Healthy aims: developing new medical implants and diagnostic equipment

Healthy Aims is a €23-million, four-year project, funded under the EU’s Information Society Technology Sixth Framework program to develop intelligent medical implants and diagnostic systems (www.healthyaims.org). The project has 25 partners from 10 countries, including commercial, clinical, and research groups. This consortium represents a combination of disciplines to design and fabricate new medical devices and components as well as to test them in laboratories and subsequent clinical trials. The project focuses on medical implants for nerve stimulation and diagnostic equipment based on straingauge technology

Modeling and Simulation of Enzymatic Biofuel Cells with Three-Dimensional Microelectrodes

The enzymatic biofuel cells (EBFCs) are considered as an attractive candidate for powering future implantable medical devices. In this study, a computational model of EBFCs based on three-dimensional (3-D) interdigitated microelectrode arrays was conducted. The main focus of this research is to investigate the effect of different designs and spatial distributions of the microelectrode arrays on mass transport of fuels, enzymatic reaction rate, open circuit output potential and current density. To optimize the performance of the EBFCs, numerical simulations have been performed for cylindrical electrodes with various electrode heights and well widths. Optimized cell performance was obtained when the well width is half of the height of the 3-D electrode. In addition, semi-elliptical shaped electrode is preferred based on the results from current density and resistive heating simulation

A Novel Non-Enzymatic Glucose Biofuel Cell with Mobile Glucose Sensing

Herein, we report a novel non-enzymatic glucose biofuel cell with mobile glucose sensing. We characterized the power generation and biosensing capabilities in presence of glucose analyte. This system was developed using a non-enzymatic glucose biofuel cell consisting of colloidal platinum coated gold microwire (Au-co-Pt) employed as an anode and the cathode which was constructed using a Gas diffusion electrode (GDE) with a platinum catalyst. The non-enzymatic glucose biofuel cell produced a maximum open circuit voltage of 0.54 V and delivered and a maximum short circuit current density of 1.6 mA/cm2 with a peak power density of 0.226 mW/cm2 at a concentration of 1 M glucose. The non-enzymatic glucose biofuel cell produced an open circuit voltage of 0.38 V and delivered and a short circuit current density of 0.225 mA/cm2 with a peak power density of 0.022 mW/cm 2 at a concentration of 5 mM glucose. These findings showed that glucose biofuel cells can be further investigated in the development of a self-powered glucose biosensor. When used as self-powered glucose sensor, the system showed a good sensitivity of 0.616 μA mM−1 and linear dependence with a correlation coefficient of 0.995 in the glucose concentration range of 2 mM to 50 mM. The system was further characterized by testing the performance of the system at various temperature, pH and amidst various interfering and competing chemical species such as uric acid, ascorbic acid, fructose, maltose and galactose. A charge pump circuit consisting of a blinking LED was connected to the biofuel cell to amplify the input voltage to power small electronic devices. The blinking frequency of the LED corresponds to the glucose concentration. An android mobile phone camera application was used to measure this LED blinking frequency which was in turn converted into the glucose concentration readings using image processing in MATLAB. The user was notified via text message and an email

Doctor of Philosophy

dissertationEnzymatic biofuel cells use enzymes to catalyze electrochemical reactions, directly converting chemical energy to electricity. In this research, three enzymatic biofuel cell devices were created and a focus was placed on their electrode structure in order to improve current density, power density, and/or biocompatibility. The first device, a flow-through glucose biofuel cell, was fabricated from laser-cut poly(methyl methacrylate) and utilized a porous anode to increase current density through improved mass transfer. The maximum current and power density of 705 μA cm-2 and 146 μW cm-2 were among the highest for a flowing biofuel cell in the literature. The second device was a contact lens lactate biofuel cell fabricated in two iterations: one using buckypaper electrodes and the other with carbon paste electrodes, both electrode types being molded into a contact lens. These were the first reported examples of a biofuel cell on a contact lens. The first prototype suffered from poor stability as well as biocompatibility issues, but the second prototype was more stable and amenable to possibly being worn on the eye. The current and power density of the second prototype were, respectively, 22 ± 4 μA cm-2 and 2.4 ± 0.9 μW cm-2 at 0.18 ± 0.06 V. As the device was limited by its cathode, simulations were created to investigate two important factors: carbon nanotube (CNT) connectivity to the electrode and enzyme loading on the CNT surface. It was found that ca. 20% of the CNTs were connected to the electrode; furthermore, only 1-2% of the enzyme was wired to the electrode through the CNT network and roughly 20% of the CNT surfaces were in communication with enzyme. The ferrocene redox polymer/lactate oxidase enzyme-mediator anode system used on the second contact lens biofuel cell prototype performed very well, so it was also used in the third device-a self-powered lactate sensor. Coupled with a bilirubin oxidase cathode, the sensor had a detection range between 0-5 mM lactate, a sensitivity of 45 μA cm-2 mM-1, and a current and power density of 657 ± 17 μA cm-2, 122 ± 5 μW cm-2, respectively

High-power biofuel cells based on threedimensional reduced graphene oxide/ carbon nanotube micro-arrays

Miniaturized enzymatic biofuel cells (EBFCs) with high cell performance are promising candidates for powering next-generation implantable medical devices. Here, we report a closed-loop theoretical and experimental study on a micro EBFC system based on three-dimensional (3D) carbon micropillar arrays coated with reduced graphene oxide (rGO), carbon nanotubes (CNTs), and a biocatalyst composite. The fabrication process of this system combines the top–down carbon microelectromechanical systems (C-MEMS) technique to fabricate the 3D micropillar array platform and bottom–up electrophoretic deposition (EPD) to deposit the reduced rGO/CNTs/enzyme onto the electrode surface. The Michaelis–Menten constant KM of 2.1 mM for glucose oxidase (GOx) on the rGO/CNTs/GOx bioanode was obtained, which is close to the KM for free GOx. Theoretical modelling of the rGO/CNT-based EBFC system via finite element analysis was conducted to predict the cell performance and efficiency. The experimental results from the developed rGO/CNT-based EBFC showed a maximum power density of 196.04 µW cm−2 at 0.61 V, which is approximately twice the maximum power density obtained from the rGO-based EBFC. The experimental power density is noted to be 71.1% of the theoretical value

Power Approaches for Implantable Medical Devices.

Implantable medical devices have been implemented to provide treatment and to assess in vivo physiological information in humans as well as animal models for medical diagnosis and prognosis, therapeutic applications and biological science studies. The advances of micro/nanotechnology dovetailed with novel biomaterials have further enhanced biocompatibility, sensitivity, longevity and reliability in newly-emerged low-cost and compact devices. Close-loop systems with both sensing and treatment functions have also been developed to provide point-of-care and personalized medicine. Nevertheless, one of the remaining challenges is whether power can be supplied sufficiently and continuously for the operation of the entire system. This issue is becoming more and more critical to the increasing need of power for wireless communication in implanted devices towards the future healthcare infrastructure, namely mobile health (m-Health). In this review paper, methodologies to transfer and harvest energy in implantable medical devices are introduced and discussed to highlight the uses and significances of various potential power sources

Carbon Nanotube-Enzyme Conjugates for the Fabrication of Diagnostic Biosensors

The fabrication of multi-analyte biotransducers continues to be a major technical challenge when the length scales of the individual transducer elements are on the order of microns Generation-3 (Gen-3) biosensors and advanced enzyme biofuel cells will benefit from direct electron transfer to oxidoreductases facilitated by single-walled carbon nanotubes (SWNTs). Direct electron transfer helps to mitigate errors from the instability in oxygen tension, eliminate use of a mediator and produce a device with low operating potential close to the redox potential of the enzymes. Supramolecular conjugates of SWNT-glucose oxidase (GOx-SWNT) may be produced via ultrasonic processing. Using a Plackett-Burman experimental design to investigate the process of tip ultrasonication, conjugate formation was investigated as a function of ultrasonication times and functionalized SWNTs of various tube lengths. Supramolecular conjugates formed from shorter, -OH functionalized SWNTs using longer sonication times gave the most favored combination for forming bioactive conjugates

PVDF as a Biocompatible Substrate for Microfluidic Fuel Cells

A reliable, flexible, and biocompatible power source for implantable and wearable devices has always been one of the biggest challenges for medical device design engineers. Microfluidic fuel cells (MFCs) are one of the candidates to generate a constant and reliable energy. However, the aspects of this approach, such as use of expensive materials, limitation of achievable power density and biocompatibility, have not yet been fully addressed. These challenges have restricted the application of MFCs to lab-on-chip systems that are deemed to be promising for implantable medical devices. Recently, porous materials such as natural papers and synthetic polymers (in the form of either nanofibers or porous membranes), when used as the MFC substrate, have shown that they can address the above-mentioned challenges. More importantly, these porous materials induce an inherent capillary flow in the fuel, eliminating the need of a pump. This may lead to an increased fuel efficiency and miniaturization of MFCs. However, the search for a porous biomaterial that displays high mechanical strength but remains flexible without degrading in a biological environment is not straightforward. In this research, Polyvinylidene Fluoride (PVDF), a non-biodegradable, biocompatible, flexible, and inexpensive material, was investigated for the first time as a channel substrate in a dynamic state MFC. To achieve the desired porosity, flexibility, and material strength of the substrate, PVDF nanofibers were fabricated using the electrospinning technique. Furthermore, hydrophilic PVDF nanofibers were successfully achieved by oxygen plasma surface treatment. The desired PVDF-based MFC was conceptualized using Axiomatic Design Theory (ADT) and FCBPSS (F: function, C: context, B: behavior, P: principle, SS: structure-state) methods. To investigate the electrochemical output of the designed PVDF-based MFC, a hydrophilic porous PVDF membrane was used as the substrate to induce a capillary action in the fuel (hydrogen peroxide). The PVDF-based MFC studied here successfully produced a power density of 0.158 mW/cm^2 at 0.08 V that is ~60% higher compared to the previous dynamic state paper-based biofuel cell reported in the literature. Moreover, the power density of MFC studied here is comparable to previous studies of static state single compartment MFCs using the same fuel type and concentration. Therefore, the results from this work demonstrate, for the first time, that the porous PVDF is a suitable material for the channel substrate in a dynamic state MFC. The potential application of this cell, in medicine, is utilizing the hydrophilic porous PVDF in electrochemical, implantable, and wearable medical devices. This approach can also be applied to any self-powered point-of-care diagnostic system