructose) was sandwiched by electrodes made of graphene-coated carbon fiber. The electrode surface not contacting the gel was exposed to air. In addition, grooves were added to the gel surface to further increase the oxygen supply. The power density of the fuel cell was examined in terms of the electrode area exposed to air. The output increased almost in proportion to the area of the electrode exposed to air. Optimization of the concentration of fuel, gel, and the amount of enzyme at the cathode were also examined. The maximum power density in the proposed system was approximately 121μW/cm2, an enhancement of approximately 2.5 times that in the case of using liquid fuel. For the power density after 24h, the fuel gel was superior to the fuel liquid.

The demand for enzymatic biofuel cells (EBFCs) as power sources or auxiliary power sources for small devices is expected to increase in the near future. EBFCs have advanced properties and do not require a separator, depending on the substrate specificity of the enzyme. Two direct electron transfer (DET)-type enzymes were used to modify anodes (length 5mm, width 4mm) by a chemical modification method using a condensation agent. The DET-type enzymes used in this study were pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) with glucose as a reaction substrate and fructose dehydrogenase (FDH) using fructose as a reaction substrate. Carboxyl groups were attached to multi-walled carbon nanotubes (MWCNTs) that act as catalyst carriers, activated to other functional groups, and reacted with the amino groups of the enzyme by the condensation agent to form covalent bonds. As a result, the upper limit of the concentration, considered to be the reaction limit, was raised as compared with that of EBFC modified with only one kind of enzyme for each electrode prepared by the same process. The output voltage was 0.155V, and the maximum power density was 80.08µW/cm2.

In this study, we optimized the reforming of bilirubin oxidase (BOD) using graphene-coated carbon fiber woven fabric (GCFC) as an electrode, and The performance of the cathode in which synthesized 1-pyrene butyric acid N-hydroxysuccinimide ester (PBSE) and 2,5-dimethyl-1-phenyl-1-H-pyrrole-3-carbaldehyde (DPPC) were added, was evaluated. In addition, the prototype evaluation of the atmospheric-exposure-type ascorbic acid enzyme biofuel cell (AAEBFC) using the improved GCFC cathode was performed. The area of both the anode and cathode electrodes was 5mm × 5mm. No modification was performed to the anode, and only the cathode was coated with the enzyme BOD. In the work, for the AAEBFC using the BOD-modified cathode, an output of 238.5µW/cm2 was obtained at 0.245V. Further, in the AAEBFC using the DPPC-PBSE-BOD-modified cathode, an output of 338.8µW/cm2 was obtained at 0.292V. The output in this work was improved by approximately 1.4 times by the additives.

Technological developments in direction control of axonal outgrowth are a must for advances in regenerative medicine of the nervous system. In order to solve the problem, we fabricate a new neural cell culture sheet by applying the soft lithography technique to micro-patterning of the extracellular matrix and using thin-film biodegradable polymer for the scaffold. Micro-trenches were coated with Dulbecco's phosphate-buffered saline (-) containing laminin, using micro-molding in capillaries (MIMIC), a soft lithography technique. Biodegradable thin films with micro-trenches were fabricated by UV-curing a polyanhydride solution covering the negative SU-8 mold through thiol-ene polymerization. Both approaches were performed conveniently, rapidly, and accurately. It is thought that these techniques are excellent in terms of convenience and high speed, and can contribute greatly to regenerative medicine.

In fields such as medicine and chemistry, methods for transporting microdroplets are currently necessitated, which include the analysis of reagents, mixing, and separation. As microdroplets become finer, their movement becomes difficult to control as a result of surface tension. This has resulted in the use of an excessive amount of reagents. In this study, we evaluated the dynamic characteristics of microdroplets and the excitation force. Microdroplets were dropped onto a tilted glass substrate, and the displacement of the microdroplets was measured while changing the droplet amount, vibration frequency, and vibration direction. Moreover, the behavior of the droplet just before it started to move was observed, and the relationship between the displacement of the minute droplet and the vibration force was compared and examined.

In this study, two modification methods that employ graphene-coated carbon fiber woven fabric (GCFC) as an electrode and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS) as a mediator were used to evaluate cathode performance. In addition, a prototype of an atmosphere-exposed ascorbic-acid enzyme biofuel cell (AAEBFC) consisting of an improved GCFC cathode and ABTS was evaluated. No modification was made in the anode region, and only the cathode region was coated with the enzyme of bilirubin oxidase (BOD). As a result of implementing an ABTS-modified cathode in the AAEBFC, an output of 721μW/cm2 was obtained at 0.189V. When the gel thickness was changed, an output of 1200μW/cm2 was obtained at 0.17V. To the best of our knowledge, this is currently the highest reported output for an AAEBFC fueled by ascorbic acid.